JP2013140834A - Semiconductor laser and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser capable of achieving a stable operation, and to provide a method of manufacturing the same.SOLUTION: A semiconductor laser includes: an active region 121 loading a diffraction grating 132; a distribution reflection mirror region 122 including two waveguides 151 and 152 having diffraction gratings with different cycles from each other, and reflecting light generated at and inputted from the active region 121 toward the active region 121; and a grating-assisted directional coupler 153 provided between the active region 121 and the distribution reflection mirror region 122, and coupling the waveguides 151 and 152 with a waveguide in the active region.

Description

  The present invention relates to a semiconductor laser and a manufacturing method thereof.

  In recent years, with the explosive increase in demand for the Internet, efforts to increase the speed and capacity in optical communication and optical transmission have become active. In particular, an ultrahigh-speed optical fiber transmission system of 40 Gb / s or more and a semiconductor laser capable of direct modulation of 25 Gb / s or more in an uncooled state are required. Such a semiconductor laser is, for example, for 100 gigabit Ethernet (registered trademark) in which 25 gigabits are bundled by 4 waves by LAN (local area network) -WDM (wavelength division multiplexing). As such a semiconductor laser, a distributed feedback (DFB) laser is expected.

  Basically, in a semiconductor laser, the smaller the volume of the active layer, the larger the relaxation oscillation frequency value and the higher the bit rate that can be directly modulated. For example, in a DFB laser in which an antireflection film is provided on the front end face and a high reflection film having a reflectivity of about 90% is provided on the rear end face, the resonator length is shortened to 100 μm, thereby modulating at 40 Gb / s at room temperature. It has been announced that it will be possible. However, it is difficult to manufacture a DFB laser capable of obtaining a good single longitudinal mode oscillation with a high yield simply by designing the resonator length short.

  Therefore, for the purpose of improving the yield of single longitudinal mode oscillation, a DFB laser including a distributed reflector that does not inject current has been proposed. In this DFB laser, the distributed reflector is loaded with a diffraction grating whose phase is synchronized with the same period as the diffraction grating in the active region, and the distributed reflector performs optical feedback to the active region. The diffraction grating is provided with a λ / 4 phase shift unit.

  However, it is sometimes difficult to realize a stable operation with the conventional DFB laser including the distributed reflector as described above.

Japanese Patent Publication No. 7-70785 JP 2002-353559 A Japanese Patent No. 3149799 JP-A-7-283473 Japanese Patent Laid-Open No. 5-90715

  An object of the present invention is to provide a semiconductor laser capable of realizing stable operation and a method for manufacturing the same.

  One aspect of the semiconductor laser includes an active region loaded with a diffraction grating and two waveguides having diffraction gratings with different periods, and directs light generated and input in the active region toward the active region. A distributed reflector region that reflects, and a diffraction grating type directional coupler that is provided between the active region and the distributed reflector region and couples the two waveguides and the waveguide in the active region; It is included.

  In one embodiment of the semiconductor laser manufacturing method, an active region loaded with a diffraction grating is formed above a substrate, and two waveguides having diffraction gratings having different periods are formed above the substrate, and are generated in the active region. A distributed reflector region that reflects the input light toward the active region is formed, and is provided between the active region and the distributed reflector region, and the two waveguides and a guide in the active region are provided. A diffraction grating type directional coupler for coupling with the waveguide is formed.

  According to the semiconductor laser or the like, stable operation can be realized by the action of the diffraction grating type directional coupler between the active region and the distributed reflector region.

It is sectional drawing which shows the structure of a reference example. It is a figure which shows the result of the investigation of the characteristic of a reference example. It is a figure which shows the change accompanying a plasma effect. It is a figure which shows the change of a single longitudinal mode oscillation yield. It is a figure which shows the change accompanying current injection. It is a figure which shows the point of the temporary structure. It is a figure which shows the problem of another temporary structure. It is a figure which shows the structure of the semiconductor laser which concerns on 1st Embodiment. It is a figure which shows the change of the main mode in 1st Embodiment. It is a figure which shows the relationship between the resonant intensity of GADC, and an oscillation wavelength. It is a figure which shows the effect | action of 1st Embodiment. It is a perspective view which shows the manufacturing method of the semiconductor laser which concerns on 1st Embodiment. FIG. 12 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 11; FIG. 13 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 12; FIG. 14 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 13; FIG. 15 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 14. FIG. 16 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 15; FIG. 17 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 16; FIG. 18 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 17; FIG. 19 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 18; FIG. 20 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 19; FIG. 21 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 20; FIG. 22 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 21; It is a figure which shows the structure of the modification of 1st Embodiment. It is a figure which shows the structure of the semiconductor laser which concerns on 2nd Embodiment. It is a perspective view which shows the manufacturing method of the semiconductor laser which concerns on 2nd Embodiment. FIG. 26 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 25; FIG. 27 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 26; FIG. 28 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 27; FIG. 29 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 28; FIG. 30 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 29; FIG. 31 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 30; FIG. 32 is a perspective view illustrating the manufacturing method of the semiconductor laser, following FIG. 31; FIG. 33 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 32; FIG. 34 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 33. FIG. 35 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 34; FIG. 36 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 35; It is a figure which shows the structure of the modification of 2nd Embodiment. It is a figure which shows the structure of the semiconductor laser which concerns on 3rd Embodiment. It is a perspective view which shows the manufacturing method of the semiconductor laser which concerns on 3rd Embodiment. FIG. 40 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 39. FIG. 41 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 40; FIG. 42 is a perspective view illustrating a manufacturing method of the semiconductor laser, following FIG. 41; FIG. 43 is a perspective view showing a method of manufacturing the semiconductor laser, following FIG. 42. FIG. 44 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 43. FIG. 45 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 44. FIG. 46 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 45. FIG. 47 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 46; FIG. 48 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 47; FIG. 49 is a perspective view showing a method of manufacturing the semiconductor laser, following FIG. 48; FIG. 50 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 49; FIG. 51 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 50; FIG. 52 is a perspective view illustrating a manufacturing method of the semiconductor laser, following FIG. 51; FIG. 53 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 52; FIG. 54 is a perspective view illustrating a method for manufacturing the semiconductor laser, following FIG. 53; FIG. 55 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 54. FIG. 56 is a perspective view showing a method for manufacturing the semiconductor laser, following FIG. 55; It is a figure which shows the structure of the modification of 3rd Embodiment. It is a figure which shows the structure of the optical semiconductor module which concerns on 4th Embodiment.

  In order to investigate the cause of the deterioration of the single longitudinal mode oscillation yield in the prior art, the inventor of the present application manufactured the semiconductor laser of the reference example shown in FIG. 1 and intensively studied its characteristics.

  This semiconductor laser is partitioned into an active region 1012 and a distributed reflector region 1013, and a diffraction grating 1002 is formed on the surface of the substrate 1001 in both the active region 1012 and the distributed reflector region 1013. However, the active region 1012 includes the λ / 4 phase shift portion 1002 s of the diffraction grating 1002. The λ / 4 phase shift unit 1002s is located substantially at the center in the light guide direction. A buffer layer 1003 is formed so as to cover the diffraction grating 1002, an active layer 1004 is formed in the active region 1012, and a light guide layer 1005 is formed in the distributed reflector region 1013 on the buffer layer 1003. Further, a cladding layer 1006 is formed on the active layer 1004 and the light guide layer 1005, and a contact layer 1007 and a p-electrode 1008 are formed on the cladding layer 1006 in the active region 1012. Further, an antireflection film 1010 is formed on the end surface on the active region 1012 side, and an antireflection film 1011 is formed on the end surface on the distributed reflector region 1013 side.

  As a result of investigating the characteristics of the semiconductor laser as described above, the results shown in FIG. 2 were obtained. From this result, the following matters were found as a result.

  First, as shown in FIGS. 2B and 2C, it has been found that mode jumping occurs near the threshold value due to the following reasons. First, as the current is injected into the active region 1012, the refractive index of the active region 1012 decreases due to the plasma effect, and the in-tube wavelength in the active region 1012 becomes shorter. For this reason, the phase of the guided light in the main mode (Bragg mode) rotates more than in the case where there is no refractive index fluctuation in the active region 1012. This change is shown in FIG. 3A and 3B show the state before current injection, and FIGS. 3C and 3D show the state after current injection. When the phase turns excessively as described above, the main mode 1014 (Bragg mode) drifts relatively to the long wave side within the stop band (as indicated by the one-dot chain line in FIG. Therefore, the oscillation threshold value of the main mode 1014 increases and the oscillation threshold value of the sub mode decreases. As a result, as indicated by a two-dot chain line in FIG. 3D, a mode jump occurs to the submode on the short wave side. Further, as shown in FIG. 4, an analysis result that mode competition occurs and single longitudinal mode oscillation yield deteriorates was also obtained.

  Second, as shown in FIGS. 2 (d) and 2 (e), it has been found that when the drive current is increased, mode jump occurs due to the following reasons. First, when the drive current is in an appropriate range, the refractive index of the active region 1012 is stable. On the other hand, if current injection into the active region 1012 is continued, the temperature of the active region 1012 rises. For this reason, the Bragg wavelength of the active region 1012 shifts to the long wave side. On the other hand, since no current is injected into the distributed reflector region 1013, the reflection wavelength band does not change. As a result, the Bragg wavelength deviates from the effective reflection band of the distributed reflector region 1013. This change is shown in FIG. FIGS. 5A and 5B show the state of the active region 1012 before the temperature rise, and FIGS. 5C and 5D show the state of the active region 1012 after the temperature rise. When the Bragg wavelength deviates from the effective reflection band as described above, that is, the oscillation threshold value of the main mode 1015 (Bragg mode) increases and the effective reflection band of the reflection spectrum 1016 of the distributed reflector region 1013 increases. On the other hand, when it comes off, the submode 1017 on the short wave side of the stop band of the active region 1012 enters the effective reflection band of the reflection spectrum 1016. As a result, the oscillation threshold is lowered and multimode oscillation occurs.

  Therefore, in order to improve the single longitudinal mode oscillation yield, even if the refractive index of the active region 1012 is decreased due to current injection into the active region 1012, the oscillation threshold of the sub mode is decreased and oscillation is performed. It is conceivable to prevent this from happening. Further, even if the Bragg wavelength of the active region 1012 becomes longer due to the temperature rise of the active region 1012 due to the current injection into the active region 1012, it is prevented from deviating from the effective reflection band of the distributed reflector region 1013, that is, distributed reflection. Enlarging the effective reflection band of the mirror region 1013 is also conceivable. In general, the effective reflection band of the distributed reflector region 1013 is almost inversely proportional to the length of the distributed reflector region 1013. Therefore, if the length of the distributed reflector region 1013 is shortened, the effective reflection band is expanded. However, if the length of the distributed reflector region 1013 is shortened, for example, if the length is halved, the reflectance is reduced to less than half, so that the reflection spectrum 1016 changes to a low and wide reflection spectrum 1018 as shown in FIG. This raises the oscillation threshold of the semiconductor laser. In order to compensate for this, it is conceivable to increase the coupling coefficient of the diffraction grating 1002 in the distributed reflector region 1013 by about twice, but in this case, as shown in FIG. A large number of defects are generated during the crystal growth of the layer 1005 and the cladding layer 1006, and a defect increasing region 1009 is generated. As a result, the characteristics of the semiconductor laser are deteriorated.

  It is also conceivable to combine a Y-branch waveguide and a plurality of diffraction gratings having different periods, but in this structure, when the resonance wavelength interval is wide between the plurality of diffraction gratings, the plurality of diffraction gratings With respect to the wavelength between the resonance wavelengths, a valley of reflection is obtained, and a sufficient reflectance cannot be obtained. In addition, when the interval between the resonance wavelengths is narrow, it is possible to obtain a relatively high reflectance. However, in order to secure a narrow reflection band and a wide reflection band, diffraction gratings having various resonance wavelengths are used. Since this is necessary, the semiconductor laser becomes large.

  As a result of further intensive studies based on these findings, the present inventor has arrived at the following embodiment.

(First embodiment)
First, the first embodiment will be described. FIG. 8 is a diagram illustrating the semiconductor laser according to the first embodiment.

  As shown in FIG. 8, the semiconductor laser according to the first embodiment includes an active region 121, a grating-assisted directional coupler (GADC) region 124, a distributed reflector region 122, and a front end face. A side distributed reflector region 123 is partitioned. In the light guide direction, the front end face side distributed reflector region 123, the active region 121, the GADC region 124, and the distributed reflector region 122 are arranged side by side in order from the output end face side. For example, the length of the front end face side distributed reflector region 123 is 25 μm, the length of the active region 121 is 100 μm, the length of the GADC region 124 is 100 μm, and the length of the distributed reflector region 122 is 200 μm. That is, the front end face side distributed reflector region 123 is shorter than the distributed reflector region 122. The semiconductor laser includes a main waveguide 151 continuous over the front end face side distributed reflector region 123, the active region 121, the GADC region 124, and the distributed reflector region 122, and is arranged away from the main waveguide 151. A sub-waveguide 152 is also included. The main waveguide 151 and the sub-waveguide 152 are optically coupled to each other by the GADC 153 provided in the GADC region 124. The sub waveguide 152 may extend about 10 nm into the active region 121.

For example, a diffraction grating 132 having a period of 199.505 nm is provided in a portion of the main waveguide 151 located in the active region 121, the front end face side distributed reflector region 123, or the GADC region 124. The diffraction grating 132 includes a λ / 4 phase shift unit 133 having a phase of π radians (corresponding to λ / 4 shift). Further, in the portion of the main waveguide 151 located in the distributed reflector region 122, a short period diffraction grating 131a having the same period as the portion located in the active region 121, the front end face side distributed reflector region 123 or the GADC region 124 is provided. Is provided. That is, the main waveguide 151 is provided with a diffraction grating having a constant period Λ ₁ of, for example, 199.505 nm, except for the λ / 4 phase shift unit 133. On the other hand, the sub-waveguide 152 is provided with a long-period diffraction grating 131b having a longer period than that of the main waveguide 151. The period Λ ₂ of the long-period diffraction grating 131b is, for example, 199.886 nm. The depth of the diffraction grating 132, the short period diffraction grating 131a, and the long period diffraction grating 131b is, for example, 100 nm. In this embodiment, the width of the main waveguide 151 is 1 μm, and the width of the sub-waveguide 152 is 3 μm. Therefore, the equivalent refractive index neq ₁ of the active layer included in the main waveguide 151 is the active index included in the sub-waveguide 152. This is different from the equivalent refractive index neq _{2 of the} layer. The period Λ _GADC of the _{GADC 153} is “λ ₂ / (neq ₂ −neq ₁ )”.

In such a semiconductor laser according to the first embodiment, the resonance wavelength λ ₁ of the main waveguide 151 is “2 neq ₁ Λ ₁ ”, and the resonance wavelength λ ₂ of the sub-waveguide 152 is “ ₂ neq ₂ Λ ₂ ”. During the operation of the semiconductor laser, laser light is emitted as follows.

  First, immediately after oscillation, as shown in FIG. 9A (a) and FIG. 9B (a), the light is mainly reflected when guided through the main waveguide 151 having the resonance wavelength at the current wavelength. As a result, as shown in FIG. 10A, the light is mainly reflected when being guided through the main waveguide 151 having the oscillation wavelength of the main mode 161 in the effective reflection band of the reflection spectrum 162. Thereafter, when the refractive index of the active region 121 increases as the injection current into the active region 121 (DFB laser portion) increases and the oscillation wavelength becomes longer, the GADC 153 resonates, and FIGS. 9A (b) and 9B (b) As shown in (), when the light is guided through the sub-waveguide 152 having the resonance wavelength at the wavelength at that time, the light is positively reflected, and feedback is performed to the active region 121. That is, as shown in FIG. 10B, the light is mainly reflected when being guided through the sub-waveguide 152 having the oscillation wavelength of the main mode 161 in the effective reflection band of the reflection spectrum 163. In this way, the distributed reflector region 122 reflects the light generated and input in the active region 121 toward the active region 121. A one-dot chain line in FIG. 10 indicates light traveling from the active region 121 toward the distributed reflector region 122, and a broken line indicates light reflected by the distributed reflector region 122.

  Therefore, according to the present embodiment, single mode oscillation can be maintained in a wide operating current range. Further, even if the temperature of the active region 121 rises due to current injection into the active region 121 and the Bragg wavelength of the active region 121 becomes longer, the main mode 161 is within the effective reflection band of the distributed reflector region 122. Can be maintained. That is, it is possible to suppress multimode oscillation and mode jump and maintain good single longitudinal mode oscillation. Further, the phase around due to the plasma effect up to the threshold value can be canceled. Therefore, it is possible to maintain good single longitudinal mode oscillation without shifting the oscillation mode to the long wave side in the stop band.

The relationship between the reflection spectrum 162 and the reflection spectrum 163 is not particularly limited, but the wavelength at which the reflectance on the long wave side of the reflection spectrum 162 is 50% and the wavelength at which the reflectance on the short wave side of the reflection spectrum 163 is 50%. Are preferably coincident with each other. This is because when the wavelength of the main mode 161 does not coincide with the resonance wavelength λ ₁ of the main waveguide 151 or the resonance wavelength λ ₂ of the sub-waveguide 152, and the wavelength is between them, This is because sufficient reflected light is obtained from both of the sub waveguides 152. With such a configuration, for example, even when the wavelength of the main mode 161 is an average value of the resonance wavelength λ ₁ and the resonance wavelength λ ₂ , FIG. 9A (c) and FIG. 9B (c) ) And FIG. 10C, it is possible to obtain approximately half of reflected light from the main waveguide 151 and the sub-waveguide 152, and the wavelength of the main mode 161 is equal to the resonance wavelength λ ₁ or the resonance wavelength λ _2. You can get the same feedback as you do. It should be noted that the wavelength at which the reflectance on the long wave side of the reflection spectrum 162 is 50% and the wavelength at which the reflectance on the short wave side of the reflection spectrum 163 is 50% do not have to be completely coincident with each other. Considering, in general, the wavelength in which the reflectance on the long wave side of the reflection spectrum 162 is in the range of 40% to 60% and the wavelength in which the reflectance on the short wave side of the reflection spectrum 163 is in the range of 40% to 60%. Are preferably coincident with each other. When the overlap between the reflection spectra 162 and 163 is small, it is difficult to obtain a sufficient reflectance when the wavelength of the main mode 161 is a wavelength between the resonance wavelength λ ₁ and the resonance wavelength λ ₂ . On the other hand, when the overlap between the reflection spectra 162 and 163 is large, it is easy to obtain a sufficient reflectance, but it is difficult to obtain a wide reflection band.

  Thus, according to the present embodiment, a substantially constant reflectance can be obtained even when the oscillation wavelength drifts.

  Note that the above-described effects can be obtained because the GADC 153 is used. If only the Y-branch waveguide is used, such an effect cannot be obtained. This is because the feedback of reflected light can be obtained only from one of the reflection bands.

  Next, a method for manufacturing the semiconductor laser according to the first embodiment will be described. 11 to 22 are perspective views showing the method of manufacturing the semiconductor laser according to the first embodiment in the order of steps.

  First, as shown in FIG. 11, a diffraction grating mask 102 is formed on an n-InP substrate 101 doped with an n-type impurity by using an electron beam resist (for example, ZEP520 manufactured by Nippon Zeon Co., Ltd.). Form. At this time, the diffraction grating mask 102 includes a diffraction grating pattern 102a for the short period diffraction grating 131a, a diffraction grating pattern 102b for the long period diffraction grating 131b, and a diffraction grating pattern 102c for the diffraction grating 132. The diffraction grating pattern 102c includes a λ / 4 phase shift unit 102s corresponding to the λ / 4 phase shift unit 133. In the GADC region 124, the n-InP substrate 101 is exposed.

  Next, as shown in FIG. 12, diffraction is performed on the surface of the n-InP substrate 101 by reactive ion etching (RIE) using a mixed gas of ethane and hydrogen using the diffraction grating mask 102 as an etching mask. A grating 132, a short period diffraction grating 131a, and a long period diffraction grating 131b are formed. That is, the diffraction grating patterns 102 a to 102 c of the diffraction grating mask 102 are transferred to the n-InP substrate 101.

  Thereafter, as shown in FIG. 13, the diffraction grating mask 102 is removed. Subsequently, an n-GaInAsP guide layer 103 doped with an n-type impurity, an n-InP layer 104 doped with an n-type impurity, a quantum well active layer 105, and a p-type impurity are doped on the n-InP substrate 101. The p-InP cladding layer 106 thus formed is formed by a metal-organic vapor phase epitaxy (MOVPE) method. For example, the composition wavelength of the n-GaInAsP guide layer 103 is 1.25 μm, the thickness is 120 nm, the thickness of the n-InP layer 104 is 20 nm, and the thickness of the p-InP cladding layer 106 is 250 nm. The quantum well active layer 105 includes, for example, 15 undoped AlGaInAs quantum well layers and an undoped AlGaInAs barrier layer interposed therebetween. For example, the thickness of the quantum well layer is 6 nm, the amount of compressive strain is 1.2%, the composition wavelength of the barrier layer is 1.05 μm, and the thickness is 10 nm. The quantum well active layer 105 also includes an undoped AlGaInAs separate confinement heterostructure (SCH) layer that sandwiches the quantum well layer and the barrier layer from above and below. For example, the composition wavelength of the SCH layer is 1.05 μm and the thickness is 20 nm. The emission wavelength of the quantum well active layer 105 is 1310 nm.

Next, as shown in FIG. 14, a mask 107 is formed on the p-InP cladding layer 106 so as to cover the active region 121 and expose the front end face side distributed reflector region 123, the GADC region 124, and the distributed reflector region 122. . As the mask 107, for example, a SiO ₂ film having a thickness of 400 nm is formed by a chemical vapor deposition (CVD) method and photolithography.

  Thereafter, as shown in FIG. 15, using the mask 107 as an etching mask, the p-InP cladding layer 106 and the quantum well active layer 105 are etched to expose the surface of the n-InP layer 104.

  Subsequently, as illustrated in FIG. 16, an undoped AlGaInAs layer 108 and an undoped InP layer 109 are formed on the n-InP layer 104 by MOVPE. At this time, since the mask 107 functions as a selective growth mask, the AlGaInAs layer 108 and the InP layer 109 grow only on the n-InP layer 104. For example, the composition wavelength of the AlGaInAs layer 108 is 1.15 μm, the thickness is 250 nm, and the thickness of the InP layer 109 is 250 nm.

  Next, as shown in FIG. 17, the mask 107 is removed. Thereafter, a p-type p-InP clad layer 110 doped with Zn and a p-type p-GaInAs contact layer 111 doped with Zn are formed on the p-InP clad layer 106 and the InP layer 109 by MOVPE. . For example, the thickness of the p-InP cladding layer 110 is 2.5 μm, and the thickness of the p-GaInAs contact layer 111 is 300 nm.

Subsequently, as illustrated in FIG. 18, a covering portion 112 a covering a region where the main waveguide 151 is to be formed and a covering portion 112 b covering a region where the sub waveguide 152 is to be formed are formed on the p-GaInAs contact layer 111. A mask 112 having the above is formed. In the formation of the mask 112, for example, a SiO ₂ film having a thickness of 400 nm is formed in a stripe shape as the covering portions 112a and 112b by CVD and photolithography. For example, the width of the covering portion 112a is 1 μm, the width of the covering portion 112b is 3 μm, and the interval between the covering portions 112a and 112b is 1.5 μm. The covering portions 112a and 112b also include a pattern for forming the GADC 153. For example, as a pattern for forming the GADC 153, a pattern having a period of 37.5 μm and an unevenness of 0.6 μm is formed.

  Next, as shown in FIG. 19, the compound semiconductor layer on the n-InP substrate 101 is etched by a dry etching method using the mask 112 as an etching mask. At this time, the surface of the n-InP substrate 101 is also dug by about 0.7 μm. As a result, the mesa structure 141a below the covering portion 112a and the mesa structure 141b below the covering portion 112b are formed in stripes.

  Thereafter, as shown in FIG. 20, a current confinement layer 113 is formed on the n-InP substrate 101 by the MOVPE method. As the current confinement layer 113, for example, a semi-insulating InP layer doped with Fe is formed. At this time, since the mask 112 functions as a selective growth mask, the current confinement layer 113 grows only on the n-InP substrate 101.

  Subsequently, as shown in FIG. 21, the mask 112 is removed. The mask 112 can be removed with, for example, hydrofluoric acid. Next, in the p-GaInAs contact layer 111, the part included in the active region 121 is left, and the other part is removed by photolithography and etching.

Thereafter, as shown in FIG. 22, a passivation film 114 is formed on the entire surface. For example, a SiO ₂ film is formed as the passivation film 114. Subsequently, an opening that exposes the p-GaInAs contact layer 111 is formed in the passivation film 114, and a p-electrode 115 that is in contact with the p-GaInAs contact layer 111 is formed on the passivation film 114 through the opening. Further, an n electrode 116 is formed on the back surface of the n-InP substrate 101. Next, an antireflection film 117 is formed on the end surface on the front end surface side distributed reflector region 123 side, and an antireflection film 118 is formed on the end surface on the distributed reflector region 122 side.

  In this manner, the optical semiconductor element (semiconductor laser) according to the first embodiment can be manufactured.

  In addition, as shown in FIG. 23, the front end surface side distributed reflector area | region 123 does not need to be provided. Comparing the structure in which the front end face side distributed reflector region 123 is provided with the structure in which the front end face side distributed reflector region 123 is not provided, the former has the advantage that feedback is increased, the oscillation threshold is lowered, and high-speed operation is possible. The latter has the advantage that a high light output can be obtained.

(Second Embodiment)
Next, a second embodiment will be described. FIG. 24 is a diagram showing a semiconductor laser according to the second embodiment.

  The semiconductor laser according to the second embodiment is divided into an active region 221, a GADC region 224, and a distributed reflector region 222, as shown in FIG. Further, in the light guide direction, the active region 221, the GADC region 224, and the distributed reflector region 222 are arranged side by side in order from the output end face side. For example, the active region 221 has a length of 150 μm, the GADC region 124 has a length of 100 μm, and the distributed reflector region 222 has a length of 200 μm. The semiconductor laser includes a main waveguide 251 that is continuous over the active region 221, the GADC region 124, and the distributed reflector region 222, and further includes a sub-waveguide 252 that is spaced apart from the main waveguide 251. ing. The main waveguide 251 and the sub waveguide 252 are optically coupled to each other by the GADC 253 provided in the GADC region 224.

For example, a diffraction grating 232 having a period Λ ₁ of 236.055 nm is provided in a portion of the main waveguide 251 located in the active region 221. Further, a portion of the main waveguide 251 located in the distributed reflector region 222 is provided with a long-period diffraction grating 231b having a longer period than that of the portion located in the active region 221. The period Λ ₂ of the long-period diffraction grating 231b is, for example, 236.436 nm. On the other hand, the sub-waveguide 252 is provided with a short-period diffraction grating 231a having the same period as the portion of the main waveguide 251 located in the active region 221. The depths of the diffraction grating 232, the short period diffraction grating 231a, and the long period diffraction grating 231b are, for example, 100 nm. In the present embodiment, the width of the main waveguide 251 is 1.5 μm, and the width of the sub waveguide 252 is 4 μm. Therefore, the equivalent refractive index neq ₁ of the active layer included in the main waveguide 251 is included in the sub waveguide 252. This is different from the equivalent refractive index neq ₂ of the active layer. The period Λ _GADC of the _{GADC 253} is “λ ₂ / (neq ₂ −neq ₁ )”.

  The effect similar to 1st Embodiment can be acquired also by such 2nd Embodiment.

  Next, a semiconductor laser manufacturing method according to the second embodiment will be described. 25 to 36 are perspective views showing the semiconductor laser manufacturing method according to the second embodiment in the order of steps.

  First, as shown in FIG. 25, a diffraction grating mask 202 is formed on an n-InP substrate 201 doped with an n-type impurity by using an electron beam resist (for example, ZEP520 manufactured by Nippon Zeon Co., Ltd.). Form. At this time, the diffraction grating mask 202 includes a diffraction grating pattern 202a for the short period diffraction grating 231a, a diffraction grating pattern 202b for the long period diffraction grating 231b, and a diffraction grating pattern 202c for the diffraction grating 232. In the GADC region 224, the n-InP substrate 201 is exposed.

  Next, as shown in FIG. 26, the diffraction grating 232, the short-period diffraction grating 231a, and the long grating are formed on the surface of the n-InP substrate 201 by RIE using the diffraction grating mask 202 as an etching mask and using a mixed gas of ethane and hydrogen. A periodic diffraction grating 231b is formed. That is, the diffraction grating patterns 202 a to 202 c of the diffraction grating mask 202 are transferred to the n-InP substrate 201.

  Thereafter, as shown in FIG. 27, the diffraction grating masks 202a, 202b and 202c are removed. Subsequently, an n-GaInAsP guide layer 203 doped with an n-type impurity, an n-InP layer 204 doped with an n-type impurity, a quantum well active layer 205, and a p-type impurity are doped on the n-InP substrate 201. The p-InP clad layer 206 thus formed is formed by the MOVPE method. For example, the composition wavelength of the n-GaInAsP guide layer 203 is 1.30 μm, the thickness is 120 nm, the thickness of the n-InP layer 204 is 20 nm, and the thickness of the p-InP cladding layer 206 is 250 nm. The quantum well active layer 205 includes, for example, 15 undoped GaInAsP quantum well layers and an undoped GaInAsP barrier layer interposed therebetween. For example, the thickness of the quantum well layer is 5.1 nm, the amount of compressive strain is 1.2%, the composition wavelength of the barrier layer is 1.20 μm, and the thickness is 10 nm. The quantum well active layer 205 also includes an undoped GaInAsP SCH layer that sandwiches these quantum well layers and barrier layers from above and below. For example, the composition wavelength of the SCH layer is 1.15 μm and the thickness is 20 nm. The emission wavelength of the quantum well active layer 205 is 1550 nm.

Next, as shown in FIG. 28, a mask 207 is formed on the p-InP cladding layer 206 so as to cover the active region 221 and expose the GADC region 124 and the distributed reflector region 222. As the mask 207, for example, a SiO ₂ film having a thickness of 400 nm is formed by CVD and photolithography.

  29, the p-InP cladding layer 206 and the quantum well active layer 205 are etched using the mask 207 as an etching mask to expose the surface of the n-InP layer 204.

  Subsequently, as illustrated in FIG. 30, an undoped GaInAsP layer 208 and an undoped InP layer 209 are formed on the n-InP layer 204 by the MOVPE method. At this time, since the mask 207 functions as a selective growth mask, the GaInAsP layer 208 and the InP layer 209 grow only on the n-InP layer 204. For example, the composition wavelength of the GaInAsP layer 208 is 1.25 μm, the thickness is 230 nm, and the thickness of the InP layer 209 is 250 nm.

  Next, as shown in FIG. 31, the mask 207 is removed. Thereafter, a p-type p-InP clad layer 210 doped with Zn and a p-type p-GaInAs contact layer 211 doped with Zn are formed on the p-InP clad layer 206 and the InP layer 209 by MOVPE. . For example, the thickness of the p-InP cladding layer 210 is 2.5 μm, and the thickness of the p-GaInAs contact layer 211 is 300 nm.

Subsequently, as illustrated in FIG. 32, on the p-GaInAs contact layer 211, a covering portion 212a covering a region where the main waveguide 251 is to be formed and a covering portion 212b covering a region where the sub waveguide 252 is to be formed are covered. A mask 212 having the above is formed. In the formation of the mask 212, for example, a SiO ₂ film having a thickness of 400 nm is formed in stripes as the covering portions 212a and 212b by CVD and photolithography. For example, the width of the covering portion 212a is 1.5 μm, the width of the covering portion 212b is 4 μm, and the interval between the covering portions 212a and 212b is 1.8 μm. The covering portions 212a and 212b also include a pattern for forming the GADC 253. For example, as a pattern for forming the GADC 253, a pattern having a period of 42.5 μm and an unevenness of 0.6 μm is formed.

  Next, as shown in FIG. 33, the compound semiconductor layer on the n-InP substrate 201 is etched by a dry etching method using the mask 212 as an etching mask. At this time, the surface of the n-InP substrate 201 is also dug by about 0.7 μm. As a result, the mesa structure 241a below the covering portion 212a and the mesa structure 241b below the covering portion 212b are formed in stripes.

  Thereafter, as shown in FIG. 34, a current confinement layer 213 is formed on the n-InP substrate 201 by MOVPE. As the current confinement layer 213, for example, a semi-insulating InP layer doped with Fe is formed. At this time, since the mask 212 functions as a selective growth mask, the current confinement layer 213 grows only on the n-InP substrate 201.

  Subsequently, as shown in FIG. 35, the mask 212 is removed. The masks 212a and 212b can be removed with, for example, hydrofluoric acid. Next, in the p-GaInAs contact layer 211, the part included in the active region 221 is left, and the other part is removed by photolithography and etching.

Thereafter, as shown in FIG. 36, a passivation film 214 is formed on the entire surface. For example, a SiO ₂ film is formed as the passivation film 214. Subsequently, an opening exposing the p-GaInAs contact layer 211 is formed in the passivation film 214, and a p-electrode 215 in contact with the p-GaInAs contact layer 211 is formed on the passivation film 114 through the opening. Further, an n electrode 216 is formed on the back surface of the n-InP substrate 201. Next, an antireflection film 217 is formed on the end surface on the active region 221 side, and an antireflection film 218 is formed on the end surface on the distributed reflector region 222 side.

  Thus, the optical semiconductor device (semiconductor laser) according to the second embodiment can be manufactured.

  As shown in FIG. 37, a front end face side distributed reflector region 223 may be provided as in the first embodiment. Comparing the structure provided with the front end face side distributed reflector region 223 with the structure not provided, the former has the advantage that feedback is increased, the oscillation threshold is lowered, and high-speed operation is possible. The latter has the advantage that a high light output can be obtained.

(Third embodiment)
Next, a third embodiment will be described. FIG. 38 is a diagram showing a semiconductor laser according to the third embodiment.

  As shown in FIG. 38, the semiconductor laser according to the third embodiment is divided into an active region 321, a GADC region 324, a distributed reflector region 322, and a front end face side distributed reflector region 323. Further, in the light guide direction, a front end face side distributed reflector region 323, an active region 321, a GADC region 324, and a distributed reflector region 322 are arranged side by side in order from the output end face side. For example, the front end face side distributed reflector region 323 has a length of 25 μm, the active region 321 has a length of 100 μm, the GADC region 124 has a length of 100 μm, and the distributed reflector region 322 has a length of 200 μm. That is, the front end face side distributed reflector region 323 is shorter than the distributed reflector region 322. The semiconductor laser includes a main waveguide 351 continuous over the front end face side distributed reflector region 323, the active region 321, and the distributed reflector region 322, and further, a sub-guide disposed apart from the main waveguide 351. A waveguide 352 is also included. The main waveguide 351 and the sub waveguide 352 are optically coupled to each other by the GADC 353 provided in the GADC region 324. In the first embodiment and the second embodiment, the sub waveguide 152 or 252 is located in the same plane as the main waveguide 151 or 251, whereas in the third embodiment, the sub waveguide 352 includes the sub waveguide 352. It is located above the main waveguide 351.

For example, a diffraction grating 332 having a period of 199.505 nm is provided in a portion of the main waveguide 351 located in the active region 321, the front end face side distributed reflector region 323, or the GADC region 324. The diffraction grating 332 includes a λ / 4 phase shift unit 333 having a phase of π radians (corresponding to λ / 4 shift). Further, in the portion of the main waveguide 351 located in the distributed reflector region 322, a short period diffraction grating 331a having the same period as that of the portion located in the active region 321, the front end face side distributed reflector region 323 or the GADC region 324 is provided. Is provided. That is, the main waveguide 351 is provided with a diffraction grating having a period Λ ₁ of, for example, 199.505 nm, except for the λ / 4 phase shift unit 333. On the other hand, the sub-waveguide 352 is provided with a long-period diffraction grating 331b having a longer period than that of the main waveguide 351. The period Λ ₂ of the long-period diffraction grating 331b is, for example, 199.886 nm. The depths of the diffraction grating 332, the short period diffraction grating 331a, and the long period diffraction grating 331b are, for example, 100 nm. In this embodiment, although the details will be described later, the compound semiconductor layer included in the main waveguide 351 is different from the compound semiconductor layer included in the sub-waveguide 352. For this reason, the active layer included in the main waveguide 351 is different. The equivalent refractive index neq ₁ is different from the equivalent refractive index neq _{2 of the} active layer included in the sub-waveguide 352. The period Λ _GADC of the _{GADC 353} is “λ ₂ / (neq ₂ −neq ₁ )”.

  The same effects as those of the first embodiment and the second embodiment can be obtained by the third embodiment.

  Next, a method for manufacturing an optical semiconductor element (semiconductor laser) according to the third embodiment will be described. 39 to 56 are perspective views showing the method of manufacturing the optical semiconductor element according to the third embodiment in the order of steps.

  First, as shown in FIG. 39, a diffraction grating mask 302 is formed on an n-InP substrate 301 doped with an n-type impurity by using an electron beam resist (for example, ZEP520 manufactured by Nippon Zeon Co., Ltd.) by an electron beam exposure method. Form. At this time, the diffraction grating mask 302 includes a diffraction grating pattern 302 a for the short period diffraction grating 331 a and a diffraction grating pattern 302 c for the diffraction grating 332. The diffraction grating pattern 302c includes a λ / 4 phase shift unit 302s corresponding to the λ / 4 phase shift unit 333.

  Next, as shown in FIG. 40, a diffraction grating 332 and a short-period diffraction grating 331a are formed on the surface of the n-InP substrate 301 by RIE using a mixed gas of ethane and hydrogen using the diffraction grating mask 302 as an etching mask. To do. That is, the diffraction grating patterns 302 a and 302 c of the diffraction grating mask 302 are transferred to the n-InP substrate 301.

  Thereafter, as shown in FIG. 41, the diffraction grating mask 302 is removed. Subsequently, an n-GaInAsP guide layer 303 doped with an n-type impurity, an n-InP layer 304 doped with an n-type impurity, a quantum well active layer 305, and a p-type impurity are doped on the n-InP substrate 301. The p-InP clad layer 306 thus formed is formed by the MOVPE method. For example, the composition wavelength of the n-GaInAsP guide layer 303 is 1.25 μm, the thickness is 120 nm, the thickness of the n-InP layer 304 is 20 nm, and the thickness of the p-InP cladding layer 306 is 250 nm. The quantum well active layer 305 includes, for example, 15 undoped AlGaInAs quantum well layers and an undoped AlGaInAs barrier layer interposed therebetween. For example, the thickness of the quantum well layer is 6 nm, the amount of compressive strain is 1.2%, the composition wavelength of the barrier layer is 1.05 μm, and the thickness is 10 nm. The quantum well active layer 305 also includes an undoped AlGaInAs SCH layer that sandwiches the quantum well layer and the barrier layer from above and below. For example, the composition wavelength of the SCH layer is 1.05 μm and the thickness is 20 nm. The emission wavelength of the quantum well active layer 305 is 1310 nm.

Next, as shown in FIG. 42, a mask 307 is formed on the p-InP cladding layer 306 to cover the active region 321 and expose the front end face side distributed reflector region 323, the GADC region 324, and the distributed reflector region 322. . As the mask 307, for example, a 400 nm thick SiO ₂ film is formed by CVD and photolithography.

  Thereafter, as shown in FIG. 43, using the mask 307 as an etching mask, the p-InP cladding layer 306 and the quantum well active layer 305 are etched to expose the surface of the n-InP layer 304.

  Subsequently, as shown in FIG. 44, an undoped AlGaInAs layer 308 and an undoped InP layer 309 are formed on the n-InP layer 304 by MOVPE. At this time, since the mask 307 functions as a selective growth mask, the AlGaInAs layer 308 and the InP layer 309 grow only on the n-InP layer 304. For example, the composition wavelength of the AlGaInAs layer 308 is 1.15 μm, the thickness is 250 nm, and the thickness of the InP layer 309 is 250 nm.

  Next, as shown in FIG. 45, the mask 307 is removed. Thereafter, a p-GaInAsP guide layer 310 doped with a p-type impurity is formed on the p-InP cladding layer 306 and the InP layer 309 by MOVPE. For example, the composition wavelength of the p-GaInAsP guide layer 310 is 1.25 μm and the thickness is 120 nm.

Thereafter, as shown in FIG. 46, a mask 311 is formed on the p-GaInAsP guide layer 310 to expose the active region 321 and the front end face side distributed reflector region 323 and cover the GADC region 324 and the distributed reflector region 322. . As the mask 311, for example, a SiO ₂ film having a thickness of 400 nm is formed by CVD and photolithography.

  Subsequently, as shown in FIG. 47, using the mask 311 as an etching mask, the p-GaInAsP guide layer 310 is etched to expose the surfaces of the p-InP cladding layer 306 and the InP layer 309.

  Next, as shown in FIG. 48, a p-InP layer 312 doped with a p-type impurity is formed on the p-InP cladding layer 306 and the InP layer 309 by the MOVPE method. At this time, since the mask 311 functions as a selective growth mask, the p-InP layer 312 grows only on the p-InP cladding layer 306 and the InP layer 309. For example, the thickness of the p-InP layer 312 is 120 nm.

  Thereafter, as shown in FIG. 49, the mask 311 is removed. Subsequently, a diffraction grating mask 313 is formed on the p-GaInAsP guide layer 310 and the p-InP layer 312 using an electron beam resist (for example, ZEP520 manufactured by Nippon Zeon Co., Ltd.) by an electron beam exposure method. At this time, the diffraction grating mask 313 includes a diffraction grating pattern 313a for the long-period diffraction grating 331b, a diffraction grating pattern 313b for the GADC 353, and a covering portion 313c that covers the active region 321 and the front end face side distributed reflector region 323. Make it.

  Subsequently, as shown in FIG. 50, the long-period diffraction grating 331b and the GADC 153 are formed on the surface of the p-GaInAsP guide layer 310 by RIE using a mixed gas of ethane and hydrogen using the diffraction grating mask 313 as an etching mask. To do. That is, the diffraction grating patterns 313 a and 313 b of the diffraction grating mask 313 are transferred to the p-GaInAsP guide layer 310 and the p-InP layer 312.

  Next, as shown in FIG. 51, the diffraction grating mask 313 is removed. Thereafter, a p-type p-InP clad layer 314 doped with Zn and a p-type p-GaInAs contact layer 315 doped with Zn are formed on the p-GaInAsP guide layer 310 and the p-InP layer 312. For example, the thickness of the p-InP cladding layer 314 is 2.5 μm, and the thickness of the p-GaInAs contact layer 315 is 300 nm.

Subsequently, as shown in FIG. 52, a mask 316 is formed on the p-GaInAs contact layer 315 so as to cover a region where the main waveguide 351 and the sub waveguide 352 are to be formed. As the mask 316, for example, a SiO ₂ film having a thickness of 400 nm and a width of 1.5 μm is formed by a CVD method and photolithography.

  Next, as shown in FIG. 53, the compound semiconductor layer on the n-InP substrate 301 is etched by a dry etching method using the mask 316 as an etching mask. At this time, the surface of the n-InP substrate 301 is also dug by about 0.7 μm. As a result, the mesa structure 341 below the mask 316 is formed in a stripe shape.

  Thereafter, as shown in FIG. 54, a current confinement layer 317 is formed on the n-InP substrate 301 by the MOVPE method. As the current confinement layer 317, for example, a semi-insulating InP layer doped with Fe is formed. At this time, since the mask 316 functions as a selective growth mask, the current confinement layer 317 grows only on the n-InP substrate 301.

  Subsequently, as shown in FIG. 55, the mask 316 is removed. The mask 316 can be removed with, for example, hydrofluoric acid. Next, in the p-GaInAs contact layer 315, the part included in the active region 321 is left, and the other part is removed by photolithography and etching.

Thereafter, as shown in FIG. 56, a passivation film 318 is formed on the entire surface. For example, a SiO ₂ film is formed as the passivation film 318. Subsequently, an opening exposing the p-GaInAs contact layer 315 is formed in the passivation film 318, and a p-electrode 319 in contact with the p-GaInAs contact layer 315 is formed on the passivation film 318 through the opening. Further, an n electrode 320 is formed on the back surface of the n-InP substrate 301. Next, an antireflection film 342 is formed on the end surface on the front end face side distributed reflector region 323 side, and an antireflection film 343 is formed on the end surface on the distributed reflector region 322 side.

  In this manner, the optical semiconductor element (semiconductor laser) according to the third embodiment can be manufactured.

  As shown in FIG. 57, the front end face side distributed reflector region 323 may not be provided. Comparing the structure in which the front end face side distributed reflector region 323 is provided with the structure in which the front end face side distributed reflector region 323 is not provided, the former has the advantage that feedback is increased, the oscillation threshold is lowered, and high-speed operation is possible. The latter has the advantage that a high light output can be obtained.

  When the inventors of the present invention have verified the characteristics of the semiconductor lasers of these embodiments, no mode jump occurs at the oscillation threshold in any of the embodiments, and mode jump occurs up to a drive current of at least 150 mA. Therefore, stable single longitudinal mode operation was obtained.

(Fourth embodiment)
Next, a fourth embodiment will be described. The fourth embodiment relates to an optical semiconductor module including the semiconductor laser of any of the first to third embodiments. FIG. 58 is a diagram illustrating a configuration of an optical semiconductor module according to the fourth embodiment.

  In the optical semiconductor module according to the present embodiment, as shown in FIG. 58, the semiconductor laser 431 according to any of the first to third embodiments includes a coaxial package 433 having a pair of lead pins 436 and a pair of lead pins 437. It is mounted on. A light receiving element 432 for back monitoring is installed on the rear end face side of the semiconductor laser 431. The pair of lead pins 436 is connected to the semiconductor laser 431, and the pair of lead pins 437 is connected to the light receiving element 432. The lead pin (terminal) 436 is connected to an electrical signal source that drives the semiconductor laser 431. On the other hand, the lead pin 437 is connected to a monitor device that monitors the output of the semiconductor laser 431. Further, a lens 435 for condensing the laser beam 431L emitted from the front end surface of the semiconductor laser 431 and making it incident on the optical fiber is provided on the cap 434. Here, the lens 435 functions as an optical output port for outputting the signal light emitted from the semiconductor laser 431.

  The material constituting the semiconductor laser is not limited to the above. For example, in the first and third embodiments, an AlGaInAs-based compound semiconductor is used for the quantum well active layer, and in the second embodiment, a GaInAsP-based compound semiconductor is used. In the third embodiment, a GaInAsP-based compound semiconductor may be used, and in the second embodiment, an AlGaInAs-based compound semiconductor may be used. Further, a bulk semiconductor may be used for the active layer instead of the quantum well. Further, the conductivity type of each semiconductor may be a conductivity type opposite to that of the above embodiment. For example, a p-type conductive substrate may be used, and the conductivity type of each compound semiconductor layer may be a reverse conductivity type. Further, a semi-insulating substrate such as a silicon substrate is used as the substrate, and the substrate may be manufactured by a bonding method.

  In the above embodiment, a current confinement structure using a semi-insulating material is employed, but in any case, a current confinement structure having a pnpn thyristor structure may be employed. Further, although the embedded waveguide is used in the above embodiment, a waveguide having another structure such as a ridge waveguide may be used.

  In the above embodiment, the surface diffraction grating is employed, but an embedded diffraction grating may be employed. Furthermore, in the above embodiment, the diffraction grating is loaded on the substrate side with respect to the active layer, but the diffraction grating may be loaded on the opposite side of the substrate. Further, the position of the phase shift portion is not limited to the center of the active region, and can be arranged at a position other than the center of the active region within the design range within the active region. In the above-described embodiment, the value of the coupling coefficient is the same between the active region and the distributed reflector region, but they may be different from each other. The amount of phase shift by the phase shift unit is not limited to λ / 4, and may be any value within the design range. Moreover, there may not be a phase shift part like 2nd Embodiment.

  Further, in the above embodiment, among the diffraction gratings in the distributed reflector region, those having a period different from the period of the diffraction grating in the active region are diffracted longer than the period of the diffraction grating in the active region. Although it is a grating, a short-period diffraction grating may be used depending on the combination of the coupling coefficient of the diffraction grating and the distributed reflector region, and the propagation constants of the main waveguide and the sub-waveguide. The reflection band of the distributed reflector region depends on the coupling coefficient of the diffraction grating and the distributed reflector region, and the center wavelength of the reflection spectrum is determined by the propagation constants of the main waveguide and the sub-waveguide. For this reason, depending on the combination of the coupling coefficient of the diffraction grating and the distributed reflector region, and the propagation constants of the main waveguide and the sub-waveguide, the short-period diffraction grating can achieve more effective superposition of the two reflection spectra. It may be preferable.

  In the third embodiment, the sub waveguide may be located closer to the substrate than the main waveguide. Similarly to the second embodiment, the period of the portion located in the distributed reflector region of the diffraction grating provided in the main waveguide is longer than the portion located in the active region, and is provided in the sub-waveguide. The period of the diffraction grating may be substantially equal to the period of the portion located in the active region in the diffraction grating provided in the main waveguide.

  In the above embodiment, the GADC is formed on the sub-waveguide side, but the GADC may be formed on the main waveguide side.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1)
An active region loaded with a diffraction grating; and
A distributed reflector region that includes two waveguides having diffraction gratings with different periods from each other, and reflects the light generated and input to the active region toward the active region;
A diffraction grating type directional coupler provided between the active region and the distributed reflector region and coupling the two waveguides and the waveguide in the active region;
A semiconductor laser comprising:

(Appendix 2)
Between the two waveguides, there is a wavelength where the reflectance on the long wave side of the reflection spectrum of one waveguide is in the range of 40% to 60% and the reflectance on the short wave side of the reflection spectrum of the other waveguide. 2. The semiconductor laser as set forth in appendix 1, wherein the wavelengths in the range of 40% to 60% coincide with each other.

(Appendix 3)
3. The semiconductor laser according to appendix 1 or 2, wherein the two waveguides are located in the same plane with respect to the surface of the substrate.

(Appendix 4)
3. The semiconductor laser according to appendix 1 or 2, wherein the two waveguides are positioned in a direction perpendicular to the surface of the substrate.

(Appendix 5)
5. The semiconductor laser according to any one of appendices 1 to 4, further comprising an antireflection film formed on both end faces.

(Appendix 6)
Any one of Supplementary notes 1 to 5, further comprising a front end face side distributed reflector region that is provided on a side opposite to the distributed reflector region with respect to the active region and shorter than the distributed reflector region. The semiconductor laser described in 1.

(Appendix 7)
One of the two waveguides is continuous with the waveguide in the active region,
7. The semiconductor laser according to claim 1, wherein a period of the diffraction grating of the one waveguide coincides with a period of the waveguide of the active region.

(Appendix 8)
One of the two waveguides is continuous with the waveguide in the active region,
7. The semiconductor laser according to any one of appendices 1 to 6, wherein a period of the diffraction grating of the other waveguide coincides with a period of the waveguide of the active region.

(Appendix 9)
The semiconductor laser according to any one of appendices 1 to 8, wherein the active region and the distributed reflector region have an active layer of an AlGaInAs compound semiconductor or a GaInAsP compound semiconductor.

(Appendix 10)
10. The semiconductor laser according to any one of appendices 1 to 9, wherein the active region has a phase shift portion.

(Appendix 11)
Forming an active region loaded with a diffraction grating above the substrate;
Forming a distributed reflector region on the substrate including two waveguides provided with diffraction gratings having different periods from each other, and reflecting the light generated and input in the active region toward the active region;
Forming a diffraction grating type directional coupler provided between the active region and the distributed reflector region and coupling the two waveguides and the waveguide in the active region;
A method of manufacturing a semiconductor laser, comprising:

(Appendix 12)
Between the two waveguides, there is a wavelength where the reflectance on the long wave side of the reflection spectrum of one waveguide is in the range of 40% to 60% and the reflectance on the short wave side of the reflection spectrum of the other waveguide. 12. The method of manufacturing a semiconductor laser as set forth in appendix 11, wherein a wavelength within a range of 40% to 60% is made to coincide with each other.

(Appendix 13)
13. The method of manufacturing a semiconductor laser according to appendix 11 or 12, wherein the two waveguides are positioned in the same plane with respect to the surface of the substrate.

(Appendix 14)
13. The method of manufacturing a semiconductor laser according to appendix 11 or 12, wherein the two waveguides are positioned in a direction perpendicular to the surface of the substrate.

(Appendix 15)
15. The method of manufacturing a semiconductor laser according to any one of appendices 11 to 14, further comprising a step of forming an antireflection film on both end faces.

(Appendix 16)
Any one of appendixes 11 to 15, further comprising a step of forming a front end face side distributed reflector region shorter than the distributed reflector region on a side opposite to the distributed reflector region with respect to the active region. 2. A method for manufacturing a semiconductor laser according to item 1.

(Appendix 17)
One of the two waveguides is continuous with the active region waveguide;
17. The method for manufacturing a semiconductor laser according to any one of appendices 11 to 16, wherein a period of the diffraction grating of the one waveguide is matched with a period of the waveguide of the active region.

(Appendix 18)
One of the two waveguides is continuous with the active region waveguide;
17. The method of manufacturing a semiconductor laser according to any one of appendices 11 to 16, wherein the period of the diffraction grating of the other waveguide is matched with the period of the waveguide of the active region.

(Appendix 19)
Any one of appendices 11 to 18, wherein the step of forming the active region and the step of forming the distributed reflector region include a step of forming an active layer of an AlGaInAs compound semiconductor or a GaInAsP compound semiconductor. A method for producing a semiconductor laser according to the item.

(Appendix 20)
20. The method of manufacturing a semiconductor laser according to any one of appendices 11 to 19, wherein the step of forming the active region includes a step of forming a phase shift portion.

121, 221, 321: active region 122, 222, 322: distributed reflector region 123, 223, 323: front end surface reflector region 124, 224, 324: diffraction grating coupled directional coupler (GADC) region 131 a, 231 a 331a: short period diffraction grating 131b, 231b, 331b: long period diffraction grating 132, 232, 332: diffraction grating 133, 333: λ / 4 phase shift unit 151, 251 and 351: main waveguide 152, 252 and 352: sub Waveguides 153, 253, 353: GADC

Claims (10)

An active region loaded with a diffraction grating; and
A distributed reflector region that includes two waveguides having diffraction gratings with different periods from each other, and reflects the light generated and input to the active region toward the active region;
A diffraction grating type directional coupler provided between the active region and the distributed reflector region and coupling the two waveguides and the waveguide in the active region;
A semiconductor laser comprising:   Between the two waveguides, there is a wavelength where the reflectance on the long wave side of the reflection spectrum of one waveguide is in the range of 40% to 60% and the reflectance on the short wave side of the reflection spectrum of the other waveguide. 2. The semiconductor laser according to claim 1, wherein the wavelengths in the range of 40% to 60% coincide with each other.   3. The semiconductor laser according to claim 1, wherein the two waveguides are located in the same plane with respect to the surface of the substrate.   3. The semiconductor laser according to claim 1, wherein the two waveguides are positioned in a direction perpendicular to the surface of the substrate.   5. The semiconductor laser according to claim 1, further comprising antireflection films formed on both end faces.   6. The device according to claim 1, further comprising a front end face side distributed reflector region that is provided on a side opposite to the distributed reflector region with respect to the active region and shorter than the distributed reflector region. The semiconductor laser according to item. One of the two waveguides is continuous with the waveguide in the active region;
7. The semiconductor laser according to claim 1, wherein a period of the diffraction grating of the one waveguide coincides with a period of the waveguide of the active region. One of the two waveguides is continuous with the waveguide in the active region,
7. The semiconductor laser according to claim 1, wherein a period of the diffraction grating of the other waveguide coincides with a period of the waveguide of the active region. Forming an active region loaded with a diffraction grating above the substrate;
Forming a distributed reflector region on the substrate including two waveguides provided with diffraction gratings having different periods from each other, and reflecting the light generated and input in the active region toward the active region;
Forming a diffraction grating type directional coupler provided between the active region and the distributed reflector region and coupling the two waveguides and the waveguide in the active region;
A method of manufacturing a semiconductor laser, comprising:   Between the two waveguides, there is a wavelength where the reflectance on the long wave side of the reflection spectrum of one waveguide is in the range of 40% to 60% and the reflectance on the short wave side of the reflection spectrum of the other waveguide. 10. The method of manufacturing a semiconductor laser according to claim 9, wherein the wavelengths in the range of 40% to 60% are made to coincide with each other.

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