JP2002333535A - Optical amplifier with multiplexing filter - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To perform wavelength multiplexing of pump light with high efficiency while achieving both a wide pass band and low excess loss. SOLUTION: A multiplexing filter 301 couples a plurality of optical waveguides having a refractive index of a core higher than a refractive index of a clad to an optical waveguide at an arbitrary coupling ratio at different positions.
One (N is an integer of 2 or more) optical couplers 302a to 302
c and N sandwiched between the optical couplers 302a to 302c.
An optical path length difference is given to a plurality of optical waveguides at a location (303b is ΔL, 303b is 2ΔL). The excitation light from the plurality of excitation light sources is multiplexed by a plane lightwave circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier with a multiplexing filter, and more particularly, to an optical amplifier with a high efficiency and low cost for a high-density wavelength division multiplexing system.

[0002]

2. Description of the Related Art In an optical communication system, a booster amplifier and an in-line amplifier are known as optical amplifiers mainly used. These amplifiers compensate for the span loss of the transmission line connected downstream of the optical amplifier to maintain a sufficient optical signal-to-noise ratio (OSNR) of the signal light component, and to perform high-density wavelength multiplexing (hereinafter, referred to as DWDM). In the case of a system, the signal light output is determined from the viewpoint of suppressing signal deterioration due to the optical nonlinear optical effect in the transmission path. In normal optical transmission, the optical output of each signal light is 0d
It is often set around Bm. In DWDM transmission,
Since each signal light is set to the transmission output, the output of the optical amplifier is as follows. (Output of optical amplifier) = (Number of wavelengths of DWDM system) × (Output of one signal: about 0 dBm) Equation 1 Accordingly, as the number of wavelengths increases, the output of the optical amplifier needs to be higher.

On the other hand, a rare earth-doped optical fiber amplifier or a fiber Raman amplifier is an amplifier using optical pumping, and the energy conversion efficiency from pumping light to signal light is in the following range. Er-doped fiber amplifier for C band: conversion efficiency <60-70% Er-doped fiber amplifier for L band: conversion efficiency <30-40% Tm-doped fiber amplifier for S band: conversion efficiency <30-40% For 1.3 μm band Pr-doped fiber amplifier: Conversion efficiency <10-25% Fiber Raman amplifier: Conversion efficiency <5-25% Since the conversion efficiency is equal to or less than the above value, the pumping light required for the optical amplifier is from 200 mW. A value of about 2 W is required.

As an excitation light source for an optical amplifier, a semiconductor laser (hereinafter, referred to as an LD) is desirable because of its good stability, small size, and low power consumption.
Currently, the pump LD using a single mode optical fiber for the pigtail has an output of at most 300 per LD.
It is about mW. For this reason, if the above-described conversion efficiency is considered, it is necessary to use a plurality of LDs together as an excitation light source. As a multiplexing method of such an excitation light source, a polarization multiplexing method and a wavelength multiplexing method have been conventionally used.

FIG. 1 is a diagram for explaining a method of multiplexing an excitation light source by a conventional polarization multiplexing method, and FIG.
FIG. 1B shows the configuration of an optical amplifier, and FIG. 1B shows the configuration of a polarization combiner. The optical fiber amplifier is connected to an input of an amplification fiber 101 such as a rare earth-doped optical fiber or a high NA fiber having a large stimulated Raman scattering coefficient, and a multiplexer / demultiplexer 102 for multiplexing pump light and signal light. Fiber 10
1 and the signal light input of the multiplexer / demultiplexer 102, an in-line polarization independent isolator 103 for preventing parasitic oscillation.
a and 103b are connected. Note that the inline polarization independent isolator 103a, 103b may be a circulator.

The pumping light input to the multiplexer / demultiplexer 102 has a pumping L
A polarization combiner 104 having D105a and 105b as inputs is connected. In order to increase the power of the pumping light, the polarization combiner 104 combines the outputs from two LDs having the same oscillation wavelength or combines the outputs from two LDs having different oscillation wavelengths. can get.

[0007] The polarization combiner 104 shown in FIG.
Fiber collimators 141a and 141b for inputting pump light in the orthogonal polarization state, a prism 142 for inputting two principal axes of the birefringent crystal 143 at a fixed angle, and an output of the birefringent crystal 143 And a fiber collimator 144 for coupling the optical fiber with the output fiber.
In the polarization combining method, a polarization preserving fiber is used as a pigtail fiber of an excitation LD module, and an LD module that outputs linearly polarized light at the pigtail end is prepared in advance. The linearly polarized waves from the LD module are made orthogonal to each other at two input sections of the polarization combiner, and multiplexed by a polarization beam splitter or the like.

FIG. 2 is a view for explaining a conventional multiplexing method of an excitation light source by a wavelength synthesizing method. In FIG. 2 (a),
FIGS. 2B and 2C show the configuration of an optical amplifier.
2 shows a configuration of the wavelength synthesizer. The optical fiber amplifier connects the multiplexer / demultiplexer 102 to the input of the amplification fiber 101,
An in-line polarization independent isolator 103 is connected to the output of the amplification fiber 101 and the signal light input of the multiplexer / demultiplexer 102.
a and 103b are connected. A wavelength synthesizer 201 having pump LDs 202a and 202b as inputs is connected to the pump light input of the multiplexer / demultiplexer 102.

FIG. 2B shows a wavelength synthesizer for multiplexing wavelengths using a dielectric multilayer film. The wavelength synthesizer 201 includes:
Fiber collimators 211a and 211b, a prism 212 for bending an optical path, and a dielectric multilayer filter 213 designed to transmit λ1 and reflect λ2 in advance
And a fiber collimator 21 for coupling the output fiber
4 is provided. Fiber collimators 211a, 21
When excitation light from two LDs is input via 1b,
The excitation lights of the two wavelengths are multiplexed via the dielectric multilayer filter 213 and coupled to the fiber collimator 214 on the output side. By optimizing the design of the dielectric multilayer filter 213, it is possible to multiplex pumping light having a considerably broad oscillation spectrum centered on λ1 and λ2.

FIG. 2C shows a wavelength combiner for combining wavelengths using a fiber type Mach-Zehnder interferometer. Two directional couplers formed by fusing and stretching two fibers are arranged in series to obtain a multiplexing / demultiplexing characteristic. In this method, the fusion-stretched portion has a lower loss than a single fiber coupler, and two adjacent wavelengths can be multiplexed / demultiplexed. From the graph of the pass loss shown on the right side of FIG. 2C, the pass bandwidth is considerably narrow, and when two wavelengths at 5 nm intervals are combined, the pass band is limited to 1-1.5 nm.

[0011]

However, the polarization synthesizer 104 uses the birefringence crystal 143, the polarization beam splitter, or the polarization characteristics of the dielectric multilayer film to combine the light. Fiber collimators 141a, 141
The use of b, 144 is indispensable, which causes a problem that excess loss is about 0.5 to 1 dB.

The wavelength combiner 201 is also a polarization combiner 1.
04, the fiber collimators 211a, 211a
Since b and 214 are essential, the excess loss is 0.5 to 1
There was a problem that it was about dB.

Further, the wavelength synthesizer 201 using the fiber type Mach-Zehnder interferometer has a pass band of 1
There was also a problem of being limited to -1.5 nm.

The present invention has been made in view of such a problem, and an object thereof is to provide a planar lightwave circuit PL.
It is an object of the present invention to provide an optical amplifier with a multiplexing filter that can achieve both a wide passband and a low excess loss by using a multiplexing circuit configured by C (Planer Lightwave Circuit) technology.

[0015]

According to the present invention, in order to achieve the above object, the invention according to claim 1 is characterized in that a plurality of pumping light sources having different wavelengths are pumped by a multiplexing filter. In the optical amplifier with a multiplexing filter that multiplexes and amplifies the signal light by the pump light, the multiplexing filter includes:
A plurality of optical waveguides each having a core whose refractive index is higher than the cladding refractive index, and N + 1 (N is an integer of 2 or more) optical couplers coupling the optical waveguides at different positions at an arbitrary coupling ratio; With a multiplexing filter, the pump light of the plurality of excitation light sources is multiplexed by a plane lightwave circuit that gives an optical path length difference to the plurality of N optical waveguides sandwiched between the optical couplers. Optical amplifier.

According to this configuration, by using a multiplexing filter including an asymmetric multi-stage Mach-Zehnder interferometer using at least three optical couplers, a wide pass band and low excess loss are compatible. And the pump light can be efficiently multiplexed.

According to a second aspect of the present invention, in the first aspect, the coupling ratio of the first optical coupler from the input side of the multiplexing filter is 50%, Assuming that the optical path length difference between the plurality of optical waveguides at a location sandwiched between the first optical coupler is ΔL, the optical path lengths of the plurality of optical waveguides at other N-1 locations sandwiched between the optical couplers are provided. The difference is ± 2mΔL ± m′λ / 2 (m and m ′ are 0
And λ is the wavelength of the excitation light).

According to a third aspect of the present invention, at least one of the optical couplers according to the first or second aspect is a multi-mode interferometer type optical multiplexing / demultiplexing circuit.

According to a fourth aspect of the present invention, in the first, second or third aspect, the plurality of optical waveguides on the input side of the multiplexing filter have a Bragg grating in which the refractive index of the core is periodically changed. A reflective circuit is provided.

According to a fifth aspect of the present invention, the plurality of excitation light sources according to any one of the first to fourth aspects are semiconductor lasers, and the semiconductor lasers are mounted on the planar lightwave circuit. Features.

According to a sixth aspect of the present invention, the planar lightwave circuit according to the fifth aspect is formed by partially removing a core and a clad of the planar lightwave circuit in order to mount the semiconductor laser. It includes a mounting portion and an electrode connected to the semiconductor laser, and is formed on a Si substrate.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. A multiplexing filter including an asymmetric multistage Mach-Zehnder interferometer using at least three or more directional couplers is used as a multiplexing circuit of the pump light of the optical amplifier.

FIG. 3 is a diagram for explaining a multiplexing filter according to the first embodiment of the present invention. FIG. 3 (a)
3 shows a configuration of a multiplexing filter, FIG. 3B shows a transmission spectrum, and FIG. 3C shows a structure of an MMI type multiplexer / demultiplexer. In FIG. 3A, the multiplexing filter 301 includes:
Three directional couplers 302 made of a silica-based optical waveguide
a to 302c and two sets of delay circuits 303a and 303b (N = 2, m = 1, m ')
= 0). Here, N represents the number of stages, and m and m 'are described below.

The optical path length difference (2
ΔL) is the optical path length difference (Δ
L) is set to be twice as long as ΔL
Corresponds to the wavelength interval of the pump light that can be multiplexed between the input port 1 and the input port 2. A desired spectrum can be realized by adjusting the coupling ratio of the directional coupler and the optical path length difference ΔL of the delay circuit. Here, how many times the optical path length difference is increased is represented by m, and a correction value to be added is represented by m ′. Therefore, the optical path length difference is represented by ± 2mΔL ± m′λ / 2, where m and m ′ are integers including 0, and λ is the wavelength of the pump light. The wavelength of the excitation light may be selected, for example, between the wavelengths λ1 and λ2 of the two excitation light sources or a wavelength in the vicinity thereof.

As shown in FIG. 3B, the multiplexing filter 301 has a periodic spectrum, and provides flat-top, low-loss, and wide-band transmission characteristics.
If the transmission spectrum is set so as to match the wavelengths λ1 and λ2 of the pump light source, it is possible to obtain pump light in which λ1 and λ2 are combined from the output port. As a result, a high pump light source output is obtained, and a highly efficient optical amplifier can be configured.

In this embodiment, the multiplexing filter is constituted by using the directional couplers.
a to 302c, at least one of them has the configuration shown in FIG.
The multimode interferometer (MMI) type optical multiplexing / demultiplexing circuit shown in FIG.

FIG. 4 is a block diagram showing a multiplexing filter according to a second embodiment of the present invention. The multiplexing filter 401 is made of a silica-based optical waveguide and has a two-stage lattice structure, similarly to the multiplexing filter 301 shown in FIG. Bragg gratings 404a and 404b are formed in the linear portion of the input waveguide. The Bragg grating has a structure in which the refractive index of the PLC core is periodically modulated, and operates as an element that reflects only a specific wavelength.

An ultraviolet laser and a phase mask are used to form a Bragg grating, and ultraviolet irradiation-induced refraction change is applied. The reflection wavelength of the Bragg grating is
It can be set arbitrarily by changing the period of the refractive index modulation. In the present embodiment, the reflection wavelength of the Bragg grating is set to a desired wavelength of the pumping light source, and a resonator structure is configured by combining with the pumping light source on the input port side. This allows
The wavelength stability of the pump light source can be remarkably improved, and a highly stable and highly efficient optical amplifier can be configured.

FIG. 5 is a block diagram showing a multiplexing filter according to a third embodiment of the present invention. The multiplexing filter 501 is made of a silica-based optical waveguide and has a two-stage lattice structure, similarly to the multiplexing filter 301 shown in FIG. An LD is used as an excitation light source, and a multiplexing filter 5 is used.
The platforms 504a and 504b for mounting the LD are formed on the PLC constituting the PLC 01. The PLC is manufactured on a Si substrate, and the LD mounting platforms 504a and 504 are provided.
b is formed on the surface of the Si substrate from which the glass PLC layer has been removed by etching.

LD mounting platforms 504a, 50
4b, a solder pattern for fixing the LD, an electrode pattern, a marker for passive alignment, and the like are formed. The excitation LD is mounted on a platform using a marker and fixed with solder. With this configuration, the number of components in the excitation section can be reduced, and a high-efficiency, high-amplifier can be configured at low cost.

Although the two-stage filter has been described as the multiplexing filter according to the first to third embodiments, the present invention is not limited to the number N of filters or the parameters m and m '. The number of stages can be increased or m and m 'can be changed as needed. When two or more excitation lights are multiplexed, a multiplexing filter can be manufactured by combining a plurality of filters.

FIG. 6 is a block diagram showing a four-channel multiplexing filter according to an embodiment of the present invention. The four-channel multiplexing filter for multiplexing the four excitation light sources includes two types of filters A 601a and 601b and a filter B 602.
Are combined in multiple stages. At this time, the optical path length difference ΔL1 between the filters A 601a and 601b is set to be の of the optical path length difference ΔL2 of the filter B602. The pump lights multiplexed by the two filters A 601 a and 601 b are multiplexed again by the filter B 602.

Assuming that the wavelength interval between the four pump lights is Δλ,
The wavelength interval multiplexed by the filters A 601a and 601b is 2Δλ, and the wavelength interval multiplexed by the filter B 602 is Δλ. By making this combination more stages,
A filter having eight or more channels can be configured.

According to the present embodiment, by using a multiplexing filter including an asymmetric multi-stage Mach-Zehnder interferometer using at least three directional couplers,
A wide passband and low excess loss can be compatible,
Excitation light can be efficiently combined.

Further, the size of the optical amplifier itself can be reduced, so that there is a problem in mounting such as extra length processing of the fiber and fusion splicing for a plurality of times, and an optical fiber caused by securing a space for the fusion reinforcing portion and the extra length processing area. Obstacles to miniaturization of the amplifier can be eliminated.

Further, by utilizing the advanced optical circuit integration technology of the PLC technology and the high degree of freedom of the waveguide layout, the mounting process is simplified by, for example, combining the connection points between the input / output waveguide and the fiber. , Compact mounting, etc. are realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Example 1 In Example 1, an Er-doped silica fiber was used as an amplification fiber. The composition of the fiber used was a silica-based optical fiber in which Al, Ge, and Er were added to the core. Al addition concentration is 2wt%,
The Er doping concentration is 1000 ppm (wt), and the relative refractive index difference between the core claddings is 1.8%. In the 1.48 μm band excitation of about 300 mW, the wavelength is 1.53 to 1.56.
A fiber length that can realize a gain flatness of μm was used.

The entire configuration of the optical amplifier (hereinafter, referred to as EDFA) is the same as that shown in FIG. A fiber collimator type element using a dielectric multilayer film was used for multiplexing / demultiplexing the signal light and the pump light, and a two-stage polarization-independent (Faraday rotator) isolator was used. The excitation light source has an oscillation center wavelength of 1.48 μm and 1.4.
Two 6-μm Fabry-Perot semiconductor LD modules were used. The amount of excitation light from the pigtail end of the LD module is 200 when the drive current is 500 mW.
mW.

FIG. 7 is a diagram showing the transmission characteristics of the multiplexing filter according to the first embodiment of the present invention. The multiplexing of the pump light uses the 2 × 1 multiplexing filter shown in FIG. 3A, where N = 2, m = 1, and m ′ = 0. The multiplexing filter was formed on a Si substrate using a quartz PLC technique.
The transmission loss was about 2 dB, and the amount of excitation light emitted from the multiplexing filter was 360 mW. At this time, the drive currents of the two LDs were both 500 mA.

The evaluation of the amplification characteristics was carried out as follows.
The evaluation was performed using 64 multiplexed optical signals arranged at equal intervals between 582 nm and 1.56101 nm. EDFA
The input signal light level to -25 dBm / ch. And All signal inputs are at -7 dBm.

FIG. 8 is a diagram showing the output characteristics of the multiplexing filter according to the first embodiment of the present invention. As shown by the solid line, when a drive current of 500 mA was applied to each LD, the output from the multiplexing filter shown in FIG. 3A was 360 mW. On the other hand, in the wavelength synthesizer described in FIG. 2B, the output of the pump light was 330 mW.

FIG. 9 is a diagram showing the output characteristics of the EDFA using the multiplexing filter according to the first embodiment of the present invention. E using the multiplexing filter described in FIG.
The DFA has an average output of +4 dBm / ch. And all signal outputs are +2
2 dBm was realized. The EDFA using the wavelength combiner described in FIG. 2B has an average output of +2.5 dBm / ch. And
The total signal output was +20.5 dBm.

The conventional wavelength synthesizer is 1.5 d longer than the case where the multiplexing filter according to the first embodiment of the present invention is used.
B output decreased. Thus, the effectiveness of the present invention was confirmed.

Table 1 summarizes the configuration of the optical amplifier in each embodiment, and Table 2 summarizes the output characteristics.

[0046]

[Table 1]

[0047]

[Table 2]

[Embodiment 2] In Embodiment 2, the same optical amplifier configuration as in Embodiment 1 is used, and E is used as an amplification fiber.
Four Fabry-Perot semiconductor LDs using r-doped tellurite-based optical fibers and having wavelengths arranged at equal intervals of 10 nm from 1.46 μm to 1.48 μm as excitation LDs
Module used. The amount of excitation light from the pigtail end of the LD module was 200 mW when the drive current was 500 mW.

The tellurite-based Er-doped fiber, which is an amplification fiber, has a relative refractive index difference of 1.5%
The addition concentration of r is 1000 ppm (wt), and the cutoff wavelength is 1.4 μm. The fiber length was set to 13 m, and the fiber length was designed so that almost flat gain was obtained in the L band (1.57 μm to 1.61 μm). The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For the evaluation of the gain characteristics, signal light multiplexed by 64 waves arranged at regular intervals of 0.8 nm from 1.5500 μm to 1.6012 μm was used. The input level of the signal light is -25 dBm / ch. And

Table 2 shows the output characteristics of the second embodiment. For wavelength multiplexing, a 4 × 1 multiplexing filter having the configuration shown in FIG. 6 was used. The amount of excitation light emitted from the multiplexing filter is 70
It was 0 mW. The driving current at this time is 500 mA for all four LDs. When a drive current of 500 mA flows through each LD, the average output of the amplifier is +5 dBm / ch. And all the signal outputs realized +22 dBm.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the output of the pump light from the wavelength synthesizer is 650 m.
W, and the signal output from the optical amplifier at this time is +20.
dBm, and the 2 dB output was reduced as compared with the case where the multiplexing filter of the second embodiment was used.

[Embodiment 3] In Embodiment 3, the configuration of an optical amplifier similar to that of Embodiment 1 was used, and an amplification fiber having the same composition and structure as that of Embodiment 1 was used. 1.46 μm and 1.48 μm as LD chips for excitation
The two Fabry-Perot type semiconductor LD chips were used.

For wavelength multiplexing, 2 × 1 of the configuration shown in FIG.
A multiplexing filter was used. Specifically, the asymmetric Mach
The zender circuit portion has the same design as that of the first embodiment, but a silicon terrace structure is introduced in the input waveguide portion, and the LD chip is directly connected to the input waveguide of the PLC by junction down. The output of the LD chip is 200 mW when a drive current of 500 mA is applied to each LD.
It is. The wavelength synthesis output after mounting directly on the PLC by junction down was 200 mW when a drive current of 500 mA was passed through each LD.

For the evaluation of the amplification characteristics, the same system as in Example 1 was used. The average output is +1 dB for wavelength multiplexed signals
m / ch. And all the signal outputs realized +19 dBm.

In the third embodiment, the multiplexing filter and the LD
Since there is no optical fiber between the module and the module, the extra length processing of the fiber becomes very simple, and as a result, the volume of the optical amplifier can be reduced as compared with the conventional configuration.

[Fourth Embodiment] In the fourth embodiment, the same optical amplifier configuration as in the first embodiment is used, and T
Using an m-doped fluoride optical fiber (Zr-based fluoride), the LDs for excitation were 1.41 μm and 1.42 μm.
Two Fabry-Perot semiconductor LD modules were used. The amount of excitation light from the pigtail end of the LD module is
When the driving current was 500 mW, both were 200 mW.

The fluoride-based Tm-doped fiber, which is an amplification fiber, has a relative refractive index difference of 2.5% between core clads and a Tm-doped fiber.
Addition concentration 6000 ppm (wt), cutoff wavelength 1.
0 μm. The fiber length is 6 m, and the S band (1.
(45 .mu.m to 1.49 .mu.m). The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For the evaluation of the gain characteristics, eight-wave multiplexed signal lights arranged at equal intervals between 1.46 μm and 1.51 μm were used. The input level of the signal light is -14 dBm / c
h. And

Table 2 shows the output characteristics of the fourth embodiment. For wavelength multiplexing, a 2 × 1 multiplexing filter having the configuration shown in FIG. 3 was used. The amount of excitation light emitted from the multiplexing filter is 36
It was 0 mW. The drive current at this time is 500 mA for both LDs. When a drive current of 500 mA flows through each LD, the average output of the amplifier is +11 dBm / ch. And all the signal outputs realized +20 dBm.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the pump light output from the wavelength synthesizer is 340 m.
W, and the signal output from the optical amplifier at this time is +18
dBm, and the 2 dBm output was lower than that in the case where the multiplexing filter of the fourth embodiment was used.

[Fifth Embodiment] In a fifth embodiment, the same optical amplifier configuration as that of the first embodiment is used, and T
An m-doped fluoride optical fiber (Zr-based fluoride, Tb added to the cladding) was used, and the LD for excitation was 1.21.
μm and 1.20 μm two Fabry-Perot semiconductors L
The D module was used. The amount of excitation light from the pigtail end of the LD module is as follows when the driving current is 500 mW.
Both were 150 mW.

The fluoride-based Tm-doped fiber, which is an amplification fiber, has a relative refractive index difference of 3.7% between core claddings and a Tm
Addition concentration 2000 ppm (wt), cutoff wavelength 1.
0 μm. 1 wt% of Tb is added to the clad portion. The fiber length was set to 20 m, and the fiber length was designed so that a high gain could be obtained in the 1.65 μm band. The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For evaluation of gain characteristics, a 1.65 μm signal light was used. The input level of the signal light was -5 dBm.

Table 2 shows the output characteristics of the fifth embodiment. For the wavelength multiplexing, a 2 × 1 multiplexing filter having the configuration shown in FIG. 4 was used. The amount of excitation light emitted from the multiplexing filter is 25
It was 0 mW. The drive current at this time is 500 mA for both LDs. When a drive current of 500 mA was applied to each LD, a signal output of +10 dBm was realized with respect to the signal light described above.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the pump light output from the wavelength synthesizer is 200 m
W, and the signal output from the optical amplifier at this time is +7.
5 dBm, which is a 2.5 dB lower output than in the case where the multiplexing filter of the fifth embodiment is used.

[Sixth Embodiment] In the sixth embodiment, the configuration of the optical amplifier similar to that of the first embodiment is used, and P is used as the amplification fiber.
An r-doped fluoride optical fiber (In-based fluoride) was used, and the LD for excitation was 1.02 μm and 1.01 μm.
Two Fabry-Perot semiconductor LD modules were used. The amount of excitation light from the pigtail end of the LD module is
When the drive current was 300 mW, both were 150 mW.

The fluoride-based Pr-doped fiber, which is an amplifying fiber, has a relative refractive index difference of 3.7% between core claddings, Pr
Addition concentration 500 ppm (wt), cutoff wavelength 0.9
μm. The fiber length was set to 20 m, and the fiber length was designed so that a high gain was obtained in the 1.3 μm band. The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For evaluation of the gain characteristics, a signal light of 1.30 μm was used. The input level of the signal light was -5 dBm.

Table 2 shows the output characteristics of the sixth embodiment. For the wavelength multiplexing, a 2 × 1 multiplexing filter having the configuration shown in FIG. 4 was used. The amount of excitation light emitted from the multiplexing filter is 2
It was 50 mW. The driving current at this time is two LDs
Both are 500 mA. When a drive current of 500 mA was passed through each LD, the signal output realized +13 dBm with respect to the above-described signal light.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the pump light output from the wavelength synthesizer is 200 m
W, and the signal output from the optical amplifier at this time is +12
dBm, and the 1 dB output was lower than that in the case where the multiplexing filter of the sixth embodiment was used.

[Seventh Embodiment] In the seventh embodiment, the same optical amplifier configuration as in the first embodiment is used, and P
Using an r-doped fluoride optical fiber (In-based fluoride), the LD for excitation is 0.98 μm and 0.99 μm.
Two Fabry-Perot semiconductor LD modules were used. The amount of excitation light from the pigtail end of the LD module is
When the drive current was 300 mW, both were 200 mW.

The fluoride Pr-doped fiber, which is an amplifying fiber, has a relative refractive index difference of 3.7% between core clads and Pr
Addition concentration 500 ppm (wt), cutoff wavelength 0.9
μm. The fiber length was set to 25 m, and the fiber length was designed so as to obtain a high gain in the 1.3 μm band. The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For evaluation of the gain characteristics, a signal light of 1.30 μm was used. The input level of the signal light was -5 dBm.

Table 2 shows the output characteristics of the seventh embodiment. For the wavelength multiplexing, a 2 × 1 multiplexing filter having the configuration shown in FIG. 4 was used. The amount of excitation light emitted from the multiplexing filter is 36
It was 0 mW. The drive current at this time is 500 mA for both LDs. When a drive current of 500 mA flows through each LD, the signal output is +
13 dBm was realized.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the pump light output from the wavelength synthesizer is 330 m
W, and the signal output from the optical amplifier at this time is +1
The output was 1.5 dBm, and the output was reduced by 1.5 dB as compared with the case where the multiplexing filter of the seventh embodiment was used.

[Eighth Embodiment] In the eighth embodiment, the same optical amplifier configuration as in the first embodiment is used, and a high-concentration Ge-doped silica-based optical fiber having a relative refractive index difference of 3.7% (6 km) is used as an amplification fiber. Long) using a fiber Raman amplifier. 1.43 μm and 1.45 μm 2 for LD for excitation
Two Fabry-Perot semiconductor LD modules were used. The amount of excitation light from the pigtail end of the LD module is
When the driving current was 500 mW, both were 200 mW. The component arrangement of the entire optical amplifier is the same as that of the first embodiment.

For the evaluation of the gain characteristics, wavelength multiplexed light having the same wavelength arrangement and input level as in the first embodiment was used.

Table 2 shows the output characteristics of the eighth embodiment. For wavelength multiplexing, a 2 × 1 multiplexing filter having the configuration shown in FIG. 3 was used. The amount of excitation light emitted from the multiplexing filter is 36
It was 0 mW. At this time, the drive current is 500 mA for both LDs. When a drive current of 500 mA was applied to each LD, a signal light output of +13 dBm was realized for the wavelength multiplexed signal.

On the other hand, when the wavelength synthesizer shown in FIG. 2B is used, the pump light output from the wavelength synthesizer is 330 m.
W, and the signal output from the optical amplifier at this time is +1
The output was 1.5 dBm, and the output was reduced by 1.5 dB as compared with the case where the multiplexing filter of the eighth embodiment was used.

[0081]

As described above, according to the present invention,
Since a wide pass band and a low excess loss can be compatible, wavelength multiplexing of pump light can be performed with high efficiency, and D
It is possible to realize a high-output optical amplifier that is important when applied to a WDM system or the like.

Further, according to the present invention, by integrating the wavelength synthesizing portion and the pump light source, it is possible to realize a more compact and highly integrated optical amplifier.

Further, according to the present invention, since the bandwidth of the multiplexing filter is wide, the wavelength tolerance of the pumping light source is increased and the cost of the LD can be reduced.

Further, according to the present invention, the mass production of the multiplexing filter can be performed by the PLC technology.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a method of multiplexing a pump light source by a conventional polarization multiplexing method. (A) shows the configuration of the optical amplifier, and (b) shows the configuration of the polarization combiner.

FIG. 2 is a diagram for explaining a method of multiplexing an excitation light source by a conventional wavelength synthesis method. (A) shows the configuration of the optical amplifier, and (b) and (c) show the configuration of the wavelength combiner.

FIG. 3 is a diagram for explaining a multiplexing filter according to the first embodiment of the present invention. (A) shows the configuration of the multiplexing filter, (b) shows the transmission spectrum, and (c)
Shows the structure of the MMI type multiplexer / demultiplexer.

FIG. 4 is a configuration diagram showing a multiplexing filter according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a multiplexing filter according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a four-channel multiplexing filter according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating transmission characteristics of the multiplexing filter according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating output characteristics of a multiplexing filter according to the first embodiment of the present invention.

FIG. 9 is a diagram illustrating output characteristics of an EDFA using a multiplexing filter according to the first embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 101 amplifying fiber 102 multiplexer / demultiplexer 103a, 103b in-line type polarization independent isolator 104 polarization combiner 105a, 105b, 202a, 202b pump LD 201 wavelength combiner 211a, 211b, 214 fiber collimator 212 prism 213 dielectric multilayer Membrane filters 301, 401, 501 Combining filters 302a-302c, 402a-402c, 502a-
502c Directional couplers 303a, 303b, 403a, 403b, 503a,
503b Delay circuit 404a, 404b Bragg grating 504a, 504b LD mounting platform 601a, 601b Filter A 602 Filter B

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Masuda, Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Jun Mori 2-chome, Otemachi, Chiyoda-ku, Tokyo No. 1 Inside Nippon Telegraph and Telephone Corporation (72) Yoshinori Hibino 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Yasuyuki Inoue 2-chome Otemachi, Chiyoda-ku, Tokyo No.3-1 Inside Nippon Telegraph and Telephone Corporation (72) Inventor Manabu Oguma 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Tsutomu Kito Otemachi, Chiyoda-ku, Tokyo 2-3-1, Nippon Telegraph and Telephone Corporation F-term (reference) 2H047 KA04 KA12 KB04 KB06 LA03 LA18 RA00 TA31 5F072 AK06 JJ01 KK30 PP07 YY17

Claims (6)

[Claims] 1. An optical amplifier with a multiplexing filter for multiplexing pumping lights of a plurality of pumping light sources having different wavelengths with a multiplexing filter and amplifying a signal light by the pumping light. The filter includes: a plurality of optical waveguides each having a core whose refractive index is higher than that of the cladding; and N + 1 optical couplers (N is an integer of 2 or more) coupling the optical waveguides at different positions at an arbitrary coupling ratio. And combining the excitation lights of the plurality of excitation light sources by a plane lightwave circuit that gives an optical path length difference to the plurality of N optical waveguides sandwiched between the optical couplers. Optical amplifier with filter. 2. The coupling ratio of the first optical coupler from the input side of the multiplexing filter is 50%, and a portion sandwiched between the input of the multiplexing filter and the first optical coupler. Is the optical path length difference between the plurality of optical waveguides at ΔL, the optical path length difference between the plurality of optical waveguides at the other N-1 positions between the optical couplers is ± 2 mΔL
2. The optical amplifier with a multiplexing filter according to claim 1, wherein ± m′λ / 2 (m and m ′ are integers including 0, and λ is the wavelength of the pumping light). 3. The optical amplifier with a multiplexing filter according to claim 1, wherein at least one of the optical couplers is a multimode interferometer type optical multiplexing / demultiplexing circuit. 4. A Bragg grating type reflection circuit in which the refractive index of the core is periodically changed is provided in the plurality of optical waveguides on the input side of the multiplexing filter. Or an optical amplifier with a multiplexing filter according to 3. 5. The multiplexing filter according to claim 1, wherein said plurality of excitation light sources are semiconductor lasers, and said semiconductor lasers are mounted on said planar lightwave circuit. With optical amplifier. 6. The planar lightwave circuit includes a mounting portion formed by partially removing a core and a clad of the planar lightwave circuit for mounting the semiconductor laser, and an electrode connected to the semiconductor laser. The optical amplifier with a multiplexing filter according to claim 5, comprising: a Si substrate.