JP2005072402A - Semiconductor laser device, semiconductor laser module using the same and optical fiber amplifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device which enables a high output operation with an excellent reliability. <P>SOLUTION: In the semiconductor laser device having a p-type clad layer, an n-type clad layer and an active layer, the n-type clad layer comprises two or more layers which have a different composition containing InP and GaInAsP, in particular preferably, a superlattice structure. Also, a refractive index of the n-type clad layer is greater than that of the p-type clad layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device, and more particularly to a high-power semiconductor laser device used as a pumping light source for an optical fiber amplifier such as an EDFA or a Raman amplifier.

  In recent years, data traffic has increased dramatically due to the rapid spread of the Internet and the rapid increase of intra-company LAN connections. Under such circumstances, a WDM (wavelength multiplex transmission) system that enables high-speed and large-capacity data transmission has been developed and has become widespread.

In a WDM system, a plurality of optical signals are placed on different wavelengths, thereby realizing large-capacity transmission of several tens of gigabits to several terabits per second with a single fiber. In particular, an existing WDM system requires an optical fiber amplifier such as an erbium-doped fiber amplifier (hereinafter referred to as EDFA) or a Raman amplifier, which enables broadband and long-distance transmission. Here, the EDFA amplifies light in the wavelength 1550 nm band as a transmission signal in the special optical fiber by exciting a special optical fiber doped with an erbium (Er) element with an excitation light source having a wavelength of 1480 nm or 980 nm. This is an optical fiber amplifier.

The Raman amplifier is an optical fiber amplifier that uses a normal transmission line fiber as a gain medium and does not require a special fiber unlike an EDFA. Since a Raman gain is obtained in a long wavelength band about 100 nm longer than the wavelength of the excitation light source, amplification is possible in an arbitrary wavelength band. For this reason, by selecting a plurality of excitation light sources, a transmission band having a wide band and a flat gain can be realized as compared with a conventional EDFA-based WDM transmission system.

In order to improve the stability of the WDM system and reduce the number of relays, a high-power and broadband optical phi amplifier is required. As a pumping light source for this optical fiber amplifier, particularly a pumping light source for high power EDFA or Raman amplifier, a buried heterostructure (BH structure) semiconductor laser made of GaInAsP formed on an InP substrate is used.

In order to achieve high reliability and high output operation in the GaInAsP semiconductor laser, the element resistance and thermal resistance are reduced by increasing the element length and the active layer width, and the heat generated from the active layer is reduced. It is effective to suppress.
Here, when the active layer width is widened, the active layer structure is optimized so that the difference in equivalent refractive index between the region including the active layer and the region not including it is reduced in order to suppress higher-order transverse modes. There is a need to. The smaller the equivalent refractive index difference is, the smaller the refractive index of the region including the active layer is, so that the electric field distribution of light oozes out to the cladding layer.
When a laser structure is formed on an n-type InP substrate, zinc (Zn) is generally used as a dopant for the p-type upper cladding layer. Since Zn has the property of absorbing light, it absorbs light that has oozed out into the upper cladding layer, which has been a factor that hinders the high-power operation of the semiconductor laser. In response to this, the following techniques are disclosed (see Non-Patent Document 1). In this semiconductor laser device having an n-type InP substrate, GaInAsP having a band gap composition wavelength of 0.95 μm is used for the n-type cladding layer. Since GaInAsP has a higher refractive index than InP used for the p-type cladding layer, the laser light intensity distribution is shifted closer to the n-type cladding layer than the distribution centering on the conventional active layer, Light absorption by Zn in the p-type cladding layer is suppressed.

Y. Nagashima, S. Onuki, Y. Shimose, A. Yamada and T. Kikugawa, PD 1.4``Novel Asymmetric-Cladding 1.48-um Pump Laser with Extremely High Slope Efficiency and CW Output Power of> 1W '', LEOS 2002 Post Deadline Papers of "The 15th Annual Meeting of the IEEE Lasers & Electro-Optics Society", Scotland, November 10, 2002

  However, in the structure as described above, since GaInAsP having a composition wavelength of 0.95 μm is used as the cladding layer, it is necessary to crystal-grow a GaInAsP having a considerable thickness, for example, 7.5 μm on the substrate. In general, when GaInAsP is grown on InP, there is a problem that it is difficult to obtain a high-quality crystal while maintaining lattice matching conditions. In particular, as the thickness of GaInAsP to grow increases, strain energy based on the difference in lattice constant between InP and GaInAsP accumulates with growth, making it difficult to achieve high-quality crystals, and a semiconductor laser to be manufactured It is disadvantageous in terms of high output operation and reliability of the device.

  The present invention has been made in view of the above, and an object thereof is to provide a semiconductor laser that is excellent in reliability and capable of high output operation.

  In order to achieve the above object, the invention described in claim 1 is a semiconductor laser device having a p-type cladding layer, an n-type cladding layer, and an active layer, wherein the n-type cladding layer contains InP and GaInAsP. And the refractive index of the n-type cladding layer is larger than the refractive index of the p-type cladding layer.

  According to a second aspect of the present invention, in the above semiconductor laser device, the composition wavelength of the GaInAsP is 1.0 μm or more.

  According to a third aspect of the present invention, in the semiconductor laser device according to the first or second aspect, the two or more layers having different compositions form a superlattice structure. is there.

  According to a fourth aspect of the present invention, in the semiconductor laser device according to any one of the first to third aspects, the active layer has a quantum well structure.

  According to a fifth aspect of the present invention, in the semiconductor laser device according to any one of the first to fourth aspects, the semiconductor laser device has a separate confinement hetero (SCH) structure.

  According to a sixth aspect of the present invention, in the semiconductor laser device of the fifth aspect, the SCH structure is composed of a single layer or two or more layers, and the effective band gap composition wavelength of the superlattice structure is: It is characterized by being not more than the composition wavelength of the layer having the smallest band gap composition wavelength among the layers constituting the SCH structure.

  The invention according to claim 7 is the semiconductor laser device according to any one of claims 1 to 6, an optical waveguide for guiding laser light emitted from the semiconductor laser device to the outside, and the semiconductor laser device. A semiconductor laser module comprising an optical coupling means for optically coupling the optical waveguide.

  According to an eighth aspect of the present invention, there is provided the laser module according to the seventh aspect, an optical waveguide for transmitting signal light, and optical multiplexing means for causing excitation light emitted from the semiconductor laser module to enter the optical waveguide. And an optical fiber amplifying device.

  The effects of the present invention will be described below. The semiconductor laser device according to claim 1 of the present invention is such that the n-type cladding layer is composed of two or more layers having different compositions containing InP and GaInAsP, and the refractive index of the n-type cladding layer is the p-type. Since it is larger than the refractive index of the cladding layer, the intensity distribution of the laser beam can be shifted closer to the n-type cladding layer, and light absorption in the p-type cladding layer can be suppressed. Therefore, high output operation can be realized in the semiconductor laser device manufactured on the InP substrate.

  In the semiconductor laser device according to the second aspect of the present invention, since the composition wavelength of GaInAsP in the n-type cladding layer is 1.0 μm or more, a high-quality crystal n-type cladding layer can be obtained, and a high output Thus, a semiconductor laser device with excellent reliability can be obtained.

  In the semiconductor laser device according to claim 3 of the present invention, since two or more layers having different compositions form a superlattice structure, strain energy is accumulated during crystal growth of the n-type cladding layer. Can be suppressed. For this reason, a good crystallinity can be obtained, and a semiconductor laser device having high output and excellent reliability can be obtained.

  In the semiconductor laser device according to the fourth aspect of the present invention, since the active layer has a quantum well structure, there is an effect that it is particularly advantageous for high output.

  Since the semiconductor laser device according to the fifth aspect of the present invention has a separate confinement hetero (SCH) structure, there is an effect that it is further advantageous for high output.

  According to the invention described in claim 6 of the present invention, the effective band gap composition wavelength of the superlattice structure is equal to or less than the composition wavelength of the layer having the smallest band gap composition wavelength among the layers constituting the SCH structure. As a result, there is an effect that carriers are successfully injected from the n-type clad layer containing the superlattice crystal into the active layer via the SCH layer.

  According to the seventh aspect of the present invention, since the laser module is configured using the semiconductor laser device according to any one of the first to sixth aspects, a high-power and high-reliability laser module is obtained. Can do.

  According to the eighth aspect of the present invention, since the optical amplifying device is configured using the laser module according to the seventh aspect, a high-performance and highly reliable optical amplifying device can be obtained.

Embodiments of a semiconductor laser device, a semiconductor laser device module, and an optical amplifying device according to the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited by these embodiments.
In the following description, unless otherwise specified, the composition of a compound semiconductor is represented by the maximum wavelength (bandgap composition wavelength) of light that can be absorbed by a semiconductor having the composition.

[Embodiment 1]
First, the semiconductor laser device according to the first embodiment will be described. As will be described later, the semiconductor laser device according to the first embodiment has a buried hetero type having a GRIN-SCH-MQW (graded-index separate confinement heterostructure multi quantum well) structure. This is a semiconductor laser device, which is configured using a GaInAsP-based material on an n-type InP substrate. In particular, the n-type cladding layer is characterized by using a superlattice structure containing InP and GaInAsP having a composition wavelength of 1.0 μm or more and having an equivalent composition wavelength of 1.0 μm or less. However, the band gap composition wavelength of GaInAsP is preferably a value that does not exceed the oscillation wavelength of the semiconductor laser device.

  FIG. 1 is a longitudinal sectional view of the semiconductor laser device according to the first embodiment. 1A shows a longitudinal sectional view in the longitudinal direction, and FIG. 1B shows a sectional view parallel to the light emitting surface. FIG. 1C is an enlarged view of a part of FIG. In FIG. 1, a semiconductor laser device 10 includes an n-type lower cladding layer 2A, an undoped lower optical confinement layer 3A, an active layer 4, an undoped upper optical confinement layer 3B, and a p-type on an n-type InP semiconductor substrate 1. The upper cladding layer 2B and the p-type GaInAsP contact layer 5 are stacked. The materials constituting the upper cladding layer, the lower cladding layer, and the active layer will be described later. These layers are formed using an epitaxial growth method such as a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. As a dopant for the cladding layer made of InP, Zn is used for the p-type, and Se, S, etc. are used for the n-type.

  As shown in FIG. 1B, the upper cladding layer 2B, the active layer 4 and the lower cladding layer 2A constitute a mesa stripe 7. The mesa stripe 7 is formed using photolithography and etching. A p-type block layer 8 and an n-type block layer 9 are formed on the side of the mesa stripe 7 to embed the mesa stripe 7.

  In addition, the semiconductor laser device 10 includes an n-side lower electrode 6A on the lower surface of the InP substrate 1, and a p-side upper electrode 6B on the surface of the p-type GaInAsP contact layer 5.

  Further, as shown in FIG. 1A, the front end face f from which light is emitted and the rear end face r facing the front end face f form a resonator having a resonator length L. The front end face and the rear end face are made by cleavage. On the front end face f and the rear end face r, a low reflection film 11 and a high reflection film are coated for high output operation, respectively.

  The p-side upper electrode 6B and the n-side lower electrode 6A are connected to a power source (not shown). The current supplied from the power source is supplied from the p-side upper electrode 6B to the p-type GaInAsP contact layer 5, the p-type upper cladding layer 2B, the upper optical confinement layer 3B, the active layer 4, the lower optical confinement layer 3A, and the n-type lower cladding layer. 2A passes through the n-type InP substrate 1 and reaches the n-side lower electrode 6A. The active layer 4 emits light by the injected current, and laser oscillation is generated by a resonator formed by the front end face f and the rear end face r.

  The buried hetero (BH) structure in which the p-type block layer 8 and the n-type block layer 9 are embedded in the mesa stripe 7 has a role of injecting a current into the active layer 4 and oscillates in a stable horizontal single transverse mode. Enable. Further, as long as the lateral mode can be controlled, the BH structure is not necessary. For example, a ridge structure or a self-aligned structure (SAS) may be used.

  In addition, the semiconductor laser device 10 shown in the first embodiment has a resonator length L, reflectivities of the low reflection film 11 and the high reflection film 12, and a structure in the vicinity of the active layer 4 as a structure enabling high output operation. The active layer 4 is doped, and the structure of the n-type lower cladding layer 2A, which is a feature of the present invention, is characterized. Hereinafter, these features will be described.

(Resonator length and reflectivity of reflecting film) The resonator length L is determined according to the specifications of the semiconductor laser device such as optical output, power consumption, and operating current, and is 800 μm or more for high output operation. It is desirable to do. In this embodiment, L = 1300 μm. The reflectance of the low reflection film 11 is desirably 5% or less, and the reflectance of the high reflection film 12 is desirably 90% or more. In the present embodiment, for L = 1300 μm, the reflectance of the low reflective film 11 is 1.5%, and the reflectance of the high reflective film 12 is 98%. Note that these appropriate values for the reflectivity vary depending on the active layer structure such as the resonator length L, the equivalent refractive index difference, the optical confinement coefficient, and the internal loss.

(Composition, thickness, etc. of layer near active layer) FIG. 2 is a bandgap diagram near the active layer in the semiconductor laser device according to the present embodiment. The active layer 4 has a multiple quantum well (MQW) structure in which well layers 4A and barrier layers 4B are alternately stacked. FIG. 2 particularly shows the case where the number of well layers is five. In the present embodiment, a multiple quantum well structure is used for the active layer. However, there is no problem even if a single quantum well structure having one well is formed.

In addition, the lower optical confinement layer 3A and the upper optical confinement layer 3B include a plurality of layers 3A ₁ , 3A ₂ ,..., 3A _n and 3B ₁ , 3B whose band gap energy increases stepwise as the distance from the active layer 4 increases. _2, and ..., graded index consisting 3B _n and (GRIN) structures. This GRIN-SCH structure is preferably linear. That is, as shown in FIG. _2, 3A _1, 3A 2, connect ..., envelope connecting the energy band edge of 3A _n h1 and _{3B 1,} 3B 2, ..., the energy band edge of 3B _n It is preferable that the envelope h2 is a straight line.

  The upper and lower optical confinement layers are designed so that their thickness and composition are symmetrical to each other. However, an asymmetric structure in which the thickness of the lower light confinement layer 3A is thicker than that of the upper light confinement layer 3B is also effective for high output operation by combining with the structure of the n-type lower clad layer described later.

  Moreover, it is preferable that the active layer has a strained multiple quantum well structure for high output operation. As for the strain amount of the well layer, if the absolute value is 0.5% or more, high output operation is possible regardless of whether the strain is compressive strain or tensile strain. More preferably, the well layer has compressive strain. The strain compensation structure in which a tensile strain is generated in the barrier layer and the strain amount of the well layer is 1.5% or more can realize a high output operation more advantageously.

As an example of the preferable MQW-GRIN-SCH structure as described above, a GaInAsP-based material is used in this embodiment, and the composition wavelength of the material of each layer is as shown in Table 1. In Table 1, the light confinement layer is shown for each layer of the lower light confinement layer 3A, but the same applies to the upper light confinement layer 3B. That is, 3A ₁ may be read as 3B ₁ or the like.

Table 1 Composition wavelength of each layer in MQW-GRIN-SCH structure shown in FIG.

The thicknesses of the upper light confinement layer 3B and the lower light confinement layer 3A are preferably 30 to 40 nm.
Note that the thickness and composition of the layer near the active layer are not limited to those shown above. For example, the structure of the optical confinement layer is not limited to the linear GRIN-SCH structure as long as the desired high output operation is possible.

(Doping to the active layer) In this embodiment, as disclosed in Japanese Patent Application Laid-Open No. 2002-368341 by the same applicant, the active layer 4 is doped with an n-type impurity. Thereby, since the element resistance is reduced, the thermal resistance of the element can be reduced, and a low power consumption operation is possible even at the time of high current injection. For example, selenium (Se), sulfur (S), silicon (Si), or the like can be used as the impurity. Further, p-type impurities such as zinc (Zn), beryllium (Be), and magnesium (Mg) may be used in place of the n-type impurity. Note that it is not always necessary that the entire region of the active layer 4 is doped with impurities, and a partial region may be used. Further, when the doping concentration is in the range of 1E + 17 cm ^{−3 to} 3E + 18 cm ⁻³ , it is particularly advantageous for high output operation. Note that if a desired high output operation is possible, the active layer may not be doped.

(Clad Layer Structure) Next, the structure of the clad layer, which is a feature of the present invention, will be described. 1B and 1C, the p-type upper clad layer 2B is made of InP doped with Zn. On the other hand, the n-type lower cladding layer 2A is doped with Se or the like, and is an ultrathin film of InP (the symbol is 2A ₁ ) and quaternary mixed crystal GaInAsP (the symbol is 2A ₂ ) in several molecular layers. As a superlattice crystal formed by alternately laminating.

GaInAsP in the superlattice crystal has the effect of increasing the refractive index of the n-type cladding layer regardless of the composition. However, the inventors pay attention to the fact that when crystal growth of GaInAsP having a small composition wavelength on InP, the crystal quality is greatly influenced by the difference in the growth apparatus and the growth conditions, in order to obtain a good GaInAsP crystal. It was found that the composition wavelength of GaInAsP is preferably 1.0 μm or more.
The composition and thickness of GaInAsP are determined so that the composition wavelength of GaInAsP and the composition wavelength of the superlattice crystal are set to desired values, respectively.

A method for controlling the composition wavelength of the superlattice crystal as described above will be described below. A superlattice crystal SL composed of an ultrathin film of InP and GaInAsP can be expressed by the following structural formula. Note that λQ represents a quaternary GaInAsP having a composition wavelength λ. However, N is an integer and represents the number of periods of the superlattice.
[(ΛQ) _p / (InP) _q ] · N (Formula 1)
Here, p and q are the number of molecular layers of GaInAsP and InP, respectively. The band gap energy Eg _SL and the refractive index n _SL of the superlattice crystal can be expressed as follows.
Eg _SL = p / (p + q) · Eg _λQ + q / (p + q) · Eg _InP (Formula 2)
n _SL = p / (p + q) · n _λQ + q / (p + q) · n _InP (Formula 3)
Further, from the formula 2, the composition wavelength Λ _SL of the superlattice crystal is expressed as follows.
Λ _SL = λ · Λ _InP (p + q) / (Λ _InP · p + λ · q) (Equation 3)
That is, the composition wavelength Λ _SL and the refractive index n _SL of the superlattice crystal can be set to desired values by appropriately selecting the composition wavelength λ of GaInAsP and the number of molecular layers p and q of each ultrathin film.

Further, the total thickness t of the superlattice crystal is t = (p + q) · N · t _1ML (Formula 4)
It is represented by Here, t _1ML is a film thickness corresponding to one molecular layer, and in the case of an InP system, it is 0.29344 nm (half of the lattice constant of InP).

  Control of the number of molecular layers p and q of each ultrathin film in the growth of the superlattice crystal is possible by obtaining the relationship between the number of molecular layers and the amount of raw material supplied in advance. When a raw material corresponding to one molecular layer is supplied, the growth surface is 100% covered with a new molecular layer in the two-dimensional epitaxial growth model. However, p and q are not necessarily integers.

In this embodiment, the composition wavelength λ of GaInAsP is 1.0 μm, and the number of molecular layers of each ultrathin film is p = 3 and q = 3. The composition wavelength of this superlattice crystal is 0.958 μm from Equation 3. However, Λ _InP = 0.92 μm was used. Further, the refractive index is 3.2059 from the equation (2). However, n _1.0Q = 3.2325 and n _InP = 3.1792 were used. Therefore, the refractive index of the n-type lower cladding layer 2A is larger than the refractive index of 3.1792 of the p-type upper cladding layer 2B made of InP.

  FIG. 3 schematically shows an effective refractive index distribution in a direction perpendicular to the substrate and an intensity distribution of light generated in the active layer 4. The light intensity distribution is biased toward the n-type lower cladding layer as shown in FIG. Therefore, light absorption by Zn which is a dopant in the p-type upper cladding layer is suppressed, so that a laser operation with a small internal loss is possible, and a high-power semiconductor laser device can be obtained.

  Further, when trying to realize the refractive index distribution as described above, conventionally, for example, the entire region of one of the cladding layers has been formed of a single quaternary mixed crystal GaInAsP. As a result, there has been a problem in the reliability of the manufactured semiconductor laser device. On the other hand, by using a superlattice structure composed of InP and GaInAsP as in this embodiment, accumulation of lattice strain energy in the crystal growth of the cladding layer is suppressed, and a high-power semiconductor laser device with excellent reliability is achieved. It is possible to obtain.

  In the present embodiment, the n-type lower cladding layer 2A is composed of a superlattice crystal composed of InP and GaInAsP. good. The n-type lower cladding layer 2A may be a superlattice crystal made of InP and InGaAs.

[Embodiment 2]
Next, a second embodiment of the present invention will be described. The second embodiment includes the semiconductor laser device shown in the first embodiment, an optical waveguide for guiding laser light emitted from the semiconductor laser device to the outside, the semiconductor laser device, and the optical waveguide. And optical coupling means for optically coupling the two. In this embodiment, an optical fiber is used as the optical waveguide and a lens is used as the optical coupling means. However, the present invention is not limited to these kinds of components.

  4 is a longitudinal sectional view showing a configuration of a semiconductor laser module according to Embodiment 2 of the present invention. In FIG. 4, this semiconductor laser module 50 has a laser device 51 corresponding to the semiconductor laser device shown in the first embodiment or the second embodiment. The semiconductor laser device 51 has a junction-down configuration in which the p-side upper electrode is joined to the heat sink 57a. As a housing of the semiconductor laser module 50, a Peltier element 58 as a temperature control device is disposed on the inner bottom surface of a package 59 formed of ceramic or the like. A base 57 is disposed on the Peltier element 58, and a heat sink 57 a is disposed on the base 57. The Peltier element 57 is supplied with a current (not shown), and is cooled and heated depending on its polarity, but mainly functions as a cooler in order to prevent oscillation wavelength shift due to temperature rise of the semiconductor laser device 51. That is, the Peltier element 58 is cooled and controlled to a lower temperature when the laser beam has a longer wavelength than the desired wavelength, and when the laser beam has a shorter wavelength than the desired wavelength. Is heated and controlled at a high temperature. Specifically, this temperature control is performed based on the detection value of the thermistor 58a disposed on the heat sink 57a and in the vicinity of the semiconductor laser device 51. The control device (not shown) normally has a temperature of the heat sink 57a. The Peltier element 58 is controlled so as to be kept constant. A control device (not shown) controls the Peltier element 58 so that the temperature of the heat sink 57a is lowered as the drive current of the semiconductor laser device 51 is increased. By performing such temperature control, the output stability of the semiconductor laser device 51 can be improved, which is also effective in improving the yield. The heat sink 57a is preferably formed of a material having high thermal conductivity such as diamond. This is because if the heat sink 57a is formed of a material having a high thermal conductivity, heat generation when a high current is applied is suppressed.

On the base 57, the heat sink 57a in which the semiconductor laser device 51 and the thermistor 58a are arranged, the first lens 52, and the current monitor 56 are arranged. Laser light emitted from the semiconductor laser device 51 is guided onto the optical fiber 55 through the first lens 52, the isolator 53, and the second lens 54. The second lens 54 is provided on the package 59 on the optical axis of the laser beam, and is optically coupled to an optical fiber 55 that is externally connected. The detector 56 monitors and detects light leaking from the reflective film side of the semiconductor laser device 51.
In order to realize a stable Raman gain in the excitation light source for the Raman amplifier, it is required that the oscillation wavelength is stabilized regardless of the drive current. From this viewpoint, as a more desirable modification of the present embodiment, a module having a fiber Bragg grating on a fiber pigtail without using the isolator 53 may be used.

  In the second embodiment, since the semiconductor laser device shown in the first embodiment is modularized, a high output and high reliability laser module can be obtained.

[Embodiment 3]
Next, a third embodiment of the present invention will be described. In the third embodiment, the semiconductor laser module shown in the modification of the second embodiment described above is applied to an optical amplifier, particularly a Raman amplifier.

  FIG. 5 is a block diagram showing a configuration of a Raman amplifier according to Embodiment 3 of the present invention. This Raman amplifier is used in a WDM communication system. In FIG. 5, this Raman amplifier uses semiconductor laser modules 60a to 60d having the same configuration as the semiconductor laser module shown in the second embodiment, and further includes an optical waveguide for transmitting signal light, and the semiconductor laser module. And an optical multiplexing means for causing the emitted excitation light to enter the optical waveguide. In the present embodiment, an optical fiber is used as the optical waveguide, and a coupler is used as the optical multiplexing means, but it is of course not limited to these types of components.

  Each of the semiconductor laser modules 60a and 60b outputs laser light having a plurality of oscillation longitudinal modes to the polarization combining coupler 61a via the polarization maintaining fiber 71, and each of the semiconductor laser modules 60c and 60d includes the polarization maintaining fiber. A laser beam having a plurality of oscillation longitudinal modes is output to the polarization beam combining coupler 61b via 71. Here, the laser beams oscillated by the semiconductor laser modules 60a and 60b have the same wavelength. The laser beams oscillated by the semiconductor laser modules 60c and 60d have the same wavelength, but are different from the wavelengths of the laser beams oscillated by the semiconductor laser modules 60a and 60b. This is because Raman amplification has polarization dependency, and is output as laser light whose polarization dependency has been eliminated by the polarization combining couplers 61a and 61b.

  The laser beams having different wavelengths output from the polarization combining couplers 61 a and 61 b are combined by the WDM coupler 62, and the combined laser light is amplified as pumping light for Raman amplification via the WDM coupler 65. It is output to the fiber 64. Amplifying fiber 64 to which the excitation light is input receives the signal light to be amplified and is Raman amplified.

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

  The control circuit 68 controls the laser output state of each of the semiconductor laser modules 60a to 60d, for example, the light intensity based on a part of the input amplified signal light, and provides feedback so that the gain band of Raman amplification has a flat characteristic. Control.

  In the Raman amplifier shown in the third embodiment, since the semiconductor laser module shown in the second embodiment is used, the Raman amplifier has high performance and excellent reliability.

  In the present embodiment, an example in which the optical module shown in the second embodiment is applied to a Raman amplifier is shown. However, the present invention is not limited to a Raman amplifier and can be applied to other types of optical amplifiers. Needless to say.

1 is a longitudinal section showing an outline of a semiconductor laser device according to a first embodiment of the present invention. 3 is a band gap diagram in the vicinity of an active layer of the semiconductor laser device according to the first embodiment of the present invention. It is a figure which shows the effective refractive index distribution in the direction perpendicular | vertical to the board | substrate in the semiconductor laser apparatus which concerns on Embodiment 1 of this invention, and the intensity distribution of the light which arises in the active layer 4. FIG. It is a longitudinal cross-sectional view which shows the structure of the semiconductor laser module which concerns on Embodiment 2 of this invention. It is a block diagram which shows the structure of the Raman amplifier which concerns on Embodiment 3 of this invention.

Explanation of symbols

1 InP semiconductor substrate 2A Lower clad layer 2A ₁ InP
2A ₂ GaInAsP
2B upper cladding layer 3A lower optical confinement layer _{3A 1, 3A 2, ···,} 3A n layer 3B upper optical confinement layer _3B 1 constituting the lower optical confinement _layer, 3B _{2, ···,} 3B _n upper optical confinement layer Active layer 4A Well layer 4B Barrier layer 5 GaInAsP contact layer 6A n-side lower electrode 6B p-side upper electrode 7 Mesa stripes 10, 20, 51 Semiconductor laser device 11 Reflective film 12 Reflective film f Front end face r Rear end face h1 envelope h2 envelopes 50, 60a, 60b, 60c, 60d Semiconductor laser module 52 First lens 53, 66 Isolator 54 Second lens 55 Optical fiber 56 Detector 57 Base 58 Peltier element 59 Package 61a Polarization combining coupler 64 For amplification Fiber 65 WDM coupler 67 Monitor light distribution coupler 68 Control circuit 70 Optical output fiber 71 polarization-maintaining fiber

Claims (8)

In a semiconductor laser device having a p-type cladding layer, an n-type cladding layer, and an active layer, the n-type cladding layer is composed of two or more layers having different compositions containing InP and GaInAsP, and the n-type cladding layer The refractive index of the semiconductor laser device is larger than the refractive index of the p-type cladding layer. The semiconductor laser device according to claim 1, wherein a band gap composition wavelength of the GaInAsP is 1.0 μm or more. 3. The semiconductor laser device according to claim 1, wherein the two or more layers having different compositions form a superlattice structure. The semiconductor laser device according to claim 1, wherein the active layer has a quantum well structure. The semiconductor laser device according to claim 1, wherein the semiconductor laser device has a separate confinement hetero (SCH) structure. The SCH structure is composed of a single layer or two or more layers, and the effective band gap composition wavelength of the superlattice structure is the composition wavelength of the layer having the smallest band gap composition wavelength among the layers constituting the SCH structure. The semiconductor laser device according to claim 5, wherein: The semiconductor laser device according to claim 1, an optical waveguide that guides laser light emitted from the semiconductor laser device to the outside, and light that optically couples the semiconductor laser device and the optical waveguide A semiconductor laser module comprising a coupling means. 8. A laser module according to claim 7, comprising: an optical waveguide for transmitting signal light; and optical multiplexing means for causing excitation light emitted from the semiconductor laser module to enter the optical waveguide. Optical fiber amplifier.

Images