JP2004103808A - Semiconductor laser module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a stable amplifying operation by reducing the Brillouin scattering and change of DOP generated following the change of a drive current. <P>SOLUTION: The semiconductor laser module is provided with a semiconductor laser element 20 which outputs the laser beam including two or more oscillation longitudinal modes within the half-value width of the oscillation wavelength spectrum, and a first lens 21 which is provided at the area near the light emitting end face of the semiconductor laser element 20 with the main surface thereof included for the optical axis of the laser beam emitted from the semiconductor laser element 20. Accordingly, the reflected return light from the first lens 21 can be reduced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor laser module including a semiconductor laser element that outputs a plurality of oscillation longitudinal mode laser beams, and more particularly to a semiconductor laser module that can obtain a stable optical output even when a drive current changes. .
[0002]
[Prior art]
Due to the rapid spread of the Internet in recent years and the rapid increase in connections between corporate LANs, an increase in data traffic has become a problem. In order to prevent a reduction in communication performance, high-density wavelength division multiplexing (DWDM: Dense- (Wavelength \ Division \ Multiplexing) transmission systems have made remarkable developments and have become widespread.
[0003]
In the DWDM transmission system, large-capacity transmission that is 100 times larger than that of the related art is realized by using one fiber by putting a plurality of optical signals on different wavelengths. In particular, the existing DWDM transmission system enables broadband and long-distance transmission by using an erbium-doped fiber amplifier (hereinafter, EDFA). Here, when the EDFA passes through a special optical fiber doped with an element called erbium with a pumping laser having a wavelength of 1480 nm or 980 nm, light having a wavelength of 1550 nm as a transmission signal is amplified in the special fiber. This is an optical fiber amplifier that applies the principle of being performed.
[0004]
On the other hand, an EDFA is a centralized optical amplifier in which a portion that excites an optical signal is concentrated, and the EDFA reduces transmission line optical fiber loss leading to accumulation of noise and nonlinearity that causes signal distortion and noise. There was a limitation of receiving it. Furthermore, the EDFA enables optical amplification in a wavelength band determined by the band gap energy of erbium, and it has been difficult to widen the band to realize further multiplexing.
[0005]
Therefore, a Raman amplifier has been attracting attention as an optical fiber amplifier instead of the EDFA. The Raman amplifier is a distributed optical amplifier that does not require special fibers such as erbium-doped fibers as in EDFAs and uses a normal transmission path fiber as a gain medium, so it can be used in conventional DWDM transmission systems based on EDFAs. It has a feature that a transmission band having a flat gain can be realized in a relatively wide band.
[0006]
FIG. 12 is a longitudinal sectional view showing a configuration of a semiconductor laser module including a conventional Fabry-Perot type semiconductor laser element used in a Raman amplifier or the like. 12, in a semiconductor laser module 300, a thermo module 200 is arranged on an inner bottom surface of a package 202 formed of a Cu—W alloy or the like. A base 197 is arranged on the thermo module 200, a carrier 198 is arranged on the base 197, and a submount 199 is arranged thereon. The semiconductor laser device 191 is disposed on the submount 199.
[0007]
The thermo module 200 is supplied with a current (not shown), and performs cooling and heating depending on its polarity. The thermo module 200 mainly functions as a cooler in order to prevent an oscillation wavelength shift due to a temperature rise of the semiconductor laser element 191. That is, the thermo module 200 controls to cool when the laser light has a longer wavelength than the desired wavelength, and when the laser light has a shorter wavelength than the desired wavelength, Control to heat. This temperature control is specifically controlled based on a detection value of a thermistor (not shown) arranged on the submount 199 and near the semiconductor laser element 191. And the thermo module 200 is controlled so that the temperature of the semiconductor laser element 191 is kept constant.
[0008]
In addition to the carrier 198, a first lens 192, an optical isolator 193, and a monitor photodiode 196 are arranged on the base 197. Laser light emitted from the semiconductor laser element 191 is condensed by the second lens 194 via the first lens 192 and the optical isolator 193. The laser light collected by the second lens 194 is guided into the optical fiber 203 fixed by the ferrule 201. The monitor photodiode 196 monitors and detects light leaked from the back reflection film side of the semiconductor laser device 191.
[0009]
In this semiconductor laser module 300, the return light to the semiconductor laser element 191 is reduced by using the optical isolator 193, and a non-reflection film is formed on the light incident surface of each optical component like the non-reflection film 101 for the second lens 194. Then, the incident end of the optical fiber 203 is polished obliquely to reduce the return light to the semiconductor laser device. In the semiconductor laser module 300, the non-reflection film 102 is further provided on the incident end of the optical fiber 203.
[0010]
In addition, for example, Patent Document 1 describes a module having an optical isolator, in which a collimating lens and an optical fiber end face are inclined to prevent return light due to reflection. Also, for example, Patent Documents 2 and 3 disclose an optical module having a plurality of semiconductor laser elements that oscillate in a longitudinal mode. Furthermore, for example, Patent Literature 4 describes a semiconductor laser module that can reduce stimulated Brillouin scattering.
[0011]
[Patent Document 1]
JP-A-3-135511
[Patent Document 2]
JP-A-2002-204024
[Patent Document 3]
JP-A-2002-141599
[Patent Document 4]
JP 2002-141609 A
[0012]
[Problems to be solved by the invention]
However, even if the optical isolator 193, the non-reflection films 101 and 102 are provided, and the optical fiber 203 is obliquely endfaced, there is reflected return light incident on the semiconductor laser element 191. There is a problem that the laser oscillation operation of the element 191 becomes unstable.
[0013]
For example, in the semiconductor laser element 191, when the reflected return light is incident again, as shown in FIG. 7, a phenomenon occurs that “oscillation” occurs in the oscillation spectrum waveform, and the number of oscillation longitudinal modes substantially decreases. I do. This phenomenon of “missing tooth” causes an unstable oscillation operation that occurs or does not occur depending on the magnitude of the drive current Iop applied to the semiconductor laser element 191.
[0014]
Here, in Raman amplification or the like, a process of changing the optical output of the pump light to change the gain characteristic of each signal wavelength band is performed. The optical output of the pump light generally uses the semiconductor laser element 191 which is a pump light source. This is performed by changing the value of the drive current Iop. Here, when the above-mentioned substantial change in the number of oscillation longitudinal modes occurs, the magnitude of light output carried by each oscillation longitudinal mode changes, and the amount of stimulated Brillouin scattering changes. In other words, the number of oscillation longitudinal modes substantially decreases due to the phenomenon of "missing teeth", the optical output of the oscillation longitudinal mode that does not substantially include "missing teeth" increases, and exceeds the stimulated Brillouin scattering threshold. There is a problem that the generation amount of Brillouin scattering sharply increases. When the stimulated Brillouin scattering occurs, a part of the incident pump light is reflected backward, and does not contribute to Raman gain generation. This lowering of the pump light intensity causes an unstable Raman gain.
[0015]
In addition, when the phenomenon of “missing teeth” occurs, the oscillation longitudinal mode interval substantially increases, and when depolarization is performed using a non-polarizing element, the polarization degree (depending on the change in the driving current Iop of the semiconductor laser element 191) is changed. DOP: Degree \ Of \ Polarization changes. Here, the Raman amplification is based on the condition that the polarization direction of the signal light matches the polarization direction of the pump light. That is, in Raman amplification, the amplification gain has polarization dependence, 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 by depolarization or the like. Changes the DOP, and stable Raman amplification cannot be performed.
[0016]
The present invention has been made in view of the above, and it is possible to reduce a stimulated Brillouin scattering and a change in DOP caused by a change in a driving current Iop, and to output a pumping light capable of performing a stable amplification operation. The purpose is to provide.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor laser module according to claim 1 includes a semiconductor laser device that outputs laser light including two or more oscillation longitudinal modes within a half-width of an oscillation wavelength spectrum, and a semiconductor laser device. A lens provided near the emission end face and having a main surface inclined with respect to the optical axis of the laser light output from the semiconductor laser element.
[0018]
According to the first aspect of the present invention, the main surface of the lens is inclined with respect to the optical axis to reduce reflected return light from the lens to the semiconductor laser element side, thereby reducing internal resonance formed inside the semiconductor laser element. Of the composite resonator formed by the resonator and the external resonator formed between the reflection end face of the semiconductor laser device and the lens, eliminating the formation of the external resonator, and the oscillation longitudinal mode accompanying the change in the drive current. It tries to suppress "missing teeth". As a result, even if the driving current is changed, the amount of stimulated Brillouin scattering does not change, and the DOP does not change, realizing a stable laser light output.
[0019]
Further, in the semiconductor laser module according to claim 2, in the above invention, the semiconductor laser element includes a first reflection film provided on an emission end face of the laser light and a second reflection film provided on a reflection end face of the laser light. A diffraction grating is provided in the vicinity of an active layer formed between the active layer and a combination of oscillation parameters including a resonator length formed by the active layer and a wavelength selection characteristic of the diffraction grating. It is characterized by outputting laser light including two or more oscillation longitudinal modes.
[0020]
Further, in the semiconductor laser module according to claim 3, in the above invention, the semiconductor laser element is a Fabry-Perot type semiconductor laser element, and has two or more oscillation longitudinal modes within a half width of an oscillation wavelength spectrum. The laser light is output.
[0021]
According to a fourth aspect of the present invention, in the above-described semiconductor laser module, the inclination angle of the main surface of the lens with respect to the optical axis is 4 ° or less.
[0022]
The semiconductor laser module according to claim 5, wherein in the above invention, an optical fiber for receiving laser light output from the semiconductor laser element via the lens and transmitting the laser light to the outside, the lens and the optical fiber And an optical isolator provided between them.
[0023]
Further, in the semiconductor laser module according to claim 6, in the above invention, the optical isolator has a one-stage structure of a polarizer / Faraday rotator / polarizer and 1.5 or more stages obtained by further adding a Faraday rotator / polarizer. Wherein the polarizer at least on the side of the semiconductor laser element is disposed at an angle of 4 ° with respect to the optical axis.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a semiconductor laser module according to the present invention will be described in detail with reference to the drawings.
[0025]
FIG. 1 is a longitudinal sectional view showing a configuration of a semiconductor laser module according to an embodiment of the present invention. 1, the semiconductor laser module 100 includes a first lens 21 whose main surface is inclined with respect to the optical axis, instead of the first lens 192 shown in FIG. In addition, a semiconductor laser device 20 that outputs a plurality of oscillation longitudinal modes is provided instead of the semiconductor laser device 191. Other configurations are the same as those of the semiconductor laser module 300 shown in FIG. 12, and the same components are denoted by the same reference numerals.
[0026]
The first lens 21 is a lens, and has a main surface inclined by 3 ° with respect to the optical axis of laser light emitted from the semiconductor laser element 20. For this reason, the first lens 21 has a lens holder holding portion 23 disposed in a concave portion on the base 197 provided on the base 197, the lens holder 22 is fixed by the lens holder holding portion 23, and the lens holder 22 is further fixed. By means of 22, the main surface of the first lens 21 is held in a state inclined by 3 ° with respect to the optical axis of the semiconductor laser device 20.
[0027]
In FIG. 1, the main surface of the first lens 21 is inclined while maintaining perpendicular to the vertical plane (XZ plane) of the semiconductor laser module 100. However, the present invention is not limited to this. You may make it incline, maintaining perpendicular | vertical with respect to 100 horizontal planes (YZ plane). In this case, in consideration of the stability of holding the first lens 21, it is preferable that the first lens 21 be tilted while being perpendicular to the horizontal plane.
[0028]
As described above, by inclining the main surface of the first lens 21 by 3 ° with respect to the optical axis of the laser light emitted from the semiconductor laser element 20, there is almost no reflected return light to the semiconductor laser element 20, and the drive current Iop Is changed, the laser light having the oscillation spectrum of “missing tooth” shown in FIG. 7 is not output.
[0029]
Here, the semiconductor laser device 20 will be described. FIG. 2 is an oblique cutaway view showing a schematic configuration of the semiconductor laser element 20 in the semiconductor laser module 100 according to the embodiment of the present invention. FIG. 3 is a longitudinal sectional view of the semiconductor laser device 20 shown in FIG. 2 in the longitudinal direction. FIG. 4 is a sectional view of the semiconductor laser device 20 shown in FIG. In FIG. 2, the semiconductor laser element 20 has an n-InP buffer layer 2 serving as a buffer layer and a lower cladding layer of n-InP and a compressive strain on the (100) plane of the n-InP substrate 1 in sequence. A GRIN-SCH-MQW (Graded Index-Separate Component / Heterostructure / Multi / Quantum / Well) active layer 3, a p-InP spacer layer 4, a p-InP cladding layer 6, and a p-InGaAsP contact layer 7 are stacked.
[0030]
As shown in FIG. 3, a reflective film 14 having a high light reflectance of 80% or more is formed on a light reflecting end face which is one end face in the longitudinal direction of the semiconductor laser element 20, and a light which is the other end face. On the emission end face, an emission-side reflection film 15 having a low light reflectance of 2% or less, preferably 1% or less is formed. Light generated in the GRIN-SCH-MQW active layer 3 of the optical resonator formed by the reflection film 14 and the emission-side reflection film 15 is reflected by the reflection film 14 and passes through the emission-side reflection film 15 to form a laser beam. Is emitted.
[0031]
Further, in FIG. 3, the semiconductor laser device 20 has a p-InGaAsP diffraction grating 13 periodically arranged in the p-InP spacer layer 4. In particular, here, the diffraction grating 13 extends 100 μm from the emission-side reflection film 15 so that the light having a center wavelength of 1480 nm is selected from the laser light generated in the gain region of the GRIN-SCH-MQW active layer 3. It has a thickness of 20 nm and is formed at a pitch of about 220 nm. The diffraction grating 13 is desirably arranged in contact with the emission-side reflection film 15, but is not necessarily arranged so as to be in a range where the function of the diffraction grating 13 is exhibited, for example, in a range of about 20 μm to 100 μm. , It can be arranged to be separated from the emission side reflection film 15. Further, the diffraction grating 13 may remain on the reflection film 14 side due to a variation in the cleavage position of the semiconductor laser element 20 that occurs during the manufacture of the semiconductor laser element 20. The diffraction grating 13 may be arranged over the entire surface of the active layer, or may be arranged on a part of the active layer.
[0032]
Further, as shown in FIG. 4, the upper part of the n-InP buffer layer 2, the GRIN-SCH-MQW active layer 3, and the p-InP spacer layer 4 including the diffraction grating 13 are processed into a mesa stripe shape. Are embedded with p-InP blocking layers 8 and n-InP blocking layers 9 formed as current blocking layers. A p-side electrode 10 is formed on the upper surface of the p-InGaAsP contact layer 7, and an n-side electrode 11 is formed on the back surface of the n-InP substrate 1.
[0033]
When the above-described semiconductor laser device 20 is used as a light source for pumping a Raman amplifier, its oscillation wavelength λ₀Is set to 1100 nm to 1550 nm, and the resonator length L is set to 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 element can be expressed by the following equation, where the equivalent refractive index is “n”. That is,
Δλ = λ₀ ²/ (2nL)
It is. Here, the oscillation wavelength λ₀Is 1480 nm and the effective refractive index is 3.5, when the resonator length L is 800 μm, the longitudinal mode mode interval Δλ is about 0.39 nm, and when the resonator length is 3200 μm, the longitudinal mode mode interval is Δλ is about 0.1 nm. In other words, the longer the resonator length L, the narrower the mode interval Δλ in the longitudinal mode, and the more severe the selection conditions for oscillating single longitudinal mode laser light.
[0034]
On the other hand, the diffraction grating 13 selects a longitudinal mode according to its Bragg wavelength. FIG. 5 is a diagram for explaining the selected wavelength characteristic by the diffraction grating 13. The selected wavelength characteristic by the diffraction grating 13 is represented as an oscillation wavelength spectrum 30 as illustrated.
[0035]
In particular, as shown in FIG. 5, the semiconductor laser device 20 is designed such that the presence of the diffraction grating 13 causes a plurality of oscillation longitudinal modes to exist within the wavelength selection characteristic represented by the half-width Δλh of the oscillation wavelength spectrum 30. Is done. In a conventional semiconductor laser device, if the resonator length L is 800 μm or more, single longitudinal mode oscillation is difficult. Therefore, a semiconductor laser device having such a resonator length L has not been used. In 20, the laser beam including a plurality of oscillation longitudinal modes within the half width Δλh of the oscillation wavelength spectrum is output by positively setting the resonator length L to 800 μm or more. In FIG. 5, three oscillation longitudinal modes 31 to 33 are provided within the half-width Δλh of the oscillation wavelength spectrum.
[0036]
When a laser beam having a plurality of oscillation longitudinal modes is used, a peak value of a laser output can be suppressed and a higher laser output value can be obtained as compared with a case where a single longitudinal mode laser beam is used. FIG. 6 is an explanatory diagram for describing each profile of a single longitudinal mode laser beam and a plurality of oscillation longitudinal mode laser beams. For example, the semiconductor laser device 20 has a 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 single longitudinal mode oscillation semiconductor laser device when the same laser output is obtained, and has a high peak value.
[0037]
Here, when the semiconductor laser device 20 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. However, if the peak value is high, stimulated Brillouin scattering occurs. However, a problem that noise is increased occurs. Stimulated Brillouin scattering occurs when the laser output exceeds a threshold Pth at which stimulated Brillouin scattering occurs, as shown in FIG. Therefore, in the semiconductor laser device 20, in order to obtain the same laser output power as the profile shown in FIG. 6A, as shown in FIG. Laser light is emitted in the oscillation longitudinal mode. Thereby, a high pumping light output power can be obtained, and as a result, a high Raman gain can be obtained.
[0038]
In FIG. 5, the wavelength interval (mode interval) Δλ of the oscillation longitudinal modes 31 to 33 is set to 0.1 nm or more. This is because when the semiconductor laser element 20 is used as a light source for excitation of a Raman amplifier, the possibility of stimulated Brillouin scattering increases if the mode interval Δλ is 0.1 nm or less. As a result, it is preferable that the above-mentioned resonator length L is 3200 μm or less according to the above-described equation of the mode interval Δλ. From such a viewpoint, it is desirable that the number of oscillation longitudinal modes included in the half width Δλh of the oscillation wavelength spectrum 30 is plural.
[0039]
Therefore, as described above, the semiconductor laser element 20 provided in the semiconductor laser module 100 according to this embodiment has a diffraction grating so that two or more oscillation longitudinal modes are included in the half width of the oscillation wavelength spectrum. Since the arrangement position of 13 and the cavity length L are set, it is possible to stably obtain a high-output laser output without causing stimulated Brillouin scattering.
[0040]
The semiconductor laser element 20 in the semiconductor laser module 100 is described in the embodiments of Japanese Patent Application Nos. 2000-323118, 2001-134545 and 2001-228669, in addition to the above-described configuration. Also, various "semiconductor laser devices" can be used.
[0041]
By the way, even when such a semiconductor laser device 20 is used, as described above, due to the reflected return light to the semiconductor laser device 20, the oscillation longitudinal mode caused by the change in the drive current Iop as shown in FIG. "Tooth loss" occurred, and as a result, the number of oscillation longitudinal modes decreased, and a change in stimulated Brillouin scattering and a change in DOP occurred, thereby exhibiting an unstable oscillation operation. Here, the present inventors have found that this “missing tooth” is caused by the internal resonator formed by the internal resonator of the semiconductor laser element 20 itself, that is, the output side reflection film 15 including the diffraction grating 13 and the reflection film 14, As described above, it is considered that the first lens 21 is formed by an oscillation phenomenon of a composite resonator including an external resonator formed between the reflection film 14 and the first lens 21. By tilting 3 ° with respect to the optical axis, the reflected return light from the first lens 21 to the semiconductor laser element 20 is eliminated, so that the above-described external resonator is not formed.
[0042]
Due to the oblique arrangement of the first lens 21, even when the drive current Iop is changed, laser light having an oscillation spectrum of the internal resonator itself of the semiconductor laser device 20 as shown in FIG. 8 was output. That is, even if the drive current Iop is changed, laser light having an oscillation spectrum that does not cause “missing tooth” can be output.
[0043]
As a result, the mode interval of the oscillating longitudinal mode generated at the time of “missing tooth” does not increase, and the fluctuation of DOP can be suppressed. That is, when the mode interval is widened, the minimum value of the DOP corresponding to the length of the polarization maintaining fiber used for the depolarizer or the like shifts in the direction of decreasing the length, and as a result, the DOP fluctuates. In the embodiment, since the mode interval does not change, even if the drive current Iop changes, the DOP does not change, and a stable and small DOP can be obtained. Also, as a result of the experiment, when the driving current of the semiconductor laser module was 200 mA, the DOP before the first lens 21 was inclined was about 47%, but the first lens 21 was inclined by 3 ° with respect to the optical axis. DOP could be reduced to about 15%.
[0044]
Here, an experimental result of the drive current dependence of stimulated Brillouin scattering of laser light output from the semiconductor laser module 100 having the above-described first lens 21 obliquely arranged will be described. FIG. 9 is a diagram showing a configuration of a measuring apparatus for measuring the drive current dependence of the generation of stimulated Brillouin scattering in the laser light output from the semiconductor laser module 100. FIG. 10 is a diagram showing a measurement result of the drive current dependence of the generation of stimulated Brillouin scattering.
[0045]
In the measuring device shown in FIG. 9, the semiconductor laser module 100 and the reflected light measuring means 43 are arranged on one side via a coupler 41, and the transmission optical fiber 44 and the input light measuring means 45 are arranged on the other side. One and the other are connected to each other via a coupler 41, and the transmission optical fiber 44 is connected to an output light measuring means 46. The transmission optical fiber 44 is, for example, a NZDF (non-zero dispersion fiber) 37 km True Wave (R) -RS.
[0046]
In the measuring apparatus shown in FIG. 9, light having a certain ratio with the intensity of the laser light output from the semiconductor laser module 100 enters the input light measuring means 45, and the transmission optical fiber 44 enters the reflected light measuring means 43. Light having a fixed ratio with the intensity of the light scattered back by the light enters.
[0047]
Here, when stimulated Brillouin scattering occurs, the intensity of light incident on the reflected light measuring means 43 increases. Therefore, the ratio between the light incident on the transmission optical fiber 44 from the semiconductor laser module 100 and the intensity of the light scattered back by the transmission optical fiber 44 (hereinafter referred to as “return loss”) is taken. Can be used to determine whether stimulated Brillouin scattering has occurred.
[0048]
FIG. 10 shows a change in the return loss when the drive current Iop for the semiconductor laser module 100 is changed as described above. In FIG. 10, in the conventional semiconductor laser module 300, when the drive current Iop is changed from 100 mA to 1300 mA, the return loss greatly changes between −28 dB and −5 dB. Even if the current Iop is greatly changed from 100 mA to 1300 mA, the return loss is stable at approximately −15 dB. That is, the return loss of the semiconductor laser module 100 hardly depends on the drive current. In other words, generation of stimulated Brillouin scattering in the semiconductor laser module 100 hardly depends on the drive current. Further, in the conventional semiconductor laser module 300, the return loss has a large peak value of −5 dB, but the return loss of the semiconductor laser module 100 is almost −15 dB, and a large return loss, that is, a large stimulated Brillouin scattering Can be suppressed. This is because the occurrence of the “missing tooth” shown in FIG. 7 can be suppressed by the oblique arrangement of the first lens 21 described above.
[0049]
By the way, the main surface of the first lens 21 in the above-described semiconductor laser module 100 is inclined by 3 ° with respect to the optical axis of the semiconductor laser element 20. However, if this inclination is too inclined, the output of the laser light may decrease. Come. FIG. 11 is a diagram illustrating the dependence of the laser light output from the semiconductor laser module 100 on the inclination of the first lens. In FIG. 11, the light output of the laser light is normalized by a maximum value near 0 °. In FIG. 11, the measured value suddenly decreases the light output when the angle exceeds 3 °, and the calculated value sharply decreases the light output when the angle exceeds 4 °. Therefore, in consideration of the error of the actually measured value, it is preferable that the inclination of the first lens has an inclination of 4 ° or less. Further, the first lens may be a collimating lens or an aspheric lens having a lens shape, for example.
[0050]
Note that, as the optical isolator 193 described above, it is preferable to use an optical isolator having a 1.5-stage structure (polarizer / Faraday rotator / polarizer / Faraday rotator / polarizer) or a structure having more stages. Further, it is more preferable that the optical isolator 193 is arranged such that at least the polarizer on the side where the semiconductor laser element is located is inclined by about 4 ° with respect to the optical axis. Further, a non-reflection film may be formed on the incident surface of the optical isolator 193. As a result, return light can be reduced more reliably.
[0051]
In the above-described embodiment, the semiconductor laser device 20 in the semiconductor laser module 100 includes the diffraction grating 13 provided near the active layer such as the GRIN-SCH-MQW active layer 3 and outputs a plurality of oscillation longitudinal modes. However, the present invention is not limited to this. For example, a Fabry-Perot semiconductor laser device having no diffraction grating 13 may be used. The point is that the semiconductor laser element 20 may be a multi-mode laser that outputs a plurality of oscillation longitudinal modes.
[0052]
Further, in the above-described embodiment, the oscillation wavelength λ of the semiconductor laser₀Is set to 1480 nm as an example, but it is needless to say that the present invention can be applied to a case where a semiconductor laser device having another oscillation wavelength such as 980 nm is provided.
[0053]
The above-described semiconductor laser module 100 is used as an excitation light source such as a Raman amplifier, and can be used particularly for a forward excitation method or a bidirectional excitation method.
[0054]
【The invention's effect】
As described above, according to the present invention, the main surface of the lens is inclined with respect to the optical axis to reduce the reflected return light from the lens to the semiconductor laser element side, and is formed inside the semiconductor laser element. Of the composite resonator formed by the internal resonator and the external resonator formed between the reflection end face of the semiconductor laser element and the lens, eliminating the formation of the external resonator, and the oscillation accompanying the drive current change. It is designed to suppress "missing teeth" in the vertical mode. As a result, even if the drive current is changed, the amount of stimulated Brillouin scattering does not change, the DOP does not change, and a stable laser light output can be realized. This provides an effect that a Raman amplifier capable of performing the above-described amplification operation can be realized.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a semiconductor laser module according to an embodiment of the present invention.
FIG. 2 is an oblique cutaway view showing a schematic configuration of the semiconductor laser device shown in FIG. 1;
3 is a longitudinal sectional view of the semiconductor laser device shown in FIG. 2 in a longitudinal direction.
FIG. 4 is a sectional view taken along line AA of the semiconductor laser device shown in FIG. 3;
FIG. 5 is an explanatory diagram for explaining selected wavelength characteristics of the semiconductor laser device shown in FIG. 1 by a diffraction grating.
FIG. 6 is an explanatory diagram for explaining each profile of a single longitudinal mode laser beam and a plurality of oscillation longitudinal mode laser beams.
FIG. 7 is a diagram illustrating an oscillation wavelength spectrum having tooth skipping that occurs when a drive current is changed in a conventional semiconductor laser device.
FIG. 8 is a diagram showing an oscillation wavelength spectrum output from the semiconductor laser module according to the embodiment of the present invention;
FIG. 9 is a measurement diagram for measuring a return loss corresponding to the amount of stimulated Brillouin scattering generated.
FIG. 10 is a diagram showing the drive current dependence of return loss between the semiconductor laser module according to the embodiment of the present invention and a conventional semiconductor laser module.
FIG. 11 is a diagram showing a first lens tilt angle dependency of a laser beam output from a semiconductor laser module according to an embodiment of the present invention.
FIG. 12 is a longitudinal sectional view showing a configuration of a conventional semiconductor laser module.
[Explanation of symbols]
1 @ n-InP substrate
2 n-InP buffer layer
3 GRIN-SCH-MQW active layer
4 p-InP spacer layer
6 p-InP cladding layer
7 p-InGaAsP contact layer
8 @ p-InP blocking layer
9 n-InP blocking layer
10 p side electrode
11 n side electrode
13 diffraction grating
14 reflective film
15 ° Outgoing side reflective film
20mm semiconductor laser device
21 ° first lens
22mm lens holder
23 lens holder holder
193 optical isolator
100mm semiconductor laser module
101, 102 non-reflective film
194 Second lens
196 monitor photodiode
197 base
198 career
199mm sub mount
200 thermo module
201 ferrule
202 package

Claims (6)

A semiconductor laser device that outputs laser light including two or more oscillation longitudinal modes within the half-value width of the oscillation wavelength spectrum,
A lens provided near the emission end face of the semiconductor laser element, the main surface of which is inclined with respect to the optical axis of laser light output from the semiconductor laser element;
A semiconductor laser module comprising: The semiconductor laser device includes a diffraction grating provided near an active layer formed between a first reflection film provided on an emission end face of the laser light and a second reflection film provided on a reflection end face of the laser light. A laser beam including two or more oscillation longitudinal modes within a half width of an oscillation wavelength spectrum is output by setting a combination of oscillation parameters including a resonator length formed by an active layer and a wavelength selection characteristic of the diffraction grating. The semiconductor laser module according to claim 1, wherein 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a Fabry-Perot type semiconductor laser device, and outputs laser light including two or more oscillation longitudinal modes within a half-width of an oscillation wavelength spectrum. Semiconductor laser module. 4. The semiconductor laser module according to claim 1, wherein an inclination angle of the main surface of the lens with respect to an optical axis is 4 ° or less. 5. An optical fiber that receives laser light output from the semiconductor laser element through the lens and transmits the laser light to the outside,
An optical isolator provided between the lens and the optical fiber,
The semiconductor laser module according to claim 1, further comprising: The optical isolator has a structure of 1.5 or more stages in which a Faraday rotator / polarizer is further added to a one-stage structure of a polarizer / Faraday rotator / polarizer. The semiconductor laser module according to claim 5, wherein the polarizer is disposed at an angle of 4 °.

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