JP2003318480A - Semiconductor laser module and optical fiber amplifier using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser module that is reduced in RIN and, in addition, can suppress the occurrence of stimulated Brillouin scattering. <P>SOLUTION: This semiconductor laser module is provided with a semiconductor laser element 1 which contains a diffraction grating and emits laser light of a plurality of longitudinal oscillation modes; a reflector 4 which is provided on the outside of the element 1 and emits the laser light emitted from the element 1 by reflecting part of the laser light in a reflected wavelength band including an oscillated wavelength band; and a reflected quantity controller 2 which is provided between the laser element 1 and reflector 4, passes the laser light emitted from the element 1, and sets and controls the quantity of the reflected return light from the reflecting end of the reflector 4 to -10 to -40 dB. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention suppresses the effect of stimulated Brillouin scattering (SBS: Stimulated Brillouin Scattering) and provides relative intensity noise (RIN: Relative I).
The present invention relates to a semiconductor laser module capable of outputting laser light with reduced ntensity noise) and an optical fiber amplifier using the same.

[0002]

2. Description of the Related Art In recent years, due to the rapid spread of the Internet and the rapid increase of LAN connections within companies, an increase in data traffic has become a problem. In order to prevent deterioration of communication performance, high-density wavelength division is used. Multiplex (DWD
M: Dense-Wavelength Division Multiplexing (Transmission) systems have made remarkable progress and are widely used.

In the DWDM transmission system, a plurality of optical signals are put on different wavelengths, respectively, so that a single fiber realizes large-capacity transmission up to 100 times that of the conventional one. In particular, the existing DWDM transmission system uses an erbium-doped fiber amplifier (hereinafter, EDFA),
It enables wide band and long distance transmission. Where EDF
A is a transmission signal having a wavelength of 1550 n when light is passed through a special optical fiber containing an element called erbium with a pumping laser having a wavelength of 1480 nm or 980 nm.
It is an optical fiber amplifier applying the principle that light in the m band is amplified in the special fiber.

On the other hand, the EDFA is a centralized optical amplifier in which a portion for exciting an optical signal is concentrated, and causes loss of a transmission line optical fiber leading to accumulation of noise, signal distortion and noise. There was a limitation of being non-linear.
Further, the EDFA enables optical amplification in a wavelength band determined by the band gap energy of erbium, and it has been difficult to broaden the band for realizing further multiplexing.

Therefore, a Raman amplifier has been attracting attention as an optical fiber amplifier replacing the EDFA. The Raman amplifier is a distributed optical amplifier that uses an ordinary transmission line fiber as a gain medium without requiring a special fiber such as an erbium-doped fiber unlike the EDFA. Therefore, it can be applied to a conventional EDFA-based DWDM transmission system. Compared with this, it has a feature that a transmission band having a wide band and a flat gain can be realized.

FIG. 26 is a block diagram showing the configuration of a conventional Raman amplifier used in a DWDM transmission system. In FIG. 26, the Fabry-Perot type semiconductor laser devices 180a to 180d and the fiber grating 18 are provided.
The semiconductor laser modules 182a to 182d provided with the pair 1a to 181d, respectively, output the laser light which is the source of the pumping light to the polarization beam combiners 161a and 161b. Each semiconductor laser module 182a, 18
The wavelengths of the laser lights output by 2b are the same, but the polarization plane of each laser light is 90 ° by the polarization combining coupler 161a.
Different. Similarly, the wavelengths of the laser lights output from the semiconductor laser modules 182c and 182d are the same, but the polarization planes of the laser lights are different by 90 ° by the polarization beam combiner 161b. Polarization combiner 16
1a and 161b are laser lights that are polarization-combined respectively.
Output to the DM coupler 162. In addition, polarization combining coupler 1
The wavelengths of the laser lights output from 61a and 161b are different.

The WDM coupler 162 is a polarization combining coupler 1
The laser lights output from 61a and 161b are combined.
The laser light output from the WDM coupler 162 is incident on the amplification fiber 164 as excitation light via the isolator 160 and the WDM coupler 165. The signal light to be amplified, which is input from the signal light input fiber 169 through the isolator 163, is passed through the amplification fiber 164, but at that time, it is combined with the above-described pump light and Raman-amplified. .

The signal light (amplified signal light) that has been Raman-amplified in the amplification fiber 164 is the WDM coupler 165.
And is input to the monitor light distribution coupler 167 via the isolator 166. Monitor light distribution coupler 167
Outputs a part of the amplified signal light to the control circuit 168 and uses the remaining amplified signal light as the output light.
Output to.

The control circuit 168 controls each of the semiconductor laser elements 180a to 180d based on the input amplified signal light.
The light emission state of, for example, the light intensity is controlled, and feedback control is performed so that the gain band of Raman amplification has a flat characteristic.

As described above, in Raman amplification, since the signal light is amplified in the state where the polarization directions of the amplified signal light and the pumping light match, the influence of the deviation of the polarization plane between the amplified signal light and the pumping light is affected. Therefore, the polarization of the pumping light is eliminated (depolarized: depolarized) by polarization combining by the polarization combining couplers 161a and 161b, and the degree of polarization (DOP: Degree Of Polarization) is reduced. It is being reduced.

[0011]

However, in the above-described semiconductor laser modules 182a to 182d, the laser light emitted from the semiconductor laser elements 180a to 180d is the fiber gratings 180a to 18d.
The semiconductor laser device 18 uses the reflected light from 0d as the return light.
0a to 180d, the relative intensity noise (RIN: Re
lative intensity noise).

In particular, in Raman amplification, the process of amplification occurs early, so if the pumping light intensity fluctuates, the Raman gain also fluctuates, and this fluctuation in Raman gain is directly reflected as fluctuation in the amplified signal intensity. There was a problem that it was output and stable Raman amplification could not be performed.

By the way, FIG. 26 shows a Raman amplifier.
In addition to the backward pumping method in which the signal light is pumped from the rear like the Raman amplifier shown in FIG. 2, there are a forward pumping method in which the signal light is pumped in from the front and a bidirectional pumping method in which the signal light is bidirectionally pumped. At present, the backward pumping method is widely used as the Raman amplifier. The reason is that in the forward pumping method in which weak signal light travels in the same direction as strong pumping light, fluctuations in pumping light intensity are easily transferred to signal light, and nonlinear effects such as four-wave mixing easily occur. This is because there is a problem that the polarization dependence of light is likely to appear. Therefore, the pumping light source 190 (semiconductor laser modules 182a to 182) used in the forward pumping method is used.
d, a configuration including the polarization combining couplers 161a and 161b and the WDM coupler 162) cannot increase the pumping light intensity, and is smaller than the pumping light intensity of the pumping light source used in the backward pumping method. It was necessary to operate with strength. However, if the driving current of the semiconductor laser devices 180a to 180d becomes too small in order to reduce the excitation light intensity, the influence of relaxation oscillation appears on the low frequency side of RIN, which causes a problem of increasing RIN. Therefore, the emergence of a stable pumping light source applicable to the forward pumping method is desired.

On the other hand, as the output power of the semiconductor laser module constituting the pumping light source 190 is increased, new problems are occurring. The excitation light emitted from the excitation light source 190 enters the optical fiber for transmission amplification through the optical fiber, but when light having an intensity higher than a certain threshold enters the optical fiber, stimulated Brillouin scattering occurs. Stimulated Brillouin scattering is a nonlinear optical phenomenon in which incident light interacts with an acoustic wave (phonon) to cause scattering (reflection). By losing the equivalent of phonon energy,
It is observed as a phenomenon in which light of about 11 GHz lower frequency is reflected in the direction opposite to the incident light.

In the optical fiber amplifier using the optical fiber amplification using Raman amplification, when the stimulated Brillouin scattering of the excitation light occurs as described above, a part of the incident excitation light is reflected backward. Therefore, it does not contribute to Raman gain generation. In addition, this scattered light may generate unintended noise. This decrease in pumping light intensity does not pose a problem when the pumping light transmission distance is short. However, in the above-described optical fiber amplifier using the remote pump, since it is necessary to transmit the pumping light over a long distance before reaching the amplification optical fiber from the pumping light source, the decrease in the light intensity cannot be ignored. In the case of an optical fiber amplifier using a remote pump, the intensity of the pumping light is reduced at a rate higher than the optical loss in a normal optical fiber, so that the amplification gain is reduced in the amplification optical fiber. Occurs.

In order to solve the above-mentioned problems of the prior art, the present invention reduces the RIN and suppresses the occurrence of stimulated Brillouin scattering, and a high output semiconductor laser module and an optical fiber amplifier using the same. The purpose is to provide.

[0017]

In order to achieve the above object, a semiconductor laser module according to a first aspect of the present invention is a semiconductor laser device that emits laser light having one or more oscillation longitudinal modes, and the semiconductor laser device. Provided outside,
The reflector is provided between the semiconductor laser element and the reflector, which reflects a part of the light in the reflection wavelength band including the oscillation wavelength band of the laser light emitted by the semiconductor laser element and emits the laser light. And a return light controller that transmits the laser light emitted from the semiconductor laser device and controls the amount of reflected return light from the reflection end of the reflector to a predetermined value.

According to the invention of claim 1, the reflector is
A semiconductor laser device is provided outside the semiconductor laser device, reflects a part of light in a reflection wavelength band including an oscillation wavelength band of laser light emitted by the semiconductor laser device, and emits the laser light, and a return light controller is configured to operate the semiconductor laser device. It is provided between the element and the reflector, transmits the laser beam emitted from the semiconductor laser element, and controls the light amount of the reflected return light from the reflection end of the reflector to a predetermined value, and returns the reflected light. The coherent destruction by light is caused to broaden the spectral line width of each oscillation longitudinal mode emitted from the semiconductor laser device to relatively increase the threshold value of stimulated Brillouin scattering, and the reflected return light has an appropriate amount of light. Will be reduced.

In the semiconductor laser module according to a second aspect of the present invention, in the above invention, the return light controller attenuates the light quantity of the reflected return light with respect to the light quantity incident from the semiconductor laser element to −10 to −40 dB. It is characterized by performing setting control.

According to the invention of claim 2, the return light controller sets the light quantity of the reflected return light to -10 to -40d with respect to the light quantity entered from the semiconductor laser device.
The setting control for attenuating to B is performed, and the reflected return light is specifically set to suppress stimulated Brillouin scattering and reduce RIN.

According to a third aspect of the present invention, in the above-mentioned invention, the return light controller includes a Faraday rotator, a polarizing plate provided on the Faraday rotator on the side of the semiconductor laser element, and A magnetic applying unit that is provided around the Faraday rotator and changes the rotation angle of the Faraday rotator by applying a magnetic force to the Faraday rotator; and the magnetic applying unit changes the magnetic force to change the Faraday rotator. Adjusting means for adjusting the angle, and adjusting the light amount of the reflected return light by adjusting the adjusting means.

According to a fourth aspect of the present invention, in the above-mentioned invention, the semiconductor laser module further comprises temperature adjusting means for adjusting the temperature of the Faraday rotator, and the Faraday rotation angle is changed by the temperature adjusting means. It is characterized in that the amount of reflected return light is adjusted.

According to a fifth aspect of the present invention, in the semiconductor laser module according to the above-mentioned invention, the return light controller causes the partial reflection index change of the optical fiber to occur by applying stress to the optical fiber, and the reflected return light is incident. Is a polarization plane controller for adjusting the polarization plane, and the light quantity of the reflected return light is adjusted by the polarization plane adjustment by the polarization plane controller.

According to a sixth aspect of the semiconductor laser module in the above invention, the return light controller is an optical isolator, and the optical isolator is
It is characterized in that the transmission center wavelength of the optical isolator is shifted with respect to the oscillation wavelength of the semiconductor laser device to adjust the light quantity of the reflected return light.

A semiconductor laser module according to a seventh aspect of the invention is provided with a semiconductor laser element that emits laser light having one or more oscillation longitudinal modes, and is provided outside the semiconductor laser element, and the semiconductor laser element emits the laser light. A reflector for reflecting a part of light in a reflection wavelength band including an oscillation wavelength band of laser light and emitting the laser light, wherein the reflectance of the reflector is relative to the amount of light incident from the semiconductor laser device. The amount of reflected return light from the reflector is -10 to -40d.
It is characterized in that the reflectance is in the range of being attenuated to B.

According to the invention of claim 7, the reflector comprises:
Provided outside the semiconductor laser device, the semiconductor laser device emits the laser light by reflecting a part of the light in the reflection wavelength band including the oscillation wavelength band of the laser light emitted from the semiconductor laser device, and the reflectance of the reflector is , The light quantity of the reflected return light from the reflector with respect to the light quantity incident from the semiconductor laser device is -10 to
The reflectance is set to a range that attenuates to -40 dB, and the stimulated Brillouin scattering is suppressed and RIN is reduced with a simple configuration.

A semiconductor laser module according to an eighth aspect of the present invention is provided with a semiconductor laser element that emits laser light having one or more oscillation longitudinal modes, and is provided outside the semiconductor laser element, and the semiconductor laser element emits the laser light. A plurality of reflectors for emitting a part of light in a reflection wavelength band including the oscillation wavelength band of the laser light and emitting the laser light, and the reflectance of each reflector is emitted from the semiconductor laser device. The total amount of reflected return light from each reflector with respect to the amount of light is -10 to -4.
The reflectance of each reflector is set so as to be 0 dB.

According to the eighth aspect of the present invention, the plurality of reflectors are provided outside the semiconductor laser device, and one of the light beams in the reflection wavelength band including the oscillation wavelength band of the laser light emitted from the semiconductor laser device. The laser light is emitted by reflecting the light from the reflector, and the reflectance of each reflector is such that the total amount of reflected return light from each reflector with respect to the amount of light emitted from the semiconductor laser device is −1.
The reflectance of each reflector is set so as to be 0 to -40 dB, and stimulated Brillouin scattering is suppressed, and in particular RIN can be reduced.

According to a ninth aspect of the semiconductor laser module of the above invention, the reflectance of each reflector is:
It is characterized by being almost the same.

A semiconductor laser module according to a tenth aspect of the present invention is characterized in that, in the above invention, the reflector is a fiber black grating.

According to the eleventh aspect of the present invention, in the semiconductor laser module according to the above invention, the reflector has a reflecting film for reflecting a part of the light in the reflection wavelength band, and bidirectionally collimates the light. It is a facing collimator.

According to a twelfth aspect of the present invention, in the semiconductor laser module according to the above invention, the semiconductor laser element is provided with a diffraction grating for selecting an oscillation wavelength in at least a part of the inside of the semiconductor laser element. And

A semiconductor laser module according to a thirteenth aspect of the present invention is provided with a semiconductor laser element that emits laser light having one or more oscillation longitudinal modes, and is provided outside the semiconductor laser element, and is emitted by the semiconductor laser element. The amount of return light in the reflection wavelength band including the oscillation wavelength band of the laser light is -1
It has a reflection film set to 0 to -40 dB, and is provided with an input terminal for guiding the laser light emitted from the semiconductor laser element to an external optical fiber.

According to the thirteenth aspect of the present invention, it is possible to suppress the stimulated Brillouin scattering and output the laser beam with reduced RIN, with a simple structure in which only the reflection film is formed on the input end face of the input terminal. You can

A semiconductor laser module according to a fourteenth aspect of the present invention is characterized in that, in the above-mentioned invention, the semiconductor laser element is coupled by a lensed fiber.

An optical fiber amplifier according to a fifteenth aspect of the present invention is a semiconductor laser module according to any one of the first to fourteenth aspects, an amplification optical fiber, and pumping light output from the semiconductor laser module. And a coupler for multiplexing the signal light propagating in the amplification optical fiber.

According to the invention of claim 15, claim 1
14 is used as a pumping light source for an optical fiber amplifier, stimulated Brillouin scattering is suppressed, and RIN is reduced, so that a high amplification gain can be obtained. it can.

According to a sixteenth aspect of the present invention, in the above invention, the amplification optical fiber is
It is characterized in that the signal light is amplified by Raman amplification.

According to a seventeenth aspect of the present invention, in the above invention, the amplification optical fiber is
It is an erbium-doped fiber, and the semiconductor laser module and the amplification optical fiber are arranged remotely.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a semiconductor laser module according to the present invention and an optical fiber amplifier using the same will be described below with reference to the drawings.

(Embodiment 1) First, Embodiment 1 of the present invention will be described. 1 is a diagram showing a configuration of a semiconductor laser module according to a first embodiment of the present invention. In FIG. 1, this semiconductor laser module is
Diffraction grating 13 provided in a partial region along the active layer 11
Semiconductor laser device 1 having the following (Japanese Patent Application No. 2000-3231)
18), and the laser light output from the semiconductor laser device 1 is connected to the optical fiber 3 via the reflection amount adjuster 2. The semiconductor laser device 1 outputs laser light of a plurality of oscillation longitudinal modes selected by the diffraction grating 13.

The optical fiber 3 reflects a part of the light incident from the input terminal 12 provided on the semiconductor laser device 1 side to the semiconductor laser device 1 side as reflected return light, and outputs the remaining light to the output terminal. It has a reflector 4 which outputs via 14. The optical fiber 3 is a polarization maintaining fiber. The reflector 4 is realized by a fiber Bragg grating (FBG). The FBG is a filter that reflects only light of a specific wavelength by periodically changing the refractive index of the core portion of the optical fiber along the traveling direction. However, as shown in FIG. 2, the wavelength selectivity L4 of this FBG includes a wavelength band selected by the diffraction grating 13 and has a wavelength selectivity L13 of a wider band than the wavelength selectivity L4. The input terminal 12 is optically coupled by a lensed fiber,
The optical coupling portion is not limited to a spherical optical fiber having a spherical shape, and a wedge type optical fiber having a wedge coupling type optical fiber may be used, or an optical fiber whose incident surface is obliquely polished may be used. The reflectance of the reflector 4 which is a fiber Bragg grating is about 1%.

The reflection amount adjuster 2 transmits the light emitted from the semiconductor laser device 1 and outputs it to the optical fiber 3 side.
The amount of reflected return light reflected from the optical fiber 3 is −10 dB with respect to the amount of incident light from the semiconductor laser device 1.
Adjustment is performed to attenuate to a predetermined value that provides a reflection amount of -40 dB. In other words, the reflection in the optical isolator is positively used to adjust. The reflection amount (dB) is as follows: reflection amount (dB) = ₁₀ log ₁₀ (light intensity of reflected return light (m
W) / light intensity of incident light (mW)).

FIG. 3 is a diagram showing a detailed configuration of the reflection amount adjuster 2 shown in FIG. In FIG. 3, the reflection amount adjuster 2 is a reflection amount adjuster using a Faraday rotator. In a normal optical isolator, the Faraday rotator 24
Polarizing plates are provided at both ends of the, the incident light is rotated by 45 °, the reflected light is further rotated by 45 °, and consequently the reflected light is rotated by 90 °, and the polarization plane of the reflected light is orthogonal to the polarization plane of the incident light. The reflected light does not return to the incident side. On the other hand, in the reflection amount adjuster 2 shown in FIG. 3, the polarizing plate on the side on which the reflected light is incident is removed.

The reflection amount adjuster 2 includes a Faraday rotator 24.
A polarizing plate 23 is provided on the incident side of, and laser light having a polarization plane matching the incident light L11 is incident on the Faraday rotator 24. A magnetic field is applied to the Faraday rotator 24 by a coil 25 wound around the Faraday rotator 24, and the Faraday rotation angle is set to an arbitrary angle θ instead of 45 °. The outgoing light L12 whose polarization plane is rotated by the angle θ is input to the Faraday rotator 24 by using the reflected return light from the reflector 4 as the reflected light L13, and is further rotated by the angle θ. As a result, as shown in FIG. 4, the reflected light L13 emitted from the Faraday rotator 24 is incident on the polarizing plate 23 as the reflected light 13a with its polarization plane rotated by an angle 2θ. The polarizing plate 23 can transmit the same polarization plane component as the incident light L11 and attenuate the reflected light L13 to a predetermined value. That is, the amount of reflection is -10 to -40 dB by adjusting the magnetic field applied to the Faraday rotator 24 and setting the Faraday rotation angle.
Can be attenuated to a predetermined value.

Here, the laser light having a plurality of oscillation longitudinal modes output from the semiconductor laser device 1 passes through the reflection amount adjuster 2 and enters the optical fiber 3. About 1% of the laser light that has entered the optical fiber 3 is reflected by the reflector 4, and the remaining laser light is emitted through the output terminal 14. The reflected laser beam is input to the reflection amount adjuster 2, the reflection amount is attenuated to a predetermined value within the range of −10 to −40 dB, and the laser beam enters the semiconductor laser device 1.

In this case, in the semiconductor laser device 1, if there is reflected return light from the outside, that is, the reflection amount adjuster 2 side,
The phase alignment between the phase of each oscillation longitudinal mode generated in the semiconductor laser device 1 and the phase of the reflected return light becomes unstable, and a phenomenon called coherence destruction occurs in which the line width of each oscillation longitudinal mode widens (reference "Regimes of Feedback Effe
ct in 1.5-μm Distributed feedback Lasers ”RW
TKACH, ARCHRAPPLYVY (JOURNAL OF LIGHTWAVE TECHNO
LOGY, VOL.LT-4 No.11 NOVEMBER 1986 pp1655-1661))).

On the other hand, the semiconductor laser device 1 shown in FIG.
Since a plurality of oscillation longitudinal modes are formed, it is possible to suppress the peak value of the laser output and obtain a high laser output value as compared with the case of using the laser light of the single longitudinal mode. For example, the semiconductor laser device 1 shown in FIG.
With the profile shown in (b), a high laser output can be obtained with a low peak value. On the other hand, FIG.
Is 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 1 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 will occur. Occurs, which causes a problem that noise increases. The occurrence of stimulated Brillouin scattering has a threshold value Pth at which stimulated Brillouin scattering occurs, and when the same laser output power is obtained, as shown in FIG.
As shown in (b), by providing a plurality of oscillation longitudinal modes and suppressing their peak values, it is possible to obtain high pumping light output power within the threshold Pth of stimulated Brillouin scattering, and as a result, high Raman Gain can be obtained.

Therefore, in the case of having a plurality of oscillation longitudinal modes, the above-mentioned coherent destruction results in FIG.
As shown in (3), the spectral line width of each oscillation longitudinal mode broadens, the peak value is further suppressed, the threshold value Pth of stimulated Brillouin scattering is further increased relatively, and the occurrence of stimulated Brillouin scattering can be surely suppressed.

Here, the reflection amount adjuster 2 sets the reflection amount of the reflected light with respect to the incident light to -10 to -40 dB.
Coherent destruction occurs in this range, and if the value of the reflection amount is increased within this range, the spectral line width of each oscillation mode widens and the peak value decreases, and it is possible to reliably suppress the occurrence of stimulated Brillouin scattering. This is because, when the value of the reflection amount is increased, RIN is deteriorated.

Therefore, by setting the reflection amount by the reflection amount adjuster 2 to -10 to -40 dB, it is possible to both suppress the occurrence of stimulated Brillouin scattering and reduce RIN.

Here, the semiconductor laser device 1 shown in FIG.
The specific configuration of will be described. FIG. 6 is a longitudinal sectional view in the longitudinal direction of the semiconductor laser device 1 shown in FIG. In addition, FIG. 7 shows AA of the semiconductor laser device 1 shown in FIG.
It is a line sectional view. 6 and 7, the semiconductor laser device 1 includes an n-InP clad layer 32 that serves as a buffer layer and a lower clad layer made of n-InP on the (100) plane of the n-InP substrate 41 in order. GRIN-SCH-MQW (Graded Index-Separate) with compression distortion
Confinement Heterostructure Multi Quantum Well) active layer 11, p-InP spacer layer 34, p-In
It has a structure in which a P clad layer 36 and an InGaAsP contact layer 37 are laminated.

Within the p-InP spacer layer 34, a film thickness of 2
Having a length of 0 nm, a length Lg of 50 μm from the low reflection film 45 on the emission side toward the high reflection film 44 on the reflection side, and a coupling coefficient κ =
A diffraction grating 13 of 25 cm −1 (κL = 0.125) is provided. The diffraction grating 13 is periodically formed with a pitch of about 220 nm and selects a laser beam having a center wavelength of 1.48 μm. The p-InP spacer layer 34 including the diffraction grating 13, the active layer 11 having the GRIN-SCH-MQW structure having a compressive strain, and the n-InP buffer layer 32 are processed into a mesa stripe shape, and the length of the mesa stripe is increased. On both sides in the direction, a p-InP blocking layer 39b and an n-InP blocking layer 39a formed as current blocking layers are buried. This current blocking layer not only realizes efficient current injection into the active layer 11 of the GRIN-SCH-MQW structure,
This structure is effective for realizing a stable horizontal single transverse mode.

On the upper surface of the InGaAsP contact layer 37, 60 μ from the low reflection film 45 toward the high reflection film 44.
The insulating film 38 is formed up to m. The insulating film 38 is made of SiN. The insulating film 38 is
It is preferable that it has good thermal conductivity, and in addition, AlN, A
It may be made of l ₂ O ₃ , MgO, TiO _2, or the like. Further, the insulating film 38 may have a stripe shape having a width exceeding the width of the mesa stripe structure because it is sufficient that current is not injected into the mesa stripe structure below the insulating film 38.

A p-side electrode 40 is formed on the upper surface of the insulating film 38 and on the upper surface of the p-InGaAsP contact layer 37 other than the area covered with the insulating film 38. In addition,
A bonding pad (not shown) is preferably formed on the p-side electrode 40. The thickness of this bonding pad is preferably about 5 μm. For example, when assembling a semiconductor laser device by the junction down method, this bonding pad functions as a cushioning material that softens the shock during assembly. Further, this thickness prevents the solder from sneaking around at the time of joining with the heat sink, and can prevent a short circuit due to the sneaking of the solder. On the other hand, the n-InP substrate 31
An n-side electrode 41 is formed on the back surface of the. Each semiconductor laser element having the p-side electrode 40 and the n-side electrode 41 formed on the semiconductor wafer is separated by cleavage.

After that, a high reflection film 44 having a high light reflectance of 80% or more, preferably 98% or more is formed on the light reflecting end surface, which is one end surface in the longitudinal direction of the semiconductor laser device 1, and the other end surface. A low reflection film 45 having a low light reflectance of 2% or less, preferably 0.1% or less is formed on the light emitting end face. GRIN-SCH-MQW of optical resonator formed by high reflection film 44 and low reflection film 45
The light generated in the active layer 11 of the structure is reflected by the high reflection film 44 and emitted as laser light through the low reflection film 45. At this time, the wavelength is selected by the diffraction grating 13 and emitted.

This semiconductor laser device 1 is premised on being used as a pumping light source for a Raman amplifier, and its oscillation wavelength λ ₀ is 1100 nm to 1550 nm and the cavity length L is 800 μm or more and 3200 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 ₀₂ / (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 50 shown in FIG.

This semiconductor laser device 1 includes a diffraction grating 13
Is included, and 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 50. Conventional DBR (Distributed Bragg
Reflector) Semiconductor laser device or DFB (Distrib)
In the uted feedback) semiconductor laser device, when the resonator length L is 800 μm or more, it is difficult to oscillate in a single longitudinal mode. Therefore, the semiconductor laser device having such resonator length L is not used. However, in this semiconductor laser device 1, the cavity length L is positively set to 800 μm or more, so that a plurality of oscillation longitudinal modes are included in the half-width Δλh of the oscillation wavelength spectrum to perform laser output. In FIG. 8, the half-width Δλ of the oscillation wavelength spectrum is
There are three oscillation longitudinal modes 51 to 53 in h. As a result, as described above, the semiconductor laser device 1 having a high output and capable of suppressing stimulated Brillouin scattering is realized.

The wavelength interval (mode interval) Δλ of the oscillation longitudinal modes 51 to 53 is set to 0.1 nm or more. This is because when the semiconductor laser device 1 is used as a pumping light source for a Raman amplifier, if the mode interval Δλ is 0.1 nm or less, stimulated Brillouin scattering is likely to occur. As a result, it is preferable that the above-described resonator length L is 3200 μm or less according to the above-described equation of the mode interval Δλ.

If the oscillation wavelength spectrum width is too wide, the multiplexing loss due to the wavelength combining coupler becomes large, and noise and gain fluctuations are 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 50 is 3 nm.
Hereafter, it is necessary to set it to preferably 2 nm or less.

By the way, above the diffraction grating 13,
Between the InGaAsP contact layer 37 and the p-side electrode 40, the length Li = from the low reflection film 45 to the high reflection film 44.
An insulating film 38 of 60 μm is formed. Therefore, p
The injection current applied from the side electrode 40 to the n-side electrode 41 flows in the current injection region E2 below the region not covered by the insulating film 38, and is the lower non-current injection region covered by the insulating film 38. The inflow to E1 is suppressed.

Since the active layer 11 in the current injection region E2 emits light by the injection current, the G active layer 11 in the non-current injection region E1 performs photon recycling by the light from the active layer 11 in the current injection region E2. Even if there is no injection current, it functions as a buffer amplifier that transmits the laser light to the low reflection film 45 side and outputs it, and does not attenuate the laser light.

In particular, in the active layer 11 in the non-current injection region E1, since the energy of light from the active layer 11 in the current injection region E2 is almost equal to the bandgap energy of the active layer 11, even if no current is injected, It absorbs the energy of the input light and functions as a supersaturated absorption region in which stimulated emission and spontaneous emission are repeated, and the photon lifetime is reduced. As a result, the spectral line width of each oscillation longitudinal mode widens, the peak value of each oscillation longitudinal mode is further reduced,
Generation of stimulated Brillouin scattering can be suppressed.

The semiconductor laser device 1 is composed of the diffraction grating 1
3 outputs a plurality of oscillation longitudinal modes due to the wavelength selectivity in which 3 has fluctuation with respect to the central wavelength.
However, it is possible to increase the number of oscillation longitudinal modes by positively causing fluctuations.

FIG. 9 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. In FIG. 9, this diffraction grating 13
Of the oscillation wavelength spectrum is widened to increase the number of oscillation longitudinal modes within the full width at half maximum Δλh.

As shown in FIG. 9, the diffraction grating 13 has a structure in which the average period is 220 nm and the period fluctuation (deviation) of ± 0.02 nm is repeated in the period C. This ±
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 Δλh of the oscillation wavelength spectrum.

For example, FIG. 10 shows that different periods Λ ₁ and Λ ₂
FIG. 3 is a diagram showing an oscillation wavelength spectrum of a semiconductor laser device having the diffraction grating of FIG. In FIG. 10, the diffraction grating with the period Λ ₁ forms an oscillation wavelength spectrum of wavelength λ ₁ and selects three oscillation longitudinal modes within this oscillation wavelength spectrum. On the other hand, the diffraction grating with the period Λ ₂ 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 55 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 55. 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. 11 (a), a periodic fluctuation may be provided as a diffraction grating in which the period Λ ₁ and the period Λ ₂ are alternately repeated once. Further, as shown in FIG. 11B, a periodic fluctuation may be provided as a diffraction grating in which the period Λ ₁ and the period Λ ₂ are alternately repeated a plurality of times. Further, as shown in FIG. 11C, a diffraction grating having a plurality of continuous cycles Λ ₁ and a plurality of continuous cycles Λ ₂ may have periodic fluctuations. Further, the periods having discretely different values between the periods Λ ₁ and Λ ₂ may be complementarily arranged.

By the way, the semiconductor laser device 1 used in the above-mentioned semiconductor laser module has a diffraction grating 13 therein, and a plurality of desired oscillation longitudinal modes are formed by the wavelength selectivity of the diffraction grating 13 and reflected. The fiber Bragg grating of the device 4 does not determine the oscillation wavelength of the semiconductor laser device 1 but merely has a function of reflecting about 1% of the input laser light. The wavelength selectivity of the longitudinal mode may be provided.

FIG. 12 is a diagram showing the structure of a modification of the semiconductor laser module according to the first embodiment of the present invention. In FIG. 12, the semiconductor laser device 1 shown in FIG.
Instead of the above, a Fabry-Perot type semiconductor laser element 61 having no built-in diffraction grating 13 is provided, and a reflector 64 is provided instead of the reflector 4 shown in FIG. The other configurations are the same as the configurations shown in FIG. 1, and the same components are designated by the same reference numerals.

The reflector 64, which is a fiber Bragg grating, has the same selection wavelength as the wavelength selectivity L13 shown in FIG. 2 and performs the same wavelength selection as the diffraction grating 13. Further, the reflector 64 has a reflectance of about 1%, like the reflector 4. That is, the reflector 64 also has the functions of the reflector 4 and the diffraction grating 13. Even with such a configuration, the reflection amount adjuster 2 adjusts the reflection amount to the semiconductor laser element 61 by -10 to-.
The amount of reflection is adjusted to 40 dB so that both suppression of stimulated Brillouin scattering and reduction of RIN are satisfied.

The reflection amount adjuster 2 shown in the first embodiment described above adjusts the reflection amount by changing the magnetism applied by the coil 25, but the Faraday rotation angle has a temperature dependency. Therefore, the reflection amount may be adjusted by further changing the temperature of the Faraday rotator 24.

(Second Embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment described above, part of the laser light emitted from the semiconductor laser device 1 was reflected to the semiconductor laser device 1 side using the fiber Bragg grating, but in the second embodiment,
A part of the laser light emitted from the semiconductor laser device 1 is reflected to the semiconductor laser device 1 side by using the facing collimator.

FIG. 13 is a diagram showing a structure of a semiconductor laser module according to a second embodiment of the present invention. FIG.
In this semiconductor laser module, the reflector 4
Instead, an opposed collimator 70 is provided so that a part of the laser light from the semiconductor laser element 1 input from the reflection amount adjuster 2 is reflected to the semiconductor laser element 1 side. This reflectance is the same as that of the reflector 4, and is about 1%. Other configurations are the same as those of the first embodiment, and the same components are designated by the same reference numerals.

The opposed collimator 70 guides the light input from the input terminal 12 through the optical fiber 73a and collimates it by the collimator lens 74a through the ferrule 71a. The collimated light is focused on one end of the ferrule 74b by the collimator lens 74b and guided to the output terminal 14 via the optical fiber 73b. Here, a reflection film 72 is provided at one end of the ferrule 71a, and this reflection film 72 reflects a part of the light reaching the ferrule 71a to the semiconductor laser element 1 side as reflected return light. Therefore, the reflectance of the reflector 72 is about 1%.
It is a degree. Note that this reflectance is the same as that of the reflector 4 in that it includes at least the wavelength selection band of the diffraction grating 13.

In the structure shown in FIG. 13, the reflection film 72 is provided at one end of the ferrule 71a to obtain about 1% of the reflected light. However, as shown in FIG. 14, the reflection film 72 is not provided, Alternatively, one end of the ferrule 71a may be a flat end surface, and about 4% of Fresnel reflected light generated when the ferrule 71a is emitted into the air from the optical fiber may be used. In this case, the reflection amount adjuster 2 adjusts the amount of Fresnel reflected light and returns it to the semiconductor laser device 1.

In the second embodiment, the facing collimator 7
0 is used to reflect a part of the laser light emitted from the semiconductor laser element 1, and the reflection amount adjuster 2 sets the reflection amount of the reflected laser light to −10 to −40 dB. As in the first embodiment, the stimulated Brillouin scattering can be suppressed and the RIN can be reduced.

(Third Embodiment) Next, a third embodiment of the present invention will be described. Embodiments 1 and 2 described above
In each case, the reflection amount adjuster 2 using the Faraday rotator 24 shown in FIG. 3 is used, but in the third embodiment, a polarization plane controller which is an in-line reflection amount adjuster is used. There is.

FIG. 15 is a diagram showing a structure of a semiconductor laser module according to a third embodiment of the present invention. Figure 15
In this semiconductor laser module, the polarization plane controller 82 is used as the reflection amount adjuster 2 shown in FIG. The optical fiber 3 adjusted by the polarization controller is a single mode fiber. A polarizing plate 81 is provided on the semiconductor laser device 1 side of the polarization controller 82 and between the semiconductor laser device 1 and the polarization controller 82.
The polarization direction of the polarizing plate 81 is set so that the laser light emitted from the semiconductor laser device 1 is 100% transmitted. Other configurations are the same as those of the first embodiment, and the same components are designated by the same reference numerals.

As the polarization controller 82, for example, "Pola RITE" (R) from General Photonics can be used. The polarization plane controller 82 sandwiches the optical fiber 3 and has a rotatable pressing body 8 at the center thereof.
3 is sandwiched between the upper body 83a and the lower body 83b,
By rotating the pressing knob 84 provided on the upper body 83a side around the axis of the pressing knob 84, the pressing knob 84 is pressed by the arrow 1A, and stress is applied to the optical fiber 3. The polarization separation degree is set by this stress distribution, and the angle ε shown in FIG. 16 is determined. Further, the pressing knob 84 is moved around the optical axis, that is, the arrow 8
By rotating in four directions, the polarization plane angle θ shown in FIG. 16 is set. By the combination setting of the angle ε and the polarization plane angle θ as described above, the intensity of light reflected back to the polarization plane with respect to the transmission polarization plane of the polarizing plate 81 is determined. That is, the reflection amount of the reflected return light can be changed by pressing and rotating the optical fiber 3, and the reflection amount can be changed from −10 to −4.
It can be set to a predetermined value within 0 dB. As a result,
Similar to the first and second embodiments, stimulated Brillouin scattering can be suppressed and RIN can be reduced.

Although the polarizing plate 81 is provided in the third embodiment described above, the polarizing plate 81 may not be provided. This is because the semiconductor laser element 1 does not affect oscillation even if laser light having a polarization plane different from the polarization plane of the laser light emitted from the semiconductor laser element 1 is incident as reflected light. Of course, it is preferable to provide the polarizing plate 81 because the reflected light having the same plane of polarization as the emitted laser light can be adjusted.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. Embodiments 1 to 3 described above
In each case, the final attenuation amount is adjusted using the reflection amount adjuster 2. However, in the fourth embodiment, the reflector 4 itself has a reflection amount of −10 to −40 dB. There is.

FIG. 17 is a diagram showing the structure of a semiconductor laser module according to the fourth embodiment of the present invention. FIG. 17
In this semiconductor laser module, a reflector 4a is provided instead of the reflector 4 shown in FIG. 1, and the reflection amount adjuster 2 is removed. Other configurations are the same as those of the first embodiment, and the same components are designated by the same reference numerals.

The reflector 4a reflects a part of the laser light input from the semiconductor laser element 1 and outputs the remaining laser light to the output terminal 14, but the reflected return light corresponding to the light intensity of the input laser light. Is set to a desired value within the range of -10 to -40 dB. In the fourth embodiment, the reflection amount adjuster 2 is not required, and the stimulated Brillouin scattering can be suppressed and the RIN
Can be reduced.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. Embodiments 1 to 4 described above
In the above, the light emitted from the semiconductor laser device 1 is reflected at one reflection point, for example, the position of the reflector 4. However, in the fifth embodiment, a plurality of reflection points are provided and the RIN is changed in frequency. I try to disperse.

FIG. 18 is a diagram showing a structure of a semiconductor laser module according to a fifth embodiment of the present invention. FIG.
In this semiconductor laser module, a plurality of reflectors 94-1 to 94-n respectively corresponding to the reflector 4 are dispersedly arranged on the optical fiber 93 corresponding to the optical fiber 3. Other configurations are the same as those of the first embodiment, and the same components are designated by the same reference numerals. However, when returning the same amount of reflection to the semiconductor laser device 1, each reflector 94-1
The amount of reflection of each of the reflectors 94-1 to 94-n is set smaller than the amount of reflection of the reflector 4, and the total amount of attenuation of each of the reflectors 94-1 to 94-n corresponds to the amount of reflection.

For example, when it is desired to set the reflection amount to -40 dB, ten reflectors 94-1 to 94-10, which are fiber Bragg gratings having the same reflectance, are dispersed and arranged on the optical fiber 93. In this case, each reflector 94
-1 to 94-10 may be set to a reflectance of 0.01%. A reflectance of 0.01% has a reflection amount of -50 dB, which is 1
When the reflection amounts of the 0 reflectors 94-1 to 94-10 are added, the total reflection amount becomes -40 dB. Also, here, 100 reflectors 94-1 having the same reflectance of 0.01% are used.
When 94 to 100 are dispersedly arranged on the optical fiber 93,
The total reflection amount is set to -30 dB. Furthermore, ten reflectors 94-1 to 94-10 having a reflectance of 0.1%
Are dispersedly arranged on the optical fiber 93, the total reflection amount is -3.
It is set to 0 dB.

In this case, even if the reflectances are all the same, since the light excluding the reflected light is incident on the reflector in the next stage, the reflected return light of each reflector is different, Since the reflectance is small, it can be set that the transmitted light is almost the same. Moreover, manufacturing reflectors that all have the same reflectivity is easier than manufacturing different reflectors. Of course, it is preferable to set the reflectance strictly, but in this case, the semiconductor laser device 1
The reflectance is sequentially increased as the distance from the reflector increases, and the reflection amount of each reflector is set to be the same.

Here, the resonance frequency of RIN differs between each of the reflectors 94-1 to 94-n and the semiconductor laser device 1, and the entire RIN is dispersed in frequency. FIG. 19 is a diagram schematically showing the frequency dispersion of RIN. As shown in FIG. 19, the RIN spectrum S1 when one reflector is provided is dispersed into the RIN spectrum S2 when a plurality of reflectors are provided, and the intensity of each spectrum S2 is dispersed and reduced. . In this case, the larger the number of reflectors 94-1 to 94-n, that is, the larger the number of divisions, the smaller the peak value of RIN. As a result, RIN can be further reduced. This is
The amount of reflected return light can be increased, the degree of coherence destruction can be further increased, and the threshold value for stimulated Brillouin scattering can be further increased.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, an existing optical isolator is positively used as a reflection adjuster.

FIG. 20 is a diagram showing a structure of a semiconductor laser module according to a sixth embodiment of the present invention. Figure 20
In this semiconductor laser module, the optical isolator 102 is used as the reflection amount adjuster 2 shown in FIG. Other configurations are the same as those of the first embodiment, and the same components are designated by the same reference numerals.

When the optical isolator 102 is an ideal optical isolator, the amount of reflection is zero, but it is ideal by shifting the oscillation wavelength of the semiconductor laser device 1 and the center wavelength of the transmittance of the optical isolator 102. The characteristics of the various isolators deteriorate and reflection occurs. The optical isolator 102 positively utilizes the deterioration characteristic due to the wavelength shift and tries to set the reflection amount to a predetermined value within the range of -10 to -40 dB. Also by this, the stimulated Brillouin scattering can be suppressed and the RIN can be reduced.

In the first to sixth embodiments described above, the semiconductor laser device 1 has a plurality of oscillation longitudinal modes, that is, so-called multimode oscillation. However, the present invention is not limited to this. It can also be applied to a semiconductor laser module having an element. Also in this case, stimulated Brillouin scattering can be suppressed and RIN can be reduced.

(Seventh Embodiment) Next, a seventh embodiment of the present invention will be described. Embodiments 1 to 6 described above
In the above, the reflectors 4, 4a, 94-1 to 94-n, 64 are used to reflect a part of the laser light emitted from the semiconductor laser element 1. However, in the seventh embodiment, the laser light is emitted. The laser light thus generated is reflected by the incident end face of the ferrule that is incident on the optical fiber.

FIG. 21 is a diagram showing a structure of a semiconductor laser module according to a seventh embodiment of the present invention. Figure 21
In this semiconductor laser module, the ferrule 1 that guides the laser light emitted from the semiconductor laser device 1 to the optical fiber 13 without providing the reflector 4 as shown in FIG.
The low reflection film 112a is provided on the end face of the low reflection film 1.
It is set so that about 12% of the reflected light is returned by 12a. The reflection amount adjuster 2 has the above-described first to sixth embodiments.
Is provided between the semiconductor laser device 1 and the ferrule 112, and the return light to the semiconductor laser device 1 is −10 to −10.
Adjust to -40 dB.

As shown in FIG. 22, the reflection amount adjuster 2 is not provided, and the reflection amount of the low reflection film 122a provided on the incident end surface of the ferrule 122 is set to be -10 to -40 dB. Good. As a result, it is possible to make the configuration fixed, but simpler. In particular, it becomes possible to arrange the semiconductor laser device 1 in the housing.

In the seventh embodiment, since the low reflection films 112a and 122a are provided on the incident end face of the ferrule to set the reflection amount, the stimulated Brillouin scattering can be suppressed and the RIN can be reduced as in the first embodiment. It can be reduced.

(Embodiment 8) Next, an embodiment 8 of the invention will be described. In the eighth embodiment, the semiconductor laser module shown in the first to seventh embodiments is used as a pumping light source for a Raman amplifier.

FIG. 23 is a block diagram showing the structure of a Raman amplifier adopting the forward pumping method. In FIG.
In this Raman amplifier, the WDM coupler 165 ′ provided near the isolator 163 has semiconductor laser modules 100 a ′ to 100 d ′ corresponding to the semiconductor laser modules shown in the first to sixth embodiments, and the polarization combining coupler 1.
61a ′, 161b ′ and WDM coupler 162 ′ are sequentially connected, and the pumping light output from the WDM coupler 162 ′ is output in the same direction as the signal light to perform forward pumping. In this case, the semiconductor laser modules 100a'-100
d ′ is the optical output that does not suppress the occurrence of stimulated Brillouin scattering because the semiconductor laser module described in the first to sixth embodiments is used, and since RIN is small, forward pumping is effectively performed. be able to.

FIG. 24 is a block diagram showing the structure of a Raman amplifier adopting the bidirectional pumping method. In addition,
The same components as those shown in FIG. 23 are designated by the same reference numerals. In FIG. 24, this Raman amplifier is shown in FIG.
In the configuration of the Raman amplifier shown in FIG.
Semiconductor laser modules 100a to 100d corresponding to the semiconductor laser modules shown in the first to sixth embodiments or the conventional semiconductor laser module and polarization combining couplers 161a and 161b are further provided to perform backward pumping and forward pumping.

Each semiconductor laser module 100a, 10
0b outputs the laser light to the polarization beam combiner 161a,
Each of the semiconductor laser modules 100c and 100d outputs laser light to the polarization beam combiner 161b. Here, the laser lights oscillated by the semiconductor laser modules 100a and 100b have the same wavelength, and the laser lights oscillated by the semiconductor laser modules 100c and 100d have the same wavelength, but the semiconductor laser modules 100a and 100b.
Is different from the wavelength of the laser light that oscillates. This is because the Raman amplification has polarization dependence, and the polarization combining couplers 161a and 161b output laser light whose polarization dependence has been eliminated.

The laser lights having different wavelengths output from the respective polarization combining couplers 161a and 161b are combined by the WDM coupler 162, and the combined laser light is W
The Raman amplification pumping light is output to the amplification fiber 164 via the DM coupler 165. The signal light to be amplified is input to the amplification fiber 164 to which the pumping light is input, and Raman amplification is performed.

Also in the case of this bidirectional pumping method, since the semiconductor laser modules 100a 'to 100d' for forward pumping use the semiconductor laser modules shown in the above-described first to sixth embodiments, the induction Brillouin is used. Since the scattering can be suppressed and the RIN is small, forward excitation can be effectively performed.

In the eighth embodiment, the first to seventh embodiments will be described.
By constructing an excitation light source using the semiconductor laser module shown in FIG. 1, stimulated Brillouin scattering can be suppressed and R
Raman amplification including forward pumping with a small IN can be effectively realized.

The Raman amplifier shown in FIG. 23 or 24 can be applied to the WDM communication system as described above. FIG. 25 is a block diagram showing a schematic configuration of a WDM communication system to which the Raman amplifier shown in FIG. 23 or 24 is applied.

In FIG. 25, 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 280 and integrated in one optical fiber 285. On the transmission path of the optical fiber 285, as shown in FIG.
3 or a plurality of Raman amplifiers 281 and 283 corresponding to the Raman amplifier shown in FIG. 24 are arranged according to the distance and amplify the attenuated optical signal. This optical fiber 285
The signal transmitted above is demultiplexed by the optical demultiplexer 284 into optical signals of a plurality of wavelengths λ _{1 to} λ _n , and a plurality of receivers Rx1.
~ Received by Rxn. In addition, an optical signal having an arbitrary wavelength is added to and taken out from the optical fiber 285.
A DM (Add / Drop Multiplexer) may be inserted.

In the eighth embodiment described above, the case where the semiconductor laser module shown in the first to seventh embodiments is used as the pumping light source for Raman amplification is shown, but the present invention is not limited to this, and, for example, 0. It can be used as a light source for EDFA excitation such as 98 μm. Particularly, in the remote pump EDFA in which the transmission distance of the pumping light to the EDF is from several km to several tens of km, by using the semiconductor laser module described in the first to sixth embodiments, the stimulated Brillouin scattering during the transmission can be achieved. It is possible to effectively suppress a decrease in amplification gain due to RIN and RIN.

[0111]

As described above, the features of claims 1 to 6 and 1
According to the inventions of 0 to 12 and 14 to 17, the reflector realized by using the fiber Bragg grating, the facing collimator, or the like is provided outside the semiconductor laser element, and the oscillation wavelength of the laser light emitted by the semiconductor laser element is provided. A return light controller that reflects a part of light in a reflection wavelength band including a band and emits the laser light, and is realized by a Faraday rotator, an opposing collimator, an optical isolator, or the like is the semiconductor laser device and the reflector. The laser light emitted from the semiconductor laser device is transmitted between the two, and the light amount of the reflected return light from the reflection end of the reflector is set and controlled to a predetermined value, causing coherent destruction by the reflected return light. Then, the spectrum line width of each oscillation longitudinal mode emitted by the semiconductor laser device is widened to make the threshold value of the stimulated Brillouin scattering relatively. Enhances, the reflected return light is an appropriate amount, RIN is reduced, an effect that it is possible to increase the amplification efficiency of the optical fiber amplifier.

According to the invention of claim 7, the reflector is provided outside the semiconductor laser device, and a part of the light in the reflection wavelength band including the oscillation wavelength band of the laser light emitted from the semiconductor laser device is provided. And emits the laser beam, and the reflectance of the reflector is set to −1 with respect to the amount of light reflected from the reflector with respect to the amount of light incident from the semiconductor laser device.
The reflectance is set to the range of 0 to -40 dB to be attenuated, the stimulated Brillouin scattering is suppressed with a simple structure, and the RIN
And an optical fiber amplifier with high amplification efficiency can be realized.

According to the inventions of claims 8 and 9,
A plurality of reflectors are provided outside the semiconductor laser device,
The semiconductor laser device emits the laser light by reflecting a part of the light in the reflection wavelength band including the oscillation wavelength band of the laser light emitted from the semiconductor laser device, and the reflectance of each reflector is emitted from the semiconductor laser device. The reflectance of each reflector is set so that the total light quantity of the reflected return light from each reflector with respect to the light quantity is -10 to -40 dB, and stimulated Brillouin scattering is suppressed, and in particular RI
The effect that N can be reduced further is exhibited.

According to the thirteenth aspect of the invention, since the return light of -10 to -40 dB is obtained by the reflection film of the input terminal without providing the return light controller, the guiding structure is simple. Suppresses Brillouin scattering, RI
The effect of being able to reduce N is produced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a semiconductor laser module according to a first embodiment of the present invention.

FIG. 2 is a diagram showing wavelength selection characteristics of the diffraction grating and the reflector shown in FIG.

FIG. 3 is a diagram showing a detailed configuration of a reflection amount adjuster shown in FIG.

FIG. 4 is a diagram illustrating polarization planes of incident light and reflected return light that enter a polarizing plate.

FIG. 5 is a diagram illustrating that the threshold value of stimulated Brillouin scattering is relatively increased due to an increase in the number of oscillation longitudinal modes and coherent collapse.

6 is a vertical cross-sectional view showing a detailed configuration of the semiconductor laser device shown in FIG.

7 is a cross-sectional view taken along the line AA of the semiconductor laser device shown in FIG.

8 is a spectrum diagram showing a plurality of oscillation longitudinal modes output by the semiconductor laser device shown in FIG.

FIG. 9 is a diagram showing a periodic change of a diffraction grating.

FIG. 10 is a diagram showing a composite oscillation wavelength spectrum.

FIG. 11 is a diagram showing a modification of the diffraction grating for selecting a plurality of oscillation longitudinal modes.

FIG. 12 is a diagram showing a modification of the semiconductor laser module according to the first embodiment of the present invention.

FIG. 13 is a diagram showing a structure of a semiconductor laser module according to a second embodiment of the present invention.

FIG. 14 is a diagram showing a configuration of a modified example of the semiconductor laser module according to the second embodiment of the present invention.

FIG. 15 is a diagram showing a configuration of a semiconductor laser module which is Embodiment 3 of the present invention.

16 is a diagram showing the relationship between the polarization and the polarization plane by the adjustment of the polarization plane controller shown in FIG.

FIG. 17 is a diagram showing a structure of a semiconductor laser module according to a fourth embodiment of the present invention.

FIG. 18 is a diagram showing a structure of a semiconductor laser module according to a fifth embodiment of the present invention.

19 is a diagram showing frequency dependence of RIN according to the configuration of the semiconductor laser module shown in FIG.

FIG. 20 is a diagram showing a structure of a semiconductor laser module according to a sixth embodiment of the present invention.

FIG. 21 is a diagram showing a structure of a semiconductor laser module according to a seventh embodiment of the present invention.

FIG. 22 is a diagram showing the configuration of a modified example of the semiconductor laser module according to the seventh embodiment of the present invention.

FIG. 23 is a block diagram showing the configuration of a Raman amplifier that is Embodiment 8 of the present invention.

FIG. 24 is a block diagram showing a configuration of a modified example of the Raman amplifier that is Embodiment 8 of the present invention.

FIG. 25 is a block diagram showing the configuration of a communication system using a Raman amplifier that is Embodiment 8 of the present invention.

FIG. 26 is a block diagram showing a configuration of a conventional Raman amplifier.

[Explanation of symbols]

1, 61 Semiconductor Laser Element 2 Reflection Adjuster 3, 93 Optical Fibers 4, 4a, 94-1 to 94-n, 64 Reflector 11 Active Layer 12 Input Terminal 13 Diffraction Grating 14 Output Terminal 23 Deflection Plate 24 Faraday Rotor 25 coil 31 n-InP substrate 32 n-InP buffer layer 33 GRIN-SCH-MQW active layer 34 p-InP spacer layer 36 p-InP clad layer 37 InGaAsP contact layer 38 insulating film 39a n-InP blocking layer 39b p-InP Blocking layer 40 P-side electrode 41 N-side electrode 43 Diffraction grating 44 High reflection film 45 Low reflection film 50 Oscillation wavelength spectrum 51 to 53 Oscillation longitudinal mode 55 Composite oscillation wavelength spectrum 70 Opposed collimators 71a and 71b Ferrule 72 Reflection films 73a and 73b Light Fibers 74a, 74b Collimator lens 8 Polarization plane controller 83 Rotatable pressing body 102 Optical isolators 112a, 122a Low reflection films 161a, 161b Polarization combining coupler 162, 165 WDM coupler 163 Isolator 164 Amplifying fiber 167 Monitor light distribution coupler 168 Control circuit 169, 170 Signal light output Fibers 100, 100a, 100b, 100c, 100d, 1
00a ', 100b', 100c ', 100d', 18
2, 182a, 182b, 182c, 182d Semiconductor laser modules 181a, 181b, 181c, 181d Fiber grating E1 Non-current injection region E2 Current injection region

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01S 5/50 610 H01S 5/50 610 (72) Inventor Yasushi Oki 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F term (reference) 2K002 AA02 AB30 BA01 CA15 DA10 EA30 EB15 HA24 5F072 AB13 FF09 HH02 HH06 JJ20 KK07 KK30 PP07 QQ07 YY17 5F073 AB21 AB28 BA01 EA24 EA27

Claims (17)

[Claims] 1. A semiconductor laser device that emits laser light having one or more oscillation longitudinal modes, and a reflection wavelength that is provided outside the semiconductor laser device and that includes an oscillation wavelength band of the laser light emitted by the semiconductor laser device. A reflector that emits the laser light by reflecting a part of the band light, and is provided between the semiconductor laser device and the reflector,
A semiconductor laser device comprising: a return light controller that transmits the laser light emitted from the semiconductor laser device and controls the amount of light returned from the reflection end of the reflector to a predetermined value. module. 2. The return light controller performs setting control for attenuating the light quantity of the reflected return light with respect to the light quantity incident from the semiconductor laser element to −10 to −40 dB. Semiconductor laser module. 3. The Faraday rotator, the polarizing plate provided on the semiconductor laser element side of the Faraday rotator, and the Faraday rotator around the Faraday rotator. A magnetic applying unit that applies a magnetic force to change the rotation angle of the Faraday rotator; and the magnetic applying unit that adjusts the Faraday rotation angle by changing the magnetic force. The semiconductor laser module according to claim 1, wherein the amount of the reflected return light is adjusted by adjustment. 4. The temperature adjusting means for adjusting the temperature of the Faraday rotator is further provided, and the light quantity of the reflected return light is adjusted by changing the Faraday rotation angle by the temperature adjusting means. 3. The semiconductor laser module according to item 3. 5. The return light controller is a polarization plane controller that adjusts the polarization plane of the incident reflected return light by causing a partial refractive index change of the optical fiber by applying stress to the optical fiber. The light quantity of the reflected return light is adjusted by adjusting the polarization plane by a controller.
Alternatively, the semiconductor laser module described in 2. 6. The return light controller is an optical isolator, and the optical isolator adjusts the light quantity of the reflected return light by shifting the transmission center wavelength of the optical isolator with respect to the oscillation wavelength of the semiconductor laser device. The semiconductor laser module according to claim 1 or 2, wherein 7. A semiconductor laser device that emits laser light having one or more oscillation longitudinal modes, and a reflection wavelength that is provided outside the semiconductor laser device and that includes an oscillation wavelength band of laser light emitted by the semiconductor laser device. A reflector that reflects a part of the band light and emits the laser beam, and the reflectance of the reflector is a value of a reflected return light from the reflector with respect to the amount of light incident from the semiconductor laser element. A semiconductor laser module having a reflectance within a range in which the amount of light is attenuated to -10 to -40 dB. 8. A semiconductor laser device that emits a laser beam having one or more oscillation longitudinal modes, and a reflection wavelength that is provided outside the semiconductor laser device and that includes an oscillation wavelength band of the laser beam emitted by the semiconductor laser device. A plurality of reflectors that reflect a part of the band light and emit the laser light; and the reflectance of each reflector is the reflection return from each reflector with respect to the amount of light emitted from the semiconductor laser device. A semiconductor laser module, wherein the reflectance of each reflector is set such that the total amount of light is -10 to -40 dB. 9. The semiconductor laser module according to claim 8, wherein the reflectances of the respective reflectors are substantially the same. 10. The semiconductor laser module according to claim 1, wherein the reflector is a fiber black grating. 11. The reflector is an opposed collimator that has a reflecting film that reflects a part of the light in the reflection wavelength band and bidirectionally collimates the light.
9. The semiconductor laser module according to any one of 9. 12. The semiconductor laser device according to claim 1, wherein at least a part of the inside of the semiconductor laser device is provided with a diffraction grating for selecting an oscillation wavelength. Semiconductor laser module. 13. A semiconductor laser device that emits laser light having one or more oscillation longitudinal modes, and a reflection wavelength that is provided outside the semiconductor laser device and that includes an oscillation wavelength band of the laser light emitted by the semiconductor laser device. An input terminal for guiding the laser light emitted from the semiconductor laser device to an external optical fiber, and having a reflection film in which the amount of return light of the band is set to -10 to -40 dB. Semiconductor laser module. 14. The semiconductor laser module according to claim 1, wherein the semiconductor laser device is coupled by a lensed fiber. 15. The semiconductor laser module according to claim 1, an amplification optical fiber, a pumping light output from the semiconductor laser module, and a signal propagating in the amplification optical fiber. An optical fiber amplifier comprising: a coupler for multiplexing light. 16. The amplification optical fiber amplifies the signal light by Raman amplification.
The optical fiber amplifier according to. 17. The optical fiber amplifier according to claim 15, wherein the amplification optical fiber is an erbium-doped fiber, and the semiconductor laser module and the amplification optical fiber are arranged remotely.