JP2000101174A - Pump device for pumping active fiber of optical amplifier and corresponding optical amplifier - Google Patents

Abstract

(57) [Problem] To provide a pump device capable of obtaining higher coupling efficiency than a conventional optical amplifier. A pump device that couples a pump beam to an active optical fiber configured to amplify an optical signal optically couples a first portion of the pump beam to an active fiber. , A first optical coupler (15) having an insertion loss of 0.2 d or less with respect to an optical signal.
0) and a second optical coupler (160) optically coupled to the first coupler (150) and receiving a second portion of the pump beam from the first coupler (150). Second of pump beam
The portion is further optically coupled to the active fiber (130) and provides at least a portion of the second portion of the pump beam to the active fiber (130). It has a coupling efficiency of at least 70% for the pump beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION It is an object of the present invention to provide a pump device for pumping an active fiber of an optical amplifier. In particular, it is an object of the invention to provide, for example, wavelength division multiplexing (WD)
M: wavelength division mul
An optical amplifier suitable for use in an optical transmission system, such as a multiplexing optical transmission system, includes a pump beam (p).
The purpose of the present invention is to provide a pump device that combines the pump radiation. The present invention also relates to an optical amplifier using the above-described pump device.

[0002]

BACKGROUND OF THE INVENTION Conventional optical fiber amplifiers include an active fiber having a rare earth doped core. Injecting pump power at the characteristic wavelength of the rare-earth element into the active fiber excites the rare-earth ion and gains an information signal in the core that propagates along the fiber.

[0003] Rare earth elements used for doping include:
Typically, erbium (Er), neodymium (Nd), ytterbium (Yb), samarium (Sm), and praseodymium (Pr) are included. The specific rare earth element or plural rare earth elements to be used are determined according to the wavelength of the input signal light and the wavelength of the pump light. For example, Er ions are used for input signal light having a wavelength of 1.55 μm and pump power having a wavelength of 1.48 μm or 0.98 μm. Also, a wider pump wavelength band can be used.

[0004] Conventional pump sources include single mode laser diodes and multimode broadband lasers, which are coupled to active fiber via single mode pump fiber and multimode pump fiber, respectively. To obtain pump power. Single mode lasers typically provide pump power as low as 100 mW. On the other hand, the wide area laser is 500m
Provides pump power as high as W. However,
These high power lasers cannot efficiently inject light into the small core of a single mode fiber. As a result, the use of high power broadband lasers requires the use of wide core and multi-mode fibers to pump the optical amplifier. On the other hand, this inactive
The pump fiber is typically coupled via a coupler to the active fiber, e.g., the inner cladding of a double-clad active fiber acting as a multi-mode core to the pump power. input.

In a double clad amplification fiber, a pump
Power is directed into the multi-mode cladding inside the fiber, from where it is transferred to a single-mode core doped with active dopants. The double cladding fiber pump mechanism is described, for example, in WO95 /
10868. This document discloses an optical fiber amplifier comprising a fiber having two concentric cores. The pump power provided by the multi-mode source couples transversely to the outer core (equivalent to the inner core) of the fiber via the multi-mode fiber and the multi-mode optical coupler. pump·
Power propagates through the outer core, interacts with the inner core, and pumps active material contained in the inner core. This pumping technique is disclosed in US Pat.
It is also described in No. 1. This patent shows a single mode optical fiber having a doped core and a doped inner cladding.

A known basic amplification system is coupled to an amplification fiber, eg, an Er / Yb-doped double clad fiber, via a conventional fused fiber wavelength division multiplexing (WDM) coupler. Some include mode pump sources. The WDM coupler operates as a multi-mode coupler for pump power and transmits a single mode signal along the amplifier fiber without substantially coupling to the pump fiber. During pump operation, most of the outer mode of pump power is transmitted to the amplification fiber, leaving the inner mode of pump power unused. For multimode or double cladding amplification fiber, the fused fiber coupler is
It has a theoretical coupling coefficient that is directly proportional to the area ratio of the two fibers that make up the coupler itself. In the ideal case where the two fibers are identical, the coupling coefficient will be about 50%, but actually ranges from 45 to 48%. This means that only about 45 to 48% of the total pump power passes from the pump fiber to the inner cladding of the double clad active fiber, and the remaining 52 to 55% is pumped.・ It remains in the fiber.

Some systems use two fibers having different diameter cores to improve the coupling coefficient of a multi-mode coupler. However, such a configuration often wastes power because it is difficult to match the taper shapes of two cores of different sizes.

In order to increase the coupling efficiency, the Applicant has examined the possibility of using a micro optic coupler. The micro-optical coupler combines a light beam using a wavelength selection mirror and a focusing lens system. In this structure, the micro optical coupler is a conventional WDM.
It provides much higher coupling efficiency than couplers, typically in the 89% range. Applicants have noted that micro-optical couplers have several disadvantages, which limit their use to pump coupling in fiber amplifiers. That is, if a single micro-optical coupler is used upstream of the active fiber and pump light is supplied to the active fiber in the same propagation direction, the transmitted signal passing through the coupler suffers a power loss. This is much larger than the loss caused by fused fiber couplers, and can be excessively large (especially considering that the signal is attenuated before being amplified, this leads to an increase in the noise figure of the amplifier. ). Alternatively, a single micro-optical coupler can be
Placing the pump beam downstream of the fiber and feeding the active fiber in a counter-propagating direction reduces the signal-to-noise ratio and may again be excessive. Furthermore, due to the high coupling efficiency achievable by using micro-optical couplers and the high pump power supplied to the fiber, the inhomogeneous dispersion (inh
Omogenious distribution occurs.

Some recent systems have attempted to restore the pump power loss in conventional fused fiber couplers by different pumping schemes using fused fiber couplers. That is, different solutions have been proposed that include a second optical coupler in addition to the first optical coupler arranged according to the single coupler configuration described above. The second coupler is
With respect to the first coupler, it is located at the opposite end of the active fiber and is coupled to the first coupler via a multi-mode pump fiber to receive residual pump power (ie, by the first coupler). Part of the pump power not directly supplied to the active fiber). Further, the second coupler is configured to couple the residual pump power to the same active fiber in a counter-propagating direction or to a different active fiber in a co-propagating direction. Pump schemes proposed to restore pump power using the techniques described above include only fused fiber couplers. Applicants have recognized that the addition of a second fiber coupler does not significantly improve the overall pump power transfer over the single coupler system described above. In fact, the second coupler receives from the pump fiber mainly the internal mode left by the first coupling in which the first coupler operates, and the active mode of the internal mode.
Transfer to fiber is inefficient.

[0010] EP Patent Application No. 97114 in the name of the present applicant
No. 622.0 proposes a technique for improving the total coupling efficiency in the aforementioned two-coupler pump system. To achieve this improvement, a pump coupling the first and second couplers
Along the fiber connection, a mode scrambler (mod
e scrambler, i.e., a device that handles the scrambling of the internal mode on the residual pump beam, regenerates a large number of external modes, which can be efficiently transferred to the active fiber via a second coupler And Under ideal conditions, 5 of the pump power signal
0% is incident on the active fiber at each of the couplers. This results in a total coupling efficiency of the coupling system of 75%. However, in practice, the total coupling efficiency is around 68%.

EP Patent Application No. 97114 in the name of the present applicant
No. 620.4 proposes a different solution to the same problem. This is a fusion biconical reduction technique (fusion b
iconic taping technology
ue) consists of the use of two different couplers. In practice, the first and second couplers are active
It has a different amount of deposition and shrinkage than the fiber to achieve an increased coupling coefficient. This alternative pump solution allows for a total coupling efficiency of about 66%.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to couple a pump beam to an active fiber (or multiple active fibers) to provide better coupling efficiency to known optical amplifiers. It is to provide a pump device.

Applicants have identified a first coupler that has a very low insertion loss for a signal (even if it has a very low pump coupling efficiency) and a first coupler (if it has a relatively high insertion loss). It has been found that very high coupling efficiencies can be achieved by providing couplers with (even) high pump coupling efficiencies.

That is, the present applicant has found that a very high coupling efficiency can be obtained by the double coupler configuration. In this configuration, a first coupler is configured to receive a pump beam from a pump source and couple it to the active fiber. The first coupler applies 0.2 to the optical signal.
It has an insertion loss of less than dB. The second coupler is also configured to receive the remaining portion of the pump beam from the first coupler and couple it to the active fiber. The second coupler has a coupling efficiency of less than 70% for the pump beam.

[0015] Couplers can be connected to opposing ends of a single active fiber section (where a second coupler counter-fibers the fiber).
mp)), or two separate active fibers
Can be connected to sections. In this case, the second coupler preferably pumps the second section of fiber in the same propagation direction, while the first coupler can pump the first section in either direction.

The present applicant can obtain a total coupling efficiency of up to 85% when the first coupler is a fused optical coupler and the second coupler is a minute optical coupler in a double coupler configuration. Have been found to be much higher than the maximum coupling efficiency achievable with known configurations.

[0017]

According to a first aspect, the present invention relates to a pump device for coupling a pump beam to an active fiber of an optical amplifier. The optical amplifier is configured to amplify an optical signal, wherein the pump device receives and carries a multi-mode pump beam, and a first mode of the pump beam.
A first optical coupler optically coupling a portion to the active fiber; and a second optical portion coupled to the first coupler for receiving a second portion of the pump beam from the first coupler;
A second optical coupler coupled to the active fiber and providing at least a portion of a second portion of the pump beam to the active fiber, wherein the first optical coupler is configured to: The second optical coupler has an insertion loss of 0.2 dB or less, and the second optical coupler has a coupling efficiency of at least 70% with respect to the pump beam.

Preferably, the first optical coupler is a fused fiber coupler, and the second optical coupler is a micro optical coupler. Preferably, the sum of the optical power of the first portion of the pump beam and the optical power of the at least a portion of the second portion of the pump beam is 75% of the total optical power of the pump beam.
More than%. More preferably, said sum is at least 85% of the total optical power of said pump beam.

Preferably, the pump device further comprises:
A pump optical fiber that optically couples the second optical coupler to the first optical coupler;
A multi-mode optical fiber configured to transmit light without substantial energy transfer between modes.

Preferably, the first optical coupler is a first access fiber and a multi-mode fiber, and the second access coupler is optically coupled to the multi-mode optical fiber and receives the pump beam. Fiber and
A third access fiber of the same type as the first access fiber and coupled to the active fiber and configured to provide a first portion of the pump beam to the active fiber; A fourth access fiber of the same type as the fiber, into which the second portion of the pump beam is carried, wherein the second coupler is the fourth access fiber of the first optical coupler;
A multi-mode fiber optically coupled to a fiber, the first access fiber receiving a second portion of the pump beam; and a second portion of the pump beam coupled to the second active fiber. A second access fiber that is a dual cladding fiber configured to feed the at least a portion of the second active fiber to the second active fiber, and a third access fiber that carries the optical signal.

Preferably, the first access fiber of the first coupler is a single mode fiber coupled to an optical input and configured to receive the optical signal; The third access fiber is
A single mode fiber coupled to the optical output and configured to provide the optical signal to the optical output.

According to a second aspect, the present invention relates to an optical amplifier, comprising: an optical input for inputting an optical signal, an optical output for outputting the optical signal, and an output between the input and the output. And an active fiber configured to amplify the optical signal, a pump source for generating a pump beam, and a pump source for optically coupling the pump beam to the active fiber. Including devices.

[0023] Preferably, said active fiber is a double cladding fiber. Preferably, said active fiber consists of two fiber sections, each coupled to a respective one of said two couplers.

According to another aspect, the invention relates to an optical amplifying device comprising two optical amplifiers as described above arranged in series. Preferably, the optical amplifying device further includes a preamplifier arranged in series with the optical amplifier.

Preferably, the optical amplifying device further includes at least one noise removal filter arranged in series with the optical amplifier. According to another aspect, the present invention provides an optical transmitter configured to transmit an optical signal, an optical receiver for receiving the optical signal, and optically coupling the transmitter to the receiver. An optical transmission system including an optical fiber link, further comprising: an active filter disposed along the optical fiber link to amplify the optical signal; a pump source for generating a pump light beam; And a pump device as described above, coupled to the active fiber.

According to yet another aspect of the invention, the invention is directed to a method of coupling a pump beam to an active fiber configured to amplify an optical signal. The method comprises:-guiding an optical signal;-guiding a multi-mode pump beam;-coupling the optical signal and the pump beam to the active beam.
Inputting the optical signal with a predetermined insertion loss, supplying a first power portion to the active fiber, and inputting the pump beam to obtain a residual power portion; Inputting said residual power portion to said active fiber with a predetermined coupling efficiency and supplying a second power portion to said active fiber, wherein said insertion loss is 0.2 dB or less; Characterized by an efficiency of at least 70%. Preferably, the sum of the first and second power portions is more than 75% of the optical power of the pump beam, more preferably at least 85% of the optical power of the pump beam.

The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the scope of the invention. The drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, explain the advantages and principles of the invention.

[0028]

Referring to FIG. 1, an optical transmission system 1 includes a first terminal site 10, a second terminal site 20,
It includes an optical fiber line 30 connecting the terminal sites 10 and 20 at a point, and at least one line site 40 interposed between the terminal sites 10 and 20 along the optical fiber line 30.

For simplicity, the optical transmission system 1 described below is unidirectional, that is, signals are transmitted from one terminal site to another (in this case, from the first terminal site to the second terminal site). However, any considerations below
It is also considered to be effective in a two-way system in which signals travel in both directions. Further, the optical transmission system 1
Is suitable for transmitting up to 128 channels, but from the following description, the number of channels is not a requirement to limit the scope and spirit of the present invention, and more than 128 channels may be required for a particular optical transmission system. It will be clear that it can be used on demand.

The first terminal site 10 preferably comprises a multiplexing part (MUX) 11, a transmission power amplifying part (TPA)
12 and a plurality of input channels 16. The second terminal site 20 preferably includes a receive pre-amplification (RPA) section 14, a demultiplexing section (DMUX) 15, and a plurality of output channels 17.

Each input channel 16 is received in the multiplexing section 11. The multiplexing part 11 is described below with reference to FIG. 3, but the input channel 16 is preferably divided into three sub-bands, indicated by the blue band BB, the first red band RB1 and the second red band RB2. Multiplex or aggregate. However, instead, the multiplexing part 11
It is also possible to aggregate the input channels 16 into more or less than three sub-bands.

The three partial bands BB, RB1, RB2 are:
Received sequentially by TPA portion 12, at least one line site 40, and second terminal site 20, as separate subbands or combined broadband. A plurality of sections of fiber optic line 30 connect at least one line site 40 to TPA portion 12, RPA portion 14, and possibly other line sites 40 (not shown).
Connect to The TPA section 12 will be described later with reference to FIG. 4, but receives the separate subbands BB, RB1, RB2 from the multiplexing section 11, performs their amplification and optimization, and then combines them into a single broadband. SWB is merged and transmitted on the first section of the optical fiber line 30. Line site 40 is described below with reference to FIG. 6, but receives a single wideband SWB and combines the single wideband SWB into three sub-bands BB, RB1, R
B2, and finally add and remove signals in each of the sub-bands BB, RB1 and RB3, amplify and optimize the three sub-bands BB, RB1, RB2 and again combine them into a single wideband SWB Annexed. For add and drop operations, the line site 40 includes an optical add / drop multiplexer (OADM: OADM) of a known type.
optical Add / Drop Multiplex
er), for example, EP Patent Application 9811 in the name of the Applicant.
It may be provided with the type described in US Pat.

The second section of the fiber optic line 30 connects the output of the line site 40 to another line site 40.
(Not shown) or RPA part 1 of second terminal site 20
4 The RPA portion 14, which will be described later with reference to FIG. These can then be output.

The demultiplexing part 15 will be described later with reference to FIG. 8, which receives three partial bands BB, RB1 and RB2 from the RPA part 14 and converts the three partial bands BB, RB1 and RB2. The output channel 17 is divided into individual wavelengths. Input channel 16 and output channel 1
The number of sevens may not be equal due to the fact that some channels may be deleted and / or subscribed at line site (or multiple line sites) 40.

According to the above description, each sub-band BB, R
For each of B1 and RB2, the corresponding input of the TPA part 12 and R
An optical link is defined between the corresponding output of the PA section 14.

FIG. 2 shows the spectrum of an amplifier used in the optical transmission system 1 and corresponding approximately to different gains for the channel of the signal passing through the fiber link and to different assignments of the three sub-bands BB, RB1, RB2. It is a qualitative graph of an emission range. That is, the first partial band BB
Preferably covers the range 1529 nm to 1535 nm, corresponds to the first amplification wavelength range of the erbium-doped fiber amplifier, and allocates up to 16 channels. The second partial band RB1 is between 1541 nm and 156 nm.
Up to 48 channels are allocated, corresponding to 1 nm and corresponding to the second amplification wavelength range of an erbium-doped fiber amplifier. The third sub-band RB2 covers the range from 1575 nm to 1602 nm and, according to the invention, corresponds to the amplification wavelength range of the erbium / ytterbium-doped fiber amplifier and allocates up to 64 channels.
The gain spectrum graph of the erbium / yttrium doped fiber amplifier shows 157 for amplification.
It performs best in the range of 5-1602 nm, but down to 1565 nm and higher at 1620 nm.
Channels can be advantageously allocated up to nm. More specifically, Applicants have recognized that a lower limit of 1570 nm is preferred for channel allocation in the RB2 band, due to the shape of the power spectrum curve of the Er / Yb co-doped fiber in this wavelength range. Was.

Adjacent channels in the proposed 128 channel system have a fixed spacing of 50 GHz. Alternatively, a known four-wave-mixing phe- ph is achieved by making the frequency intervals irregular.
Nomenon) can be reduced.

In the erbium amplification band, the RB1 band and the RB2 band have very flat gain characteristics, while
The band contains a significant hump in the gain response.
As described below, in order to use the spectral emission range of the erbium-doped fiber in the BB band, the optical transmission system 1 uses an equalizing unit to flatten the gain characteristics in the range. As a result, the spectral emission range of the erbium-doped fiber, ie, 1
By dividing 529-1602 nm into three sub-bands, including BB, RB1 and RB2 bands, respectively, the optical transmission system 1 effectively utilizes the spectral emission range of the erbium-doped fiber, and High WDM can be obtained.

The various modules of the invention shown in FIG. 1 will now be described in more detail. FIG. 3 is a more detailed diagram of the multiplexing part 11 of the first terminal site 10.
The first terminal site 10 includes, in addition to the multiplexing part 11 and the TPA part 12 (not shown in FIG. 3), an optical line termination part (OLTE).
riminal section 41 and a wavelength conversion part (WCS: wave length convert).
r section) 42.

OLTE 41 is compatible with SONET, ATM, I
Can support standard line termination equipment for use in P or SDN systems, transmit and receive (RX / RX)
Units (not shown) are included in an amount equal to the number of channels in WDM system 10. In a preferred embodiment, OL
The TE 41 has 128 TX / RX units.
In the multiplexing part 11, the OLTE 41 transmits a plurality of signals at a general wavelength. As shown in FIG. 3, in a preferred embodiment, the OLTE 41 comprises a first group of 16 channels,
The second group of 48 channels and the third group of 64 channels are output. However, as indicated above, the number of channels can vary depending on the needs and requirements of a particular optical transmission system.

As will be readily appreciated by those skilled in the art, OLT
E41 comprises a collection of as few as three separate OLTEs, which can also provide information frequencies to WCS. Therefore, WCS 42 includes 128 wavelength conversion modules WCM1 to WCM128.

Each of the units WCM1 to WCM16 has
Each of the first group of signals transmitted from the OLTE 41 is received, and the WCMs 17 to 64
From each of the second group of signals transmitted from
Each of CM 65 to WCM 128 receives one of the third group of signals transmitted from OLTE 41. Each unit can convert the signal from all wavelengths to a selected wavelength and retransmit the signal. These units are OC
-48 or STM-16 can receive and retransmit the signal in a standard format,
The preferred operations of 1-128 are transparent to the particular data format employed.

Each WCM 1-128 is preferably OL
A photodiode (not shown) that receives an optical signal from the TE 41 and converts it into an electric signal, a laser or light source (not shown) that generates a fixed carrier frequency, and externally sets the fixed carrier wavelength using the electric signal. Mach-Zehnder mo
A module with an optical modulator, such as a modulator (not shown). Alternatively, WCM1
Each of the 128 includes a photodiode (not shown) along with a laser diode (not shown) to directly modulate the laser diode with an electrical signal to convert the received wavelength to the carrier wavelength of the laser diode. You may. In yet another alternative, each of the WCMs 1-128 receives a light signal from a trunk fiber line, for example, via a wavelength demultiplexer, and converts it to an electrical signal (eg, SDH or SONET). Standard compliant) and a module with a directly modulated or externally modulated laser source. With the latter alternative, the re-generation of the signal from the output of the trunk fiber line,
In addition, transmission in the optical communication system according to the present invention is enabled, and thus the total link length can be extended.

In FIG. 3, the signals are OLTE41 and WCM.
Although shown as being provided and generated in combination with 1-WCM 128, the signal can be provided and generated directly by any signal source and there is no limitation on its origin.

The multiplexing section 11 includes three wavelength multiplexers (WM) 43, 44, 45. In a preferred 128 channel system, units WCM1-WCM16
Are output by the WM 43, and are output from the WCMs 17 to 64.
Each selected wavelength signal is received by the WM 44,
Each selected wavelength signal output from WCM 65 to WCM 128 is received by WM 45. WM43, W
M44, WM45 are three bands BB, RB1, RB2
Are combined into three respective wavelength division multiplexed signals. As shown in FIG. 3, the WM 43 is a 16-channel wavelength multiplexer such as a conventional 1 × 16 planar optical splitter, and the WM 44 is a 48-channel optical multiplexer such as a conventional 1 × 64 planar optical splitter having 16 unused ports. Channel wavelength multiplexer, WM45
Is a 64-channel wavelength multiplexer, such as a conventional 1x64 planar optical splitter. Each wavelength multiplexer provides an optical monitoring channel (not shown) to the optical transmission system 1.
A second port (e.g., 2x16 and 2
x64 splitter). Similarly, WM4
3, 44, 45 may have more inputs than used in the present system and may provide room for system growth.
For example, those skilled in the art will recognize that silica on passive silicon (Si
O ₂ —Si) or silica on silica (SiO ₂ —Si)
A wavelength multiplexer using O ₂ ) technology could be fabricated. For example, to reduce insertion loss, WM
Other techniques may be used. Examples include AWGs (arrayed wavelength gratings), fiber gratings, and interference filters.

Referring to FIG. 4, the BB, RB1 and RB2 bands output from the multiplexing section 11 are
Received by The signals in the BB, RB1, and RB2 bands are the OLTE 41, WCS 42, and W
It is also possible to supply to the TPA section 12 from a signal source other than the configuration of M43, 44, and 45. For example, BB, RB
The 1, RB2 band signals may be generated by the customer and supplied directly to the TPA section 12, without departing from the spirit of the invention described in detail below.

The TPA section 12 includes the respective bands BB, RB1,
Three amplification portions 51, 52, 53 corresponding to RB2;
A coupling filter 54 and an equalization filter 61 are included. Amplifying sections 51, 52 are preferably two-stage erbium-doped fiber amplifiers (other rare earth-doped fiber amplifiers can be used), while amplifying sections 5 and 52 are provided.
3 is an erbium / ytterbium doped (Er / Yb) fiber amplifier according to the invention. This will be described in detail with reference to FIG.

The outputs of the amplifiers 51, 52 and 53 are received by a filter 54, and this filter 54
Merge the B1 and RB2 bands into a single wideband (SWB). Each of the amplifiers 51, 52 is pumped by one or more laser diodes, which provide optical gain to the signal it amplifies. The characteristics of each amplifier, including length and pump wavelength, are selected to optimize its performance for the particular sub-band that the amplifier amplifies. For example, the first stage of the amplification sections 51 and 52 has a laser operating at 980 nm.
Pumped by a diode (not shown) and in the linear or saturated region, respectively, the BB band and RB
Amplify one band. Suitable laser diodes are available from the applicant. Laser diodes are commercially available 980/1550 WDM couplers (not shown), such as Lundy Ave., San Jose, California, USA. (Randy Avenue) 1
Model SWDM091 of 885 E-TEK DYNAMICS, INC (E-Tech Dynamics)
5SPR can be used to couple into the optical path of the preamplifier. The 980 nm laser diode gives the amplifier a lower noise figure compared to other possible pump wavelengths.

The second stage of each amplification section 51-53 preferably operates in saturation. The second stage of the amplification section 51
Preferably, the BB band is amplified using a separate 980 nm pump source (not shown) that is doped with erbium and is coupled to the BB band optical path using the aforementioned WDM coupler (not shown). The 980nm pump source is
It gives the signal better gain behavior and noise figure in the low band range from 1529 to 35 nm. Amplification part 5
2 is preferably doped with erbium,
Laser diode pump operating at 1480nm
The RB1 band is amplified using the source. Such laser diodes are available from Ontario, Canada, Nepean,
JDS FITE of Heston Drive570
It is commercially available, such as model FOL1402PAX-1 supplied by L, INC (JDS Fitel). The 1480 nm pump source is 154
For more channels in the region ranging from 2-61 nm, it has the better saturation conversion efficiency behavior required for the RB1 channel. Or 98 with increased power
0 nm pump laser or multiplexed 980 nm pump
A source may be used. Portion 53 will be described in detail below with reference to FIG.

A filter 61 is placed in the RB1 band amplifier chain to facilitate equalization of the signal level and SNR corresponding to the RB1 band at the system output. That is, the filter 61 is a de-emphasis filter (de-e) that attenuates the wavelength region of high amplification in the RB1 band.
mphasis filter). When a de-emphasis filter is used, a long-period Bragg grating technique, a split beam Fourier filter, or the like can be employed. As an example, the de-emphasis filter has an operating wavelength range of 1541 to 1561 nm,
Peak transmission wavelengths 1541 to 1542 nm and 155
With a wavelength of 9 to 1560 nm, low but relatively constant transmission is possible at the wavelength between these peaks. FIG.
Indicates a suitable filter shape and relative attenuation performance of the de-emphasis filter 61. The graph of FIG. 5 shows that the de-emphasis
It has a peak transmission area around 560 nm, about 1546n
It shows a relatively constant or flat attenuation region between m and 1556 nm. The de-emphasis filter 61 for the erbium-doped fiber amplifier is
To help flatten the gain response in the high band, only about 3-4 dB of attenuation needs to be added to the wavelength between the peaks. Depending on the gain flattening requirements of the system actually employed, such as the dopants used in fiber amplifiers or the wavelengths of the pump sources for these amplifiers, the de-emphasis filter 61 may not have the attenuation characteristics shown in FIG. It may have different properties.

Alternatively, the de-emphasis filter 6
1 is omitted, and in the multiplexing part 11 of the first terminal site 10, the calibration attenuation (calibrated attenuation) is performed.
ation) to obtain the de-emphasis processing.

After passing through the amplifier of the TPA 12, the amplified BB, RB1, and RB2 bands are amplified by the amplification portions 51, 52,
53, and are received by the filter 54. Filter 54 is a band-coupled filter, for example, two cascaded interfering three-port filters.
l three port filter) (not shown). The first filter sets the BB band to R
Combined with the B1 band, the second filter combines the BB / RB1 band provided by the first filter with the RB2 band.

The wavelength different from the communication channel, for example, 1
At 480 nm, insertion of an optical monitor (not shown) and service line via a WDM 1480/1550 interference filter (not shown) can also be added at the common port. The optical monitor detects the optical signal and confirms that the optical transmission system 1 is not interrupted. The service line insertion provides access to the line service module, through an optical supervisory control channel, alarm telemetry, survey, performance and data monitoring, control and housekeeping alarms, and voice frequency call. Lines can be managed.

The single wideband output from filter 54 of TPA section 12 is 100 kilometers,
Signals within a single broadband SWB are attenuated as they travel the length of the transmission fiber (not shown) of fiber optic line 30. Thus, line site 40 has a single broadband S
A signal within WB is received and amplified. As shown in FIG. 6, a line site 40 includes several amplifiers (AMPs) 6.
4 to 69, three filters 70 to 72, an equalization filter (EQ) 74, and three OADM stages 75 to 77.

Filter 70 receives a single wideband SWB and separates the RB2 band from the BB and RB1 bands. Amplifier 64 receives and amplifies the BB and RB1 bands, while filter 71 receives the output from amplifier 64 and separates the BB and RB1 bands. The BB band is equalized by the equalization filter 74 and the first OAD
It is received by the M stage 75 where certain signals are removed and / or added and further amplified by the amplifier 65. RB band 1 has already passed through de-emphasis filter 61 at TPA 12 and is first amplified by amplifier 66 and then to second OADM stage 76
, Where certain signals are removed and / or added, and further amplified by amplifier 67. The RB2 band is first amplified by amplifier 68 and then received by third OADM stage 77 where certain signals are removed and / or added, and further amplified by amplifier 69. Then, the amplified B
The B, RB1 and RB2 bands are recombined by filter 72 into a single wideband SWB.

Amplifier 64 for receiving a single wideband SWB
Consists of a single optical fiber amplifier, preferably operating in the linear region. That is, the amplifier 64 operates in a state where its output power depends on its input power. Depending on the actual implementation, amplifier 64 may instead be a single-stage or multi-stage amplifier. By operating in the linear state, the amplifier 64 can operate in the BB band and RB1
Helps ensure relative power independence between channels in the band. In other words, the output power (and signal-to-noise ratio) of each channel in one of the two sub-bands BB, RB1 is increased or decreased by the amplifier 64 operating in a linear state in the other sub-bands RB1, BB. Does not change much. To obtain robustness for some or all of the channels in a high-density WDM system, the first stage amplifier (amplifier 64 or amplifier 68) may be used before extracting a portion of the channel for separate equalization and amplification. Line)
Site 40 must operate in the unsaturated region. In the preferred embodiment, amplifiers 64 and 68 are erbium-doped fiber amplifiers and are 980 nm
Pumped laser diodes (not shown) are pumped in the same direction of propagation and preferably obtain a noise figure of less than 5.5 dB for each band.

The filter 71 comprises, for example, a three-port device, preferably an interference filter, and a deletion port (dropp) for supplying the BB band to the equalization filter 74.
ort) and a reflection port for supplying the RB1 band to the amplifier 66.

The amplifier 66 is preferably a single erbium-doped fiber amplifier, the output power of which is substantially independent of its input power.
Operate in saturation. Thus, the amplifier 66
Compared to the channel in the B band, the channel in the RB1 band has a power boost (power boost).
Functions to add t). In a preferred embodiment,
Since the number of channels in the RB1 band is larger than that in the BB band, that is, 48 for 16
One band of channels typically has reduced gain as it passes through amplifier 64. As a result, the amplifier 66
Helps to balance the power of the channel in the RB1 band compared to the BB band. Of course, when the channel between the BB band and the RB1 band takes another configuration, the amplifier 66 becomes unnecessary, or
It may be required on the BB band side of the site 40.

For the channel in the RB1 band, the amplifier 6
4 and 66 can be considered as a two-stage amplifier collectively.
The stage operates in a linear mode and the second stage operates in saturation. Amplifiers 64 and 66 are preferably pumped using the same laser diode pump source to facilitate output power stabilization between channels within the RB1 band. In this way, the residual pump power from amplifier 64 is supplied to amplifier 66, as described in EP 695049. That is, the line site 40 is a WD located between the amplifier 64 and the filter 71 that extracts the remaining 980 nm pump light at the output of the amplifier 64.
Includes M coupler. This WDM coupler is described, for example, in Lundy Ave., San Jose, California, USA. (Randy Avenue) 1885 E-TEK DYNA
Model number SWDMCP supplied by MICS, INC
R3PS110 may be used. The output from the WDM coupler is connected to a second WDM coupler (not shown) of the same type, which is arranged in the optical path downstream of the amplifier 66. The two couplers are joined by an optical fiber 78 and carry the remaining 980 nm pump signal with relatively little loss.
The second WDM coupler passes the remaining 980 nm pump power to amplifier 66 in a counter-propagating direction.

From the amplifier 66, the RB1 band signal is converted into a signal of a known type, that is, EP Patent Application No. 9811 in the name of the applicant.
OADM stage 76 of the type described in US Pat.
Transported to From the OADM stage 76, the RB1 band signal is supplied to the amplifier 67. Suitable erbium-doped
In the fiber amplifier, the amplifier 67 includes the amplifiers 64 and 66.
Has a pump wavelength of, for example, 1480 nm from a laser diode source (not shown) having a pump power exceeding the laser (not shown) driving the. 1480n
The wavelength of m is, for an erbium-doped filter,
High output power output provides good conversion efficiency when compared to other pump wavelengths. Or a high power 980n
m pump source, or two pump sources at 980 nm, or one at 975 nm and the other at 986 nm
Using a group of multiplexed pump sources such as
It is also possible to drive the amplifier 67. Amplifier 67
Preferably operates in saturation and provides power boost to signals within the RB1 band, and may comprise a multi-stage amplifier if necessary.

After passing through the amplifier 64 and the filter 71, the BB band enters the equalizing filter 74. As discussed above, the gain characteristic of the erbium-doped fiber over the spectral emission range has a peak or hump in the BB band region, but remains relatively flat in the RB1 band region. As a result, the BB band or single broadband SWB (including the BB band) is
When amplification is performed by the fiber amplifier, channels in the BB band region are amplified irregularly. Also, as discussed above, if one attempts to overcome this unequalization amplification problem by applying equalization means, the equalization is applied over the entire spectrum of the channel, resulting in a continuous gain mismatch. did. However, the spectrum of the channel is BB
By dividing the BB band and the RB1 band, the BB band is equalized in the narrowed operating area of the BB band.
It is possible to appropriately flatten the gain characteristics of the channel in the band.

In the preferred embodiment, the equalization filter 74
Is a long period chirp Bragg grating that provides selected attenuation at different wavelengths.
It consists of a two-port device based on the chipped Bragg grating technology. For example, the BB band equalizing filter 74 has a wavelength of 1529 nm to 1536 nm.
nm operating wavelength range, the wavelength at the bottom of the valley is 1
It is between 530.0 nm and 1530.7 nm. The equalizing filter 74 does not need to be used alone, but is combined in cascade with another filter (not shown) to obtain an optimum filter shape and to apply gain equalization to a specific amplifier used in the WDM system 1. You can bring it. Equalization filter 74 can be manufactured by one of ordinary skill in the art, or is available from a number of sources in the art. It should be noted that the particular structure used for the equalizing filter 74 is within the purview of those skilled in the art, and may include a specialized Bragg grating, such as a long period grating, an interference filter, or a Mach-Zehnder optical filter. Will be understood.

From the equalizing filter 74, the signal in the BB band is output to, for example, the OADM stage 7 of the same type as the OADM stage 76.
5 and then to the amplifier 65. In a preferred erbium-doped fiber amplifier, amplifier 65
Has a pump wavelength of 980 nm. It is provided by a laser diode source (not shown), is coupled to the optical path via a WDM coupler (not shown),
In the counter-propagating direction. Since channels in the BB band pass through both amplifier 64 and amplifier 65, equalization filter 74 may be configured to compensate for the gain mismatch caused by both amplifiers. Thus, depending on the need for overall amplification and line power for the BB band, the decibel reduction (dec) for the equalization filter 74
ibeldrop) must be determined. Amplifier 65 preferably operates in saturation, provides power boost to the signal in the BB band, and may comprise a multi-stage amplifier if necessary.

The RB2 band is received from the fiber amplifier 68. Fiber amplifier 68 is preferably an erbium-doped fiber amplifier pumped by 980 nm or 1480 nm pump light, depending on the requirements of the system. From the amplifier 68, the channels of the RB2 band are, for example, OAs of the same type as the OADM stages 75 and 76.
It is conveyed to the DM stage 77 and then supplied to the amplifier 69. In accordance with the present invention, amplifier 69 includes an erbium / ytterbium co-doped amplifier, adapted to amplify the RB2 band.
r), which will be described in detail with reference to FIG.

After passing through the amplifiers 65, 67, 69, respectively, the amplified BB, RB1, RB2 bands are again merged into a single wideband SWB by the filter 72. As with the filter 54 of FIG.
May include three cascaded interfering three-port filters (not shown), a first filter combining the BB band with the RB1 band, and a second filter including the first
The BB and RB1 bands provided by the filter are combined with the RB2 band.

As with the TPA part 12, the line site 4
0 is also the optical monitor and, for example, WDM 1480/15
Service line insertion and extraction (not shown) by 50 interference filters (not shown) may be included. One or more of these elements can be included at any of the interconnection points of line site 40.

In addition to the amplifiers 64-69, the filters 70-72 and 74, and the OADM stages 75-77, the line site 40 includes a scatter compensation module (DCM: d
ispersion compensating mo
(not shown) to compensate for color scatter that may occur during signal transmission along the long-distance communication link. DCM (not shown) is preferably 1
Consisting of subunits coupled upstream of one or more amplifiers 65, 67, 69, it compensates for channel scattering in one or more of the BB, RB1, RB2 bands and may have several forms. For example, a DCM has an optical circulator whose first port has three bands BB,
Connection may be made to receive channels in RB1 and RB2. A chirped Bragg grating may be attached to the second port of the circulator. The channel emerges from the second port and is reflected at the chirped Bragg grating to compensate for color scattering. The scatter compensated signal then exits the next port of the circulator and continues transmission in the WDM system. Other devices besides chirped Bragg gratings, such as a length of scattering compensating fiber, can also be used to compensate for color scattering.
The design and use of the DCM part is not a limitation of the present invention, and the DCM part may or may not be employed in the WDM system 1, depending on the overall requirements for the implementation of the system.

After the line site 40, the merged single broadband SWB signal passes through a length of long haul optical transmission fiber of the fiber optic line 30. First and second
When the distance between the terminal sites 10 and 20 is long enough to cause attenuation of the optical signal, that is, when the distance is 100 km or more,
One or more additional line sites 40 for performing amplification may be used. A practical configuration uses five ranges of long-haul transmission fiber separated by four amplifier line sites 40 (each with a power loss of 0.22 dB / km and a total range loss of about 25 dB). Length).

Following the final transmission fiber range, the RPA portion 14 starts with a single broadband S from the last line site 40.
Receive the WB and prepare the signal of a single wideband SWB for reception and detection at the end of the communication link. As shown in FIG. 7, the RPA portion 14 includes an amplifier (AMP).
81 to 85, filters 86 and 87, an equalization filter 88,
And if necessary, three router modules 91-
93 may be included.

Filter 86 receives a single wideband SWB and separates the RB2 band from the BB and RB1 bands.
Amplifier 81 is preferably doped with erbium,
Amplify the BB and RB1 bands and help improve the signal to noise ratio of the channels in the BB and RB1 bands. Amplifier 81 is pumped, for example, by a 980 nm pump or a pump at any other wavelength,
Try to get a low noise figure of the amplifier. On the other hand, the BB and RB1 bands are separated by a filter 87.

The TPA part 12 and the line site 40
As in the case of, the amplifiers 82 and 83 amplify the BB band and the RB1 band, respectively, by the 980 nm pump. To facilitate output power stabilization between channels within the RB1 band, amplifiers 81 and 83 use the same 980 nm laser diode by using a spliced optical fiber 89 that transmits the residual 980 nm pump signal with relatively low loss. -It is preferable to pump using a pump source. That is, the WDM coupler that is disposed between the amplifier 81 and the filter 87 and extracts the 980 nm pump light remaining at the output of the amplifier 81 and the amplifier 81 are linked.
This WDM coupler is, for example,
San Jose, Lundy Ave. (Randy Avenue) 1885 E-TEK DYNAMICS, INC
May be supplied as the model number SWDMCPR3PS110. The outputs from this WDM coupler are of the same type, and are output from a second
Connect to WDM coupler. The two couplers are joined by an optical fiber that carries the residual 980 nm pump signal with relatively low loss. The second WDM coupler has a residual 980.
The nm pump power is passed to the amplifier 83 in the counter-propagation direction. Thus, amplifiers 81-83, filter 87, and equalization filter 88 perform the same functions as amplifiers 64, 65, 67, filter 71, and equalization filter 74 at line site 40, and depending on the requirements of the overall system. , The same or equivalent parts.

The amplifier 84 is coupled to a filter 86,
Receive and amplify the B2 band. Amplifier 84 is, for example, the same erbium-doped amplifier as amplifier 68 of FIG. Then, the channel of the RB2 band is received by the amplifier 85. Amplifier 85 is preferably an erbium-doped amplifier of a known type.

The RPA section 14 further comprises a routing stage 90 so that the channel spacing in the BB, RB1 and RB2 bands can be adapted to the channel separation capability of the demultiplexing section 15. That is, the channel separation capability of the demultiplexing section 15 is relatively large (for example,
100 GHz grid), while the channels in the WDM system 1 are dense (eg, 50 GHz)
In this case, the RPA part 14 is the
0 may be included. Other structures may be added to the RPA section 14 depending on the channel separation capability of the demultiplexing section 15.

The routing stage 90 includes three router modules 91-93. Each router module 91
93 separates each band into two sub-bands. Each sub-band includes half of the channel of the corresponding band. For example, if the BB band contains ₁₆ channels λ _{1 to} λ ₁₆ and each is separated by 50 GHz, the router
Module 91 splits the BB band into channels λ ₁ , λ ₃ ,. . . , Λ ₁₅ and channels λ ₂ , λ ₄ ,..., Separated by 100 GHz and alternated with the channels in the sub-band BB ′. . . , Λ ₁₆ having a second sub-band B
B ". Similarly, the router module 92,
93 designates the RB1 band and the RB2 band as the first partial band RB1 'and RB2' and the second partial band RB
1 ", RB2".

Each router module 91-93 includes, for example, a coupler (not shown) having a series of first Bragg gratings attached to a first port and a series of second Bragg gratings attached to a second port. )including. The Bragg grating attached to the first port has a reflection wavelength corresponding to every other channel (ie, even channel), while the Bragg grating attached to the second port has the remaining channel (ie, odd channel). Channel). This grid arrangement also works when dividing a single input path into two output paths with twice the channel spacing.

After passing through the RPA part 14, BB, RB
The 1, RB2 bands or their respective subbands are received by the demultiplexing section 15. As shown in FIG. 8, the demultiplexing section 15 includes six wavelength demultiplexers (WD).
95 ', 95 ", 96', 96", 97 ', 97 ", which are the respective sub-bands BB', BB", RB1 ',
RB1 ″, RB2 ′, RB2 ″ are received, and an output channel 17 is generated. The demultiplexing part 15 further receives the output channels 17, receiving units Rx 1 to Rx 128
Including.

The wavelength demultiplexer preferably consists of an array of waveguide grating devices, but alternative structures that provide the same or similar wavelength separation are also contemplated. For example, using interference filters, Fabry-Perot filters, or in-fiber Bragg gratings as before, the sub-bands BB ', BB ", RB1', RB1", RB2 ', RB2',
It is also possible to demultiplex the channels in RB2 ″.

In a preferred arrangement, the demultiplexing section 15 is
Combines filter and AWG filter technologies. is there
Or Fabry-Perot filter or in-fiber
A Lag grating may be used. WD95 'and 95 "are good
More preferably, an 8-channel demultiplexer using an interference filter is used.
And the first sub-band BB 'and the
The two partial bands BB "are received and demultiplexed. That is, WD
95 'is the channel? ₁, Λ_Three,. . . , Λ_FifteenDemultiplex
And WD95 ″ is the channel λ_Two, Λ_Four,. . . , Λ₁₆Many
Separate by weight. Both WD95 'and WD95 "
While, 1x8 type AWG 100GHz demultiplexer
It may be sa. Similarly, WD96 ', 96 "
Band RB1 'and the second partial band RB1 ", respectively.
Multiplexed and demultiplexed into channel λ₁₇~ Λ₆₄And generate WD
97 ', 97 "are the first partial band RB2' and the second
The subbands RB2 ″ are respectively received and demultiplexed, and the
Le λ₆₅~ Λ₁₂₈Generate WD96 'and WD9
6 "Both are 1x32 type AWG 100GHz demultiplexer
A lexer, but you can
Using only 24 ports is under-equipped (under
equipment). WD97 'and WD9
7 "uses all available demultiplexer ports
1x32 type AWG100GHz demultiplexer
And it is sufficient. The output channel 17 is WD95 ', 9
Separated by 5 ", 96 ', 96", 97', 97 "
Each channel of the output channel 17
The channel is controlled by one of the receiving units Rx1 to Rx128.
Is received.

FIG. 9 shows an optical amplifier 108 including a pump device according to the present invention. The optical amplifier 108 can be used, for example, in the optical transmission system 1 and can be used to amplify a signal in the RB2 band.
3 and included in the amplification section 69 of FIG.

The amplifier 108 is a bidirectional pump optical amplifier, and has an input port 110 for inputting an optical signal to be amplified.
An output port 120 for output of the amplified optical signal, an active fiber 130 optically coupled to the input port 110 to the output port 120 and configured to amplify the optical signal, a pump Source 145,
And a pump device 140 for optically coupling the pump beam to the active filter 130.

The active fiber 130 is, for example,
Erbium and ytterbium co-doped double cladding fiber, described below with reference to FIG. FIG. 11 shows a sectional view of the optical fiber 130 which is not to scale. Fiber 130 includes a core 139 having a first refractive index n _1, surrounds the core 139, an inner cladding 141 having a core 139 and coaxial with and a second refractive index n ₂ <n _1, an inner cladding 141 And the outer cladding 14 is coaxial with the inner cladding 141 and has a third refractive index n ₃ <n _2.
2 As shown in FIG. 12, in the normal operating state of the amplifier, the transmitted signal is confined to the core 139, but the pump light is supplied to the inner cladding 141 and is gradually absorbed by the core 139 to excite the active medium. I do.

The active fiber 130 is, for example,
An outer cladding 142 having an outer diameter of 90 μm, an inner cladding 141 having an outer diameter of 65 μm, and an outer diameter of about 5 μm.
m of cores 139. The core 139 is, for example, E
SiO ₂ / P ₂ O ₅ / Al ₂ O ₃ co-doped with r / Yb
Wherein the weight percentage of P ₂ O ₅ is greater than 10 percent (preferably about 20%), the weight percentage of Al ₂ O ₃ is less than 2%, and the concentration of erbium is between 600 ppm and 1000 ppm; The concentration of ytterbium is between about 1000 ppm and 20,000 ppm. For example, the ratio between ytterbium and erbium is about 20: 1. The step in the refractive index between the core 139 and the inner cladding 141 is, for example, Δn = n ₁ −
n ₂ = 0.013 +/− 0.002, and the step of the refractive index between the inner cladding 141 and the outer cladding 142 is, for example, Δn ′ = n ₂ −n ₃ = 0.017.
+/- 0.003 (primarily due to fluoride doping of outer cladding 142). The core 139 and the inner cladding 141 define a single mode waveguide for carrying a transmission signal, for example, a first aperture ratio NA ₁
= 0.19 +/- 0.02. On the other hand, the inner cladding 141 and outer cladding 142 define a multi-mode waveguide for carrying a pump beam, for example, the second numerical aperture NA ₂ = 0.22 +/- 0.0
One.

To produce fiber 130, two different preforms (not shown) are used. To obtain a core 139 and inner cladding 141 with a first preform, known "chemical vapor deposition" (CVD) SiO ₂ is deposited and P ₂ O ₅ by the method, then a rare earth by known "solution doping" method Fabricated by introducing erbium and ytterbium. The first preform consists of a core 139 and inner cladding 141
So that a preset geometric ratio is obtained between
Process appropriately.

The outer cladding 142 is obtained using a second commercial preform. The second preform has a pure SiO ₂ in the central region and a peripheral region of the SiO ₂ doped with fluoride. The central region of the second preform is removed to obtain a central longitudinal hole for introducing the first preform. The three-layer preform thus obtained is drawn by a usual method to obtain the optical fiber 130.

Referring to FIG. 9, the pump device 14
0 sets pump source 145 to active fiber 1
A first optical coupler 150 optically coupled to the first coupler 150;
0 to receive active pump light that was not directly applied to the active fiber 130, and to supply the residual pump light to the active fiber 130.
Second optical coupler 1 optically coupled to coupler 150
60.

Preferably, the pump source 145 is a multimode laser with a pump power of 400 mW
Provides a pump beam between 920 nm and 980 nm. Pump source 145 is optically coupled to optical coupler 150 by multimode optical fiber 170. Pump source 140 is available, for example, from Lundy Ave. (Randy Avenue) 1885 E-TEK DYNAMI
The model number may be MECP7PR6 supplied by CS, INC (E-Tech Dynamics).

The first optical coupler 150 has an insertion loss for an optical signal of 0.2 dB or less and the second optical coupler 160
Preferably has a pump coupling efficiency of less than 70%, more preferably less than 80%. In other words, the optical signal transmitted from input 110 to active filter 130 is
Passing through the first coupler 150 causes less than 0.2 dB of attenuation, and the second coupler 160 couples the residual pump light to the active filter 130 with less than 70% coupling efficiency.

Preferably, the first optical coupler 150 is a fused fiber coupler having an insertion loss for an optical signal of about 0.1 dB, for example, 960/1550 nm or 920/15.
50m double cladding WDM coupler. For example, couplers 124 and 126 are Model MW 9850-P05 manufactured by the applicant.

The first coupler 150 is optically coupled to a first access fiber 151, for example, the input port 110, and receives a signal to be amplified.
Fiber and a second access fiber 152, for example,
Multi-mode (with single cladding) optically coupled to pump source 140 to receive pump light
And the same type as the first access fiber 151, which is optically coupled to the active fiber 130 and which couples the optical signal to be amplified to approximately 50% of the power of the pump beam (typically About 48
%) And a third access fiber 153 for supplying with a first portion of the pump beam,
A fourth access fiber 1 of the same type as 52 and carrying a second part of the pump beam defining a residual pump beam.
54.

The optical coupler 160 is a double-cladding WDM coupler of a micro optical component (mirror type),
% Pump coupling efficiency. Coupler 160 may be, for example, a Lundy Av of San Jose, California, USA
e. (Randy Avenue) 1885 E-TEK
Model No. FWDMCPR1PR supplied by DYNAMICS, INC (E-Tech Dynamics)
S10 is recommended. Coupler 160 includes first, second, and third access fibers 161, 162, 163;
Includes a not-shown converging lens system for properly shaping the light beam and delivering the light beam between its access fibers, and a reflection-selective surface, for example, a dichroic mirror shown at 164 and schematically represented by oblique segments. . The actual tilt of the dichroic mirror inside the coupler depends on the direction of the incoming light beam carrying the signal and pump rays.

The selective reflection surfaces in the couplers 111 and 112 are:
Transparent to the wavelength of the channel in the RB2 band,
It is reflective for the wavelength of the pump beam. Thus, the channels in the RB2 band pass through the reflective surface with substantially no loss, while the pump light is reflected by the reflective surface and impinges on the cladding of the amplification fiber 130. Alternatively, coupler 160 may include a selective reflective surface that is reflective to the wavelength of the RB2 band channel and transparent to the wavelength of the pump beam.

The coupler 160 has a first access fiber 161 connected to a first optical coupler 150 by a pump optical fiber 180, preferably a multi-mode fiber.
Optically coupled to a fourth access fiber 154 of
A second portion of the pump beam, the residual pump beam, is received and a second access fiber 162 is optically coupled to the active fiber 130 for receiving an amplified optical signal from the active fiber 130 and for receiving an active optical signal.
Providing a major portion (about 90%) of the second portion of the pump beam (reflected by mirror 164) from fiber 130 to the inner cladding of active fiber 130;
A third access fiber 163 is optically coupled to the output port 120 and supplies the amplified optical signal transmitted through the mirror 164 to the output port 120.

More specifically, in the preferred embodiment disclosed herein, the first access fiber 161 comprises
Core diameter 65μm, cladding diameter 90μ
m, a multi-mode fiber having an aperture ratio NA = 0.22. The second access fiber 162 is a double cladding fiber having the same geometric properties as the amplification fiber 108. Third access fiber 163
Has a core wavelength cutoff of 1300 nm ± 30 nm, a cladding diameter of 125 μm, and an aperture ratio NA =
0.2 single mode fiber.

The coupler 160 detects that the optical signal passing from the second access fiber 162 to the third access fiber 163 has an insertion loss measured at 1550 nm of about 1.02 dB, and the optical signal passing through the first access fiber 161 For an optical signal passing through the access fiber 162, the insertion loss measured at 989 nm is about 0.22 dB.
It is. Further, the coupler 160 provides a 98 connection between the second access fiber 162 and the third access fiber 163.
The light separation measured at 0 nm is greater than 30 dB,
Access fiber 161 and second access fiber 1
The light separation measured at 1550 nm between
It is larger than B.

The specific coupling arrangement described above is adapted to provide approximately 85% of the pump power generated by the pump source 140 to the active filter 130, thus providing a very efficient pump. It is.

The coupling of the residual pump beam to the active fiber 130 by the second coupler 160 is performed by the second coupler 1.
Pump optical fiber 180 is a typical multi-mode fiber, since it is substantially independent of the mode distribution of the pump beam received by 60, a scrambling device () that redistributes energy between optical modes. scr
No tumbling device is required. next,
The residual pump beam is transmitted from the first coupler 150 to the second coupler 160 without significant energy transfer between modes.

In an alternative configuration not shown, the second coupler 16
0 is optically coupled to a further active fiber arranged in series with the aforementioned active fiber 130, and has the same propagation direction (the second coupler is connected to the two active fibers). The residual pump beam is provided in the opposite propagation direction (if located between the fibers) or in the counter-propagating direction (if the second coupler is located downstream with respect to the further active fiber). The first of the two alternatives is preferred in that still another active fiber can compensate for signal power loss due to the second coupler.

The pump device 140 was tested with the optical amplifier 108 by supplying an optical signal of 1550 nm at an input power of +3 dBm to the input 110 and detecting it at the output 120. The following results were obtained using a 4 m long Er / Yb active filter.

-Output power = 17 dBm-Noise figure = 5.8 dB Applicants have also used the same experimental conditions, but with a 6 m long active fiber, a single micro-optical coupler in the same propagating pump or backpropagating mode. The same test was performed using the pump device included in the method and the following results were obtained.

The same propagation pump method :-output power = 16.8 dBm-noise figure = 6 dB counter-propagation pump method -output power = 17 dBm-noise figure = 7 dB If so, it was confirmed that the pump device of the present invention exhibited higher performance than other pump devices at least in terms of noise figure.

FIG. 10 shows the amplification section 53 of FIG.
Is a preferred embodiment of the amplifying section 69 of the present invention, showing an amplifying unit 100 configured to amplify channels in the RB2 band to 22 dBm. The amplification unit 100 consists essentially of a preamplifier 103 and a double-stage amplifier 104, each stage of the amplifier 104 being of the same type as the amplifier 108 of FIG.

More specifically, the amplifying unit 100
Are input 101, output 102, erbium fiber preamplifier 103, erbium / ytterbium fiber amplifier 104, first optical isolator 105 and second
The optical isolator 106 is included. The preamplifier 103 and the amplifier 104 are arranged in series, and the preamplifier 103 is positioned between the input 101 and the amplifier 104 and performs initial amplification on the channel of the RB2 band received at the input 101. The preamplifier 103 is, for example, 9
It may be a known type of single-stage erbium-doped fiber amplifier pumped at 70-980 nm. The preamplifier 103 receives the RB2 band from the input 101 and sets the RB2 channel to 15 to the first power level.
Amplify 17 dBm. The first amplification performed by the preamplifier 103 is important to reach a high power level at the output of the amplifier 104. In addition, the preamplifier 10
3 also improves the noise figure (NF) of the amplification section 100,
Channels in the B2 band can be equalized.

The first isolator 105 includes the preamplifier 1
03 and the amplifier 104, and is configured to block light traveling from the amplifier 104 to the preamplifier 103. The second isolator 106 is disposed between the amplifier 104 and the output 102, and is configured to block light traveling from the output 102 to the optical amplifier 104. Depending on the requirements of the system, the first or second isolators 105, 106 may be separately located or omitted, or other isolators may be added between the input 101 and the output 102. .

The amplifier 104 is a two-stage amplifier, and each stage has a bidirectional pump function. Amplifier 104 includes first and second amplification stages 108 ', 108 ", which are substantially identical to optical amplifier 108 of the present invention, the components of which are indicated by the same reference numerals as in FIG. They were distinguished by "'" and "". First and second amplification stages 10
8 ', 108 "differ only in the length of each active fiber, and preferably in fiber 130'.
Is 16 m and the fiber 130 ″ is 18 m.

A noise reduction filter 107 is arranged between the two amplification stages 108 'and 108 "
It is preferable to suppress the portions of amplified spontaneous emission of 0 ′ and 130 ″.

The pump device of the present invention is substantially different from a pump device that includes a single dichroic coupler (which provides better performance than a pump device using a fused fiber coupler). But with better output signal power but better distribution of pump light into the active fiber, and better performance with respect to noise figure, especially due to population inversion with higher homogeneity and lower insertion loss .

It will be readily appreciated by those skilled in the art that the present invention is not limited to the embodiments described above, which are provided here by way of example. Pump device 140, optical amplifier 108, amplifying unit 100 and transmission system 1
Can, in fact, be varied in various ways within the scope of protection defined by the claims.

That is, the pump device of the present invention can also be used to pump multi-mode active fibers (or two or more multi-mode active fibers) instead of double-cladding fibers. It has the advantage of being usable. In this case, the access fibers of the first and second couplers 150, 160 are directly coupled to the active fiber, resulting in a multi-mode fiber.

Further, in a less preferred embodiment, the order of the two couplers is changed so that the fused fiber coupler activates the pump beam in a counter-propagating direction relative to the transmitted signal.
The fiber may be fed to the micro-optical coupler so that the residual pump beam is fed to the active fiber in the same propagation direction with respect to the transmission signal.

Further, the use of the pump device and optical amplifier of the present invention is not limited to the particular signal transmission wavelength band and pump light wavelength discussed above, but may be, for example, between about 1525 and 1620 nm. Er / Yb
It can also be used to pump active fibers operating in the full emission range of

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical transmission system according to the present invention.

FIG. 2 is a qualitative graph of a spectrum gain characteristic of the optical transmission system of FIG. 1, showing a signal transmission band (BB, RB1, RB2).

FIG. 3 is a more detailed diagram of a multiplexing part of the optical transmission system in FIG. 1;

FIG. 4 is a more detailed diagram of a transmission power amplifying part of the optical transmission system in FIG. 1;

FIG. 5 is a graph of a filter characteristic shape of a de-emphasis filter of the optical transmission system of FIG. 1;

FIG. 6 is a detailed view of an intermediate station of the optical transmission system of FIG. 1;

FIG. 7 is a detailed view of a reception pre-amplification part of the optical transmission system of FIG. 1;

FIG. 8 is a detailed view of a multiplexing part of the optical transmission system of FIG. 1;

FIG. 9 is a schematic diagram of an optical amplifier including a pump device of the present invention.

FIG. 10 is a schematic diagram of an amplification section including the amplifier of FIG. 9;

FIG. 11 is a schematic diagram of a double cladding fiber used in the optical amplifier of the present invention.

FIG. 12 is a schematic diagram of a multi-mode pump operation of a double cladding fiber used in the optical amplifier of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical transmission system 10 1st terminal site 11 Multiplexing part (MUX) 12 Transmission power amplification part (TPA) 16 Input channel 14 Reception preamplification (RPA) part 15 Demultiplexing part (DMUX) 17 Output channel 20 Second terminal Site 30 Optical fiber line 40 Line site 41 Optical line termination part 42 Wavelength conversion part 43,44,45 Wavelength multiplexer (WM) 51,52,53 Amplification part 54 Coupling filter 61 Equalization filter 64-69 Amplifier (AMP) 70-72 Filter 74 Equalization Filter (EQ) 75-77 OADM Stage 81-85 Amplifier (AMP) 86,87 Filter 88 Equalization Filter 91-93 Router Module 95 ', 95 ", 96', 96", 97 ', 97 "
Wavelength demultiplexer 100 Amplification unit 101 Input 102 Output 103 Erbium fiber preamplifier 104 Erbium / Ytterbium fiber amplifier 105 First optical isolator 106 Second optical isolator 108 Amplifier 108 ′, 108 ″ First and second amplification stages 110 Input Port 120 Output Port 130 Active Fiber 130 ′, 130 “Fiber 139 Core 140 Pump Device 141 Inner Cladding 142 Outer Cladding 145 Pump Source 150 First Optical Coupler 151 First Access Fiber 152 Second Access Fiber 153 Third access fiber 154 Fourth access fiber 160 Second optical coupler 161 First access fiber 162 Second access fiber 163 Third access fiber 164 Dichroic mirror 180 Pump optical fiber BB, RB1, RB2 Partial band Rx1 to Rx128 Receiving unit WCM1 to WCM128 Wavelength conversion module

 ──────────────────────────────────────────────────の Continued on the front page (71) Applicant 591011856 Pirelli Cavies System e. p. A (72) Inventor Roberta Castagnetti Milan, Italy, 20052 Monza, Via Montebianco 16 (72) Inventor Giovanni Sacchi Italy 20126 Viale Salca, Milan 87

Claims (16)

[Claims] 1. A pump device for coupling a pump beam to an active fiber of an optical amplifier, wherein said active fiber (130) is a double cladding fiber and said optical amplifier (108) is an optical signal. A multi-mode optical fiber (170) configured to amplify and pump a multi-mode pump beam, and a first portion of the pump beam to the active fiber (130). A first optical coupler (150) optically coupled to the first coupler (15);
0) and optically coupled to the first coupler (150) for receiving a second portion of the pump beam from the first coupler (150) and further coupled to the active fiber (130) for at least one of the second portion of the pump beam. A second optical coupler (160) for supplying a portion to the active fiber (130), wherein the first optical coupler (150) has an insertion loss of 0.2 dB or less for the optical signal; The second optical coupler (160) is at least 70%
A pump device having a coupling efficiency of: 2. The pump device according to claim 1, wherein said first optical coupler is a fused fiber coupler, and said second optical coupler is a micro optical coupler. Pump device. 3. The pump device according to claim 1, wherein the sum of the optical power of the first portion of the pump beam and the optical power of the at least a portion of the second portion of the pump beam is the pump power. A pump device characterized by more than 75% of the light power of the light beam. 4. The pump device according to claim 3, wherein said sum is at least 85% of the optical power of said pump beam. 5. The pump device according to claim 1, further comprising a pump optical fiber (180) for optically coupling said second optical coupler to said first optical coupler. The pump optical fiber (180)
Is a multi-mode optical fiber configured to transmit light with substantially no energy transfer between modes. 6. The pump device according to claim 1, wherein the first optical coupler is connected to the first optical coupler.
0) is a first access fiber (151) and a multi-mode fiber, the second access fiber (152) being optically coupled to the multi-mode optical fiber (170) and receiving the pump beam. ) And the first
The same type as the access fiber (151), coupled to the active fiber (130), and directing a first portion of the pump beam to the active fiber (13).
0), and a third access fiber (153) configured to feed the second access fiber (15).
A fourth access fiber (154) of the same type as (2), into which the second portion of the pump beam is introduced, wherein the second coupler (160) comprises the first optical coupler (150). A multi-mode fiber optically coupled to said fourth access fiber (154);
A first access fiber (161) for receiving a second portion of the pump beam; and a second active fiber (130) coupled to the at least a portion of the second portion of the pump beam for the second active fiber.・ Fiber (1
30) a second access fiber (162) which is a double cladding fiber configured to feed
And a third access fiber (1) for carrying the optical signal.
63) A pump device comprising: 7. The pump device according to claim 6, wherein the first access fiber (151) of the first coupler (150) is coupled to an optical input (110) for receiving the optical signal. Wherein the third access fiber (163) of the second coupler (160) is coupled to an optical output (120) for coupling the optical signal to the optical output (120). A pump device, characterized in that the pump device is a single mode fiber configured to supply. 8. An optical input (110) for inputting an optical signal.
An active fiber interposed between the input (110) and the output (120) and configured to amplify the optical signal; and an optical output (120) for outputting the optical signal. A pump device (140) according to any one of the preceding claims, wherein a pump source (145) for generating a pump beam and the pump beam is optically coupled to the active fiber. And an optical amplifier comprising: 9. An optical amplifier according to claim 8, wherein said active fiber comprises two fiber sections, each coupled to a respective one of said two couplers. amplifier. 10. An optical amplifying device comprising two optical amplifiers (108 ′, 108 ″) according to claim 8 arranged in series. 11. The optical amplifying device according to claim 10, further comprising a preamplifier (103) arranged in series with said optical amplifier (108 ′, 108 ″). 12. The optical amplifying device according to claim 10, further comprising: the optical amplifier.
8 ″), comprising at least one noise removing filter (107) arranged in series with the optical amplifying device. 13. An optical transmitting device configured to transmit an optical signal, an optical receiving device receiving the optical signal, and an optical fiber link optically coupling the transmitting device to the receiving device. An optical filter disposed along the fiber optic link for amplifying the optical signal; a pump source for generating a pump beam; and transmitting the pump beam to the active fiber. An optical transmission system comprising a pump device according to any one of claims 1 to 7 for coupling. 14. A method of coupling a pump beam to an active fiber configured to amplify an optical signal, the active fiber comprising a dual cladding fiber.
A fiber, the method comprising:-guiding an optical signal;-guiding a multi-mode pump beam;-coupling the optical signal and the pump beam to the active beam.
Inputting to the fiber, inputting the optical signal with a predetermined insertion loss, supplying a first power portion to the active fiber, and inputting the pump beam to obtain a residual power portion; Inputting said residual power portion to said active fiber with a predetermined coupling efficiency and supplying a second power portion to said active fiber, wherein said insertion loss is 0.2 dB or less; A method characterized in that the efficiency is at least 70%. 15. The method according to claim 14, wherein the sum of said first and second power portions is greater than 75% of the optical power of said pump beam. 16. The method according to claim 15, wherein said sum is at least 85% of the optical power of said pump beam.