JP2008218548A - Semiconductor waveguide element, semiconductor laser and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure for suppressing reflection or scattering at a butt joint. <P>SOLUTION: A semiconductor waveguide element consisting of a series connection in the optical waveguide direction of two or more optical waveguides each including one or more layer of lower clad 1, optical waveguide 15 having an optical refractive index larger than that of the lower clad 1, and upper clad 4 having a refractive index smaller than that of the optical waveguide layer 15, respectively, is configured such that the bonding surface 14 of an active waveguide layer 2 and a nonactive waveguide layer 3 has an inclination in the direction intersecting the waveguide direction perpendicularly. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength tunable semiconductor laser used as an optical fiber communication light source and an optical measurement light source, and more particularly to an optical wavelength (frequency) multiplexing system light source in optical communication and an optical measurement light source covering a wide band wavelength band. It is.

  While research on optical wavelength (frequency) multiplex communication systems has been conducted in response to an increase in the amount of communication information, a wide range of wavelength adjustment functions are required as a light source for transmission and a tunable light source for synchronous detection. In the field of optical measurement, it is desired to realize a wavelength tunable light source that covers a wide wavelength band.

  Various variable wavelength light sources have been studied so far, and they can be broadly divided into those that change continuously in one oscillation mode and those that change discontinuously with mode jumping. Can be divided. In consideration of application to an actual system, it is preferable that the wavelength changes continuously from the viewpoint of controllability. As a means for controlling the wavelength of the wavelength tunable light source, the oscillation wavelength is controlled by using the refractive index change of the optical waveguide layer by temperature adjustment, and the oscillation wavelength by using the refractive index change of the optical waveguide layer by current injection. Two of them are mainly used. In terms of the wavelength change speed, it is preferable to use a change in refractive index due to current injection because faster wavelength switching is possible.

  As a wavelength tunable light source capable of continuously changing the oscillation wavelength by using the change in the refractive index of the optical waveguide layer by the current injection described above, a double waveguide laser (TTG laser) or a distributed reflection laser (DBR laser) is used. Semiconductor lasers such as those described above have been studied, and values of 7 nm for TTG lasers and 4.4 nm for DBR lasers have been reported as continuous wavelength variable widths. In recent years, so-called short resonator DRB lasers in which the active layer region is shortened in order to suppress the mode jump of the DBR laser have been studied.

  As the discontinuous wavelength variable width with mode jump, a value of 10 nm is obtained by the DBR laser. Moreover, as a semiconductor laser that is discontinuous but has a wide wavelength tunable width, a Y-branch laser, a super-periodic structure diffraction grating laser, and the like have been prototyped, and a wavelength tunable width of 50 to 100 nm is obtained.

  However, the conventional TTG laser and DBR laser as described above have the following problems.

In the TTG laser, a current is injected into an active waveguide layer that amplifies light to cause a laser oscillation operation, and a current is independently supplied to a wavelength control inactive waveguide layer formed in the immediate vicinity of the active waveguide layer. By injecting, the oscillation wavelength is changed. Here, if the period of the diffraction grating is Λ and the equivalent refractive index of the waveguide is n, the Bragg wavelength λb is expressed by the following equation (1).
λb = 2nΛ (1)

The laser oscillates in one resonant longitudinal mode near this Bragg wavelength. When current is injected into the inactive waveguide layer, the equivalent refractive index of the waveguide changes, and the Bragg wavelength also changes in proportion to the equation (1). Here, the change rate Δλb / λb of the Bragg wavelength is equal to the change rate Δn / n of the equivalent refractive index as shown in the following equation (2).
Δλb / λb = Δn / n (2)

In addition, the resonance longitudinal mode wavelength also changes as the equivalent refractive index changes due to current injection. In the case of a TTG laser, since the equivalent refractive index of the entire resonator changes uniformly, the change ratio Δλr / λr of the resonance longitudinal mode wavelength is expressed by the ratio Δn / of the change of the equivalent refractive index as shown in the equation (3). equal to n.
Δλr / λr = Δn / n (3)

  From the formulas (2) and (3), in the TTG laser, the change in the Bragg wavelength is equal to the change in the resonance longitudinal mode, so that the oscillation wavelength continuously changes while the first oscillation mode is maintained. Has characteristics.

  However, in order to perform a single transverse mode oscillation operation, the width of the double waveguide needs to be 1 to 2 μm, and the thickness of the n-type spacer layer formed between the active layer and the wavelength control layer Since it is necessary to reduce the thickness to 1 μm or less, a buried structure used in a normal semiconductor laser cannot be formed, and a structure for efficiently injecting current into each waveguide layer is manufactured. There was a problem that it was very difficult.

  In contrast, the DBR laser has a structure in which an active waveguide layer and an inactive waveguide layer for amplifying light are coupled in series, and therefore, a buried stripe structure for performing current confinement in the same manner as a normal semiconductor laser. Further, independent current injection into each waveguide layer can be easily realized by separating the electrodes formed above each waveguide layer.

The mechanism for changing the Bragg wavelength by changing the equivalent refractive index by injecting current into the inactive waveguide layer is the same as that of the TTG laser, but the region where the equivalent refractive index changes is limited to a part of the resonator. For this reason, the change amount of the Bragg wavelength does not match the change amount of the resonance longitudinal mode wavelength. The change rate Δλr / λr of the resonant longitudinal mode wavelength is the change rate Δn / n of the equivalent refractive index by the ratio of the effective length Le of the distributed reflector to the total resonator length L, as shown in the equation (4). Less than.
Δλr / λr = (Le / L) · (Δn / n) (4)

  Therefore, from the equations (2) and (4), the DBR laser has a drawback that the mode jump occurs because the Bragg wavelength and the resonance longitudinal mode wavelength are relatively separated as the wavelength control current is injected. It was. In order to prevent mode jumping, it is necessary to provide a phase adjustment region in which no diffraction grating is formed, and to match the amount of change in the resonant longitudinal mode and the amount of change in the Bragg wavelength by injecting current there.

  However, this method requires an external circuit for controlling the wavelength control current to the two electrodes, and there is a problem that the device structure and control become complicated. Another method that does not cause mode jumping is a short-cavity DBR laser that shortens the cavity length and widens the longitudinal mode interval. However, since the active layer needs to be shortened, a large output can be obtained. There was a problem that it was difficult.

  The continuous wavelength tunable width in the TTG laser and the DBR laser is limited to the amount of change in the refractive index of the wavelength control layer, and the value remains at about 4 to 7 nm. In order to further widen the wavelength variable width, it is necessary to use a means that allows mode jumping and that the wavelength change amount of the wavelength filter is larger than the refractive index change amount. Both the Y-branch laser and the super-periodic structure diffraction grating laser use a means for increasing the filter wavelength change amount more than the refractive index change amount. In these lasers, in order to change the filter wavelength greatly and to obtain sufficient wavelength selectivity, it is necessary to control the current flowing through the two electrodes, and also to provide an electrode for controlling the resonance longitudinal mode wavelength. Become. As a result, in order to adjust the oscillation wavelength, it is necessary to control the injection current to the three electrodes, and there is a problem that the control becomes very complicated.

  With respect to these problems, Patent Document 1, Non-Patent Document 1, and the like disclose a distributed active DFB laser (TDA-DFB-LD). The distributed active DFB laser can continuously change the oscillation wavelength by about 4 to 7 nm by controlling the injection current to one electrode, and can also efficiently inject current into the active waveguide layer and the inactive waveguide layer. Although the semiconductor laser is obtained and mode jump is involved, the oscillation wavelength can be changed over a range of about 50 to 100 nm by controlling the injection current to the two electrodes. According to such a structure, since the active layer volume can be sufficiently secured, it is possible to achieve high output.

  FIG. 17 shows the structure of a distributed active DFB laser disclosed in Non-Patent Document 1. FIG. 17A is a top view of the distributed active DFB laser, and FIG. 17B is a cross-sectional view taken along line xx ′ in FIG.

  As shown in FIG. 17, the distributed active DFB laser has an active waveguide layer 302 and an inactive waveguide layer (wavelength control region) 303 alternately on the lower clad 301 with constant lengths La and Lt, respectively. It has a structure that is periodically coupled in series. An upper clad 304 is formed on the active waveguide layer 302 and the inactive waveguide layer 303, and unevenness, that is, a diffraction grating 305 is formed between the active waveguide layer 302 and the inactive waveguide layer 303 and the upper clad 304. Is formed. Furthermore, an active layer electrode 307 and a wavelength control electrode 308 are provided on the upper clad 304 corresponding to the active waveguide layer 302 and the inactive waveguide layer 303, respectively. A common electrode 310 is provided below the lower clad 301.

  In the distributed active DFB laser shown in FIG. 17, gain is generated along with light emission by injection of the current Ia into the active waveguide layer 302, and the period of the diffraction grating 305 formed between the active waveguide layer 302 and the upper clad 304 is increased. Only the corresponding wavelength is selectively reflected to cause laser oscillation.

On the other hand, when the current It is injected into the inactive waveguide layer 303, the refractive index of the inactive waveguide layer 303 changes due to the plasma effect generated according to the carrier density. The optical period of the diffraction grating 305 formed between the upper clad 304 changes. Then, the equivalent refractive index of the inactive waveguide layer 303 changes, and the resonant longitudinal mode wavelength is shifted to the short wavelength side by the ratio of the length of the wavelength control region to the length of one cycle. If the length of one cycle of the repetitive structure is L and the wavelength control region length is Lt, the rate of change of the resonance longitudinal mode wavelength is expressed by the following equation (5).
Δλr / λr = (Lt / L) · (Δn / n) (5)

On the other hand, each wavelength of the plurality of reflection peaks is also shifted to the short wavelength side as a result of the change in the equivalent refractive index due to the current It injection. Since the reflection peak wavelength is proportional to the average equivalent refractive index change within one cycle of the repetitive structure, the change ratio Δλs / λs of the reflection peak wavelength is expressed by the following equation (6).
Δλs / λs = (Lt / L) · (Δn / n) (6)

  From the equations (5) and (6), the reflection peak wavelength and the resonance longitudinal mode wavelength are shifted by the same amount. Therefore, in this laser, the wavelength continuously changes while maintaining the mode in which it oscillates first.

  The structure of a distributed active DFB laser disclosed in Patent Document 1 is shown in FIG.

  Similarly to the distributed active DFB laser shown in FIG. 17, this distributed active DFB laser also has an active waveguide layer 402 and an inactive waveguide layer 403 alternately formed on the lower cladding 401 with constant lengths La and Lt, respectively. The upper clad 404 is formed on the active waveguide layer 402 and the non-active waveguide layer 403, and has an unevenness between the active waveguide layer 402 and the upper clad 404, that is, A diffraction grating 405 is formed. Furthermore, an active layer electrode 407 and a wavelength control electrode 408 are provided on the upper clad 404 corresponding to the active waveguide layer 402 and the inactive waveguide layer 403, respectively. A common electrode 410 is formed below the lower clad 401. In this distributed active DFB laser, the diffraction grating 405 is formed only partially, but the wavelength continuously changes in the same manner as the distributed active DFB laser of FIG.

  Further, in Patent Document 1, as shown in FIG. 19, it has the same structure as the distributed active DFB laser shown in FIG. 18, and the repetition periods of the active waveguide layer 402 and the inactive waveguide layer 403 are L1, A structure in which two different lasers L2 are coupled in series is also disclosed. Note that members that are substantially the same as those shown in FIG. 18 are given the same reference numerals, and descriptions thereof are omitted.

  As a distributed active DFB laser shown in FIGS. 17 to 19, as means for alternately and periodically coupling the active waveguide layer 302 (or 402) and the inactive waveguide layer 303 (or 403), A butt joint technique using a selective growth method is used. Patent Document 2 states that the coupling between the active waveguide layer and the inactive waveguide layer can be optically uniformed by forming an island-shaped selective growth mask used when performing a butt joint.

Japanese Patent No. 3237733 Japanese Patent Publication No. 7-109922 Ishii et al., “A Tunable Distributed Amplification DFB Laser Diode (TDA-DFB-LD)”, IEEE Photonics Letters, vol.10, no.1, January 1998, p.30-32

  In the conventional distributed active DFB laser described above, the active region and the inactive region are alternately repeated with a short region length, and the butt joint surface is provided so as to be orthogonal to the waveguide direction. Even if the reflection / scattering loss at the butt joint coupling between the active waveguide layer and the inactive waveguide layer is a small amount per coupling, it becomes a non-negligible amount for the entire device, increasing the threshold current and increasing the output efficiency. There is a risk of causing problems such as lowering. Similarly, fluctuations in the growth film thickness and composition during selective growth at the butt joint increase scattering and deteriorate the coupling efficiency. In particular, in the above-described distributed active DFB laser, it is necessary to shorten the length of each region in order to widen the reflection peak interval. Compared with an integrated device that requires a normal butt joint, the film thickness and composition on the side of the mask in selective growth. It is conceivable that the influence of fluctuation becomes relatively large.

  This invention solves such a problem, and it aims at providing the structure which suppresses reflection and scattering of a butt joint part.

  A semiconductor waveguide device according to a first invention for solving the above problems includes a first semiconductor clad layer and an optical waveguide layer having an optical refractive index larger than that of the first semiconductor clad layer on a semiconductor substrate. And an optical waveguide including at least one second semiconductor clad layer having a refractive index smaller than that of the optical waveguide layer, wherein three or more optical waveguides are coupled in series in the direction of the optical waveguide. At least one coupling surface between the layers is inclined with respect to a direction orthogonal to the waveguide direction.

  A semiconductor waveguide device according to a second invention for solving the above-mentioned problems is characterized in that, in the first invention, the normal of the coupling surface is inclined at least 5 degrees with respect to the waveguide direction. And

  According to a third aspect of the present invention, there is provided the semiconductor waveguide device according to the first aspect, wherein the normal of the coupling surface is inclined at an angle of 10 degrees to 54 degrees with respect to the waveguide direction. It is characterized by that.

  A semiconductor waveguide device according to a fourth invention for solving the above-mentioned problems is characterized in that, in any one of the first to third inventions, all the inclinations of the coupling surfaces are equal.

  A semiconductor waveguide element according to a fifth invention for solving the above-mentioned problems is the semiconductor waveguide element according to any one of the first to third inventions, wherein the coupling surface is equal for every two surfaces continuous along the waveguide direction. It has an inclination angle.

  A semiconductor waveguide device according to a sixth invention for solving the above-mentioned problems is characterized in that, in any one of the first to third inventions, the coupling surface has an equal inclination angle every other surface. .

  A semiconductor waveguide device according to a seventh aspect of the present invention for solving the above-described problems is the coupling surface according to any one of the first to third aspects, wherein the distance is at least within a range of less than 2 d / sin (2θ). Have different inclination angles.

  A semiconductor waveguide device according to an eighth invention for solving the above-mentioned problems is characterized in that, in any of the first to seventh inventions, a semi-insulating current blocking layer doped with ruthenium is provided. .

  A semiconductor laser according to a ninth invention for solving the above-mentioned problems is characterized by comprising the semiconductor waveguide device according to any one of the first to eighth inventions.

  A method for manufacturing a semiconductor waveguide device according to a tenth aspect of the present invention for solving the above problems includes a first semiconductor cladding layer, an optical waveguide layer having an optical refractive index larger than that of the first semiconductor cladding layer, In the method of manufacturing a semiconductor waveguide device in which three or more optical waveguides each including one or more second semiconductor cladding layers each having a refractive index smaller than that of the optical waveguide layer are coupled in series in the optical waveguide direction, Forming a first optical waveguide layer on the first semiconductor cladding layer, and etching the first optical waveguide layer using an island mask having an inclination with respect to a direction orthogonal to the waveguide direction And a step of re-growing the second optical waveguide layer after the etching using the island mask.

  According to the semiconductor laser of the present invention, since reflection and scattering of the butt joint portion can be suppressed, the entire resonator can be obtained even in a structure such as a distributed active DFB laser having a structure in which an active region and an inactive region are alternately repeated. Loss, and an increase in threshold current and a decrease in output efficiency can be prevented.

  Embodiments of the present invention will be described in detail in the following examples.

  The first embodiment of the present invention will be described in detail with reference to FIGS.

  1A is a top view of a distributed active DFB laser as a semiconductor laser according to the present embodiment, FIG. 1B is a sectional view taken along line xx ′ of FIG. 1A, and FIG. 1 (a) is a cross-sectional view taken along line yy ′, FIG. 1 (d) is a cross-sectional view taken along line zz ′ of FIG. 1 (c), and FIGS. FIG. 3 is a top view of FIG. 2 (a), FIG. 4 is an explanatory view showing light refraction at the interface between substances having different refractive indexes, and FIG. 5 is a relationship between the band gap wavelength and the refractive index difference. FIG. 6 is a graph showing the relationship between the incident angle and the reflectance, and FIG. 7 is a graph showing the coupling ratio of the reflected wave with respect to the incident angle to the refractive index boundary.

  As shown in FIG. 1, the semiconductor laser according to the present embodiment includes an optical waveguide layer 15 having an optical refractive index larger than that of the lower cladding 1 on the lower cladding (semiconductor substrate) 1 made of n-type InP, and the optical waveguide. Each layer includes at least one upper cladding layer 4 having a refractive index lower than that of the layer 19.

  The optical waveguide layer 19 is formed by serially coupling the active waveguide layer 2 and the inactive waveguide layer 3 alternately in series along the light propagation direction (four periods in FIG. 1). The active waveguide layer 2 and the non-active waveguide layer 3 adjacent to each other are coupled by a butt joint.

  The active waveguide layer 2 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 3 is an inactive region having a length Lt made of GaInAsP having no optical gain and having a composition different from that of the active waveguide layer 2, and is a wavelength control region. In this example, the region lengths La and Lt were 29.5 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 2 and the inactive waveguide layer 3 was 59 μm.

  An upper clad 4 made of p-type InP is formed on the active waveguide layer 2 and the inactive waveguide layer 3, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 19 and the upper clad 4. A diffraction grating 5 is formed in which concaves and convexes are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 19 is periodically modulated. In this example, the diffraction grating period was set to 243 nm in order to obtain an oscillation wavelength of 1.55 μm.

  On the upper cladding 4, a contact layer 6 having a multilayer structure of highly doped p-type InGaAsP and / or InGaAs is provided for ohmic contact between the active waveguide layer 2 and the inactive waveguide layer 3, and An active layer electrode 7 and a wavelength control electrode 8 are provided thereon so as to correspond to the active waveguide layer 2 and the inactive waveguide layer 3, respectively. The active layer electrode 7 and the wavelength control electrode 8 are electrically separated by an insulating film 9, and the active layer electrodes 7 and the wavelength control electrodes 8 are integrated to form a comb shape. ing. A common electrode 10 is provided below the lower cladding 1.

  Further, as shown in FIG. 1C, a p-type semiconductor 11 and an n-type semiconductor 12 made of InP are formed as current blocking layers 13 on both sides of the active waveguide layer 2 (inactive waveguide layer 3) having a width Ws. Are alternately formed to form a buried heterostructure (BH). Thereby, the current Ia or It is efficiently injected into the active waveguide layer 2 or the inactive waveguide layer 3. In this embodiment, the waveguide width Ws is 1.5 μm.

  Further, as shown in FIG. 1D, the active waveguide 2 and the inactive waveguide 3 have their coupling surfaces 14 (seven locations in FIG. 1) inclined at an angle θ with respect to the plane perpendicular to the waveguide direction. ing. In other words, the normal line of the coupling surface 14 has an inclination angle θ with respect to the waveguide direction.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 2, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 3. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be largely changed by the current It injection.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described with reference to FIGS. The production proceeds in the order of FIG. 2 (a), FIG. 2 (b), and FIG. 2 (c).

As shown in FIG. 2A, a wafer in which a GaInAsP active waveguide layer 2 and a part of an InP upper cladding 4 are first grown on a lower cladding 1 as an n-type InP substrate by metal organic vapor phase epitaxy. And the island-like masks 15 (four in FIG. 2) are made of SiO ₂ or SiN only on the upper clad 4 and just above the region where the active waveguide layer 2 is to be left. Here, in the present specification, the island shape indicates a state in which the islands are intermittently arranged along the waveguide direction. That is, in this embodiment, the island mask 15 is intermittently produced with the period L along the waveguide direction.

  As shown in FIG. 3, the island-shaped mask 15 has a normal of an end surface intersecting the waveguide direction inclined at an angle θ with respect to the waveguide direction. In this embodiment, the island masks 15 are arranged in the same shape and in the same direction, and are set so that the opposing end faces of the adjacent island masks 15 are parallel. In other words, the island mask 15 has a parallelogram shape. Here, in the present embodiment, since the region length La of the active waveguide layer 2 is 29.5 μm, it is necessary to include a margin during the process, but the length of the island mask 15 in the waveguide direction is approximately 29.5 μm. In addition, since the distance between the island-shaped masks 15 corresponds to the region length Lt of the inactive waveguide layer 3, it is approximately 29.5 μm in this embodiment. The mask width, that is, the length of the island mask 15 in the direction orthogonal to the waveguide direction was 3.5 μm.

  Next, as shown in FIG. 2B, a part of the upper cladding 4 and the active waveguide layer 2 are etched using the island mask 15. Further, as shown in FIG. 2C, the island-shaped mask 15 is used as it is, and a part of the inactive waveguide layer 3 and the upper cladding layer 4 is regrown by selective growth. By this method, as shown in FIG. 1D, the active waveguide layer 2 and the inactive waveguide layer 3 are alternately arranged, and the normal of the coupling surface 14 is inclined at an angle θ with respect to the waveguide direction. Thus, integrated waveguides can be made.

Thereafter, a diffraction grating pattern is produced on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form the diffraction grating 5. Further, after regrowing a part of the upper clad made of p-type InP by metal organic vapor phase epitaxial growth, in order to suppress the transverse mode, the waveguide is formed in a stripe shape having a width of 1.5 μm using SiO ₂ or SiN as a mask. Process. Then, using the etching mask as it is, an InP current blocking layer made of a p-type semiconductor / n-type semiconductor is grown on both sides of the striped waveguide by a selective growth method. Thereafter, the selective growth mask is removed, and the remaining InP upper cladding 4 and GaInAs contact layer 6 are grown.

Next, the contact layer 6 and a part of the upper clad layer 4 are etched to form an insulating film 9 made of SiO ₂ on the exposed contact layer 6 and upper clad layer 4. Make a hole in the part corresponding to the injection part. Then, electrode patterns as the active layer electrode 7 and the non-active layer electrode 8 are formed by lift-off. The active layer electrode 7 and the inactive electrode 8 are provided immediately above the active waveguide layer 2 and the inactive waveguide layer 3, respectively, and the active layer electrodes 7 and the inactive waveguides 8 are integrated with each other. It has a shape.

  Then, the effect of a present Example is demonstrated.

  In this embodiment, the active waveguide layer 2 and the inactive waveguide layer 3 are GaInAsP layers having different compositions. Therefore, the butt joint is a combination of layers having different refractive indexes.

At the interface between materials having different refractive indexes, light is reflected when light enters from one material to the other. For example, the interface 18 between the refractive index N ₁ of the material 16 and the refractive index N ₂ of the material 17 shown in FIG. 4, when the light from the material 16 side is incident, the reflectivity R of light at the bonding interface, the following (7).
R = ((N ₁ −N ₂ ) / (N ₁ + N ₂ )) ² (7)

  In the distributed active DFB laser according to the present embodiment, since the difference in refractive index between the active waveguide region and the inactive waveguide region is small, the absolute value of the reflectance R is very small from Equation (7). However, on the other hand, as shown in FIG. 1, a single element (distributed active DFB laser in this embodiment) has a plurality of coupling surfaces 14 (seven surfaces in FIG. 1) that combine regions having different refractive indexes. Exists. For this reason, there is a possibility that the influence of light reflection is increased to a level that cannot be ignored in one entire element. Therefore, in an element having a plurality of coupling surfaces 14, it is important to keep the reflectivity R as low as possible or prevent the reflected wave from being coupled to the waveguide even if reflection occurs.

When light is incident obliquely on the boundary surfaces of substances having different refractive indexes, the incident angle is θ ₁ , and the refraction angle is θ ₂ , which is expressed by the following formula (8) according to Snell's law. In addition, refraction occurs at the interface. In this embodiment, the incident angle θ ₁ is an inclination angle in the light propagation direction with respect to the normal line of the boundary surface 18.
sin θ ₁ / sin θ ₂ = N ₂ / N ₁ (8)

Here, when the incident angle θ ₁ coincides with the Brewster angle θ _B , reflection of a component parallel to the incident surface can be eliminated. The Brewster angle θ _B can be expressed by the following equation (9).
θ _B = tan ⁻¹ (N ₂ / N ₁ ) (9)

  FIG. 5 shows the relationship between the refractive index difference between GaInAsP lattice-matched with InP and GaInAs having a bandgap wavelength of 1.55 μm and the band gap wavelength of GaInAsP lattice-matched with InP. The wavelength of the propagating light is 1.55 μm. As shown in FIG. 5, the refractive index of the semiconductor varies depending on the band gap wavelength. For example, a semiconductor with a band gap wavelength of 1.55 μm and a semiconductor with a band gap wavelength of 1.40 μm have a refractive index difference of about 0.09.

  When actually producing a waveguide structure, GaInAs having a band gap wavelength of 1.55 μm and GaInAsP lattice-matched with InP are used as a core, and a structure in which light is confined in the core by a semiconductor having a lower refractive index than these. Take.

  For example, as a simple waveguide structure, a semiconductor having a band gap wavelength of 1.55 μm was used as the core when considering the equivalent refractive index of a waveguide structure in which a core having a thickness of 0.15 μm is sandwiched between InP clads. The equivalent refractive index in this case is 3.12, and the equivalent refractive index when a semiconductor with a band gap wavelength of 1.40 μm is used as the core is 3.19. The equivalent refractive index difference between these waveguides is about 0.02 or less. Become.

FIG. 6 shows the relationship between the incident angle θ _{1 of} light incident on the boundary surface 18 shown in FIG. The incident angle θ ₁ is an angle between the direction orthogonal to the boundary surface 18 and the light propagation direction. The graph shown in FIG. 6 shows that the refractive index of the material 16 on the incident side is N ₁ = 3.20, and the refractive index difference Δn between the material 16 and the material 17 is Δn = N ₁ −N ₂ = 0.005, 0.01. , 0.015, and 0.02 are shown.

In this embodiment, since the refractive index difference between the active waveguide layer 2 and the inactive waveguide layer 3 in the distributed active DFB laser is small, the Brewster angle θ _B is approximately 45 degrees from the equation (9). That is, when the inclination angle θ of the active waveguide layer 2, the inactive waveguide layer 3, and the coupling surface 14 is approximately 45 degrees, the reflectance R becomes 0, and the reflectance R is near the inclination angle θ = 45 degrees. Very small.

Taking the case where the refractive index difference Δn = 0.01 as an example, the reflectance R can be reduced when the incident angle θ ₁ is 10 degrees or more and 54 degrees or less from FIG. In particular, in order to suppress the reflectance R to less than half when light is incident perpendicular to the boundary surface, that is, when the incident angle θ ₁ = 0, the incident angle θ _{1 is set} to about 28 to 52 degrees. A value between may be used. Further, in order to suppress the reflectance R to 1/3 or less of the reflectance R at the incident angle θ ₁ = 0, the incident angle θ ₁ may be set to a value between about 33 degrees and 51 degrees. As can be seen from FIG. 6, should the incident angle theta ₁ is a Brewster angle theta _B lower than about, the incident angle theta ₁ is compared is greater than the Brewster angle theta _B, reflection with respect to the incident angle theta ₁ The change in the rate R is moderate.

Note that it is not always necessary to suppress all reflections at the boundary surface, and if the reflected wave does not have to be coupled to the waveguide even if reflection occurs, the selection range of the incident angle θ ₁ can be expanded as follows. .

FIG. 7 shows the relationship between the incident angle to the boundary surface and the coupling ratio of the reflected wave to the waveguide when the optical mode field width is 1.5 μm. Note that the reflected wave coupling factor is a reflection when the incident angle θ ₁ = 0, that is, when the boundary surface is orthogonal to the waveguide direction, so that the difference in refractive index at the boundary surface may not be taken into consideration. The coupling rate of the wave to the waveguide is shown as 1.

From FIG. 7, if the incident angle θ ₁ is about 5 degrees or more, the reflected wave coupling rate to the waveguide can be reduced to half, and the incident angle θ ₁ is about 7 to reduce the reflected wave coupling rate to about 30% or less. It is sufficient that the incident angle θ ₁ should be about 9 degrees or more in order to reduce the reflected wave coupling ratio by one digit.

  From the above, in the distributed active DFB laser shown in FIG. 1, compared with the case where the coupling surface 14 between the active waveguide layer 2 and the inactive waveguide layer 3 is orthogonal to the waveguide direction, the reflected wave coupling is performed. In order to suppress the rate to, for example, half or less, the angle of the coupling surface 14 needs to be 5 degrees or more and less than 90 degrees with respect to the waveguide direction. In addition, compared with the case where the coupling surface 14 is orthogonal to the waveguide direction, in order to suppress the reflected wave coupling ratio to 30% or less, the angle of the coupling surface with respect to the waveguide direction is set to 7 degrees or more and less than 90 degrees. There is a need to. Further, in order to reduce the reflected wave coupling ratio by an order of magnitude compared to the case where the coupling surface is orthogonal to the waveguide direction, the angle of the coupling surface with respect to the waveguide direction needs to be 9 degrees or more and less than 90 degrees. is there.

  Further, in order to reduce the reflectance R at the coupling surface 14 between the active waveguide layer 2 and the inactive waveguide layer 3 to, for example, half or less compared to the case where the coupling surface 14 is orthogonal to the waveguide direction. In order to reduce the inclination angle θ of the coupling surface 14 to about 28 ° to 52 ° or less than one third, the inclination angle θ of the coupling surface 14 is about 33 ° to 51 °, and the coupling surface is in the waveguide direction. In order to make the reflectance R substantially zero as compared with the case where they are orthogonal to each other, the inclination angle θ of the coupling surface 14 needs to be 45 degrees.

  It is obvious that the effect of suppressing the influence of the reflected wave as described above increases as the number of coupled waveguides increases.

  Therefore, in the case of this embodiment, if the inclination angle θ of the coupling surface 14 that is the refractive index boundary surface with respect to the waveguide is set to the above angle, the reflectivity R generated by the refractive index difference at the coupling surface 14 is obtained. And the coupling of the reflected wave to the waveguide can be reduced.

  In the present embodiment, both end faces intersecting the waveguide direction of the island mask 15 are set at the same inclination angle with respect to the waveguide direction, and the adjacent island masks 15 face each other. The end faces are set to be parallel. As a result, the lengths of the island masks 15 in the waveguide direction are all equal, and the length along the waveguide direction of the region where the inactive waveguide layer is selectively grown is constant.

  In general, in the selective growth, the raw material that has reached the mask at the time of re-growth cannot grow on the mask, but moves on the mask to the semiconductor to grow. As the mask size is larger, the amount of growth on the side of the mask increases, and the difference in growth amount from a place away from the mask increases. In addition, since the moving distance (migration length) differs depending on the raw material, the variation in composition between the side of the mask and the part away from the mask also increases. Usually, the growth film thickness and composition vary over a region of several μm to several tens of μm from the mask and over a region of 100 μm or more depending on conditions.

  In the case of a device in which the selective growth region is repeated at a short interval as in the distributed active DFB laser of the present embodiment, the distance between adjacent island masks 15 is as short as 100 μm or less, and the selective growth region is on both sides. Therefore, when the distance between the island-shaped masks 15 is 100 to 200 μm or less, it is important to make the mask shape with as little fluctuation as possible.

  If the island mask 15 is designed as in this embodiment, the length of the island mask 15 along the waveguide direction and the distance between the island masks 15 are equal, so that the flatness is improved and the composition variation is small. Is possible.

  Furthermore, the region actually used as the waveguide is about 1 μm wide near the center of the active region. In Patent Document 2, a mask having a length of 200 μm and a width of 40 μm is used. Even if the width is 40 μm, the effect of flatness is obtained. The following is sufficient, and it is desirable that the width of the island-shaped mask 15 is as narrow as possible because the influence on the growth film thickness fluctuation and composition fluctuation during selective growth is reduced. Thus, the width of the island mask 15 (the length in the direction orthogonal to the waveguide direction) is preferably 1.0 μm or more and 10 μm or less.

  In the present embodiment, a current block is realized by combining the p-type semiconductor 11 and the n-type semiconductor 12, but the current block is semi-insulating with doping Fe (iron), Ru (ruthenium) or the like. InP may be used.

  In addition, the active waveguide layer and the inactive waveguide layer may not be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which quantum wells are stacked with a barrier layer interposed therebetween, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having an intermediate refractive index between the active layer and the cladding layer may be introduced.

  Furthermore, the semiconductor used in this element is not limited to a combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs, and an active waveguide layer and an inactive waveguide layer. The combination of the band gap wavelengths is not limited to the above.

  Further, the semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method described above, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, in the present embodiment, an example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other embodiments having three or more regions are also described. Applicable in integrated devices. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  The second embodiment of the present invention will be described in detail with reference to FIGS.

  8A is a top view of a distributed active DFB laser as a semiconductor laser according to the present embodiment, FIG. 8B is a cross-sectional view taken along line xx ′ shown in FIG. 8A, and FIG. FIG. 9A is a sectional view taken along line yy ′ of FIG. 8A, and FIG. 9 is an explanatory view showing an example of a mask used for manufacturing a semiconductor waveguide device according to this example.

  As shown in FIG. 8, the distributed active DFB laser according to this example includes an optical waveguide layer 119 having an optical refractive index larger than that of the lower cladding 1 on the lower cladding (semiconductor substrate) 101 made of n-type InP. Each layer includes one or more upper cladding layers 104 having a refractive index lower than that of the optical waveguide layer 119.

  The optical waveguide layer 119 is formed by serially coupling the active waveguide layer 102 and the inactive waveguide layer 103 alternately in series along the light propagation direction (four periods in FIG. 8). The active waveguide layer 102 and the inactive waveguide layer 103 adjacent to each other are coupled by a butt joint.

  The active waveguide layer 102 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 103 is an inactive region having a length Lt made of GaInAsP having no optical gain and having a composition different from that of the active waveguide layer 102, and is a wavelength control region. In this embodiment, the region lengths La and Lt are 48.7 μm and 24.3 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 102 and the inactive waveguide layer 103 is 73 μm.

  An upper clad 104 made of p-type InP is formed on the active waveguide layer 102 and the inactive waveguide layer 103, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 119 and the upper clad 104. A diffraction grating 105 is formed in which concaves and convexes are formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 119 is periodically modulated. In this example, the diffraction grating period was set to 243 nm in order to obtain an oscillation wavelength of 1.55 μm.

  A contact layer 106 made of a highly doped p-type InGaAsP and / or InGaAs or a multilayer structure thereof is provided on the upper cladding 104 for ohmic contact between the active waveguide layer 102 and the inactive waveguide layer 103, and An active layer electrode 107 and wavelength control electrodes 108 (four in FIG. 8) are provided thereon so as to correspond to the active waveguide layer 102 and the non-active waveguide layer 103, respectively. Note that the active layer electrode 107 and the wavelength control electrode 108 are electrically separated by an insulating film 109. For example, if the active layer electrodes 107 and the wavelength control electrodes 108 are short-circuited by wires or the like outside the device, respectively. Thus, the same operation as in the first embodiment can be obtained. A common electrode 110 is provided below the lower clad 101.

  Furthermore, the active waveguide 102 and the non-active waveguide 103 have their coupling surfaces 114 inclined with respect to the plane orthogonal to the waveguide direction. In other words, the normal line of the coupling surface 114 has an inclination angle with respect to the waveguide direction.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 102, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 103. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be largely changed by the current It injection.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

  First, an active waveguide layer 102 is formed on the lower clad 101 made of n-type InP by metal organic vapor phase epitaxy. Thereafter, the inactive waveguide layer 103 is coupled to the active waveguide layer 102 by a butt joint.

  The process of coupling the active waveguide layer 102 and the inactive waveguide layer 103 by the butt joint is substantially the same as the process described in the first embodiment shown in FIG. 2, but in this embodiment, the process shown in FIG. As shown, the shape of the island mask 115 (four in FIG. 9) is different from the island mask 15 described in the first embodiment. That is, the end face of the island mask 115 that intersects the waveguide direction is inclined with respect to the waveguide direction, and the island mask 115 is formed in a parallelogram. In the first embodiment, the adjacent island masks 15 are arranged in the same direction as shown in FIG. 3, whereas in the present embodiment, the adjacent island masks 115 are arranged in line symmetry. Has been. The mask width was 6 μm.

  Next, a part of the upper clad 104 and the active waveguide layer 102 are etched using the island mask 115 shown in FIG. Further, the island-shaped mask 115 is used as it is, and a part of the inactive waveguide layer 103 and the upper cladding layer 104 is regrown by selective growth. By this method, an integrated waveguide in which the active waveguide layer 102 and the inactive waveguide layer 103 are coupled alternately so that the coupling surface is inclined with respect to the waveguide direction can be manufactured.

Thereafter, a diffraction grating pattern is produced on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form the diffraction grating 105. Further, after part of the upper clad 104 made of p-type InP is regrown by metal organic vapor phase epitaxial growth, in order to suppress the transverse mode, the waveguide is formed in a stripe shape having a width of 1.5 μm using SiO ₂ or SiN as a mask. Is processed. Then, using the etching mask as it is, a semi-insulator current blocking layer 113 made of a semiconductor doped with Ru (or Fe) is grown on both sides of the striped waveguide by a selective growth method.

Thereafter, the selective growth mask is removed, and then a part of the contact layer 106 and the upper cladding layer 104 is etched to form a current separation groove 116 (seven locations in FIG. 8) for separation between the regions. Then, a SiO ₂ insulating film 109 is formed, and holes are formed in the insulating film 109 on the active waveguide layer 102 and the inactive waveguide layer 103. An electrode pattern is formed by lift-off so that the active layer electrodes 107 and the non-active layer electrodes 108 are short-circuited on the element.

  Note that Fe is often used as a doping material for the semi-insulator 113, but using Ru can suppress mutual diffusion with Zu, which is a p-type InP dopant. it can. Further, by using Ru, the capacitance is reduced as compared with the current blocking layer made of p-type and n-type semiconductors, so that the modulation characteristics can be improved. In addition, the modulation characteristic can be improved to 10 GHz or more by suppressing the leakage current between the regions 102 and 103 by the current separation groove 116.

  The effect by a present Example is demonstrated. According to the present embodiment, in particular, the same effects as those of the first embodiment described above can be obtained with respect to the reduction of the reflectance R at the butt joint between the active waveguide layer 102 and the inactive waveguide layer 103. Furthermore, the following effects are obtained as compared with the first embodiment described above.

  That is, in Example 1, the thickness of the regrowth and the flatness of the composition are emphasized, and as shown in FIG. 3, the distance between the end faces of the adjacent island masks 15 is constant between the island masks 15. Arranged to be. In the semiconductor waveguide device according to the first embodiment, if the end face of the island-shaped mask 15 is set to be inclined by about 45 degrees with respect to the waveguide direction, the reflectivity R at the coupling surface is reduced, and the waveguide It is considered that the reflected wave to be combined is reduced.

  However, in the crystal growth, there is a possibility that the growth rate differs depending on the crystal orientation due to the influence of the crystal orientation, so the waveguide is not necessarily inclined so that the butt joint coupling surface is inclined by 45 degrees with respect to the waveguide direction. It is not always optimal to make a connection between them. Therefore, as described in the first embodiment, it is necessary to select the angle of the coupling surface with respect to the waveguide direction within a range in which the reflected wave coupled to the waveguide can be suppressed. However, in the case of the semiconductor waveguide device shown in the first embodiment, since all the mask end faces are parallel, when the inclination angle of the mask end face with respect to the waveguide direction is nearly perpendicular, resonance between the end faces having the same angle. There is also concern that this will occur.

  In contrast, in this embodiment, the length of the island-shaped mask 115 in the waveguide direction and the amount of the material on the island-shaped mask 115 moving onto the semiconductor are kept constant as compared with the first embodiment. Adjacent island masks 115 are arranged symmetrically with respect to each other. According to the present embodiment, compared with the semiconductor waveguide device according to the first embodiment, the number of coupling surfaces having the same inclination with respect to the waveguide direction is reduced. It is possible to reduce the resonance between the surfaces and stabilize the resonance mode.

  Note that by making the pair of end faces intersecting the waveguide direction of the island mask parallel and making the length in the island mask waveguide direction constant, the amount of movement of the material on the island mask onto the semiconductor becomes equal. The effect can be expected even if there is only one island mask.

  In addition, the active waveguide layer and the inactive waveguide layer may not be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which quantum wells are stacked with a barrier layer interposed therebetween, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having an intermediate refractive index between the active layer and the cladding layer may be introduced.

  Furthermore, the semiconductor used in this element is not limited to a combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs, and an active waveguide layer and an inactive waveguide layer. The combination of the band gap wavelengths is not limited to the above.

  Further, the semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method described above, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, as a method of etching part of the contact layer 106 and the upper cladding layer 104, the active waveguide layer 102 and the inactive waveguide layer 103 are short in length and short in repetition period. Although an etching method with a small amount of side etching such as dry etching is desirable, there is no problem even with a method using wet etching or the like.

  In addition, in the present embodiment, an example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other embodiments having three or more regions are also described. Applicable in integrated devices. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  A third embodiment of the present invention will be described in detail with reference to FIGS.

  FIG. 10A is a top view of a distributed active DFB laser as a semiconductor laser according to the present embodiment, FIG. 10B is an xx ′ cross-sectional view shown in FIG. 10A, and FIG. FIG. 11A is an explanatory view showing an example of a mask used for manufacturing the semiconductor waveguide device according to the present example.

  As shown in FIG. 10, the distributed active DFB laser according to this example includes an optical waveguide layer 219 having an optical refractive index larger than that of the lower cladding 1 on the lower cladding (semiconductor substrate) 201 made of n-type InP, Each includes one or more upper cladding layers 204 having a refractive index lower than that of the optical waveguide layer 219.

  The optical waveguide layer 219 is configured by serially coupling active waveguide layers 202 and inactive waveguide layers 203 in series (4 periods in FIG. 10) alternately along the light propagation direction. The active waveguide layer 202 and the non-active waveguide layer 203 adjacent to each other are coupled by a butt joint.

  The active waveguide layer 202 has an optical gain with respect to light in the oscillation wavelength band, and is an active region having a length La made of GaInAsP. The inactive waveguide layer 203 is an inactive region having a length Lt made of GaInAsP having no optical gain and having a composition different from that of the active waveguide layer 202, and is a wavelength control region. In this example, the region lengths La and Lt were 22.3 μm and 44.7 μm, respectively, and the repetition period L (= La + Lt) of the active waveguide layer 202 and the inactive waveguide layer 203 was 67 μm.

  An upper clad 204 made of p-type InP is formed on the active waveguide layer 202 and the non-active waveguide layer 203, and a light propagation direction (hereinafter referred to as a light guide) is formed between the optical waveguide layer 219 and the upper clad 204. A diffraction grating 205 is formed in which unevenness is formed at the same period over the entire length and the equivalent refractive index of the optical waveguide layer 219 is periodically modulated. In this example, the diffraction grating period was 241 nm in order to obtain an oscillation wavelength of 1.55 μm.

  On the upper clad 204, a contact layer 206 having a highly doped p-type InGaAsP and / or InGaAs multilayer structure for ohmic contact between the active waveguide layer 202 and the non-active waveguide layer 203 is provided. An active layer electrode 207 and wavelength control electrodes 208 (four each in FIG. 10) are provided thereon so as to correspond to the active waveguide layer 202 and the non-active waveguide layer 203, respectively. Note that the active layer electrode 207 and the wavelength control electrode 208 are arranged independently and are electrically separated by the insulating film 209. For example, the active layer electrode 207 and the wavelength control electrode 208 are connected to each other outside the element by a wire or the like. By short-circuiting, the same operation as in the first embodiment can be obtained. A common electrode 211 is provided below the lower clad 201.

  Further, as shown in FIG. 10C, the semiconductor waveguide device according to this example has a ridge structure in which polyimide is embedded on both sides of the optical waveguide layer 190 having a width Ws. In this embodiment, the width of the waveguide, that is, the ridge width Ws is set to 2.5 μm.

  When GaInAsP having a band gap wavelength of 1.55 μm is used for the active waveguide layer 202, a laser having a band gap wavelength shorter than that, for example, GaInAsP having a band gap wavelength of 1.4 μm, is used for the inactive waveguide layer 203. Since it does not contribute to the oscillation gain, the carrier density is not constant. Thereby, the refractive index can be largely changed by the current It injection.

  Next, an example of a manufacturing method of the distributed active DFB laser according to the present embodiment will be described.

  First, an active waveguide layer 202 is formed on the lower clad 201 made of n-type InP by metal organic vapor phase epitaxy. Thereafter, the inactive waveguide layer 203 is coupled to the active waveguide layer 202 by a butt joint.

  The process of coupling the active waveguide layer 202 and the inactive waveguide layer 203 by the butt joint is substantially the same as the process illustrated in FIG. 2 and described in the first embodiment, but in this embodiment, FIG. As shown, the shape of the island mask 215 (four in FIG. 11) is different from the island mask 15 described in the first embodiment. That is, the end face of the island mask 215 that intersects the waveguide direction is inclined with respect to the waveguide direction, and the island mask 215 has a trapezoidal shape that is symmetric with respect to the plane orthogonal to the waveguide direction. In the first embodiment, the adjacent island masks 15 are arranged in the same direction. In the second embodiment, the adjacent island masks 115 are arranged so as to be line-symmetric. The adjacent island masks 215 are arranged point-symmetrically. The mask width was 6 μm.

  Next, a part of the upper clad 204 and the active waveguide layer 202 are etched using the island mask 215 shown in FIG. Further, the island mask 215 is used as it is, and the inactive waveguide layer 203 and a part of the upper cladding layer 4 are regrown by selective growth. By this method, an integrated waveguide in which the active waveguide layer 202 and the inactive waveguide layer 203 are coupled alternately and so that the coupling surface is inclined with respect to the waveguide direction can be manufactured.

Thereafter, a diffraction grating pattern is formed on the applied resist by using an electron beam exposure method, and the semiconductor is etched using this as a mask to form a diffraction grating 205. Further, after part of the upper clad 204 made of p-type InP is regrown by metal organic vapor phase epitaxial growth, in order to suppress the transverse mode, the waveguide is formed in a stripe shape having a width of 1.5 μm using SiO ₂ or SiN as a mask. Is processed.

Then, the selective growth mask is removed, an SiO ₂ or SiN film is formed, and a pattern of electrode separation grooves is formed only on the ridge using a thick resist. Next, a current separation groove 216 is formed by etching part of the contact layer 206 and the upper cladding layer 204 for separation between the regions. Subsequently, polyimide is embedded in the side of the ridge and in the separation groove and solidified in an oven of 350 degrees, and then a SiO ₂ insulating film is formed, and insulating films on the active waveguide layer 202 and the inactive waveguide layer 203 are formed. Make a hole in 209. An electrode pattern is formed by lift-off so that the active layer electrodes 102 and the non-active layer electrodes 103 are short-circuited on the element.

In this embodiment, the ridge is formed by wet etching using a sold resist as a mask. However, the ridge may be formed by dry etching using SiO ₂ or SiN as a mask.

  In this embodiment, a dielectric is used to reduce the capacity and protect the ridge structure, but both sides may be air. Moreover, although polyimide which is an organic material is used as a dielectric, other materials such as BCB may be used. By using a dielectric, the capacitance is reduced as compared with the current blocking layer, and therefore the modulation characteristics can be improved. In addition, the modulation characteristic can be improved to 10 GHz or more by suppressing the leakage current between the regions 202 and 203 by the current separation groove 216.

  The effect by a present Example is demonstrated. According to the present embodiment, in particular, with respect to the reduction of the reflectance R at the butt joint between the active waveguide layer 202 and the non-active waveguide layer 203, the same effects as those of the first and second embodiments described above are obtained. It is done. Furthermore, according to the present embodiment, the following effects can be obtained as compared with the first and second embodiments described above.

  That is, in Example 1, the distance between the end faces of the adjacent island masks 15 is constant as shown in FIG. 3 with emphasis on the film thickness and the flatness of the composition during regrowth. Arranged. However, in the case of the first embodiment, when all the end faces are parallel and the angle is nearly perpendicular to the waveguide, the end faces having the same angle may resonate. Although the flatness is somewhat reduced, the length of the island mask 115 in the waveguide direction and the amount by which the material on the island mask 115 moves onto the semiconductor are kept the same as in the first embodiment and are adjacent to each other. By arranging the island-shaped masks 115 line-symmetrically, the bonding surface having the same angle was reduced.

  On the other hand, in this embodiment, the length of the island mask 215 in the waveguide direction and the amount of the material on the island mask 215 moving onto the semiconductor are kept constant, while the adjacent island mask 215 The arrangement is such that the distances between the end faces are equal, and the uniformity and flatness of the composition can be ensured while reducing the bonding faces having the same angle.

  The active waveguide layer and the inactive waveguide layer do not have to be a bulk material. For example, a quantum well structure, a multilayer quantum well structure in which quantum wells are stacked with a barrier layer interposed therebetween, a quantum wire, a quantum dot, or the like Further, it may have a low-dimensional quantum well structure. In order to enhance light confinement and carrier confinement in the active layer, a separate confinement heterostructure (SCH) that introduces a layer having an intermediate refractive index between the active layer and the cladding layer may be introduced.

  Furthermore, the semiconductor used in this element is not limited to a combination of InP and GaInAsP, and may be another semiconductor such as GaAs, GaInNAs, AlGaInAs, InAs, and GaInNAs, and an active waveguide layer and an inactive waveguide layer. The combination of the band gap wavelengths is not limited to the above.

  Further, the semiconductor growth method is not limited to the metal organic vapor phase epitaxial growth method described above, and a molecular beam epitaxial growth method or other means may be used. The method of forming the diffraction grating is not limited to the electron beam exposure method, and a two-bundle interference exposure method or other means may be used.

  In addition, as a method of etching part of the contact layer 206 and the upper cladding layer 204, the active waveguide layer 202 and the inactive waveguide layer 203 are short in length and have a short repetition period. Although an etching method with a small amount of side etching such as dry etching is desirable, there is no problem even with a method using wet etching or the like.

  In addition, in the present embodiment, an example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other embodiments having three or more regions are also described. Applicable in integrated devices. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  A fourth embodiment of the present invention will be described in detail with reference to FIGS. FIG. 12 is an explanatory diagram showing an example of a mask used for manufacturing a distributed active DFB laser as a semiconductor laser according to the present invention, and FIG. 13 is an explanatory diagram showing another example of a mask used for manufacturing a semiconductor laser according to the present invention. is there.

  The present embodiment is different from the first embodiment in that the shape of the mask used when the active waveguide layer and the inactive waveguide layer constituting the optical waveguide layer are butt-joined is different, and other configurations, For example, the laser structure of the semiconductor waveguide device according to the present embodiment is substantially the same as that of the first embodiment described above, and the manufacturing process of the butt joint is as described in the first embodiment with reference to FIG. Hereinafter, the description overlapping with the description in the first embodiment will be omitted, and different portions will be mainly described.

  As shown in FIG. 12, the end face of the island mask 315 that intersects the waveguide direction has an inclination with respect to the waveguide direction. In this embodiment, a plurality of (four in FIG. 12) island-shaped masks 315 each have an asymmetric trapezoidal shape with respect to a plane orthogonal to the waveguide direction, and have different shapes, respectively. Are arranged intermittently. Note that end surfaces of the adjacent island masks 315 facing each other are set to be parallel to each other.

  In the first embodiment, the adjacent island masks 15 are arranged in the same direction. In the second embodiment, the adjacent island masks 115 are arranged so as to be line-symmetric. A mask is used, and adjacent masks are arranged so as to be point-symmetric. On the other hand, in this embodiment, the angles of the pair of end faces intersecting the waveguide direction of each island mask 315 are different from each other, while the distance between adjacent island masks 315 is constant. The opposite end faces of the island-shaped mask 315 are made the same and provided in parallel. The mask width was 7.5 μm.

  The effect by a present Example is demonstrated. According to the present embodiment, in particular, with respect to the reduction of the reflectance R at the butt joint between the active waveguide layer and the inactive waveguide layer, the same effects as those of the first to third embodiments described above can be obtained. Furthermore, according to the present embodiment, the following effects can be obtained as compared with the first to third embodiments described above.

  That is, in Example 1, the distance between the end faces of the adjacent island masks 15 is constant as shown in FIG. 3 with emphasis on the film thickness and the flatness of the composition during regrowth. Arranged. However, in the case of the first embodiment, when all the end faces are parallel and the angle is nearly perpendicular to the waveguide, the end faces having the same angle may resonate. Although the flatness is somewhat reduced, the length of the island mask 115 in the waveguide direction and the amount by which the material on the island mask 115 moves onto the semiconductor are kept the same as in the first embodiment and are adjacent to each other. By arranging the island-shaped masks 115 line-symmetrically, the bonding surface having the same angle was reduced. Further, in Example 3, the length of the mask in the waveguide direction changes along the mask width direction, but the coupling surface having the same angle is reduced by arranging the masks so that the distance between adjacent masks is equal. However, the uniformity and flatness of the composition were ensured.

  In contrast, in this example, the coupling surface having the same inclination with respect to the waveguide direction was further reduced while arranging the gaps between adjacent masks to be constant, thereby reducing the influence of resonance due to reflection. This can be further reduced.

  The island mask 315 shown in FIG. 12 is obtained by changing the inclination of the end face of each island mask 215 with respect to the waveguide direction as compared with the island mask 215 shown in FIG. 11 and described in the third embodiment. However, the effect of this embodiment can also be obtained by changing a part of the island-shaped mask 115 shown in FIG. 9 and described in the embodiment 2 to have a shape as shown in FIG.

  That is, as shown in FIG. 13, the shape of the island mask 415 is equal to the angle of both end faces intersecting the waveguide direction, that is, a parallelogram, and the end face facing the adjacent island mask 415 is formed. The shape of each island mask 415 is made different so that the angles are different. Thereby, while making the length of the waveguide direction of the active waveguide layer constant, the inclination angle with respect to the waveguide direction of the coupling surface of the active waveguide layer and the inactive waveguide layer can be made different, Resonance due to reflection can be suppressed while the influence of the material moving on the island mask 415 near the end of the island mask 415 is the same.

  In this embodiment, the example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other integrated devices having three or more regions. Is applicable. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  A fifth embodiment of the present invention will be described in detail based on FIG. FIG. 14 is an explanatory view showing an example of a mask used for manufacturing a distributed active DFB laser as a semiconductor laser according to the present invention.

  The present embodiment is different from the second embodiment in the shape of the mask used when the active waveguide layer and the inactive waveguide layer constituting the optical waveguide layer are butt-joined. The laser structure is the same as in Example 2, but a semiconductor containing Al is used for the active layer, and Ru-doped InP is used for the semi-insulator layer. Thereby, it is possible to prevent the threshold current from increasing even under high temperature and to improve the modulation characteristics. Other configurations are generally the same as those of the second embodiment described above, and redundant description is omitted.

  As shown in FIG. 14, the end face of the island mask 515 that intersects the waveguide direction has an inclination with respect to the waveguide direction. In this embodiment, the end faces of the plurality of (four in FIG. 14) island-shaped masks 515 intersecting the waveguide direction have different inclination angles with respect to the waveguide direction, and intermittently in the waveguide direction. Has been placed.

  In the first embodiment, the adjacent island masks 15 are arranged in the same direction, and in the second embodiment, the adjacent island masks 115 are arranged so as to be line symmetric. In Embodiment 3, a trapezoidal mask is used, and adjacent masks are arranged so as to be point-symmetric. In the fourth embodiment, the active waveguide layer and the inactive waveguide layer are formed such that the distance between the island masks 315 or the length of the island mask 415 is constant along the direction orthogonal to the waveguide direction. The inclination angle of the coupling surface is the same for every two consecutive coupling surfaces, and the inclination angle is otherwise different. On the other hand, in this embodiment, the angles of the coupling surfaces are all different. The mask width was 10 μm.

  The effect by a present Example is demonstrated. According to the present embodiment, in particular, with respect to the reduction of the reflectance R at the butt joint between the active waveguide layer and the inactive waveguide layer, the same effects as those of the first to fourth embodiments described above can be obtained. Furthermore, according to the present embodiment, the following effects can be obtained as compared with the first to fourth embodiments described above.

  That is, in Example 1, the distance between the end faces of the adjacent island masks 15 is constant as shown in FIG. 3 with emphasis on the film thickness and the flatness of the composition during regrowth. Arranged. However, in the case of the first embodiment, when all the end faces are parallel and the angle is nearly perpendicular to the waveguide, the end faces having the same angle may resonate. Although the flatness is somewhat reduced, the length of the island mask 115 in the waveguide direction and the amount by which the material on the island mask 115 moves onto the semiconductor are kept the same as in the first embodiment and are adjacent to each other. By arranging the island-shaped masks 115 line-symmetrically, the bonding surface having the same angle was reduced. Further, in Example 3, the length of the mask in the waveguide direction changes along the mask width direction, but the coupling surface having the same angle is reduced by arranging the masks so that the distance between adjacent masks is equal. However, the uniformity and flatness of the composition were ensured. In Example 4, the distance between the island-shaped masks 315 or the length of the island-shaped mask 415 in the waveguide direction was made equal along the width direction, and the coupling surfaces having the same inclination angle were further reduced. This makes it possible to further reduce the influence of resonance due to reflection.

  On the other hand, in this embodiment, the inclination angles of the respective coupling surfaces are all different. Thereby, the uniformity of selective growth is slightly reduced, but the influence of resonance due to reflection can be further reduced. In this embodiment, in order to obtain the best state, island masks 515 are arranged as shown in FIG. 14 so that the angles of the coupling surfaces are all different, but they are not surfaces orthogonal to the waveguide direction. Needless to say, the coupling surfaces separated to some extent may have the same inclination angle.

Specifically, in the simplest case, it is only necessary to prevent the light reflected on one surface from reaching the other surface between the coupling surfaces having the same inclination angle, so that the waveguide of the island mask 515 When the width in the direction orthogonal to the direction is d and the angle of the butt joint surface with respect to the waveguide direction is θ, the distance x between the coupling surfaces having the same inclination angle only needs to satisfy the relationship of the following expression (10).
x> 2d / sin (2θ) (10)

  In this embodiment, the example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other integrated devices having three or more regions. Is applicable. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  The sixth embodiment of the present invention will be described in detail with reference to FIGS. FIG. 15 is an explanatory view showing an example of a mask used for manufacturing a distributed active DFB laser as a semiconductor laser according to the present invention, and FIG. 16 is an explanatory view showing another example of a mask used for manufacturing a semiconductor laser according to the present invention. is there.

  This embodiment is different from the third embodiment in the shape of the mask used when the active waveguide layer and the inactive waveguide layer constituting the optical waveguide layer are butt-joined. Other configurations, for example, the laser structure are substantially the same as in the above-described third embodiment, and the manufacturing process of the butt joint is as described in the first embodiment with reference to FIG. The overlapping description is omitted.

  As shown in FIG. 15, the end face of the island mask 615 that intersects the waveguide direction has an inclination with respect to the waveguide direction and has a line-symmetric trapezoidal shape. In this embodiment, all (four in FIG. 15) island masks 615 are formed in the same shape and are intermittently arranged in the same direction. End faces orthogonal to the waveguide direction have different inclination angles with respect to the waveguide direction, and are disposed intermittently in the waveguide direction.

  In the first embodiment, the adjacent island masks 15 are arranged in the same direction, and in the second embodiment, the adjacent island masks 115 are arranged so as to be line symmetric. In Embodiment 3, a trapezoidal mask is used, and adjacent masks are arranged so as to be point-symmetric. In the fourth embodiment, the active waveguide layer and the inactive waveguide layer are formed such that the distance between the island masks 315 or the length of the island mask 415 is constant along the direction orthogonal to the waveguide direction. The inclination angle of the coupling surface is the same for every two consecutive coupling surfaces, and the inclination angle is otherwise different. In the fifth embodiment, the angles of the coupling surfaces are all different. In contrast, in this embodiment, island masks 615 having the same trapezoidal shape are intermittently arranged. The mask width was 6.5 μm.

  The effect by a present Example is demonstrated. According to the present embodiment, in particular, for the reduction of the reflectance R at the butt joint between the active waveguide layer and the inactive waveguide layer, the same effects as those of the first embodiment described above can be obtained. Furthermore, according to the present embodiment, the following effects can be obtained as compared with the first embodiment described above.

  That is, in Example 1, the distance between the end faces of the adjacent island masks 15 is constant as shown in FIG. 3 with emphasis on the film thickness and the flatness of the composition during regrowth. Arranged. However, in the case of the first embodiment, when all the end faces are parallel and the angle is nearly perpendicular to the waveguide, the end faces having the same angle may resonate. Although the flatness is somewhat reduced, the length of the island mask 115 in the waveguide direction and the amount by which the material on the island mask 115 moves onto the semiconductor are kept the same as in the first embodiment and are adjacent to each other. By arranging the island-shaped masks 115 line-symmetrically, the bonding surface having the same angle was reduced.

  Further, in Example 3, the length of the mask in the waveguide direction changes along the mask width direction, but the coupling surface having the same angle is reduced by arranging the masks so that the distance between adjacent masks is equal. However, the uniformity and flatness of the composition were ensured. In Example 4, the distance between the island-shaped masks 315 or the length of the island-shaped mask 415 in the waveguide direction was made equal along the width direction, and the coupling surfaces having the same inclination angle were further reduced. This makes it possible to further reduce the influence of resonance due to reflection. In Example 5, the inclination angles of the respective coupling surfaces are all different, and the uniformity of selective growth is slightly reduced, but the influence of resonance due to reflection can be further reduced.

  However, in the case of the shape of the second to fifth embodiments, when the lateral waveguide confinement structure, that is, the mesa structure of the ridge or the buried heterostructure, is formed from the design position of the waveguide. When misalignment occurs, the length of one cycle consisting of a combination of the active waveguide region and the inactive waveguide region, or the ratio of the active waveguide region and the inactive waveguide region in one cycle varies depending on the location. . In the case of a distributed active DFB laser, the ratio between the active waveguide region and the inactive waveguide region is set so that the ratio of the change in the resonant longitudinal (axial) mode matches the ratio of the change in the reflection peak. It is necessary to equalize the combination of the region and the inactive waveguide region. When trapezoidal islands are arranged side by side as in this embodiment, the ratio of the design shape changes even if the trapezoidal islands are shifted in parallel with the waveguide assumed in the design, but all active guides in the resonator are changed. The ratio is the same for the combination of the waveguide region and the inactive waveguide region.

  FIG. 15 clearly shows the idea of this embodiment, that is, the ratio between the active waveguide region and the inactive waveguide region is constant even if the position is shifted in the direction orthogonal to the waveguide. Although the description has been made using the isosceles trapezoid in which the two corners at the end points of the upper base are equal to each other and the two corners at the end points of the lower base are equal to each other, the adjacent masks may have the same shape. For example, as shown in FIG. 16, a pair of end faces intersecting with the waveguide direction of the island mask 715 may have different inclination angles with respect to the waveguide direction.

  In this embodiment, the example in which the butt joint surface is inclined with respect to the waveguide direction in the distributed active DFB laser has been described. However, the present invention is not limited to the above-described embodiment, and other integrated devices having three or more regions. Is applicable. In this embodiment, for the distributed active DFB laser, two types of waveguide regions are alternately repeated, and all butt joints are formed by one selective growth. In the case of a configuration having three or more types of waveguide regions, selective growth is performed twice or more. Even in this case, the arrangement of the coupling end surface angles of the butt joint is the same as that of the present embodiment. Thus, the effect of the present invention can be obtained.

  In the first to sixth embodiments described above, an example in which the coupling surface is inclined with respect to the direction orthogonal to the waveguide direction is shown for the semiconductor waveguide element in which eight optical waveguides are coupled. However, if it is a semiconductor waveguide device in which three or more optical waveguides are coupled, the effects described in the first to sixth embodiments can be obtained.

  In the first to third embodiments, the diffraction grating is formed after a part of the upper cladding layer is grown. However, the present invention is not limited to the above-described embodiment, and an active waveguide layer is manufactured. After that, before forming the upper clad layer, the active waveguide layer is etched using the island mask, and the inactive waveguide layer is regrown by selective growth using the island mask as it is, so that the active waveguide After the layers and the inactive waveguide layers are coupled alternately and so that the coupling surface is inclined with respect to the waveguide direction, a diffraction grating is formed. It goes without saying that changes are possible.

  The present invention relates to a wavelength tunable semiconductor laser used as a light source for optical fiber communication and a light source for optical measurement. For example, the present invention relates to a light source for optical wavelength (frequency) multiplexing system in optical communication and a light source for optical measurement that covers a wide wavelength band. Applicable.

1A is a top view of the semiconductor laser according to the first embodiment of the present invention, FIG. 1B is a cross-sectional view taken along line xx ′ shown in FIG. 1A, and FIG. 1C is FIG. ) Of FIG. 1C, and FIG. 1D is a cross-sectional view of FIG. 1C. 2 (a) to 2 (c) are explanatory diagrams showing a process for producing a butt joint in the present invention. FIG. 3 is a top view of FIG. It is explanatory drawing which shows refraction of the light in the interface of the substance from which a refractive index mutually differs. It is a graph which shows the relationship between a band gap wavelength and a refractive index difference. It is a graph which shows the relationship between an incident angle and a reflectance. It is a graph which shows the coupling factor of the reflected wave with respect to the incident angle to a refractive index boundary. 8A is a top view of the semiconductor waveguide device according to the second embodiment, FIG. 8B is a cross-sectional view taken along line xx ′ shown in FIG. 8A, and FIG. 8C is FIG. 8A. It is yy 'sectional drawing. It is explanatory drawing which shows an example of the mask used for preparation of the semiconductor waveguide element based on Example 2 of this invention. 10A is a top view of the semiconductor waveguide device according to the present embodiment, FIG. 10B is a cross-sectional view taken along line xx ′ shown in FIG. 10A, and FIG. 10C is FIG. It is yy 'sectional drawing. It is explanatory drawing which shows an example of the mask used for preparation of the semiconductor waveguide element based on Example 3 of this invention. It is explanatory drawing which shows an example of the mask used for preparation of the semiconductor waveguide element based on Example 4 of this invention. It is explanatory drawing which shows the other example of the mask used for preparation of the semiconductor waveguide element based on Example 4 of this invention. It is explanatory drawing which shows an example of the mask used for preparation of the semiconductor waveguide element based on Example 5 of this invention. It is explanatory drawing which shows an example of the mask used for preparation of the semiconductor waveguide element based on Example 6 of this invention. It is explanatory drawing which shows the other example of the mask used for preparation of the semiconductor waveguide element based on Example 6 of this invention. FIG. 17A is a top view of a conventional distributed active DFB laser, and FIG. 17B is a sectional view taken along line xx ′ in FIG. It is sectional drawing which shows the other conventional distributed active DFB laser. It is sectional drawing which shows the other conventional distributed active DFB laser.

Explanation of symbols

1, 101, 201, 301, 401 Lower cladding 2, 102, 202, 302, 402 Active waveguide layer 3, 103, 203, 303, 403 Inactive waveguide layer 4, 104, 204, 304, 404 Upper cladding 5 , 105, 205, 305, 405 Diffraction grating 6, 106, 206 Contact layer 7, 107, 207, 307, 407 Active layer electrode 8, 108, 208, 308, 408 Wavelength control electrode 9, 109, 209 Insulating film 10, 110, 210, 310, 410 Common electrode 13 Current blocking layer 14 Coupling surface 113 Semi-insulator 213 Dielectric 15, 115, 215, 315, 415, 515, 615, 715 Island mask

Claims (10)

An optical device including at least one first semiconductor clad layer, an optical waveguide layer having an optical refractive index larger than that of the first semiconductor clad layer, and a second semiconductor clad layer having a refractive index smaller than that of the optical waveguide layer. In a semiconductor waveguide device in which three or more waveguides are coupled in series in the direction of the optical waveguide,
At least one coupling surface between the optical waveguide layers has an inclination with respect to a direction orthogonal to the waveguide direction. A semiconductor waveguide device, wherein:   2. The semiconductor waveguide device according to claim 1, wherein a normal line of the coupling surface is inclined by 5 degrees or more with respect to a waveguide direction.   2. The semiconductor waveguide device according to claim 1, wherein a normal line of the coupling surface is inclined at an angle of 10 degrees to 54 degrees with respect to the waveguide direction.   4. The semiconductor waveguide device according to claim 1, wherein the coupling surfaces all have the same inclination. 5.   4. The semiconductor waveguide device according to claim 1, wherein the coupling surface has an equal inclination angle for every two continuous surfaces along the waveguide direction. 5.   4. The semiconductor waveguide device according to claim 1, wherein the coupling surface has an equal inclination angle every other surface.   4. The semiconductor waveguide device according to claim 1, wherein the coupling surfaces have different inclination angles at least in a range where the distance is less than 2 d / sin (2θ). 5.   8. A semiconductor waveguide device according to claim 1, further comprising a semi-insulating current blocking layer doped with ruthenium.   A semiconductor laser comprising the semiconductor waveguide device according to claim 1. An optical waveguide including at least one first semiconductor cladding layer, an optical waveguide layer having an optical refractive index larger than that of the first semiconductor cladding layer, and a second semiconductor cladding layer having a refractive index lower than that of the optical waveguide layer. In a method for producing a semiconductor waveguide device in which three or more waveguides are coupled in series in the direction of an optical waveguide,
Etching the first optical waveguide layer using a step of forming a first optical waveguide layer on the first semiconductor clad layer and an island mask having an inclination with respect to a direction orthogonal to the waveguide direction A method for manufacturing a semiconductor waveguide element, comprising: a step; and a step of re-growing the second optical waveguide layer after etching using the island mask.

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