JP2002287185A - Multi-frequency light source - Google Patents

Abstract

(57) [PROBLEMS] To use WDM to emit WDM light whose number of channels is equal to or greater than the number of channels of incident WDM light and whose optical output has small wavelength dependence. Provide a frequency light source. A multi-frequency light source for increasing the number of channels of WDM light using four-wave mixing, wherein an optical multiplexer (2) combines incident WDM light from a light source section (C) and pump light of a pump light source (1).
And then enters the optical fiber 3 where the FWM
After realizing the interaction, a four-wave mixing unit A having an optical filter 4A for removing only the pump light and a four-wave mixing unit B replacing the optical filter 4A with an optical filter transmitting only the FWM light are combined. To form the optical composite part D ₁
A multi-frequency light source U _{1 that} emits WDM light whose number of channels is greater than the number of channels of the incident WDM light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-frequency light source, and more particularly, to a multi-frequency light source used in a wavelength division multiplexing optical communication system.

[0002]

2. Description of the Related Art Wavelength division multiplexing
ltiplexing (WDM)
At present, the transmission capacity per channel is 10Gbits /
With s, WDM transmission of 160 channels or more is realized. In this case, the used wavelength region is 1530 to 1610 nm.

[0003] In order to increase the number of channels in order to further increase the transmission capacity, the wavelength range used in WDM transmission is being further expanded.
Research has been conducted to actively use the short wavelength band of 530 nm or less (prior art 1: JX Cai, et.al., E
COC2000, Munich, PD1. 12, 2000, Prior art 2: T. Sak
amoto, S. Aozasa, T. Kanamori, K. Hoshino and M. S
himizu, OFC2000, Baltimore, PD4-1, 2000.).

However, when WDM transmission is to be realized using a large number of light sources in such a wide wavelength band, a backup light source used when a used light source fails. As a light source used in a wide wavelength band, for example, a SC (Super-Continuum) light source (prior art 3: T. Morioka, et. Al., Electron. Lett., 31,
1995, pp. 1064-1066) and a multi-frequency light source using four-wave mixing (prior art 4: Japanese Patent Application Laid-Open No. 8-288930).
No. 1) has been proposed.

[0005] Among these, the SC light source generates only pulsed light, and thus there is a problem that the modulation format of usable signal light is limited. On the other hand, Four Wave Mixing (Four Wave Mixing:
FWM) is used to generate FWM by using continuous light having two or more different frequency components (Continuous Wave light: hereinafter, referred to as CW light) as a seed light source.
A multi-frequency light source of W light can be realized. Since the light of each channel of the realized multi-frequency light source is CW light, the multi-frequency light source has an advantage that selection of a modulation method is not restricted in principle.

In the above-mentioned prior art 4 relating to the multi-frequency light source using the FWM, in order to make it economically inexpensive, a small number of C with different frequencies is used.
Attempts are being made to realize multi-frequency CW light using W light as a seed light source. Therefore, a plurality of CW lights serving as seed light sources are 2-3.
Are constituted by different frequency components. However, newly generated FWM light (hereinafter referred to as 1 or 2) due to FWM interaction using only the incident 2 or 3 CW light as a seed.
If only the following FWM light is used, the upper limit of the frequency components of the multi-frequency light source that can be realized is 4 or 8, respectively.

For this reason, in order to realize a multi-frequency light source having a sufficiently large number of channels, the primary FWM light is used as a seed to cause FWM interaction with the incident CW light to produce a secondary FW.
M light is generated, and the second-order FWM light is used as a seed to generate a third-order FWM light one after another. Thus, high-order FWM light (Prior Art 5: N. Shibata, R.
P.Brawn and RGWaarts, J. Quantum Electron., QE-2
3, 1987, pp. 1205-1210) is inevitable to realize a multi-frequency light source while increasing the upper limit of the number of channels.

As disclosed in Prior Art 5,
Since the higher-order FWM light becomes weaker as its order increases, the light intensity of the multi-frequency CW light generated by the FWM interaction in the nonlinear medium is observed at the exit end of the nonlinear medium. Strength is generally not uniform. Considering this from the standpoint of developing a multi-frequency light source, there is a problem that the light intensity of the CW light generated by the above-described FWM interaction has poor frequency flatness.

From the above, it can be considered that only a first-order FWM light should be used for realizing a multi-frequency light source using the FWM. The FWM involves three photons having two or three different frequencies (energy) in its elementary process to cause a nonlinear interaction in a nonlinear medium having a third-order nonlinear polarization. Can be regarded as a phenomenon that generates photons whose frequency (energy) is different from any of the photons. In the present invention, hereinafter, FWM will be used consistently in such a meaning.

[0010] The light generated in this way is the above-mentioned FW.
M light. Further, among the three photons involved in the non-linear interaction, light having a frequency component of light having the smallest amplitude as a light wave (any one of them if they are of the same type) is probe light, The other two are called pump light. Hereinafter, in order to accurately describe the present invention, the above-described concept of the first-order FWM light is further limited to the following meaning.

Focusing on one kind of light wave of the probe light having a single frequency, if the light intensity of the probe light is almost the same as that of the pump light, the FWM generated between the probe light and the pump light due to the participation of the probe light Generally, there are a plurality of interactions. In normal applications, these are all first-order FWM interactions, and the resulting FWM light is all first-order FWM.
WM light.

However, in the following description, considering the case where the light intensity of the probe light is sufficiently weaker than the light intensity of the pump light, the light of the FWM light out of the FWM light generated by the first-order FWM interaction is considered. The interaction with the highest intensity is called primary FWM interaction, and the FWM light obtained by this is called primary FWM light. Therefore, when the probe light is composed of WDM multi-channel light waves and the light intensity of each channel of the probe light is much smaller than the light intensity of the pump light, the FWM mutual transmission between the pump light and the probe light of each channel is made. The action is the most dominant of the interactions, which is the first order FWM interaction. First-order FWM generated by this first-order FWM interaction
Light therefore exists only in the number of channels of the probe light.

For this reason, after the occurrence of the FWM interaction, the generation of the first-order FWM light having the number of channels corresponding to the number of the channels of the probe light causes the number of channels as the whole emitted light to be reduced. To increase. Research is being conducted to realize a further increase in transmission capacity by using such FWM interaction for WDM transmission.

For example, in WDM transmission, light existing in a certain frequency band and multi-channeled by wavelength division multiplexing (hereinafter referred to as WDM light) is used as probe light, and the probe light and the light intensity of the probe light are used. More than 100
A pump light having a light intensity twice or more is multiplexed, and the multiplexed light is made incident on a non-linear medium such as an optical fiber or a semiconductor optical amplifier, where an FWM interaction is generated. Research on converting a frequency band into another frequency band at a time is known (prior art 6: O.Aso, S.Arai, S., T.Yagi, M.Tadakuma, Y.Suzuk).
i and S. Namiki, Electron Lett., 36, 2000, pp. 709-
711).

In the above-mentioned prior art 6, after the FWM interaction, the light emitted from the optical fiber, which is a nonlinear medium, is caused by the WDM probe light, the pump light, and the FWM interaction that existed originally. These are three types of light waves of the generated FWM light. In the prior art 6, the generated FWM light is WDM light obtained by frequency-converting the incident WDM probe light (hereinafter, referred to as incident WDM light) collectively.

Therefore, in the above prior art 6, if only the first-order FWM light is extracted from the light emitted from the nonlinear medium by the optical filter, it can function as a WDM light frequency conversion device. Further, if only the pump light is removed using an optical filter having a frequency characteristic different from that of the above-described optical filter, both the primary FWM light and the incident WDM light can be extracted from the light emitted from the nonlinear medium. it can. This means that using FWM light
This means that it functions as a light source that doubles the number of channels of incident WDM light. Furthermore, FWs with different frequency conversions
Perform M interactions multiple times and in each case,
If the above operation is performed using optical filters having different frequency characteristics, the number of channels of the probe light (incident WDM light) can be efficiently increased one after another.

In this way, it is possible to further increase the number of channels of the incident WDM light which has been multi-channeled and to assemble a multi-frequency light source. By the way, the incident W
The frequency of one probe light of interest out of the DM light is represented by f
_s , the frequency of the pump light is f _p (if there are two types of pump light, f _p1 and f _p2 ), and it is generated by the first-order FWM interaction between the probe light and the pump light of frequency f _s Assuming that the frequency of the primary FWM light is f _i , the following relationship is established between these frequencies (see Prior Art 5). _{f i = 2f p -f s f} i = f p1 + f p2 -f s

Therefore, by changing the frequency of the pump light, FWs of different frequencies can be obtained from the same probe light.
M light can be generated. In this case, FW
Assuming that an optical fiber is used as the nonlinear medium that generates the M interaction, the optical fiber has a frequency at which the chromatic dispersion value becomes 0 (the zero dispersion frequency f ₀ ) and the above-mentioned f _p (or f _p1 , f _p ). It is required to have a characteristic that the following relationship is established with the value _p2 ) for efficient generation of FWM light.

[0019]

(Equation 1)

Based on this, optical fibers having different zero-dispersion frequencies are connected in series in multiple stages, a pump light having a variable frequency is used, and this is combined with the incident probe light to perform frequency conversion. A four-wave mixer has been proposed (see Reference 7: JP-A-2000-180907). In this prior art, an optical fiber having a zero-dispersion frequency f _o Set the pump light frequency f _p required for the pumping light frequency f _p vicinity in order to the frequency of the pump light of variable frequency to produce a desired FWM light The FWM interaction occurs only in the optical fiber, and the frequency conversion occurs without generating the FWM interaction with other optical fibers.

Based on this prior art 7, pump light is prepared in the same number as the number of optical fiber connection stages, and the pump light is so adjusted that each of the frequencies of the pump light satisfies the zero dispersion frequency of all the optical fibers. To WDM (WD
M pump light), multiplexes the pump light and the incident WDM light,
When the multiplexed light is incident on the multi-stage connected optical fibers, only the pump light having a frequency near the zero dispersion frequency of the optical fibers at each stage causes FWM interaction with the probe light. If this is repeated, the incident probe light generates FWM light of different frequencies at each stage and propagates through the multi-stage connected optical fiber.Therefore, a filter that collectively removes the WDM pump light is provided at the output end of the optical fiber. If they are arranged, it is considered that a multi-frequency signal can be realized at once.

However, this cannot be realized. The reason is that the correlation between the pump light and the incident WDM light is an important factor in the occurrence of the FWM interaction in the optical fiber (prior art 8: O. As).
o, S. Arai, S., T. Yagi, M. Tadakuma, Y. Suzuki and S.
Namiki, IEICE Trans, Electron., E83-C, 2000, pp.81
See 6-823).

That is, the pump light and the WDM light, which are independent lights before being incident on the optical fiber, simultaneously enter the optical fiber and, when they are simultaneously incident on the optical fiber, have a correlation between each other through the FWM interaction. It is formed. Then, after propagating in the optical fiber by the coherent length (Lcoh) defined by the following equation, the mutual correlation is deteriorated.

[0024]

(Equation 2)

(Where Δβ is an amount representing the degree of phase mismatch of the propagation constant, β ₂ is the group of optical fibers at the frequency of the pump light (or intermediate frequency if the pump light has two different frequencies). (The velocity dispersion, Δω indicates the frequency conversion band.) Therefore, for example, when first incident on an optical fiber having a large group velocity dispersion (β ₂ ) at the pump light wavelength, the corresponding Lcoh is inversely proportional to the absolute value of β _2. Since the length becomes shorter, the pump light and the WDM light rapidly deteriorate the correlation after propagating over a short distance. Then, as shown in Prior Art 8, the deterioration of the correlation reduces the frequency band of the generated FWM light. Therefore, it becomes impossible to generate FWM light, which is light obtained by frequency-converting incident WDM light, in a wide band.

Even if the pump light enters an optical fiber having a small absolute value of the group velocity dispersion after passing through an optical fiber having a large absolute value of the group velocity dispersion, there is a significant difference between the lights which have already deteriorated the correlation. No serious FWM interaction occurs.
Conversely, when the pump light and the WDM light are first incident on an optical fiber having a small absolute value of the group velocity dispersion, the FWM interaction occurs efficiently and the FWM
Although the light is generated in a wide frequency band, the correlation is rapidly deteriorated in an optical fiber having a large absolute value of the group velocity dispersion incident thereafter. Therefore, the FW generated by the first optical fiber
The frequency band in which M light can exist rapidly narrows in an optical fiber having a large absolute value of group velocity dispersion. Eventually, significant FWM light is not generated in a wide band, and does not have sufficient characteristics as a multi-frequency light source.

[0027]

SUMMARY OF THE INVENTION The present invention relates to the above-mentioned problems in the prior art, in particular, the problems in the prior art 4, that is, the conventional FWM based on a few seed light sources.
And the problem that the frequency flatness of the channel of the multi-frequency light deteriorates, which is a problem in realizing the multi-frequency light source, and the problem deduced from the prior art 7, that is, the FWM interaction in a wide frequency band. Is generated a plurality of times, and a problem in realizing a multi-frequency light source using the generated light is solved, and the frequency-converted FWM of the incident WDM light is solved.
It is an object of the present invention to provide a novel multi-frequency light source capable of generating light in a wide band and forming WDM light having the same or more channels as the number of channels of incident WDM light.

[0028]

In order to achieve the above object, according to the present invention, a WDM light comprising a plurality of frequency channels and a light intensity of a channel having a maximum light output among the WDM lights are used. The wavelength division multiplexing having a frequency bandwidth equal to or wider than the occupied frequency bandwidth of the WDM light by injecting a pump light having a light intensity of 10 times or more into a nonlinear medium to generate FWM. A multi-frequency light source that emits light is provided.

More specifically, the light source unit that emits WDM light composed of light waves of a plurality of frequencies and at least one of the four-wave mixing unit A and the four-wave mixing unit B include And a light combining section, into which the WDM light emitted from the light source section is incident, wherein the number of channels of light emitted from the light combining section is the number of channels of light emitted from the light source section. A multi-frequency light source having an emission end that is equal to or greater than the number and emits light emitted from the optical composite unit, wherein the four-wave mixing unit A
A pump light source that emits pump light having a single or two different frequencies, an input port that receives incident light that is multiplexed with the pump light to cause four-wave mixing, An optical multiplexer that multiplexes the incident light received at a port, a nonlinear medium that generates four-wave mixing by inputting the light multiplexed by the optical multiplexer, and an optical medium that emits light from the nonlinear medium. The four-wave mixing unit B includes a four-wave mixing light newly generated by light-wave mixing, the pump light, and an optical filter that removes only the pump light from the incident light. A pump light source that emits pump light having a frequency, an incident port that receives incident light that is multiplexed with the pump light and causes four-wave mixing, and the pump light and the incident port. An optical multiplexer that multiplexes the incident light with the beam, a nonlinear medium that generates four-wave mixing by entering the light multiplexed by the optical multiplexer, and exits from the non-linear medium, by four-wave mixing. A multi-frequency light source, comprising: a newly generated four-wave mixing light, the pump light, and an optical filter that transmits only the newly generated four-wave mixing light among the incident light. .

More specifically, the nonlinear medium is an optical fiber or a semiconductor optical amplifier, and the optical composite section is
A multi-frequency light source formed as a block formed by connecting one or more of the four-wave mixing units A and / or the four-wave mixing units B in series (hereinafter, this type of multi-frequency light source A frequency light source), or the optical composite unit includes an optical splitter that splits outgoing light from the light source unit and one or more of the four-wave mixing unit A and / or the four-wave mixing unit B. A block in which the number of output ports of the optical splitter is equal to or less than the number of output ports of the optical splitter, and an output end of the optical splitter is connected to an input end of the four-wave mixing unit, and the four-wave mixing in the block. A multi-frequency light source (hereinafter, this type of multi-frequency light source is referred to as a parallel block type multi-frequency light source) comprising an optical multiplexer for multiplexing the light emitted from each of the units.

In the four-wave mixing section A and the four-wave mixing section B, when an optical fiber is used as the nonlinear medium, the following optical fiber is used. That is, when the pump light has a single frequency component, an optical fiber whose frequency at which the group velocity dispersion value of the optical fiber is 0 is located near the frequency of the pump light is used. If the optical fiber has different frequency components, an optical fiber whose frequency at which the group velocity dispersion value of the optical fiber is 0 is located near the arithmetic mean of the pump light frequencies is used.

Further, since the above-mentioned multi-frequency light source uses the pump light and the multi-channel incident WDM light as seed light sources, the number of channels is increased using only the first-order FWM interaction. Therefore, by using the pump light having the light intensity 10 times or more the light intensity of each channel of the incident WDM light, the magnitude of the FWM interaction between each channel of the incident WDM light and the pump light, ie, 1
The magnitude of the next FWM interaction becomes sufficiently larger than the magnitude of the other higher-order FWM interactions, and as a result, the deterioration of the wavelength flatness of the generated FWM light is suppressed.

Further, in the serial block type multi-frequency light source of the present invention, each of the four-wave mixing units A and / or
Alternatively, since the pump light is removed once each time the light wave propagates through each four-wave mixing unit B, there is no correlation between the pump light and the incident WDM light to each four-wave mixing unit,
The FWM is obtained only by the correlation between the pump light inside the four-wave mixing unit A or the four-wave mixing unit B and the WDM light incident on the four-wave mixing unit A or the four-wave mixing unit B in each nonlinear medium. Characteristics are determined. Therefore, a wide band F
By repeating the WM interaction, a broadband multi-frequency light source can be realized as a result.

Also, in the present invention, a multi-frequency light source, wherein all the WDM light waves emitted from the light source unit are in the same polarization state and are used as incident WDM light incident on the optical composite unit, In this case, the optical composite unit has a function of changing the polarization state of the pump light, specifically, an optical multiplexing unit that polarization-maintains the pump light and the incident WDM light and multiplexes the same in the same polarization state. A multi-frequency light source for directly inputting the light multiplexed by the optical multiplexer or the polarization maintaining optical multiplexer provided with a polarization controller at the input end of the pump light to the nonlinear medium, and a polarization maintaining light as the nonlinear medium. A multi-frequency light source that emits light from an optical multiplexing unit so as to propagate while maintaining a polarization state in a nonlinear medium using a fiber, and the optical multiplexing in each four-wave mixing unit in the optical composite unit The stage includes an optical multiplexer, and a polarization controller disposed in the optical multiplexer immediately before an input port of the pump light, wherein the polarization controller newly generates light emitted from the optical composite unit. A multi-frequency light source that is set so that the intensity of the obtained FWM light is maximized, and an optical multiplexer having a polarization maintaining characteristic is used as the optical multiplexing unit in the optical combining unit, and pump light from the pump light source is used. A multi-frequency light source and one or more four-wave mixing units A and / or a plurality of four-wave mixing units A, which are incident on the optical multiplexer such that the polarization state and the polarization state of each channel of the WDM light coincide in the optical multiplexer. Light wave mixing section B
Are connected in series, in the four-wave mixing unit located closest to the light source unit, the light emitted from the optical multiplexing means or the optical multiplexer is a polarization maintaining characteristic. A multi-frequency light source, and one or more of the four-wave mixing sections A and / or the four-wave mixing sections B, which are incident on the non-linear medium so as to propagate while maintaining the polarization state in the non-linear medium having In the optical composite part formed as described above, the light emitted from the optical multiplexing means or the optical multiplexer in all four-wave mixing parts is nonlinearly propagated while maintaining the polarization state in a nonlinear medium. A multi-frequency light source incident on a medium, the optical filter in the four-wave mixing unit A is filtered to remove only the pump light while maintaining the polarization state of light emitted from the nonlinear medium. In the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in series, the former stage between adjacent four-wave mixing sections. The multi-frequency light source in which the light emitted from the four-wave mixing unit enters the next-stage four-wave mixing unit while maintaining the polarization state, and the optical filter of the four-wave mixing unit B, An optical filter that transmits only the FWM light that has undergone the frequency conversion of the incident WDM light while maintaining the polarization state of the output light is combined with one or two or more four-wave mixing units A and / or four-wave mixing units B The optical composite part is formed by this, the multi-frequency light source in which the polarization state of the incident WDM light is maintained while propagating through the optical composite part, the multi-frequency light source located at the most exit end side of the entire optical composite part The non-linear medium in the light wave mixing unit A or the four wave mixing unit B is made of an optical fiber that does not maintain polarization, and the four wave mixing unit A or the four wave mixing unit B is the four wave mixing unit A or the four wave mixing unit. A multi-frequency light source that is part B, a multi-frequency light source in which an optical equalizer for flattening the frequency dependence of light intensity at the emission end is arranged at an emission end of the optical composite unit, and the light source A multi-frequency light source is provided in which one or more of the exit ends from the part are modulated.

[0035]

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a basic configuration example U ₁ of the multi-frequency light source of the present invention. This multi-frequency light source U ₁ is the same as the above-mentioned series block type multi-frequency light source,
Is a single unit, and the optical composite unit D1 is formed by the _single four-wave mixing unit A.

In the multi-frequency light source U ₁ of FIG. 1, the light source section C comprises a multi-channel light source C ₁ and an optical multiplexer C ₂ . Multi-channel light source C _1, the oscillation varies made by assembling a plurality of the CW light source frequency, also as an optical multiplexer C ₂ is for example an array waveguide diffraction grating (Arrayed Waveguide
Grating: AWG) is used. Light from the multi-channel light source C ₁ are multiplexed by the optical multiplexer C _2, it becomes in the WDM light having the light frequency or frequencies of a single frequency, and enters the later-described four-wave mixing section A.

The four-wave mixing unit A includes a pump light source 1 that oscillates a pump light frequency f _p, the incident light from the light source section C mentioned above the pump light from the pump light source 1 to the optical composite section D ₁ (incident WDM Multiplexed light, a non-linear medium 3 for generating FWM interaction in the multiplexed light, and pump light out of pump light, incident WDM light, and FWM light emitted from the non-linear medium 3. It is composed of a pump light removing optical filter 4A for removing only the light.

In this case, as the optical filter 4A, for example, a band pass filter (BPF) can be used. Note that an optical fiber and a semiconductor optical amplifier can be used as the nonlinear medium 3, but the following description will be made for a case where an optical fiber is used as the nonlinear medium.

In the four-wave mixing section A, the following optical phenomenon occurs to realize frequency conversion. This will be described with reference to FIGS. First, the incident light W from the light source section C
A pump light of DM light and the frequency f _p are multiplexed by the optical multiplexer 2. At this time, the frequency band F _{1 in which} the incident WDM light exists.
And is F ₁ indicated by the solid line in FIG.

The multiplexed light enters the optical fiber 3, where it causes FWM interaction to generate FWM light. Its FWM light, as shown by the broken line in FIG. 2, around the around the frequency f _p of the pump light is present in the frequency band F ₂ constituting the frequency band and symmetry of the incident WDM light. Pump light, FWM light, and incident WDM light are emitted from the optical fiber 3, but only the pump light is removed by the optical filter 4A.

As a result, from the four-wave mixing section A, the WDM
FWM light that is light and has the same number of channels and incident W
The DM light is emitted, and eventually, the emitted light is 2 of the incident WDM light.
It will have twice the number of channels. Here, in order to satisfy the phase matching condition for efficiently realizing the FWM interaction in the optical fiber 3, when the pump light is light of a single frequency, the optical fiber 3 used has a group velocity dispersion it is necessary to zero-dispersion frequency value f _o frequency becomes 0 is present near a frequency f _p of the pump light.
When the pump light is light having two different frequency components f ₁ and f ₂ , it is necessary to use an optical fiber whose zero dispersion frequency is near the arithmetic mean of the frequencies f ₁ and f _2. become.

One or both of the plurality of four-wave mixing sections A and the four-wave mixing sections B are connected in series to form an optical composite section, and the inside of each of the four-wave mixing sections constituting the optical composite section is formed. by adjusting the frequency f _p and the zero dispersion frequency of each optical fiber 3 of each pump light to each other, the incident WD of the optical composite section
For any frequency band in which the M light exists, the number of channels is set such that the frequency band of the FWM light generated by the FWM interaction does not overlap with the frequency band F _{1 of the} WDM light incident on each four-wave mixing unit. Can be increased.

[0043] More specifically, by utilizing this, for example, it is possible to form the multi-frequency light source U ₂ of the series block type as shown in FIG. This multi-frequency light source U ₂
Two four-wave mixing section A-1, the A-2 are connected in series to form a light composite portion D _2, incident WDM from the light source unit C to the optical composite section D ₂
Light enters the four-wave mixing unit A-1.

Here, in the four-wave mixing section A-1, the optical fiber 3-1 has a zero-dispersion frequency in the vicinity of the frequency _fp1 of the pump light from the pump light source 1-1. The optical fiber 3-2 in the mixing section A-2 is designed so that its zero dispersion frequency is located near the frequency _fp2 of the pump light from the pump light source 1-2. In the frequency light source U ₂ , the following optical phenomenon occurs in the optical composite unit D ₂ , and the number of channels of the incident WDM light from the light source unit C is increased.

First, in the four-wave mixing section A-1, the incident WDM light, which is the CW light from the light source section C, and the pump light having the frequency f _p1 are multiplexed by the optical multiplexer 2-1. The incident WDM at this time
The light frequency band exists at F ₁ shown in FIG. This F ₁
Is W. Further, the spacing between the frequency f _p1 the lowest frequency of the light and the pump light in a frequency band F ₁ is open by W / 2.

The light multiplexed by the optical multiplexer 2-1 is transmitted to the optical fiber 3
−1, where FWM interaction occurs to generate FWM light. Then, as shown in FIG.
The frequency f _p1 of the pump light from 1-1 with the axis of symmetry, the frequency band F ₁ of the incident WDM light is frequency converted to a frequency band F ₃ collectively, FWM light is generated in the frequency band F _3. The bandwidth of this frequency band F ₃ is a W. Therefore, of the light emitted from the optical fiber 3-1, only the pump light having the frequency _fp1 is removed by the optical filter (BPF) 4A-1, and as a result,
Four-wave from the mixing unit A-1 has a frequency band F ₁ and F _3, CW light is emitted with twice the number of channels of the incident WDM light.

Frequency band F ₁ and frequency band F ₃ have a frequency interval W
Only open, and each other's frequency bandwidth is also W,
Two different frequency bands. Further, the four-wave mixing unit A-1
In order to double the number of channels of the WDM light emitted from the
Should be passed. However, by using the four-wave mixing unit A-2 designed as follows, the output WDM
The number of light channels is the WDM output from the four-wave mixing unit A-1.
Broadband WDM light that is twice as large as the number of light channels and distributed continuously can be obtained.

The light emitted from the four-wave mixing unit A-1 is incident on the four-wave mixing unit A-2, and the light is output to the frequency f from the pump light source 1-2.
The light is multiplexed with the _p2 pump light by the optical multiplexer 2-2. Then, the multiplexed light enters the optical fiber 3-2, where FWM light is generated by FWM interaction. In this case, the optical filter (BPF) 4A-1 of the preceding four-wave mixing generation unit A-1 eliminates the correlation between the pump light having the frequency _{fp2 and} the light incident on the four-wave mixing unit A-2. since, it allows to consider only correlation was mediated FWM interaction, and the interaction between the pump light of the incident light and the frequency f _p2 to four-wave mixing section a-2 is inside the optical fiber 3-2 .

As described above, the FWM light is generated at a position axially symmetric about the pump light on the frequency axis.
Since the frequency band F ₁ and the frequency band F ₃ are open only the frequency interval W, FWM light generated frequency bands F ₁ or a frequency band F ₃ as probe light frequency of the pump light so as to fill the gaps of the band Can be designed. Figure 4 shows a case where the FWM light frequency band F ₃ and the probe light, the frequency band between the frequency band F ₁ and the frequency band F ₃ are filled. Moreover this time, since the distance between the FWM light frequency f _p2 of the pump light to the frequency band F ₁ and the probe light are open only 2W, FWM light frequency band F _1, F _2, F ₃
Generated in the frequency band F ₄ which does not overlap with the frequency band of the throat. Moreover, the frequency band F ₄ is generated in the position immediately adjacent to the frequency band F _3. If the zero-dispersion frequency of the optical fiber 3-2 to realize the condition that in the vicinity of f _p2, WDM light becomes probe light that exists in the frequency band F ₁ and the frequency band F _3, WDM light is emitted to the above I do.

Of the light emitted from the optical fiber 3-2, only the pump light having the frequency _fp2 is removed by the optical filter (BPF) 4A-2 having a frequency characteristic different from that of the optical filter 4A-1, whereby at four times the bandwidth of the light emitted from the light source station C, a and WDM light consecutive frequency band is formed is emitted from the multi-frequency light source U _2. Serial block type multi-frequency light source U ₂ shown in FIG. 3, by appropriately selecting the values of the pump light frequency f _p1 in the first four-wave mixing section A-1, bands not continuous on the probe light and the frequency axis In the four-wave mixing unit A-2 in the second stage, the value of the pump light frequency _fp2 is appropriately selected, so that the four-wave mixing unit A-1 F so as to fill the empty frequency band located between the probe light and the FWM light at
It is characterized in that WM is generated. In particular, such an aspect can be applied to avoiding noise generated due to higher-order FWM light when the pump light is a light wave of one frequency.

The above-mentioned series block type multi-frequency light source U ₂
Enables the number of channels to be four times the number of channels emitted from the light source unit by causing the FWM interaction to be repeated twice. That is, F ₁ constituting the frequency band of the WDM light incident on each four-wave mixing unit A,
By make the pump light from this band F ₁ to the position of the frequency band separated by size W / 2 of the frequency bandwidth, an empty frequency band spaced frequency intervals bandwidth W from the frequency band F ₁ It is generating a frequency band F ₃ to the position. Then, the band width of the frequency band F ₃ is also a W.

[0052] Then, four and the bandwidth of the frequency-converted signal by wave mixing utilizing that it is the same as the bandwidth of the signal to be transformed, the empty band between the frequency band F ₁ and the frequency band F ₃ The pump light is set on the frequency axis so as to fill the width W.
Specifically, the frequency band of the band width W that is not present in the signal by make a pump light of four-wave mixing section A-2 to the high frequency side of the low-frequency side or the frequency band F ₃ frequency bands F ₁ Can be filled.

However, the mode for quadrupling the number of channels is not limited to one of the modes shown in FIGS. In another method, the number of channels can be quadrupled by causing the FWM interaction to be repeated twice. Figure 5 shows another series block type multi-frequency light source U _3. In this multi-frequency light source U ₃ , an optical composite portion D ₃ having the same structure as the above-mentioned multi-frequency light source U ₂ is formed.

However, in the optical composite section D ₃ , the frequency f _p3 of the pump light from the pump light source 1-3 and the zero dispersion frequency of the optical fiber 3-3 in the four-wave mixing section A-3 are respectively shown in FIG. F in the four-wave mixing unit A-1 indicated by
_p1, it is different from the zero dispersion frequency, also the four-wave mixing section A-
4, the frequency _fp4 of the pump light from the pump light source 1-4 and the zero dispersion frequency of the optical fiber 3-4 are different from _fp2 and the zero dispersion frequency of the four-wave mixing unit A-2 shown in FIG. 3, respectively. I have.

In the case of this multi-frequency light source U ₃ , the optical composite unit D ₃
6, an optical phenomenon as shown in FIG. 6 occurs, and the number of channels of the WDM light incident from the light source unit C is increased. First,
In the four-wave mixing section A-3, the incident WDM light, which is the CW light from the light source section C, and the pump light having the frequency _fp3 are multiplexed by the optical multiplexer 2-3. The frequency band of the incident WDM light at this time is shown in FIG.
A F ₁ shown in its bandwidth and W.

The multiplexed light enters the optical fiber 3-3,
Then, an FWM interaction occurs to generate FWM light.
As shown in FIG. 6, the FWM light has the frequency _fp3 of the pump light 1-3 as a symmetric axis and the frequency band F of the incident WDM light.
₁ is in the CW light is frequency-converted into a frequency band F ₂ collectively. Its bandwidth is also W. Of the light emitted from the optical fiber 3-3, only the pump light of frequency f _p3 is removed by the optical filter (BPF) 4A-3. As a result, CW light having frequency bands F ₁ and F ₂ and having twice the number of channels and bandwidth 2 W of the incident WDM light is emitted from the four-wave mixing unit A-3.

This CW light enters the four-wave mixing section A-4,
Pump light of frequency _fp4 from pump light source 1-4 and optical multiplexer 2
Combined at -4. Then, the multiplexed light is converted into an optical fiber 3-
4, where FWM interaction produces FWM light. In this case, as shown in FIG. 6, the frequency f _p4 of the pump light by stand close to the lowest frequency component of the frequency band F _2, the frequency band F _3, F ₄ simultaneously in frequency band F ₂ It can be generated at adjacent positions. That F
As a result, as shown in FIG. 6, the WM light is generated in the optical fiber 3-4 as WDM light in which both the number of channels and the frequency band are quadrupled compared to the light emitted from the light source unit C.

[0058] Then, among the light emitted from the optical fiber 3-4, only the pump light of frequency f _p4 is removed by the optical filter (BPF) 4A-4 having a different frequency characteristic from the optical filter 4A-3 . As a result, CW light having frequency bands F ₁ , F ₂ , F ₃ , and F ₄ is emitted from the multi-frequency light source U ₃ . That is, aspects of the number of channels increases in the multi-frequency light source U ₃ may make a pump light in the vicinity of the WDM light to increase the frequency band, spread bandwidth by generating FWM light band adjacent one after another It is a mode of going. In that sense, this is different from the series block type multi-frequency light source of the same configuration shown in FIGS. In this manner, CW light having four times the number of channels of incident WDM light, which is CW light, is obtained using the two-stage four-wave mixing unit A.

Each of the above-mentioned multi-frequency light sources U ₂ and U ₃ is formed by connecting two four-wave mixing units A in series to form an optical composite unit, thereby forming a channel for the WDM light incident from the light source unit C. WDM light (CW) having four times the number of channels
Light). This can be generalized as follows. If N optical four-wave mixing units A are connected in series to form an optical composite unit, the number of pump light sources becomes N.
However, one pump light source may emit pump light having two different frequencies. Here, assuming that the incident WDM light having n channels is incident on the optical composite unit, finally, multi-frequency WDM light having 2 × n × N channels is emitted from the optical composite unit. Will be done.

FIG. 7 shows another example U of the multi-frequency light source of the present invention.
₄ shows the configuration. The multi-frequency light source U ₄ is the parallel block type multi-frequency light source described above.
A four-wave mixer A and two four-wave mixers B shown in FIG. 8 are arranged in parallel with each other to form a block, and an optical splitter 5 is provided upstream of the block, and an optical multiplexer is provided downstream. light composite unit D ₄ and 6 were respectively arranged are configured.

As shown in FIG. 8, the four-wave mixing section B incorporated in the multi-frequency light source U ₄ has a frequency characteristic of transmitting only the FWM light instead of the pump light removing optical filter A 4. The configuration is the same as that of the four-wave mixing unit A, except that the FWM light transmitting optical filter 4B is arranged. In the multi-frequency light source U ₄ , the following frequency conversion is realized in the optical composite unit D ₄ .

First, a multi-channel WDM light is emitted from the light source section C by a plurality of CW light sources (not shown) having different oscillation frequencies and an optical multiplexer (also not shown). The WDM light is all of the channels are included in the frequency band F ₁ shown in FIG. The incident WDM light is split by the optical splitter 5, and each of the split light enters the four-wave mixing unit A and the four-wave mixing unit B.

In the four-wave mixing section A, the incident branch light (frequency band F ₁ ) and the pump light having the frequency _fp5 from the pump light source 1-5 are multiplexed by the optical multiplexer 2-5, and the optical fiber 3 -5 at FW
Receiving M interaction, as shown in FIG. 9, the frequency f _p5
The FWM light is generated in the frequency band F ₂ in the axis of symmetry. Then, only the pump light having the frequency _fp5 is removed by the optical filter 4A. Therefore, from the four-wave mixing unit A, a WDM having twice the number of channels of the split light is provided.
Light (branched light and FWM light) is emitted.

[0064] four in wave mixing section B-1, occur FWM interaction between the WDM light and the pump light frequency band F ₁ frequency f _p6 to the axis of symmetry of the pump light in the same manner, the frequency band F
₃ FWM light is generated. Then, from the optical fiber 3-6, the FWM light, the WDM light (branched light) incident on the four-wave mixing unit B-1, and the pump light are emitted.
Since only M light is extracted by the optical filter 4B-1, the light emitted from the four-wave mixing section B-1, as shown in FIG. 9, and only the FWM light frequency band F _3.

[0065] Similarly in the four-wave mixing section B-2, occur FWM interaction frequency f _p7 of the pump light between the WDM light and the pump light frequency band F ₁ to the axis of symmetry, FWM frequency band F ₄ Light is generated. And from optical fiber 3-6,
The FWM light, the WDM light (branched light) incident on the four-wave mixing unit B-2 and the pump light are emitted. From these, only the FWM light is extracted by the optical filter 4B-2. light emitted from -2, as shown in FIG. 9, and only the FWM light frequency band F _4.

All of the lights emitted from the four-wave mixing unit A, the four-wave mixing unit B-1, and the four-wave mixing unit B-2 are multiplexed by the optical multiplexer 6. Therefore, the outgoing light from the multi-frequency light source U ₄ has frequency bands F ₁ , F ₂ , F ₃ , and F ₄ , and the number of channels is four times the number of channels of the incident WDM light from the light source unit C. Generated WDM light. Incidentally, in the multi-frequency light source U _4, for example, four-wave mixing section A, four FWM interaction in wave mixing section B-1, B-2 at different frequencies from each other, and among the _{f p5, f p6, f p} 7 , And the group velocity dispersion is zero as an optical fiber to be incorporated in each corresponding four-wave mixer so that broadband FWM interaction occurs in the pump light. Using an optical fiber whose frequency becomes near the frequency of the pump light described above,
The same effects as described above can be obtained by optimizing the frequency characteristics of the optical filters on which the light emitted from the optical fiber enters.

For example, in FIG. 9, in order for the WDM light emitted from the multi-frequency light source U ₄ to consist of light waves of a continuous channel on the frequency axis, the lowest frequency of the channel constituting the frequency band F ₁ is set to f. _x and frequency band F
Assuming that the frequency interval of the channel constituting ₁ is Δf, f ₅ = f _x −Δf / 2

[0068]

(Equation 3)

Each pump light may be arranged so as to satisfy the relationship of f ₇ = f ₅ −W−Δf.
As described above, the multi-frequency light source U ₄ can generate WDM light having four times the number of channels of the WDM light incident from the light source unit C.

In general, one four-wave mixing unit A
And (M−1) four-wave mixing sections B are arranged in parallel to form an optical composite section D _{4. When} incident WDM light having n channels is incident on this section, finally, Means that multi-frequency WDM light having M × (n + 1) channels is generated from n + M light sources. It should be noted that each of the multi-frequency light sources U ₁ , U ₂ , U ₃ , and U ₄ is a case where the frequency of the pump light is a single frequency. If the pump light has two different frequencies, _assuming that the respective frequencies are f _p1 and f _p2 , the following equation is obtained:

[0071]

(Equation 4)

By considering the value converted into the frequency of the pump light in the system in the same manner as described above, a multi-frequency light source can be realized. In that case, multi-frequency light source that series block type Type of U ₂ is shown in FIG. 3, four wave mixing unit N-1 the number of A, if the number of channels of the incident WDM light is n, eventually N + 2N including pump light
Can generate multi-frequency WDM light having 2nN channels.

The parallel block type multi-frequency light source U ₄ shown in FIG. 7 finally outputs multi-frequency WDM light having M × (n + 1) channels from an n + 2M light source. Can be generated. Figure 10 shows the structure of a multi-frequency light source U ₅ of the present invention. In the case of this multi-frequency light source U ₅ , the optical composite unit D ₅ is formed by one four-wave mixing unit A, and is constituted by this and the light source unit C, which is the same as that of the multi-frequency light source U ₁ shown in FIG. Same as above, except for the following:

First, the multi-channel light source C ₁ in the light source section C emits linearly polarized light, and the multi-channel light source C ₁ and the optical multiplexer C ₂ are connected to a polarization maintaining optical fiber (Polarization Mainta).
An ining fiber (PMF) 7 is connected, and a polarization controller 8 is connected immediately after the pump light source 1 in the four-wave mixing unit A. In this multi-frequency light source U ₅ , linearly polarized light is emitted from a multi-channel light source C ₁ composed of a plurality of CW light sources having different oscillation frequencies, and these are combined by an optical multiplexer C ₂ while maintaining the polarization state of each channel by a PMF _7. WDM light having the same polarization state is emitted from the light source unit C, and then enters the four-wave mixing unit A.

By the way, in order for the pump light from the pump light source 1 and the WDM light incident on the optical composite section D ₅ to cause an FWM interaction in the optical fiber 3, the pump light and the optical composite section D ₅ must be coupled to each other. It is necessary to match the respective polarization states with the incident WDM light. Therefore, this multi-frequency light source U
_{In 5} , a polarization controller 8 is provided immediately after the pump light source 1 and immediately before the optical multiplexer 2 as an optical multiplexing means for multiplexing the WDM light and the pump light incident on the optical composite unit D ₅ while aligning the polarization state. And thereby change the polarization state of the pump light,
Adjusted by the polarization controller 8 so as to coincide with the polarization state of the incident WDM light to the optical composite unit D _5.

Then, the incident W to these optical composite parts D ₅
After the DM light and the pump light are multiplexed by the optical multiplexer 2, the light is incident on the optical fiber 3, generates FWM light by FWM interaction, and then only the pump light is removed by the optical filter 4A. The configuration of the multi-frequency light source U ₅ described above, it goes without saying that can be employed also for four-wave mixing section B.

In the case of the multi-frequency light source U ₅ , the polarization state of the pump light can be controlled by monitoring the light intensity of the FWM light at the emission end and feeding it back to the polarization controller 8. In principle, if the polarization states of the pump light and the incident WDM light match, the output FWM
It is known that the light intensity is the highest, and the light intensity is the lowest if they are orthogonal (see Prior Art 9, K. Inoue, J. Q.
uantum Electron., vol. 28, 1992, pp. 883-894.). However, in general, rather than matching the polarization state of each light after grasping the polarization state of each light,
While monitoring the light intensity of the resulting FWM light, observe the change in the light intensity of the FWM light when the polarization state is changed, and determine the polarization state so that the FWM light with the highest light intensity is realized. The method is more practical in terms of both performance and cost.

FIG. 11 shows still another example of a multi-frequency light source U ₆ of the present invention. This multi-frequency light source U ₆ combines the WDM light incident on the optical composite unit D ₆ and the pump light by aligning the polarization states thereof. The optical multiplexer 2 of the light source unit C and the four-wave mixing unit A is
Except that while, constructed between the pump light source 1 and the optical multiplexer 2, and between the optical multiplexer 2 and the incident end of the optical fiber 3 in all PMF7 of, in the case of the multi-frequency light source U ₅ described above It has the same configuration.

In the case of the multi-frequency light source U ₆ , the pump light and the incident WDM light incident on the optical fiber 3 are all in the same polarization state, and undergo FWM interaction in the optical fiber 3. Needless to say, the above-described configuration can be adopted for the four-wave mixing unit B. In summary, the polarization state of the light in each channel of the pump light and the incident WDM light affects the intensity of the FWM light generated by the first-order FWM interaction. Therefore, while changing the polarization state of the pump light, the polarization controller is set so that the intensity of the FWM light generated by the FWM interaction is maximized.
In order to realize this efficiently, it is preferable to make the polarization state of each channel of the WDM light immediately before the light enters the nonlinear medium.

[0080] illustrates yet another multi-frequency light source Example U ₇ in FIG. 12 of the present invention. The multi-frequency light source U ₇ is a serial block type multi-frequency light source configured by using two four-wave mixing units A′-1 and A′-2, which will be described later, connected in series as an optical composite unit D ₇ .
The linearly-polarized incident WDM light emitted from the light source section C is subjected to FWM interaction by the same number of times as the number of the four-wave mixing sections A ′ connected in series while maintaining the polarization state. As a result, the number of channels of the WDM light at the output end of the multi-frequency light source U ₇ is than the number of channels of the incident WDM light from the light source unit C to the optical composite part D ₇ emitted a light source that emits increased.

The polarization state of each channel of the WDM light emitted from the light source section C and incident on the optical composite section D ₇ is aligned with the linear polarization, and the two four-wave mixing constituting the optical composite section D ₇ are performed. The part A′-1 and the four-wave mixing part A′-2 each preserve the polarization state of the propagating light. Also, the pump light and four-wave mixing unit
It is known from prior art 9 that if the WDM light incident on A'-1 and A'-2 is in the same linear polarization state, the FWM light generated inside the nonlinear medium 3 'is also in the same polarization state. ing.

When only the pump light is removed from the light emitted from the optical fiber 3′-8 while maintaining the polarization state by the pump light removing filter 4A′-8, the four-wave mixing unit A′-1 outputs WDM light and FWM light incident on the four-wave mixing unit A'-2 are emitted. These are incident W on the four-wave mixing section A'-2.
It becomes DM light. Then, the incident WD into the four-wave mixing unit A'-2
Since the polarization of all the channels of the M light is uniform, the pump light emitted from the pump light source 1-9 is multiplexed by the optical multiplexer 2'-9 so as to be in the same polarization state as these polarization states. ,
When the light enters the optical fiber 3'-9, the FWM interaction occurs efficiently, and the FWM of the WDM light incident on the four-wave mixing unit A'-2
Light is generated.

Out of all the outgoing light from the optical fiber 3′-9, only the pump light is removed by the pump light removing filter 4A′-9 while maintaining the polarization state of the other light wave, and the rest is the optical composite part D ₇ is emitted from. As a result, uniform all polarization states, and the WDM light channel number than WDM light emitted from the light source unit C is increased four times is emitted from the optical composite unit U _7.

[0084] Figure 13 shows yet another multi-frequency light source Example U ₈ of the present invention. The multi-frequency light source U ₈ is an in-line block type multi-frequency light source to "four-wave mixing section A 'and A was constructed using connected in series to the two described later as the light composite section D _8, from the light source unit C The emitted linearly polarized incident WDM light is subjected to FWM interaction by the same number of times as the sum of the number of the four-wave mixing units A ′ and the number of the four-wave mixing units A ″.

[0085] The basic structure is the same as that of the series-blocking multi-frequency light source U ₇ shown in FIG. 12, closest to the position four-wave mixing in the multi-frequency light source U ₃ exit end shown in FIG. 5 The difference is that the part A is replaced by a four-wave mixing part A ″. As shown in the prior art 8, the pump light and the optical fiber immediately before the light enters the optical fiber 3-11 which is a nonlinear medium. If the polarization of the incident WDM light to
Even if the optical fiber does not have the polarization maintaining characteristic, it is possible to cause a sufficiently wide band FWM interaction by shortening the fiber length.

Therefore, the emission WD from the multi-frequency light source
If it is not necessary to align the polarization states of the M light, the light path of the optical fiber 3-11 four-wave mixing section A "located closest to the exit end side of the optical composite section D ₈ therefrom to the exit end polarization state there is no need to keep. Figure 14 shows yet another multi-frequency light source example U ₉ of the present invention. the multi-frequency light source U ₉ is
Light composite section D ₉ as a single four-wave mixing portion A "and two four-wave mixing section B" -1, a parallel block type multi-frequency light source configured using in parallel the B "-2, the light source The number of channels of the linearly polarized incident WDM light emitted from the portion C is increased.

The multi-frequency light source U ₉ serves as an optical multiplexing means for multiplexing the WDM light and the pump light incident on the optical composite unit D ₉ while aligning the polarization states thereof, and divides the light source unit C and the four-wave mixing unit A. , The pump light source 1 and the polarization maintaining optical multiplexers 2'-12, 2'-1
3, 2'-14, and polarization-maintaining optical multiplexer 2'-12.
2'-14 and except that between the entrance end of the optical fiber 3-12,3-13,3-14 bound in all PMF7, is the same configuration as that of multi-frequency light source U ₄ mentioned above I have.

In the case of this multi-frequency light source U ₉ , the optical fiber 3
-12, 3-13, and 3-14, the pump light and the incident WDM light are all in the same polarization state,
Subject to M interaction. Needless to say, the above-described configuration can be adopted for the four-wave mixing unit B.

The four-wave mixing unit A ″ and the four-wave mixing unit B ″ −1, used in the parallel block type multi-frequency light source U ₉ ,
B "-2 is both the most emitting end side of the multi-frequency light source U ₉ in the light composite section D _9. Thus, for the same reason as the case of a multi-frequency light source U ₈ shown in FIG. 13, multi-frequency Light source U ₉
If it is not necessary to align the polarization states of the light waves emitted at the output end of the optical fiber 3-12, 3-13, and 3-14, the optical paths from the optical fiber 3-12, 3-13, and 3-14 to the output end need to maintain polarization. Absent.

Also, by maintaining the polarization of the optical path between the optical fibers 3-12, 3-13, 3-14 and the subsequent emission ends,
The polarization state of the light emitted from the multi-frequency light source U ₉ can all agree. Still another multi-frequency light source example U of the present invention
₁₀ is shown in FIG. The multi-frequency light source U ₁₀ uses a single four-wave mixing unit B ′, which will be described later, as the optical composite unit D ₁₀ , and thus has a linearly polarized incident WD having multiple channels.
M light, while maintaining its polarization state,
This is a light source that increases the number of channels by WM interaction and emits light while maintaining the polarization state constant.

In FIG. 15, the light source section C is connected to a four-wave mixing section B 'which emits only FWM light having the same polarization state as that of linearly polarized incident WDM light. as with the multi-frequency light source U ₅ shown in 10 for emitting WDM light of the linearly polarized light. The four-wave mixing unit B ′ is provided with a pump light source 1 ′ that emits linearly polarized light as pump light, a polarization maintaining optical multiplexer 2 ′, a polarization maintaining optical fiber 3 ′, and a polarization maintaining light that transmits only the FWM light. Filter 4
B ′, and all of them have a PM shown by a broken line in FIG.
Except for the structure connected by F7, there is no difference from the case of the four-wave mixing unit B already described in FIG.

Therefore, the incident WDM light behaves the same as the four-wave mixing section B of the multi-frequency light source U ₈ . As a result, all of the polarization-maintaining optical fiber 3 'is FWM light in the same polarization state, the pump light, and the incident WDM light to the optical composite part D ₁₀ from the light source unit C emits. Then, only the FWM light is extracted from these lights by the optical filter 4B '.
This FWM light has a uniform polarization state and is linearly polarized light.

Further, the optical filter 4B 'in the four-wave mixing section B', which transmits only FWM light, is replaced with the optical filter 4A ', which removes only pump light while maintaining polarization, as already described in FIG. And a four-wave mixing unit A ′ having polarization maintaining characteristics can be realized. FIG. 16 shows a multi-frequency light source U having the four-wave mixing section A ′.
Shows the _11.

[0094] four-wave mixing by replacing those so as not have a polarization retaining characteristics the light path to the exit end of the optical fiber 3 and later the optical composite part D ₁₁ of the above-mentioned four-wave mixing section A ' part a "can be realized, and as not having polarization retaining characteristics the light path to the exit end of the subsequent optical composite unit D ₁₁ 'optical fiber 3 in the' four-wave mixing section B as shown in FIG. 15 The four-wave mixing unit B ″ can be realized by replacing the above-mentioned one.

By forming an optical composite section using a plurality of the four-wave mixing sections A 'and / or the four-wave mixing sections B' described above, a series block type of the configuration described in FIG. Can be realized. Further, by using a plurality of four-wave mixing sections A ′ and forming an optical composite section with the four-wave mixing section closest to the emission end side as the four-wave mixing section A ″, the device operates with linearly polarized light already in FIG. It is possible to realize a series block type multi-frequency light source having the configuration described above.

By forming an optical composite section composed of blocks in which four-wave mixing sections A ″ and four-wave mixing sections B ″ are arranged in parallel, a parallel block type multi-frequency light source having a configuration as shown in FIG. 14 is realized. can do. When configuring the parallel block type multi-frequency light source described with reference to FIG. 14, the four-wave mixing unit A ″ and a plurality of four-wave mixing units B ″ are connected in parallel to form an optical composite unit. Thus, a multi-frequency light source in which the polarization states of the respective channels of the output WDM light are uniform can be realized.

In the case of the multi-frequency light source provided with the optical composite section having the configuration shown in FIGS. 13 and 14, the polarization states of the emitted lights are not uniform, but all the elements are composed of the four-wave mixing section A 'and the four-wave mixing section. The manufacturing cost is lower than in the case of the multi-frequency light source constituted by the part B '. Note that one or both of the above-described optical composite unit and one or both arranged at the position closest to the emission end are:
When the four-wave mixing section A ′ or the four-wave mixing section B ′ is connected in series as shown in FIG. 12, the four-wave mixing section closest to the emission end of the formed optical composite section is When the four-wave mixing section A ′ and the four-wave mixing section B ′ are arranged in parallel as shown in FIG. 4, the four-wave mixing section A ′ is located immediately before the emission end of the formed optical composite section. All of the four-wave mixing unit A ′ and the four-wave mixing unit B ′ that emit light incident on the optical multiplexer 6.

In the case of the above-described multi-frequency light source of the present invention, the frequency dependence of the light intensity of the WDM light emitted from the optical composite unit is smaller than in the case of the multi-frequency light source utilizing higher-order FWM interaction. However, the light intensity is not completely flat and has some frequency dependence. To solve such a problem, it is preferable to dispose a filter-type optical component having a transmission characteristic with a frequency characteristic at the emission end of the optical composite unit, since the frequency dependence of the light intensity of the emitted light can be eliminated.

For example, as an optical fiber amplifier, a gain flattening filter combining a plurality of etalon filters (Prior Art 10, Kazuyoshi Mizuno, et al., Furukawa Electric Time Report, 105
No., pp. 36-41, 2000). By using this technique, an optical attenuator having a characteristic of compensating for the frequency dependence of the light intensity of the light emitted from the optical composite unit,
That is, an optical equalizer can be manufactured. By using this technique, the frequency dependency of the WDM light emitted from the optical composite unit can be eliminated.

In the light source section, the CW light emitted from the multi-channel light source C ₁ is modulated before being multiplexed by the optical multiplexer C ₂ and then multiplexed into WDM light. Thus, a frequency-converted copy of the output signal light can be produced.

[0101]

As is apparent from the above description, in the present invention, a multi-channel WDM light is caused to cause a first-order FWM interaction centering on a pump light having a higher light intensity. Thus, a multi-frequency light source with less frequency dependence of optical power is realized. In addition, the above-mentioned primary FW
By causing multiple M interactions, the incident WDM
WDM with more channels than optical channels
A multi-frequency light source that generates light can be realized. This has an independent pump light source, multiplexes the incident WDM light and the pump light, and then enters the nonlinear medium (optical fiber or semiconductor optical amplifier) to generate FWM interaction.
Next, an optical composite unit is formed by combining a four-wave mixing unit A provided with an optical filter that removes only pump light and a four-wave mixing unit B in which the optical filter is replaced with an optical filter that transmits only FWM light. Thus, the effect of preventing the deterioration of the correlation between the incident WDM light and the pump light in the FWM interaction is realized.

When the incident light from the light source section is linearly polarized light, the FWM interaction can be multiplexed while maintaining the polarization state of the incident light by providing the entire optical composite section with polarization maintaining characteristics. Therefore, the dependency of the FWM interaction on the incident polarization can be eliminated. Therefore, the multi-frequency light source of the present invention has great industrial value as a light source used in the WDM communication system.

[Brief description of the drawings]

1 is a schematic diagram illustrating a multi-frequency light source U ₁ of the present invention.

FIG. 2 is an explanatory view showing an optical phenomenon in multi-frequency light source U _1.

Figure 3 is a schematic diagram illustrating a multi-frequency light source U ₂ of the present invention.

4 is an explanatory diagram showing an optical phenomenon in multi-frequency light source U _2.

5 is a schematic diagram illustrating a multi-frequency light source U ₃ of the present invention.

6 is an explanatory view showing an optical phenomenon in multi-frequency light source U _3.

7 is a schematic diagram illustrating a multi-frequency light source U ₄ of the present invention.

FIG. 8 is a schematic diagram showing a four-wave mixing unit B.

9 is an explanatory view showing an optical phenomenon in multi-frequency light source U _4.

It is a schematic diagram illustrating a multi-frequency light source U ₅ of the present invention; FIG.

11 is a schematic diagram illustrating a multi-frequency light source U ₆ of the present invention.

12 is a schematic diagram illustrating a multi-frequency light source U ₇ of the present invention.

13 is a schematic diagram illustrating a multi-frequency light source U ₈ of the present invention.

14 is a schematic diagram illustrating a multi-frequency light source U ₉ of the present invention.

15 is a schematic diagram illustrating a multi-frequency light source U ₁₀ and four-wave mixing section B 'of the present invention.

16 is a schematic diagram illustrating a multi-frequency light source U ₁₁ and four-wave mixing section A 'of the present invention.

[Description of Signs] 1,1-1,1-2,1-3,1-4,1-5,1-6,1-7,1-8,1-9,1
-10, 1-11, 1-12, 1-13, 1-14 Pump light source 2,2-1,2-2,2-3,2-4,2-5,2-6,2-7 Wave 2 ', 2'-8, 2'-9, 2'-10, 2'-11, 2'-12, 2'-13, 2'-1
4 Optical multiplexer with polarization maintaining characteristics 3,3-1,3-2,3-3,3-4,3-5,3-6,3-7,3-11 Optical fiber (non-linear medium) 3 ', 3'-8, 3'-9, 3'-10 Polarization-maintaining optical fiber (non-linear medium) 4A, 4A-1, 4A-2, 4A-3, 4A-4, 4A-11 For pump light removal Optical filters 4A ', 4A'-8, 4A'-9 Pump light removing optical filters 4B, 4B-1 and 4B-2 having polarization maintaining characteristics Filters transmitting only FWM light 4B' Having polarization maintaining characteristics Optical filter that transmits only FWM light 5 optical splitter 6 optical multiplexer 7 polarization maintaining optical fiber 8 polarization controller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04J 14/00 H04B 9/00 E 14/02 Y H04B 10/28 10/26 10/14 10/04 10 / 06 (72) Inventor Misao Sakano 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Masateru Tadakuma 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. In-house F term (reference) 2K002 AA02 AB12 BA01 CA13 CA15 DA10 DA11 HA31 5F072 AB07 AK06 JJ20 KK11 MM07 QQ04 SS02 YY17 5F073 AB22 BA01 5K002 BA02 BA04 BA05 CA01 CA05 CA13 CA14 DA02 FA02

Claims (19)

[Claims] 1. A wavelength division multiplexed light comprising channels of a plurality of frequencies, and a pump light having a light intensity 10 times or more higher than a light intensity of a channel having a maximum light output among the wavelength division multiplexed light, A wavelength-division multiplexed light having a frequency bandwidth equal to or wider than the occupied frequency bandwidth of the wavelength-division multiplexed light is emitted by entering the nonlinear medium to generate four-wave mixing. Frequency light source. 2. A light source unit for emitting wavelength-division multiplexed light composed of light waves of a plurality of frequencies, and a four-wave mixing unit A and a four-wave mixing unit B so as to include at least one of these two types. An optical composite part, which is formed by combining one or more pluralities, and the wavelength division multiplexed light emitted from the light source part is incident thereon, and the number of channels of the light emitted from the optical composite part is the number of channels of the light emitted from the light source part. A multi-frequency light source having an emission end that is equal to or greater than the number of channels and emits light emitted from the optical composite unit, wherein the four-wave mixing unit A has a single or two different frequencies. A pump light source that emits pump light, an incident port that receives incident light that is multiplexed with the pump light and causes four-wave mixing, and multiplexes the pump light and the incident light that is received at the incident port. Shining light A non-linear medium that generates four-wave mixing by injecting the light multiplexed by the optical multiplexer, and a four-wave mixed light newly generated by four-wave mixing, emitted from the non-linear medium, The four-wave mixing unit B includes a pump light, and a pump light source that emits pump light having a single or two different frequencies. An incident port for receiving incident light that is multiplexed with pump light to cause four-wave mixing, an optical multiplexer for multiplexing the pump light and the incident light received at the incident port, and the optical multiplexer. A non-linear medium that generates four-wave mixing by injecting the light multiplexed in the above, and four-wave mixing light newly generated by four-wave mixing, the pump light, and the pump light that are emitted from the non-linear medium. Of the incident light, multi-frequency light source, characterized in that it consists of an optical filter that transmits only the new four-wave mixing light generated. 3. The multi-frequency light source according to claim 1, wherein said nonlinear medium is an optical fiber or a semiconductor optical amplifier. 4. The optical composite section according to claim 1, wherein one or more of the four-wave mixing sections A and / or the four-wave mixing sections B are connected in series. Multi-frequency light source. 5. The optical splitter according to claim 1, wherein one or more of the four-wave mixing units A and / or the four-wave mixing units B are arranged in parallel with each other, and the light splitter splits light emitted from the light source unit. Are connected to the incident ends of the four-wave mixing unit A and the four-wave mixing unit B, respectively, and output light from the respective outgoing ends of the four-wave mixing unit A and the four-wave mixing unit B. 2. An optical multiplexer for multiplexing is arranged.
3. The multi-frequency light source according to any one of to 3 above. 6. The polarization state of the lightwave of each channel of the wavelength division multiplexed light emitted from the light source unit is the same polarization state when the lightwave enters the incident port of the optical composite unit. 5. The multi-frequency light source according to any one of 5. 7. In the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in series, a position closest to the light source section is provided. The optical multiplexing means for multiplexing the polarization state of the pump light in the four-wave mixing unit and the polarization state of each channel of the wavelength division multiplexed light incident on the input port of the four-wave mixing unit as the same polarization state. 7. The multi-frequency light source according to claim 4, wherein the combined light is incident on a nonlinear medium that generates four-wave mixing. 8. In the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in parallel, all of the optical composite sections are formed. The polarization state of each pump light in the four-wave mixing unit A and the four-wave mixing unit B, and the polarization state of the wavelength-division multiplexed light incident on all the input ports of the four-wave mixing unit A and the four-wave mixing unit B in the optical composite unit. With the polarization state of each channel, comprising an optical multiplexing means for multiplexing as the same polarization state,
7. The multi-frequency light source according to claim 5, wherein the lights multiplexed by the four-wave mixing units are incident on a nonlinear medium that generates four-wave mixing. 9. The optical multiplexing means in each of the four-wave mixing units in the optical multiplexing unit includes an optical multiplexer, and a polarization controller disposed in the optical multiplexer immediately before a pump light input port. The polarization controller according to claim 7 or 8, wherein the polarization controller is set so that the intensity of the newly generated four-wave mixing light in the light emitted from the optical composite unit is maximized. Frequency light source. 10. The polarization state of pump light from the pump light source and the polarization state of each channel of the wavelength division multiplexed light using an optical multiplexer having polarization maintaining characteristics as the optical multiplexing means in the optical multiplexing unit. 9. The multi-frequency light source according to claim 7, wherein the light is incident on the optical multiplexer so that the light beams coincide with each other in the optical multiplexer. 11. The optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in series, positioned at a position closest to the light source section. 8. An outgoing light from the optical multiplexing means or the optical multiplexer in the four-wave mixing section to be incident on the nonlinear medium so as to propagate while maintaining a polarization state in a nonlinear medium having polarization maintaining characteristics. , 9 or 10 multi-frequency light source. 12. In the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in parallel, the light combining section in all four-wave mixing sections is provided. The light emitted from the wave means or the optical multiplexer is incident on the nonlinear medium so as to propagate while maintaining the polarization state in the nonlinear medium.
Any multi-frequency light source. 13. The four-wave mixing unit A, wherein:
Is an optical filter that removes only the pump light while maintaining the polarization state of the light emitted from the nonlinear medium, and the optical filter of the four-wave mixing unit B is a filter for the light emitted from the nonlinear medium. 13. The multi-frequency light source according to claim 11, wherein the multi-frequency light source is formed as an optical filter that transmits only newly generated four-wave mixing light while maintaining the polarization state. 14. A pre-stage between adjacent four-wave mixing sections in the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in series. 14. The multi-frequency light source according to any one of claims 4, 6, 7, 9 to 11, and 13, wherein the light emitted from the four-wave mixing unit of (1) enters the next-stage four-wave mixing unit while maintaining the polarization state. 15. In the optical composite section formed by connecting one or more of the four-wave mixing sections A and / or the four-wave mixing sections B in series, the four-wave mixing section is located at a position farthest from the light source section. 4. A portion of the four-wave mixing section from the input end of the nonlinear medium to the output end of the optical composite section which does not maintain the polarization state.
3. The multi-frequency light source according to any one of items 3 and 14. 16. The multi-frequency device according to claim 1, wherein the wavelength division multiplexed light after the input port is kept in a polarization state up to an output end of the optical composite unit in the optical composite unit. light source. 17. The multi-frequency light source according to claim 6, wherein the polarization state held is a linear polarization state. 18. An optical equalizer for flattening the frequency dependence of the light intensity at the emission end is disposed between the emission end of the optical composite unit and the emission end of the multi-frequency light source. Item 19. The multi-frequency light source according to any one of Items 1 to 17. 19. The multi-frequency light source according to claim 1, wherein a carrier of one or more channels of the wavelength division multiplexed signal emitted from the emission end of the light source unit is modulated.