JP4961732B2 - Light modulator integrated light source - Google Patents

Description

  The present invention relates to an optical modulator integrated light source in which a light source such as a laser and an electroabsorption optical intensity modulator are monolithically integrated.

  With the explosive demand for broadband multimedia communication services such as the Internet, the development of larger capacity and higher performance optical fiber communication systems is required. This light source device, which is a key component, especially light source devices for trunk optical fiber communication systems with long transmission distances, is capable of high-speed modulation, as well as light intensity modulation that causes optical waveform degradation after long-distance transmission. It is required that phase modulation (wavelength chirping) be suppressed as much as possible.

  Among these, electroabsorption-type optical intensity modulators that apply electroabsorption effects that change the optical absorption coefficient according to the applied electric field, such as the Franz-Keldish effect of bulk compound semiconductors and the quantum confined Stark effect of multiple quantum well structures, ,Attention has been paid. This electroabsorption optical intensity modulator is capable of high-speed response and has a smaller wavelength chirping at the time of optical intensity modulation than when directly modulating the drive current of the semiconductor laser diode. Furthermore, the electroabsorption optical intensity modulator can be monolithically integrated with a light source device typified by a distributed feedback semiconductor laser diode (DFB-LD), and can be expected to reduce the size and cost of the light source module. It has excellent features as a light source device (Patent Literature 1, Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, Patent Literature 6, Patent Literature 7, Patent Literature 8, Patent Literature 9, Patent Literature 10, see Patent Document 11). At present, an optical module equipped with an integrated light source (optical modulator integrated light source) monolithically integrated with a DFB-LD and an electroabsorption optical intensity modulator is a core optical fiber communication system of 2.5 to 10 Gb / s class. Many have been introduced as light sources.

  However, in the light modulator integrated light source, there are problems that cannot be avoided because of the monolithic integrated device as described below. A leakage current flowing through a finite resistance (hereinafter referred to as separation resistance) between the laser region and the optical modulator region (hereinafter referred to as isolation region) changes the number of carriers that should be injected into the active layer in the laser region. End up. For this reason, the separation resistor causes not only the light output fluctuation but also the oscillation wavelength fluctuation (FM modulation) through the effective refractive index change proportional to the carrier density change. The latter is wavelength chirping itself when directly modulating the LD, and is a serious problem that cancels out the low chirp operation in the optical modulator region.

  Since the separation resistance is given by the parallel combined resistance of the electrode contact layer and the cladding layer in the separation region, it is considered that the electrode contact layer with higher conductivity is removed over the entire separation region as a measure for improving the problem due to the separation resistance. It is done. However, the isolation resistance that can be realized by this method is at most several kΩ, which is insufficient in practice for suppressing the oscillation wavelength fluctuation described above. Therefore, generally, an improvement measure such as etching to a part of the cladding layer or ion implantation of an element that impairs conductivity is used in combination with the above-described improvement measure.

Japanese Patent No. 3254053 JP 2000-277869 A JP 2001-053387 A JP 2003-202529 A JP 63-186210 A Japanese Patent Laid-Open No. 3-091279 JP-A-5-063179 JP-A-7-058310 Japanese Patent Laid-Open No. 9-121075 Japanese Patent Laid-Open No. 10-084166 Japanese Patent Laid-Open No. 11-163568

  In the optical modulator integrated light source, it is necessary to consider the influence of electron-hole pairs (hereinafter, photocarriers) generated by light absorption in the separation region in addition to the above-described problems. This is because the absorption between valence bands, which is proportional to the photocarrier density, changes not only the intensity of the signal light but also the refractive index felt by the signal light, so that the signal light is modulated to this phase while passing through the separation region. By receiving. A particular problem is that the distribution of the photocarriers dynamically changes by modulating the reverse bias voltage applied to the optical modulator region. Therefore, when the optical modulator region is driven, intensity modulation and phase modulation are preliminarily superimposed on the signal light before reaching the optical modulator region.

  In order to solve this problem, it is necessary not to generate photocarriers in the separation region or to devise a method in which the photocarrier distribution does not depend on the reverse bias voltage applied to the light modulator region. As the latter means, a method of making the potential distribution in the separation region constant in the longitudinal axis direction can be considered. Considering only the purpose of fixing the potential, as disclosed in Patent Document 1, a method of forming an electrode in the separation region and applying a fixed potential has been reported. However, if an electrode for fixing the potential of the separation region is provided, this electrode will undesirably short-circuit the optical modulator region and the laser region, which causes a problem of increasing leakage current. Can not. Since no particularly effective solution has been proposed for this problem, the light modulator integrated light source is actually used with the above-mentioned problems.

  The present invention has been made to solve the above-described problems, and the longitudinal distribution of the photocarriers generated in the separation region changes in accordance with the reverse bias voltage applied to the optical modulator region. The above-mentioned wavelength chirping problem caused by doing so is effectively improved without a special complicated process such as newly using a separate circuit element component, and the transmission characteristics of the optical modulator integrated light source are improved. The purpose is to do so.

An optical modulator integrated light source according to the present invention includes an optical waveguide layer made of a first conductivity type semiconductor formed on a lower cladding layer and an active layer formed in a light emitting region on the optical waveguide layer. A light absorption layer formed on the optical waveguide layer subsequent to the active layer, a light modulator region configured by a part of the light absorption layer and optically modulating the signal light oscillated from the light source, A separation region that is constituted by a part of the light absorption layer and is disposed between the light emitting region and the light modulator region, electrically separating the light emitting region and the light modulator region, the active layer, and the light absorption and an upper clad layer made of a semiconductor of a second conductivity type formed to cover the layer, at the upper cladding layer on the side of the light emitting region of the isolation region provided in contact with the light emitting region of the upper clad layer in the isolation region Less high resistance area, which has higher resistance than other parts The phrase is obtained as also provided. Accordingly, the potential of the region closer to the light modulator region in the separation region is substantially equal to the potential of the light modulator region, and the photocarriers generated here are more easily swept out to the external circuit than the connected electrodes.

In the optical modulator integrated light source, the light source is, for example, a semiconductor laser, or, for example, a semiconductor laser that oscillates in a single axis mode. In this case, a diffraction grating formed in the light emitting region is provided, and a resonator is constituted by this diffraction grating. In this case, the diffraction grating may be formed closer to the lower cladding layer than the active layer. The diffraction grating may be formed on the upper clad layer side from the active layer. The light source may be a semiconductor optical amplifier. The light modulator integrated light source further includes a first electrode formed on the upper cladding layer in the light emitting region and a second electrode formed on the upper cladding layer in the light modulator region. And the second electrode are separated by at least the separation region.

  In the light modulator integrated light source, the high resistance region may be formed by introducing impurities. Further, the high resistance region may be constituted by a groove formed in the light absorption layer. Further, the absorption edge of the semiconductor constituting the light absorption layer in the region where the isolation region is formed may have a shorter wavelength composition than the absorption edge of the semiconductor constituting the light absorption layer in the other region. .

  As described above, according to the present invention, in the upper cladding layer of the isolation region, a high resistance region having a higher resistance is provided on the light emitting region side. It is effectively improved without a special complicated process such as newly used, and an excellent effect is obtained that the transmission characteristics of the optical modulator integrated light source are improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A and 1B are a perspective view and a cross-sectional view showing a configuration example of an optical modulator integrated light source according to an embodiment of the present invention. FIG. 1B is a cross section horizontal (along) in the waveguide direction (longitudinal axis of the separation region) of the optical modulator integrated light source. FIG. 1B is a cross-sectional view of a region in a circle indicated by a wavy line in FIG.

  The optical modulator integrated light source shown in FIG. 1 includes an optical waveguide layer 103 having a first conductivity (first conductivity type) and an undoped active layer 104 on a substrate 101 on which a diffraction grating 102 is partially formed. Growing and forming. In addition, after removing the undoped active layer 104 in the region without the diffraction grating 102, the light modulation integrated light source shown in FIG. The undoped active layer 104 and the undoped light absorption layer 105 have a butt-coupled (butt = coupling) structure, and realize a highly efficient and low reflection coupling characteristic from the undoped active layer 104 to the undoped light absorption layer 105. ing. The undoped active layer 104 and the undoped light absorption layer 105 are buried with an upper cladding layer 106 having a second conductivity (second conductivity type). The substrate 101 becomes the lower cladding layer.

  Further, the laser region (light emitting region) 107 having the undoped active layer 104 and the optical modulator region 108 having undoped light absorption are electrically separated by the separation region 110. In order to suppress the influence of the leakage current between the laser region 107 and the optical modulator region 108 to a level that can be practically ignored, the separation region 110 has an electrode contact layer 109 (on the optical modulator region 108 side) from the position where both regions contact. The electrode) is partially removed by a certain length. Further, the isolation region 110 is provided with a high resistance region 111 in which the effective conductivity of the upper cladding layer 106 is partially reduced (effective resistivity is increased) by using, for example, an ion implantation technique. . The high resistance region 111 only needs to be provided on the laser region 107 side in the isolation region 110. The high resistance region 111 may be provided so as to substantially contact the laser region 107. The diffraction grating may be formed on the upper clad layer 106 side.

  In addition, the window structure 112 and the low reflection film 113 are provided in combination in order to suppress wavelength chirping caused by the residual end face reflection on the optical modulator region 108 side. On the other hand, a highly reflective film 114 is applied to the end face on the laser region 107 side. Note that the light absorption layer 105 in the separation region 110 may be formed so that the absorption edge has a shorter wavelength composition (high energy) than the light absorption layer 105 in the light modulation region 108. By doing in this way, attenuation of the signal light in the light absorption layer 105 in the separation region 110 can be suppressed.

  In the optical modulator integrated light source shown in FIG. 1, when a predetermined voltage is applied between the electrode 115 and the back electrode 117 to forward bias the laser region 107 and inject current into the undoped active layer 104, a single axis mode is obtained. It oscillates at. Further, by changing the reverse bias voltage applied to the light modulator region 108, the light absorption coefficient of the undoped light absorption layer 105 increases due to the electroabsorption effect, and the signal light emitted from the end surface on the light modulator region 108 side. The intensity can be modulated. In the above description, the semiconductor laser (DFB-LD) having a diffraction grating provided in the entire laser region as a resonator is used as the light source. However, another form of semiconductor laser may be used. . For example, a DBR (Distributed Bragg Reflector) -LD in which a diffraction grating is provided in a part of the laser region may be used. The same applies if the light source is composed of a semiconductor optical amplifier.

  Here, the above-described high resistance region 111 will be described in more detail. 2. Description of the Related Art Conventionally, a technique for isolating elements by increasing the resistance of a semiconductor material using an ion implantation technique has been used. This high resistance technology is promising as an element isolation technology because it can be applied to a wafer (semiconductor substrate) for which a growth process has been completed. However, even if the separation resistance of the separation region is increased to infinity, the potential distribution along the longitudinal axis of the separation region is linear as long as the conductivity (resistivity) in the longitudinal direction of the separation region is uniform. However, since the region where the photocarrier is discharged to the external circuit is limited, the problem of wavelength chirping due to the photocarrier generated in the separation region cannot be solved.

  On the other hand, the optical modulator integrated light source shown in FIG. 1 artificially creates a state in which the conductivity of the separation region 110 is not uniform in the longitudinal axis direction, so that most of the photocarriers generated in the separation region 110 can be easily formed. A structure that can be swept out is realized. Specifically, in the separation region 110 of the optical modulator integrated light source, a structure in which the conductivity of the upper cladding layer 106 is further lowered (the resistivity is further increased) is introduced on the laser region 107 side. This length is more effective as the portion to be increased in resistance is shorter. As a result, the potential of the region closer to the optical modulator region 108 in the separation region 110 becomes substantially equal to the potential of the optical modulator region 108, and the photocarriers generated here are the electrodes 116 of the optical modulator region 108. It is easy to be swept out to an external circuit via

  In addition, most of the potential difference between the laser region 107 and the optical modulator region 108 is almost received by the short portion of the isolation region 110 that is close to the laser region 107 side and has a high resistance. For this reason, even if the longitudinal distribution of the photocarrier changes according to the reverse bias voltage applied to the optical modulator region 108, this influence does not affect the entire separation region 110, but the high resistance of these regions. It remains almost only in the length of the resistance region 111. The shorter this length is, the smaller the phase change received by the signal light passing therethrough, the phase change received before the signal light reaches the optical modulator region 108, and further by driving the optical modulator region 108. The instantaneous angular frequency change can be suppressed to such a level that there is no practical problem.

  The length of the high resistance region 111 with respect to the length of the isolation region 110 is desirably ¼ or less of the entire length of the separation region 110, and preferably 1/10 or less in order to be more effective. Of course, the length and conductivity (resistivity) of the high resistance region 111 are appropriately set in order to suppress the influence of the leakage current to the laser region 107 when the optical modulator region 108 is driven to a practically negligible level. There is a need to. As this means, after removing the electrode contact layer 109 in the separation region 110, ion species that lower the conductivity (increase the resistivity) may be ion-implanted to the side closer to the laser region 107 of the separation region 110.

  Further, it is effective to remove a part by etching or to use these together. At this time, not only the conductivity (resistivity) of the upper cladding layer 106 is changed, but the conductivity of the layer showing conductivity among any of the buried layers is lowered (the resistivity is increased). Alternatively, in the case of ion implantation, the accelerating voltage may be adjusted to implant not only the upper cladding layer 106 in the isolation region but also the active layer 104 and the light absorption layer 105 below this ion species. Further, the resistance state of the high resistance region 111 does not need to be constant, and the closer to the laser region 107, the higher the resistance state 111 may be.

  Furthermore, it is also effective to remove the light absorption layer 105 in the isolation region 110 in order to suppress the number of photocarriers generated by light absorption. Since the structure may be considered to be basically the same as a window structure widely used in an optical modulator integrated light source, the influence of reflection at the discontinuous boundary concerned is estimated to be small enough to be ignored in practice. If the optical waveguide layer 103 is left in the separation region 110, the influence of reflection can be further suppressed.

  In this way, by changing the conductivity (resistivity) of the separation region 110 along the longitudinal axis direction and making the resistance closer to the laser region 107 side higher, the optical modulator region 108 side of the separation region 110. Can create a state that is approximately equal to the potential of the light modulator region 108. As a result, most of the photocarriers generated in the separation region 110 can be efficiently swept out from the electrode 116 in the optical modulator region 108 to an external circuit. Even if the longitudinal distribution of the photocarrier changes according to the reverse bias voltage applied to the optical modulator region 108, the length of the region (high resistance region 111) to be increased in resistance is also the full length of the isolation region 110. Compared to the case where the low efficiency of the separation region 110 is uniform, the phase change that the signal light receives can be suppressed. By these actions, wavelength chirping due to photocarriers generated in the separation region 110 of the optical modulator integrated light source is effectively suppressed, and as a result, an ideal optical fiber with small optical waveform deterioration after long-distance transmission. Transmission characteristics can be realized.

  Next, another configuration example of the optical modulator integrated light source in the embodiment of the present invention will be described. FIG. 2 is a perspective view (a) and a sectional view (b) showing a configuration example of another light modulator integrated light source according to the embodiment of the present invention. 2B is a horizontal (along) cross section in the waveguide direction (longitudinal axis of the separation region) of the optical modulator integrated light source. FIG. 2B is a cross-sectional view of a region within a circle indicated by a wavy line in FIG.

  The optical modulator integrated light source shown in FIG. 2 first has an optical waveguide made of n-InGaAsP from below on a substrate 201 made of (001) n-InP on which an asymmetric phase shift diffraction grating 202 having a period of 240 nm is partially formed. Layer 203 (thickness 180 nm, wavelength composition 1250 nm), strained multiple quantum well active layer 204 (well layer: 6 layers, thickness 6 nm, 0.6% compressive strain, barrier) made of undoped InGaAsP / InGaAsP having an absorption edge wavelength of 1570 nm Layer: thickness 8 nm, SCH layer: thickness 30 nm), and upper clad layer 205 made of p-InP is grown in this order by metal organic vapor phase epitaxy (MOVPE).

  In addition, the p-InP layer (upper cladding layer 205) and the undoped InGaAsP / InGaAsP layer (active layer 204) in the region without the diffraction grating 202 are etched away using inductively coupled plasma etching (ICP). Thereafter, in the region removed by etching, an undoped strained multiple quantum well light absorbing layer 206 having an absorption edge wavelength of 1490 nm (well layer: number of layers: 7 nm, thickness: 6 nm, 0.5% stretch strain, barrier layer: thickness) 8 nm, SCH layer: 30 nm in thickness) is selectively regrown by MOVPE to have a structure in which the active layer 204 and the light absorption layer 206 are butt-coupled (butt = coupling).

The active layer 204 and the light absorption layer 206 are etched by the ICP method until reaching the substrate 201 in a stripe shape having a width of 1.5 μm, and then the buried cladding layer 207 (thickness 1.2 μm) made of p-InP and p It is embedded with an electrode contact layer 208 (thickness 100 nm) made of ⁺ -InGaAs. The coupling efficiency and reflection loss in the 1550 nm band between the active layer 204 and the light absorption layer 206 are 99% or more and −45 dB or less, respectively. In addition, an isolation region 211 is provided to electrically isolate the DFB laser region 209 having the active layer 204 and the optical modulator region 210 having undoped light absorption. The isolation region 211 is formed in a portion where the electrode contact layer 208 on the side of the optical modulator region 210 is removed over a length of 20 μm from the position where the region contacts in order to suppress the influence of the leakage current between the two regions to a practically negligible level. Has been.

  Further, titanium (Ti) was ion-implanted over a length of 5 μm from the portion where the DFB laser region 209 and the isolation region 211 were in contact to the optical modulator region 210 side, thereby reducing the conductivity of the upper cladding layer 205 and the buried cladding layer 207. A high resistance region 212 (increased resistivity) is provided. Due to the high resistance region 212, the combined resistance (hereinafter referred to as separation resistance) between the two regions is 100 kΩ or more, which is a practically sufficient value for suppressing the influence of leakage current flowing through the separation region 211. Here, a high resistance region having higher resistance is formed by introducing titanium as an impurity. However, the present invention is not limited to this, and by introducing hydrogen or other elements, high resistance can be achieved. It goes without saying.

Further, in order to suppress wavelength chirping due to reflection at the end face of the optical modulator region 210 side, a window structure 213 excluding the waveguide structure of the optical modulator region 210 from the end face over a length of 20 μm, A 05% low reflection film 214 is provided. The effective residual reflectance is suppressed to 10 ⁻⁴ or less. Further, a high reflection film 215 having a reflectivity of 90% is applied to the end face on the laser region 209 side. The length of the light modulator region 210 is 180 μm (not including the window region and the separation region). The length of the laser region 209 is 400 μm and the κL product is 1.4.

  In the optical modulator integrated light source shown in FIG. 2, when a predetermined voltage is applied between the electrode 216 and the back electrode 218, the laser region 209 is forward biased to inject current into the active layer 204. Oscillated in a single axis mode at a threshold current of 7 mA and an oscillation wavelength of 1550 nm (detuning: −20 nm). The intensity of the signal light emitted from the end face on the optical modulator region 210 side (hereinafter referred to as optical output) is 18 mW at a temperature of 25 ° C., a forward bias current of 100 mA by the electrode 217, and the side mode suppression ratio (SMSR) is 50 dB. there were. By changing the reverse bias voltage applied to the light modulator region 210, the light absorption coefficient of the light absorption layer 206 increases due to the electroabsorption effect, and the light output can be modulated. The extinction ratio was 0 to −2 V and a practical value of 13 dB or more was obtained. The capacity of the optical modulator region 210 when the reverse bias voltage is -1 V is 0.35 pF, and the small signal frequency response band at the time of 50Ω termination is 15 GHz or more, which is a sufficiently high speed for practical use as a communication light source element in the 10 Gb / s band. Is obtained.

  In addition, the α-parameter of the optical modulator region 210 is small enough that there is no practical problem in realizing 10 Gb / s-80 km transmission using a single mode fiber with -0.4 when the reverse bias voltage is -1V. The value is suppressed. When 10 Gb / s-80 km transmission was performed using the optical modulator integrated light source shown in FIG. 2, the reception sensitivity was reduced to 0.2 dB or less, and good characteristics with no practical problems were realized.

  Next, another configuration example of the optical modulator integrated light source in the embodiment of the present invention will be described. FIG. 3 is a perspective view (a) and a cross-sectional view (b) showing a configuration example of another optical modulator integrated light source in the embodiment of the present invention. FIG. 3B is a horizontal (along) cross section in the waveguide direction (longitudinal axis of the separation region) of the optical modulator integrated light source. FIG. 3B is a cross-sectional view of a region within a circle indicated by a wavy line in FIG.

  In the optical modulator integrated light source shown in FIG. 3, first, an optical waveguide layer 303 having a third conductivity (conductivity type: i-type) and an undoped active layer 304 are formed on a substrate 301 on which a diffraction grating 302 is partially formed. Has grown and formed. Further, after deleting the undoped active layer 304 in the region without the diffraction grating 302, the light modulation integrated light source shown in FIG. The undoped active layer 304 and the undoped light absorption layer 305 have a butt-coupled structure (butt = coupling), and realize a highly efficient and low reflection coupling characteristic from the undoped active layer 304 to the undoped light absorption layer 305. ing. Note that the undoped active layer 304 and the undoped light absorption layer 305 are buried with an upper cladding layer 306 having second conductivity.

  Further, the laser region 307 having the undoped active layer 304 and the optical modulator region 308 having undoped light absorption are electrically separated by the separation region 310. In order to suppress the influence of the leakage current between the laser region 307 and the optical modulator region 308 to a practically negligible level, the separation region 310 has an electrode contact layer 309 on the optical modulator region 308 side from the position where both regions contact. It is a configuration in which a certain length is partially removed. In addition, the isolation region 310 is provided with a high resistance region 311 constituted by a groove formed by selectively removing the cladding layer 306 by etching. In the optical modulator integrated light source shown in FIG. 3, the window structure 312 and the low reflection film 313 are used in combination in order to suppress wavelength chirping caused by the residual end face reflection on the optical modulator region 308 side. . On the other hand, a highly reflective film 314 is provided on the end surface on the laser region 307 side.

  The optical modulator integrated light source shown in FIG. 3 is the same as the optical modulator integrated light source shown in FIG. 1 except that the high resistance region 311 is formed by grooves. Also, the high resistance region 311 is a region where the effective conductivity of the upper cladding layer 306 is lowered (the effective resistivity is increased), similarly to the high resistance region 111. In the optical modulator integrated light source shown in FIG. 3, when a predetermined voltage is applied between the electrode 315 and the back electrode 317, the laser region 307 is forward-biased to inject current into the undoped active layer 304, thereby uniaxial mode. Oscillates. Also, by changing the reverse bias voltage applied to the optical modulator region, the light absorption coefficient of the undoped light absorption layer 305 increases due to the electroabsorption effect, and the signal light intensity emitted from the end surface on the optical modulator region side is modulated. can do.

  Next, another configuration example of the optical modulator integrated light source in the embodiment of the present invention will be described. 4A and 4B are a perspective view and a cross-sectional view showing a configuration example of another light modulator integrated light source according to the embodiment of the present invention. 4B is a horizontal (along) cross section in the waveguide direction (longitudinal axis of the separation region) of the optical modulator integrated light source. FIG. 4B is a cross-sectional view in a region within a circle indicated by a wavy line in FIG.

  The optical modulator integrated light source shown in FIG. 4 first has an optical waveguide made of n-InGaAsP from below on a substrate 401 made of (001) n-InP on which an asymmetric phase shift diffraction grating 402 having a period of 240 nm is partially formed. Layer 403 (thickness 180 nm, wavelength composition 1250 nm), strained multiple quantum well active layer 404 (well layer: 6 layers, thickness 6 nm, 0.6% compressive strain, barrier) made of undoped InGaAsP / InGaAsP having an absorption edge wavelength of 1570 nm Layer: thickness 8 nm, SCH layer: thickness 30 nm), and upper clad layer 405 made of p-InP in this order is grown by metal organic vapor phase epitaxy (MOVPE).

  Further, the p-InP layer (upper cladding layer 405) and the undoped InGaAsP / InGaAsP layer (active layer 404) in the region without the diffraction grating 402 are removed by etching using inductively coupled plasma etching (ICP). Thereafter, in the region removed by etching, an undoped strained multiple quantum well light absorption layer 406 having an absorption edge wavelength of 1490 nm (well layer: number of layers: 7 nm, thickness: 6 nm, 0.5% stretch strain, barrier layer: thickness) 8 nm, SCH layer: 30 nm in thickness) is selectively regrown by MOVPE to have a structure in which the active layer 404 and the light absorption layer 406 are butt-coupled (butt = coupling).

The active layer 404 and the light absorption layer 406 are etched by an ICP method in a stripe shape having a width of 1.5 μm until reaching the substrate 401, and then the buried cladding layer 407 (thickness 1.2 μm) made of p-InP and p It is embedded with an electrode contact layer 408 (thickness: 100 nm) made of ⁺ -InGaAs. The coupling efficiency and reflection loss in the 1550 nm band between the active layer 404 and the light absorption layer 406 are 99% or more and −45 dB or less, respectively, and good coupling characteristics that do not impede practical use are realized. In addition, an isolation region 411 is provided in order to electrically isolate the DFB laser region 409 having the active layer 404 and the optical modulator region 410 having undoped light absorption. The isolation region 411 is formed in a portion where the electrode contact layer 408 on the side of the optical modulator region 410 is removed over a length of 20 μm from the position where the region contacts in order to suppress the influence of the leakage current between the two regions to a practically negligible level Has been.

  Further, a groove having a length of 5 μm is formed on the optical modulator region 410 side from a portion where the DFB laser region 409 and the separation region 411 are in contact with each other, and a high resistance region 412 including the groove is provided. The high resistance region 412 can be formed by selectively removing the p-InP upper clad layer 405 and the buried clad layer 407 by ICP. Due to the high resistance region 412, the combined resistance (hereinafter referred to as separation resistance) between the two regions is 100 kΩ or more, which is a practically sufficient value for suppressing the influence of leakage current flowing through the separation region 411.

A window structure 413 excluding the waveguide structure of the light modulator region 410 and a low reflection film 414 having a reflectance of 0.05% are provided over a length of 20 μm from the end surface on the light modulator region 410 side. The effective residual reflectance is suppressed to 10 ⁻⁴ or less. Further, a highly reflective film 415 having a reflectance of 90% is applied to the end face on the laser region 409 side. The length of the light modulator region 410 is 180 μm (not including the window region and the separation region). The laser region 409 has a length of 400 μm and a κL product of 1.4.

  The optical modulator integrated light source shown in FIG. 4 differs from the configuration of the optical modulator integrated light source shown in FIG. 2 in that the separation resistance by the high resistance region 412 is 10 kΩ. The characteristics are realized. When 10 Gb / s-80 km transmission was performed using the optical modulator integrated light source shown in FIG. 4, the reception sensitivity was reduced to 0.4 dB or less, and good characteristics with no practical problems were realized.

1A and 1B are a perspective view and a cross-sectional view showing a configuration example of an optical modulator integrated light source according to an embodiment of the present invention. It is the perspective view (a) and sectional drawing (b) which showed the structural example of the other optical modulator integrated light source in embodiment of this invention. It is the perspective view (a) and sectional drawing (b) which showed the structural example of the other optical modulator integrated light source in embodiment of this invention. It is the perspective view (a) and sectional drawing (b) which showed the structural example of the other optical modulator integrated light source in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Substrate, 102 ... Diffraction grating, 103 ... Optical waveguide layer, 104 ... Active layer, 105 ... Light absorption layer, 106 ... Upper clad layer, 107 ... Laser region, 108 ... Optical modulator region, 109 ... Electrode contact layer, DESCRIPTION OF SYMBOLS 110 ... Isolation area | region, 111 ... High resistance area | region, 112 ... Window structure, 113 ... Low reflection film, 114 ... High reflection film, 115 ... Electrode, 116 ... Electrode, 117 ... Back electrode.

Claims (8)

An optical waveguide layer made of a first conductivity type semiconductor formed on the lower cladding layer;
A light source comprising an active layer formed in a light emitting region on the optical waveguide layer;
A light absorbing layer formed on the optical waveguide layer following the active layer;
A light modulator region configured by a part of the light absorption layer to light-modulate the signal light oscillated from the light source;
A separation region configured by a part of the light absorption layer, disposed in a region sandwiched between the light emitting region and the light modulator region, and electrically separating the light emitting region and the light modulator region;
An upper cladding layer made of a second conductivity type semiconductor formed to cover the active layer and the light absorption layer;
A high resistance region provided in contact with the light emitting region in the upper cladding layer on the light emitting region side of the isolation region and having a higher resistance than the other part of the upper cladding layer in the isolation region;
A first electrode formed on the upper cladding layer of the light emitting region;
And at least a second electrode formed on the upper cladding layer in the light modulator region,
The first electrode and the second electrode are separated with at least the separation region interposed therebetween ,
Before Symbol high resistance region, before Symbol upper cladding layer bottom of even optical modulator integrated, characterized in that since a part of which is composed of an upper clad layer in a groove formed on the light absorbing layer, leaving the light source. The light modulator integrated light source according to claim 1.
The light modulator integrated light source, wherein the light source is a semiconductor laser. The light modulator integrated light source according to claim 2,
An optical modulator integrated light source, wherein the light source is a semiconductor laser that oscillates in a single mode. The light modulator integrated light source according to claim 3,
An optical modulator integrated light source comprising a diffraction grating formed in the light emitting region. The light modulator integrated light source according to claim 4,
The light modulator integrated light source, wherein the diffraction grating is formed closer to the lower cladding layer than the active layer. The light modulator integrated light source according to claim 4,
The light modulator integrated light source, wherein the diffraction grating is formed closer to the upper cladding layer than the active layer. The light modulator integrated light source according to claim 1.
An optical modulator integrated light source, wherein the light source is a semiconductor optical amplifier. The light modulator integrated light source according to any one of claims 1 to 7,
The absorption edge of the semiconductor constituting the light absorption layer in the region where the isolation region is formed has a shorter wavelength composition than the absorption edge of the semiconductor constituting the light absorption layer in the other region. An optical modulator integrated light source.

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