JP2007251064A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve output power and quality of laser beam. <P>SOLUTION: The semiconductor device comprises such a layer structure that an S-shaped ridge optical waveguide 25 consisting of an InP cladding layer 15 and an InGaAs contact layer 16 and having a line width of 30 μm and a curvature of 680 μm (curvature<way width of optical waveguide ×25) is formed on the layer structure of an InGaAsP guide layer 12/an InGaAsP activity layer 13/an InGaAsP guide layer 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a high-power semiconductor laser device having a waveguide structure.

  Conventionally, semiconductor lasers have been widely used as light sources constituting various types of media. And so that a semiconductor laser can be applied to various uses, high output and miniaturization are achieved.

  However, it is known that the semiconductor laser has a multi-mode laser beam and the beam quality deteriorates as the laser output is increased.

Therefore, high output using an optical amplifier has been widely used. For example, a distributed feedback type that oscillates in a single mode by matching the mode (light intensity) of the output laser light and the gain region. A technique for obtaining laser light with high output and high beam quality by amplifying laser light of a semiconductor laser using an optical amplifier is disclosed (for example, see Patent Document 1 and Non-Patent Document 1).
Japanese Patent No. 3306104 IEEE PHOTON. TECH. LETT. VOL.9 1997 pp.440-442

  However, even if the optical amplifier is used to amplify the light, if the amplification is repeated to obtain a high output, the beam quality is deteriorated.

  Further, when the output of the semiconductor laser is increased, in the edge-emitting type light-emitting device, the light intensity at the light extraction port from which light is extracted becomes strong, so that heat is generated at the end surface, and the light emission efficiency is reduced due to the heat generation. For this reason, when the current value is increased to obtain a desired light intensity, the end face further generates heat, and a vicious cycle in which the light emission efficiency further decreases due to further heat generation continues to break down from the end face.

  The present invention has been made in view of the above, and an object of the present invention is to provide a high-power semiconductor laser device capable of obtaining laser light with high laser light emission efficiency and good beam quality, and achieves the object. The task is to do.

  In the present invention, when the optical waveguide is configured to have a width where the beam becomes multimode, the configuration in which the curved portion having the curvature exceeding the critical angle of the unnecessary mode which deteriorates the beam quality is provided in the optical waveguide. This was achieved based on the knowledge that the unnecessary mode leakage was intentionally generated in the middle of the process, and it was effective to improve the quality of the beam.

In order to achieve the above object, a semiconductor laser device of the present invention has at least an N-type high refractive index layer, an active layer, a P-type high refractive index layer, and a P-type high refractive index layer on a semiconductor substrate. A low P-type cladding layer has a layer structure in which the semiconductor substrate is sequentially laminated, and at least one layer of the layer structure has a curvature r (μm) satisfying the following formula, and two or more modes have a line width. The structure has a waveguide structure including at least one curved portion.
Curvature r <Line width of waveguide structure (μm) × 25 Formula

Here, the curvature r is an amount representing the degree of the curve of the curved portion, and is a value represented by 1 / r ′ when a curved line, that is, a curved line segment, is considered as a part of a circle having a radius r ′ ( (Curvature of the circumference), and the curvature increases as the curve becomes tighter.
The line width is the width of the waveguide structure in the layer structure in the plane direction orthogonal to the stacking direction of the layer structure.

In the semiconductor laser device of the present invention, at least one layer or two or more layers in the layer structure composed of the four layers described above have a waveguide structure having a predetermined width and curved portion, specifically, two A curved portion is provided in a waveguide structure having the above-described line width, and the curved portion is configured to have a curvature satisfying the relationship of “curvature r <line width of waveguide structure × 25”. Unlike the case of a linear structure, the incident angle of light propagating by reflection is generally higher than that of the fundamental mode in which the beam propagates through the waveguide structure while repeating incidence and reflection at a shallow angle on the inner wall. In the next mode, since the incident angle θ ^b incident on the reflecting surface is large, the incident angle θ ^b of the higher order mode exceeds the critical angle θ, which is the limit angle at which light is reflected, and higher order in the process of propagating the curved part. Mode leaks out of the waveguide structure Since the selectively removed out, high-quality beam with suppressed higher order modes is obtained.
That is, when the waveguide structure is configured to have a wide width to increase the output, it is possible to suppress the deterioration of the beam quality due to the multimode and obtain a high output and high quality beam.

  It is effective that the line width of the curved portion provided in the waveguide structure is 10 μm or more. That is, if the line width is 10 μm or more, it is effective for increasing the output, and two or more modes including the fundamental mode can be easily reached, and it is effective for obtaining a high quality beam of the fundamental mode except for the higher mode. Is.

The layer structure constituting the semiconductor laser device of the present invention includes a laser part formed in a semiconductor laser structure that oscillates a laser, and an optical amplification part formed in a semiconductor optical amplifier structure that amplifies light incident from the laser part. Can be formed into a composite structure.
The composite structure is effective in reducing the size of a semiconductor laser device that can obtain a high-quality beam with high output.

The semiconductor laser device of the present invention may have a waveguide structure including at least one of the above-described curved portions in either one or both of the laser portion and the light amplification portion.
In particular, a waveguide structure including at least one curved part is formed in the laser part, and the light amplification part is gradually widened in the direction away from the side close to the laser part (perpendicular to the stacking direction of the layer structure). Alternatively, it is desirable that the width is wide along a substantially orthogonal plane.

  Obtaining a high-quality beam mainly consisting of fundamental modes that suppress higher-order modes within the region of the laser part that oscillates light, and amplifies the quality-enhanced beam at an optical amplification part that gradually becomes wider Can do. Therefore, it is possible to selectively amplify a beam having a clean mode while suppressing propagation and amplification of a higher-order mode and obtain a high-quality beam with higher output.

  A contact layer can be further provided on the side away from the semiconductor substrate of the P-type cladding layer constituting the layer structure. In this case, for example, a layer structure in which a waveguide structure including at least one curved portion is formed by a P-type cladding layer and a contact layer can be configured.

  In order to suppress the transverse higher order mode, it is effective to provide a diffraction grating in the laser part formed in the semiconductor laser structure. By providing a diffraction grating at the laser part, it is possible to suppress the long mode of the waveguide structure.

  At least one of the end face of the laser part formed in the semiconductor laser structure and the end face of the optical amplification part formed in the semiconductor optical amplifier structure is a center line passing through the center in the width direction perpendicular to the stacking direction of the layer structure of the optical waveguide It is desirable to be provided so as to be inclined (≠ 90 °).

Since the end face of the laser part (and at least one of the end faces of the light amplification part is inclined with respect to the center line passing through the center in the road width direction of the optical waveguide, the end face reflectance of each part is significantly reduced. At the time of laser output, for example, when laser light emitted from the laser part is incident on the light amplification part, it is reflected at the laser part side end face of the light amplification part or reflected at the end face opposite to the laser part side end face of the light amplification part. The return light returning in the direction opposite to the light propagation direction of the optical waveguide is reduced by reflection, and the return light from the external optical component can be prevented from being coupled to the optical waveguide. It is effective for conversion.
Further, the Fabry-Perot mode is remarkably suppressed, the single mode operation is improved, and the non-reflective coating process can be omitted in the manufacturing process, which is useful in terms of cost reduction.

  It is desirable that the waveguide structure has a current injection region and a current non-injection region. For example, by providing a current non-injection region on the laser emission end face of the optical amplification portion, it is possible to prevent the end face of the emission end from being destroyed while increasing the output.

  In addition, it is preferable that an electrode is provided on the curved portion of the waveguide structure in at least a part of the outer region from the center line in the width direction orthogonal to the stacking direction of the layer structure of the waveguide structure. . By selecting an area closer to the outer circumference (outward of the circle) from the center in the width direction of the curved part, and providing an area where no electrode is formed closer to the inner circumference from the area where the electrode is provided, Since the light intensity distribution is formed closer to the outer periphery from the center in the width direction of the curved portion, it is possible to give a gain to the fundamental mode and at the same time to give a loss to the higher order mode.

Furthermore, in the semiconductor laser device of the present invention, a semiconductor chip composed of a single substrate is used as a semiconductor substrate, and a waveguide structure including at least one curved portion is provided on the single semiconductor chip. By providing a plurality of layer structures (including the case of having a composite structure of a laser part and an optical amplification part), it can be suitably configured as an array light source.
It is possible to reduce the size by integrating a plurality on the same semiconductor chip.

  According to the present invention, it is possible to provide a high-power semiconductor laser device capable of obtaining laser light with high laser light emission efficiency and good beam quality.

  Hereinafter, embodiments of the semiconductor laser device of the present invention will be described in detail with reference to the drawings, and an array light source will also be described through the description.

(First embodiment)
A semiconductor laser device according to a first embodiment of the present invention will be described with reference to FIGS. In the semiconductor laser device of this embodiment, a contact layer is further provided adjacent to a P-type cladding layer provided on a semiconductor substrate, and the P-type cladding layer and the contact layer are formed in an S-shaped curved structure and stacked. The optical waveguide that propagates the laser light is configured.

As shown in FIG. 1, the semiconductor laser device of the present embodiment has an 0.2 μm thick InGaAsP guide layer (carrier concentration) sequentially on an N-type InP substrate (S-doped, carrier concentration 10 ¹⁸ cm ⁻³ ) 11. 10 ¹⁷ cm ⁻³ ; N-type high refractive index layer 12, 0.3 μm thick InGaAsP active layer (carrier concentration 0 cm ⁻³ ) 13, 0.2 μm thick InGaAsP guide layer (carrier concentration 10 ¹⁷ cm ⁻³⁾ A P-type high-refractive-index layer) 14, and an InP clad layer (Zn-doped, carrier concentration 10 ¹⁷ cm ⁻³ ; P-type clad; Layer) 15 and an InGaAs contact layer (high-concentration Zn-doped, carrier concentration 10 ¹⁸ cm ⁻³ ) 16 are laminated in a ridge shape.

The S-shaped curved portion formed by laminating the InP cladding layer 15 and the InGaAs contact layer 16 on the ridge has a line width w of 30 μm in the plane direction orthogonal to the laminating direction of the layer structure, and the curvature of each curved portion of the S-shape. r has a structure of 680 μm so that only the fundamental mode can be reflected, functions as an optical waveguide for propagating light, and leaks a higher-order mode at the two curved portions of the S-shaped portion. Can be selectively reflected and propagated (hereinafter, an S-shaped curved portion may be referred to as an optical waveguide 25).
The line width w is preferably 5 μm or more, more preferably 10 μm or more, still more preferably 100 μm or more, and particularly preferably 200 μm or more.

As described above, by providing the InP cladding layer 15 and the InGaAs contact layer 16 as an optical waveguide on the InGaAsP guide layer 14 to provide a ridged S-shaped structure, the light of the active layer is applied when a voltage is applied. The gain region moves to the side of the optical waveguide 30 provided in the ridge shape, propagates along the optical waveguide 25, and is emitted from one end face coated with the low reflection layer. At this time, the higher order mode (broken line) As shown in FIG. 2- (a), the light beam is reflected after being incident on the wall surface at an incident angle θ ^b (θ ^b > θ ^a ) deeper than the fundamental mode (solid line) incident on the road wall surface at the incident angle θ ^a. Propagates in the optical waveguide. Therefore, when the S-shaped curved part of the optical waveguide 25 is reached, the high-order mode having a deep incident angle confined in the straight part has a critical incident angle in the curved part as shown in FIG. Exceeds the angle θ and leaks out of the optical waveguide and cannot be propagated. As shown in FIG. 2- (b), the fundamental mode does not exceed the critical angle θ that is the limit angle at which light is reflected. High output can be obtained by widening the width of the waveguide, and high-quality beams can be emitted while suppressing higher-order modes.

  The InP substrate 11 is a layer composed of sulfur-doped InP, and can be composed of GaAs or the like in addition to InP.

  Each of the InGaAsP guide layer 12 and the InGaAsP guide layer 14 is a high refractive index layer capable of confining and propagating light of the active layer 13, and has N-type and P-type properties, respectively. These guide layers can be formed using AlGaAs or the like in addition to InGaAsP.

  The InGaAsP active layer 13 is a layer that generates light when a voltage is applied, and has a quantum well structure (not shown) provided with a periodic structure along the light traveling direction. This active layer can be formed using InGaAs / GaAs, InGaAs / InGaP, or the like in addition to InGaAs.

The InP cladding layer 15 is a layer composed of Zn-doped InP, and can be composed of AlGaAs or the like in addition to InP.
The InGaAs contact layer 16 is a layer composed of InGaAs doped with Zn at a high concentration, and can be composed of GaAs or the like in addition to InGaAs.

As described above, on the surface of the InGaAs contact layer 16 formed in an S-shaped ridge, Ti 100 nm is further deposited on the deposited Pt film 50 nm along the S-shape, and Au 100 nm is further formed thereon. A P electrode 17 of a metal multilayer film (Pt / Ti / Au film) is deposited.
As the electrode material constituting the P electrode 17, a multilayer film such as a Ti / Au film can be used in addition to the Pt / Ti / Au film.

On the side of the InP substrate 11 where the guide layer, the active layer, and the like are not provided, a metal multilayer film (Ti / Au film) N electrode 18 is formed by depositing Au 100 nm on the deposited Ti film 50 nm. Yes.
As the electrode material constituting the N electrode 18, a multilayer film such as a Pt / Ti / Au film can be used in addition to the Ti / Au film.

  Semiconductor layer formed by stacking N electrode 18 / InP substrate 11 / InGaAsP guide layer 12 / InGaAsP active layer 13 / InGaAsP guide layer 14 / InP clad layer 15 / InGaAs contact layer 16 / P electrode 17 as described above As shown in FIG. 1, one end face of the structure is coated with a low reflection layer 19 having a low reflectivity in relation to the wavelength of light propagating in the layer structure, and the other end face is connected to the light wavelength. Therefore, the high reflection layer 20 having a high reflectivity is coated, and light in the layer structure is propagated toward the low reflection layer 19 and output.

Next, a method for manufacturing the semiconductor laser device of this embodiment will be described.
-1) Formation of each layer on the substrate
An N-type InP substrate (S-doped, carrier concentration 10 ¹⁸ cm ⁻³ ) is prepared, this InP substrate is heated to 500 to 700 ° C., and MOCVD (metal organic chemical vapor deposition method; carrier gas: hydrogen (H ₂₎ ), Source gases: trimethylgallium (hereinafter abbreviated as TMGa), trimethylindium (hereinafter abbreviated as TMIn), tertiary butylphosphine (hereinafter abbreviated as TBP), and tertiary butylarsine (hereinafter abbreviated as TBAs). 1), an N-type InGaAsP guide layer (carrier concentration 10 ¹⁷ cm ⁻³ ) 12 having a thickness of 0.2 μm is grown on the InP substrate 11 as shown in FIG.

MOCVD (metal organic chemical vapor deposition) is a thin film growth method of a compound body generally used for production of a semiconductor laser or the like. The source gas is mainly liquid organic metal (eg, TMGa, TMIn, TBP, TBAs), and is bubbled with a carrier gas (eg, hydrogen (H ₂ )) and supplied as a gas to the reaction chamber. The source gas is decomposed on the substrate heated to 500 to 700 ° C., and a thin film is grown on the substrate.

Subsequently, the MOCVD method [carrier gas: hydrogen (H ₂ ), source gas: TMGa, TMIn, TBP, TBAs] is continuously performed after the formation of the InGaAsP guide layer 12 while being heated to 500 to 700 ° C. as described above. An InGaAsP active layer (carrier concentration 0 cm ⁻³ ) 13 having a thickness of 0.3 μm is grown on the InGaAsP guide layer 12 by the usual method used, and subsequently, the MOCVD method [carrier P-type InGaAsP guide layer (carrier concentration 10 ¹⁷ cm ⁻³ ) 14 having a thickness of 0.2 μm is grown by a conventional method using gas: hydrogen (H ₂ ), source gas: TMGa, TMIn, TBP, TBAs]. And laminate.

On the InGaAsP guide layer 14, an InP clad layer (Zn-doped, carrier concentration 10 ¹⁷ cm ⁻³ ) having a thickness of 1 μm is formed by an ordinary method using MOCVD [carrier gas: hydrogen (H ₂ ), source gas: TMIn, TBP]. ) 15 is further crystal grown. Subsequently, an InGaAs contact layer (highly doped with Zn, with a carrier concentration of 10 ¹⁸ ) is formed on the InP cladding layer 15 by a conventional method using MOCVD [carrier gas: hydrogen (H ₂ ), source gases: TMIn, TBAs, TMGa]. cm ⁻³ ) 16 was laminated to form a layer structure of five layers on the InP substrate.

-2) Optical waveguide formation-
The surface of the InGaAs contact layer 16 having the layer structure formed as described above is patterned by a photolithography method generally used in a semiconductor manufacturing process so that a region other than an S-shaped region serving as an optical waveguide is exposed. A film is formed.
Using this photoresist film as a mask, the InGaAsP guide layer 14 exposes the InGaAs contact layer 16 and the InP cladding layer 15 in regions other than the S-shaped region where the optical waveguide is to be formed by dry etching using chlorine gas. Etching is performed, and as shown in FIG. 1, an optical waveguide 25 having a ridge structure is formed by providing a step in an S-shape having two curved portions. The optical waveguide 25 is composed of an InP cladding layer 15 and an InGaAs contact layer 16.
Thereafter, the remaining photoresist film is removed using acetone (organic solvent) or a resist stripping solution.

-3) Electrode formation
Next, a SiN film (insulating) is formed on the entire surface of the optical waveguide 25 provided in the layer structure (that is, the surface of the S-shaped InGaAs contact layer 16) and the entire surface of the exposed InGaAsP guide layer 14 by plasma CVD. The electrode window is patterned by a photolithographic method generally used in the semiconductor manufacturing process, and only the surface of the optical waveguide 25 is etched using buffered hydrofluoric acid (HF). Note that the SiO ₂ film may be formed by plasma CVD.

  Then, a resist pattern for P electrode lift-off is formed over the entire region other than the region of the optical waveguide 25 by a photolithography method generally used in a semiconductor manufacturing process, and the InGaAs contact layer 16 constituting the optical waveguide is formed using a vacuum evaporation apparatus. P electrode 17 is vapor-deposited on the S-shaped surface. Thereafter, unnecessary electrode materials formed on the photoresist film are removed together with the photoresist film by a lift-off method using a resist stripping solution.

  Thereafter, the side of the InP substrate 11 where the guide layer, the active layer or the like is not formed is polished with an abrasive such as diamond fine particles until the thickness of the substrate reaches 100 μm. After polishing, a Ti film is deposited using a vacuum deposition apparatus to form an N electrode 18.

After obtaining a layer structure provided with the S-shaped optical waveguide 25 as described above, a SiN film is formed on one end of this layer structure by a sputtering apparatus to coat the low reflection layer 19 and the other end. Then, a TiO / SiO film is formed by a sputtering apparatus to coat the highly reflective layer 20.
As described above, the semiconductor laser device of this embodiment can be manufactured.

  In this embodiment, the optical waveguide is provided in an S shape, that is, two curved portions are formed. However, one or three or more curved portions may be provided, depending on the purpose and case. It is possible to obtain the effect of the present invention by appropriately selecting.

Further, although the optical waveguide is configured by the InP cladding layer 15 and the InGaAs contact layer 16, the optical waveguide may be configured by only the cladding layer without forming the contact layer. An optical waveguide composed of multiple clad layers may be formed by forming the layers.
When the clad layer is formed in a multilayer, it can be formed in a multilayer structure of two or more layers including a first clad layer having a low refractive index and a second clad layer having a refractive index higher than that of the first clad layer. Specifically, for example, a two-layer structure in which a clad layer having a refractive index ρ ^{1 and} a clad layer having a refractive index ρ ² (ρ ¹ <ρ ² ) are sequentially stacked on the InGaAsP guide layer 14 from the guide layer side. Can do. The multilayer structure is preferably such that the refractive index gradually increases from the InGaAsP guide layer 14 side in that the gain region can be moved to the optical waveguide side of the ridge structure. Multiple layers may be used.

(Second Embodiment)
A second embodiment of the semiconductor laser device of the present invention will be described with reference to FIG. In the present embodiment, a diffraction grating is provided on the InGaAsP guide layer 14 having the layer structure of the first embodiment.

  Each layer other than the diffraction grating and the layer provided with the diffraction grating can be formed in the same manner as in the first embodiment by using the materials and methods used in the first embodiment, and has the same configuration as in the first embodiment. Elements are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 3, the semiconductor laser device of this embodiment is positioned at a linear portion of the optical waveguide 25 on one end side coated with the low-reflection layer 19 having a layer structure and on the other end side coated with the high-reflection layer 20. A diffraction grating 31 is provided on the InGaAsP guide layer 14 so that the length direction is substantially perpendicular to the direction of the linear portion of the optical waveguide 25.

The diffraction grating 31 has a structure in which InGaAs (carrier concentration 10 ¹⁷ cm ⁻³ ) is formed so as to obtain periodicity at 280 nm. Each diffraction grating has a width of 140 nm and a thickness of 100 nm. Is formed.

The diffraction grating can be configured by the same method as InGaAs by appropriately selecting InGaAsP or the like in addition to InGaAs. The period A is obtained as A = λ ₀ / n _r (λ ₀ : oscillation wavelength, n _r : effective refractive index).

In the diffraction grating 31, the InGaAsP guide layer 14 is laminated in the same manner as in the first embodiment, and then phosphoric acid and hydrogen peroxide solution are added onto the InGaAsP guide layer 14 by an electron beam drawing apparatus (Crestec Co., Ltd.). It can be provided by forming a diffraction grating having a width of 140 nm and a thickness of 100 nm so that periodicity is obtained at 280 nm using a mixed solution diluted with water.
Thereafter, an InP layer 32 having a thickness of 1000 nm is grown by a conventional method using MOCVD [carrier gas: hydrogen (H ₂ ), source gas: TMIn, TBP] so as to embed the diffraction grating.

In this embodiment, the diffraction grating 31 is formed on the linear portions on both sides of one end and the other end of the layer structure. However, the diffraction grating may be formed only on one side.
Further, the size and number of diffraction gratings can be appropriately selected depending on the case.

(Third embodiment)
A third embodiment of the semiconductor laser device of the present invention will be described with reference to FIG. In this embodiment, the layer structure of the first embodiment is formed into a semiconductor optical amplifier structure having a laser part formed in a semiconductor laser structure having a diffraction grating on the InGaAsP guide layer 14 and an S-shaped optical waveguide. And a light-amplifying site.

  Each layer other than the diffraction grating and the layer provided with the diffraction grating can be formed in the same manner as in the first embodiment by using the materials and methods used in the first embodiment, and has the same configuration as in the first embodiment. Elements are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 4, the layer structure is functionally separated at the laser part 41 and the light amplification part 42. The laser part 41 is a region having a length a from the other end coated with the highly reflective layer 20 having a layer structure. In this region, the diffraction grating 31 is formed on the InGaAsP guide layer 14, and the optical waveguide is long. The mode of the direction can be suppressed, and laser light can be incident on and propagated to the light amplification portion 42.

  The laser part is preferably a distributed feedback semiconductor laser having a quantum well structure in which a periodic structure is provided along the light traveling direction using a diffraction grating.

  The light amplification part 42 is an area formed at a distance b from the laser part 41 to one end coated with the low reflection layer 19, which is formed continuously with the laser part 41. A curved portion of the shape is formed so that the light from the laser part is propagated while being amplified, and at the same time, a high-quality beam can be emitted while suppressing higher-order modes.

The diffraction grating 31 has a structure in which InGaAs (carrier concentration 10 ¹⁷ cm ⁻³ ) is formed so as to obtain periodicity at 280 nm. Each diffraction grating has a width of 140 nm and a thickness of 100 nm. Is formed.
The diffraction grating can be configured by selecting InGaAsP other than InGaAs as in the second embodiment. The period A is obtained as A = λ ₀ / n _r (λ ₀ : oscillation wavelength, n _r : effective refractive index).

  The diffraction grating 31 can be provided so as to obtain periodicity at 280 nm by laminating the InGaAsP guide layer 15 in the same manner as in the first embodiment, and then performing MOCVD. The InP layer 32 is crystal-grown by a conventional method using a method so as to embed the diffraction grating.

  In addition, the other end opposite to the one end coated with the low-reflectance layer 19 having a low reflectivity in the layer structure has a low reflectivity in relation to the wavelength of light propagating in the layer structure, as shown in FIG. The low reflection layer 21 is coated.

  As in this embodiment, a semiconductor laser device that can obtain a high-quality and high-quality beam can be reduced in size by forming a composite structure having a laser part and an optical amplification part.

(Fourth embodiment)
A fourth embodiment of the semiconductor laser device of the present invention will be described with reference to FIG. In the present embodiment, one end face and the other end face of the layer structure of the first embodiment are each configured to be inclined with respect to the center line of the optical waveguide.

  Each layer can be formed in the same manner as in the first embodiment using the materials and methods used in the first embodiment, and the same reference numerals are given to the same components as in the first embodiment. Detailed description thereof will be omitted.

  As shown in FIG. 5, in the semiconductor laser device of the present embodiment, one end face coated with the low-reflection layer 19 having a layer structure and the other end face coated with the high-reflection layer 20 are respectively optical waveguides 25. Are formed so as to have an inclination angle α not perpendicular to the center line A passing through the center in the width direction perpendicular to the stacking direction of the layer structure.

Since it is configured with an angle (90-α) with respect to the direction of the center line A that is the light propagation direction of the optical waveguide, that is, an inclined surface that forms an inclination angle α with a line orthogonal to the direction of the center line A, end face reflection The rate can be greatly reduced. For example, as shown in FIG. 5, at the time of laser output, the reflected light reflected at the end face does not return to the optical waveguide 25, the end face reflectivity is lowered, the return light to the semiconductor laser is reduced, and the semiconductor laser operation is improved.
Although not shown, return light from an external optical component can be prevented from being coupled to the waveguide.

  The range of the inclination angle α is not particularly limited as long as the return light reduction effect is obtained, but it is effective to set the range of 3 ° to 10 °.

  The inclined surface inclined with respect to the direction of the center line A is prepared by forming a layer structure as shown in FIG. 1 in advance and then cutting so that a desired inclined surface (end surface) is formed. Can do.

(Fifth embodiment)
A fifth embodiment of the semiconductor optical amplifier composite semiconductor laser device of the present invention will be described with reference to FIG. In the present embodiment, a current non-injection region is formed on the laser emission end side of the optical waveguide provided in the first embodiment.

  Each layer except the current non-injection region can be formed in the same manner as in the first embodiment by using the material and method used in the first embodiment, and the same components as those in the first embodiment are the same. The detailed description is abbreviate | omitted.

  In the present embodiment, as shown in FIG. 6, a current non-injection region 45 is formed in a predetermined region from the emission end face of the optical waveguide 25 that emits laser, and when laser is emitted from the end face of this optical waveguide. When the light intensity increases, the end face of the emission end face can be prevented from being broken.

This current non-injection region 45 is formed by previously covering the surface of the surface InGaAs contact layer with an insulating film and forming the P electrode in that state before forming the P electrode on the optical waveguide 25. be able to.
The insulating film can be provided by forming a SiN film or a SiO film using, for example, a plasma CVD method.

  The insulating film preferably has a thickness in the range of 0.1 to 0.2 μm, and the distance from the emission end face is not particularly limited.

(Sixth embodiment)
A sixth embodiment of the semiconductor optical amplifier composite semiconductor laser device of the present invention will be described with reference to FIG. In the present embodiment, the downstream side of the curved portion in the light propagation direction of the optical waveguide of the first embodiment is configured to have a structure (light amplification structure) in which the road width gradually increases toward the emission end. .

  Each layer can be formed in the same manner as in the first embodiment using the materials and methods used in the first embodiment, and the same reference numerals are given to the same components as in the first embodiment. Detailed description thereof will be omitted.

  The semiconductor laser device according to the present embodiment has an InP structure formed on the layer structure of the N electrode 18 / InP substrate 11 / InGaAsP guide layer 12 / InGaAsP active layer 13 / InGaAsP guide layer 14 formed as in the first embodiment. The optical waveguide 25 having a ridge structure composed of the cladding layer 15 and the InGaAs contact layer 16 is provided (the P electrode 17 is provided on the optical waveguide). The light propagating toward the light exits from the end face of the optical waveguide 25.

This optical waveguide 25 has a ridged S-shaped structure as in the first embodiment, and the light that travels from one end where the high reflection layer 20 is provided to the other end where the low reflection layer 19 is provided. On the downstream side of the S-shaped structure in the propagation direction, the path width (width in the plane direction perpendicular to the laminating direction of the layer structure) w of the optical waveguide 25 gradually increases from the width (w ⁰ ) before spreading to the other end. and it has a configuration that spread to wide (w = w ⁰ ~w exit) to. The path width w of the optical waveguide is such that the exit of the path width w at the exit end of the optical waveguide 25 is (1 /) where L is the length of the region where the path width gradually increases (the length of the optical amplification structure). 25000) × (L / w ⁰ ) to (1/35000) × (L / w ⁰ ).

  In the S-shaped structure (curved part) of the optical waveguide, since the higher-order mode having a deep incident angle confined in the straight part as described above cannot leak and propagate beyond the critical angle θ, it is downstream of the S-shaped structure. On the side, the fundamental mode is mainly propagated, and the road width is widened on the downstream side of the S-shaped structure to obtain a high output, so that a high-quality beam can be obtained at a high output while suppressing higher-order modes. it can.

  To widen the downstream side of the optical waveguide in the light propagation direction, when forming the optical waveguide, a photoresist film is formed in a pattern that widens from the S-shape of the optical waveguide toward the exit end face, and this is used as a mask. It can be formed by dry etching.

(Seventh embodiment)
A seventh embodiment of the semiconductor optical amplifier composite semiconductor laser device of the present invention will be described with reference to FIG. In the present embodiment, the layer structure of the first embodiment is formed by using a laser part formed in a semiconductor laser structure having an S-shaped optical waveguide and a semiconductor optical amplifier structure. This is a composite structure including a light amplifying portion in which the road width on the downstream side of the curved portion in the light propagation direction is gradually increased toward the exit end face.

  Each layer other than the cladding layer 53 can be formed in the same manner as in the first embodiment using the materials and methods used in the first embodiment, and the same components as those in the first embodiment are the same. The detailed description is abbreviate | omitted.

As in the sixth embodiment, the semiconductor laser device of the present embodiment is formed in the same manner as in the first embodiment. N electrode 18 / InP substrate 11 / InGaAsP guide layer 12 / InGaAsP active layer 13 / InGaAsP guide layer 14 In this structure, an optical waveguide 25 having a ridge structure composed of an InP cladding layer 15 and an InGaAs contact layer 16 is provided (a P electrode 17 is provided on the optical waveguide). The light propagating in the structure toward the low reflection layer 19 side is emitted from the end face of the optical waveguide.
The optical waveguide 25 has a ridged S-shaped structure, and an S-shaped structure in the light propagation direction from one end where the high reflective layer 20 is provided to the other end where the low reflective layer 19 is provided. On the downstream side, the path width of the optical waveguide 25 (the width in the plane direction perpendicular to the laminating direction of the layer structure) is gradually widened until it reaches the other end.

In this embodiment, the layer structure is functionally separated at the laser part 51 and the light amplification part 52 as shown in FIG. The laser part 51 is a region having a length c from one end where the highly reflective layer 20 having a layer structure is coated. In this region, an S-shaped curved portion of the optical waveguide 25 is formed, and a high-order mode is formed. A suppressed beam can be propagated, and a high-quality beam can be incident and propagated to the light amplification portion 52.
If the laser part is formed in a bent structure, higher output can be expected.

Further, the light amplification portion 52 is a region having a distance d from the laser portion 51 to the other end coated with the continuous low reflection layer 19. In this region, the path width of the optical waveguide 25 (the stacking direction of the layer structure) The width in the plane direction orthogonal to w) is configured to gradually widen from the width (w ⁰ ) before spreading to the other end (w = w ^{0 to} w exit). Path width w of the optical waveguide is a range satisfying path width w exit at the exit end of the optical waveguide 25 is a (1/25000) × (d / w 0) ~ (1/35000) × (d / w 0) It is spreading.

  Further, as shown in FIG. 8, an optical waveguide is formed in the optical amplification portion 52 on the InGaAsP guide layer 14 in a region where the optical waveguide whose path width w gradually increases as described above is not formed. A cladding layer 53 having a thickness of 1 μm is formed so that the height of the non-existing region coincides with the surface of the optical waveguide, and diffuses when the return light propagates. It is advantageous to operate.

That is, in the S-shaped structure of the optical waveguide, the higher-order mode confined in the straight portion cannot propagate as described above, so that the light amplification portion formed on the downstream side of the S-shaped structure in the light propagation direction Can mainly amplify a beam with high quality at the light amplification portion where the fundamental mode is propagated and gradually becomes wider.
As a result, it is possible to selectively amplify a beam having a clean mode and to emit a high-quality beam with higher output while suppressing propagation and amplification of higher-order modes.

  To widen the downstream side of the optical waveguide in the light propagation direction, when forming the optical waveguide, a photoresist film is formed in a pattern that widens from the S-shape of the optical waveguide toward the exit end face, and this is used as a mask. It can be formed by dry etching.

  The clad layer 53 is formed by forming an insulating film such as SiO or SiN by sputtering after forming the optical waveguide, patterning it by photolithography, and then dissolving it with hydrofluoric acid to open the window. After removing the resist, Pt, Ti, Au or the like can be deposited.

(Eighth embodiment)
An eighth embodiment of the semiconductor optical amplifier composite semiconductor laser device of the present invention will be described with reference to FIGS. In the present embodiment, a region where no P electrode exists is formed in a part of the S-shaped curved portion of the optical waveguide formed in the first embodiment, and a gain region is formed near the outer periphery of the curved portion. Is.

  Each layer can be formed in the same manner as in the first embodiment using the materials and methods used in the first embodiment, and the same reference numerals are given to the same components as in the first embodiment. Detailed description thereof will be omitted.

  The semiconductor laser device according to the present embodiment has an InP structure formed on the layer structure of the N electrode 18 / InP substrate 11 / InGaAsP guide layer 12 / InGaAsP active layer 13 / InGaAsP guide layer 14 formed as in the first embodiment. Light having a structure in which a ridged S-shaped optical waveguide 25 having a curvature (r) of 680 nm comprising the cladding layer 15 and the InGaAs contact layer 16 is provided, and the light propagated in the layer structure toward the low reflection layer 19 side. Is emitted from the end face of the optical waveguide 25.

On the surface of the optical waveguide 25, as shown in FIG. 9, in each region of two curved regions that bend at the curvature r of the S-shaped portion, that is, in regions S and T that are not linear regions as shown in FIG. 9 or FIG. The P electrode 56 exists near the outer periphery from the center (center line A) in the width direction of the curved region, and the region near the inner periphery from the P electrode 56 is a non-electrode region (electrode non-forming region) 57. A gain with high light intensity can be obtained. That is, as shown in FIG. 10, a light intensity distribution having a peak near the center line A is obtained in the straight line region, whereas a light intensity distribution peak (around the outer periphery where the P electrode 56 exists is centered in the curved region ( Gain region).
A region 57 where no P electrode is present is formed on the inner side of the curved region of the optical waveguide 25.

  In this way, by providing the P electrode provided on the optical waveguide in a shape in which a region in which no electrode exists is formed on the inner side of the curved region, the light intensity distribution in the fundamental mode is changed in the width direction of the curved region. It can be formed from the center to the outer periphery, and can be controlled to give gain to the fundamental mode and loss to the higher-order mode, and to suppress the higher-order mode and obtain a high-quality beam with high output. it can.

  What is necessary is just to select according to the case about the area and positional relationship of an electrode non-formation area | region. In addition, although it is not always necessary to provide the electrode non-formation region in all the curved parts, it is preferable to provide the electrode non-formation region in all the points in terms of high output.

Here, the example which considered the relationship between the path width w of an optical waveguide and the curvature r is shown.
For example, when the path width (line width) w of the optical waveguide is 30 μm and the curvature r is 1000 μm, the relationship of “curvature r <line width of waveguide structure × 25” is not satisfied, and as shown in FIG. In addition to the mode (solid line), there is a primary mode (dashed line). On the other hand, when the path width (line width) w of the optical waveguide is 30 μm and the curvature r is 680 μm, the relationship of “curvature r <line width of waveguide structure × 25” is satisfied and the primary mode (broken line) is The fundamental mode (solid line) with no higher order mode suppressed is obtained. When a higher-order mode remains in the optical waveguide, an electrode is provided closer to the outer periphery from the center in the width direction (center line A) of the curved region, and an electrode non-forming region where no electrode is formed closer to the inner periphery than this electrode Higher-order modes can be suppressed by adopting an electrode arrangement as follows.

  In the same manner as the formation of the insulating film in the fifth embodiment, the P electrode 56 in the present embodiment is formed by previously forming a region on the surface of the surface InGaAs contact layer where no electrode is formed before forming the P electrode on the optical waveguide 25. It can be formed by covering with an insulating film and forming the P electrode in that state.

(Ninth embodiment)
A ninth embodiment of the semiconductor optical amplifier composite semiconductor laser device of the present invention will be described with reference to FIG. This embodiment is an array in which a plurality of layer structures having S-shaped curved portions (optical waveguides) formed on an InP substrate in the fifth embodiment (first embodiment) are arranged on the same semiconductor chip. It is a light source.

  Each layer can be formed in the same manner as in the first embodiment using the materials and methods used in the first and fifth embodiments, and the same components as those in the first and fifth embodiments are the same. The detailed description is abbreviate | omitted.

  In this embodiment, as shown in FIG. 12, an InP clad layer 15 and an InGaAs contact layer are formed on a single semiconductor chip 60 and on a layer structure of an InGaAsP guide layer 12 / InGaAsP active layer 13 / InGaAsP guide layer. Two layer structures each having 16 ridged S-shaped optical waveguides 25 (P electrodes 17 are provided on the optical waveguides) are arranged. Since a plurality of layer structures are provided on a single substrate, a high-power laser device can be miniaturized.

  As the semiconductor chip, a GaAs substrate, an InP substrate, or the like can be used.

  In the present embodiment, the two layer structures provided with the ridged S-shaped structure are provided on the same substrate. However, the number of layer structures provided on the same substrate is appropriately determined according to the purpose and the like. You can choose. In addition, the optical waveguide constituting each layer structure in this case is S-shaped, that is, in addition to two curved portions, one or three curved portions may be provided, depending on the purpose and case. It is possible to obtain the effect of the present invention by appropriately selecting.

1 is a perspective view showing a schematic configuration of a semiconductor laser device according to a first embodiment of the present invention. (A) It is a figure which shows the mode of propagation of a fundamental mode and a higher mode, (b) is a figure for demonstrating the mode of propagation of the light of a fundamental mode, (c) is the figure of the light of a higher mode. It is a figure for demonstrating the mode of propagation. It is a perspective view which shows schematic structure of the semiconductor laser apparatus which concerns on 2nd Embodiment of this invention. It is a perspective view which shows schematic structure of the semiconductor laser apparatus which concerns on 3rd Embodiment of this invention. It is a conceptual diagram for demonstrating the direction of the light reflected with the end surface inclined with respect to the centerline A of an optical waveguide. It is a perspective view which shows schematic structure of the semiconductor laser apparatus which concerns on 5th Embodiment of this invention. It is a perspective view which shows schematic structure of the semiconductor laser apparatus which concerns on 6th Embodiment of this invention. It is a perspective view which shows schematic structure of the semiconductor laser apparatus which concerns on 7th Embodiment of this invention. It is a top view which shows the structure of the P electrode of the semiconductor laser apparatus concerning 8th Embodiment of this invention. It is a conceptual diagram which shows the mode of the peak (gain area | region) of the light intensity distribution in the semiconductor laser apparatus concerning 8th Embodiment of this invention. It is a graph for demonstrating generation | occurrence | production of the mode when not satisfy | filling the relationship of curvature r <line width of a waveguide structure x25 ". It is a perspective view which shows schematic structure of the semiconductor laser apparatus concerning 9th Embodiment of this invention.

Explanation of symbols

11... InP substrate 12... InGaAsP guide layer (N-type high refractive index layer)
13 ... InGaAsP active layer 14 ... InGaAsP guide layer (P-type high refractive index layer)
15 ... InP clad layer (P-type clad layer)
16 ... InGaAs contact layers 17, 18, 56 ... electrode 25 ... optical waveguide 31 ... diffraction grating 41, 51 ... laser part 42, 52 ... optical amplification part 45 ... current non-injection region 57 ... region 60 where no electrode exists ... semiconductor chip

Claims (11)

On the semiconductor substrate, at least an N-type high refractive index layer, an active layer, a P-type high refractive index layer, and a P-type cladding layer having a refractive index lower than that of the P-type high refractive index layer are sequentially stacked from the semiconductor substrate side. A semiconductor laser device having a layered structure, wherein at least one layer of the layered structure has a waveguide structure in which a curvature r satisfies the following formula and includes at least one curved line portion having two or more modes.
Curvature r <Line width of waveguide structure × 25 Formula   The semiconductor laser device according to claim 1, wherein the line width is 10 μm or more.   The layer structure is configured as a composite structure including a laser part formed in a semiconductor laser structure and a light amplification part formed in a semiconductor optical amplifier structure that amplifies light incident from the laser part. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is characterized.   4. The semiconductor laser device according to claim 3, wherein at least one of the laser part and the light amplification part has a waveguide structure including at least one of the curved parts.   5. The laser part according to claim 3 or 4, wherein the laser part has a waveguide structure including at least one of the curved parts, and the light amplification part gradually becomes wider in a direction away from the laser part. The semiconductor laser device described.   6. The semiconductor laser device according to claim 1, further comprising a contact layer on a side of the P-type cladding layer away from the semiconductor substrate.   7. The semiconductor laser device according to claim 3, wherein the laser part formed in the semiconductor laser structure includes a diffraction grating.   At least one of the end face of the laser part formed in the semiconductor laser structure and the end face of the optical amplification part formed in the semiconductor optical amplifier structure is in the width direction perpendicular to the stacking direction of the layer structure of the waveguide structure. The semiconductor laser device according to claim 3, wherein the semiconductor laser device is inclined with respect to a center line.   The semiconductor laser device according to claim 1, wherein the waveguide structure has a current injection region and a current non-injection region.   10. The curve portion according to claim 1, wherein the curved portion has an electrode in at least a part of a region near the outer periphery from a center line in a width direction orthogonal to the stacking direction of the layer structure of the waveguide structure. Semiconductor laser equipment.   2. The semiconductor chip according to claim 1, wherein the semiconductor substrate is a semiconductor chip formed of a single substrate, and has a plurality of layer structures provided with a waveguide structure including at least one curved portion on the semiconductor chip. The semiconductor laser device according to any one of 1 to 10.

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