JP2009147154A - Array semiconductor laser, semiconductor laser device, semiconductor laser module, and raman amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output multiplexed laser beams, without to use complex optical components. <P>SOLUTION: In an array semiconductor laser 1, a plurality of stripe-shaped active layers 14a to 14d are formed, with spacing therebetween, from a backward end surface to an emission end surface, in a surface parallel to the semiconductor substrate surface above the semiconductor substrate. As for each of the active layers 14a to 14d, the optical axis line of a beam which is waveguided slants toward the direction of the normal of the emission end surface at the position of the emission end surface, and bends so that all the plurality of laser beams emitted from the emission end surface through each of the active layers reach the same position. Diffraction gratings 21a to 21d are formed at the upper part or the lower part of the bending portion of the active layers 14a to 14d, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an array type semiconductor laser, a semiconductor laser device, a semiconductor laser module, and a Raman amplifier.

In order to expand the gain band in a Raman amplifier, it has been proposed to use a plurality of semiconductor lasers each emitting pumping light (laser light) having different wavelengths. In Patent Document 1, a plurality of semiconductor lasers each emitting laser beams of different wavelengths are prepared, and a combination of laser beams emitted from each of the plurality of semiconductor lasers is combined in a Raman amplifier. Used as excitation light.
JP 2000-98433 A

  However, in order to multiplex laser beams emitted from each of a plurality of independent semiconductor lasers, an optical member for multiplexing or the like is naturally required. In Patent Document 1 described above, a polarization beam combiner for polarization combining and a WDM coupler for multiplexing are provided. Optical fibers for guiding laser light are also required between the plurality of independent semiconductor lasers and the polarization combiner, and between the polarization combiner and the WDM coupler.

  An object of the present invention is to be able to output a combined laser beam without using a complicated optical member.

  It is another object of the present invention to be able to output a polarization-synthesized laser beam without using a complicated optical member.

  In the array type semiconductor laser according to the present invention, a plurality of stripe-shaped active layers are formed in a plane parallel to the substrate surface of the semiconductor substrate above the semiconductor substrate from the rear end surface to the emission end surface, spaced apart from each other, Each of the plurality of active layers has an optical axis of light guided through the active layer inclined obliquely with respect to the normal direction of the emission end face at the position of the emission end face, and from the emission end face through each of the plurality of active layers. Each of the plurality of emitted laser beams is bent so as to reach the same position, and a diffraction grating whose Bragg wavelength monotonously increases or decreases is provided above or below at least a part of each of the plurality of active layers. The optical resonator is formed by the rear end face and the diffraction grating. The position where a plurality of laser beams emitted from the emission end face through each of the plurality of active layers reaches (passes) may be a single point or a region having a certain extent.

  In one embodiment, the diffraction grating that monotonously increases or decreases the Bragg wavelength is formed by forming diffraction gratings having a uniform pitch above or below the bent portions of the plurality of active layers, respectively. Since the diffraction grating is formed above or below the bent portion of the active layer, even if the pitch is uniform, the optical path of light between the many unit gratings constituting the diffraction grating becomes longer toward the emission end face. Become. For this reason, the wavelength of light reflected by the diffraction grating (Bragg wavelength) is chirped, and oscillation (resonance) of light including a plurality of wavelength components is achieved. The oscillation wavelength is not single mode but multimode. The laser light emitted from the emission end face through the active layer includes a plurality of wavelength components.

  In another embodiment, the diffraction grating that monotonously increases or decreases the Bragg wavelength is formed by forming chirped diffraction gratings with varying pitches above or below the plurality of active layers. Even in a chirped diffraction grating having a varying pitch, the wavelength of light reflected by the diffraction grating (Bragg wavelength) is chirped, and oscillation (resonance) of light including a plurality of wavelength components is achieved. The oscillation wavelength becomes multimode, and the laser light emitted through the active layer contains a plurality of wavelength components.

  According to the present invention, the plurality of stripe-shaped active layers are bent so that all of the plurality of laser beams emitted from the emission end face reach the same position. Therefore, the plurality of laser lights emitted from the emission end face (described above) (Each laser beam includes a plurality of wavelength components) reaches the same position. For this reason, it is possible to obtain a high-power multimode laser beam without requiring an optical member for combining the laser beams, and to efficiently make the laser beams incident on one optical fiber or one lens member. be able to.

  Further, since each of the active layers has an optical axis of light guided through the active layer at the position of the emission end face, the optical axis is inclined with respect to the normal direction of the emission end face. Light is emitted obliquely from the end face. Compared with the case where the light is emitted from the emission end face in the normal direction, the reflectance of the laser beam at the emission end face is lowered, and inappropriate end face reflection can be suppressed.

  Preferably, the diffraction gratings formed above or below the plurality of active layers have different pitches (average pitch in the case of a chirped diffraction grating). The center wavelengths of the plurality of laser beams can be made different from each other. By adjusting the average pitch of the diffraction grating, the center wavelengths of the plurality of laser beams can be separated from each other at a desired interval. A plurality of laser beams having desired center wavelengths, each of which is in a multi-mode, are emitted from the emission end face.

  In one embodiment, a plurality of striped active layers included in the array type semiconductor laser are paired, and a plurality of active layers having the same central wavelength are formed above or below the two active layers forming the pair. A diffraction grating that reflects light including wavelength components is formed, and includes a polarization plane rotating unit that rotates the polarization plane of the laser light emitted through one of the two active layers forming the pair by 90 degrees. It is done. Of the two laser beams having the same center wavelength, the polarization of one laser beam can be a horizontal polarization, and the polarization of the other laser beam can be a vertical polarization. As described above, since a plurality of laser beams emitted from the emission end face of the array type semiconductor laser reach the same position, a laser beam having a horizontal polarization plane and a laser beam having a vertical polarization plane are combined in the polarization synthesis. Therefore, it is possible to obtain a synthesized (polarized synthesized) laser beam without requiring an optical member.

  The present invention also provides an external resonator type semiconductor laser device using a diffraction grating formed in an optical fiber. In the external cavity semiconductor laser device according to the present invention, a plurality of stripe-shaped active layers are spaced from each other in a plane parallel to the substrate surface of the semiconductor substrate above the semiconductor substrate from the rear end surface to the emission end surface. An array type gain chip is formed, and an optical fiber in which a chirped diffraction grating whose Bragg wavelength monotonously increases or decreases is formed. Each of the plurality of active layers of the array-type gain chip has the optical axis of light guided through the active layer obliquely with respect to the normal direction of the exit end face at the exit end face, A plurality of lights emitted from the emission end face through the layer are bent so as to enter the optical fiber. An optical resonator is constituted by the rear end face of the array type gain chip and the chirped diffraction grating in the optical fiber.

  In the external resonator type semiconductor laser device according to the present invention, an optical resonator is constituted by the rear end face of the array type gain chip and the chirped diffraction grating formed in the optical fiber. An array-type gain chip does not oscillate by itself (thus, it is not called “laser” but called “gain chip”). A plurality of stripe-shaped active layers are formed on the array-type gain chip, and each of the active layers has a normal direction of the exit end face at the position of the exit end face where the optical axis of the light guided through the active layer is located. Since the plurality of lights emitted from the emission end face through each of the plurality of active layers are bent so as to reach the same position, an optical member for combining the lights is required. Therefore, a plurality of lights emitted from the array type gain chip can be efficiently incident on the optical fiber on which the chirped diffraction grating is formed.

  When light from an array-type gain chip is incident on an optical fiber on which a chirped diffraction grating is formed, the wavelength of the light reflected by the chirped diffraction grating is chirped, and oscillation of light containing multiple wavelength components is achieved. The Since the oscillation wavelength is made multimode, the laser light includes a plurality of wavelength components.

  In one embodiment, a plurality of stripe-shaped active layers included in the array-type gain chip are paired, and light emitted through one of the two active layers forming the pair is reflected. Polarization plane rotating means for rotating the polarization plane by 90 degrees is provided. A polarization-synthesized laser beam can be obtained without requiring an optical member for polarization synthesis.

  The present invention also provides a module in which an array type gain chip included in an array type semiconductor laser, an array type semiconductor laser, and a polarization plane synthesizing unit as described above or an external resonator type semiconductor laser device is packaged. is doing. The module according to the present invention includes an array type gain chip included in the array type semiconductor laser, a semiconductor laser device including the array type semiconductor laser and a polarization plane rotating means, or the external resonator type semiconductor laser device, and the array. A lens for converging a plurality of laser beams emitted from the emission end face of the semiconductor laser or a plurality of light emitted from the array gain chip, and a cooling element for cooling the array semiconductor laser or the array gain chip It is stored in the housing. An optical fiber for guiding laser light to the outside of the casing is connected to the casing. When the array-type gain chip is stored in the housing, an optical fiber connected to the housing having a chirped diffraction grating formed therein is used.

  Furthermore, since the array type semiconductor laser (semiconductor laser module) according to the present invention can emit multi-mode laser light including a plurality of wavelength components, it is suitable for use as a light source for excitation light in a Raman amplifier. ing. The present invention relates to a semiconductor laser module in which an array-type semiconductor laser or the like is housed in a housing, and a Raman having an optical fiber on which laser light from the semiconductor laser module is incident as excitation light and causes stimulated Raman scattering. An amplifier is provided.

(First embodiment)
FIG. 1 is a perspective view showing the appearance of the array type semiconductor laser of the first embodiment together with an active layer and a diffraction grating included in the array type semiconductor laser. FIG. 2 is a plan view of the array type semiconductor laser shown in FIG. In FIG. 2, for the sake of clarity, the active layer and the diffraction grating included in the array type semiconductor laser are drawn with solid lines.

  The array type semiconductor laser 1 is an edge emitting semiconductor laser, and both end faces (the emitting end face 1a and the rear end face 1b) are cleaved in parallel with each other. The emission end face 1a of the array type semiconductor laser 1 is coated with an antireflection film 51, and the rear end face 1b is coated with a reflection film 52.

  In the array type semiconductor laser 1, four stripe-like (stripes, fine lines) active layers are spaced apart from each other from the rear end face 1b to the emission end face 1a in a plane parallel to the substrate surface. Is formed. Hereinafter, the four stripe-shaped active layers are referred to as first, second, third and fourth active layers 14a to 14d, respectively. Each of the first to fourth active layers 14 a to 14 d has one end in contact with the rear end face 1 b of the array type semiconductor laser 1 and the other end in contact with the emission end face 1 a of the array type semiconductor laser 1.

  In general, a semiconductor laser is configured by laminating a plurality of semiconductor layers having different compositions, types and amounts of impurities on a semiconductor substrate. The stripe-shaped first to fourth active layers 14a to 14d are formed in a form capable of confining light in a stripe shape in one or a plurality of layers.

  Each of the first to fourth active layers 14a to 14d includes a portion extending straight from the rear end surface 1b toward the emission end surface 1a (linear portion), and a portion bent (bent) on the way to the emission end surface 1a. Part). The angles of the bent portions of the first to fourth active layers 14a to 14d are slightly different. For this reason, all of the four laser beams emitted from the emission end face 1a through the first to fourth active layers 14a to 14d are emitted obliquely from the emission end face 1a, and one point outside the array type semiconductor laser 1 ( (Including a range having a certain extent)) (details will be described later).

  The diffraction gratings 21a to 21d are formed at positions corresponding to the bent portions of the first to fourth active layers 14a to 14d and below the first to fourth active layers 14a to 14d. . Each of the diffraction gratings 21a to 21d is formed at a uniform pitch (including a variation that can be regarded as a substantially uniform pitch). The diffraction gratings 21a to 21d are all directed in a direction parallel to the emission end face 1a and the reflection end face 1b of the array type semiconductor laser 1. The diffraction gratings 21a to 21b may be formed above the first to fourth active layers 14a to 14d or on the semiconductor substrate.

  Upper surface electrodes 41a, 41b, 41c, and 41d are provided apart from each other in a range corresponding to the upper side of each of the first to fourth active layers 14a to 14d on the upper surface of the array type semiconductor laser 1. A bottom electrode 42 is provided on the entire bottom surface of the array type semiconductor laser 1.

  When a current is passed between the upper surface electrode 41a and the lower surface electrode 42 above the first active layer 14a, light is generated in the first active layer 14a. The light generated in the first active layer 14a travels along the first active layer 14a (the optical waveguide including the first active layer 14a), and the diffraction grating 21a, the rear end face 1b (and the reflection film 52), Reflection is repeated between the two, whereby the light resonates and becomes laser light. The laser beam is emitted from the emission end face 1a.

  Similarly, in the second to fourth active layers 14b to 14d, when current is passed between the upper surface electrodes 41b to 41d and the lower surface electrode 42, light is generated in the second to fourth active layers 14b to 14d. The generated light is repeatedly reflected between the diffraction gratings 21b to 21d and the rear end face 1b (and the reflection film 52), whereby the light resonates to become laser light and is emitted from the emission end face 1a.

  FIG. 3 is an enlarged view of the first active layer 14a and the diffraction grating 21a in the vicinity of the emission end face 1a of the array type semiconductor laser 1. FIG. Also in FIG. 3, the first active layer 14a and the diffraction grating 21a are drawn by solid lines for easy understanding. Further, the illustration of the upper surface electrode 41a and the illustration of the antireflection film 51 are omitted.

As described above, the diffraction grating 21a is formed at a uniform pitch. However, since the diffraction grating 21a is formed below the bent portion of the first active layer 14a, the optical path of the light between the unit gratings even if the spacing between the unit gratings constituting the diffraction grating 21a is uniform. Becomes longer toward the exit end face 1a. For this reason, the wavelength (Bragg wavelength) of the light reflected by the diffraction grating 21a is chirped. That is, the diffraction grating 21a reflects light of a plurality of wavelength components, and the laser light emitted from the emission end face 1a through the first active layer 14a includes a plurality of wavelength components (including a plurality of longitudinal modes). (Multi mode oscillation). The wavelength (λ _I ) of the light reflected at the portion of the diffraction grating 21a where the optical path between the unit gratings is relatively short (the part far from the emission end face 1a) is relatively short, and the optical path of the light between the unit gratings is relatively short. The wavelength (λ _II ) of the light reflected by the long diffraction grating 21a (the portion close to the emission end face 1a) is relatively long (λ _I <λ _II ).

  Since the diffraction gratings 21b to 21d are also formed below the bent portions of the second to fourth active layers 14b to 14d, they are emitted from the emission end face 1a through the second to fourth active layers 14 in the same manner as described above. The laser beam to be emitted also includes a plurality of wavelength components (including a plurality of longitudinal modes).

Returning to FIGS. 1 and 2, as described above, the diffraction gratings 21a to 21d formed below the first to fourth active layers 14a to 14d in the stripe shape are all formed at a uniform pitch. However, the pitches of the diffraction gratings 21a to 21d are different from each other. Specifically, the pitch Λ ₁ of the diffraction grating 21a formed below the first active layer 14a is wider than the pitch Λ _{2 of the} diffraction grating 21b formed below the second active layer 14b. (Λ ₁ > Λ ₂ ). The pitch Λ ₂ of the diffraction grating 21b below the second active layer 14b is wider than the pitch Λ ₃ of the diffraction grating 21c below the third active layer 14c (Λ ₂ > Λ ₃ ). The pitch Λ ₃ of the diffraction grating 21c below the third active layer 14c is wider than the pitch Λ ₄ of the diffraction grating 21d below the fourth active layer 14d (Λ ₃ > Λ ₄ ). That is, the pitches of the diffraction gratings 21a to 21d formed below the first to fourth active layers 14a to 14d have a relationship of Λ ₁ > Λ ₂ > Λ ₃ > Λ ₄ . 1 and 2, the pitch of the diffraction gratings 21a to 21d is drawn with emphasis.

The center wavelength of the multi-mode laser beam emitted from the semiconductor laser including the diffraction grating is defined by the pitch of the diffraction grating. As described above, since the diffraction gratings 21a to 21d formed below the first to fourth active layers 14a to 14d have different pitches, they are emitted through the first to fourth active layers 14a to 14d. The center wavelengths λ ₁ , λ ₂ , λ ₃ , and λ ₄ of the _four laser beams emitted from the end face 1a are different from each other. When the pitch of the diffraction grating is wide, the wavelength of the laser light becomes a long wavelength. As described above, the pitches of the diffraction gratings 21a to 21d formed below the first to fourth active layers 14a to 14d have a relation of Λ ₁ > Λ ₂ > Λ ₃ > Λ ₄ , respectively. The center wavelengths of the laser beams emitted through the first to fourth active layers 14a to 14d have a relationship of λ ₁ > λ ₂ > λ ₃ > λ ₄ . From the emission end face 1a of the array type semiconductor laser 1, four laser beams having different center wavelengths and including a plurality of wavelength components are emitted from each of the emission end faces 1a.

FIG. 4 shows the traveling directions of the four laser beams emitted from the emission end face 1 a through the first to fourth active layers 14 a to 14 d of the array type semiconductor laser 1. In FIG. 4, theta ₁ through? _4, the angle formed between the normal direction of four laser beam and emitting end face 1a incident on the emitting end face 1a (hereinafter, referred to as "waveguide angle") each, alpha ₁ ~ α ₄ represents each angle formed by the four laser beams emitted from the emission end face 1a and the normal direction of the emission end face 1a (hereinafter referred to as “emission angle”).

  As described above, each of the first to fourth active layers 14a to 14d is bent in the middle from the rear end face 1b to the emission end face 1a (see FIGS. 1 and 2). For this reason, all of the four laser beams emitted from the emission end face 1a of the array type semiconductor laser 1 through the first to fourth active layers 14a to 14d are obliquely incident on the emission end face 1a and obliquely enter the emission end face 1a. To exit. Compared with the case where the laser beam is incident on the emission end face 1a perpendicularly, the reflectance of the laser beam at the emission end face 1a can be kept low.

Moreover, four active layers waveguide angle theta ₁ through? ₄ of 14a~14d, any of the four laser beam outside the single point of the array type semiconductor laser 1 reaches (reach point or passing point) (pass) Has an angle that is (guided). In this embodiment, the waveguide angle theta ₁ through? ₄ of the first to fourth active layer 14a~14d has a _{θ 1> θ 2> θ 3} > θ 4 relationship. Of course, the emission angles α _{1 to} α _{4 of the four} laser beams emitted from the first to fourth active layers 14a to 14d also have a relationship of α ₁ > α ₂ > α ₃ > α ₄ . Since the refractive index of the air layer is smaller than the refractive index of the semiconductor layer of the array type semiconductor laser 1, the laser light incident on the air layer is refracted. That is, there is a relationship of waveguide angle θ _i <output angle α _i (i = 1, 2, 3, 4).

  The laser light emitted from the emission end face 1a through each of the first to fourth active layers 14a to 14d reaches (passes) one external point (arrival point, passing point). For this reason, by arranging an optical fiber or a lens member at or near the position of the arrival point, any of the four laser beams having different center wavelengths and each containing a plurality of wavelength components can be efficiently processed. It can be incident on a single optical fiber or lens member.

  The array type semiconductor laser 1 has different optical path lengths of four laser beams from the emission end face 1a to the arrival point. In order to make the optical path lengths coincide with each other, an optical path length difference correcting member made of a material having a negative refractive index may be inserted between the array type semiconductor laser 1 and the optical fiber (or lens member). .

  FIG. 5 is a graph of a laser beam (hereinafter referred to as a combined laser beam) after the four laser beams emitted from the array type semiconductor laser 1 are combined (wavelength on the horizontal axis and spectral intensity on the vertical axis). ). In FIG. 5, the solid line indicates the spectrum, and the broken line indicates the spectrum envelope.

As described above, the array type semiconductor laser 1 emits four laser beams having different center wavelengths λ ₁ , λ ₂ , λ ₃ , and λ ₄ (λ ₁ > λ ₂ > λ ₃ > λ _4). ). These four laser beams are combined at one point (arrival point, passing point) outside the array type semiconductor laser 1.

The combined laser beam is obtained by combining _four laser beams having different center wavelengths λ ₁ , λ ₂ , λ ₃ , and λ ₄ and each including a plurality of wavelength components. Therefore, as shown in FIG. 5, the spectrum draws _four envelopes E ₁ , E ₂ , E ₃ and E ₄ . Multiple laser beams each containing multiple wavelength components (multiple oscillation longitudinal modes) can be combined without providing a complicated optical system (coupler, optical fiber for guiding laser light from a semiconductor laser to a coupler, etc.) The combined laser beam can be obtained.

  6A to 13C show a manufacturing process of the array type semiconductor laser 1 shown in FIGS. In these drawings, (A) is a plan view in which the lower side of the paper is the emission end face. (B) And (C) is an end elevation which follows the BB line and CC line in (A), respectively. In FIGS. 6A to 13C, the stacking (thickness) direction of the semiconductor layer, the width of the diffraction grating, the pitch of the diffraction grating, and the like are emphasized for convenience of drawing and easy understanding. It is.

  6A to 6C, an InGaAsP (indium-gallium-arsenic-phosphorus) diffraction grating forming layer 12 is grown on an n-type InP (indium-phosphorus) substrate 11, and thereafter A resist 36 is applied on the entire surface of the InGaAsP diffraction grating forming layer 12. For the crystal growth of the InGaAsP diffraction grating forming layer 12 and other semiconductor layers described later, metal organic chemical vapor deposition (MOCVD) (Metal Organic Chemical Vapor Deposition) can be used.

  Referring to FIGS. 7A to 7C, the resist 36 is exposed by pattern drawing with an electron beam. As described above, the array type semiconductor laser 1 finally formed has the first to fourth stripe-shaped active layers 14a to 14d having bent portions, and a pitch is formed below the bent portions. Different diffraction gratings 21a to 21d are formed (see FIG. 2). Pattern drawing using an electron beam is performed in a direction perpendicular to the optical resonance axis direction along each of the regions to be bent among the regions where the first to fourth active layers 14a to 14d are to be formed. It is performed with different pitches.

  With reference to FIGS. 8A to 8C, after the above-described exposure of the resist 36, development is performed, and the resist 36 exposed in the exposure is removed. In this state, the whole is immersed in an etching solution containing sulfuric acid and hydrogen peroxide solution. Diffraction gratings 21 a to 21 d are formed on the diffraction grating forming layer 12. Thereafter, all resist 36 is removed.

  With reference to FIGS. 9A to 9C, an InP spacer layer 13, an InGaAsP active layer 14, and an InP clad layer 15 are grown in order. Although not shown or described in detail, the InGaAsP active layer 14 has a multiple quantum well structure in which a plurality of well layers and barrier layers are alternately stacked. An optical separation and confinement layer may be further laminated on the upper layer and the lower layer of the active layer.

10A to 10C, a p-type InP clad layer 18 is crystal-grown on the upper surface of the InP clad layer 15, and SiO ₂ is formed on the p-type InP clad layer 18 by plasma CVD. Deposit a film. For each of the regions to be the first to fourth active layers 14a to 14d, four (four) stripe-shaped masks bent in the middle from the position to be the rear end face to the position to be the emission end face Is transferred onto the SiO ₂ film by a photolithography process (detailed processes are omitted). The SiO ₂ film other than the portion masked by the resist is removed. On the upper surface of the p-type InP cladding layer 18, four striped SiO ₂ masks 19 having bent portions remain.

Referring to FIGS. 11A to 11C, etching is performed with the striped SiO ₂ mask 19 left. The periphery of the striped SiO ₂ mask 19 is etched away to form four mesa structures. First to fourth stripe-shaped active layers 14a to 14d are formed.

Referring to FIGS. 12A to 12C, a p-type InP blocking layer 31 and an n-type InP blocking layer 32 are sequentially crystal-grown. Both sides of the four mesa structures are filled with the p-type InP block layer 31 and the n-type InP block layer 32. Thereafter, the SiO ₂ mask 19 is removed.

  Referring to FIGS. 13A to 13C, a p-type InP clad layer 33 and a p-type InGaAs contact layer 34 are successively grown. Thereafter, the lower surface (back surface) of the n-type InP substrate 11 is polished until the total thickness becomes about 100 μm. Upper surface electrodes (p-type electrodes) 41a to 41d are deposited on the upper surface of the p-type InGaAs contact layer 34 along the range where the diffraction gratings 21a to 21d are formed so as to cover the active layers 14a to 14d, respectively. A bottom electrode (n-type electrode) 42 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. An antireflection film 51 having a low light reflectance is coated on the emission end face, and a reflection film 52 having a high light reflectance is coated on the rear end face. The array type semiconductor laser 1 is completed.

(Modification)
FIG. 14 shows another modification of the array type semiconductor laser, and shows a plan view of the array type semiconductor laser 1A. 15A to 15D are cross-sectional views of the diffraction gratings 22a to 22d formed below the first to fourth active layers 14a to 14d. The diffraction gratings 22a to 22d have a uniform pitch at the point where the diffraction gratings 22a to 22d are formed not below the bent portions of the first to fourth active layers 14a to 14d but below the linear portions, and at the diffraction gratings 22a to 22d. However, the chirping is different from the array type semiconductor laser 1 shown in FIGS. The same members as those of the array type semiconductor laser 1 of the first embodiment are denoted by the same reference numerals to avoid redundant description.

The average pitches of the diffraction gratings 22a to 22d formed below the linear portions of the first to fourth active layers 14a to 14d are different from each other (FIGS. 15A to 15D). Therefore, similar to the array type semiconductor laser 1 of the first embodiment, the center wavelengths λ _{1 to} λ ₄ of the laser beams emitted from the emission end face 1a through the first to fourth active layers 14a to 14d are different from each other. λ ₁ > λ ₂ > λ ₃ > λ ₄ .

  In the array type semiconductor laser 1 (FIGS. 1 and 2) of the first embodiment described above, each of the diffraction gratings 21a to 21d is formed at a uniform pitch. In the first embodiment, such diffraction gratings 21a to 21a are formed below the bent portions of the first to fourth active layers 14a to 14d, respectively, so that the oscillation wavelength is made multimode. On the other hand, in the array type semiconductor laser 1A of the modified example, the pitches of the diffraction gratings 22a to 22d are changed (FIGS. 15A to 15D). Also in the modified array type semiconductor laser 1A, the wavelengths of light reflected by the diffraction gratings 22a to 22d are chirped, and four laser beams emitted from the emission end face 1a through the first to fourth active layers 14a to 14d. Each include a plurality of wavelength components (including a plurality of longitudinal modes) (multi-mode oscillation).

  All of the four laser beams each having a plurality of wavelength components and having different center wavelengths reach (pass through) one point (arrival point or passing point) outside the array type semiconductor laser 1A. The wave is the same as that of the array type semiconductor laser 1 described above. Therefore, the spectrum of the combined laser beam after being emitted from the array type semiconductor laser 1A in the modified example and combined is the same as that shown in FIG. Note that the diffraction gratings 22a to 22d may be formed on the entire linear portion of the first to fourth active layers 14a to 14d.

(Second embodiment)
FIG. 16 shows a plan view of an array type semiconductor laser 2 (semiconductor laser module) of the second embodiment provided with a quarter wavelength plate.

  Four stripe-shaped active layers 14a to 14d are formed at a predetermined interval from the rear end face 1b to the emission end face 1a, and all of them are bent on the way to the emission end face 1a. Is the same as the array type semiconductor laser 1 (FIGS. 1 and 2) of the first embodiment described above. Further, the first embodiment also has a diffraction grating having a uniform pitch at a position corresponding to a bent portion in each of the active layers 14a to 14d and below the active layers 14a to 14d. This is the same as the array type semiconductor laser 1 of FIG.

  Diffraction gratings 23a to 23d are formed below the bent portions of the first to fourth active layers 14a to 14d formed in the array type semiconductor laser 2.

Both of the two laser beams emitted from the emission end face 1a through the first and second active layers 14a and 14b have the center wavelength λ ₁ and from the emission end face 1a through the third and fourth active layers 14a and 14b. Both of the two emitted laser beams have a center wavelength λ ₂ . Since the angle of the bent portion of the first active layer 14a is larger than the angle of the bent portion of the second active layer 14b, the pitch Λ ₁ of the diffraction grating 23a below the first active layer 14a is set to the second active layer. By making it slightly narrower than the pitch Λ ₂ of the diffraction grating 23b below 14b, the two laser beams emitted from the emission end face 1a through the first and second active layers 14a and 14b have the same central wavelength λ ₁ . Can be. Similarly, by making the pitch Λ ₃ of the diffraction grating 23c below the third active layer 14c slightly narrower than the pitch Λ ₄ of the diffraction grating 23d below the fourth active layer 14d, the third and fourth active layer 14c, can be any two of the laser light emitted from the exit end face 1a through 14d shall have the same center wavelength lambda _2.

The pitches Λ ₁ and Λ ₂ of the diffraction grating 23a formed below the bent portions of the first and second active layers 14a and 14b are below the third and fourth active layers 14c and 14d. The pitch Λ ₃ and pitch Λ _{4 of the} formed diffraction grating 21b are wider. Therefore, the center wavelength λ ₁ of the two laser beams emitted from the emission end face 1a through the first and second active layers 14a and 14b is emitted from the emission end face 1a through the third and fourth active layers 14a and 14b. two longer than the center wavelength lambda ₂ of the laser beam (λ _1> λ _2). Since the diffraction gratings 23a to 24d are all formed below the bent portions of the active layers 14a to 14d, the laser beams emitted from the emission end face 1a through the first to fourth active layers 14a to 14d are all. Includes multiple wavelength components.

  A quarter-wave plate 61 is provided on the optical path of laser light emitted from the emission end face 1a through the first active layer 14a and on the optical path of laser light emitted from the emission end face 1a through the third active layer 14c. Is provided. The laser light emitted through the first active layer 14a and the third active layer 14c has a polarization plane rotated by 90 degrees by the quarter-wave plate 61, and becomes vertically polarized laser light. On the other hand, the laser light emitted through the second active layer 14b and the fourth active layer 14d is not subjected to polarization plane rotation, and therefore the horizontally polarized laser light is emitted as it is.

  FIG. 17 shows a laser beam (combined laser beam) after combining four laser beams emitted from the array type semiconductor laser 2 (semiconductor laser module) having the quarter wavelength plate 61 shown in FIG. The spectrum of is shown. In FIG. 17, the solid line indicates the spectrum of horizontally polarized laser light, and the alternate long and short dash line indicates the spectrum of vertically polarized laser light.

As described above, from the array semiconductor laser 2, the laser beam horizontally polarized laser beam and the center wavelength of the vertical polarization is lambda ₁ center wavelength is lambda _1, the center wavelength is lambda ₂ vertical A polarized laser beam and a horizontally polarized laser beam having a center wavelength of λ ₂ are emitted. All of these four laser beams contain a plurality of wavelength components. For this reason, as shown in FIG. 17, an envelope E ₁ is drawn by horizontal and vertical polarization laser beams having a center wavelength of λ ₁ , and two horizontal and vertical polarization lasers having a center wavelength of λ ₂ are drawn. An envelope E ₂ is drawn by the light.

  In the array type semiconductor laser 2 of the second embodiment, it is possible to obtain polarized and combined laser light (combined laser light). Without providing a complicated optical system member (coupler, optical fiber for guiding laser light from the semiconductor laser to the coupler, etc.), it is possible to obtain a laser beam that has been combined and polarized and combined.

  Also in the array type semiconductor laser 2 of the second embodiment, the pitch of the diffraction gratings 23a and 23b itself is changed below the bent portions of the active layers 14a to 14d as in the modification of the first embodiment. Instead, the diffraction gratings 23a and 23b may be formed below the linear portions of the active layers 14a to 14d.

(Third embodiment)
FIG. 18 shows the third embodiment and is a block diagram showing a configuration of an external resonator type semiconductor laser device using a fiber Bragg grating.

  The external resonator type semiconductor laser device 4 includes an array type gain chip 3, a quarter wavelength plate 61, a collimating lens 62, and an optical fiber 63. A diffraction grating 63a is formed inside the optical fiber 63 by applying a periodic refractive index modulation to the core portion thereof. The diffraction grating 63a is chirped, and light having a plurality of wavelengths is reflected by the diffraction grating 63a.

  Both end faces (the emission end face 3a and the rear end face 3b) of the array-type gain chip 3 are cleaved in parallel with each other. The outgoing end face 3a is coated with an antireflection film 51, and the rear end face 3b is coated with a reflective film 52 having a high light reflectance.

  In the array-type gain chip 3, two stripe-like (striped and fine-line-shaped) active layers 14e and 14f are formed in a plane parallel to the substrate surface from the rear end face 3b to the emission end face 3a. Are formed with an interval of. The two stripe-shaped active layers 14e and 14f are referred to as a first active layer 14e and a second active layer 14f, respectively. One end of each of the first and second active layers 14 e and 14 fb is in contact with the emission end face 3 a of the array type gain chip 3, and the other end is in contact with the rear end face 3 b of the array type gain chip 3.

  The stripe-shaped first and second active layers 14e and 14f are formed to bend in a direction facing each other on the way to the emission end face 3a. The light generated in the first and second active layers 14 e and 14 f is emitted obliquely from the emission end face 3 a and enters the collimator lens 62.

  A quarter-wave plate 61 is provided at a position where light emitted through the first active layer 14e passes. The light emitted through the first active layer 14e is rotated by 90 degrees by the quarter-wave plate 61 to be vertically polarized. Light emitted through the second active layer 14f remains horizontally polarized.

  Upper surface electrodes 41e and 41f are provided in ranges corresponding to the upper surfaces of the first and second active layers 14e and 14f on the upper surface of the array-type gain chip 3, respectively. A bottom electrode (the bottom electrode is not visible in FIG. 18) is provided on the entire bottom surface of the array type gain chip 10. The array type gain chip 3 has a diode structure, and when a forward current is passed between the upper surface electrodes 41e and 41f and the lower surface electrodes above the first and second active layers 14e and 14f, , Light is generated in the second active layers 14e and 14f.

  The light generated in the first active layer 14e travels along the first active layer 14e and is emitted from the emission end face 3a. The light emitted from the emission end face 3 a is rotated by 90 ° by the quarter-wave plate 61 and then converted into parallel light by the collimator lens 62 and enters the optical fiber 63.

  The light incident on the optical fiber 63 enters the diffraction grating 63a in the optical fiber 63 and is reflected here. As described above, since the diffraction grating 63 is chirped, light of a plurality of wavelengths is reflected by the diffraction grating 63a. The light reflected by the diffraction grating 63a returns to the first active layer 14e through the collimating lens 62 and the quarter wavelength plate 61, and is reflected by the rear end face 3b (reflection film 52) of the array type gain chip 10. The Light reflection is repeated between the rear end face 3b (reflection film 52) of the array-type gain chip 3 and the diffraction grating 63a, and laser oscillation occurs. A vertically polarized laser beam including a plurality of wavelength components can be obtained.

  The light generated in the second active layer 14f travels along the second active layer 14f and is emitted from the emission end face 3a. The light emitted from the emission end face 3 a is collimated by the collimator lens 62 and enters the optical fiber 63. The light reflected by the diffraction grating 63a in the optical fiber 63 returns to the second active layer 14f through the collimating lens 62, and is reflected by the rear end face 3b (reflective film 52) of the array type gain chip 10. Light reflection is repeated between the rear end face 3b (reflection film 52) of the array-type gain chip 3 and the diffraction grating 63a, and laser oscillation occurs. A horizontally polarized laser beam including a plurality of wavelength components can be obtained.

  FIG. 19 shows the spectrum of the laser light obtained by the external resonator type semiconductor laser device 4 shown in FIG. In FIG. 19, the solid line indicates the spectrum of horizontally polarized laser light, and the alternate long and short dash line indicates the spectrum of vertically polarized laser light.

  In the external cavity semiconductor laser device 4, as described above, vertically polarized and horizontally polarized laser beams including a plurality of wavelength components can be obtained. For this reason, as shown in FIG. 19, the envelope E is drawn by the spectrum of the vertically polarized laser beam and the horizontally polarized laser beam.

  In the external resonator type semiconductor laser device 4 using the fiber Bragg grating of the third embodiment, it is possible to obtain a laser beam having a plurality of wavelength components synthesized by polarization. Polarized and synthesized laser light can be obtained without providing a complicated optical system (coupler, optical fiber for guiding laser light from the gain chip to the coupler, etc.).

  FIG. 20 is a plan view showing an example of a semiconductor laser module provided with the arrayed semiconductor laser 1 described above.

  A plate-like cooling element 71 is fixed in a package 77 of the semiconductor laser module 70. An array type semiconductor laser 1, a thermistor 72, and a light receiving element 73 are fixed on the cooling element 71.

  Based on the ambient temperature detected by the thermistor 72, the temperature of the cooling element 71 is controlled (cooled).

  The light receiving element 73 receives light slightly emitted from the rear end face of the array type semiconductor laser 1 and monitors the operation of the array type semiconductor laser 1. The light receiving element 73 is disposed on the cooling element 71 so that the light receiving surface thereof is inclined with respect to the rear end face of the array type semiconductor laser 1. This is to prevent the light from the rear end face of the array type semiconductor laser 1 incident on the light receiving surface of the light receiving element 73 from returning to the array type semiconductor laser 1 again.

  As described above, four laser beams each including a plurality of wavelength components are emitted obliquely from the emission end face of the array type semiconductor laser 1. The four laser beams emitted obliquely are emitted from the package 77 after passing through a lens 74 for collimating and converging light and an optical isolator 75 for blocking return light. The combined laser light is incident on the optical fiber 76 connected (connected) to the package 77.

  In the same manner as described above, the array-type semiconductor laser 1A (FIG. 14) of the modified example described above or the module (FIG. 16) including the quarter-wave plate 61 and the array-type semiconductor laser 2 of the second embodiment is also packaged in the same manner as described above. Needless to say, it can be stored in 77. Further, also in the external resonator type semiconductor laser device 4 (FIG. 18) of the third embodiment, the array type gain chip 3 and the quarter wavelength plate 61 can be accommodated in the package 77. When the array type gain chip 3 and the quarter wave plate 61 are accommodated in the package 77, the optical fiber 76 connected to the package 77 has a diffraction grating 63a (FIG. 18) formed therein. Is used.

  FIG. 21 shows a block diagram of a Raman amplifier using the above-described semiconductor laser module 70 as a light source for pumping light.

  In the Raman amplifier 80, the laser light output from the semiconductor laser module 70 is input to the amplification optical fiber 81 through the coupler 82 as excitation light. Stimulated Raman scattering occurs in the amplification optical fiber 81, 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 fiber 81, the signal light is amplified by the gain generated in the amplification optical fiber 81 (Raman amplification). The semiconductor laser 1 included in the semiconductor laser module 70 emits four laser beams including a plurality of wavelength components, and these laser beams are used as excitation light, so that stimulated Brillouin scattering hardly occurs in the amplification optical fiber 81. The signal light can be transmitted through a fiber over a long distance.

The perspective view of the array type semiconductor laser of 1st Example is shown. The top view of the array type semiconductor laser of 1st Example is shown. The enlarged view of the first active layer and the diffraction grating in the vicinity of the emission end face of the array type semiconductor laser is shown. The traveling directions of the four laser beams emitted from the array type semiconductor laser are shown. The spectrum in the laser beam after combining the four laser beams emitted from the array type semiconductor laser is shown. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. (A), (B), and (C) show the manufacturing process of an array type semiconductor laser. The top view of the array type semiconductor laser in the modification of 1st Example is shown. (A)-(D) show sectional drawing of a diffraction grating. The top view of the array type semiconductor laser of 2nd Example is shown. The spectrum in the laser beam after combining the four laser beams emitted from the array type semiconductor laser of the second embodiment is shown. 1 is a block diagram of an external resonator type semiconductor laser device. The spectrum of the laser beam obtained by an external resonator type semiconductor laser device is shown. 1 shows a block diagram of a semiconductor laser module. 1 shows a block diagram of a Raman amplifier.

Explanation of symbols

1, 1A, 2 Array type semiconductor laser 3 Array type gain chip 4 External cavity type semiconductor laser device
14a, 14b, 14c, 14d, 14e, 14f Active layer
21a, 21b, 21c, 21d, 22a, 22b, 22c, 22d, 23a, 23b, 63a
70 Semiconductor laser module
71 Cooling element
63, 76, 81 optical fiber
77 packages
80 Raman amplifier

Claims (9)

A plurality of stripe-shaped active layers are formed in a plane parallel to the substrate surface of the semiconductor substrate above the semiconductor substrate from the rear end surface to the emission end surface, spaced apart from each other,
Each of the plurality of active layers has an optical axis line of light guided through the active layer obliquely with respect to the normal direction of the emission end face at the position of the emission end face, and the emission end face through each of the plurality of active layers. Are bent so that all of the optical axes of the laser beams emitted from the laser beam reach the same position.
A diffraction grating having a Bragg wavelength monotonously increasing or decreasing is formed above or below at least a portion of each of the plurality of active layers;
An optical resonator is constituted by the rear end face and the diffraction grating.
Array type semiconductor laser. Diffraction gratings having a uniform pitch are formed above or below the bent portions of the plurality of active layers, respectively.
The array type semiconductor laser according to claim 1. Chirped diffraction gratings with varying pitches are respectively formed above or below the plurality of active layers,
The array type semiconductor laser according to claim 1. The diffraction gratings above or below the plurality of active layers have different pitches from each other,
The array type semiconductor laser according to any one of claims 1 to 3. An array type semiconductor laser according to any one of claims 1 to 4,
A plurality of stripe-shaped active layers included in the array type semiconductor laser are paired two by two, and light including a plurality of wavelength components having the same center wavelength above or below the two active layers forming the pair A diffraction grating is formed,
A polarization plane rotating means for rotating the polarization plane of the laser light emitted through any one of the two active layers forming the pair by 90 degrees;
Semiconductor laser device. An array type gain chip in which a plurality of stripe-shaped active layers are formed in a plane parallel to the substrate surface of the semiconductor substrate above the semiconductor substrate from the rear end surface to the emission end surface; and Bragg An optical fiber having a chirped diffraction grating with a monotonically increasing or decreasing wavelength;
Each of the plurality of active layers of the array-type gain chip has the optical axis of light guided through the active layer obliquely with respect to the normal direction of the exit end face at the exit end face, A plurality of lights emitted from the emission end face through the layer are bent so as to enter the optical fiber,
An optical resonator is constituted by the rear end face of the array type gain chip and the chirped diffraction grating in the optical fiber.
External cavity semiconductor laser device. A plurality of stripe-shaped active layers included in the array-type gain chip are paired, and the polarization plane of light emitted through one of the two active layers forming the pair is 90 degrees. Equipped with rotating polarization plane rotating means,
The external resonator type semiconductor laser device according to claim 6. An array type gain chip included in the array type semiconductor laser according to any one of claims 1 to 4, the semiconductor laser device according to claim 5, or the external resonator type semiconductor laser device according to claim 6. A lens for converging a plurality of laser beams emitted from the emission end face of the array type semiconductor laser or a plurality of lights emitted from the array type gain chip, and cooling for cooling the array type semiconductor laser or the array type gain chip The element is stored in the housing,
An optical fiber that is connected to the housing and guides the laser light or light to the outside of the housing;
Semiconductor laser module. The semiconductor laser module according to claim 8, and an optical fiber in which laser light from the semiconductor laser module is incident as excitation light and causes stimulated Raman amplification,
Raman amplifier equipped with.

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