JP2003324237A - Semiconductor laser device and semiconductor laser module and optical fiber amplifier using the device and module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a semiconductor laser device and a semiconductor laser module suited to a light source for an optical fiber amplifier capable of stably obtaining a high gain, and the optical fiber amplifier using the device and the module. <P>SOLUTION: In the semiconductor laser device of ridge structure, a diffraction grating is formed in the vicinity of an active layer formed between a 1st reflection film formed on a laser light exiting end face and a 2nd reflection film formed on a laser light reflecting end face. Further in the laser device laser light including two or more oscillation vertical modes 31-33 in the half band width Δλh of an oscillation wavelength spectral 30 is outputted by setting up the combination of oscillation parameters including the length of a resonator formed by the active layer and the wavelength selection characteristic of the diffraction grating. When a material of an Al mixed crystal group is contained in the active layer, a high output can be generated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device suitable for a pumping light source, a semiconductor laser module and an optical fiber amplifier using the same.

[0002]

2. Description of the Related Art In recent years, an increase in data traffic has become a problem due to the rapid spread of the Internet and the rapid increase in intra-company LAN connections. Therefore, in order to solve the problem, a WDM (wavelength division multiplex) transmission system has made remarkable progress and has become widespread. In the WDM transmission system, a plurality of signal lights are put on different wavelengths, respectively, so that a single fiber realizes a large capacity transmission up to 100 times that of the conventional one. In this WDM transmission system, optical amplification by an optical fiber amplifier such as an erbium-doped fiber amplifier (hereinafter referred to as EDFA) or Raman amplifier is indispensable, and this optical amplification enables wideband / long-distance transmission. Here, the EDFA is a special optical fiber (hereinafter referred to as EDF) doped with an element called erbium and has a wavelength of 1
This is an optical fiber amplifier that applies the principle that, when pumping light in the 480 nm band or 980 nm band is transmitted, light in the 1550 nm band that is a transmission signal is amplified in the EDF.

Further, as a form of the EDFA, when the signal light is amplified in the middle of the transmission optical fiber laid on the seabed, the pumping laser is arranged on land and the pumping light emitted from the pumping laser is arranged. A so-called remote pump type has been proposed in which the light is incident on the EDF via an optical fiber for transmission. In the remote pump type EDFA, the pumping laser is placed on land to maintain the pumping laser.
It can be easily replaced.

On the other hand, the Raman amplifier is a distributed type optical fiber amplifier which uses a normal transmission line fiber as a gain medium without requiring a special fiber such as an erbium-doped fiber like the EDFA, and is based on the conventional EDFA. Compared with the WDM transmission system described above, it is possible to realize a transmission band having a wide band and a flat gain. Since the amplification gain of the Raman amplifier is smaller than that of the EDFA, the pumping laser is required to have a high output characteristic equal to or higher than that of the EDFA.

Therefore, in order to improve the stability of the WDM transmission system and reduce the number of relays, the pumping laser is required to have a stable and high optical output capability. Semiconductor laser devices having various structures such as a buried hetero (BH) structure and a self-aligned structure (SAS) are used as pumping lasers. Currently, particularly high-power semiconductor laser devices are actively developed for the above-mentioned reasons. Has been done to. Especially WD
For the Raman amplifier, which is promising as an optical fiber amplifier used in the M transmission system, a semiconductor laser device with high output specifications is required.

FIG. 27 is a block diagram showing the configuration of a conventional Raman amplifier used in a WDM transmission system.
In FIG. 27, semiconductor laser modules 182a-1
Reference numeral 82d is a Fabry-Perot type semiconductor laser device 180.
a-180d and fiber gratings 181a-18
1d and 1d are provided as a pair, and the laser light that is the source of the excitation light is output to the polarization combining couplers 61a and 61b.
Here, the laser lights output from the semiconductor laser modules 182a and 182b have the same wavelength, but are polarization-combined by the polarization combining coupler 61a. Similarly, the laser lights output from the semiconductor laser modules 182c and 182d have the same wavelength but are polarization-combined by the polarization combining coupler 61b. The polarization combining couplers 61 a and 61 b output the polarization-combined laser lights to the WDM coupler 62. The wavelengths of the laser lights output from the polarization combining couplers 61a and 61b are different.

The WDM coupler 62 is a polarization combining coupler 61.
The laser lights output from a and 61b are combined. The combined laser light is transmitted by the isolator 60 and the WDM coupler 65.
And propagates as amplification light to the amplification fiber 64. The amplification fiber 64 includes a signal light input fiber 69.
The signal light to be amplified is input from the above through the isolator 63, and this signal light is Raman-amplified by the energy of the above-mentioned pump light.

The signal light Raman-amplified in the amplification fiber 64 (amplified signal light) passes through a WDM coupler 65 and an isolator 66, and a monitor light distribution coupler 67.
Entered in. The monitor light distribution coupler 67 outputs a part of the amplified signal light to the control circuit 68, and outputs the remaining amplified signal light to the signal light output fiber 70 as output laser light.

The control circuit 68 controls the light emitting state, for example, the light intensity, of each of the semiconductor laser elements 180a to 180d based on a part of the input amplified signal light so that the gain band of Raman amplification becomes flat. Feedback control.

FIG. 28 is a diagram showing a schematic structure of a semiconductor laser module using a fiber grating.
In FIG. 28, a semiconductor laser module 201 has a semiconductor laser element 202 and an optical fiber 203.
The semiconductor laser device 202 has an active layer 221 whose both end surfaces are formed by a light reflecting surface 222 and a light emitting surface 223. The light generated in the active layer 221 is reflected by the light reflecting surface 222 and output from the light emitting surface 223.

The light emitting surface 223 of the semiconductor laser device 202
An optical fiber 203 is arranged in the vicinity of the light emitting surface 22.
Optically coupled with 3. A fiber grating 233 is formed on the core 232 in the optical fiber 203 at a position separated from the light emitting surface 223 by a predetermined distance. The fiber grating 233 functions as an external resonator that selectively reflects light having a characteristic wavelength. That is, a resonator is formed between the fiber grating 233 and the light reflecting surface 222, and the laser light of the specific wavelength selected by the fiber grating 233 is amplified to output laser light 2
It is output as 41.

[0012]

However, the above-mentioned semiconductor laser module 201 (182a to 182) is used.
In d), relative intensity noise (RIN: Relative Intensity)
There was a problem that noise) became large. There are several possible causes for this, but the following two causes are considered to be the main ones. The first is the fiber grating 2
Since the distance between 33 and the semiconductor laser element 202 is long, the light whose coherence is deteriorated is returned to the semiconductor laser element 202. The second is that the reflecting surface is the light reflecting surface 222 of the semiconductor laser element 202. 223, the fiber grating 233 and the resonator as a whole have two or more composite resonator structures. Due to these causes, in the RIN spectrum, the semiconductor laser device 202
A peak value is generated for each frequency corresponding to the round-trip time of light between the light reflection surface 222 and the fiber grating 233. In Raman amplification, the process of amplification occurs quickly, so if the pumping light intensity fluctuates due to RIN, the Raman gain also fluctuates. That is, the fluctuation of the Raman gain is output as it is as the fluctuation of the amplified signal strength, which causes a problem that stable Raman amplification cannot be performed.

Further, the semiconductor laser module 2 described above
In No. 01, it was necessary to optically couple the optical fiber 203 having the fiber grating 233 and the semiconductor laser element 202, and it took time and labor to align the optical axis at the time of assembly. Further, such a mechanical optical coupling operation in the resonator may cause mechanical vibration and change the oscillation characteristics of the laser, and it may not be possible to provide stable excitation light. There was a problem.

As the Raman amplifier, in addition to the backward pumping method for pumping the signal light from the rear like the Raman amplifier shown in FIG. 27, the forward pumping method for pumping the signal light from the front and both There is a bidirectional excitation method that excites from the direction. At present, the backward pumping method is widely used as the Raman amplifier. The reason is that in the forward pumping method in which the weak signal light travels in the same direction as the strong pump light, fluctuations in the pump light intensity are easily transferred to the signal light.
This is because there are problems that nonlinear effects such as light wave mixing are likely to occur, and that polarization dependence of excitation light is likely to appear. Therefore, the emergence of a stable pumping light source applicable to the forward pumping method is desired. That is, when a semiconductor laser module using a conventional fiber grating is used, there is a problem that applicable pumping methods are limited.

Further, Raman amplification in the Raman amplifier is conditioned on that the polarization direction of the signal light and the polarization direction of the pumping light coincide with each other. That is, in Raman amplification, there is a polarization dependency of the amplification gain, and it is necessary to reduce the influence of the deviation between the polarization direction of the signal light and the polarization direction of the pump light. For that purpose, it is necessary to reduce the polarization dependence by the orthogonal polarization synthesis of the excitation light, depolarization, and the like. That is, it is necessary to reduce the degree of polarization (DOP: Degree Of Polarization).

Furthermore, since Raman amplification has a relatively low amplification factor, the emergence of a high-power pumping light source for Raman amplification has been desired.

The present invention has been made in view of the above, and provides a semiconductor laser device, a semiconductor laser module, and an optical fiber amplifier using the semiconductor laser device, which are stable and can obtain a high gain. The purpose is to

[0018]

In order to achieve the above object, a semiconductor laser device according to a first aspect of the present invention is a semiconductor laser device, wherein a first cladding layer, a first reflection film provided on a laser beam emitting end face, and the laser beam are provided. An active layer formed on the first cladding layer between the second reflective film provided on the reflective end surface and a plurality of oscillation longitudinal modes provided partially or entirely near the active layer. A diffraction grating to be selected and a second cladding layer formed on the active layer, the active layer comprising:
It is characterized in that it contains an Al mixed crystal material.

According to the present invention, a plurality of oscillation longitudinal modes can be provided by the wavelength selection characteristic of the diffraction grating, and the overflow of carriers in the active layer can be suppressed.

A semiconductor laser device according to a second aspect of the present invention includes a first cladding layer, a first reflection film provided on a laser light emission end face and a second reflection film provided on the laser light reflection end face. Which is an active layer formed on the first cladding layer, a second cladding layer formed on the active layer and partially having a ridge portion, and diffraction for selecting a plurality of oscillation longitudinal modes. It is characterized by having a lattice.

According to the present invention, in the ridge structure, a plurality of oscillation longitudinal modes can be provided by the wavelength selection characteristic of the diffraction grating.

A semiconductor laser device according to a third aspect of the present invention is characterized in that, in the above invention, the diffraction grating is provided in the ridge portion.

A semiconductor laser device according to a fourth aspect is characterized in that, in the above invention, the diffraction grating is provided in a region sandwiching the ridge portion in the second cladding layer.

A semiconductor laser device according to a fifth aspect of the present invention is characterized in that, in the above-mentioned invention, the active layer contains an Al mixed crystal material.

According to a sixth aspect of the present invention, in the semiconductor laser device according to the above invention, the active layer is (Al _x Ga).
It is characterized by having a barrier layer and a well layer of _1-x ) _y In _1-y As (0 <x, y <1).

According to a seventh aspect of the present invention, in the above-mentioned invention, the semiconductor laser device is characterized in that the active layer has an optical waveguide layer containing an Al mixed crystal material.

According to an eighth aspect of the present invention, in the semiconductor laser device according to the above invention, the optical waveguide layer is (Al _x
Ga _1-x ) _y In _1-y As (0 <x, y <1) is included.

According to a ninth aspect of the present invention, in the semiconductor laser device according to the above invention, the first cladding layer and / or
Alternatively, the second clad layer is characterized by containing an Al mixed crystal system material.

According to a tenth aspect of the present invention, in the semiconductor laser device according to the above invention, the first cladding layer and / or the second cladding layer is an Al mixed crystal semiconductor layer and a non-Al mixed crystal semiconductor. It is characterized by having a laminated structure with layers.

According to the eleventh aspect of the present invention, in the semiconductor laser device according to the above invention, the diffraction grating is the first
It is characterized in that it is provided on the reflection film side or in the vicinity of the first reflection film.

According to a twelfth aspect of the present invention, in the semiconductor laser device according to the above invention, the diffraction grating is the second one.
It is characterized in that it is provided on the reflection film side or in the vicinity of the second reflection film.

According to a thirteenth aspect of the present invention, in the semiconductor laser device according to the above invention, the diffraction grating is the first
It is characterized in that it is provided on the reflective film side or in the vicinity of the first reflective film and on the second reflective film side or in the vicinity of the second reflective film.

According to a fourteenth aspect of the present invention, in the above invention, the semiconductor laser device is characterized in that the desired number of oscillation longitudinal modes is two or more within the half-width of the oscillation wavelength spectrum.

According to a fifteenth aspect of the present invention, in the above-mentioned invention, the semiconductor laser device is characterized in that the diffraction grating has a diffraction grating length of 300 μm or less.

A semiconductor laser device according to a sixteenth aspect of the present invention is characterized in that, in the above invention, the diffraction grating length of the diffraction grating is not more than (300/1300) times the resonator length. .

A semiconductor laser device according to a seventeenth aspect is characterized in that, in the above-mentioned invention, a multiplication value of the coupling coefficient of the diffraction grating and the diffraction grating length is 0.3 or less.

Further, a semiconductor laser device according to an eighteenth aspect of the present invention is characterized in that, in the above invention, the diffraction grating has a predetermined period fluctuation in a grating period.

A semiconductor laser device according to a nineteenth aspect of the present invention is characterized in that, in the above invention, the diffraction grating changes the grating period randomly or at a predetermined period.

According to a twentieth aspect of the present invention, in the semiconductor laser device according to the above invention, the first reflection film and the second reflection film are provided.
The resonator formed by the active layer formed between the reflective film and the reflective film has a length of 800 μm or more.

Further, a semiconductor laser device according to a twenty-first aspect is characterized in that, in the above-mentioned invention, the full width at half maximum of the oscillation wavelength spectrum is 3 nm or less.

A semiconductor laser module according to a twenty-second aspect of the present invention is a semiconductor laser device according to any one of the first to twenty-first aspects, and a light for guiding the laser light emitted from the semiconductor laser device to the outside. A fiber, and an optical coupling lens system for optically coupling the semiconductor laser device and the optical fiber are provided.

According to a twenty-third aspect of the present invention, in the semiconductor laser module according to the above invention, a photodetector for measuring the optical output of the semiconductor laser device, an isolator, and a temperature control module for controlling the temperature of the semiconductor laser device. And is further provided.

According to a twenty-fourth aspect of the present invention, in the semiconductor laser module, the first reflection film provided on the emission end face of the laser light and the second reflection film provided on the reflection end face of the laser light are located between the first reflection film and the first reflection film. A semiconductor laser device comprising: an active layer formed on a cladding layer; and a diffraction grating which is provided in the vicinity of the active layer, partially or entirely, and which selects a plurality of oscillation longitudinal modes. An optical fiber for guiding the emitted laser light to the outside, and an optical coupling lens system for optically coupling the semiconductor laser device and the optical fiber are provided.

An optical fiber amplifier according to a twenty-fifth aspect comprises the semiconductor laser device according to any one of the first to twenty-first aspects or the semiconductor laser module according to any one of the twenty-second to twenty-fourth aspects. A pumping light source, an optical fiber for transmitting signal light, an amplification optical fiber connected to the optical fiber, a coupler for causing the pumping light emitted from the pumping light source to enter the amplification optical fiber,
It is characterized by having.

An optical fiber amplifier according to a twenty-sixth aspect comprises the semiconductor laser device according to any one of the first to twenty-first aspects or the semiconductor laser module according to any one of the twenty-second to twenty-fourth aspects. A pumping light source, an optical fiber for transmitting signal light, and a coupler for making pumping light emitted from the pumping light source incident on the optical fiber, and performing optical amplification by Raman amplification. .

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor laser device, a semiconductor laser module and an optical fiber amplifier using the same according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to this embodiment.

(First Embodiment) First, a semiconductor laser device according to the first embodiment will be described. FIG. 1 is a cross-sectional view of a semiconductor laser device according to a first embodiment as viewed obliquely. 2 is a cross-sectional view taken along the line AA of the semiconductor laser device shown in FIG. 1, which is parallel to the emitting end face. Also,
FIG. 3 is a sectional view taken along the line BB of the semiconductor laser device shown in FIGS. 1 and 2, that is, a longitudinal sectional view in the longitudinal direction. 1 to 3, the semiconductor laser device 20 according to the first embodiment has a so-called ridge structure, and n
On the (100) plane of the -InP substrate 1, the n-InP lower cladding layer 2 also serving as a buffer layer and the GRIN-SC are sequentially formed.
H-MQW (Graded Index-Separate Confinement Hete
rostructure Multi Quantum Well) Active layer 3, p-In
In the structure in which the P upper cladding layer 5 and the p-InGaAsP contact layer 7 are stacked, a part of the p-InP upper cladding layer 5 and the p-InGaAsP contact layer 7 are formed.
And form a mesa stripe (ridge shape).
This mesa stripe realizes current confinement and optical confinement utilizing the refractive index difference between air and the semiconductor (p-InP upper cladding layer 5).

Further, in the figure, a diffraction grating 13, which is one of the features of the present invention, is provided in the area shown as the diffraction grating layer 4. This diffraction grating 13 is
It is made of p-InGaAsP, has a film thickness of 20 nm, and is periodic at a pitch of about 220 nm over a range of length Lg = 50 μm from the reflection end surface of the emission side reflection film 15 toward the reflection film 14 side. The laser light having the center wavelength of 1.48 μm is selected. Further, the diffraction grating 13 sets the driving current − by setting the multiplication value of the coupling coefficient κ of the diffraction grating and the diffraction grating length Lg to 0.3 or less.
The linearity of the light output characteristic is improved and the stability of the light output is improved (see Japanese Patent Application No. 2001-134545). When the resonator length L is 1300 μm, the diffraction grating length Lg is about 3
Since the oscillation occurs in a plurality of oscillation longitudinal modes when the length is 00 μm or less, the diffraction grating length Lg is preferably 300 μm or less.

By the way, in proportion to the length of the resonator length L,
Since the oscillation longitudinal mode interval also changes, the diffraction grating length Lg is
The value is proportional to the resonator length L. That is, in order to maintain the relationship of the diffraction grating length Lg: resonator length L = 300: 1300, the relationship that a plurality of oscillation longitudinal modes can be obtained when the diffraction grating length Lg is 300 μm or less is Lg × (1300 (μm) / L ) ≦ 300 (μm). That is, the diffraction grating length L
g is set so as to maintain the ratio with the resonator length L, and is set to a value equal to or less than (300/1300) times the resonator length L (see Japanese Patent Application No. 2001-134545).

Further, as shown in the drawing, on the surface of the above mesa stripe, except for the central portion of the p-InGaAsP contact layer 7, Si which functions as an insulating film and a protective film is formed.
The N _x film 9 is formed. In addition, p-InGaAsP
The p-side electrode 10 is formed so as to cover the exposed portion of the contact layer 7 and the surface of the SiN _x film 9, and thus the p-side electrode 10 is formed.
Electrical contact is made between the side electrode 10 and the p-InGaAsP contact layer 7. On the other hand, the n-side electrode 11 is formed on the back surface of the n-InP substrate 1.

A reflecting film 14 having a high light reflectance of 80% or more, preferably 98% or more is formed on a light reflecting end surface which is one end surface in the longitudinal direction of the semiconductor laser device 20.
The light emitting end face, which is the other end face, has an emission side reflection film having a low light reflectance of 10% or less, preferably 5%, 1%, 0.5% or less, and more preferably 0.1% or less. 15 is formed. GRIN-SCH-MQW active layer 3 of the optical resonator formed by the reflection film 14 and the emission side reflection film 15
The light generated inside is reflected by the reflection film 14 and emitted as laser light through the emission side reflection film 15, and at this time, the wavelength is selected by the diffraction grating 13 and emitted.

The laser light output from the semiconductor laser device 20 has only to oscillate in a single transverse mode, and the structure of the active layer or the optical waveguide is not limited to the above. In the present invention, the active layer is particularly preferable. Is formed by including an Al mixed crystal material. Specifically, GRIN-S
The well layer and the barrier layer forming the CH-MQW active layer 3 are
(Al _x Ga _1-x ) _y In _1-y As (0 <x, y <1). It is preferable that the well layer has a compressive strain of about 1.4% and the barrier layer has a tensile strain of about 0.1%. Also, the SCH layer can be formed of InGaAsP,
It is more preferable to use an Al mixed crystal system material such as (Al _x Ga _1-x ) _y In _1-y As (0 <x, y <1).

When an Al mixed crystal type material is used for the active layer and / or the optical waveguide layer in this way, carrier overflow is suppressed. As a result, higher output, reduction in temperature dependence of light output, and reduction in temperature dependence of threshold current are realized. The suppression of carrier overflow is due to the large energy difference between the well layer and the barrier layer in the Al mixed crystal material, as compared with the conventional AlInmixed crystal GaInAsP and the like.

FIG. 4 is an energy level diagram for explaining the suppression of carrier overflow. As can be seen from FIG. 4, even when the injection current is increased, if the energy difference ΔEc between the conduction band of the barrier layer and the conduction band of the well layer is large, the overflow of electrons can be suppressed, and the valence band of the barrier layer and the well can be suppressed. If the energy difference ΔEv in the valence band of the layer is large, hole overflow can be suppressed. Here, since the electron has a smaller effective mass than the hole, the electron is more dominant in the problem of overflow, and in order to suppress the carrier overflow, it is effective to make ΔEc larger than ΔEv.

Here, the energy difference ΔEg between the energy band gap Eb of the barrier layer and the energy band gap Ew of the well layer is defined as ΔEg = Eb−Ew. It is known that ΔEc is a product of ΔEg and the material system, and ΔEc = 0.4ΔEg in the GaInAsP system and ΔEc = 0.72ΔEg in the AlGaInAs system. That is, AlGaInA
It can be seen that it is effective to use an AlGaInAs-based material for the active layer in order to suppress carrier overflow, since s-based ΔEc is larger.

The first embodiment is premised on that the semiconductor laser device 20 is used as a pumping light source for a Raman amplifier, and its oscillation wavelength λ ₀ is 1100 nm to ₁ nm.
600 nm, and the cavity length L is 800 μm or more 32
It is set to 00 μm or less. By the way, in general, the mode interval Δλ of the longitudinal mode generated by the resonator of the semiconductor laser device can be expressed by the following equation when the effective refractive index is “n”. That is, Δλ = λ ₀ ² / (2 · n · L). Here, when the oscillation wavelength λ ₀ is 1480 μm and the effective refractive index is 3.5, when the resonator length L is 800 μm, the mode interval Δλ of the longitudinal mode is about 0.39 nm, and the resonator length is 3200 μm. At this time, the mode interval Δλ of the longitudinal mode is about 0.1 nm. That is, the longer the resonator length L, the longer the mode interval Δλ of the longitudinal mode.
Becomes narrower, and the selection condition for oscillating a single longitudinal mode laser beam becomes stricter.

On the other hand, the diffraction grating 13 selects the longitudinal mode according to its Bragg wavelength. The selected wavelength characteristic by the diffraction grating 13 is represented as an oscillation wavelength spectrum 30 shown in FIG. As shown in FIG. 5, in the first embodiment,
A plurality of oscillation longitudinal modes are made to exist within the wavelength selection characteristic indicated by the half-width Δλh of the oscillation wavelength spectrum 30 by the semiconductor laser device 20 having the diffraction grating 13. Conventional DBR (Distributed Bragg Reflector) semiconductor laser device or DFB (Distributed Feedbac)
k) In the semiconductor laser device, if the cavity length L is 800 μm or more, it is difficult to oscillate in the single longitudinal mode. Therefore, the semiconductor laser device having the cavity length L is not used. However, in the semiconductor laser device 20 of the first embodiment, the half-width Δλ of the oscillation wavelength spectrum is set by positively setting the cavity length L to 800 μm or more.
A plurality of oscillation longitudinal modes are included in h for laser output. In FIG. 5, there are three oscillation longitudinal modes 31 to 33 within the half width Δλh of the oscillation wavelength spectrum.

When a laser beam having a plurality of oscillation longitudinal modes is used, the peak value of the laser output of each oscillation longitudinal mode is suppressed and the entire oscillation wavelength spectrum is compared with the case where a laser beam of a single longitudinal mode is used. It is possible to obtain a high laser output value. For example, the semiconductor laser device shown in the first embodiment has the profile shown in FIG. 6B and can obtain a high laser output with a low peak value.
On the other hand, FIG. 6A shows a profile of a semiconductor laser device of single longitudinal mode oscillation when obtaining the same laser output, and has a high peak value.

Here, when the semiconductor laser device is used as a pumping light source for a Raman amplifier, it is preferable to increase the pumping light output power in order to increase the Raman gain, but if the peak value is high, stimulated Brillouin scattering occurs. However, there is a problem that noise is increased. The generation of stimulated Brillouin scattering has a threshold value Pth at which stimulated Brillouin scattering occurs, and in the case of obtaining the same laser output power, a plurality of oscillation longitudinal modes are provided, as shown in FIG.
By suppressing the peak value, a high pumping light output power can be obtained within the threshold value Pth of stimulated Brillouin scattering, and as a result, a high Raman gain can be obtained.

Here, the oscillation longitudinal modes 31 to 33 are used.
The wavelength interval (mode interval) Δλ is set to 0.1 nm or more. This is because when the semiconductor laser device 20 is used as a pumping light source for a Raman amplifier, the mode interval Δλ is 0.
This is because if the thickness is 1 nm or less, stimulated Brillouin scattering is likely to occur. As a result, the above-mentioned resonator length L is 3200 according to the above-described equation of the mode interval Δλ.
It is preferable that the thickness is μm or less.

From the above viewpoint, the oscillation wavelength spectrum 3
The number of oscillation longitudinal modes included in the half width Δλh of 0 is
It is desirable that the number is plural and that the spectrum width of each oscillation longitudinal mode is also wide. By the way, in Raman amplification, since the amplification gain has polarization dependence, it is necessary to reduce the influence of the deviation between the polarization direction of the signal light and the polarization direction of the pump light. As a method for this, there is a method of depolarizing the pumping light, and specifically, a method of polarization combining output lights from the two semiconductor laser devices 20 using a polarization combining coupler. Another method is to use a polarization maintaining fiber having a predetermined length as the depolarizer and propagate the laser light emitted from one semiconductor laser device 20 to this polarization maintaining fiber. When the latter method is used as the depolarization method, the coherency of the laser light decreases as the number of oscillation longitudinal modes increases and the oscillation longitudinal mode spectral width increases, so the polarization required for depolarization is reduced. The length of the wavefront holding fiber can be shortened. In particular, when the number of oscillation longitudinal modes is 4 or 5, the required length of the polarization maintaining fiber is drastically shortened. Therefore, the semiconductor laser device 2 is used for the Raman amplifier.
In the case of depolarizing the laser light emitted from 0, the emitted laser light of one semiconductor laser device 20 is unpolarized even if the emitted light of the two semiconductor laser devices is not polarization-combined and used. Since it is easy to convert and use it, it is possible to reduce the number of components used in the Raman amplifier and promote miniaturization.

Here, if the oscillation wavelength spectrum width is too wide, the multiplexing loss due to the wavelength synthesizing coupler becomes large, and noise or gain fluctuation is caused by the movement of the wavelength within the oscillation wavelength spectrum width. Therefore, the full width at half maximum Δλh of the oscillation wavelength spectrum 30 is 3 nm.
Hereafter, it is necessary to set it to preferably 2 nm or less.

Further, in the conventional semiconductor laser device, as shown in FIG. 27 or FIG. 28, the semiconductor laser module uses the fiber grating.
As described above, the light with deteriorated coherence is fed back to the semiconductor laser element 202, or the relative intensity noise (RIN) increases due to the composite resonator structure.
Although it is not possible to perform stable forward pumping Raman amplification, the semiconductor laser device 20 according to the first embodiment is shown.
However, since the laser light emitted from the emission side reflection film 15 is used as it is as the excitation light source of the Raman amplifier without using the fiber grating 233, the relative intensity noise becomes small, and as a result, the fluctuation of the Raman gain becomes small. Therefore, stable Raman amplification can be performed.

Further, in the semiconductor laser module shown in FIG. 27 or FIG. 28, since mechanical coupling is required in the resonator, the oscillation characteristics of the laser may change due to vibration or the like. In the semiconductor laser device according to No. 1, stable optical output can be obtained without changing the oscillation characteristics of the laser due to mechanical vibration or the like.

In the first embodiment described above, the diffraction grating 13 outputs a plurality of oscillation longitudinal modes by the wavelength selectivity having fluctuation with respect to the center wavelength. It is possible to obtain a semiconductor laser device capable of positively fluctuating and increasing the number of oscillation longitudinal modes.

FIG. 7 is a diagram showing a periodic change in the grating period of the diffraction grating 13. This diffraction grating 13 is
It is a chirped grating in which the grating period is changed periodically. As shown in FIG. 7, the diffraction grating 13 has an average period of 220 nm and is ± 0.02 nm.
It has a structure in which the cycle fluctuation (deviation) of is repeated at cycle C. Due to the periodic fluctuation of ± 0.02 nm, it is possible to have about 3 to 6 oscillation longitudinal modes within the half-width Δλ _h of the oscillation wavelength spectrum.

FIG. 8 is a diagram showing an oscillation wavelength spectrum of a semiconductor laser device having diffraction gratings having different periods Λ ₁ and Λ ₂ . In FIG. 8, the diffraction grating with the period Λ ₁ has the wavelength λ ₁
The oscillation wavelength spectrum is formed, and three oscillation longitudinal modes are selected in this oscillation wavelength spectrum. On the other hand, the period Λ ₂
The diffraction grating forms an oscillation wavelength spectrum of wavelength λ ₂ , and selects three oscillation longitudinal modes within this oscillation wavelength spectrum. Therefore, the composite oscillation wavelength spectrum 45 formed by the diffraction grating with the periods Λ ₁ and Λ ₂ includes 4 to 5 oscillation longitudinal modes in the composite oscillation wavelength spectrum 45. As a result, more oscillation longitudinal modes can be easily selected and output as compared with the case where a single oscillation wavelength spectrum is formed, and the optical output can be increased.

The structure of the diffraction grating 13 is not limited to the chirped grating in which the grating period is changed at a constant period C, and the grating period is set to the period Λ ₁ (220 nm + 0.02 nm) and the period Λ ₂ (220n).
m-0.02 nm) may be randomly changed.

Further, as shown in FIG. 9A, a periodic fluctuation may be provided as a diffraction grating in which different periods Λ ₃ and Λ ₄ are alternately repeated once. In addition, as shown in FIG. 9B, different periods Λ ₅ and Λ ₆
As a diffraction grating in which and are repeated alternately,
You may make it have a period fluctuation. Furthermore, FIG.
(C), the plurality of times of cycles lambda ₇ consecutive, as a diffraction grating having a plurality of times of cycles lambda ₈ consecutive with a period different from the period lambda _7, may be provided with a periodic fluctuation . Further, between the periods Λ ₃ , Λ ₅ , and Λ ₇ and the periods Λ ₄ , Λ ₆ , and Λ ₈ , the periods having discrete different values are complemented, and the period is changed stepwise. May be.

As described above, according to the semiconductor laser device of the first embodiment, with respect to the cavity length L,
Diffraction grating 13 partially provided on the emitting side reflection film 15 side
In addition to forming multiple oscillation longitudinal modes, the modulation frequency signal is superimposed on the bias current to widen the spectrum width of the oscillation longitudinal mode and suppress the occurrence of stimulated Brillouin scattering when used as a pumping light source for a Raman amplifier. However, the laser light having a desired oscillation wavelength can be stably output with high efficiency.

Further, since the active layer and / or the optical waveguide layer contains an Al mixed crystal system material, the advantage of the characteristics of Al, that is, the suppression of carrier overflow can be enjoyed, and the high output of laser light and the temperature characteristics can be obtained. Can be improved.

In the first embodiment described above, the diffraction grating 13 is provided on the emitting side reflection film 15 side. However, the present invention is not limited to this, and the reflecting film 14 side or the reflecting film 14 side and the emitting side reflection film are provided. You may make it provide a diffraction grating on both 15 sides. In this case, since the diffraction grating on the side of the reflection film 14 has wavelength selectivity and reflection characteristics, the product of the coupling coefficient κ and the diffraction grating length Lg is set to a large value, for example, “2” or more. Good to do.

In place of the n-InP lower cladding layer 2, another material may be used as long as it has a composition lattice-matched with InP. In particular, when the AlInAs lower buffer layer of Al mixed crystal system is used, it is possible to further improve the temperature characteristics and lower the resistance.

Furthermore, as disclosed in Japanese Patent Application No. 2001-303732, element resistance and thermal resistance can be reduced by doping the active layer region with n-type impurities. It should be noted that the region in which the impurity doping is performed may be a part of all well layers and barrier layers instead of all well layers as disclosed in the same patent application. Also, similar impurity doping may be applied to the SCH layer.

(Second Embodiment) Next, a semiconductor laser device according to a second embodiment will be described. In the semiconductor laser device according to the first embodiment, the diffraction grating layer is provided in the upper clad layer not included in the mesa stripe, but in the semiconductor laser device according to the second embodiment, the upper clad layer included in the mesa stripe is included. It is characterized in that a diffraction grating layer is provided inside or in a region not included in the mesa stripe and located on both sides of the mesa stripe.

FIG. 10 is a sectional view parallel to the emission end face of the semiconductor laser device according to the second embodiment. Also, FIG.
1 is A- in the semiconductor laser device shown in FIG.
It is the sectional view on the A line, ie, the longitudinal sectional view in the longitudinal direction. 10 and 11, the same parts as those in FIGS. 2 and 3 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIGS. 10 and 11, the diffraction grating 13 described in the first embodiment has the diffraction grating layer 21 located in the portion of the p-InP upper cladding layer 5 where the mesa stripe is formed. It is formed. That is, in this semiconductor laser device, the diffraction grating 13 constitutes a part of the mesa stripe. The function of the diffraction grating 13 is as described in the first embodiment.

FIG. 12 is a sectional view parallel to the emission end face of another semiconductor laser device according to the second embodiment. Also,
FIG. 13 shows the semiconductor laser device shown in FIG.
It is CC sectional view taken on the line, that is, a longitudinal sectional view in the longitudinal direction.
12 and 13, parts common to those in FIGS. 2 and 3 are designated by the same reference numerals, and description thereof will be omitted.

As shown in FIGS. 12 and 13, the diffraction grating 13 described in the first embodiment is a portion of the p-InP upper cladding layer 5 where the mesa stripe is not formed, and both of the mesa stripe are formed. It is formed in the diffraction grating layers 22a and 22b located aside. That is, in this semiconductor laser device, the diffraction grating 13 is divided with the mesa stripe in between. In addition, the diffraction grating layers 22a, 2
The diffraction gratings 13 respectively formed in 2b are p-In
It is realized as a boundary shape between the P upper cladding layer 5 and the SiN _x layer 9.

The diffraction grating of the second embodiment is formed at a position farther from the active layer than the diffraction grating described in the first embodiment. Further, in the case of FIG. 12, it is also deviated from the region where the light intensity is strong in the lateral direction. In such cases,
Since the light intensity at the diffraction grating portion is weak, the coupling coefficient κ has a small value. On the other hand, in order to select a desired oscillation longitudinal mode by the diffraction grating, the product of the coupling coefficient κ and the diffraction grating length Lg needs to have a certain range of values. Therefore, in the second embodiment, it is necessary to lengthen the diffraction grating Lg, and in an extreme case, it is necessary to form the diffraction grating over the entire resonator length. However, when the diffraction grating length Lg is increased, there is a problem that the full width at half maximum Δλ _h of the oscillation wavelength spectrum becomes narrow. Therefore, it is preferable to give the grating cycle a predetermined cycle fluctuation or to change the grating cycle randomly or in a predetermined cycle because a sufficient plurality of oscillation longitudinal modes can be obtained even in such a case. The functions of these diffraction gratings 13 are as described in the first embodiment.

As described above, according to the semiconductor laser device of the second embodiment, in the semiconductor laser device of the ridge structure described in the first embodiment, the position of the diffraction grating is the upper part included in the mesa stripe. It is provided in the clad layer or in a region which is not included in the mesa stripe and is located on both sides of the mesa stripe. Even in such a structure, the same effect as that of the first embodiment can be obtained. .

(Third Embodiment) Next, a semiconductor laser device according to a third embodiment will be described. In the semiconductor laser device described in the second embodiment, each of the lower clad layer and the upper clad layer is composed of a layer formed of an Al mixed crystal material and a layer formed of an Al non-mixed crystal material. It is characterized by that.

FIG. 14 is a sectional view parallel to the emitting end face of the semiconductor laser device according to the third embodiment. Also, FIG.
5 is A- in the semiconductor laser device shown in FIG.
It is the sectional view on the A line, ie, the longitudinal sectional view in the longitudinal direction. Particularly, FIGS. 14 and 15 correspond to the modified examples of FIGS. 10 and 11 described in the second embodiment. 14 and 15, parts common to those in FIGS. 10 and 11 are designated by the same reference numerals, and description thereof will be omitted.

FIG. 16 is a sectional view parallel to the emitting end face of another semiconductor laser device according to the third embodiment.
FIG. 17 shows the semiconductor laser device shown in FIG.
It is the sectional view on the AA line, ie, the longitudinal sectional view in the longitudinal direction.
In particular, FIGS. 16 and 17 correspond to the modified examples of FIGS. 12 and 13 described in the second embodiment. In addition,
16 and 17, parts common to those in FIGS. 12 and 13 are designated by the same reference numerals, and description thereof will be omitted.

As shown in FIGS. 14 to 17, the lower cladding layer is composed of an n-InP cladding layer 2a and an n-AlInAs cladding layer 2b laminated thereon, and the upper cladding layer is an n-AlInAs layer. The clad layer 5a and the n-InP clad layer 5b laminated on the clad layer 5a.

As described above, by including the Al mixed crystal system material in the lower and upper cladding layers, the advantage of using Al as described in the first embodiment, that is, the improvement of the temperature characteristics and the reduction of the resistance are achieved. Can be increased.

As described above, according to the semiconductor laser device of the third embodiment, in the semiconductor laser device of the ridge type structure described in the second embodiment, the cladding layer contains the Al mixed crystal material. Therefore, it is possible to enjoy the same effect as in the first embodiment,
It is possible to further improve the temperature characteristics and lower the resistance brought about by the above, and it is possible to further increase the output of the laser light.

In the third embodiment described above, both the lower clad layer and the upper clad layer are made to contain an Al mixed crystal material, but only one of them may be used. Specifically, (upper clad layer, lower clad layer) = (InP /
AlInAs, InP), (InP / AlInAs, A
A combination of (InnAs) and (InP, InP / AlInAs) is conceivable. Here, the lower clad layer is In
In the case of using P and AlInAs, in order to improve carrier injection efficiency, it is preferable to perform high-concentration impurity doping on a thin region near the boundary between InP and AlInAs and belonging to AlInAs. In the lower clad layer, an InP layer may be laminated on the AlInAs layer.

The first to third embodiments described above are also applicable.
Describes a semiconductor laser device adopting a ridge structure. However, the idea of including an Al mixed crystal material in an active layer, an optical waveguide layer, or a clad layer is disclosed in Japanese Patent Application No.
Buried hetero (BH) disclosed in 1-134545
The structure and the self-aligned structure (SAS) disclosed in Japanese Patent Application No. 2002-048679 can be applied, and the same effects as described above can be given to those structures.

However, the ridge type structure is superior to the hetero (BH) structure and the self-aligned structure (SAS) in that the buried growth process is not required. In particular, in the case of buried growth, when an Al mixed crystal material such as that described above is used, it is necessary to give due consideration to the effect of oxidation of that portion, so high technology is required, and an Al mixed crystal material is used. It is preferable to employ a ridge type structure for the semiconductor structure. Further, the ridge structure has a hetero (B
As in the H) structure, the active layer is formed in the entire lateral direction of the semiconductor laser device without interruption, so that it becomes easy to reduce the difference in the refractive index between the light emitting region and the region, and as a result, the light emitting region is reduced. It is possible to easily realize high output by widening the lateral width of the region.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, the semiconductor laser device shown in the first to third embodiments described above is modularized.

FIG. 18 is a vertical sectional view showing the structure of the semiconductor laser module according to the fourth embodiment. In FIG. 18, a semiconductor laser module 50 has a semiconductor laser device 51 corresponding to the semiconductor laser device shown in the first to third embodiments described above. The semiconductor laser device 51 has a junction-down structure in which the p-side electrode is joined to the heat sink 57a. As a housing of the semiconductor laser module 50, a Peltier element 58 as a temperature control device is arranged on the inner bottom surface of a package 59 formed of ceramic or the like. A base 57 is arranged on the Peltier element 58, and a heat sink 57a is arranged on the base 57. Peltier element 58
An electric current (not shown) is applied to the device, and it cools and heats depending on its polarity, but mainly functions as a cooler. The temperature control is specifically controlled on the heat sink 57a based on the detection value of the thermistor 58a arranged in the vicinity of the semiconductor laser device 51, and a control device (not shown) normally keeps the temperature of the heat sink 57a constant. The Peltier element 58 is controlled so as to be maintained.

In the semiconductor laser device according to the first to third embodiments, the oscillation wavelength is selected by the diffraction grating, and the fluctuation of the oscillation wavelength due to the driving current is much smaller than that of the Fabry-Perot (FP) laser without the diffraction grating. Small. But,
Even so, as the drive current increases, the temperature of the light emitting region increases, and the oscillation wavelength becomes longer. It is also possible to control the Peltier element 58 so as to prevent such an oscillation wavelength shift due to the temperature of the semiconductor laser device 51. That is, the Peltier element 58 cools the laser light to a lower temperature when the wavelength of the laser light is longer than the desired wavelength, and controls the temperature to a low temperature when the laser light has a shorter wavelength than the desired wavelength. Is heated and controlled to a high temperature. In the present invention, the current applied to the Peltier element 58 for correcting the wavelength shift is
It is smaller than an FP laser and is preferable because it leads to a reduction in power consumption.

By performing such temperature control,
The wavelength stability of the semiconductor laser device 51 can be improved, which is also effective in improving the yield. The heat sink 57a is preferably formed of a material having a high thermal conductivity such as diamond. this is,
This is because if the heat sink 57a is made of diamond, heat generation when a high current is applied is suppressed.

The semiconductor laser device 51 is provided on the base 57.
And the heat sink 57 in which the thermistor 58a is arranged.
a, the first lens 52, and the current monitor 56 are arranged. The laser light emitted from the semiconductor laser device 51 is
The light is guided onto the optical fiber 55 via the first lens 52, the isolator 53, and the second lens 54. The second lens 54 is on the optical axis of the laser light and has a package 59.
It is optically coupled to an optical fiber 55 which is provided above and is externally connected. The current monitor 56 is used for the semiconductor laser device 5.
The light leaked from the reflection film side of No. 1 is detected by the monitor.

Here, the semiconductor laser module 50
Then, the semiconductor laser device 51 and the optical fiber 5 are arranged so that the return light reflected by other optical components does not return to the inside of the resonator.
An isolator 53 is interposed between the isolator 53 and the element 5. Unlike the conventional semiconductor laser module using the fiber grating, the isolator 53 is not an in-line fiber type, but the isolator can be built in the semiconductor laser module 50, so that the insertion loss due to the isolator is small and the relative strength is lower. Noise (RIN) can be achieved and the number of components can be reduced.

In the fourth embodiment, the first to third embodiments are provided.
Since the semiconductor laser device shown in 1 is modularized, insertion loss due to the isolator can be reduced, and noise reduction and the number of parts can be promoted.

As described in the first to third embodiments, since the semiconductor laser device 51 incorporated in the semiconductor laser module 50 has good temperature characteristics, it has a large optical amplification such as a system having a short transmission distance. When the gain is not required, the Peltier element 58 and the control device for the Peltier element 58 may be eliminated to focus on the cost reduction. Figure 1
FIG. 9 is a vertical cross-sectional view showing the configuration of the semiconductor laser module in the case where such an emphasis is placed on price reduction. In addition,
19, the same parts as those in FIG. 18 are designated by the same reference numerals and the description thereof will be omitted.

19, the semiconductor laser module 50 'has a very compact structure without the Peltier element 58, the current monitor 56, the thermistor 58a, and the isolator 53 shown in FIG. In addition,
Even when the semiconductor laser device 51 is not configured to include a material of Al mixed crystal system, such a case is required when high-power pumping light is not particularly required such as EDFA in a system having a short transmission distance. It is also possible to employ a semiconductor laser module having a structure in which a mechanism for controlling temperature and a mechanism for reducing noise are eliminated.

(Fifth Embodiment) Next, an optical fiber amplifier according to a fifth embodiment will be described. The fifth embodiment is characterized in that the semiconductor laser module shown in the above-mentioned fourth embodiment is applied to a Raman amplifier.

FIG. 20 is a block diagram showing the configuration of the Raman amplifier according to the fifth embodiment. In FIG. 20,
This Raman amplifier uses the semiconductor laser modules 60a to 60d having the same configuration as the semiconductor laser module shown in the above-mentioned fourth embodiment, and the semiconductor laser modules 182a to 182d shown in FIG. The configuration is replaced with 60d.

Each semiconductor laser module 60a, 60b
Outputs a laser beam having a plurality of oscillation longitudinal modes to the polarization beam combiner 61a via the polarization maintaining fiber 71, and each of the semiconductor laser modules 60c and 60d outputs a plurality of laser beams via the polarization maintaining fiber 71. The laser light having the oscillation longitudinal mode is output to the polarization beam combiner 61b. Here, the laser lights oscillated by the semiconductor laser modules 60a and 60b have the same wavelength, and the laser lights oscillated by the semiconductor laser modules 60c and 60d have the same wavelength, but the semiconductor laser modules 60a and 60b oscillate. It is different from the wavelength of laser light. This is because the Raman amplification has polarization dependence, and the polarization combining coupler 61
A laser beam whose polarization dependence is eliminated by a and 61b is output.

The laser beams having different wavelengths output from the respective polarization combining couplers 61a and 61b are transmitted by the WDM coupler 6
The laser light combined by 2 is output to the amplification fiber 64 as Raman amplification pumping light via the WDM coupler 65. The signal light to be amplified is input to the amplification fiber 64 to which the pumping light is input, and Raman amplification is performed.

The signal light (amplified signal light) that has been Raman-amplified in the amplification fiber 64 passes through a WDM coupler 65 and an isolator 66, and a monitor light distribution coupler 67.
Entered in. The monitor light distribution coupler 67 outputs a part of the amplified signal light to the control circuit 68, and outputs the remaining amplified signal light to the signal light output fiber 70 as output laser light.

The control circuit 68 controls each of the semiconductor laser modules 60a-60d based on a part of the amplified signal light input.
Is controlled by feedback control so that the gain band of Raman amplification has a flat characteristic.

In the Raman amplifier shown in the fifth embodiment, for example, the semiconductor laser module 182a in which the semiconductor light emitting device 180a and the fiber grating 181a shown in FIG. 27 are coupled by the polarization maintaining fiber 71a.
Since the semiconductor laser module 60a incorporating the semiconductor laser device shown in the first to third embodiments is used instead of the above, the use of the polarization maintaining fiber 71 can be reduced and the Raman amplifier It is possible to reduce the size and weight and reduce the cost.

In the Raman amplifier shown in FIG. 20,
The polarization combining couplers 61a and 61b are used.
, The semiconductor laser modules 60a and 60c are directly connected to the WD through the polarization maintaining fiber 71, respectively.
The light may be output to the M coupler 62. In this case, the polarization planes of the semiconductor laser modules 60a and 60c are incident on the polarization-maintaining fiber 71 at 45 degrees. Here, as described above, each of the semiconductor laser modules 60a and 60c has a plurality of oscillation longitudinal modes, so that the polarization maintaining fiber length 71 can be shortened. This makes it possible to eliminate the polarization dependence of the optical output output from the polarization maintaining fiber 71,
It is possible to realize a more compact Raman amplifier with a smaller number of components.

In addition, the semiconductor laser modules 60a-6
If a semiconductor laser device having a large number of oscillation longitudinal modes is used as the semiconductor laser device built in 0d, the required length of the polarization maintaining fiber 71 can be shortened. In particular, when the number of oscillation longitudinal modes becomes 4 or 5, the required length of the polarization-maintaining fiber 71 is drastically shortened, so that simplification and downsizing of the Raman amplifier can be promoted. Furthermore, as the number of oscillation longitudinal modes increases, the coherence length becomes shorter, and the degree of polarization (DOP: De
gree of polarization) can be reduced, and the polarization dependence can be eliminated, which also facilitates simplification and miniaturization of the Raman amplifier.

In addition, in this Raman amplifier, the optical axis alignment is easier than in a semiconductor laser module using a fiber grating, and there is no mechanical optical coupling in the resonator. The stability and reliability of can be improved.

Further, in the semiconductor laser devices of the above-described first to third embodiments, since the semiconductor laser device has a plurality of oscillation modes and the spectrum width of the oscillation longitudinal mode is widened by the application of the modulation frequency signal, the stimulated Brillouin scattering is obtained. Since high-power pumping light can be generated without generating, it is possible to obtain stable and high Raman gain.

Although the Raman amplifier shown in FIGS. 20 and 21 is of the backward pumping type, it is of the forward pumping type because the semiconductor laser modules 60a-60d output stable pumping light as described above. Also, stable Raman amplification can be performed even with the bidirectional pumping method.

For example, FIG. 22 is a block diagram showing the configuration of a Raman amplifier adopting the forward pumping method. Figure 2
In the Raman amplifier shown in FIG. 2, the WDM coupler 65 'is provided in the vicinity of the isolator 63 in the Raman amplifier shown in FIG. The WDM coupler 65 'includes semiconductor laser modules 60a to 60d and polarization combining couplers 61a and 6a.
1b and the WDM coupler 62 respectively corresponding semiconductor laser modules 60a'-60d ', polarization combining couplers 61a', 61b ', and a circuit having the WDM coupler 62' are connected, and the pumping light output from the WDM coupler 62 'is connected. Is output in the same direction as the signal light for forward pumping. In this case, the semiconductor laser modules 60a'-60d '
Uses the semiconductor laser device used in the first to third embodiments described above, the RIN is small and the forward pumping can be effectively performed.

Similarly, FIG. 23 is a block diagram showing the structure of a Raman amplifier adopting the forward pumping method. FIG. 23
In the Raman amplifier shown in FIG. 21, the WDM coupler 65 ′ is provided near the isolator 63 in the Raman amplifier shown in FIG. The WDM coupler 65 'includes semiconductor laser modules 60a, 60c and semiconductor laser modules 60a', 60c corresponding to the WDM coupler 62, respectively.
'And a circuit having a WDM coupler 62' is connected,
Forward pumping is performed in which the pumping light output from the WDM coupler 62 'is output in the same direction as the signal light. In this case, since the semiconductor laser modules 60a 'and 60c' use the semiconductor laser device used in the above-described first to fourth embodiments, the RIN is small and the forward pumping can be effectively performed.

FIG. 24 is a block diagram showing the structure of a Raman amplifier adopting the bidirectional pumping method. Figure 24
The Raman amplifier shown in FIG. 20 has the same structure as the Raman amplifier shown in FIG. 20, but the WDM coupler 65 ′ shown in FIG. 22, the semiconductor laser modules 60a ′ to 60d ′, the polarization combining couplers 61a ′ and 61b ′, and the WDM coupler 62. ′ Is further provided to perform backward excitation and forward excitation. In this case, since the semiconductor laser modules 60a'-60d 'use the semiconductor laser device used in the first to third embodiments described above, the RIN is small and the forward pumping can be effectively performed.

Similarly, FIG. 25 is a block diagram showing the structure of a Raman amplifier adopting the bidirectional pumping method. Figure 2
The Raman amplifier shown in FIG. 4 further includes the WDM coupler 65 ′ shown in FIG. 23, the semiconductor laser modules 60a ′ and 60c ′, and the WDM coupler 62 ′ in the configuration of the Raman amplifier shown in FIG. Excite and perform. In this case, the semiconductor laser modules 60a ′, 60
Since c ′ uses the semiconductor laser device used in the above-described first to third embodiments, RIN is small, and forward pumping can be effectively performed.

The Raman amplifiers shown in FIGS. 22 to 25 described above can be applied to the WDM communication system as described above. FIG. 26 is a block diagram showing a schematic configuration of a WDM communication system to which the Raman amplifier shown in FIGS. 20 to 25 is applied.

In FIG. 26, a plurality of transmitters Tx1 to Tx are provided.
The optical signals of wavelengths λ _{1 to} λ _n sent from xn are combined by the optical combiner 80 and integrated into one optical fiber 85. On the transmission path of the optical fiber 85, a plurality of Raman amplifiers 81 and 83 corresponding to the Raman amplifiers shown in FIGS. 22 to 25 are arranged according to the distance and amplify the attenuated optical signal. The signal transmitted on this optical fiber 85 is
The optical demultiplexer 84 demultiplexes the optical signals having a plurality of wavelengths λ _{1 to} λ _n , and the optical signals are received by the plurality of receivers Rx1 to Rxn.
An ADM (Add / Drop Multiplexe) that adds and takes out an optical signal of an arbitrary wavelength on the optical fiber 85.
r) may be inserted.

In the fifth embodiment described above, the semiconductor laser device shown in the first to third embodiments or the semiconductor laser module shown in the fourth embodiment is used as the pumping light source for Raman amplification. However, not limited to this, it is obvious that it can be used as a light source for EDFA excitation such as 980 nm and 1480 nm.

[0119]

As described above, according to the semiconductor laser device of the present invention, the optical output peak value can be suppressed and the optical output power can be increased by the existence of the plural oscillation longitudinal modes. When used in a fiber amplifier,
It is possible to achieve high optical amplification while suppressing stimulated Brillouin scattering. Further, since the light emitted from the first reflective film is used as it is as the excitation light source without using the fiber grating, the relative intensity noise is reduced as compared with the conventional semiconductor laser device using the fiber grating. When used in a fiber amplifier, it is possible to perform stable optical amplification. Furthermore, since the active layer and the like contain a material of Al mixed crystal system,
The advantage of the characteristics of Al, that is, the suppression of carrier overflow can be enjoyed, and it is possible to achieve high output of laser light and improvement of temperature characteristics.

Further, according to the semiconductor laser device of the present invention, in the ridge structure, the optical output peak value can be suppressed and the optical output power can be increased due to the existence of a plurality of oscillation longitudinal modes. When it is used for, it is possible to achieve high optical amplification while suppressing stimulated Brillouin scattering. Further, since the light emitted from the first reflection film is used as it is as a light source for excitation without using a fiber grating, relative intensity noise is reduced as compared with a semiconductor laser device using a conventional fiber grating. When used in a fiber amplifier, it is possible to perform stable optical amplification.

Further, according to the semiconductor laser module of the present invention, since the above-mentioned semiconductor laser device is used, it is possible to provide the semiconductor laser module in which the occurrence of stimulated Brillouin scattering is suppressed for the same reason.

Further, according to the optical fiber amplifier of the present invention, it is possible to provide an optical fiber amplifier having a stable amplification gain and a high gain by using the above-mentioned semiconductor laser device or semiconductor laser module. .

[Brief description of drawings]

FIG. 1 is a cutaway view of a semiconductor laser device according to a first embodiment, viewed obliquely.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG.

FIG. 4 is an energy level diagram for explaining suppression of carrier overflow.

5 is a diagram showing a relationship between an oscillation wavelength spectrum and an oscillation longitudinal mode of the semiconductor laser device shown in FIG.

FIG. 6 is a diagram showing a relationship between laser light output powers of a single-oscillation longitudinal mode and a plurality of oscillation longitudinal modes and a threshold value of stimulated Brillouin scattering.

FIG. 7 is a diagram showing a periodic change of a grating period of a diffraction grating.

FIG. 8 is a diagram showing an oscillation wavelength spectrum when a chirped grating is applied to a diffraction grating.

FIG. 9 is a diagram showing a modification for realizing periodic fluctuation of the diffraction grating.

FIG. 10 is a cross-sectional view parallel to the emission end face of the semiconductor laser device according to the second embodiment.

11 is a cross-sectional view taken along the line AA of FIG.

FIG. 12 is a sectional view of another semiconductor laser device according to the second embodiment, which is parallel to the emission end face.

FIG. 13 is a sectional view taken along line CC of FIG.

FIG. 14 is a cross-sectional view parallel to the emission end face of the semiconductor laser device according to the third embodiment.

15 is a cross-sectional view taken along the line AA of FIG.

FIG. 16 is a sectional view parallel to the emission end face of another semiconductor laser device according to the third embodiment.

17 is a cross-sectional view taken along the line AA of FIG.

FIG. 18 is a vertical sectional view showing a configuration of a semiconductor laser module according to a fourth embodiment.

FIG. 19 is a vertical cross-sectional view showing another configuration of the semiconductor laser module according to the fourth embodiment.

FIG. 20 is a block diagram showing a configuration of a Raman amplifier according to a fifth embodiment.

21 is a block diagram showing an application example of the Raman amplifier shown in FIG.

22 is a block diagram showing a modification of the Raman amplifier shown in FIG. 19 and showing a configuration of a Raman amplifier adopting a forward pumping method.

23 is a block diagram showing an application example of the Raman amplifier shown in FIG.

24 is a block diagram showing a configuration of a Raman amplifier adopting a bidirectional pumping method, which is a modification of the Raman amplifier shown in FIG.

FIG. 25 is a block diagram showing an application example of the Raman amplifier shown in FIG. 24.

FIG. 26 is a block diagram showing a schematic configuration of a WDM communication system using the Raman amplifier shown in FIGS. 20 to 25.

FIG. 27 is a block diagram showing a schematic configuration of a conventional Raman amplifier.

28 is a diagram showing a configuration of a semiconductor laser module used in the Raman amplifier shown in FIG. 27.

[Explanation of symbols]

1 n-InP substrate 2 n-Inp lower clad layer 2a, 5b n-InP clad layer 2b, 5a n-AlInAs clad layer 3 GRIN-SCH-MQW active layer 4, 21, 22a, 22b Diffraction grating layer 5 p-InP Upper clad layer 7 p-InGaAsP contact layer 9 SiN _x layer 10 p-side electrode 11 n-side electrode 13 diffraction grating 14 reflection film 15 emission side reflection film 20 semiconductor laser device 30 oscillation wavelength spectrum 31 to 33 oscillation longitudinal mode 45 compound oscillation wavelength Spectrum 53,60,63,66 isolator 50,60a-60d, 60a'-60d 'semiconductor laser module 52 first lens 54 second lens 55 optical fiber 56 current monitor 57 base 57a heat sink 58 Peltier element 58a thermistor 59 package 61a, 61b, 61a ', 6 1b 'Polarization combining coupler 62,65,62', 65 'WDM coupler 64 Amplifying fiber 67 Monitor optical distribution coupler 68 Control circuit 69 Signal light input fiber 70 Signal light output fiber 71 Polarization plane preserving fiber 81,83 Raman amplifier Lg Diffraction grating length

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junji Yoshida             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F term (reference) 2K002 AA02 AB30 BA01 CA15 DA10                       EB15 HA24                 5F072 AB07 AK06 HH06 JJ05 MM07                       PP07 QQ07 YY17                 5F073 AA13 AA46 AA65 AA74 AA83                       AB27 AB28 AB30 BA09 CA15                       EA01 FA07 FA08 FA15 FA25                       GA12 GA23

Claims (26)

[Claims] 1. A first clad layer, a first reflective film provided on a laser light emitting end face, and a second reflective film provided on the laser light reflective end face and on the first clad layer. A formed active layer; a diffraction grating provided in the vicinity of the active layer partially or entirely and selecting a plurality of oscillation longitudinal modes; and a second clad layer formed on the active layer. The semiconductor laser device, wherein the active layer contains an Al mixed crystal material. 2. A first clad layer, a first reflective film provided on a laser light emitting end surface, and a second reflective film provided on the laser light reflective end surface, and on the first clad layer. A formed active layer, a second clad layer formed on the active layer and partially having a ridge portion, and a diffraction grating for selecting a plurality of oscillation longitudinal modes. Semiconductor laser device. 3. The semiconductor laser device according to claim 2, wherein the diffraction grating is provided in the ridge portion. 4. The semiconductor laser device according to claim 2, wherein the diffraction grating is provided in a region sandwiching the ridge portion in the second cladding layer. 5. The semiconductor laser device according to claim 1, wherein the active layer contains an Al mixed crystal material. 6. The active layer comprises (Al _x Ga _{1 -x} ) _y In
The semiconductor laser device according to claim 1, further comprising a barrier layer and a well layer of _1-y As (0 <x, y <1). 7. The semiconductor laser device according to claim 1, wherein the active layer has an optical waveguide layer containing an Al mixed crystal material. 8. The optical waveguide layer comprises (Al _x Ga _1-x ) _y
The semiconductor laser device according to claim 7, wherein the semiconductor laser device includes In _1-y As (0 <x, y <1). 9. The semiconductor laser device according to claim 1, wherein the first cladding layer and / or the second cladding layer contains an Al mixed crystal material. 10. The first clad layer and / or the second clad layer has a laminated structure of an Al mixed crystal semiconductor layer and a non-Al mixed crystal semiconductor layer. The semiconductor laser device according to any one of items 1 to 8. 11. The semiconductor laser device according to claim 1, wherein the diffraction grating is provided on the first reflection film side or in the vicinity of the first reflection film. 12. The semiconductor laser device according to claim 1, wherein the diffraction grating is provided on the second reflection film side or in the vicinity of the second reflection film. 13. The diffraction grating is provided on the first reflection film side or in the vicinity of the first reflection film and on the second reflection film side or in the vicinity of the second reflection film. The semiconductor laser device according to any one of 1. 14. The semiconductor laser device according to claim 1, wherein the desired number of oscillation longitudinal modes is two or more within a half width of an oscillation wavelength spectrum. 15. The diffraction grating has a diffraction grating length of 300.
15. The semiconductor laser device according to claim 1, wherein the semiconductor laser device has a thickness of μm or less. 16. The semiconductor laser according to claim 1, wherein the diffraction grating length of the diffraction grating is equal to or less than a value of (300/1300) times the cavity length. apparatus. 17. The semiconductor laser device according to claim 1, wherein a multiplication value of a coupling coefficient of the diffraction grating and a diffraction grating length is 0.3 or less. 18. The semiconductor laser device according to claim 1, wherein the diffraction grating has a grating period with a predetermined period fluctuation. 19. The semiconductor laser device according to claim 18, wherein the diffraction grating changes the grating period randomly or at a predetermined period. 20. The resonator formed by an active layer formed between the first reflective film and the second reflective film has a length of 800 μm or more.
19. The semiconductor laser device according to any one of 19. 21. The full width at half maximum of the oscillation wavelength spectrum is
21 nm or less, The semiconductor laser device as described in any one of Claims 1-20 characterized by the above-mentioned. 22. The semiconductor laser device according to claim 1, an optical fiber for guiding the laser light emitted from the semiconductor laser device to the outside, the semiconductor laser device, and the light. A semiconductor laser module comprising: an optical coupling lens system for optically coupling a fiber. 23. The photodetector for measuring the optical output of the semiconductor laser device, an isolator, and a temperature control module for controlling the temperature of the semiconductor laser device, further comprising: The described semiconductor laser module. 24. An active layer formed on the first clad layer between a first reflective film provided on a laser light emitting end face and a second reflective film provided on the laser light reflecting end face. A semiconductor laser device provided partially or entirely near the active layer and having a diffraction grating for selecting a plurality of oscillation longitudinal modes, and a laser beam emitted from the semiconductor laser device is guided to the outside. And a light coupling lens system that optically couples the semiconductor laser device and the optical fiber with each other. 25. A pumping light source comprising the semiconductor laser device according to claim 1 or the semiconductor laser module according to any one of claims 22 to 24, and transmitting signal light. An optical fiber amplifier, comprising: an optical fiber; an amplification optical fiber connected to the optical fiber; and a coupler for causing excitation light emitted from the excitation light source to enter the amplification optical fiber. . 26. A pumping light source comprising the semiconductor laser device according to claim 1 or the semiconductor laser module according to any one of claims 22 to 24, and transmitting signal light. An optical fiber amplifier comprising: an optical fiber; and a coupler for causing pumping light emitted from the pumping light source to enter the optical fiber, and performing optical amplification by Raman amplification.