JP2006108370A - Distributed feedback semiconductor laser device and semiconductor laser module employing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DFB laser capable of obtaining an output essentially obtainable upon laser oscillation. <P>SOLUTION: In the DFB laser 1 having an MQW-SCH active layer 4 and a grating provided on the MQW-SCH active layer 4 in a lamination structure provided on an n-type semiconductor substrate 2, a difference is more than 150 meV between the oscillation wavelength of the DFB laser 1 and the wavelength of a compound semiconductor band gap constituting the grating layer 6 of the grating. Here, a high refractive index semiconductor material is made to correspond to a semiconductor material having the smallest band gap energy among semiconductor materials constituting the grating. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a distributed feedback semiconductor laser element and a semiconductor laser module using the same.

  In recent years, CATV systems and mobile communication systems use orthogonal frequency division multiplexing (OFDM), which uses multiple subcarriers to transmit in parallel at low speed, thereby enabling high-speed transmission of high-band multimedia communication. Have achieved. As the light source, a distributed feedback laser (Distributed Feedback laser; hereinafter referred to as DFB laser) having excellent single wavelength characteristics is generally used.

  In particular, in a relatively short-distance urban trunk line system and subscriber system, an uncooled DFB that can be directly modulated and does not perform temperature control of the element, for example, is used without being cooled by an element cooling component such as a Peltier element. The introduction of a laser is under consideration. Such an uncooled DFB laser is required to operate in a wide temperature range, for example, −40 ° C. to + 85 ° C. so that it can be used in an environment where the temperature is not controlled.

In general, a DFB laser has a structure (hereinafter referred to as a diffraction grating) in which a real part or an imaginary part of a refractive index periodically changes in a resonator so that feedback is applied only to light of a specific wavelength. It has wavelength selectivity. Therefore, the oscillation wavelength λ _DFB of the DFB laser can be set independently of the gain peak wavelength λ _PEAK of the active layer. When the period of the diffraction grating of the DFB laser is Λ and the equivalent refractive index of the waveguide is n _eff , the oscillation wavelength λ _DFB of the DFB laser is expressed as λ _DFB = 2 · Λ · n _eff . Note that the gain peak wavelength λ _PEAK of the active layer corresponds to a photoluminescence (PL) wavelength λ _PL .

  In the DFB laser, the diffraction grating is provided in the p-side semiconductor layer, the n-side semiconductor layer, or both, but suppresses a leakage current near the buried structure and is between the oscillation wavelength and the wavelength having the gain peak. From the viewpoint that it must be precisely controlled, it is preferably provided in the p-side semiconductor layer formed on the active layer.

In the DFB laser, a buried hetero (BH) structure is often used. In the case of a BFB DFB laser, an n-type semiconductor substrate is often used because of the ease of embedding technology. Further, when a diffraction grating is provided in the p-side semiconductor layer when an n-type semiconductor substrate is used, the diffraction grating is formed after the active layer is formed, and the active layer corresponding to the gain peak wavelength λ _PEAK is formed. After measuring the PL wavelength λ _PL , the period Λ of the diffraction grating that determines the oscillation wavelength λ _DFB can be determined. Therefore, it is possible to easily control the detuning amount Δλ (Δλ = λ _DFB −λ _PEAK ), which is the difference between the gain peak wavelength λ _PEAK and the oscillation wavelength λ _DFB necessary for obtaining good laser oscillation characteristics. It is.
Further, when the diffraction grating is provided in the p-side cladding layer, the distance from the active layer can be increased, so that the regrowth conditions when embedding the periphery of the diffraction grating can be stabilized.

  An example of the DFB laser as described above will be described with reference to FIG. The DFB laser described here is described in Patent Document 1.

  The DFB laser 100 shown in FIG. 6 has a BH structure in which the oscillation wavelength is set to 1550 nm and the resonator length L is 300 μm. Specifically, an n-InP buffer layer 103, an MQW-SCH active layer 104, a p-InP spacer layer 105, a GaInAsP diffraction grating layer 106, and a GaInAsP diffraction grating layer 106 are embedded on an n-InP substrate 102. It has a laminated structure of an −InP buried layer 107 and a p-InP upper cladding layer 108.

  Here, the GaInAsP diffraction grating layer 106 and the p-InP buried layer 107 form a diffraction grating for controlling the oscillation wavelength. That is, the refractive index coupled DFB laser is provided with a diffraction grating that periodically changes the refractive index in the resonator. In the refractive index coupled DFB laser, the real part of the complex refractive index whose refractive index is dominant is periodically fluctuated inside the resonator.

    Of the laminated structure, the p-InP upper cladding layer 108, the p-InP buried layer 107, the GaInAsP diffraction grating layer 106, the p-InP spacer layer 105, the MQW-SCH active layer 104, and the n-InP buffer layer 103. The upper layer is processed in a mesa stripe shape so that the MQW-SCH active layer 104 has a width of about 1.5 μm. On both sides of the mesa stripe, a current (carrier) block layer composed of a p-type semiconductor layer (p-InP layer) 111 and an n-type semiconductor layer (n-InP layer) 112 is laminated, and the BH structure is formed. Is formed.

  A p-InP cladding layer 109 and a p-GaInAs contact layer 110 are stacked on the p-InP upper cladding layer 108 and the layers (n-InP layers) 112 made of n-type semiconductors on both sides thereof. Further, on the p-GaInAs contact layer 110, a Ti / Pt / Au multilayer metal film is formed as the p-side electrode 114, and the insulating film 115 is formed except for the region where the p-type electrode 114 is formed. . Further, an AuGeNi film is formed as an n-side electrode 116 on the back surface of the n-InP substrate 102.

  Further, a trench 113 is formed so as to penetrate the current (carrier) blocking layer in order to reduce parasitic capacitance. Further, for the purpose of increasing the output, a non-reflective coating film (not shown) is formed on the front end face (outgoing end face) of the DFB laser 100, and a highly reflective coating film (not shown) is formed on the rear end face. ing.

JP 2003-234541 A

  FIG. 7 is a band diagram of the conduction band in the vicinity of the MQW-SCH active layer 104 of the DFB laser 100. As shown in FIG. 7, the MQW-SCH active layer 104 includes a plurality of barrier layers 117, a well layer 118, and a separate light confinement layer (hereinafter referred to as SCH layer) 119. Further, the p-InP spacer layer 105 and the p-InP buried layer 107 on the MQW-SCH active layer 104 have a band diagram composed of solid lines, and the portion where the GaInAsP diffraction grating layer 106 exists has a band diagram composed of dotted lines. is doing.

Here, the DFB laser 100 shown in FIG. 6 injects current into the MQW-SCH active layer 104, and when the injection current exceeds a threshold value, the coupling of electrons and holes in the well layer 118 is active. To be done.
In practice, however, electrons are not limited to the well layer 118 but overflow to the outside of the MQW-SCH active layer 104, resulting in a problem that an output that should originally be obtained cannot be obtained.

  The inventors investigated the cause and found the following. The band energy of the conduction band of the p-InP spacer layer 105 should ideally be as shown by the solid line in FIG. However, it was actually found that the value was smaller than the design value, as indicated by the alternate long and short dash line. This is because the band gap energy of the GaInAsP diffraction grating layer 106 is very small compared to the band gap energy of the p-InP spacer layer 105, so that the band energy of the conduction band of the relatively thin spacer layer 105 is the GaInAsP diffraction grating layer. Under the influence of 106, it becomes smaller than the original value, and as a result, the barrier against electrons of the p-InP spacer layer 105 is reduced, and it is considered that the overflow of electrons occurred.

  Accordingly, an object of the present invention is to provide a DFB laser (distributed feedback semiconductor laser element) capable of obtaining an output that should be originally obtained during laser oscillation.

  The invention according to claim 1 is composed of an n-type semiconductor layer and a p-type semiconductor layer laminated on a semiconductor substrate, an active layer laminated between the two semiconductor layers, and a semiconductor material having a different band gap energy. A distributed feedback semiconductor laser device comprising a diffraction grating having a periodic structure, wherein the diffraction grating is formed in the p-type semiconductor layer, and a band gap energy value of a high refractive index semiconductor material in the diffraction grating The absolute value of the difference between the values obtained by converting the oscillation wavelength of the distributed feedback semiconductor laser device into energy is 150 meV or more. Here, the high refractive index semiconductor material corresponds to a semiconductor material having the smallest band gap energy among the semiconductor materials constituting the diffraction grating.

  The distributed feedback semiconductor laser element according to claim 2 is characterized in that, in the above invention, the semiconductor substrate is n-type.

  The distributed feedback semiconductor laser device according to claim 3 is characterized in that, in the above invention, the duty ratio of the diffraction grating is 30% or less.

  The distributed feedback semiconductor laser device according to claim 4 is characterized in that, in the above invention, the distributed feedback semiconductor laser device is a refractive index coupled type.

  The distributed feedback semiconductor laser device according to claim 5 is characterized in that, in the above invention, the product of the coupling coefficient κ and the resonator length L of the distributed feedback semiconductor laser device is 0.8 or more and 2.0 or less. And

  A distributed feedback semiconductor laser device according to a sixth aspect is characterized in that, in the above invention, the diffraction grating includes at least one phase shift region.

  The distributed feedback semiconductor laser device according to claim 7 is characterized in that, in the above invention, the product of the coupling coefficient κ and the resonator length L of the distributed feedback semiconductor laser device is 1.6 or more and 4.0 or less. And

  In the distributed feedback semiconductor laser device according to claim 8, in the above invention, the absolute value of the detuning amount Δλ, which is the difference between the gain peak wavelength and the oscillation wavelength of the distributed feedback semiconductor laser device, is 20 nm or less. Features.

  The distributed feedback semiconductor laser device according to claim 9 is the above-described invention, wherein the active layer has a well layer and a barrier layer, and at least the p-type semiconductor layer has a band gap energy larger than that of the barrier layer, and The optical confinement layer has a band gap energy smaller than that of the innermost layer of the p-type semiconductor layer.

  A semiconductor laser module according to a tenth aspect of the present invention includes the distributed feedback semiconductor laser element according to any one of the first to tenth aspects, wherein the optical confinement layer includes a plurality of layers having different band gap energies. It is characterized by comprising.

  According to the DFB laser and the semiconductor laser module according to the present invention, an output that should be originally obtained can be obtained.

  A partially broken perspective view of a DFB laser 1 according to an embodiment of the present invention is shown in FIG. In the DFB laser 1 of the present embodiment, the difference between the band gap energy of the diffraction grating layer 6 and the value obtained by converting the oscillation wavelength of the DFB laser into an energy band gap is 150 meV or more, compared to the conventional DFB laser. It is characterized in that it is composed of a simple compound semiconductor. In this way, the spacer layer 5 is not affected by the diffraction grating layer 6, and the band energy of the conduction band of the spacer layer 5 can be maintained in an ideal state. As a result, the overflow of electrons from the MQW-SCH layer 4 can be suppressed.

  Of the laminated structure, the upper cladding layer 8, the buried layer 7, the diffraction grating layer 6, the spacer layer 5, the MQW-SCH active layer 4, and the upper layer of the buffer layer 3 are arranged so that the MQW-SCH active layer 4 It is processed into a mesa stripe shape so as to have a width of mode unity. A current (carrier) blocking layer having a stacked structure of a layer 11 made of a p-type semiconductor and a layer 12 made of an n-type semiconductor is formed on both sides of the mesa stripe, and the DFB laser 1 has a BH structure.

  On the upper clad layer 8 and the layer 12 made of n-type semiconductor on both sides thereof, a clad layer 9 made of p-type semiconductor and a contact layer 10 are sequentially laminated. An insulating film 15 is formed on the contact layer 10 except for the region where the p-side electrode 14 is provided. An n-side electrode 16 is provided on the back surface of the n-type semiconductor substrate 2. Further, in order to reduce parasitic capacitance, a groove 13 is formed so as to penetrate the current (carrier) blocking layer. Further, a non-reflective coating film (not shown) is formed on the front end face (outgoing end face) of the DFB laser 1, and a highly reflective coating film (not shown) is formed on the rear end face.

  As the n-type semiconductor substrate 2, an InP substrate having a thickness of about 120 μm can be used. The buffer layer 3, the spacer layer 5, the buried layer 7, the upper clad layer 8, the clad layer 9, the p-type semiconductor layer 11 and n As the layer 12 made of a type semiconductor, InP can be used. In this case, GaInAsP can be used for the diffraction grating layer 6, and GaInAs can be used for the contact layer 10.

  Next, the configuration of the MQW-SCH active layer 4 will be described using a band diagram. That is, the MQW-SCH active layer 4 includes a plurality of barrier layers 17, well layers 18, and SCH layers 19, as shown in FIG. Each of these layers is made of GaInAsP lattice-matched to InP.

Here, the SCH layer 19 is formed of a semiconductor layer having a band gap energy larger than that of the barrier layer 17 and smaller than that of the spacer layer 5 which is the innermost layer of the p-type semiconductor layer. By providing such an active layer and an optical confinement waveguide layer separately, it is possible to obtain an effect that the optical confinement can be strengthened while suppressing the waveguide loss. Furthermore, as described above, when the SCH layer 19 is formed with a plurality of layers, current injection can be performed more efficiently than when the SCH layer 19 is formed as a single layer, and carrier overflow can be suppressed. An effect can be obtained.
In addition, it is preferable that n-type or p-type doping is performed on the MQW-SCH active layer 4 so that the carrier density is about 1 × 10 ¹⁸ [cm ⁻³ ], because the resistance becomes low.

  Further, when the duty ratio of the diffraction case A is smaller than 30%, more preferably smaller than 20%, the proportion of the diffraction grating layer 6 having a small band gap energy in the diffraction grating is decreased. As a result, the influence of the conduction band of the spacer layer 5 on the band energy can be reduced.

  Further, when the phase shift region 2X of the type in which the diffraction grating layer 6 periodically arranged in the diffraction grating is removed as shown in FIG. 3 can be provided, the unity of the emitted light can be improved, As in the case where the duty ratio is smaller than 30%, the proportion of the diffraction grating layer 6 having a small band gap energy in the diffraction grating is reduced. As a result, the influence of the conduction band of the spacer layer 5 on the band energy can be reduced.

  In addition, the product of the coupling coefficient κ and the resonator length L of the DFB laser has the phase shift region 2X for the purpose of maintaining high single-mode characteristics while realizing high optical output efficiency and low threshold current. If not, it is preferably 0.8 or more and 2.0 or less, and if the phase shift region 2X is provided, it is preferably 1.6 or more and 4.0 or less.

Furthermore, the absolute value of the detuning amount Δλ of the DFB laser of the present invention is preferably 20 nm or less. By doing in this way, the favorable laser oscillation characteristic which can obtain single mode oscillation in a wide temperature range with the DFB laser concerning the present invention is obtained.

  In the DFB laser having the above configuration, the influence of the diffraction grating layer 6 on the band energy of the conduction band of the spacer layer 5 is small, so that the output of the DFB laser is lower than the output value that should be originally obtained. The problem can be solved. Such a DFB laser is particularly suitable as an uncooled DFB laser used in an environment where the temperature is not controlled. This is because in the uncooled DFB laser, the thermal energy of electrons increases when used at a high temperature, and even electrons injected into the well layer 18 easily leak from the well layer 18 and exceed the spacer layer 5. .

  First, the configuration of the DFB laser according to the present embodiment will be described with reference to FIGS. FIG. 1 is a partially broken perspective view showing the configuration of the DFB laser of this embodiment, and FIG. 2 is a cross-sectional view of the DFB laser taken along the line II in FIG.

DFB laser 1, set the oscillation wavelength of 1310nm (940meV), a DFB laser of BH structure of the resonator length is 3 00Myuemu, as shown in FIG. 1, on the n-InP substrate 2, n-InP Buffer layer 3, MQW-SCH active layer 4, p-InP spacer layer 5 having a thickness of about 100 nm, diffraction grating layer 6 made of GaInAsP having a band gap energy of 1230 meV, and p-InP in which the diffraction grating layer 6 is embedded It has a laminated structure of a buried layer 7 and a p-InP upper cladding layer 8.

  The band gap wavelength of the well layer 18 of the MQW-SCH active layer 4 is 1310 nm. Although not shown in detail in the figure, the SCH layer 19 is composed of four layers whose band gap wavelength changes from 950 to 1100 nm (1300 to 1127 meV), and the absolute value of the inclination is 5.1 meV / nm. . The absolute value of the inclination refers to the inclination when the apex of the SCH layer closest to the barrier layer and the SCH layer closest to the spacer layer 5 are connected. Here, the absolute value of the tilt is preferably about 4.5 to 7.6 meV / nm in the case of a DFB laser whose oscillation wavelength is 1310 to 1650 nm. The optimum value is, for example, about 4.5 to 5.6 meV / nm when the oscillation wavelength is around 1310 nm, and 5.5 to 6.7 meV when the DFB laser has the oscillation wavelength of 1470 to 1530 nm. In the case of a DFB laser having an oscillation wavelength of about 1510 to 1570 nm, about 5.4 to 6.6 meV / nm, and in the case of a DFB laser having an oscillation wavelength of 1550 to 1610 nm, 6.6 to 7.6 meV. / Nm is preferable.

  The diffraction grating composed of the GaInAsP diffraction grating layer 6 and the p-InP buried layer 7 has a thickness of about 20 nm, a period of about 200 nm, and a duty ratio of 30%. The band gap energy of the GaInAsP diffraction grating layer constituting the diffraction grating is 1230 meV. Further, as shown in FIG. 3, the phase shift region 2X is provided in the diffraction grating. In the case of the present embodiment, a phase shift region 2X in which the phase of the diffraction grating is shifted by π / 2 is provided at the center of the diffraction grating formed in the resonator direction, and the entire diffraction grating is a λ / 8 phase shift type. A diffraction grating is formed.

  Of the laminated structure, p-InP upper cladding layer 8, p-InP buried layer 7, GaInAsP diffraction grating layer 6, p-InP spacer layer 5, MQW-SCH active layer 4, and n-InP buffer layer 3 The layer is processed into a mesa stripe so that the MQW-SCH active layer 4 has a width of about 1.5 μm. Then, both sides of the mesa stripe are buried with a current (carrier) block layer having a stacked structure of the p-InP layer 11 and the n-InP layer 12 to form a BH structure.

  On the p-InP cladding layer 8 and the n-InP layers 12 on both sides thereof, a p-InP cladding layer 9 and a highly doped GaInAs contact layer 10 having a film thickness of about 2 μm are sequentially stacked. An insulating film 15 is formed on the doped GaInAs contact layer 10 except for the region where the p-side electrode 14 is provided. The p-side electrode 14 is a Ti / Pt / Au multilayer metal film. An AuGeNi film is provided as the n-side electrode 16 on the back surface of the n-InP substrate 2. In order to reduce the parasitic capacitance, the p-GaInAs contact layer 10, the p-InP cladding layer 9, and the current (carrier) block layer composed of the p-InP layer 11 and the n-InP layer 12 are penetrated. 13 is formed. Further, a non-reflective coating film (not shown) is formed on the front end face (outgoing end face) of the DFB laser 1, and a highly reflective coating film (not shown) is formed on the rear end face.

  In producing the DFB laser 1 described above, first, using an MOCVD apparatus, an n-InP buffer layer 3, an MQW-SCH active layer 4, a p- An InP spacer layer 5 and a diffraction grating layer 6 were grown. Next, a resist film having a diffraction grating pattern with a period of about 200 nm was formed on the diffraction grating layer 6 using an electron beam (EB) drawing apparatus. By using the semiconductor material, the detuning amount Δλ becomes +0 nm. Further, at the time of forming the resist film, the resist film is left in the portion corresponding to the phase shift region 2X. Subsequently, etching was performed using a dry etching apparatus so as to penetrate the GaInAsP diffraction grating layer 6 from above the resist film.

  Next, in order to prevent the GaInAsP diffraction grating layer 6 from being deformed by heat, the growth temperature is lowered and a MOCVD apparatus is used to form a diffraction grating by stacking the p-InP buried layer 7 as shown in FIG. Thereafter, the p-InP upper cladding layer 8 was grown.

Next, using a plasma CVD apparatus, a SiN _X film is formed on the entire surface of the substrate, and stripes (width: 4 μm) extending in the direction of the resonator are formed by photolithography and reactive ion etching (RIE). Etching was performed so that the SiN _X film remained, thereby forming a SiN _X film mask (not shown). Subsequently, the upper part of the p-InP upper cladding layer 8, the diffraction grating, the p-InP spacer layer 5, the MQW-SCH active layer 4, and the n-InP buffer layer 3 is etched using the SiN _X film mask as an etching mask. Thus, a mesa stripe in which the MQW-SCH active layer 4 has a width of about 1.5 μm was formed.

Next, using the SiN _X film mask as a selective growth mask, the p-InP layer 11 and the n-InP layer 12 are selectively grown sequentially to fill both sides of the mesa stripe to form a current (carrier) block layer. . Thereafter, the SiN _X film mask was removed, and a p-InP cladding layer 9 and a highly doped GaInAs contact layer 10 having a thickness of about 2 μm were grown.

  Next, the n-InP layer 12 and the p-InP layer 12 were etched to form grooves 13, and then an insulating film 15 was formed on the entire surface. Next, a part of the insulating film 15 was opened, and a Ti / Pt / Au multilayer metal film as a p-side electrode 14 was provided in a pad shape on the highly doped GaInAs contact layer 10. Further, the back surface of the n-InP substrate 2 was polished so that the substrate thickness was about 120 μm, and an AuGeNi film was provided as the n-side electrode 16 on the back surface of the n-InP substrate 2. Further, a non-reflective coating film was formed on the front end face of the DFB laser 1 and a highly reflective coating film was formed on the rear end face, and then formed into chips.

  Next, the DFB laser 1 made into a chip was modularized. FIG. 4 shows a semiconductor laser module 23 including the DFB laser 1, the optical element 21, and the optical fiber 22. As shown in FIG. 4, the semiconductor laser module 23 collects the light emitted from the front end face 24 of the DFB laser 1 by the optical element 21 and couples it to one end of the optical fiber 22. Then, light emitted from the other end of the optical fiber 22 is used.

  A lens is used for the optical element 21 to have the above action, and an isolator, a prism for changing the optical path, and the like are incorporated as necessary to prevent the return light from the optical fiber 22. Here, reference numeral 25 denotes a rear end face of the DFB laser 1 and reference numeral 26 denotes a light receiving element for monitoring the optical output of the DFB laser 1. The semiconductor laser module 23 is not provided with a temperature adjustment function.

  A similar semiconductor laser module using the semiconductor laser module and the DFB laser 1 according to the related art shown in FIG. 6 was used as a comparative example, and the characteristics were compared under the same conditions. The results are shown in FIGS. 5 (a) and 5 (b). FIG. 5A shows the current / light output characteristics of the semiconductor laser module according to this example, and FIG. 5B shows the current / light output characteristics of the semiconductor module of the comparative example using the DFB laser according to the prior art. is there.

  As is clear from FIGS. 5A and 5B, the semiconductor laser module according to the present example maintained the linearity of the optical output even when the injection current was high injection of 200 mA. In the semiconductor module using the split DFB laser according to the prior art, the linearity of the optical output cannot be maintained.

  In this embodiment, a DFB laser using an InP substrate is used. However, all are examples, and the present invention is not limited to this embodiment. For example, even in a DFB laser using a GaAs substrate, the effect of the present invention can be obtained if the difference between the oscillation wavelength of the DFB laser and the band gap energy of the semiconductor material constituting the diffraction grating layer is 150 meV or more. . An example of such a DFB laser is a red DFB laser used for reading and writing of an optical disk.

  Further, even if the DFB laser uses a GaAs substrate and is a long wavelength DFB laser using a semiconductor containing nitride in the well layer, the oscillation wavelength of the DFB laser and the semiconductor material constituting the diffraction grating layer If the difference in the band gap energy is 150 meV or more, the effect of the present invention can be obtained.

  In this embodiment, a DFB laser having a BH structure is employed, but the present invention can also be applied to a ridge type or buried ridge type laser.

It is a partial fracture perspective view showing an outline of composition of a DFB laser concerning the present invention. 2 is a band diagram of a conduction band in the vicinity of the MQW-SCH layer of the DFB laser of FIG. 1. FIG. 2 is a cross-sectional view of the distributed feedback semiconductor laser element taken along line I-I in FIG. 1. 1 is a schematic configuration diagram of a semiconductor laser module according to a first embodiment. (A) is the current / light output characteristic of the semiconductor laser module according to this embodiment, and (b) is the current / light output characteristic of the semiconductor module of the comparative example using the DFB laser according to the prior art. It is a partially broken perspective view which shows the outline | summary of a structure of the DFB laser concerning a prior art. FIG. 7 is a band diagram of a conduction band in the vicinity of the MQW-SCH layer of the DFB laser of FIG. 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 DFB laser 2,102 Substrate 3,103 Buffer layer 4,104 MQW-SCH active layer 5,105 Spacer layer 6,106 Diffraction grating layer 7,107 Buried layer 8,108 Upper clad layer 9,109 Cladding layer 10 , 110 Contact layer 11, 111 Layer made of p-type semiconductor 12, 112 Layer made of n-type semiconductor 13, 113 Groove 14, 114 P-side electrode 15, 115 Insulating film 16, 116 N-side electrode 17, 117 Barrier layer 18, 118 Well layer 19, 119 SCH layer 2X Phase shift region 20 Semiconductor laser element 21 Optical element 22 Optical fiber 23 Semiconductor laser module 24 Front end face 25 Rear end face 26 Light receiving element

Claims (11)

Diffraction having a periodic structure composed of an n-type semiconductor layer and a p-type semiconductor layer stacked on a semiconductor substrate, an active layer stacked between the two semiconductor layers, and semiconductor materials having different bandgap energy levels A distributed feedback semiconductor laser device comprising a grating, wherein the diffraction grating is formed in the p-type semiconductor layer, and a band gap energy value of a high refractive index semiconductor material in the diffraction grating and the distributed feedback semiconductor laser. An absolute value of a difference between values obtained by converting the oscillation wavelength of the element into energy is 150 meV or more. 2. The distributed feedback semiconductor laser device according to claim 1, wherein the semiconductor substrate is n-type. 3. The distributed feedback semiconductor laser device according to claim 1, wherein a duty ratio of the diffraction grating is 30% or less. 4. The distributed feedback semiconductor laser device according to claim 1, wherein the distributed feedback semiconductor laser device is a refractive index coupling type. 5. 5. The distributed feedback according to claim 1, wherein a product of a coupling coefficient κ and a resonator length L of the distributed feedback semiconductor laser element is 0.8 or more and 2.0 or less. Type semiconductor laser device. 5. The distributed feedback semiconductor laser device according to claim 1, wherein the diffraction grating includes at least one phase shift region. 6. 7. The distributed feedback semiconductor laser device according to claim 6, wherein the product of the coupling coefficient κ and the resonator length L of the distributed feedback semiconductor laser device is 1.6 or more and 4.0 or less. 8. The distribution according to claim 1, wherein an absolute value of a detuning amount Δλ which is a difference between a gain peak wavelength and an oscillation wavelength of the distributed feedback semiconductor laser element is 20 nm or less. Feedback type semiconductor laser device. The active layer includes a well layer and a barrier layer, and an optical confinement layer having a band gap energy larger than that of the barrier layer on the p-type semiconductor layer side and smaller than that of the innermost layer of the p-type semiconductor layer. The distributed feedback semiconductor laser device according to claim 1, wherein the distributed feedback semiconductor laser device is provided. The distributed feedback semiconductor laser device according to claim 9, wherein the optical confinement layer includes a plurality of layers having different band gap energies. 11. A semiconductor laser module having no temperature adjustment function, wherein the distributed feedback semiconductor laser element according to claim 1 is incorporated.

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