JP2008172088A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost integrated semiconductor laser device to which a coating film for an end surface of a resonator is applied, as a coating film suitable for obtaining high-output characteristics and high reliability, wherein the semiconductor laser device is also a multiwavelength semiconductor laser device comprising a plurality of semiconductor lasers having different oscillating wavelengths. <P>SOLUTION: In a semiconductor laser device, a semiconductor laser 1 having an oscillating wavelength λ1 and a semiconductor laser 2 having an oscillating wavelength λ2 are formed on the same substrate 101. Rear end surface 140 of each resonator of the lasers is covered with an end surface coating film 130, wherein the coating film 130 is formed by laminating, four cycles or more alternately from the end surface side, low refractive index dielectric layers having a refractive index of n1≤1.5 and high refractive index dielectric layers having a refractive index of n2≥2.3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dual wavelength semiconductor laser device used for a light source of an optical disk or the like.

  Semiconductor lasers are widely used in many fields of electronics and optoelectronics, and are indispensable as optical devices. In particular, optical disc devices such as CD (compact disc) and DVD (digital versatile disc) are currently actively used as large-capacity recording media. A recording medium (media) used for a DVD has a smaller pit length and track interval than a CD medium. Therefore, the wavelength of the semiconductor laser used is shorter for DVD than for CD. Specifically, the oscillation wavelength of the CD laser is in the 780 nm band (765 to 800 nm), whereas the oscillation wavelength of the DVD laser is in the 660 nm band (645 to 665 nm). Therefore, in order for one optical disc apparatus to detect both CD and DVD information, two light sources of a 780 nm band laser (infrared semiconductor laser) and a 660 nm band laser (red semiconductor laser) are required. 2. Description of the Related Art In recent years, in order to reduce the size and weight of an optical pickup device that constitutes an optical disk device, a two-wavelength type semiconductor laser element that emits laser light of two types of wavelengths in one semiconductor chip has been developed and is becoming popular. .

  Further, the recording speed is increasing with the increase in recording capacity, and the trend is particularly remarkable for CD and DVD. In order to increase the speed, it is necessary to increase the output of the semiconductor laser device. In recent years, in the infrared semiconductor laser device for CD and the red semiconductor laser device for DVD, a high output exceeding 200 to 300 mW has been required from the market.

  FIG. 18A is a top perspective view of a conventional two-wavelength semiconductor laser device, and FIG. 18B is a plan view of the main part of the device. As shown in FIGS. 18A and 18B, the conventional two-wavelength semiconductor laser device 100 emits the red semiconductor laser 10 that emits the laser beam 15 in the 660 nm band from the laser emission region 17 and the laser beam 25 in the 780 nm band. It is composed of two lasers, an infrared semiconductor laser 20 that emits from the laser emission region 27. In this laser device 100, a groove 90 is provided to electrically separate the red semiconductor laser 10 and the infrared semiconductor laser 20 from each other. Further, by applying a bias to each of the p-side electrode 30 and the n-side electrode 40 provided on the upper surface side and the lower surface side of the laser device 100, each laser 10 and 20 can be operated individually. Further, the laser device 100 has a front end face 50 for extracting laser light and a rear end face 60 for reflecting light into the resonator. End face films 70 and 72 are formed on the front end face 50, and a multilayer coat film 80 is laminated on the rear end face 60.

  By the way, as one of effective means for increasing the output, Non-Patent Document 1 describes a method in which the reflectance of two end faces forming a resonator of a semiconductor laser is asymmetric. This is a common method for a semiconductor laser used for writing in an optical disk device. This method is a method of making the reflectance of each end face asymmetric by coating each end face forming the resonator with a dielectric multilayer film. Specifically, the laser beam is out of the end faces forming the resonator. Is set to a low reflectivity of about 10%, and the reflectivity of the opposite end face (rear end face) is set to a high reflectivity of about 85%.

  The reflectance of the dielectric multilayer film can be controlled by the refractive index of the dielectric used, the layer thickness, and the number of layers to be stacked. Patent Document 2 discloses that in a two-wavelength semiconductor laser device, a high-reflection rear coat film in which thin films of a low refractive index material and thin films of a high refractive index material are alternately stacked is provided on the rear end face of the resonator. Here, in correspondence with the dual wavelength, the thickness of the film that coats both end faces is obtained by using the average value λ = (λ1 + λ2) / 2 of the oscillation wavelengths of both semiconductor laser diodes and the optical length d = (1/4 + j ) × λ (j is an integer of 0 or more). Thereby, a film thickness can be set so that the reflectance of a back end surface may be 75% or more about both a red wavelength and an infrared wavelength.

As described above, in order to reduce the operating current toward increasing the output of the semiconductor laser, the rear end face (rear end face) of the resonator for both the red (660 nm band) wavelength and the infrared (780 nm band) wavelength. It is necessary to improve the slope efficiency by increasing the reflectance. In addition, a pair of a low refractive index film (SiO ₂ film) and a high refractive index film (α-Si: H film (hydrogenated amorphous silicon film)) is formed in multiple cycles as a film (rear coat film) for coating the rear end face. By laminating over, the rear end face can be made highly reflective. In addition, the greater the difference in refractive index between the low refractive index film and the high refractive index film, the higher the reflectance of the rear end face. Here, the target reflectance is required to be 85% or more for both wavelengths. Further, as a measure against reliability (inhibition of end face deterioration), it is necessary to select a material having an extinction coefficient close to 0 as a coating film material in order to reduce light absorption loss at the end face.
Japanese Patent No. 3290646 JP 2001-257413 A JP 2004-327581 A Edited by Kenichi Iga, Semiconductor Laser, 1st Edition, Ohm Corporation, p. 238

  As described above, as a method of increasing the reflectivity of the rear end face of the resonator, generally, a low-refractive index film and a high-refractive index film are used as one pair, and the number of pairs is increased to increase the reflectivity. There is a way to achieve it. At this time, the larger the refractive index difference between the low refractive index film and the high refractive index film, the higher the reflectance.

However, materials such as a-Si and a-Si: H that are used as the high refractive index material in the end face coating process disclosed in Patent Document 2 are the extinction coefficients of these materials. _Since it is larger than materials such as ₂ O ₅ and Nb ₂ O ₅ , it causes light absorption at the resonator end face, and as a result, there is a possibility that deterioration occurs at the resonator end face during high output operation. The magnitude relationship between the refractive index and extinction coefficient of a-Si, a-Si: H, Ta ₂ O ₅ and Nb ₂ O ₅ is as follows.

Refractive index a-Si> a-Si: H> Nb ₂ O ₅ > Ta ₂ O ₅
Extinction coefficient a-Si >> a-Si: H >> Nb ₂ O ₅ , Ta ₂ O ₅
In addition, in the a-Si-based high refractive index film formed by sputtering, a larger number of particles are generated than in the oxide film, so that the particles accumulate in the chamber and cause a decrease in yield.

  In Patent Document 1, a rear coat film using a first dielectric layer and a second dielectric layer made of niobium oxide achieves high reflectivity at the resonator end face and absorbs light at the resonator end face. A method for reducing losses is disclosed. However, this patent document describes that the oscillation wavelength is limited to a wavelength of 400 nm or shorter than 400 nm, and the target is a monochromatic blue-violet laser, and the application to a multi-wavelength laser is not described.

Patent Document 3 shows an example of a multilayer coating film including a tantalum oxide (Ta ₂ O ₅ ) film that achieves a reflectance of at least 40% or more. According to this multilayer coating film, since the extinction coefficient of tantalum oxide is close to zero, the light absorption loss at the resonator end face can be reduced. Further, since SiO ₂ which is a low refractive index material and Ta ₂ O ₅ which is a high refractive index material are laminated, a high reflectance can be achieved. In this case, in the case of a monochromatic semiconductor laser, it is sufficient that the reflectance can be increased only for the oscillation wavelength. However, in the case of a multi-wavelength semiconductor laser having two or more wavelengths, it is required to increase the reflectivity for both oscillation wavelengths, so it is necessary to ensure a wide wavelength band that can increase the reflectivity. When using a pair of SiO ₂ and Ta ₂ O ₅ , as shown in FIG. 11, an increase in the reflectance at the red wavelength (660 nm) is expected by increasing the number of pairs. The possible wavelength band is gradually narrowed. As a result, the reflectance at the infrared wavelength (780 nm) decreases as the number of pairs increases. That is, tantalum oxide (Ta ₂ O ₅ ) is useful as a rear coat material for a monochromatic semiconductor laser, but is not suitable for a rear coat material for a two-wavelength semiconductor laser.

  Non-Patent Document 1 merely describes a general technique for obtaining a high output operation, and a high output suitable for a multiwavelength semiconductor laser device in which semiconductor lasers having a plurality of oscillation wavelengths are formed on the same substrate. It is hard to say that the operating conditions are disclosed.

  Accordingly, an object of the present invention is a multi-wavelength semiconductor laser device including a plurality of semiconductor lasers having different oscillation wavelengths, and a resonator end face coating film suitable for obtaining high output characteristics and high reliability is provided. It is to provide an integrated semiconductor laser device without increasing the manufacturing cost.

In order to achieve the above object, a semiconductor laser device according to the present invention includes a first semiconductor laser having a first oscillation wavelength λ1 and a second semiconductor laser having a second oscillation wavelength λ2 (λ1 <λ2). An integrated semiconductor laser device formed on the same substrate, comprising: a resonator composed of a plurality of semiconductor layers stacked on the substrate; and a reflective film covering a rear end face of the resonator, The reflective film is formed by alternately stacking four or more periods of the first dielectric layer and the second dielectric layer from the rear end face side, and the first refraction of the first dielectric layer is made. The index n1 is 1.5 or less, the second refractive index n2 of the second dielectric layer is 2.3 or more, and the first dielectric layer and the second dielectric layer are respectively At least 0.001 at the first oscillation wavelength λ1 and the second oscillation wavelength λ2. m ^-1 have the following extinction coefficient, reflectivity of the rear facet is 85% or more in the first two wavelength oscillation wavelength λ1 and the second oscillation wavelength .lambda.2.

  In the semiconductor laser device of the present invention, more preferably, the reflectance of the rear end face of the resonator is set to 90% or more at both the first oscillation wavelength λ1 and the second oscillation wavelength λ2.

  In the semiconductor laser device of the present invention, when the film thickness calculation wavelength is λ, the thickness of the first dielectric layer is λ / (4 × n1), and the thickness of the second dielectric layer is λ / It is preferable that it is (4 × n2).

In the semiconductor laser device of the present invention, it is preferable that the reflection film has an Al ₂ O ₃ film having a _third refractive index n3 between the first dielectric layer in the first period and the rear end face. . In this case, the film thickness calculation wavelength is λ, the thickness of the Al ₂ O ₃ film is λ / (8 × n3), and the thickness of the first dielectric layer in the first period is λ / (8 Xn1), and the thickness of the second dielectric layer in the first cycle is preferably λ / (4 × n2), and the thickness of the first dielectric layer in the second cycle and thereafter is preferably More preferably, λ / (4 × n1), and the thickness of the second dielectric layer after the second period is λ / (4 × n2).

  In the semiconductor laser device of the present invention, the film thickness calculation wavelength λ is preferably 660 nm or more and less than 720 nm, and the film thickness calculation wavelength λ is more preferably 670 nm or more and less than 710 nm.

In the semiconductor laser device of the present invention, the plurality of semiconductor layers include a group III-V compound semiconductor, the first dielectric layer includes silicon oxide (SiO ₂ ) or aluminum oxide (Al ₂ O ₃ ), The second dielectric layer preferably contains niobium oxide (Nb ₂ O ₅ ) or zirconia oxide (ZrO ₂ ).

  In the semiconductor laser device of the present invention, it is preferable that the first oscillation wavelength λ1 is not less than 645 nm and not more than 665 nm, and the second oscillation wavelength λ2 is not less than 765 nm and not more than 800 nm.

  In the semiconductor laser device of the present invention, the active layer of the first semiconductor laser having the first oscillation wavelength λ1 includes an AlGaInP-based semiconductor material, and the active layer of the second semiconductor laser having the second oscillation wavelength λ2. Preferably includes an AlGaAs-based semiconductor material.

  According to the present invention, in a two-wavelength semiconductor laser device in which the first oscillation wavelength λ1 is, for example, 645 to 665 nm and the second oscillation wavelength λ2 is, for example, 765 to 800 nm, for example, 660 nm or more and less than 720 nm, more preferably For example, a dielectric film having a low refractive index (refractive index n1 ≦ 1.5) and a high refractive index (refractive index) are used as a reflective film covering the rear end face of the resonator using a film thickness calculation wavelength λ of 670 nm or more and less than 710 nm. By repeatedly depositing the dielectric layers having a ratio n2 ≧ 2.3) by a predetermined thickness, a high reflectance of 85% or more can be realized at both wavelengths λ1 and λ2.

Further, according to the present invention, particularly when silicon oxide (SiO ₂ ) is used as the low refractive index material and niobium oxide (Nb ₂ O ₅ ) is used as the high refractive index material, the extinction coefficient of each dielectric operation is almost equal. Since it becomes zero, it is possible to reduce the light absorption loss at the rear end face of the resonator, thereby suppressing the end face deterioration.

  As described above, according to the present invention, high reflectivity and low loss are realized on the rear end face of the resonator without complicating the structure of the end face coat film, thereby improving the slope efficiency and operating current. Can be reduced. In other words, according to the present invention, it is possible to easily provide an integrated semiconductor laser device provided with an end face coating film suitable for high output operation and having high reliability at low cost.

  Hereinafter, a semiconductor laser device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a top perspective view of the integrated semiconductor laser device of this embodiment. The integrated semiconductor laser device of this embodiment is a dual wavelength semiconductor laser device in which a red semiconductor laser having an oscillation wavelength in the 660 nm band and an infrared semiconductor laser having an oscillation wavelength in the 780 nm band are formed on the same substrate. It is an example.

  As shown in FIG. 1, in the semiconductor laser device of this embodiment, a first semiconductor laser 1 and a second semiconductor laser 2 are integrally formed on a substrate 101. In the formation region of the first semiconductor laser 1 on the substrate 101, a cladding layer 102 of the first conductivity type (for example, n-type: the same applies hereinafter), an active layer 103, and a second conductivity type (for example, P type: the same applies hereinafter) The first cladding layer 104, the etching stopper layer 105, the second conductivity type second cladding layer 106, the contact layer 107, and the insulating layer 108 are sequentially stacked. The second semiconductor laser 2 has the same configuration as that of the first semiconductor laser 1, and the first conductive type cladding layer 122 and the active layer 123 are formed in the formation region of the second semiconductor laser 2 on the substrate 101. The second conductivity type third cladding layer 124, the etching stopper layer 125, the second conductivity type fourth cladding layer 126, the contact layer 127, and the insulating layer 108 are sequentially stacked.

  The insulating layer 108 provided in the formation region of the first semiconductor laser 1 includes a side surface of a ridge stripe structure which is a trapezoidal convex portion formed of a second conductivity type second cladding layer 106, a contact layer 107, and the like. The upper surface of the etching stopper layer 105 excluding the formation region of the ridge stripe structure is covered. On the insulating layer 108 including the ridge stripe structure, a second conductivity type first electrode (for example, p-side electrode) 109 is arranged, whereby carriers (holes) are formed in the ridge stripe structure. Can be injected.

  Similarly, the insulating layer 108 provided in the formation region of the second semiconductor laser 2 is a ridge stripe structure which is a trapezoidal convex portion composed of a second conductivity type fourth cladding layer 126, a contact layer 127, and the like. And the upper surface of the etching stopper layer 125 excluding the region where the ridge stripe structure is formed. On the insulating layer 108 including the ridge stripe structure, a second conductivity type second electrode (for example, a p-side electrode) 129 is arranged, and thereby, carriers (holes) are formed in the ridge stripe structure. Can be injected.

  A first conductivity type electrode (for example, an n-side electrode) 110 is disposed on the back surface of the substrate 101. The two end faces of the resonator formed in the direction perpendicular to the ridge stripe structure in each of the first semiconductor laser 1 and the second semiconductor laser 2 are formed by dielectric films (end face coat films) 131 and 130, respectively. It is coated. Specifically, an emission surface (front end surface 141) from which laser light is emitted is coated with a dielectric film 131, and a rear end surface 140 located on the opposite side of the front end surface 141 is coated with a dielectric film 130. Yes.

  In the semiconductor laser device of the present embodiment, the ridge stripe structure is not limited to a structure having a trapezoidal cross section as shown in FIG. 1, and has, for example, a rectangular cross section with its side surfaces raised substantially vertically. It may be a structure, that is, a rectangular parallelepiped structure.

  In the semiconductor laser device of this embodiment, a separation groove 150 is provided to electrically separate the first semiconductor laser 1 and the second semiconductor laser 2. Thereby, a bias is individually applied between the p-side electrode 109 and the n-side electrode 110 of the first semiconductor laser 1 and between the p-side electrode 129 and the n-side electrode 110 of the second semiconductor laser 2. By doing so, the first semiconductor laser 1 and the second semiconductor laser 2 can be operated individually.

  In the semiconductor laser device of this embodiment, the oscillation wavelength λ1 of the first semiconductor laser 1 and the oscillation wavelength λ2 of the second semiconductor laser 2 are different from each other. For example, the first semiconductor laser 1 may be a red semiconductor laser that emits 660 nm band laser light, and the second semiconductor laser 2 may be an infrared semiconductor laser that emits 780 nm band laser light.

  Further, as described above, the semiconductor laser device of the present embodiment has the front end surface 141 for extracting laser light and the rear end surface 140 for reflecting light into the resonator. In addition, in order to control the respective reflectances of the front end surface 141 and the rear end surface 140, dielectric films 131 and 130 having a desired reflectance are formed on the front end surface 141 and the rear end surface 140 as end surface coating films. . As will be described later, the reflectivities of the dielectric films 131 and 130 are the refractive index of the dielectric material used for the dielectric films 131 and 130, the thickness of the dielectric films 131 and 130, and the dielectric films 131 and 130, respectively. It can be controlled by the number of layers of the laminate constituting the.

  Hereinafter, a more specific structure of the semiconductor laser device of this embodiment will be described. 2A and 2B show an example of a cross-sectional view along a direction orthogonal to the ridge stripe structure of each semiconductor laser in the semiconductor laser device of this embodiment, and FIG. 2A shows a red semiconductor. FIG. 2B is a cross-sectional view of an infrared semiconductor laser.

As shown in FIG. 2A, in the red semiconductor laser of the present embodiment, for example, n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P is formed on a substrate 201 made of n-type GaAs and having a thickness of 100 μm. An n-type cladding layer 202 having a thickness of 2 μm, for example, a light guide layer 203 having a thickness of 0.01 μm made of (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P, for example, a quantum having a multiple quantum well (MQW) structure containing AlGaInP / GaInP. Well active layer 204 (for example, the well layer has a thickness of 6 nm, the barrier layer has a thickness of 7 nm, and is composed of three well layers), for example, (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P An optical guide layer 205 having a thickness of 0.01 μm, for example, a p-type first cladding layer 206 having a thickness of 0.3 μm made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P, for example, p-type Ga _0.5 In _0.5 An etching stop layer 207 made of P having a thickness of 0.007 μm, a p-type second cladding layer 208 made of p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P and having a thickness of 1.0 μm, for example, a p-type having a thickness of 0.05 μm A type Ga _0.5 In _0.5 P layer 209, a contact layer 210 made of, for example, p-type GaAs having a thickness of 0.1 μm, and an insulating layer 220 made of, for example, SiO _{2 having} a thickness of 1.0 μm are sequentially stacked. The insulating layer 220 is formed with a side surface of a ridge stripe structure 215 that is a trapezoidal convex portion including a p-type second cladding layer 208, a p-type Ga _0.5 In _0.5 P layer 209, and a contact layer 210, and a ridge stripe structure 215. The upper surface of the etching stopper layer 207 not covered is covered. A 1 μm-thick p-side electrode 211 made of, for example, Ti / Pt / Au is formed on the insulating layer 220 including the ridge stripe structure 215, whereby carriers (holes) are formed in the ridge stripe structure 215. ) Can be injected. Further, an n-side electrode 212 having a thickness of 0.5 μm made of, for example, AuGe / Ni / Au / Ti / Au is formed on the back surface of the n-type GaAs substrate 201.

  In the present embodiment, the length, width and thickness of the resonator of the red semiconductor laser are 1200 μm, 120 μm and 80 μm, respectively. The width and height of the ridge stripe structure 215 are about 2.5 μm and about 1.15 μm.

Next, as shown in FIG. 2B, in the infrared semiconductor laser of the present embodiment, the n-type having a thickness of 2 μm made of, for example, n-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P is formed on the substrate 201. The cladding layer 222, for example, an optical guide layer 223 made of AlGaAs and having a thickness of 0.01 μm, for example, a quantum well active layer 224 having a multiple quantum well (MQW) structure containing AlGaAs (for example, a well layer having a thickness of 3 nm, a barrier layer The optical guide layer 225 having a thickness of 7 μm and composed of two well layers, for example, AlGaAs and having a thickness of 0.01 μm, for example, p-type (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P, having a thickness of 0 p-type third cladding layer 226 of .3Myuemu, for example, p-type Ga _0.5 an in _0.5 consists P having a thickness of 0.01μm etch stop layer 227, for example, p-type _{(Al 0.5 Ga 0.5) 0.5 in} 0.5 P P-type fourth cladding layer 228 having a thickness of 1.0μm made of the mold, for example, a thickness of 0.05 .mu.m p-type Ga _0.5 In _0.5 P layer 229, a p-type thickness 0.1μm contact layer 230 made of GaAs, Insulating layers 220 are sequentially stacked. The insulating layer 220 is formed with a side surface of a ridge stripe structure 235 which is a trapezoidal convex portion including a p-type fourth cladding layer 228, a p-type Ga _0.5 In _0.5 P layer 229, and a contact layer 230, and a ridge stripe structure 235. The upper surface of the etching stopper layer 227 not covered is covered. On the insulating layer 220 including the ridge stripe structure 235, a p-side electrode 231 having a thickness of 1 μm made of, for example, Ti / Pt / Au is formed. As a result, carriers (holes) are formed in the ridge stripe structure 235. ) Can be injected.

  In this embodiment, the length, width and thickness of the resonator of the infrared semiconductor laser are 1200 μm, 120 μm and 80 μm, respectively. The width and height of the ridge stripe structure 235 are about 2.5 μm and about 1.15 μm.

  FIGS. 3A and 3B show an example of a cross-sectional view inside the ridge stripe along a direction (resonator direction) parallel to the resonator of each semiconductor laser in the semiconductor laser device of this embodiment. FIG. 3A is a cross-sectional view of a red semiconductor laser, and FIG. 3B is a cross-sectional view of an infrared semiconductor laser. In FIGS. 3A and 3B, the same components as those in the cross-sectional views shown in FIGS.

As shown in FIGS. 3A and 3B, the laminated structure of the semiconductor layers constituting the resonator of each semiconductor laser is as described above (as shown in FIGS. 2A and 2B). However, in order to prevent end face destruction due to COD (Catastrophic Optical Damage) in each semiconductor laser and obtain a high output operation, a window region 301 is provided in the vicinity of the cavity end face of the red semiconductor laser and an infrared semiconductor laser. A window region 321 is provided in the vicinity of the resonator end face of 321 and 321. In addition, an insulating layer 220 is coated on the window regions 301 and 321 in order to prevent carrier injection into the window regions 301 and 321. The resonator of the red semiconductor laser has a front end surface 341 for extracting laser light on the front surface, and a rear end surface 340 for reflecting light to the inside of the resonator on the rear surface. . The resonator of the infrared semiconductor laser has a front end surface 351 for extracting laser light on the front surface thereof, and a rear end surface 350 for reflecting light to the inside of the resonator on the rear surface. Yes. Here, in order to control the reflectance of the front end faces 341 and 351 of each laser, an end face coating film 331 made of a dielectric material such as SiO ₂ or Al ₂ O ₃ is formed on the front end faces 341 and 351. . Further, in order to control the reflectance of the rear end faces 340 and 350 of each laser, an end face coat film 330 having a multilayer structure made of a dielectric is formed on the rear end faces 340 and 350. As described later, the reflectances of the end surface coating films 331 and 330 are as follows. The refractive index of the dielectric material used for the end surface coating films 331 and 330, the thicknesses of the end surface coating films 331 and 330, and the end surface coating films 331 and 330 are as follows. It can be controlled by the number of layers of the laminate constituting the.

  In this embodiment, in order to set the reflectance of the end face coat film 330 formed on the rear (rear side) end faces 340 and 350 of each laser to 85% or more, more preferably 90% or more, the end face coat film 330 is set. As described above, a multilayer structure of a low refractive index material layer and a high refractive index material layer is used. The reason is that by improving the reflectivity (rear side reflectivity) at the rear end faces 340 and 350, it is expected that characteristics such as slope efficiency (Se) improvement and operating current (Iop) reduction will be improved. 4 and 5 show characteristic changes when the rear side reflectance is changed (operating current (Iop) and slope efficiency (Se) at 300 mW light output). Here, FIG. 4 shows a characteristic change of the red semiconductor laser, and FIG. 5 shows a characteristic change of the infrared semiconductor laser. The inventors of the present application have found that Se and Iop tend to be saturated in both the red semiconductor laser and the infrared semiconductor laser by setting the rear side reflectance to 85% or more. Based on this knowledge, in this embodiment, it is preferable to select 85% or more as the optimum rear side reflectance with respect to the oscillation wavelength of each laser. As a result, it is possible to achieve 1.1 W / A or more for Se and 400 mA or less for Iop in the red semiconductor laser, and 0.92 W / A or more for Se and 370 mA or less for Iop in the infrared semiconductor laser. . As described above, the power consumption can be greatly reduced by setting the rear-side reflectance to 85% or more, more preferably 90% or more, for both the red and infrared wavelengths.

Examples of the high refractive index material constituting the rear end face coating film 330 include amorphous silicon (α-Si), hydrogenated amorphous silicon (α-Si: H), Nb ₂ O ₅ , Ta ₂ O _{5 and the} like. . FIG. 6 shows the wavelength dependence of the refractive index n of these high refractive index materials, and FIG. 7 shows the wavelength dependence of the extinction coefficient k of these high refractive index materials. As shown in FIG. 7, the silicon-based material (α-Si, α-Si: H) has a value whose extinction coefficient cannot be ignored at a target red wavelength (eg, 660 nm) or infrared wavelength (eg, 780 nm). On the other hand, the extinction coefficients of Nb ₂ O ₅ and Ta ₂ O ₅ are negligible at these wavelengths. Further, unlike silicon-based materials, Nb ₂ O ₅ and Ta ₂ O ₅ have the advantage that fewer particles are generated during film formation.

The rear side end face coating film 330 is composed of a pair of a SiO ₂ (refractive index 1.48) layer as a low refractive index material layer and a Ta ₂ O ₅ (refractive index 2.20) layer as a high refractive index material layer. FIG. 8 shows the result of calculating how the reflectance of the rear side end face coating film varies depending on the number of pairs when it is configured in the range of 3 to 6 pairs. Note that the thickness calculation wavelength λ is 660 nm, the thickness of the SiO ₂ layer in one pair is 660 / (4 × 1.48) nm, and the thickness of the Ta ₂ O ₅ layer in one pair is 660 / (4 × 2.20) nm. In each pair, a SiO ₂ layer as a low refractive index material layer is provided on the end face side (on GaAs). As shown in FIG. 8, when SiO _{2 is} used as the low refractive index material and Ta ₂ O ₅ is used as the high refractive index material, the rear side reflectance at the red wavelength (660 nm) is 87% for 3 pairs, 4 pairs. 93%, 5 pairs 96%, and 6 pairs 98%. As the number of pairs increases, the reflectance can be increased. On the other hand, the rear side reflectance at the infrared wavelength (780 nm) is 65% for 3 pairs, 61% for 4 pairs, 49% for 5 pairs, and 26% for 6 pairs, and the reflectance decreases as the number of pairs increases. Become. Therefore, it is very difficult to use the SiO ₂ / Ta ₂ O ₅ laminated structure as the rear end face coat film 330 in the high-power two-wavelength semiconductor laser device of this embodiment.

Next, the rear end face coating film 330 is formed by combining an SiO ₂ (refractive index 1.48) layer as a low refractive index material layer and an Nb ₂ O ₅ (refractive index 2.30) layer as a high refractive index material layer. FIG. 9 shows the result of calculating how the reflectance of the rear side end face coat film varies depending on the number of pairs when one pair is configured in the range of 3 to 6 pairs. In addition, assuming that the film thickness calculation wavelength λ is 660 nm, the thickness of the SiO ₂ layer in one pair is 660 / (4 × 1.48) nm, and the thickness of the Nb ₂ O ₅ layer in one pair is 660 / (4 × 2.30) nm. In each pair, a SiO ₂ layer as a low refractive index material layer is provided on the end face side (on GaAs). As shown in FIG. 9, when SiO _{2 is} used as the low refractive index material and Nb ₂ O ₅ is used as the high refractive index material, the rear side reflectance at the red wavelength (660 nm) is 91% for 3 pairs and 4 pairs. 96%, 5 pairs are 98%, and 6 pairs are 99%. As the number of pairs increases, the reflectance can be increased. On the other hand, the reflectance on the rear side at infrared wavelength (780 nm) is 77% for 3 pairs, 80% for 4 pairs, 80% for 5 pairs, 77% for 6 pairs, and nearly 80% for infrared wavelengths. Is obtained. That is, Nb ₂ O ₅ having a refractive index difference with SiO ₂ larger than that of Ta ₂ O ₅ is used as a high refractive index material layer for the rear side end face coating film 330 in the high power dual wavelength semiconductor laser device of this embodiment. Is possible.

Next, the SiO ₂ used in the rear facet coating film as a low refractive index material, to calculate the rear-side reflectance in the case of using each of the Ta ₂ O ₅ and Nb ₂ O ₅ as a high refractive index material, Ta ₂ O ₅ between the case of using a Nb ₂ O ₅ in the case of using a result of performing a range comparing pairs C 3-6 wavelength width can achieve 85% or more rear-side reflectance (bandwidth) Is shown in FIG. Note that the thickness calculation wavelength λ is 660 nm, the thickness of the SiO ₂ layer in one pair is 660 / (4 × 1.48) nm, and the thickness of the Ta ₂ O ₅ layer in one pair is 660 / (4 × 2.20) nm, and the thickness of the Nb ₂ O ₅ layer in one pair is 660 / (4 × 2.30) nm. In addition, regardless of whether Ta ₂ O _{5 or} Nb ₂ O ₅ is used as the high refractive index material, an SiO ₂ layer as a low refractive index material layer is provided on the end face side (on GaAs) in each pair. .

By the way, in the high-power two-wavelength semiconductor laser device, it is necessary to increase the rear side reflectance at the wavelengths of both the red laser and the infrared laser. In general, a wavelength in the range of 645 to 665 nm is used as the oscillation wavelength λ1 of the red laser, and a wavelength in the range of 765 to 800 nm is used as the oscillation wavelength λ2 of the infrared laser. Therefore, since the maximum distance between λ1 and λ2 is 155 nm, it is necessary to secure a bandwidth with a rear side reflectance of 85% or more of 155 nm or more. However, as shown in FIG. 10, when SiO _{2 is} used as the low refractive index material and Ta ₂ O ₅ is used as the high refractive index material, the bandwidth of the rear reflectivity of 85% or more is 66 nm for 3 pairs and 4 pairs. 136 nm, 5 pairs are 149 nm, 6 pairs are 153 nm, and the above conditions are not satisfied even with 6 pairs. On the other hand, when SiO _{2 is} used as the low refractive index material and Nb ₂ O ₅ is used as the high refractive index material, as shown in FIG. The pairs are 186 nm, 5 pairs are 193 nm, and 6 pairs are 195 nm. In order to satisfy the above-described conditions, four or more pairs may be stacked.

As described above, the Nb ₂ O ₅ layer is suitable for realizing a high throughput by shortening the film formation time of the rear side end face coating film 330 that can satisfy the above-described conditions as much as possible. Further, when the Nb ₂ O ₅ layer is used in combination with the SiO ₂ layer, the number of pairs that can satisfy the above-described conditions can be suppressed, and thereby the total film thickness of the rear side end face coat film 330 can be reduced. Therefore, the stress value that adversely affects the reliability can be reduced.

Considering the above simulation results, a rear side end face coating film (number of pairs: 5) having a pair of a SiO ₂ layer as a low refractive index material layer and a Ta ₂ O ₅ layer as a high refractive index material layer, and a low Each rear side end face coat is formed by forming a rear side end face coat film (number of pairs: 4) in which an SiO ₂ layer as a refractive index material layer and an Nb ₂ O ₅ layer as a high refractive index material layer are paired. The results of measuring the reflectance of the film are shown in FIGS. Here, FIG. 11 shows the measurement results of the reflectance of the rear side end face coat film having the SiO ₂ / Ta ₂ O ₅ laminated structure, and FIG. 12 shows the rear side end face coat film having the SiO ₂ / Nb ₂ O ₅ laminated structure. It is a measurement result of reflectance. As shown in FIG. 11, in the rear side end face coating film having a SiO ₂ / Ta ₂ O ₅ laminated structure (number of pairs: 5), the bandwidth Δλ having a rear side reflectance of 85% or more is 154 nm. As shown in FIG. 12, in the rear side end face coating film having the SiO ₂ / Nb ₂ O ₅ laminated structure (number of pairs: 4), the bandwidth Δλ having a rear side reflectance of 85% or more is 192 nm. That is, the actual measurement values shown in FIG. 11 and FIG. 12 are in good agreement with the calculation results shown in FIG. 10, and the rear side reflectance of the rear side end coat film having the SiO ₂ / Ta ₂ O ₅ laminated structure is 85% or more. Compared with the bandwidth Δλ, the bandwidth Δλ having a rear side reflectance of 85% or more in the rear side end face coat film having the SiO ₂ / Nb ₂ O ₅ laminated structure is wide.

Thus, when the rear side end face coating film is configured using SiO ₂ (refractive index 1.48) as a low refractive index material and Nb ₂ O ₅ (refractive index 2.3) as a high refractive index material, A rear side reflectance of 85% or more can be sufficiently secured at both the red and infrared wavelengths. On the other hand, when the rear end face coat film is formed using Ta ₂ O ₅ (refractive index 2.2) as a high refractive index material, the bandwidth Δλ having a rear side reflectance of 85% or more is narrow. It becomes very difficult to apply the side end face coating film to the two-wavelength semiconductor laser device. In the present embodiment, the reflectance at one point in the rear end face of the resonator has been described so far. However, actually, the reflectance distribution (that is, the rear side end face coat film 330) is present in the rear end face of the resonator. Therefore, it is difficult to use Ta ₂ O ₅ as a high refractive index material in order to secure a process margin.

As described above, the low refractive index of the rear side end face coat film 330 is required to ensure a wide bandwidth of 85% or more of the rear side reflectance at both oscillation wavelengths in the dual wavelength semiconductor laser device of the present embodiment. The refractive index of the material is 1.5 or less, and the refractive index of the high refractive index material of the rear side end face coating film 330 is required to be 2.3 or more. That is, at least a refractive index difference in a laminated structure of SiO ₂ (refractive index 1.48) / Nb ₂ O ₅ (refractive index 2.3), which is a specific film configuration example, is necessary. _{Even when the 2} / Nb ₂ O ₅ laminated structure is used, the number of pairs needs to be 4 or more.

In the present embodiment, the refractive index of the high refractive index material layer of the rear side end face coating film 330 is preferably 3.0 or less. The reason for this is that, in a dielectric material having a refractive index exceeding 3.0, the transparent wavelength region whose extinction coefficient is close to zero shifts to the longer wavelength side, so the red wavelength band (645 to 665 nm) and red This is because the extinction coefficient may increase in the outer wavelength band (765 to 800 nm). As an example, while the refractive index of Si is as high as 3.5, the extinction coefficient in the red wavelength band is very large as 0.3 to 0.4 cm ^−1, and the loss due to light absorption becomes large. Further, the light absorption in the end face coating film leads to heat generation, which may induce end face destruction due to COD.

On the other hand, in this embodiment, the lower limit is not particularly specified for the refractive index of the low refractive index material layer of the rear side end face coating film 330. This is because the refractive index of the low refractive index material is desirably as small as possible in order to increase the refractive index difference from the high refractive index material. Also in the transparent wavelength region described above, the low refractive index material has a value near zero for the extinction coefficient in the red wavelength band and the infrared wavelength band as compared with the ultraviolet wavelength band. As an example, the extinction coefficient of SiO ₂ having a refractive index of about 1.48 is almost zero in the red wavelength band, and the loss due to light absorption is negligible.

In this embodiment, the low-refractive index material layer and the high-refractive index material layer constituting the rear side end face coat film 330 are 0 at least in the red wavelength band (645 to 665 nm) and the infrared wavelength band (765 to 800 nm). It is preferable to have an extinction coefficient close to 0, specifically, an extinction coefficient of 0.001 cm ^-1 or less.

  Next, setting of the film thickness calculation wavelength in the present embodiment will be described. Conventionally, in order to stably maintain the high reflectivity on the rear side with respect to the oscillation wavelength of the red laser, a sufficient reflectance margin for the oscillation wavelength of the red laser can be obtained by setting the film thickness calculation wavelength to 660 nm. It was provided. In this case, with respect to the oscillation wavelength of the infrared laser, the reflectance margin is reduced as compared with the oscillation wavelength of the red laser. Therefore, as a countermeasure, in this embodiment, the film thickness calculation wavelength may be shifted in the long wavelength direction as compared with the conventional case. The reason will be described below.

FIG. 13 shows the reflection on the rear side according to the change of the film thickness calculation wavelength (λ) when SiO ₂ is used as the low refractive index material and Ta ₂ O ₅ is used as the high refractive index material in the rear end face coating film. The calculation result of how the rate profile changes is shown. The calculation was performed by changing the film thickness calculation wavelength λ within the range of 660 nm to 720 nm. Further, five pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed to form the rear side end face coating film, and the thickness of the SiO ₂ layer in one pair is λ / (4 × (refractive index of SiO ₂ )) [Nm], the thickness of the Ta ₂ O ₅ layer in one pair is λ / (4 × (the refractive index of Ta ₂ O ₅ )) [nm], and SiO as a low refractive index material layer in each pair _Two layers were provided on the end face side (on GaAs).

FIG. 14 shows the dependence of the rear-side reflectance on the film thickness calculation wavelength (λ) for each of the red wavelength (660 nm) and the infrared wavelength (780 nm) among the results shown in FIG. As shown in FIG. 14, when the film thickness calculation wavelength λ is shifted from 660 nm to the long wavelength side, the rear-side reflectance with respect to the infrared wavelength (hereinafter referred to as infrared reflectance) increases, whereas the red wavelength There is a trade-off relationship that the rear-side reflectance (hereinafter referred to as red reflectance) with respect to is reduced. In addition, when the SiO ₂ / Ta ₂ O ₅ laminated structure is used, both the red reflectance and the infrared reflectance are set to 85% or more by setting the film thickness calculation wavelength λ to 670 nm to 710 nm. Can do. However, the range of the film thickness calculation wavelength λ in which both the red reflectance and the infrared reflectance can be set to a high reflectance of 90% or more is small.

FIG. 15 shows a case where SiO ₂ is used as the low refractive index material and Nb ₂ O ₅ is used as the high refractive index material in the rear end face coat film, and the rear side reflection is performed according to the change in the film thickness calculation wavelength (λ). The calculation result of how the rate profile changes is shown. The calculation was performed by changing the film thickness calculation wavelength λ within the range of 660 nm to 720 nm. Also, four pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed to form the rear end face coating film, and the thickness of the SiO ₂ layer in one pair is λ / (4 × (refractive index of SiO ₂ )) [Nm], the thickness of the Nb ₂ O ₅ layer in one pair is λ / (4 × (refractive index of Nb ₂ O ₅ )) [nm], and SiO as a low refractive index material layer in each pair _Two layers were provided on the end face side (on GaAs).

FIG. 16 shows the dependence of the rear side reflectance on the film thickness calculation wavelength (λ) with respect to each of the red wavelength and the infrared wavelength among the results shown in FIG. 15. As in the case of using the SiO ₂ / Ta ₂ O ₅ laminated structure, when the film thickness calculation wavelength λ is shifted from 660 nm to the long wavelength side as shown in FIG. There is a trade-off relationship that the rear side reflectance (hereinafter referred to as the red reflectance) with respect to the red wavelength is lowered while the infrared reflectance is increased. In addition, when the SiO ₂ / Nb ₂ O ₅ laminated structure is used, both the red reflectance and the infrared reflectance are set to 85% or more by setting the film thickness calculation wavelength λ in the range of 660 nm to 720 nm. can do. Furthermore, by setting the film thickness calculation wavelength λ within the range of 670 nm to 710 nm, both the red reflectance and the infrared reflectance can be set to 90% or more.

FIG. 17 shows SiO ₂ / Ta ₂ O ₅ laminated structure (structure used in the calculation of FIG. 13) and SiO ₂ / Nb ₂ O ₅ laminated structure (structure used in the calculation of FIG. 15) as the rear side end face coating film. The results of plotting the wavelength range (bandwidth) in which the rear-side reflectance of 85% or more can be achieved with respect to the film thickness calculation wavelength λ of 660 nm to 720 nm when each of the above is used. As shown in FIG. 17, by shifting the film thickness calculation wavelength λ to the long wavelength side, the band can be obtained regardless of whether the SiO ₂ / Ta ₂ O ₅ laminated structure or the SiO ₂ / Nb ₂ O ₅ laminated structure is used. It can be seen that the width gradually increases. That is, increasing the film thickness calculation wavelength λ is advantageous in terms of increasing the reflectance for both the red reflectance and the infrared reflectance. Summing up the above results, in the present embodiment, in order to make the rear side reflectance as high as 85% or higher for both the red and infrared wavelength bands, as the rear side end face coating film 330, for example, It is preferable to use a SiO ₂ / Nb ₂ O ₅ laminated structure and set the film thickness calculation wavelength λ to, for example, 670 to 710 nm.

By the way, in this embodiment, it is preferable to use an Al ₂ O ₃ layer instead of the SiO ₂ layer as the dielectric film (low refractive index material layer) in contact with the semiconductor layer constituting the resonator at the resonator end face. The reason will be described below. First, a dielectric film made of oxides such as Al ₂ O ₃ , SiO ₂ , Ta ₂ O _5, Nb ₂ O _5, etc. depends on the deposition method, but the stress is small, and the end face coating film of a semiconductor laser Suitable for From the viewpoint of stress, it can be said that it is preferable that the end face coat film has a smaller thickness. Here, if Al ₂ O ₃ is used as a material in contact with the resonator end face, the heat conductivity of Al ₂ O ₃ is larger than that of SiO ₂ , so that heat dissipation at the resonator end face is improved and high output is achieved. Increases reliability during operation. Further, since the Al ₂ O ₃ film has better adhesion to GaAs than the SiO ₂ film and has excellent environmental resistance, the laser chip can be mounted in a package that is not airtight, and the reliability improvement effect is great.

On the other hand, when a SiO ₂ layer is used as the low refractive index dielectric film (low refractive index material layer), if SiO ₂ is brought into direct contact with the end face of the laser resonator as described above, end face deterioration may occur. Therefore, Al ₂ O _3, Nb ₂ O _5, ZrO _2, or the like can be used as the low refractive index material and the high refractive index material of the rear side end face coating film 330 of the present embodiment, respectively.

However, since the refractive index of Al ₂ O ₃ is higher than the refractive index of SiO _2, the use of for Al ₂ O ₃ low refractive index material, the refractive index difference between the low refractive index material and a high refractive index material This is disadvantageous for increasing the rear side reflectance. Therefore, in the present embodiment, when the rear side end face coat film 330 is formed, the film thickness calculation wavelength is set to λ, and an Al ₂ O ₃ film (refractive index n3) is first formed on the rear side end face with a film thickness λ / ( 8 × n3), a SiO ₂ film (refractive index n1) is deposited on the Al ₂ O ₃ film with a film thickness λ / (8 × n1), and then a high refractive index is formed on the SiO ₂ film. By depositing an Nb ₂ O ₅ film (refractive index n2) with a film thickness λ / (4 × n2) as a material layer, a highly reliable rear end face coat film 330 can be formed. Here, in order to further increase the reflectance of the rear side end face coating film 330, the number of pairs of SiO ₂ / Nb ₂ O ₅ laminated structures formed on the Nb ₂ O ₅ film in the first period should be increased. It ’s fine. However, the thickness of the SiO ₂ film after the second cycle is λ / (4 × n1), and the thickness of the Nb ₂ O ₅ film after the second cycle is λ / (4 × n 2). Also in this case, the film thickness calculation wavelength λ should be set to, for example, 670 to 710 nm in order to obtain a high reflectance of 85% or more for the rear side reflectance in both the red and infrared wavelength bands. Is preferred.

In this embodiment, ZrO ₂ may be used in place of Nb ₂ O ₅ as a high refractive index material for the rear side end face coating film 330.

In this embodiment, each of the low refractive index material layer and the high refractive index material layer constituting the rear side end face coating film 330 is subjected to electron cyclotron resonance (ECR) sputtering, magnetron sputtering, electron beam evaporation (EB). It can be deposited by vapor deposition) or the like. In particular, when ECR sputtering is used, a high-purity metal (Al, Ta, Nb, etc.) or high-purity Si can be used as a target, so that a dielectric film without light absorption is formed at a high deposition rate. This is preferable. In particular, when an Al ₂ O ₃ film is formed by ECR sputtering using metal Al as a target and O ₂ as a reactive gas, the Al ₂ O ₃ film is formed at a high deposition rate of about 20 nm / min. Since the film can be formed, productivity is improved.

In this embodiment, in order to further improve the deposition rate of the rear end face coat film 330, the film in contact with the exposed end face of the resonator is formed by ECR sputtering, and the film formed thereon is ECR. Film formation is performed using a film forming apparatus other than the sputtering apparatus. That is, as the film in contact with the end face of the resonator, a dielectric film with a small amount of impurities and no light absorption is required. Therefore, it is preferable to form the film by using ECR sputtering. When a film made of a high refractive index material such as Nb ₂ O ₅ is formed using an ECR sputtering apparatus, a film made of a low refractive index material such as Al ₂ O ₃ or SiO ₂ is formed using an ECR sputtering apparatus. The deposition rate is slower than in the case of film formation. Therefore, after a dielectric film (low refractive index material layer) is formed on the surface of the semiconductor layer serving as the resonator end face by ECR sputtering, the film formed on the dielectric film (sputtering apparatus other than the ECR sputtering apparatus or sputtering) is formed. The film may be formed using a film forming method having a high deposition rate other than the above.

  As described above, in the integrated semiconductor laser device of the present invention, the low refractive index dielectric film (refractive index n1 ≦ 1.5) and the high refractive index dielectric film (refractive index n2 ≧ 2.3) are repeated. By depositing, a highly reliable rear side end face coating film suitable for high output operation can be easily obtained.

  The integrated semiconductor laser device of the present invention is useful, for example, as a light source for an optical recording device that requires a high-power two-wavelength semiconductor laser device, and is also useful when applied to other light sources such as laser medicine. It is.

FIG. 1 is a top perspective view of an integrated semiconductor laser device (dual wavelength semiconductor laser device) according to an embodiment of the present invention. 2A and 2B are views showing an example of a cross-sectional configuration along a direction orthogonal to the ridge stripe structure of each semiconductor laser in the semiconductor laser device according to one embodiment of the present invention. a) is a sectional view of a red semiconductor laser, and FIG. 2B is a sectional view of an infrared semiconductor laser. 3A and 3B are cross-sectional views inside the ridge stripe along a direction (resonator direction) parallel to the resonator of each semiconductor laser in the semiconductor laser device according to one embodiment of the present invention. FIG. 3A is a cross-sectional view of a red semiconductor laser, and FIG. 3B is a cross-sectional view of an infrared semiconductor laser. FIG. 4 is a diagram showing changes in operating current and slope efficiency (when 300 mW pulse is output) when the rear-side reflectance is changed in a red semiconductor laser. FIG. 5 is a diagram showing changes in operating current and slope efficiency (when 300 mW pulse is output) when the rear-side reflectance is changed in an infrared semiconductor laser. FIG. 6 is a diagram showing the wavelength dependence of the refractive index (n) of a dielectric film generally used as an end face coating film in a semiconductor laser. FIG. 7 is a diagram showing the wavelength dependence of the extinction coefficient (k) of a dielectric film generally used as an end face coating film in a semiconductor laser. FIG. 8 is a diagram showing a result of calculating a reflectance profile when a film thickness calculation wavelength λ is 660 nm and 3 to 6 pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed on GaAs. FIG. 9 is a diagram showing a result of calculating a reflectance profile when a film thickness calculation wavelength λ is 660 nm and 3 to 6 pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed on GaAs. FIG. 10 shows a reflectance of 85% when the film thickness calculation wavelength λ is 660 nm and 3 to 6 pairs of SiO ₂ / Ta ₂ O ₅ laminated structure and SiO ₂ / Nb ₂ O ₅ laminated structure are formed on GaAs. It is a figure which shows the result of having calculated the bandwidth which can achieve the above. FIG. 11 is a diagram showing the measurement results of reflectivity when five pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed on the cavity end face of the semiconductor laser. FIG. 12 is a diagram showing the measurement results of the reflectance when four pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed on the cavity end face of the semiconductor laser. FIG. 13 shows the result of calculating the reflectance profile when five pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed on GaAs by changing the film thickness calculation wavelength λ within the range of 660 nm to 720 nm. FIG. FIG. 14 shows the red reflectance and the infrared reflectance when five pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed on GaAs by changing the film thickness calculation wavelength λ within a range of 660 nm to 720 nm. It is a figure which shows the calculated result. FIG. 15 shows the result of calculating the reflectance profile when four pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed on GaAs by changing the film thickness calculation wavelength λ within the range of 660 nm to 720 nm. FIG. FIG. 16 shows the red reflectance and infrared reflectance in the case where five pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed on GaAs by changing the film thickness calculation wavelength λ within a range of 660 nm to 720 nm. It is a figure which shows the calculated result. FIG. 17 shows 660 nm to 720 nm when 5 pairs of SiO ₂ / Ta ₂ O ₅ laminated structures are formed on GaAs and when 4 pairs of SiO ₂ / Nb ₂ O ₅ laminated structures are formed on GaAs. It is a figure which shows the result of having calculated the bandwidth which can achieve rear side reflectance 85% or more with respect to film thickness calculation wavelength (lambda). FIG. 18A is a top perspective view of a conventional two-wavelength semiconductor laser device, and FIG. 18B is a plan view of the main part of the device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st semiconductor laser 2 2nd semiconductor laser 10 Red semiconductor laser 15, 25 Laser light 17, 27 Laser emission area 20 Infrared semiconductor laser 30, 40 Electrode 50 Front end surface 60 Rear end surface 70, 72 End surface film 80 Multilayer coating Film 90 Groove 100 Laser device 101 Substrate 102 Cladding layer 103 Active layer 104 First cladding layer 105 Etching stop layer 106 Second cladding layer 107 Contact layer 108 Insulating layer 109 P-side first electrode 110 N-side electrode 122 Cladding layer 123 Active layer 124 Third cladding layer 125 Etching stop layer 126 Fourth cladding layer 127 Contact layer 129 P-side second electrode 130, 131 End surface coating film 140, 141 Resonator end surface 150 Separation groove 201 Substrate 202 N-type cladding layer 203 Light guide layer 204 amount Child well active layer 205 Optical guide layer 206 p-type first cladding layer 207 etching stop layer 208 p-type second cladding layer 209 p-type Ga _0.5 In _0.5 P layer 210 contact layer 211 p-side electrode 212 n-side electrode 215 ridge stripe structure 220 insulating layer 222 n-type cladding layer 223 light guide layer 224 quantum well active layer 225 AlGaAs light guide layer 226 p-type third cladding layer 227 etching stop layer 228 p-type fourth cladding layer 229 p-type Ga _0.5 In _0.5 P layer 230 Contact layer 231 P-side electrode 235 Ridge stripe structure 301, 321 Window region 330, 331 End face coating film 340, 341, 350, 351 Resonator end face

Claims (9)

An integrated semiconductor laser device in which a first semiconductor laser having a first oscillation wavelength λ1 and a second semiconductor laser having a second oscillation wavelength λ2 (λ1 <λ2) are formed on the same substrate,
A resonator composed of a plurality of semiconductor layers stacked on the substrate;
A reflective film covering the rear end face of the resonator,
The reflective film is formed by alternately laminating four or more periods of the first dielectric layer and the second dielectric layer from the rear end face side,
A first refractive index n1 of the first dielectric layer is 1.5 or less;
A second refractive index n2 of the second dielectric layer is 2.3 or more;
Each of the first dielectric layer and the second dielectric layer has an extinction coefficient of 0.001 cm ⁻¹ or less at least at the first oscillation wavelength λ1 and the second oscillation wavelength λ2.
A reflectance of the rear end face is 85% or more at both of the first oscillation wavelength λ1 and the second oscillation wavelength λ2. The semiconductor laser device according to claim 1,
The thickness of the first dielectric layer is λ / (4 × n1), and the thickness of the second dielectric layer is λ / (4 × n2), where λ is the film thickness calculation wavelength. A semiconductor laser device. The semiconductor laser device according to claim 1,
The semiconductor laser device, wherein the reflective film includes an Al ₂ O ₃ film having a _third refractive index n3 between the first dielectric layer in the first period and the rear end face. The semiconductor laser device according to claim 3,
When the film thickness calculation wavelength is λ, the thickness of the Al ₂ O ₃ film is λ / (8 × n3), and the thickness of the first dielectric layer in the first period is λ / (8 × n1). And the thickness of the second dielectric layer in the first period is λ / (4 × n2). The semiconductor laser device according to claim 4,
The thickness of the first dielectric layer after the second period is λ / (4 × n1), and the thickness of the second dielectric layer after the second period is λ / (4 × n2). There is a semiconductor laser device. The semiconductor laser device according to claim 2, 4 or 5,
The semiconductor laser device, wherein the film thickness calculation wavelength λ is 660 nm or more and less than 720 nm. The semiconductor laser device according to any one of claims 1 to 6,
The plurality of semiconductor layers include a III-V compound semiconductor,
The first dielectric layer includes silicon oxide (SiO ₂ ) or aluminum oxide (Al ₂ O ₃ ),
The semiconductor laser device, wherein the second dielectric layer contains niobium oxide (Nb ₂ O ₅ ) or zirconia oxide (ZrO ₂ ). In the semiconductor laser device according to claim 1,
The first oscillation wavelength λ1 is 645 nm or more and 665 nm or less,
The semiconductor laser device, wherein the second oscillation wavelength λ2 is 765 nm or more and 800 nm or less. In the semiconductor laser device according to any one of claims 1 to 8,
The active layer of the first semiconductor laser having the first oscillation wavelength λ1 includes an AlGaInP-based semiconductor material,
An active layer of the second semiconductor laser having the second oscillation wavelength λ2 includes an AlGaAs-based semiconductor material.

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