JP2007273690A - Optical semiconductor element and variable-wavelength light source equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the output power of an optical semiconductor element, such as SLD, SOA, etc, which has an oblique optical waveguide structure, without deteriorating its wide-band properties. <P>SOLUTION: The optical semiconductor element 1 has a configuration wherein a first conductivity-type electrode 41, a semiconductor active layer 15, and a second conductivity-type electrode 42 are formed on a first conductivity-type semiconductor substrate 11. The optical semiconductor element 1 is equipped with an optical waveguide 50 which is extended from a first optical waveguide opening 51 formed on the one element end surface 1R of the optical semiconductor element 1, communicates with a second optical guide opening 52 formed on the one element end surface 1R or the other element end surface 1F, and, at least, extends its part at an oblique angle to the direction of the normal of the one element end surface 1R. The optical waveguide 50 is formed in a wide pattern, which is equipped with a wide part 55 wider than the widths W1 and W2 of the first and second optical waveguide openings 51 and 52, within a certain range except the vicinities of both the first optical waveguide opening 51 and the second optical waveguide opening 52. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical semiconductor element that can be used as a super luminescent diode (SLD), a semiconductor optical amplifier (SOA), and the like, and a wavelength tunable light source including the same.

  A super luminescent diode (SLD) is an optical semiconductor element that exhibits low coherence like a light emitting diode, and can obtain an output comparable to a semiconductor laser while exhibiting a broad emission spectrum. The light emitted from the SLD is called amplified spontaneous output light (ASE light), and it is said that the spontaneous output light randomly generated in the laser medium having a large inversion distribution is amplified in the stimulated emission process while passing through the laser medium. ing.

  The SLD basically has a structure in which laser oscillation is suppressed by removing the resonator structure from the semiconductor laser. In order to suppress laser oscillation, it is necessary to suppress the light reflectance at the end face. As a structure for reducing the end face reflectance relatively easily, for example, an oblique optical waveguide structure in which at least a part of the optical waveguide is inclined with respect to the normal direction of the element end face has been proposed.

  In SLD, it is preferable that the light output is high and the half width of the emission spectrum is wide. In order to increase the light output, it is considered necessary to (1) increase the amplification gain by stimulated emission, or (2) increase the natural output light component.

  However, (1) stimulated emission is a process of emitting a photon accompanying a radiation transition of a substance, and is a process of emitting light having a phase equal to the incident light in proportion to the incident light intensity. Therefore, when the amplification gain due to stimulated emission is increased, the strong light wavelength of the natural output light that originally has a broad emission spectrum shape is preferentially amplified, and the half-value width of the emission spectrum becomes narrower with higher output. End up.

  In order to increase the light output while maintaining a broadband spectrum shape, it is considered necessary to increase the light output by (2) natural output light component. By increasing the light emitting area, the light output by the natural output light component can be increased.

  Increasing the element depth length corresponding to the cavity length of the semiconductor laser in order to increase the light emitting area is not preferable because it means that the amplification gain is also increased.

Non-Patent Document 1 discloses an SLD in which an optical waveguide is widened in a tapered shape from the light input side to the light output side for the purpose of increasing the output.
Jpn.J.Appl.Phys.Vol.38 (1999) pp.5121-5122

  In the structure described in Non-Patent Document 1, the width of the light output port of the optical waveguide is inevitably the largest. In such a structure, when the width of the light output port of the optical waveguide exceeds a certain size, the output light changes from the fundamental transverse mode to the higher order transverse mode.

  In other words, in the structure described in Non-Patent Document 1, in order to obtain output light in the fundamental transverse mode, the width of the optical output port of the optical waveguide is within a limited range in which only the fundamental transverse mode is allowed. There is a limit to increasing the light emitting area and increasing the output, because it must be wide.

  A semiconductor optical amplifier (SOA) is also an optical semiconductor element having an element configuration similar to that of an SLD, and has the same problem in increasing output.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical semiconductor element such as an SLD or SOA that can achieve high output without impairing broadband characteristics. .

The optical semiconductor element of the present invention is an optical semiconductor element in which a first conductive type electrode, a semiconductor active layer, and a second conductive type electrode are provided on a first conductive type semiconductor substrate.
The first optical waveguide port formed on one element end surface non-parallel to the substrate surface of the semiconductor substrate communicates with the second optical waveguide port formed on the one element end surface or the other element end surface, and at least An optical waveguide is formed partly extending obliquely with respect to the normal direction of the one element end face,
In addition, the width of the first optical waveguide port and the second optical waveguide are within the range in which the optical waveguide excludes the vicinity of the first optical waveguide port and the vicinity of the second optical waveguide port. It is formed by a width pattern having a wide portion wider than the width of the roadway.

  In this specification, “first conductivity type” and “second conductivity type” correspond to p-type or n-type, and indicate that the conductivity types are different.

The wide portion may have a substantially uniform width distribution in the optical waveguide direction or may have a width distribution.
The wide portion having a width distribution includes a substantially uniform width portion having a substantially uniform width distribution in the optical waveguide direction, and a continuous portion in the optical waveguide direction from the first optical waveguide opening side toward the substantially uniform width portion. Alternatively, it includes a widened portion that is widened stepwise and a narrowed portion that is continuously or stepwise reduced in the optical waveguide direction from the substantially uniform width portion toward the second optical waveguide port side. Things.

  In this specification, “the width is substantially uniform” means that a reference width of ± 10% is maintained.

  The width of the first optical waveguide port and the width of the second optical waveguide port allow only the fundamental transverse mode (single transverse mode), and the maximum width of the wide portion is the fundamental transverse mode (single transverse mode). ) And a high-order transverse mode (multi transverse mode) are preferred.

Moreover, it is preferable that the maximum width of the wide part satisfies the following formulas (I) and (II).
3 × W1 ≦ W3 ≦ 10 × W1 (I),
3 × W2 ≦ W3 ≦ 10 × W2 (II)
(W1 is the width of the first optical waveguide port, W2 is the width of the second optical waveguide port, and W3 is the maximum width of the wide portion.)

  As an aspect of the optical semiconductor element of the present invention, a singular structure having a ridge structure portion formed in a width pattern corresponding to the width pattern of the optical waveguide between the semiconductor active layer and the second conductivity type electrode. Or the thing provided with the several 2nd conductivity type clad layer is mentioned.

  As another aspect of the optical semiconductor element of the present invention, a mesa structure portion formed with a width pattern corresponding to the width pattern of the optical waveguide is provided between the semiconductor active layer and the second conductivity type electrode. The thing provided with the 1st or several 2nd conductivity type clad layer is mentioned.

  The optical semiconductor element of the present invention has an oblique optical waveguide structure in which at least a part of the optical waveguide extends obliquely with respect to the normal direction of the element end face. Does not have a structure. The optical semiconductor element of the present invention can be used as a super luminescent diode (SLD), a semiconductor optical amplifier (SOA), or the like.

  In the field of semiconductor lasers, Japanese Patent Application Laid-Open No. 7-297482 and Japanese Patent Application Laid-Open No. 2000-183463 disclose that a portion near the first optical waveguide port and a portion near the second optical waveguide port are the remaining portions. A narrower device structure is described. These element structures are intended to improve laser characteristics such as low aspect ratio of laser beam (roundness of beam shape). Therefore, in these element structures, the wide portion has a width that allows only the normal fundamental transverse mode, and the vicinity of the first optical waveguide port and the vicinity of the second optical waveguide port of the optical waveguide Is even narrower.

  In the field of SLD and SOA targeted by the present invention, the optical waveguide is within the range excluding the vicinity of the first optical waveguide opening and the vicinity of the second optical waveguide opening. No device structure having a wide portion wider than the width of the second optical waveguide port has been reported in the past. Also in the field of semiconductor lasers, the widths of the vicinity of the first optical waveguide port and the vicinity of the second optical waveguide port are widths that allow only the fundamental transverse mode, and the maximum width of the wide part is basically the same. An element structure having a width that allows both a transverse mode and a high-order transverse mode has not been reported in the past.

  The wavelength tunable light source of the present invention selects the above-described optical semiconductor element of the present invention, a resonance means for resonating light emitted from the optical semiconductor element, an oscillation wavelength from the resonance means, and the oscillation wavelength And a wavelength selection means capable of changing the wavelength.

  In the wavelength tunable light source of the present invention, the resonance means may be a member independent of the optical semiconductor element of the present invention, or the optical semiconductor element of the present invention itself may form part of the resonance means.

  Examples of the wavelength selection means include a diffraction grating capable of changing a grating plane angle with respect to the optical axis of incident light, or an optical filter capable of changing light transmission characteristics.

  The optical semiconductor element of the present invention is applicable to optical semiconductor elements such as SLD and SOA, and the optical waveguide is in a range excluding the vicinity of the first optical waveguide port and the vicinity of the second optical waveguide port. Inside, the width of the first optical waveguide port and the width pattern having a wider portion than the width of the second optical waveguide port are formed.

  In such a configuration, since the wide portion is provided in the optical waveguide, the light emission area can be increased, and the light output by the natural output light component can be increased.

  The increase in output in the present invention is not due to (1) an increase in amplification gain due to stimulated emission, but (2) an increase in natural output light component, which impairs the broadband characteristics required for SLD, SOA, and the like. High output can be realized without this.

  In the optical semiconductor device of the present invention, it is not necessary to increase the widths of the first optical waveguide port and the second optical waveguide port of the optical waveguide. The width of the optical waveguide opening can be set to allow only the fundamental transverse mode. Accordingly, it is possible to increase the light output while maintaining the mode of the output light in the basic transverse mode.

  As described above, according to the present invention, it is possible to provide an optical semiconductor element such as an SLD or an SOA that can achieve high output without impairing broadband characteristics.

“First Embodiment of Optical Semiconductor Device”
The configuration of the first embodiment of the optical semiconductor device according to the present invention will be described with reference to the drawings. 1 is an overall perspective view, FIG. 2A is an AA ′ cross-sectional view (a cross-sectional view passing through a narrow portion 54), and FIG. 2B is a BB ′ cross-sectional view (a cross-sectional view passing through a wide portion 55). ). In the present embodiment, an infrared light emitting SLD having a buried ridge stripe structure will be described as an example. In FIG. 1, the width pattern of the optical waveguide 50 when the optical waveguide 50 is projected onto the element upper surface is indicated by a broken line.

  In the optical semiconductor element 1 of the present embodiment shown in FIG. 1, the element end face (one element end face) on the back side in the figure is the rear end face 1R, and the element end face (other element end face) on the near side in the figure is the front end face (light output). Side end face) 1F. In the present embodiment, the rear end surface 1R and the front end surface 1F are perpendicular to the substrate surface of the semiconductor substrate 11, and the rear end surface 1R and the front end surface 1F are parallel to each other.

  In the optical semiconductor element 1, an optical waveguide 50 is formed which communicates from a first optical waveguide port 51 formed on the rear end surface 1R to a second optical waveguide port (light output port) 52 formed on the front end surface 1F. ing. The first and second optical waveguide ports 51 and 52 are actually located in the current injection region 15a (see FIG. 2) of the semiconductor active layer 15 and its vicinity on the rear end surface 1R and the front end surface 1F. In FIG. 1, for the sake of convenience, the pattern is shown on the pattern of the optical waveguide 50 projected on the upper surface of the element.

  Hereinafter, the layer configuration of the optical semiconductor device 1 of the present embodiment will be described.

  In the optical semiconductor element 1, a semiconductor active layer 15 and a p-type (second conductivity type) electrode 41 are sequentially provided on an upper surface of an n-type (first conductivity type) semiconductor substrate 11 from the substrate side. 11 is an element in which an n-type (first conductivity type) electrode 42 is provided on the lower surface of the figure.

  Between the semiconductor substrate 11 and the semiconductor active layer 15, an n-type buffer layer 12, an n-type lower cladding layer 13, and a non-doped lower light guide layer 14 are sequentially stacked from the semiconductor substrate 11 side. The semiconductor active layer 15 is preferably a multiple quantum well active layer.

  On the semiconductor active layer 15, a non-doped upper light guide layer 16, a p-type upper first cladding layer 17, and a p-type etching stop layer 18 are sequentially stacked.

  On the p-type etching stop layer 18, a mesa stripe-shaped ridge structure portion 20 having a laminated structure of the p-type upper second cladding layer 21 and the p-type cap layer 22 is formed. The p-type ridge structure 20 is sandwiched between n-type current blocking layers 31 that are also provided on the p-type etching stop layer 18. In the present embodiment, the ridge structure portion 20 is formed with a specific width pattern when viewed in the optical waveguide direction, and thereby the optical waveguide 50 is formed with a specific width pattern.

  A p-type upper third cladding layer 32, a p-type contact layer 33, and a p-type electrode 41 are sequentially stacked on the p-type ridge structure 20 and the n-type current blocking layer 31.

  The p-type ridge structure 20 and the n-type current blocking layer 31 are formed in a predetermined pattern, and all other layers are formed on substantially the entire surface of the semiconductor substrate 11.

Hereinafter, design examples of the composition and thickness of the semiconductor substrate 11 and each layer will be given.
Semiconductor substrate 11: n-GaAs substrate,
n-type buffer layer 12: n-GaAs layer (0.2 μm thick, carrier concentration 5.0 × 10 ¹⁷ cm ⁻³ ),
n-type lower cladding layer 13: n-In _0.49 Ga _0.51 P layer (2.0 μm thick, carrier concentration 5.0 × 10 ¹⁷ cm ⁻³ ),
Lower light guide layer 14: non-doped GaAs layer (34 nm thick),
Semiconductor active layer 15: InGaAs multiple quantum well active layer (laminated structure in which 6 nm thick quantum well layers and 10 nm thick barrier layers are alternately stacked),
Upper light guide layer 16: non-doped GaAs layer (34 nm thick),
p-type upper first cladding layer 17: p-In _0.49 Ga _0.51 P layer (0.2 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type etching stop layer 18: p-GaAs layer (10 nm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type upper second cladding layer 21: p-In _0.49 Ga _0.51 P layer (0.5 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type cap layer 22: p-GaAs layer (thickness 0.2 μm, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
n-type current blocking layer 31: n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P layer (0.5 μm thickness, carrier concentration 1.0 × 10 ¹⁸ cm ⁻³ ),
p-type upper third cladding layer 32: p-Al _0.58 Ga _0.42 As layer (1.3 μm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ),
p-type contact layer 33: p-GaAs layer (2.0 μm thick, carrier concentration 1.0 × 10 ¹⁹ cm ⁻³ ).

  In the present embodiment, the current blocking layer 31 is designed to have a conductivity type different from those of the layers 17, 18, 32 and the ridge structure portion 20 formed above and below the layer. That is, the reverse bias structure between the p-type upper first cladding layer 17 and the current blocking layer 31 invalidates the current flowing through the n-type current blocking layer 31, and the p-type upper second cladding forming the ridge structure portion 20. A current selectively flows through the layer 21. In such a configuration, a current is selectively injected into the specific region 15 a of the semiconductor active layer 15 located substantially below the ridge structure 20, and the optical waveguide 50 having a width pattern corresponding to the width pattern of the ridge structure 20 is formed. The Hereinafter, the specific region 15a is referred to as a current injection region. In the drawing, for convenience, the boundary between the current injection region 15a and the non-current injection region of the semiconductor active layer 15 is clearly shown, but the boundary between the current injection region 15a and the non-current injection region is clear. is not.

  The optical waveguide 50 is configured by a current injection region 15a of the semiconductor active layer 15 and its vicinity (such as a portion near the current injection region 15a of the light guide layers 14 and 16).

  It has been described that the width patterns of the ridge structure 20 and the optical waveguide 50 correspond to each other. In this embodiment, the shape of the ridge structure portion 20 in a certain cross section is a shape that is tapered from the substrate 11 side toward the p-type electrode 41 side, and has a distribution in the thickness direction. In such a case, the maximum width of the ridge structure 20 in a certain cross section substantially coincides with the width of the optical waveguide 50 in the cross section. Therefore, in this embodiment, the width of the ridge structure portion 20 in a certain cross section means the maximum width of the ridge structure portion 20 in the cross section.

  Hereinafter, the width pattern of the optical waveguide 50 in the present embodiment will be described.

  The optical waveguide 50 communicates from the first optical waveguide port 51 formed on the rear end surface 1R to the second optical waveguide port (light output port) 52 formed on the front end surface 1F, and the optical axis 50X is It is inclined with respect to the normal direction H of the rear end surface 1R and the front end surface 1F. The inclination angle θ with respect to the normal direction H of the rear end surface 1R and the front end surface 1F of the optical axis 50X of the optical waveguide 50 is not particularly limited, and is preferably about 3 to 7 °, for example. In the drawings, θ is exaggerated from the actual value.

  The optical waveguide 50 has a width of the first optical waveguide port 51 and the second optical waveguide port 52 within a range excluding the vicinity of the first optical waveguide port 51 and the vicinity of the second optical waveguide port 52. A wider portion 55 is provided. In the present embodiment, the light emitting area is increased by providing the wide portion 55 for the optical waveguide 50.

  That is, the optical waveguide 50 includes a narrow portion 53 formed in a range including the first optical waveguide port 51 and the vicinity thereof, and a width formed in a range including the second optical waveguide port 52 and the vicinity thereof. The narrow portion 54 and the wide portion 55 formed between the narrow portion 53 / the narrow portion 54 are configured. In the present embodiment, the width distribution of the narrow portion 53 in the optical waveguide direction, the width distribution of the narrow portion 54 in the optical waveguide direction, and the width distribution of the wide portion 55 in the optical waveguide direction are all substantially uniform.

  The width of the first optical waveguide port 51 (= width of the narrow portion 53) is W1, the width of the second optical waveguide port 52 (= width of the narrow portion 54) is W2, and the width of the wide portion 55 is W3. Then, W3> W1 and W3> W2. The width W1 of the narrow portion 53 and the width W2 of the narrow portion 24 are preferably substantially the same.

  In this embodiment, since the effect of increasing the light emitting area can be obtained satisfactorily and the fundamental transverse mode output light can be stably obtained, the widths W1 and W2 of the narrow portions 53 and 54 allow only the fundamental transverse mode. It is preferable that the width W3 of the wide portion 55 is a width that allows both the basic transverse mode and the higher-order transverse mode.

Specifically, the widths W1 and W2 of the narrow portions 53 and 54 are preferably 2.0 to 6.0 μm. Further, the width W3 of the wide portion 55 preferably satisfies the following formulas (I) and (II).
3 × W1 ≦ W3 ≦ 10 × W1 (I),
3 × W2 ≦ W3 ≦ 10 × W2 (II)

  By making the width W3 of the wide portion 55 at least three times the widths W1 and W2 of the narrow portion, the effect of increasing the light emitting area and the effect of increasing the output can be obtained effectively. However, in the element structure of this embodiment, not all of the light generated in the wide portion 55 of the optical waveguide 50 is coupled to the narrow portion 54, so that the width W 3 of the wide portion 55 is set to the width of the narrow portions 53 and 54. Even if the width W1 or W2 is extremely widened to 10 times or more, only the operating current value rises, and an optical output increase corresponding to the operating current value cannot be obtained, and the effect is saturated. Therefore, it is preferable that the width W3 of the wide portion 55 is not more than 10 times the widths W1 and W2 of the narrow portions 53 and 54.

  If the element depth length corresponding to the resonator length of the semiconductor laser is LT, LT is, for example, 0.50 to 2.0 mm. The lengths L1 to L3 in the optical waveguide direction of each of the narrow portions 53 and 54 and the wide portion 55 are not particularly limited and are preferably conditions for outputting fundamental transverse mode light.

  That is, in the present embodiment, the lengths L1 and L2 in the optical waveguide direction of the narrow portions 53 and 54, which are the conditions for outputting the fundamental transverse mode light, are secured, and within these ranges (= first light guide). The wide portion 55 may be provided in the range excluding the vicinity of the waveguide opening 51 and the vicinity of the second optical waveguide opening 52). If LT = 1.5 to 2.0 mm, L1 and L2 can be designed, for example, in the range of the minimum length required to output the fundamental transverse mode light to 0.5 mm.

  The width pattern of the optical waveguide 50 has been described above. In this embodiment, the ridge structure 20 is formed in the same width pattern as shown in FIGS. 2A and 2B. An optical waveguide 50 is formed.

  In the optical semiconductor device 1 of the present embodiment, the optical waveguide 50 is within the range excluding the vicinity of the first optical waveguide port 51 and the vicinity of the second optical waveguide port 52, and the first optical waveguide port 51. The width and the width of the second optical waveguide port 52 are larger than the width of the wide portion 55. In such a configuration, since the wide portion 55 is provided in the optical waveguide 50, the light emission area can be increased.

  The optical output of the SLD is limited by the saturation phenomenon of the optical output due to gain saturation and heat generation. In the optical semiconductor device 1 of the present embodiment, since the light emitting region is widened compared to the conventional device, the gain of the active layer for the same light output can be reduced, and as a result, the gain saturation output is improved. Can do. In addition, since the thermal resistance is reduced by expanding the light emitting region, the light output of heat saturation due to heat generation can be improved. In the present embodiment, these effects combine to increase the light output by the natural output light component.

  The increase in output in this embodiment is not due to (1) an increase in amplification gain due to stimulated emission, but (2) an increase in natural output light component. Therefore, wideband characteristics, which are necessary characteristics for SLD, SOA, etc., are achieved. High output can be achieved without loss.

  Further, in the optical semiconductor device 1 of the present embodiment, it is not necessary to increase the width of the first optical waveguide port 51 and the width of the second optical waveguide port 52 of the optical waveguide 50. The width of the optical waveguide 51 port and the width of the second optical waveguide port 52 can be set to allow only the fundamental transverse mode. Accordingly, it is possible to increase the light output while maintaining the mode of the output light in the basic transverse mode.

  As described above, according to the present embodiment, it is possible to provide the optical semiconductor element 1 capable of increasing the output without impairing the broadband property.

(Design change example of the first embodiment)
The width pattern of the optical waveguide 50 (ridge structure portion 20) can be appropriately changed in design. 3A to 3C show other width pattern examples. 3A to 3C are perspective views corresponding to FIG.

  The wide portion 55 of the optical waveguide 50 may have a width distribution in the optical waveguide direction. In the optical waveguide 50 shown in FIG. 3A, the wide portion 55 has a substantially uniform width portion 55A having a substantially uniform width distribution in the optical waveguide direction and a substantially uniform width portion 55A from the first optical waveguide port 51 side. A widened portion 55B that continuously widens in the optical waveguide direction, and a narrowed portion that continuously narrows in the optical waveguide direction from the substantially uniform width portion 55A toward the second optical waveguide port 52 side. 55C and has a width distribution in the optical waveguide direction. The width change in the optical waveguide direction in the widened portion 55B and the narrowed portion 55C may be a stepwise change. In such a configuration, the maximum width W3 of the wide portion 55 (corresponding to the width of the substantially uniform width portion 55A) is preferably 3 to 10 times the widths W1 and W2 of the narrow portions 53 and 54.

As long as resonance within the element can be suppressed, it is sufficient that at least a part of the optical axis 50X of the optical waveguide 50 extends obliquely with respect to the normal direction H of the element end faces 1R and 1F.
Therefore, the optical waveguide 50 is a combination of a portion extending obliquely with respect to the normal direction H of the element end faces 1R, 1F and a portion extending parallel to the normal direction H of the element end faces 1R, 1F. There may be. In the example shown in FIG. 3B, the narrow portion 53 and the wide portion 55 on the rear end surface 1R side extend obliquely with respect to the normal direction H of the element end surfaces 1R and 1F, and the narrow portion 54 on the front end surface 1F side. Extends parallel to the normal direction H of the element end faces 1R and 1F.

  The optical axis 50X of the optical waveguide 50 may be curved, or a combination of linear and curved shapes.

  The first optical waveguide port 51 and the second optical waveguide port 52 of the optical waveguide 50 may be formed on the same element end face. In the example shown in FIG. 3C, the optical waveguide 50 is passed from the front end face 1F to the rear end face 1R, and the optical waveguide 50 is folded back in a V shape at the rear end face 1R and returned to the front end face 1F. Even in such a configuration, the width of the first optical waveguide port 51 and the second optical waveguide are set within the range excluding the vicinity of the first optical waveguide port 51 and the vicinity of the second optical waveguide port. By forming with a width pattern having a wide portion 55 wider than the width of the waveguide port 52, the same effect as in the above embodiment can be obtained.

“Second Embodiment of Optical Semiconductor Device”
The configuration of the second embodiment of the optical semiconductor element according to the present invention will be described with reference to FIG. Also in this embodiment, an SLD will be described as an example. FIG. 4 is a cross-sectional view corresponding to FIG. 2B, and the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, the layer structure up to the p-type upper first cladding layer 17 is the same as that of the first embodiment.

  A p-type etching stop layer 18 and an n-type current blocking layer 31 are stacked on the p-type upper first cladding layer 17 in a pattern having an opening 30. A p-type upper second cladding layer 61 is formed on the n-type current blocking layer 31. The p-type upper second cladding layer 61 enters the opening 30 of the n-type current blocking layer 31, and a portion sandwiched between the n-type current blocking layers 31 of the p-type upper second cladding layer 61 is a mesa. The structure portion 60 is formed. A p-type contact layer 33 and a p-type electrode 41 are sequentially stacked on the p-type upper second cladding layer 61.

  Also in the present embodiment, as in the first embodiment, the reverse bias structure between the p-type upper first cladding layer 17 and the current blocking layer 31 invalidates the current flowing through the n-type current blocking layer 31, and p A current selectively flows through the mesa structure portion 60 of the mold upper second cladding layer 61. In such a configuration, a current is selectively injected into the specific region 15 a of the semiconductor active layer 15 located substantially below the mesa structure portion 60.

  In the present embodiment, the mesa structure portion 60 is formed in the same pattern as the width pattern of the ridge structure portion 20 of the first embodiment, whereby an optical waveguide having the same width pattern as in the first embodiment. 50 is formed (see FIG. 1).

  In the present embodiment, the shape of the mesa structure portion 60 in a certain cross section is a shape widened in a reverse taper shape from the substrate 11 side toward the p-type electrode 41 side, and has a distribution in the thickness direction. In such a case, the minimum width of the mesa structure portion 60 in a certain cross section substantially matches the width of the optical waveguide 50 in the cross section.

The layer composition of the optical semiconductor element 2 can be designed as appropriate. A design example is shown below.
Semiconductor substrate 11: n-GaAs substrate,
n-type buffer layer 12: n-GaAs layer,
n-type lower cladding layer 13: n-GaInP layer,
Lower light guide layer 14: i-InGaAsP layer,
Semiconductor active layer 15: InGaAs multiple quantum well active layer,
Upper light guide layer 16: i-InGaAsP layer,
p-type upper first cladding layer 17: p-GaInP layer,
p-type etching stop layer 18: p-GaAs layer,
n-type current blocking layer 31: n-GaInP layer,
p-type upper second cladding layer 61: p-AlGaAs layer,
p-type contact layer 33: p-GaAs layer.

  Also in this embodiment, since the optical waveguide 50 having the same width pattern as that of the first embodiment is formed, the same effect as that of the first embodiment can be obtained.

(Design change example)
The element configuration of the optical semiconductor element of the present invention can be appropriately changed within the scope not departing from the gist of the present invention.

  In the first and second embodiments of the optical semiconductor element, the SLD has been described as an example. However, the present invention is also applicable to a semiconductor optical amplifier (SOA) having an element configuration similar to that of the SLD.

“First embodiment of wavelength tunable light source”
Based on FIG. 5, the structure of 1st Embodiment of the wavelength-tunable light source which concerns on this invention is demonstrated. In the present embodiment, a wavelength-variable laser having a Littman arrangement will be described as an example.

  The wavelength tunable light source 4 of the present embodiment includes an optical semiconductor element 3 that is an embodiment of the optical semiconductor element of the present invention, a laser resonator (resonance means) 80 that resonates light emitted from the optical semiconductor element 3, and A diffraction grating (wavelength selection means) 91 that selects an oscillation wavelength from the laser resonator 80 and can change the oscillation wavelength is schematically configured. In the figure, reference numerals 71 to 73 are lenses provided as necessary.

  The optical semiconductor element 3 has the same structure as the optical semiconductor element 1 of the first embodiment, and the width pattern of the optical waveguide 50 (ridge structure portion 20) is an SLD having the pattern shown in FIG. . That is, in the optical semiconductor element 3, the optical waveguide 50 has a width pattern composed of the narrow portions 53 and 54 and the wide portion 55 as in the optical semiconductor device 1 of the first embodiment. The narrow portion 53 and the wide portion 55 on the 1R side extend obliquely with respect to the normal direction H of the element end faces 1R and 1F, and the narrow portion 54 on the front end face 1F side extends in the normal direction H of the element end faces 1R and 1F. In contrast, it has a width pattern extending in parallel.

  The optical semiconductor element 3 is provided with a partial reflection (HR) coating on the front end face 1F and a non-reflection (AR) coating on the rear end face 1R, and between the optical semiconductor element 3 and the resonant mirror 81 disposed outside. A laser resonator 80 is configured.

  In the laser resonator 80, a diffraction grating 91 is provided as wavelength selection means. In such a configuration, one oscillation wavelength is selected by the diffraction grating 91 from a plurality of wavelength modes oscillating in the laser resonator 80, and laser light in the fundamental transverse mode is output from the front end face 1 </ b> F of the optical semiconductor element 3.

  In the diffraction grating 91, the grating surface angle with respect to the optical axis of the incident light incident on the diffraction grating 91 (the optical axis of the laser resonator) can be changed, and the diffraction grating 91 is changed according to the grating surface angle of the diffraction grating 91. The oscillation wavelength selected by is changed.

  Further, if the mirror surface angle of the resonant mirror 81 with respect to the optical axis of the incident light incident on the resonant mirror 81 (the optical axis of the laser resonator) can be changed, the resonant light frequency in the laser resonator 80 can be changed.

  The laser light output from the laser resonator 80 is output to the outside via the optical fiber 75. An optical isolator 76 is disposed between the optical semiconductor element 3 and the optical fiber 75. By interposing the optical isolator 76, it is possible to prevent the reflected light from the far end of the optical fiber 75 from being coupled to the optical semiconductor element 3.

  Since the wavelength tunable light source 4 of the present embodiment includes the optical semiconductor element 3 according to an embodiment of the present invention, high output can be realized. Further, since the optical semiconductor element 3 has a broadband property necessary for SLD, according to the present embodiment, the wavelength variable light source 4 having a wide wavelength variable operation range and high output can be provided.

  Although the Littman arrangement has been described in the present embodiment, the present invention is not limited to such a configuration, and a Littrow arrangement or the like may be used.

“Second embodiment of wavelength tunable light source”
Based on FIG. 6, the structure of 2nd Embodiment of the wavelength-tunable light source which concerns on this invention is demonstrated. Also in this embodiment, a wavelength tunable laser will be described as an example. The wavelength tunable light source 5 of this embodiment has a ring-shaped laser resonator, and is called a ring laser.

  The wavelength tunable light source 5 of the present embodiment includes the optical semiconductor element 1 of the above embodiment, a laser resonator (resonance means) 82 that resonates light emitted from the optical semiconductor element 1, and an oscillation wavelength from the laser resonator 82. And an optical filter 92 (wavelength selection means) capable of changing the oscillation wavelength. In the figure, reference numerals 71 to 74 denote lenses provided as necessary.

  In the present embodiment, a ring laser resonator 82 is constituted by the optical semiconductor element 1 and the optical fiber 75 arranged in a ring shape, and an optical filter 92 as wavelength selection means is disposed in the laser resonator 82. ing. The natural output light from the optical semiconductor element 1 enters the optical filter 92, and the light transmitted through the optical filter 92 enters the optical fiber 75 arranged in a ring shape and returns to the optical semiconductor element 1. .

  In the wavelength tunable light source 5 of the present embodiment, laser oscillation occurs when the optical gain of the optical semiconductor element 1 exceeds the total loss of the ring laser resonator 82.

  The optical filter 92 is an optical element made of a multilayer dielectric film and having a characteristic of allowing only a specific wavelength to pass therethrough. Since the oscillation wavelength from the laser resonator 82 is determined by the transmission center wavelength of the optical filter 92, the optical filter 92 selects one oscillation wavelength from a plurality of wavelength modes that oscillate in the laser resonator 82.

  The optical filter 92 can change the filter surface angle with respect to the optical axis of the incident light incident on the optical filter 92, and the light transmission characteristic of the optical filter 92 can be changed according to the filter surface angle of the optical filter 92. Thus, the oscillation wavelength selected by the optical filter 92 is changed.

  An optical isolator 76 is disposed in the laser resonator 82. The optical isolator 76 is an optical element that determines the light circulation direction and contributes to a stable oscillation operation of the ring laser.

  In the present embodiment, the light in the ring laser resonator 82 can be extracted to the outside from the optical coupler 77 disposed in the ring laser resonator 82.

  Since the wavelength tunable light source 5 of the present embodiment includes the optical semiconductor element 1 according to an embodiment of the present invention, high output can be realized. Further, since the optical semiconductor element 1 has a broadband property necessary for SLD, according to the present embodiment, the wavelength variable light source 5 having a wide wavelength variable operation range and high output can be provided.

  Examples and comparative examples according to the present invention will be described.

Example 1
The optical semiconductor element (SLD) 1 of the above embodiment was manufactured by the following procedure. The composition and thickness of the semiconductor substrate 11 and each layer were as in the design examples given in the embodiment.
Crystal growth was performed by metal organic chemical vapor deposition (MOCVD). As the source gas, TEG (triethylgallium) / TMA (trimethylaluminum) / TMI (trimethylindium) / AsH ₃ (arsine) / PH ₃ (phosphine) was used. SiH ₄ (silane) was used as the n-type dopant source, and DEZ (diethyl zinc) was used as the p-type dopant source.

  First, an n-type buffer layer 12 to a p-type etching stop layer 18 and a p-type upper second cladding layer 21 before patterning are formed on the n-type semiconductor substrate 11 under conditions of a growth temperature of 600 to 700 ° C. and a pressure of 10.1 kPa. And the p-type cap layer 22 before patterning were sequentially grown (first crystal growth).

Next, a SiO ₂ selective growth mask (dielectric mask) corresponding to the pattern of the ridge structure portion 20 is formed, and using this as a mask, the p-type upper second cladding layer 21 and the p-type cap layer 22 are etched, The ridge structure 20 having the width pattern described in the above embodiment was formed (see the width pattern of the optical waveguide 50 in FIG. 1).

Next, using the SiO ₂ selective growth mask as a mask, the n-type current blocking layer 31 was grown in a region on the p-type etching stop layer 18 excluding the ridge structure portion 20 (second crystal growth).

After removing the SiO ₂ selective growth mask, the p-type upper third cladding layer 32 and the p-type contact layer 33 were successively grown on the ridge structure 20 and the n-type current blocking layer 31 (third crystal). growth).

  Next, the semiconductor substrate 11 was polished until the total thickness of the device reached about 100 μm, and the p-type electrode 41 and the n-type electrode 42 were formed by vapor deposition and heat treatment.

  An SLD bar having an element depth length LT of about 1.50 mm is cut out from the obtained element by cleavage, and an AR coating (less than 0.5% of the emission wavelength from the element itself) is applied to the rear end face 1R and the front end face 1F. (Reflectance coating).

  Finally, a chip was obtained by cleavage to obtain an SLD chip. In order to enhance the heat dissipation effect, this chip was mounted on a heat sink of a mounting substrate equipped with a drive circuit by a so-called junction down system, which is mounted with the p-type electrode 41 side as the heat dissipation side down.

In the present embodiment, the inclination angle θ of the optical axis 50X of the optical waveguide 50X with respect to the normal direction H of the rear end surface 1R and the front end surface 1F, and the widths and lengths of the narrow portions 53 and 54 and the wide portion 55 of the optical waveguide 50. Was as follows.
The inclination angle θ of the optical axis 50X of the optical waveguide 50: 7 °,
Narrow part 53 of the optical waveguide 50: width W1 = 3 μm, length L1 in the optical waveguide direction = 0.3 mm,
Narrow portion 54 of the optical waveguide 50: width W2 = 3 μm, length L2 in the optical waveguide direction = 0.3 mm,
Wide portion 55 of optical waveguide 50: width W3 = 10 μm, length L3 in the optical waveguide direction = 0.9 mm.

(Comparative Example 1)
An SLD chip for comparison was obtained and mounted on a mounting substrate in the same manner as in Example 1 except that the wide portion was not provided in the optical waveguide 50 and the width of the optical waveguide was changed to a uniform width (3 μm).

(Evaluation of Example 1 and Comparative Example 1)
For the elements of Example 1 and Comparative Example 1, the current-light output characteristics were evaluated. The results are shown in FIG.

  Although the element of Example 1 had a larger driving operation current value for obtaining the same optical output as compared with Comparative Example 1, the half-value width of the wavelength spectrum at 30 mW output was measured. On the other hand, in Example 1, it was 80 nm, and a broader emission spectrum was obtained.

  This indicates that the output of the element of Example 1 can be higher than that of Comparative Example 1 if the bands of the emission spectra are compared under the same conditions. It was shown that both can be realized.

(Example 2)
The device configuration is the same as that of the first embodiment, but the optical waveguide 50 (ridge structure portion 20) has the width pattern of the optical semiconductor device (SLD) 3 having the pattern shown in FIG. The wavelength variable light source (wavelength variable laser) 4 was manufactured.

  The width pattern of the optical waveguide 50 of the SLD 3 is such that the narrow part 53 and the wide part 55 on the rear end face 1R side extend obliquely with respect to the normal direction H of the element end faces 1R and 1F, and the narrow part 54 on the front end face 1F side. Is a width pattern extending parallel to the normal direction H of the element end faces 1R and 1F.

The narrow portions 53 and 54 and the wide portion 55 of the optical waveguide 50 were designed as follows (basically as in the first embodiment).
The narrow portion 53 and the wide portion 55 on the rear end face 1R side of the optical waveguide 50 are inclined by an inclination angle θ of 7 ° with respect to the normal direction H of the element end faces 1R and 1F.
Narrow part 53 of the optical waveguide 50: width W1 = 3 μm, length L1 in the optical waveguide direction = 0.3 mm,
Narrow portion 54 of the optical waveguide 50: width W2 = 3 μm, length L2 in the optical waveguide direction = 0.3 mm,
Wide portion 55 of optical waveguide 50: width W3 = 10 μm, length L3 in the optical waveguide direction = 0.9 mm.

(Comparative Example 2)
A comparative wavelength tunable light source (wavelength tunable laser) is provided in the same manner as in Example 2 except that the optical waveguide 50 is not provided with a wide portion and the width of the optical waveguide of the optical semiconductor element (SLD) is uniform (3 μm). Manufactured.

(Evaluation of Example 2 and Comparative Example 2)
The wavelength variable operation range of the wavelength variable light source of Example 2 and Comparative Example 2 was evaluated. While the wavelength tunable operating range of Comparative Example 2 was 60 nm, the wavelength tunable operating range of Example 2 was 120 nm. Further, in Example 2, an improvement in saturation output was also observed, and an output about twice that in Comparative Example 2 could be obtained.

  The optical semiconductor element of the present invention is an element that can be used as a super luminescent diode (SLD), a semiconductor optical amplifier (SOA), or the like. The optical semiconductor element of the present invention can be used as a light source used in the fields of communication, measurement, medical care, printing, image processing, and the like.

1 is an overall perspective view of an optical semiconductor device according to a first embodiment of the present invention. (A) is A-A 'sectional drawing of the optical semiconductor element of FIG. 1, (b) is B-B' sectional drawing. (A)-(c) is a figure which shows the example of the other width pattern of an optical waveguide Sectional drawing of 2nd Embodiment of the optical semiconductor element which concerns on this invention. The figure which shows the structure of 1st Embodiment of the wavelength variable light source which concerns on this invention. The figure which shows the structure of 2nd Embodiment of the wavelength variable light source which concerns on this invention. The figure which shows the evaluation result of Example 1 and Comparative Example 1

Explanation of symbols

1, 2 Optical semiconductor device (SLD)
1R Rear end face (one element end face)
1F Front end face (end face of other elements)
11 n-type (first conductivity type) semiconductor substrate 15 semiconductor active layer 20 ridge structure 21, 61 p-type (second conductivity type) cladding layer 41 p-type (second conductivity type) electrode 42 n-type (first conductivity type) ) Electrode 50 Optical waveguide 50X Optical axis of optical waveguide 51 First optical waveguide port 52 Second optical waveguide port 53, 54 Narrow portion 55 Wide portion 55A Substantially uniform width portion 55B Widened portion
55C Reduced width portion 60 Mesa structure portion W1 Width of first optical waveguide port W2 Width of second optical waveguide port W3 Maximum width of wide portion 4, 5 Wavelength variable light source 3 Optical semiconductor element (SLD)
80, 82 Laser resonator (resonance means)
91 Diffraction grating (wavelength selection means)
92 Optical filter (wavelength selection means)

Claims (9)

In an optical semiconductor element in which a first conductivity type electrode, a semiconductor active layer, and a second conductivity type electrode are provided on a first conductivity type semiconductor substrate,
The first optical waveguide port formed on one element end surface non-parallel to the substrate surface of the semiconductor substrate communicates with the second optical waveguide port formed on the one element end surface or the other element end surface, and at least An optical waveguide is formed partly extending obliquely with respect to the normal direction of the one element end face,
In addition, the width of the first optical waveguide port and the second optical waveguide are within the range in which the optical waveguide excludes the vicinity of the first optical waveguide port and the vicinity of the second optical waveguide port. An optical semiconductor element characterized by being formed in a width pattern having a wide portion wider than the width of the roadway.   The optical semiconductor element according to claim 1, wherein the wide portion has a substantially uniform width distribution in an optical waveguide direction. The wide part is
A substantially uniform width portion where the width distribution in the optical waveguide direction is substantially uniform;
A widened portion that is continuously or stepwise widened in the optical waveguide direction from the first optical waveguide port side toward the substantially uniform width portion;
2. The light according to claim 1, comprising a narrowed portion that is continuously or stepwise reduced in the optical waveguide direction from the substantially uniform width portion toward the second optical waveguide port side. Semiconductor element.   The width of the first optical waveguide port and the width of the second optical waveguide port allow only the fundamental transverse mode, and the maximum width of the wide portion allows both the fundamental transverse mode and the higher order transverse mode. The optical semiconductor element according to claim 1, wherein the optical semiconductor element has a width to be measured. 5. The optical semiconductor element according to claim 1, wherein the maximum width of the wide portion satisfies the following formulas (I) and (II).
3 × W1 ≦ W3 ≦ 10 × W1 (I),
3 × W2 ≦ W3 ≦ 10 × W2 (II)
(W1 is the width of the first optical waveguide port, W2 is the width of the second optical waveguide port, and W3 is the maximum width of the wide portion.)   Between the semiconductor active layer and the second conductivity type electrode, there is provided one or a plurality of second conductivity type cladding layers having a ridge structure portion formed in a width pattern corresponding to the width pattern of the optical waveguide. The optical semiconductor element according to claim 1, wherein:   Between the semiconductor active layer and the second conductivity type electrode, there is provided one or a plurality of second conductivity type cladding layers having a mesa structure portion formed in a width pattern corresponding to the width pattern of the optical waveguide. The optical semiconductor element according to claim 1, wherein: An optical semiconductor element according to any one of claims 1 to 7,
A resonance means for resonating light emitted from the optical semiconductor element;
A wavelength tunable light source comprising: a wavelength selection unit that selects an oscillation wavelength from the resonance unit and can change the oscillation wavelength.   The wavelength tunable light source according to claim 8, wherein the wavelength selection unit includes a diffraction grating capable of changing a grating plane angle with respect to an optical axis of incident light, or an optical filter capable of changing light transmission characteristics.

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