JP2001201655A - Optical demultiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical demultiplexer in which respective intensity levels of branched light are mutually the same and moreover the intensity level of branched light is not largely degraded compared with the intensity level of light before being branched in the case of branching light of respective wavelength by receiving multiple optical signals formed by multiplexing light having different wavelengths. SOLUTION: Four transmitting type wavelength filters 2, 3, 4 and 5 which transmit only light of the wavelength of a narrow band using respectively specified wavelengths λ1, λ2, λ3 and λ4 as the center are specially arranged with a prescribed relation held so that light reflected without being transmitted advances to the next stage transmitting type wavelength filter successively, further an ND filter having prescribed transmissivity is respectively arranged in the latter parts of the transmitting type wavelength filters 2, 3, 4, and light intensity of optical signals of the branched wavelengths λ1, λ2, λ3 and λ4 is set so as to be nearly the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical demultiplexer used for wavelength division multiplexing communication and the like, which receives a multiplexed optical signal formed by multiplexing light of different wavelengths and demultiplexes the light of each wavelength.

[0002]

2. Description of the Related Art Wavelength division multiplexing (WDM) for simultaneously handling a large number of optical signals having different wavelengths and realizing large-capacity optical transmission and wavelength routing.
iplexing) In optical communication, each node on the network extracts optical signals of a specific wavelength,
In order to change the route, it is necessary to once demultiplex the multiplexed optical signal.

An optical demultiplexer is used for this purpose, and FIG. 11 shows a configuration example of a conventionally used optical demultiplexer. In the figure, the 1 × 4 coupler 10 of the optical demultiplexer 100
1 inputs the multiplexed optical signal WMS. This multiplexed optical signal W
As shown in the band characteristic diagram of FIG. 12A, the MS has four types of wavelengths λ1, λ2,
This is an optical signal formed by multiplexing the lights of λ3 and λ4.
In FIG. 12A, the horizontal axis represents the wavelength, and the vertical axis represents the light intensity level.

[0004] The 1 × 4 coupler 101 outputs approximately 1/4 of the input light.
And the four divided optical signals are output to optical paths 102, 103, 104 and 105, respectively. The transmission wavelength filters 106, 107, 108, and 109 disposed on each of these optical paths are band filters that transmit light of the above-described wavelengths λ1, λ2, λ3, and λ4, respectively. Transmits only signals. FIG. 12B shows a wavelength band and a level of light transmitted through each filter at this time. In addition, FIG.
The horizontal axis indicates the wavelength, and the vertical axis indicates the light intensity level.

[0005] The output optical signal of each wavelength thus demultiplexed has a remarkably lower light intensity level than the input light, but the levels of the respective signals are almost the same.

FIG. 13 shows an example of the configuration of another conventional optical demultiplexer. In the figure, four transmission-type wavelength filters 111, 112, 113, and 114 of the optical demultiplexer 110 are all constituted by dielectric multilayer filters, and each of them is specified as shown in the band characteristic diagram of FIG. Wavelengths λ1, λ2,
Only light having a wavelength in a narrow band around λ3 and λ4 is transmitted. Note that the horizontal axis in the figure indicates the wavelength, and the vertical axis indicates the transmittance of the filter.

Transmission type wavelength filters 111, 112, 11
As shown in FIG. 13, 3, and 114 are arranged with a predetermined spatial relationship so that light reflected without being transmitted is successively directed to the next-stage transmission wavelength filter.

Therefore, a multiplexed optical signal WMS formed by multiplexing the above-mentioned four wavelengths λ1, λ2, λ3, and λ4 of the same intensity level is transmitted to a transmission wavelength filter 111 as shown in FIG. , The transmission wavelength filter 111 transmits the light of the wavelength λ1 and reflects the other light toward the transmission filter 112. The transmissive filter 112 that has received the reflected light transmits the light having the wavelength λ2 and reflects the other light toward the transmissive filter 113.
Similarly, the transmission filter 113 transmits light of wavelength λ3, and the transmission filter 114 transmits light of wavelength λ4.

FIG. 14B shows a wavelength band and a level of light transmitted through each filter at this time. As is clear from the figure, the level of the output optical signal of each wavelength demultiplexed in this manner decreases as the wavelength is demultiplexed at a later stage as described later.

[0010]

In the case of the optical demultiplexer 100 shown in FIG. 11, the wavelengths .lambda.1 and .lambda.
Although the output light signals of 2, λ3, and λ4 have the same light intensity level, the input light passes through the 1 × 4 coupler 101, so the level is reduced to about に 対 し て of the input light. Resulting in.

Further, in the case of the optical demultiplexer 110 shown in FIG. 13, the output optical signals of the wavelengths λ1, λ2, λ3, and λ4, which are demultiplexed and output, have a small decrease in the intensity level with respect to the input light. However, due to the loss due to incident reflection and the loss due to propagation in space, the intensity level decreases as the optical signal is split at a later stage in the optical path.

An object of the present invention is to provide a wavelength division multiplexed multiplexed optical signal in which the intensity levels of the demultiplexed light are equal to each other and the intensity level of the demultiplexed light is the light before the demultiplexing. It is an object of the present invention to provide an optical demultiplexer which does not significantly decrease with respect to the intensity level of the optical splitter.

[0013]

An optical demultiplexer according to the present invention is an optical demultiplexer that receives a multiplexed optical signal obtained by multiplexing optical signals of different wavelengths and demultiplexes the optical signal of each wavelength. A plurality of optical demultiplexing means for demultiplexing an optical signal of a predetermined wavelength among the optical signals input to the input unit and guiding the optical signal to a first optical path, and guiding an optical signal of another wavelength to a second optical path; One or two or more light intensity attenuating means for attenuating the intensity of the input light by a predetermined amount and outputting the light, and the second optical path of the optical demultiplexing means arranged in the preceding stage has a wavelength different from that of the preceding stage. The input sections of the optical demultiplexing means for demultiplexing an optical signal are optically connected and sequentially arranged, and at least each of the optical demultiplexing means arranged in each stage from the first stage to the last stage one stage before The light intensity attenuating means having different transmittances is arranged in the first optical path so that the demultiplexed optical signal is transmitted and output. When you enter the multiplexed optical signal to an input of said optical demultiplexing means of the first stage, the light intensity of the optical signal of each wavelength output is demultiplexed configured to substantially the same level. Further, the light intensity attenuating means may be constituted by a transmission or reflection type ND filter.

Another optical demultiplexer according to the present invention is an optical demultiplexer that receives a multiplexed optical signal obtained by multiplexing optical signals of different wavelengths and demultiplexes the optical signal of each wavelength. And a light intensity attenuating means for transmitting the light with a transmittance that varies according to the wavelength thereof, and demultiplexing an optical signal of a predetermined wavelength from among the optical signals input to the input unit, and guiding the demultiplexed light signal to a first optical path. A plurality of optical demultiplexing means for guiding optical signals of other wavelengths to the second optical path,
In the second optical path of the optical demultiplexing means disposed in the previous stage,
The input sections of the optical demultiplexing means for demultiplexing an optical signal having a wavelength different from that of the preceding stage are optically connected and sequentially arranged, and output from the light intensity attenuating means to the input section of the first-stage optical demultiplexing means. When the multiplexed optical signal is applied to the light intensity attenuating means, the light of each wavelength is demultiplexed and output from each first optical path of the plurality of light demultiplexing means. The light intensity of the signal is configured to be substantially the same level. Also,
Intensity adjustment ND of transmission or reflection type through the light intensity attenuation means
You may comprise a filter.

The optical demultiplexing means may be constituted by a dielectric multilayer filter. Further, the optical demultiplexing means may be constituted by a circulator and an FBG. Further, the optical demultiplexing means may be constituted by an MZ interferometer using FBG.

[0016]

FIG. 1 is a block diagram of an optical demultiplexer according to a first embodiment of the present invention. In FIG.
Each of the transmission wavelength filters 2, 3, 4, and 5 is formed of a dielectric multilayer filter, and has a specific wavelength λ1, λ2, λ3, and λ4 as the center as shown in the band characteristic diagram of FIG. Only light of a narrow band wavelength is transmitted. FIG.
The abscissa of the band characteristic diagram of FIG. 1 shows the wavelength, and the ordinate shows the transmittance of the filter.

Transmission wavelength filters 2, 3, 4, and 5
As shown in FIG. 1, are arranged with a predetermined spatial relationship so that light reflected without being transmitted is directed toward the transmission wavelength filter of the next stage.

On the optical path of the light passing through the transmission type wavelength filter 2, there is provided an ND for reducing the light intensity by a desired amount as described later.
(Neutral-density) filter 6 is arranged, ND filter 7 is arranged on the optical path of light passing through transmission wavelength filter 3, and ND filter is also placed on the optical path of light passing through transmission wavelength filter 4. A filter 8 is provided.

FIG. 2 shows these ND filters 6, 7, 8
Is a characteristic diagram showing the transmittance of each light, wherein the horizontal axis represents the wavelength and the vertical axis represents the light transmittance. As is clear from the drawing, the transmittance is set to be higher than that of the filter arranged at the subsequent stage, and the reason for these will be described later.

In the optical demultiplexer 1 configured as described above, the multiplexed optical signal WMS is incident on the transmission wavelength filter 2 at a predetermined angle as shown in FIG. Multiplexed optical signal WMS
Have four wavelengths λ1, λ2, λ3 at the same intensity level, as shown in the band characteristic diagram of FIG.
And λ4 are multiplexed. In FIG. 4A, the horizontal axis represents wavelength, and the vertical axis represents light intensity.

The transmission wavelength filter 2 receives the multiplexed optical signal WMS, transmits an optical signal in a wavelength band near the wavelength λ1 shown in FIG. 3, and transmits an optical signal in another wavelength band to the transmission filter 3.
Reflects toward. The transmission filter 3 receives the reflected light, transmits an optical signal in a wavelength band near the wavelength λ2 shown in FIG. 3, and reflects an optical signal in another wavelength band toward the transmission filter 4. Similarly, the transmission filters 4 and 5 receive the reflected light, respectively, transmit the optical signals in the bands near the wavelengths λ3 and λ4 shown in FIG. 3, and reflect the optical signals in other wavelength ranges.

Multiplexed optical signal WMS incident on optical demultiplexer 1
Is the loss due to input / reflection and the loss due to propagation in space. The lower the light intensity, the higher the rate of reduction in light intensity. The intensity levels of the optical signals of the respective wavelengths at the stages that have been performed sequentially decrease.

The ND filter 6 receives the demultiplexed optical signal of the wavelength λ1 and attenuates the optical signal to the optical intensity level PL of the optical signal of the wavelength λ4 transmitted through the transmission type filter 5. The amount is preset. Similarly, N
The D filter 7 is set so as to attenuate the input optical signal of the wavelength λ2 to the intensity level PL, and the ND filter 8 is set so as to attenuate the input optical signal of the wavelength λ3 to the intensity level PL. FIG. 4B is a band characteristic diagram of an optical signal of each wavelength that is demultiplexed and taken out from the optical demultiplexer 1. The horizontal axis indicates the wavelength, and the vertical axis indicates the light intensity level.

As is clear from the characteristic diagram of FIG.
According to the optical demultiplexer 1 of the first embodiment of the present invention, the optical intensity level of the optical signal of each wavelength that is output after being demultiplexed is changed to the optical intensity of the optical signal of the wavelength λ4 transmitted through the transmission filter 5. It can be adjusted to the level PL. Further, since the loss due to input / reflection and the loss due to propagation in space do not become so large, it is possible to suppress a decrease in the level of the intensity level PL of each output light with respect to the incident multiplexed optical signal WMS within an allowable range.

FIG. 5 is a block diagram of an optical demultiplexer according to a second embodiment of the present invention. In FIG. 1, the optical demultiplexer 10 has an optical path in which four spectral elements 11, 12, 13, and 14 are cascaded. The spectroscopic element 11 includes a 3P (port) circulator 11a and a reflective wavelength filter 11b. The circulator 11a guides the light incident on the input unit P1 to the reflective wavelength filter 11b, and the reflective wavelength filter 11b transmits the light. It reflects only optical signals in the band near the wavelength λ1 of the emitted light and transmits optical signals of other wavelengths. The circulator 11a outputs the optical signal of the wavelength λ1 reflected and demultiplexed by the reflection type wavelength filter 11b from its output part P3.

The spectral element 12 is a reflection type wavelength filter 12
b operates in the same manner as the spectral element 11 except that b reflects only the optical signal in the band near the wavelength λ2. The spectroscopy elements 13 and 14 also operate in the same manner as the spectroscopy element 11 except that the reflection-type wavelength filters 13b and 14b reflect only optical signals in the bands near the wavelengths λ3 and λ4.

These reflection type wavelength filters 11b, 12
b, 13b and 14b all have a reflectance of 100% for the reflected light.
However, even in this case, due to the insertion loss of the circulator, the decrease rate of the light intensity of the optical signal spectrally separated by each spectral element is determined by the subsequent stage. The higher the optical signal is, the higher the signal becomes.

The attenuator 15 receives the light of the wavelength λ1 split by the spectroscopic element 11 and attenuates the light intensity by a desired amount, as described later, and outputs the light. Similarly, the attenuators 16 and 17 attenuate the intensity levels of the optical signals of the wavelengths λ2 and λ3 separated by the spectral elements 12 and 13, respectively, by a desired amount, as described later, and output the signals. Each of these attenuators 15, 16 and 17 is composed of a transmission type or reflection type light intensity ND filter that functions as an optical attenuator whose attenuation can be set.

In the optical demultiplexer 10 configured as described above, the four types of wavelengths λ1 and λ
A multiplexed optical signal WMS formed by multiplexing the lights of 2, λ3, and λ4 is incident on the input part P1 of the 3P circulator 11a of the spectroscopic element 11.

At this time, the spectroscopy element 11 outputs the split wavelength λ.
One optical signal is output from the output part P3 of the circulator 11a, and the spectroscopic element 12 outputs the separated optical signal of the wavelength λ2 from the output part P3 of the circulator 12a. Furthermore,
The spectroscopic element 13 outputs the split optical signal of the wavelength λ3 from the output part P3 of the circulator 13a, and the splitter element 14 outputs the split optical signal of the wavelength λ4 to the circulator 1.
Output from the output part P3 of 4a.

The attenuator 15 converts the input optical signal of wavelength λ1 into the intensity level P of the optical signal of wavelength λ4 output from the output section P3 of the circulator 14a of the spectroscopic element 14.
The output is attenuated by a predetermined amount up to L2. Similarly, the attenuator 16 converts the input optical signal of the wavelength λ2 into the intensity level P
L2, and the attenuator 17 attenuates the input optical signal of wavelength λ3 to the intensity level PL2.

As described above, according to the optical demultiplexer 10 of the second embodiment of the present invention, the intensity level of the demultiplexed optical signal of each wavelength is output from the output part P3 of the circulator 14a of the spectral element 14. The intensity level P of the output optical signal of wavelength λ4
L2. Further, the intensity loss of light due to passing through each of the reflection type wavelength filters and the circulator is small, and the decrease in the intensity level PL2 of each spectrum with respect to the incident multiplexed optical signal WMS can be suppressed to about several decibels.

FIG. 6 is a block diagram of an optical demultiplexer according to a third embodiment of the present invention. In the figure, an optical demultiplexer 20 is an FBG
(Mach-Zehnder) type interferometers 21, 22, 23, and 24 in which are arranged at predetermined positions have optical paths cascaded. The MZ type interferometer 21 reflects only the optical signal in the band near the wavelength λ1 and transmits the optical signal of another wavelength.
By arranging G at a predetermined position, an optical signal in the vicinity of wavelength λ1, which is demultiplexed from the light input to the input unit 21a, is output from the reflected light output unit 21c, and light of another wavelength is transmitted to the transmitted light output unit 2c.
1b.

The MZ-type interferometer 22 reflects only an optical signal in the band near the wavelength λ2 and transmits an FB signal which transmits optical signals of other wavelengths.
By using G, an optical signal near the wavelength λ2, which is demultiplexed from the light input to the input unit 22a, is output from the reflected light output unit 22c, and light of another wavelength is output from the transmitted light output unit 22b.

The MZ interferometers 23 and 24 also have wavelengths λ
By using an FBG that reflects only the optical signals in the bands near 3 and λ4 and transmits optical signals of other wavelengths, the input unit 2
Optical signals in the vicinity of wavelengths λ3 and λ4, which are demultiplexed from the light input to 3a and 24a, are output from reflected light output units 23c and 24c, and light of another wavelength is transmitted light output units 23b and 24b.
Output from

Due to the reflection or transmission loss of each cascaded MZ interferometer, the reduction rate of the intensity level of the optical signal split by each MZ interferometer becomes higher as the optical signal is split at a later stage. The attenuator 25 receives the light of the wavelength λ1 split by the MZ interferometer 21 and attenuates the light intensity by a predetermined amount and outputs the light, as described later. Similarly, the attenuators 26 and 27 also attenuate the intensity levels of the optical signals of the wavelengths λ2 and λ3 separated by the MZ interferometers 22 and 23 by a predetermined amount, as described later, and output them.
Each of these attenuators 25, 26, and 27 is composed of a transmission type or reflection type light intensity ND filter that functions as an optical attenuator whose attenuation can be set.

In the optical demultiplexer 20 configured as described above, the four types of wavelengths λ1 and λ
Multiplexed optical signal W formed by multiplexing the lights of 2, λ3 and λ4
The MS enters the input section 21a of the MZ interferometer 21.

At this time, the MZ type interferometer 21 outputs the separated optical signal of the wavelength λ1 from the reflected light output section 21c,
The MZ type interferometer 22 outputs an optical signal of the split wavelength λ2 from the reflected light output unit 22c. Further, the MZ-type interferometer 23 outputs the split optical signal of the wavelength λ3 from the reflected light output unit 23c, and the MZ-type interferometer 24 outputs the split optical signal of the wavelength λ4 from the reflected light output unit 24c. Output.

The attenuator 25 attenuates the input optical signal of wavelength λ1 by a predetermined amount to the intensity level PL3 of the optical signal of wavelength λ4 output from the reflected light output unit 24c of the MZ interferometer 24, and outputs the signal. Similarly, the attenuator 26
Attenuates the input optical signal of wavelength λ2 to the intensity level PL3, and the attenuator 27 attenuates the input optical signal of wavelength λ3 to the intensity level PL3.

As described above, according to the optical demultiplexer 20 of the third embodiment of the present invention, the intensity level of the demultiplexed optical signal of each wavelength is determined by the reflected light output unit 24c of the MZ type interferometer 24. Can be made equal to the intensity level PL3 of the optical signal of wavelength λ4 output from. In addition, since the intensity loss of light due to reflection and transmission by the MZ interferometer is small, the incident multiplex optical signal WM
The decrease in the intensity level PL3 of each spectrum with respect to S can be suppressed within an allowable range.

FIG. 7 is a block diagram of an optical demultiplexer according to a fourth embodiment of the present invention. The optical demultiplexer 30 has a configuration in which a transmittance distribution filter 31 is newly provided except for the ND filters 6, 7, and 8 from the optical demultiplexer 1 shown in FIG. Therefore, portions common to the optical demultiplexer 1 (FIG. 1) are denoted by the same reference numerals, and description thereof will be omitted. Only different portions will be described.

The transmittance distribution filter 31 is arranged in front of the transmission type filter 2, and is configured such that light transmitted therethrough enters the transmission type wavelength filter 2 at a predetermined angle. FIG. 8 is a characteristic diagram showing the band characteristics of the transmittance distribution filter 31, in which the horizontal axis indicates wavelength and the vertical axis indicates light transmittance.

As described above, the loss rate due to the incident / reflection and the loss caused by propagating through the space, the reduction rate of the intensity level of the optical signal split by each of the transmission type wavelength filters 2, 3, 4 and 5 is as follows. The higher the optical signal split in the subsequent stage, the higher the signal. That is,
In the configuration shown in FIG. 7, the light is split in the order of the wavelength λ1, the wavelength λ2, the wavelength λ3, and the wavelength λ4, so that the decreasing rate sequentially increases in this order. On the other hand, as is clear from the characteristic diagram of FIG. 8, the transmittance distribution filter 31 has a characteristic that the transmittance changes according to the wavelength of the light passing therethrough, and the transmittance increases from the wavelength λ1 to the wavelength λ4. .

The light of each wavelength is transmitted through the transmittance distribution filter 3.
1, the attenuation rate of the light intensity until the light is passed through the transmission type filter of the corresponding wavelength to be separated is substantially the same at each wavelength.

Therefore, the multiplexed optical signal WMS formed by multiplexing the four types of light of the wavelengths λ1, λ2, λ3, and λ4 having the same intensity level is transmitted to the transmittance distribution filter 31 of the optical demultiplexer 30. When illuminated, the transmission wavelength filters 2, 3, 4, and 5 respectively separate the wavelengths λ1, λ
Optical signals of 2, λ3 and λ4 are output at substantially the same intensity level.

As described above, according to the optical demultiplexer 30 of the fourth embodiment of the present invention, the intensity levels of the demultiplexed optical signals of the respective wavelengths can be made uniform. Further, the number of components can be reduced as compared with the optical demultiplexer 1 (FIG. 1) of the first embodiment.

FIG. 9 is a block diagram of an optical demultiplexer according to a fifth embodiment of the present invention. The optical demultiplexer 40 is provided with the attenuators 15, 16, 17 from the optical demultiplexer 10 (FIG. 5).
, Except that the intensity adjustment ND filter 41 is newly provided. Therefore, portions common to the optical demultiplexer 10 (FIG. 5) are denoted by the same reference numerals, and description thereof will be omitted. Only different portions will be described.

The intensity adjusting ND filter 41 includes the spectral element 1
1 is arranged in front of the optical element 1 and the light transmitted through the
It is configured to be incident on the input part P1 of the 3P circulation 11a. As described above, each of the spectral elements 11, 12, 1 is affected by the insertion loss of the circulator.
The rate of decrease in the intensity level of the optical signal split at 3, 14 is
The higher the optical signal split in the subsequent stage, the higher the signal. That is, in the configuration of FIG. 9, since the light is split in the order of the wavelength λ1, the wavelength λ2, the wavelength λ3, and the wavelength λ4, the decreasing rate sequentially increases in this order.

On the other hand, the intensity adjusting ND filter 41 has substantially the same characteristics as the transmittance distribution filter 31 (FIG. 7), and passes through as shown in the characteristic diagram of FIG. The transmittance changes according to the wavelength of the light, and the transmittance increases from the wavelength λ1 to the wavelength λ4.

The light of each wavelength enters the intensity adjusting ND filter 41, and the attenuation rate of the light intensity until the light is separated by the spectroscopic element of the corresponding wavelength is configured to be substantially the same at each wavelength. I have.

Therefore, the multiplexed optical signal WMS formed by multiplexing the four types of light of the wavelengths λ1, λ2, λ3, and λ4 having the same intensity level is supplied to the intensity adjusting ND filter 41 of the optical demultiplexer 40. Upon irradiation, each of the spectral elements 11, 1
From wavelengths 2, 13, and 14, the wavelengths λ1, λ
Optical signals of 2, λ3 and λ4 are output at substantially the same intensity level.

As described above, according to the optical demultiplexer 40 of the fifth embodiment of the present invention, the intensity levels of the demultiplexed optical signals of the respective wavelengths can be made uniform, and the optical signals of the second embodiment can be adjusted. Compared with the duplexer 10 (FIG. 5), the number of components can be reduced.

FIG. 10 is a block diagram of an optical demultiplexer according to a sixth embodiment of the present invention. The optical splitter 50 is different from the optical splitter 20 (FIG. 6) described above in that the attenuators 25, 26, 1
Except for 7, the configuration is such that an intensity adjustment ND filter 51 is newly provided. Therefore, portions common to the optical demultiplexer 20 (FIG. 6) are denoted by the same reference numerals, and description thereof will be omitted. Only different portions will be described.

The intensity adjustment filter 51 is provided for the MZ interferometer 2
1 and is configured so that light transmitted therethrough is incident on the input unit 21 a of the MZ interferometer 21. As described above, due to the reflection or transmission loss of the MZ-type interferometer, the rate of decrease in the intensity level of the optical signal split by each of the MZ-type interferometers 21, 22, 23, and 24 is reduced by the optical signal divided at the subsequent stage. Higher. That is, in the configuration of FIG.
Since the light is split in the order of the wavelength λ1, the wavelength λ2, the wavelength λ3, and the wavelength λ4, the decreasing rate sequentially increases in this order.

On the other hand, the intensity adjusting type ND filter 51 has substantially the same characteristics as those of the transmittance distribution filter 31 (FIG. 7), and as shown in the characteristic diagram of FIG. The transmittance changes according to the wavelength of the light
The transmittance has a characteristic that the transmittance increases from the wavelength λ1 to the wavelength λ4.

Then, the light of each wavelength enters the intensity adjusting ND filter 51, and the attenuation rate of the light intensity until the light is separated by the MZ interferometer of the corresponding wavelength is substantially equal at each wavelength. ing.

Therefore, the multiplexed optical signal WMS formed by multiplexing the four types of light of the wavelengths λ1, λ2, λ3, and λ4 having the same intensity level is supplied to the intensity adjusting ND filter 51 of the optical demultiplexer 50. When irradiated, each of the MZ interferometers 21 and
From wavelengths 2, 23 and 24, the wavelengths λ 1 and λ
Optical signals of 2, λ3 and λ4 are output at substantially the same intensity level.

As described above, according to the optical demultiplexer 50 of the sixth embodiment of the present invention, the intensity levels of the demultiplexed optical signals of the respective wavelengths can be made uniform, and the optical demultiplexer of the third embodiment can be used. Compared with the duplexer 20 (FIG. 6), the number of components can be reduced.

Although the transmission type ND filter is used as the light intensity attenuating means in the above embodiment, the present invention is not limited to this, and a reflection type ND filter may be used.

[0060]

According to the optical spectroscope of the present invention, when demultiplexing a wavelength-multiplexed multiplexed optical signal, the intensity levels of the demultiplexed lights are output to be aligned with each other, and the demultiplexed light is output. Does not significantly decrease with respect to the intensity level of the light before the demultiplexing. Therefore, it is possible to equalize the levels of the demultiplexed optical signals or to omit an optical amplifier for amplifying the optical signals.
Costs associated with optical demultiplexing can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical demultiplexer according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing transmittance of each light of ND filters 6, 7, and 8;

FIG. 3 is a band characteristic diagram of transmission wavelength filters 1, 2, 3, and 4;

FIG. 4 shows a multiplexed optical signal input to the optical demultiplexer 1 and each ND
FIG. 4 is a band characteristic diagram of a split optical signal output from a filter.

FIG. 5 is a configuration diagram of an optical demultiplexer according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical demultiplexer according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical demultiplexer according to a fourth embodiment of the present invention.

8 is a band characteristic diagram of the transmittance distribution filter 31. FIG.

FIG. 9 is a configuration diagram of an optical demultiplexer according to a fifth embodiment of the present invention.

FIG. 10 is a configuration diagram of an optical demultiplexer according to a sixth embodiment of the present invention.

FIG. 11 is a diagram illustrating a configuration example of a conventional optical demultiplexer.

12 is a band characteristic diagram of input / output light of the optical demultiplexer 100 shown in FIG.

FIG. 13 is a diagram illustrating another configuration example of a conventional optical demultiplexer.

14 is a characteristic diagram of the four transmission wavelength filters shown in FIG. 13 and a band characteristic diagram of the output light of the optical demultiplexer 110. FIG.

[Description of Signs] 1 Optical demultiplexer, 2 Transmission wavelength filter, 3 Transmission wavelength filter, 4 Transmission wavelength filter, 5 Transmission wavelength filter, 6 ND filter, 7ND filter, 8 ND filter, 10 Optical demultiplexing Bowl, 11
Spectral element, 11a circulator, 11b reflective wavelength filter, 12 spectral element, 12a circulator, 12b reflective wavelength filter, 13 spectral element, 13a circulator, 13b reflective wavelength filter, 14 spectral element, 13a circulator, 13b reflective wavelength filter , 15 attenuator, 16 attenuator, 17 attenuator, 20 optical demultiplexer, 21 MZ interferometer, 21
a input section, 21b transmitted light output section, 21c reflected light output section, 22 MZ interferometer, 22a input section,
22b transmitted light output unit, 22c reflected light output unit, 23
MZ interferometer, 23a input section, 23b transmitted light output section, 23c reflected light output section, 24 MZ type interferometer,
24a input section, 24b transmitted light output section, 24c
Reflected light output section, 25 attenuator, 26 attenuator, 27 attenuator, 30 optical demultiplexer, 3
1 transmittance distribution filter, 40 optical demultiplexer, 41
Intensity adjustment filter, 50 optical demultiplexer, 51 Intensity adjustment filter.

Claims (7)

[Claims] An optical demultiplexer for inputting a multiplexed optical signal obtained by multiplexing optical signals of different wavelengths and demultiplexing the optical signal of each wavelength, wherein a predetermined one of the optical signals input to an input unit is provided. The optical signal of the wavelength is demultiplexed and guided to the first optical path, and the optical signal of another wavelength is converted to the second optical path.
A plurality of light demultiplexing means for guiding the light to the optical path, and one or two or more light intensity attenuating means for attenuating the intensity of the input light by a predetermined amount and outputting the light. In the second optical path, input sections of the optical demultiplexing means for demultiplexing an optical signal having a wavelength different from that of the previous stage are optically connected and sequentially arranged, and at least each stage from the first stage to the last stage one stage before The light intensity attenuating means having different transmittances is arranged in each of the first optical paths of the light demultiplexing means arranged in the first stage to transmit and output the demultiplexed optical signal. An optical demultiplexer characterized in that, when the multiplexed optical signal is input to the input part of the demultiplexing means, the light intensity of the demultiplexed and output optical signals of each wavelength is substantially the same level. 2. The optical demultiplexer according to claim 1, wherein said light intensity attenuating means comprises a transmission or reflection type ND filter. 3. An optical demultiplexer for inputting a multiplexed optical signal obtained by multiplexing optical signals of different wavelengths and demultiplexing the optical signal of each wavelength, wherein the input light changes according to the wavelength. A light intensity attenuating means for transmitting and transmitting the light at a transmittance; and an optical signal having a predetermined wavelength among the optical signals input to the input section, which is demultiplexed and guided to a first optical path, and an optical signal having another wavelength is transmitted to a first optical path. 2
A plurality of optical demultiplexing means for guiding the optical signal to the second optical path of the optical demultiplexing means disposed at the preceding stage, and the optical demultiplexing means for demultiplexing an optical signal having a wavelength different from that of the preceding stage. The input sections are optically connected and sequentially arranged, arranged so that an optical signal output from the light intensity attenuating means is input to an input section of the first-stage optical demultiplexing means, and the light intensity attenuating means is When irradiating the multiplexed optical signal, the optical intensities of the optical signals of the respective wavelengths that are demultiplexed and output from the respective first optical paths of the plurality of optical demultiplexing means are substantially at the same level. Optical demultiplexer. 4. The optical spectroscope according to claim 3, wherein said light intensity attenuating means comprises a transmission or reflection type intensity adjusting ND filter. 5. The optical demultiplexer according to claim 1, wherein said optical demultiplexing means is constituted by a dielectric multilayer filter. 6. The optical demultiplexing means includes a circulator and an FB
The optical demultiplexer according to claim 1, wherein the optical demultiplexer is composed of G. 5. 7. The optical demultiplexing means according to claim 1, wherein the optical demultiplexing means comprises an MZ interferometer using FBG.
An optical demultiplexer as described.