JP2009302416A - Semiconductor laser, semiconductor laser module, and raman amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser with a novel structure that projects multi-longitudinal-mode laser light. <P>SOLUTION: A light emission area 10A and a reflection area 10B are formed in series in an optical-axis direction on a semiconductor substrate 11. An active layer 13a which extends in the optical-axis direction is formed in the light emission area 10A. In the reflection area 10B, on the other hand, a plurality of block bodies 13A are formed of the same material with the active layer 13 on an extension of the active layer 13 periodically apart from one another. The plurality of block bodies 13A are surrounded with an upper clad layer 14, a lower clad layer 12, etc., having lower refractive indexes than the block bodies 13A. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor laser, a semiconductor laser module, and a Raman amplifier that emit laser light including a plurality of wavelength components and that are excellent in controllability of the center wavelength and bandwidth.

Patent Document 1 discloses a DFB (Distributed FeedBack) semiconductor laser in which a diffraction grating is formed above an active layer. Patent Document 1 describes shortening the length of the diffraction grating, chirping the period of the diffraction grating, and the like in order to emit multi-longitudinal mode laser light from the DFB semiconductor laser.
JP 2002-204024 A

In order to obtain multi-longitudinal mode laser light in a DFB semiconductor laser, in addition to shortening the length of the above-described diffraction grating (resonator) or chirping the period of the diffraction grating, a normalized coupling coefficient κL is set. It is also known to make it smaller (Patent Document 2). The coupling coefficient κ represents the degree of periodic refractive index change (unit: cm ⁻¹ ) in the optical axis direction, and L represents the diffraction grating length (unit: cm).
JP 2003-258375 A

  In order to reduce the normalized coupling coefficient κL, the coupling coefficient κ or the diffraction grating length L may be reduced. However, it is difficult to control the coupling coefficient κ small in a DFB semiconductor laser in which a diffraction grating is formed above or below the active layer. If the diffraction grating length L is too short, wavelength control becomes difficult.

  An object of the present invention is to provide a semiconductor laser having a new structure capable of emitting a laser beam in a multi-longitudinal mode.

  The semiconductor laser according to the present invention is a so-called DBR (Distributed Bragg Reflector) semiconductor laser in which a light emitting region and a reflective region are formed in series in the optical axis direction on a semiconductor substrate. In the semiconductor laser according to the present invention, an active layer extending in the optical axis direction is formed in the light emitting region, and a plurality of blocks made of the same material as the active layer are formed on the reflection region on the extension of the active layer. The bodies are formed periodically spaced from each other. The plurality of block bodies in the reflective region are surrounded by a semiconductor material having a refractive index lower than the refractive index of the block body, and the end surfaces of the light emitting regions (end surfaces in contact with the reflective regions) It is needless to say that the end face is on the opposite side from the above), and multi-longitudinal mode laser light is emitted.

  According to the present invention, since the block body (made of the same material as the active layer) and the semiconductor material (having a refractive index smaller than that of the active layer) are alternately formed in the optical axis direction, The refractive index of the medium in the axial direction changes periodically. For this reason, in the reflection region, light having a predetermined wavelength out of light generated in the active layer in the light emitting region is reflected, and functions as if a diffraction grating is formed there.

  Further, according to the present invention, the block formed of the same material as the active layer is formed to have a periodic structure with respect to the refractive index in the reflection region. For this reason, the refractive index difference of the medium in the optical axis direction is larger than that of a conventional semiconductor laser in which a diffraction grating is formed above or below the active layer (light confinement layer portion).

  In a so-called DBR semiconductor laser in which a light emitting region and a reflective region are formed in series in the optical axis direction on a semiconductor substrate, the reflectance of light in the reflective region increases as the coupling coefficient κ is relatively large. The wavelength band (reflection width) of the reflected light becomes wider. Since the semiconductor laser according to the present invention has a large refractive index difference of the medium in the optical axis direction in the reflection region, the degree of periodic refractive index change in the optical axis direction, that is, the coupling coefficient κ is large. Therefore, reflection of light of a plurality of wavelengths is realized with high efficiency in the reflection region, and laser light including a plurality of wavelength spectra, that is, laser light in a multi-longitudinal mode can be emitted with relatively high power.

  In one embodiment, an optical guide layer extending in the optical axis direction of the semiconductor laser is provided at least above or below the block body. It is possible to guide (assist) the progress of light between one end face of the semiconductor laser (end face of the reflection area) and the reflection area.

  The semiconductor laser according to the present invention emits multi-longitudinal mode laser light by having a reflection region having a relatively large coupling coefficient κ. If the coupling coefficient κ is too large, the oscillation spectrum width is controlled. The desired spectral shape cannot be obtained.

  In order to reduce the coupling coefficient κ that is too large, for example, the duty ratio a / Λ (a: the width of the block body in the optical axis direction, Λ: the width (period) of the block body and the semiconductor layer) may be reduced. Conversely, in order to further increase the coupling coefficient κ, the refractive index lower than the refractive index of the block body and higher than the refractive index of the semiconductor material surrounding the block body is formed on the upper layer or the lower layer of each of the plurality of block bodies. A coupling coefficient adjustment layer having the following may be provided. The degree of periodic refractive index change in the optical axis direction is enhanced by the coupling coefficient adjusting layer. In any case, the coupling coefficient κ having a desired size can be obtained.

  Electrodes (upper surface electrode and lower surface electrode) for allowing current to flow into the active layer are formed on the upper surface and the lower surface of the semiconductor laser, respectively. As described above, since light is generated not in the reflection region but in the active layer of the light emitting region, at least one of the upper surface electrode and the lower surface electrode may be formed only in the light emitting region.

  Preferably, an antireflection film is provided on an end surface of the reflection region (an end surface opposite to the end surface in contact with the light emitting region). Reflection of light that reaches the end face of the reflection region is suppressed by the antireflection film, so that unnecessary spectral components are prevented from being included in the spectrum of the multi-longitudinal mode laser light emitted from the semiconductor laser. .

  The present invention also provides a module in which the above-described semiconductor laser is packaged. In the module according to the present invention, the semiconductor laser and a lens for converging (condensing) the laser light emitted from the semiconductor laser are stored in a housing, and the laser light is connected to the housing to transmit the laser light to the housing. It is equipped with an optical fiber that leads to the outside. Multi-longitudinal mode laser light can be emitted from the optical fiber.

  A cooling element for cooling the heat generated by the semiconductor laser may be provided in the casing.

  The semiconductor laser (semiconductor laser module) according to the present invention can emit multi-longitudinal mode laser light, and is therefore suitable for use as an excitation light source in a Raman amplifier. The present invention provides the semiconductor laser module and a Raman amplifier provided with an optical fiber that causes laser light from the semiconductor laser module to be incident as excitation light and cause stimulated Raman amplification.

  FIG. 1 is a partially broken (omitted) perspective view of a semiconductor laser, and FIG. 2 is a longitudinal sectional view of the semiconductor laser. In FIG. 1 and FIG. 2, for the sake of clarity, hatching in the cross section is omitted, and the thickness of a plurality of semiconductor layers stacked on an n-type InP (indium-phosphorus) substrate 11 is emphasized. It is drawn.

  The semiconductor laser 1 includes a light emitting region 10A and a reflective region 10B formed continuously in the optical axis direction (a direction connecting the emission end surface 1a and the rear end surface 1b of the semiconductor laser 1). One end face of the light emitting region 10A is an emission end face 1a from which laser light is emitted. One end surface of the reflection region 10B is the rear end surface 1b. The other end surfaces of the light emitting region 10A and the reflective region 10B are in contact with each other. The exit end face 1a is preferably coated with a reflection film (antireflection film) (not shown) having a low reflectance. It is not necessary to coat the rear end face 1b with a highly reflective reflective film (not shown). This is because light can be reflected with a relatively high reflectance in the reflection region 10B, not in the rear end face 1b (details will be described later).

  A stripe-shaped active layer 13a is formed in the light emitting region 10A. The stripe-shaped active layer 13a is sandwiched from above and below by the upper clad layer 14 and the lower clad layer 12 and is sandwiched from the left and right by the block layers 15 and 16, thereby extending in a stripe shape (in a thin line shape) in the optical axis direction. The light generated in the active layer 13a is confined by the upper cladding layer 14, the lower cladding layer 12, and the current blocking layers 15 and 16. Light is generated in the active layer 13a by passing a current between the electrode 18 on the upper surface and the electrode 19 on the lower surface of the semiconductor laser 1.

  Also in the reflective region 10B, there is a semiconductor layer 13A having the same composition as the stripe active layer 13a sandwiched from above and below by the upper cladding layer 14 and the lower cladding layer 12 and sandwiched from the left and right by the current blocking layers 15 and 16 To do. As will be described later, the semiconductor layer 13A is formed by scraping the stripe-shaped active layer 13a at predetermined intervals in a direction orthogonal to the optical axis direction, and thus exists intermittently in the optical axis direction. . An upper cladding layer 14 having a refractive index smaller than that of the active layer 13a is embedded in the cut portion.

  The intermittently existing semiconductor layer 13A functions to reflect the light generated in the stripe active layer 13a in the light emitting region 10A. Hereinafter, each of the semiconductor layers 13A present intermittently is referred to as a block body 13A. A portion where the block bodies 13A and the upper cladding layer 14 are alternately arranged in the optical axis direction (a portion corresponding to the reflection region 10B) is hereinafter referred to as a reflection structure portion 13R.

  In the reflecting structure portion 13R, as described above, the block bodies 13A and the upper cladding layers 14 are alternately arranged in the optical axis direction. The refractive index of the upper cladding layer 14 and the refractive index of the block body 13A are different from each other (the refractive index of the upper cladding layer 14 is smaller than the refractive index of the block body 13A). That is, in the reflecting structure portion 13R, the refractive index of the medium periodically changes in the optical axis direction, and thus the reflecting structure portion 13R functions as if a diffraction grating is formed there. Note that the refractive indexes of the other semiconductor layers in contact with the block body 13A, that is, the lower cladding layer 12 and the block layers 15 and 16, are also smaller than the refractive index of the block body 13A.

  In the reflecting structure 13R, a diffraction grating is not formed on the upper layer or the lower layer (light confinement layer) of the active layer as in a general DFB semiconductor laser, but the active layer 13a itself (block body 13A). Is formed to have a periodic structure with respect to the refractive index. The refractive index difference between the active layer 13a (block body 13A) and the semiconductor layer surrounding the active layer 13a, particularly the upper clad layer 14, is large. For this reason, the degree of periodic refractive index change in the optical axis direction in the reflecting structure portion 13R, that is, the coupling coefficient κ, is a general DFB semiconductor laser (a diffraction grating is formed in the upper layer or lower layer of the active layer). ) Is larger than

  As described above, when a current is passed between the upper electrode 18 and the lower electrode 19 of the semiconductor laser 1, light is generated in the stripe-shaped active layer 13a formed in the light emitting region 10A. The generated light travels along the stripe-like active layer 13a. Light reflection is repeated between the emitting end face 1a of the semiconductor laser 1 and the reflecting structure 13R, and the light resonates to become laser light, which is emitted from the emitting end face 1a.

  As shown in FIG. 3, a guide layer 20 (for example, InGaAsP) (indium-gallium-arsenic-phosphorus) for guiding the progress of light in the optical axis direction is provided below the stripe-shaped active layer 13a and the block body 13A. Also good. The guide layer 20 is provided over the entirety of the light emitting region 10A and the reflecting region 10B (the entire length in the optical axis direction of the semiconductor laser 1A), whereby the light in the optical axis direction travels between the emission end face 1a and the reflecting structure portion 13R. Guided. The guide layer 20 may be provided above the stripe active layer 13a and the block body 13A, and may be provided only above or below the block body 13A.

Reflectance R of the light reflected at the reflective structure 13R is an optical axis direction of the length of the reflecting structure portion 13R (hereinafter, the reflection structure is referred to as a length L _G) vary depending on and coupling coefficient kappa. Further, the reflectance R in the reflective structure 13R varies depending on the wavelength of light.

FIG. 4 (A) a graph of the reflectance of the light reflecting structure portion 13R of the reflective structure length L _G is 50 [mu] m, FIG. 4 (B) light reflectance of the reflection structure portion 13R of the reflective structure length L _G is 100μm These graphs are shown respectively. 4A and 4B, the horizontal axis represents the wavelength detuning amount λ-λ _B from the Bragg wavelength, and the vertical axis represents the light reflectance (0 to 1). FIG. 4A shows three graphs when the coupling coefficient κ is 200 cm ⁻¹ , 300 cm ⁻¹ and 400 cm ⁻¹ , distinguished from each other by a broken line, a thin line, and a thick line. FIG. 4B shows three graphs when the coupling coefficient κ is 100 cm ⁻¹ , 200 cm ⁻¹ and 300 cm ⁻¹ , distinguished from each other by a broken line, a thin line, and a thick line.

The graphs shown in FIGS. 4 (A) and 4 (B) use the following equations, assuming that the Bragg wavelength λ _B is 1480 nm, the internal loss in the reflecting structure 13R is 0, and the equivalent refractive index n _eq is 3.14. The simulation results are shown.

Here L _G is reflected structural length, lambda _B is a Bragg wavelength, the internal loss per α is unit length, sigma is detuning the (wave number units), i is the imaginary unit, representing respectively.

Γ in Equation 1 is expressed by the following equation.

  Here, κ represents a coupling coefficient.

The detuning amount σ in Equation 1 and Equation 2 is expressed by the following equation.

n _eq represents the equivalent refractive index.

4A and 4B, the maximum reflectance R can be obtained when the wavelength λ of light is equal to the Bragg wavelength λ _B (λ−λ _B = 0). The reflectance R decreases as the wavelength of light λ increases from the Bragg wavelength λ _B.

When the detuning amount λ−λ _B exceeds the predetermined wavelength, the reflectance R decreases rapidly. 4 by comparison (A) and FIG. 4 (B), the reflective structure length L _G is short (Fig. 4 (A): the reflection structural length L _G = 50 [mu] m), detuning the reflectance R decreases abruptly The quantity λ−λ _B increases. That is, the width (reflection width) of the wavelength λ of light reflected at a relatively high reflectance R is widened. On the other hand, when the reflection structure length L _G is long (FIG. 4B: reflection structure length L _G = 100 μm), the detuning amount λ−λ _{B at} which the reflectance R decreases rapidly becomes small. That is, the width (reflection width) of the wavelength λ of light reflected at a relatively high reflectance R is narrowed. Thereby outputting a laser beam including a plurality of wavelength components from the semiconductor laser 1, i.e., when requesting a multi-mode oscillation semiconductor laser 1, the reflective structure length L _G is preferably short.

A shorter reflecting structural length L _G (see FIG. 4 (A)), the light having a wavelength width multimode oscillation is realized since the reflection becomes wider as described above is easily reflected in the reflecting structure portion 13R, reflecting structural length L _G in the other reflectance R becomes smaller than in the case long (see FIG. 4 (B)). In order to emit laser light efficiently, a reflectance R of about 0.9 (90%) is required for the reflecting structure portion 13R. From the viewpoint of the reflectance R of the light is reflected structural length L _G is longer it is convenient.

A longer reflected structural length L _G (see FIG. 4 (B)), it depending on the length of the stripe-shaped active layer 13a contribute to the generation of light (of striped active layer 13a corresponding to the light emitting region 10A Length: 1 and 2) are relatively short, the power of the emitted laser light is reduced. When determining the emission of high-power laser light to the semiconductor laser 1 is reflected structural length L _G is shorter it is convenient.

As described above, the reflective structure length L _G in the case of obtaining ease of multi-mode oscillation (the result difficulty of single mode oscillation) in the semiconductor laser 1 is relatively short. Reflecting structural length L _G in the case of obtaining the magnitude of the reflectance R to the semiconductor laser 1 is relatively long. When obtaining a predetermined power to the emitted laser beam is reflected structural length L _G is relatively short. Thus, the length of the reflecting structure length L _G is determined according to the characteristics required for the semiconductor laser 1.

  Here, if the reflectance R in the reflecting structure portion 13R is small, a large amount of light generated in the stripe-shaped active layer 13a is reflected not on the reflecting structure portion 13R but on the rear end face 1b of the semiconductor laser 1, so-called Fabry. Perot oscillation becomes dominant. This makes it difficult to control the wavelength of the laser light (wavelength selectivity) by the reflecting structure portion 13R. In order to ensure wavelength selectivity in the reflecting structure portion 13R, that is, in order to emit laser light having a desired wavelength (center wavelength) from the semiconductor laser 1, the magnitude of the reflectance R of the light in the reflecting structure portion 13R is large. have priority.

Reflectance R of the light in the reflection structure portion 13R, in addition to the length of the reflecting structure length L _G of the above, can be controlled by the coupling coefficient kappa.

When obtaining the reflectance R of about 0.9 (90%) to the reflective structure 13R, with reference to FIG. 4 (A), the coupling coefficient of about 400 cm ^-1 in the case reflection structural length L _G is 50μm κ is required. Referring to FIG. 4 (B), the coupling coefficient of about 200 cm ^-1 kappa is required if the reflective structural length L _G is 100 [mu] m.

In the semiconductor laser 1, the reflecting structure portion 13R has a structure in which block bodies 13A having the same composition as the active layer 13a and the upper cladding layer 14 are alternately arranged in the optical axis direction. The refractive index difference between the block body 13A and the upper cladding layer 14 is relatively large. For this reason, as described above, the semiconductor laser 1 has a larger degree of change in the refractive index in the optical axis direction than that of a conventional semiconductor laser in which a diffraction grating is formed in the upper layer or lower layer of the active layer, and is 300 cm ^−1. A relatively large coupling coefficient κ exceeding can be realized.

  Here, if the coupling coefficient κ is too large (see, for example, the thick line in FIG. 4B), the reflection bandwidth becomes too wide and the oscillation spectrum width cannot be controlled.

  In order to reduce the relatively large coupling coefficient κ by adopting a structure in which the block bodies 13A and the upper clad layer 14 are alternately arranged periodically in the optical axis direction, as shown in FIG. It is conceivable to reduce the duty ratio a / Λ (a: the width of the block body 13A in the optical axis direction, Λ: the width (period) of the block body 13A and the upper cladding layer 14) of the structure portion 13R. Needless to say, in order to reduce the duty ratio a / Λ, the width a of the block body 13A in the optical axis direction may be reduced, or the width Λ of the block body 13A and the upper cladding layer 14 may be increased.

  Conversely, in order to increase the coupling coefficient κ, as shown in FIG. 5B, a semiconductor layer (κ adjustment layer) 21 having a higher refractive index than that of the upper cladding layer 14 is formed above each block body 13A. (It goes without saying that the κ adjusting layer 21 has a refractive index lower than that of the block body 13A) may be further laminated (this semiconductor laser is denoted by reference numeral 1B). The degree of change in the refractive index of light in the optical axis direction (coupling coefficient κ) can be increased. Note that the κ adjustment layer 21 may be provided below each block body 13A.

Figure 6 is a reflecting structure length L _G is 100 [mu] m, the spectrum of the laser light emitted from the semiconductor laser 1, the coupling coefficient κ has a reflective structure 13R of 200 cm ^-1 (solid line reference in FIG. 4 (B)) The horizontal axis represents the wavelength of the laser beam and the vertical axis represents the light intensity.

  FIG. 7 shows another example of a semiconductor laser. The semiconductor laser 1C shown in FIG. 7 is different from the semiconductor laser 1 shown in FIGS. 1 and 2 in that an antireflection film (non-reflection film) 22 is provided on the rear end face 1b.

  As described above, when the reflectance of the reflecting structure portion 13R is about 0.9 (90%), the light reaches the rear end face 1b of the semiconductor laser, though slightly. As shown in FIG. 7, by providing an antireflection film 22 on the rear end face 1b of the semiconductor laser 1C, reflection of light reaching the rear end face 1b is suppressed, so that the spectrum of laser light emitted from the semiconductor laser 1C is reduced. Therefore, it is possible to suppress unnecessary spectral components from being included.

  FIGS. 8A to 11C show the manufacturing process of the semiconductor laser 1. 8 (A) to 8 (C), 9 (A), 9 (B), 9 (C-1) and 9 (D) show the optical axis direction connecting the emission end face 1a and the rear end face 1b of the semiconductor laser 1. FIG. A longitudinal sectional view is shown. FIG. 9C-2 is a plan view corresponding to FIG. 9C-1. FIGS. 10A to 10D and FIGS. 11A to 11C are longitudinal sectional views in a direction orthogonal to the optical axis direction of the semiconductor laser 1 (a cross section taken along line AA in FIG. 9D). ). In these drawings, the hatching showing the cross section is omitted.

  Referring to FIG. 8A, an n-type InP (indium-phosphorus) substrate 11 is prepared. Referring to FIG. 8B, an n-type InP lower cladding layer 12 is crystal-grown on a substrate 11, and then an InGaAsP (indium-gallium-arsenic-phosphorus) active layer 13 is crystal-grown. Although not shown in detail, the InGaAsP active layer 13 includes a multiple quantum well (MQW) structure in which a plurality of well layers and barrier layers are alternately stacked, and a separate closed sandwiching the multiple quantum well structure from above and below. It has an embedded heterostructure (SCH).

  Referring to FIG. 8C, a resist 23 is applied to the entire upper surface of the active layer 13.

  Referring to FIG. 9A, the resist 23 is exposed by an electron beam drawing method. The exposure is performed only in the area close to the rear end face, not near the exit end face. A plurality of resists 23 in a region near the rear end face are exposed in a streak pattern at predetermined intervals in a direction substantially perpendicular to the direction connecting the output end face and the rear end face. After the exposure to the resist 23, development is performed, and the resist 23 in a portion exposed by the exposure is removed.

  Referring to FIG. 9B, the whole is immersed in an etching solution containing sulfuric acid and hydrogen peroxide solution. The etching rate of InP constituting the lower cladding layer 12 is extremely slower than that of InGaAsP constituting the active layer 13. For this reason, the lower cladding layer 12 becomes an etch stop layer, and even the active layer 13 is etched in the portion where the resist 23 is removed. Thereby, the block body 13A is formed.

  Referring to FIG. 9C-1 and FIG. 9C-2, which is a plan view thereof, all the resists 23 are removed.

  Referring to FIG. 9D, the p-type InP upper cladding layer 14 is crystal-grown. The portion where the active layer 13 does not exist due to the etching described above is filled with the upper cladding layer 14. As a result, the block bodies 13A and the upper clad layers 14 are alternately arranged in the optical axis direction (formation of the reflection structure portion 13R) (see FIGS. 1 and 2).

10A and 10B (as described above, FIGS. 10A to 11C are longitudinal sectional views in a direction orthogonal to the optical axis direction of the semiconductor laser 1 (A in FIG. 9D). -A cross section along the line A)), an SiN _x or SiO ₂ insulating film 24 is deposited on the upper cladding layer 14 by plasma CVD (Chemical Vapor Deposition) method, and then the insulating film 24 is deposited on the insulating film 24. Resist 25 is applied.

  Referring to FIG. 10C, the resist 25 on both sides of the resist 25a is exposed except for the striped resist 25a extending in the optical axis direction connecting the emission end face and the rear end face, and the exposed resist 25 is removed. A striped resist 25a remains on the insulating film 24.

  Referring to FIG. 10D, the whole is immersed in an etching solution, and the insulating film 24 other than the portion masked by the stripe resist 25a is removed. On the upper surface of the upper cladding layer 14, the striped insulating film 24a and the striped resist 25a remain.

  Referring to FIG. 11A, striped resist 25a is removed and etching is performed using striped insulating film 24a as an etching mask. The upper cladding layer 14, the active layer 13, the lower cladding layer 12, and the substrate 11 are removed by etching around the striped insulating film 24a (on the left and right sides) to form a mesa structure. As a result, a stripe-shaped active layer 13a (see FIGS. 1 and 2) is formed.

  Referring to FIG. 11B, a p-type InP current blocking layer 15 and an n-type InP current blocking layer 16 are successively grown. Both sides of the mesa structure are buried by these current blocking layers 15 and 16. Striped insulating film 24a is removed, and then p-type InP cladding layer 17 is crystal-grown. A crystal of a p-type InGaAs contact layer may be further grown on the upper surface of the p-type InP cladding layer 17.

  Referring to FIG. 11C, the lower surface (back surface) of n-type InP substrate 11 is polished until the total thickness becomes about 100 μm. A top electrode (p-type electrode) 18 is deposited on the entire top surface of the p-type InP cladding layer 17, and a bottom surface electrode (n-type electrode) 19 is deposited on the entire bottom surface of the n-type InP substrate 11. Thereafter, both end faces (the position to be the exit end face and the position to be the rear end face) are cleaved. The exit end face is coated with an antireflection film (not shown) having a low light reflectance. The rear end face is coated with an antireflection film (not shown) having a reflectance of about several percent as necessary. When separated into chips one by one, the semiconductor laser 1 is completed.

  In the embodiment described above, the upper surface electrode 18 is formed on the entire upper surface of the semiconductor laser 1 and the lower surface electrode 19 is formed on the entire lower surface, but the range corresponding to the stripe-shaped active layer 13a contributing to light emission, that is, The upper surface electrode 18 and the lower surface electrode 19 may be formed only in the light emitting region 10A (see FIG. 2), and the upper surface electrode 18 and the lower surface electrode 19 may not be formed in the range of the reflective region 10B. Furthermore, only one of the upper surface electrode 18 and the lower surface electrode 19 may be formed only in the light emitting region 10A.

  FIG. 12 shows a longitudinal sectional view of an example of a coaxial semiconductor laser module provided with the semiconductor laser 1 described above.

  The coaxial semiconductor laser module 30 includes a CAN package 2. The outer shape of the CAN package 2 is formed by a disk-shaped stem 4 in which three leads 3 protrude downward and a hollow cylindrical cap 5 fixed on the disk-shaped stem 4. A cylindrical cap 5 contains a semiconductor laser 1 and a lens 6 that collects laser light emitted from the semiconductor laser 1. Note that a two-lens system configuration using two lenses may be used.

  The CAN package 2 is used by being fixed to a rectangular bottom plate 7. In the center of the bottom plate 7, a CAN fixing hole in which a step 7a and a screw groove 7b are formed is formed. When the CAN package 2 is inserted from the bottom to the top of the CAN fixing hole, the disk-shaped stem of the CAN package 2 is inserted. 4 contacts the stepped portion 7a. Thereafter, the stopper screw 8 with the lead through hole is screwed into the screw groove 7b of the CAN fixing hole, and thereby the CAN package 2 is securely fixed to the bottom plate 7. Screw holes 7 c are formed in the vicinity of the left and right ends of the bottom plate 7. The screw hole 7c is used when the coaxial semiconductor laser module 30 is fixed to a substrate or the like.

  A hollow cylindrical holder 31 is fixed to the tip portion of the cylindrical cap 5 of the CAN package 2. A cylindrical ferrule 32 is fixed to the tip of the cylindrical holder 31 via a sleeve 35. An optical fiber 33 passes through the cylindrical ferrule 32. A cylindrical cover 34 that surrounds a portion of the CAN package 2, the cylindrical holder 31, the cylindrical ferrule 32, and the optical fiber 33 is fixed to the bottom plate 7. Laser light emitted from the semiconductor laser 1 in the CAN package 2 is emitted from the CAN package 2 through the lens 6 and enters the optical fiber 33 through the holder 31.

  FIG. 13 shows a side sectional view of an example of the butterfly type semiconductor laser module 40 provided with the semiconductor laser 1. The semiconductor laser module 40 includes a rectangular parallelepiped package (housing), a lens 41 for condensing the laser light emitted from the semiconductor laser 1 and the semiconductor laser 1 inside the package, and preventing return light. An isolator 42 that receives light slightly emitted from the rear end face of the semiconductor laser 1 and a light receiving element 43 that monitors the operation of the semiconductor laser 1 are stored. The semiconductor laser 1 is placed on the submount 44, the lens 41 is held by a lens holder 45, and the light receiving element 43 is placed on the PD submount 46. A submount 44, a lens holder 45, a PD submount 46, and an isolator 42 are fixed on a substrate 47.

  A Peltier element 48 is fixed to the bottom surface inside the package. On the Peltier element 48, a substrate 47 on which the semiconductor laser 1, the lens 41, the isolator 42, and the light receiving element 43 are mounted is fixed.

  A circular emission port for guiding laser light emitted from the semiconductor laser 1 to the outside is formed on the front wall surface of the package, and a window glass 52 is attached to the front side thereof. A cylindrical ferrule 49 with the optical fiber 50 disposed at the center is fixed to the front wall surface of the package by a sleeve 53, and a cylindrical cover 51 surrounding the entire cylindrical ferrule 49 and a part of the optical fiber 50 is provided at the front. It is fixed on the wall. The laser light emitted from the semiconductor laser 1 reaches the front wall surface of the package through the lens 41, the isolator 42 and the window glass 52, and enters the optical fiber 50.

  As described above, the semiconductor laser 1 can emit multi-longitudinal mode laser light (see FIG. 6). The laser beam in the multi-longitudinal mode is realized by the reflection of light of a plurality of wavelengths in the reflection structure portion 13R (the arrangement structure of the block body 13A and the upper clad layer 14) formed inside the semiconductor laser 1, so that the emitted laser beam The wavelength stability of the light is high, and laser light with relatively high power can be emitted. Therefore, the semiconductor laser 1 (the coaxial semiconductor laser module 30 or the butterfly semiconductor laser module 40 provided with the semiconductor laser 1) can be applied to a Raman amplifier, a material analyzer, and the like.

  FIG. 14 shows a block diagram of a Raman amplifier using the above-described semiconductor laser module 40 as a pumping light source.

  In the Raman amplifier 60, the laser light emitted from the semiconductor laser module 40 is input to the amplification optical fiber 62 through the coupler 61 as excitation light. Stimulated Raman scattering occurs in the amplification optical fiber 62, and a gain is generated on the longer wavelength side by about 100 nm from the wavelength of the laser light (excitation light wavelength). When the signal light enters the amplification optical fiber 62, the signal light is amplified by the gain generated in the amplification optical fiber 62 (Raman amplification). Since the semiconductor laser 1 included in the semiconductor laser module 40 can emit multi-longitudinal mode laser light with relatively high power, the stimulated Brillouin scattering hardly occurs in the amplification optical fiber 62, and the signal light is spread over a long distance. Can be transmitted.

The partially broken perspective view of a semiconductor laser is shown. 1 shows a cross-sectional view of a semiconductor laser. It is sectional drawing which shows the other example of a semiconductor laser. (A), (B) shows the graph which shows the reflectance of the light in a reflection structure part, respectively. (A) is an enlarged sectional view of the reflecting structure portion, and (B) is a sectional view showing another example of the semiconductor laser. The spectrum of the laser beam emitted from the semiconductor laser is shown. It is sectional drawing which shows the other example of a semiconductor laser. (A), (B) and (C) show the manufacturing process of the semiconductor laser. (A), (B), (C-1) and (C-2), and (D) show the semiconductor laser manufacturing process. (A), (B), (C) and (D) show the manufacturing process of the semiconductor laser. (A), (B) and (C) show the manufacturing process of the semiconductor laser. It is a longitudinal cross-sectional view of a coaxial type semiconductor laser module. It is a sectional side view of a butterfly type semiconductor laser module. 1 shows a block diagram of a Raman amplifier.

Explanation of symbols

1,1A, 1B, 1C Semiconductor laser
10A light emitting area
10B reflection area
12 Lower cladding layer
13a Striped active layer
13A block body
13R Reflective structure
14 Upper cladding layer
15, 16 Current blocking layer
18 Top electrode
19 Bottom electrode
20 Guide layer
21 κ adjustment layer
22 Anti-reflective coating
30, 40 Semiconductor laser module
60 Raman amplifier

Claims (8)

A semiconductor laser in which a light emitting region and a reflective region are formed in series in the optical axis direction on a semiconductor substrate,
An active layer extending in the optical axis direction is formed in the light emitting region,
In the reflection region, a plurality of block bodies made of the same material as the active layer are periodically formed apart from each other on the extension of the active layer,
The plurality of block bodies are surrounded by a semiconductor material having a lower refractive index than the block body.
A multi-longitudinal mode laser beam is emitted from an end face of the light emitting region,
Semiconductor laser. An optical guide layer extending in the optical axis direction of the semiconductor laser is provided at least above or below the block body,
The semiconductor laser according to claim 1. A coupling coefficient adjusting layer having a refractive index lower than the refractive index of the block body and higher than the refractive index of the semiconductor material is provided on the upper layer or the lower layer of each of the plurality of block bodies.
The semiconductor laser according to claim 1. At least one of an upper electrode and a lower electrode formed on the upper and lower surfaces of the semiconductor laser, respectively, into which current for generating light in the active layer flows is formed only in the light emitting region;
The semiconductor laser according to claim 1. An antireflection film is provided on an end face of the reflection region,
The semiconductor laser according to claim 1. The semiconductor laser according to any one of claims 1 to 5 and a lens for converging a laser beam emitted from the semiconductor laser are stored in a housing.
An optical fiber that is connected to the housing and guides the laser light to the outside of the housing;
Semiconductor laser module. A cooling element for cooling the semiconductor laser;
The semiconductor laser module according to claim 6. The semiconductor laser module according to claim 6 or 7, and an optical fiber that causes the laser light from the semiconductor laser module to be incident as excitation light and to generate stimulated Raman amplification,
Raman amplifier equipped with.

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