JP2013093622A - Optical semiconductor device control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor device control method which can increase an extinction ratio while maintaining the number of well layers and modulator length unchanged.SOLUTION: There is provided a control method for an optical semiconductor device comprising: a substrate consisting of a semiconductor mixed crystal; an electroabsorption type optical modulator, formed on the substrate, which has an active section of multiquantum well structure including a quantum well layer and a barrier layer and upper/lower clad sections respectively covering the top and the bottom of the active section, and which is composed by fabricating a ridge waveguide structure having a ridge mesa section of about optical wavelength in width by etching part of the upper clad section and then filling up both sides of the ridge mesa section with an organic material having a small heat transfer coefficient; a semiconductor laser which outputs light by an injected current; and an optical waveguide device, provided between the semiconductor laser and the electroabsorption type optical modulator, in which the light output from the semiconductor laser is guided. The extinction ratio of the electroabsorption type optical modulator is controlled by changing the current injected into the semiconductor laser.

Description

  The present invention relates to an optical semiconductor device control method, and more particularly to an electroabsorption optical modulator having a strained quantum well layer and an integrated light source control method in which the optical modulator and a semiconductor laser are integrated.

  Due to the current spread of FTTH (Fiber To The Home), there is a strong demand for high-performance optical devices in the subscriber system, and the semiconductor laser that is the light source can obtain light in the vicinity of 1.3 μm, which is a severe temperature environment. It is required to operate below (85 ° C. or higher) and to have low power consumption.

  So far, strained quantum well semiconductor lasers have been researched and developed as optical semiconductor devices having low power consumption, high efficiency, and good temperature characteristics. In addition, in order to use as a signal for optical communication, it is necessary to modulate the light output from the semiconductor laser into a signal of 0 and 1, in which case, a direct modulation type that directly modulates a current for driving the semiconductor laser, Alternatively, an external modulation type modulator using an external modulator has been developed.

  Recently, a light source that requires a modulation speed of 10 Gbit / s, 25 Gbit / s, or 40 Gbit / s has been demanded as a standard for next-generation networks. In these standards, in addition to the modulation speed, fine parameters such as light output and extinction ratio are defined.

  Such an optical semiconductor device such as a semiconductor laser is formed using a semiconductor mixed crystal substrate, and is completed through a process of growing a crystal on the substrate. In the crystal growth, a material whose lattice constant matches with the substrate material is often selected, but a strained quantum well made of a material having a different lattice constant is also used. The strained quantum well layer has a condition that the composition of the multi-component material is not lattice-matched with the barrier layer or the substrate, and the film thickness is reduced so as to force the lattice constant to be the same as that of the substrate.

  Such a strained quantum well is applied, for example, to an active layer of a semiconductor laser, and by applying strain, the density of states of the energy band structure changes, and the characteristics of the semiconductor laser are improved. In addition, a multiple quantum well structure in which a plurality of strain quantum wells are grown with a barrier layer interposed therebetween is employed in many semiconductor lasers in order to improve optical output. When current is injected into this multiple quantum well, electrons are captured in each quantum well in the conduction band and holes are captured in each quantum well in the valence band, so that carriers are regenerated between the conduction band and the valence band. Bonding occurs and light emission occurs.

  By using a strained quantum well formed on an InP substrate, it is possible to obtain light having a wavelength of about 1.3 μm, which is used in subscriber optical communication, and by modulating an injection current in a laser, a modulation signal used for transmission Can be obtained. However, when the laser injection current is directly modulated, there is a problem that the waveform distortion when a signal is transmitted increases as the modulation is performed at a higher speed due to a change in the refractive index (chirp) accompanying the change in the current.

  One method for solving this problem is to use an external modulator. One of the most widely used external modulators is an electroabsorption optical modulator. In this modulator, by applying an external voltage, the absorption edge of the quantum well is lengthened using the quantum confined Stark effect. When no voltage is applied, a signal is output and ON, and when applied, the signal is absorbed and OFF. Performs switching operation. By using this electroabsorption optical modulator, it is possible to modulate a signal at high speed while controlling the chirp.

  There are several factors that determine the performance of an electroabsorption modulator, but one of the most important is the extinction ratio. The extinction ratio is the ratio of the signal intensity between the ON state and the OFF state, and generally the larger the better. There are several methods for increasing the consumed light. Generally, the methods of increasing the number of multiple quantum wells and increasing the length of the modulator are taken.

Changzheng Sun et al., “Fabrication and Packaging of 40-Gb / s AlGaInAs Multiple-Quantum-Well Electroabsorption Modulated Lasers Based on Identical Epitaxial Layer Shceme”, Journal of Lightwave Technology, vol.26, no.11, pp.1464- 1471, Jun 1, 2008

  However, when the number of quantum well layers is increased and the modulator length is increased, the insertion loss increases. Further, when the length of the modulator is increased, the electric capacity is increased, so that a high-speed electric signal cannot be efficiently sent to the multiple quantum well portion, and the maximum modulation speed is limited.

  Therefore, obtaining a large extinction ratio with respect to the number of wells and the modulator length is in a trade-off relationship with obtaining a large light output and a high-speed modulation band.

  Accordingly, the present invention has been made to solve the above-described problems, and provides an optical semiconductor device control method capable of increasing the extinction ratio without changing the number of well layers and the modulator length. The purpose is to do.

A method of controlling an optical semiconductor device according to the first invention for solving the above-described problem is as follows.
A substrate made of a semiconductor mixed crystal, an active part of a multiple quantum well structure including a quantum well layer and a barrier layer formed on the substrate, and an upper and lower cladding part covering the upper and lower sides of the active part, An electric field having a structure in which a part of the upper cladding part is etched to produce a ridge waveguide structure having a ridge mesa part with a width of about the optical wavelength, and both sides of the ridge mesa part are embedded with an organic material having a low thermal conductivity. An absorption light modulator;
A semiconductor laser that outputs light by an injection current;
An optical semiconductor device control method comprising: an optical waveguide device that is provided between the semiconductor laser and the electroabsorption optical modulator and guides light output from the semiconductor laser,
The extinction ratio of the electroabsorption optical modulator is controlled by changing an injection current to the semiconductor laser.
According to the method for controlling an optical semiconductor device according to the present invention, the temperature in the modulator can be increased and the extinction ratio can be increased by changing the input light intensity to the modulator. In addition, by adopting a ridge-type waveguide structure embedded with an organic material instead of the conventional semiconductor embedded type, it is possible to increase the temperature efficiently and increase the extinction ratio.

A method of controlling an optical semiconductor device according to the second invention for solving the above-described problem is as follows.
In the control method of the optical semiconductor device of the first invention,
The width of the ridge mesa portion is 0.5 μm or more and 2.5 μm or less, and the height of the ridge mesa portion is 1 μm or more and 3 μm or less.

An optical semiconductor device control method according to a third invention for solving the above-described problem is as follows.
In the control method of the optical semiconductor device according to the first or second invention,
The organic material is polyimide or benzocyclobutene.

An optical semiconductor device control method according to a fourth invention for solving the above-described problem is as follows.
In the control method for any one of the first to third optical semiconductor devices,
The semiconductor mixed crystal of the substrate is InP,
The well layer and barrier layer of the active part of the multiple quantum well structure are In _1-xy Al _x Ga _y As or In _1-x Ga _x As _y P _1-y , and the number of wells in the active part is 1 It is 20, It is characterized by the above-mentioned.

An optical semiconductor device control method according to a fifth invention for solving the above-described problem is as follows.
In the method for controlling an optical semiconductor device according to any one of the first to fourth inventions,
The quantum well layer in the active part of the multiple quantum well structure has a strain and thickness that achieves a wavelength such that the peak wavelength of photoluminescence is 1.2 μm to 1.3 μm, or 1.4 μm to 1.55 μm. It is characterized by having.

An optical semiconductor device control method according to a sixth invention for solving the above-described problem is as follows.
In the control method of any one of the first to fifth optical semiconductor devices,
The optical waveguide device includes a substrate made of a semiconductor mixed crystal and an active portion of a multiple quantum well structure including a quantum well layer and a barrier layer formed on the substrate, or a bulk mixed crystal, and light is guided. And a top and bottom clad portion that covers the top and bottom of the passive layer, respectively.

  According to the method of controlling an optical semiconductor device according to the present invention, the extinction ratio of an electroabsorption optical modulator configured to have a high extinction ratio, a high optical output, and a high modulation band can be obtained without changing the number of well layers and the modulator length. Since the control is performed by changing the injection current to the semiconductor laser, the extinction ratio can be increased, and the signal can be modulated at high speed while controlling the chirp.

It is the figure which showed typically the layer structure cross section of one Embodiment of the optical semiconductor device which concerns on this invention. It is a figure which shows the relationship between the extinction ratio and bias voltage in an optical semiconductor device. It is a figure which shows the relationship between the photocurrent and bias voltage in an optical semiconductor device. It is a figure which shows the relationship between the temperature rise inside an optical semiconductor device, and a bias voltage. It is the figure which showed the temperature rise dependence of the extinction ratio change of an optical semiconductor device. It is the figure which showed typically the layer structure cross section of other embodiment of the optical semiconductor device which concerns on this invention. It is the figure which showed typically the structure of other embodiment of the optical semiconductor device which concerns on this invention.

  An optical semiconductor device and a control method thereof according to the present invention will be specifically described in each embodiment.

[First embodiment]
The optical semiconductor device according to the first embodiment will be described with reference to FIGS.

As shown in FIG. 1, the optical semiconductor device according to the present embodiment includes a substrate 11 made of n-type InP, which is a semiconductor mixed crystal, and an n-InP cladding portion 14 (lower cladding portion) provided on the substrate 11. And an active layer 12 having a multiple quantum well structure comprising an In _{1 -xy} Al _x Ga _y As barrier and an In _{1 -xy} Al _x Ga _y As quantum well provided on the n-InP cladding portion 14, and an active layer 12, a p-InP clad portion 13 (upper clad portion) is etched to a desired width to produce a ridge waveguide structure having a ridge mesa portion 15, and both sides of the ridge mesa portion 15 are made of an organic material. It has a ridge type electroabsorption modulator (EAM) 10 composed of an embedded portion 16 embedded therein. The x represents an index of Al (aluminum), and the y represents an index of Ga (gallium). An electrode is provided on the ridge mesa 15 via a contact layer or the like.

  Examples of the organic material described above include organic materials having low thermal conductivity such as polyimide and benzocyclobutane (hereinafter referred to as BCB).

  The active layer 12 having the above-described multiple quantum well structure is composed of a six-fold multiple quantum well having a total insulating layer thickness of 350 nm. Here, the insulating layer is a layer that is not doped with impurities, and is the whole well and barrier of the quantum well and the whole non-doped layer sandwiched between p and n outside this. Thereby, the quantum well in the active layer 12 of the multiple quantum well structure has a strain that achieves a wavelength such that the peak wavelength of photoluminescence is 1.1 μm to 1.3 μm, or 1.4 μm to 1.55 μm, It will have a thickness. Further, as the quantum well layer, a mixed crystal whose band gap wavelength has a difference (detuning) from the input light wavelength of 50 nm at room temperature is used.

Here, a method of manufacturing the optical semiconductor device having the above-described configuration will be described.
First, a multiple quantum comprising an n-InP clad part 14 (modulator lower clad), an In _{1 -xy} Al _x Ga _y As barrier, and an In _{1 -xy} Al _x Ga _y As quantum well on an n-type InP substrate 11. A well-structured active layer 12 and a p-InP cladding portion 13 (upper cladding) are grown in order.

  Subsequently, other than the necessary portions of the p-InP clad portion 13 are removed by etching, a mesa forming process with a width and height of 2 μm, embedding with an organic material (here, BCB), and an electrode forming process, followed by cleavage. A modulator having a length of 50 μm to 300 μm is created and completed.

  The extinction characteristics of the optical semiconductor device configured as described above will be described with reference to FIG. The evaluation of the extinction characteristic is performed by inputting light from an external semiconductor laser to the EAM and changing the voltage applied to the EAM. In order to change the power of the light injected into the EAM, the current injected into the laser (20 mA, 30 mA, 40 mA, 60 mA, 80 mA, 100 mA) is used as a parameter.

  As shown in FIG. 2, the extinction characteristics hardly change when the injection current into the laser is 20 mA or 30 mA, but it is understood that the extinction ratio increases as the current increases further. When the injection current is 100 mA, an increase in the extinction ratio of 8 dB can be confirmed at a bias voltage of 4.5 V compared to the case of 20 mA.

The reason for this is explained as follows.
FIG. 3 shows the relationship between the photocurrent and the bias voltage in the optical semiconductor device configured as described above.
As shown in FIG. 3, when the bias voltage increases, the photocurrent increases, and the photocurrent also increases when the injected light power is large. In the EAM, the power represented by the product of the photocurrent and the voltage is generated as Joule heat. Therefore, the higher the bias voltage and the higher the injected light power, the higher the temperature in the EAM. . When the temperature in the EAM rises, the detuning with the input light wavelength decreases, and the extinction increases because it is closer to the absorption edge of the semiconductor.

  Here, FIG. 4 shows the bias voltage dependence of the temperature rise in the EAM, obtained by thermal analysis simulation based on the data of FIG. As shown in FIG. 4, it can be seen that a temperature increase of nearly 50 ° C. is obtained at an injection current of 100 mA and a bias voltage of 4.5V. This is because the embedded portion 16 in which both sides of the ridge mesa portion 15 are embedded with an organic material having a low thermal conductivity is provided.

FIG. 5 shows the temperature rise dependency of the extinction ratio change in the optical semiconductor device having the above-described configuration.
FIG. 5 shows that an increase in the extinction ratio of about 10 dB is expected with a 50 ° C. increase, and the extinction ratio can be adjusted without changing the structure of the EAM. By using this structure, it is possible to increase the temperature more efficiently and to obtain a larger extinction ratio as compared with the conventional structure embedded with a semiconductor.

  In the present embodiment, the detuning is set to 50 nm, but the effect exhibited by the optical semiconductor device according to the present embodiment can be obtained regardless of the detuning value from the principle. Detuning used in actual EAM is about 30 nm to 150 nm, and those values can also be used in the EAM according to the present embodiment.

  Further, although the mesa width of the ridge mesa portion 15 (ridge waveguide) is 2 μm, the smaller the mesa width is better from the viewpoint of temperature rise. However, if it is too narrow, the waveguide mode of light cannot be formed. On the other hand, if it is too wide, a plurality of waveguide modes are formed, which adversely affects the operation of the modulator. From the viewpoint of forming the waveguide mode, the minimum and maximum values of the mesa width are about 0.5 μm and 2.5 μm, respectively, and it is preferable to use the mesa width therebetween. If the height of the ridge mesa portion 15 (mesa portion) is too low, the electric field of light spreads to the upper electrode and the absorption loss increases, and if it is too high, the stability in device fabrication is not good. Therefore, it is good to set it as about 1 micrometer-3 micrometers.

  Therefore, according to the optical semiconductor device according to the present embodiment, the substrate 11 made of a semiconductor mixed crystal and the active layer 12 having a multiple quantum well structure including the quantum well layer and the barrier layer formed on the substrate 11 are provided. And an electro-absorption optical modulator comprising upper and lower cladding portions 13 and 14 respectively covering the upper and lower sides of the active layer 12, and a part of the upper cladding portion 13 is etched to have a ridge mesa portion 15 having a width of about the optical wavelength. By fabricating the ridge waveguide structure and providing the embedded portion 16 in which both sides of the ridge mesa portion 15 are embedded with an organic material having a low thermal conductivity, the intensity of the input light to the modulator is changed. The temperature inside can be increased and the extinction ratio can be increased. In addition, by adopting a ridge-type waveguide structure embedded with an organic material instead of the conventional semiconductor embedded type, it is possible to increase the temperature efficiently and increase the extinction ratio. That is, an electroabsorption modulator having a high extinction ratio, a high light output, and a high modulation band can be configured without changing the number of well layers and the modulator length.

[Second Embodiment]
An optical semiconductor device according to the second embodiment will be described with reference to FIGS.
The optical semiconductor device according to the present embodiment is a device including the EAM 10 having the same configuration as that of the optical semiconductor device according to the first embodiment described above. Omitted.

  As shown in FIGS. 6 and 7, the optical semiconductor device according to the present embodiment includes a semiconductor laser unit (hereinafter referred to as an LD unit) 20 that outputs light by an injection current, an electroabsorption modulator unit (hereinafter, referred to as an LD unit). (Referred to as an EAM portion) 10 and an optical waveguide device 30 provided between the LD portion 20 and the EAM portion 10 are integrated on the same semiconductor substrate. The LD unit 20, the optical waveguide device 30, and the EAM unit 10 are configured to guide light.

  The LD unit 20 is a semiconductor laser comprising an n-InP clad part 24 (lower clad part) provided on an n-type InP substrate 21 and an InAlGaAs barrier and InAlGaAs quantum well provided on the n-InP clad part 24. A multiple quantum well active layer 27, a diffraction grating 29 having a predetermined period Λ provided on the semiconductor laser multiple quantum well active layer 27, and a p-InP clad portion 23 (upper clad portion) provided thereon. Have. Similar to the EAM unit 10, the p-InP clad unit 23 includes a ridge mesa unit 25 etched to a desired width, and an embedded unit in which both sides of the ridge mesa unit 25 are embedded with an organic material (for example, polyimide or BCB) (see FIG. Not shown). An electrode is provided on the ridge mesa 25 via a contact layer or the like.

  The optical waveguide device 30 has a configuration similar to that of the EAM unit 10, but has a configuration without an upper electrode for insulation. That is, the optical waveguide device 30 has a structure for guiding light, and the n-InP clad part 34 (lower clad part) provided on the n-type InP substrate 31 and the n-InP clad part 34 are provided. A passive layer (active layer having a multiple quantum well structure) 38 made of an InAlGaAs barrier and an InAlGaAs quantum well is provided, and a p-InP clad portion 33 (upper clad portion) provided on the passive layer 38. Similar to the EAM unit 10, the p-InP clad unit 33 includes a ridge mesa unit 35 etched to a desired width, and an embedded unit in which both sides of the ridge mesa unit 35 are embedded with an organic material (for example, polyimide or BCB) (see FIG. Not shown). The length of the optical waveguide device 30 (the size between the LD unit 20 and the EAM unit 10) is 50 μm to 100 μm. This is because if the length is shorter than 50 μm, the LD portion 20 and the EAM portion 10 cannot be insulated, and if the length is longer than 100 μm, the light loss increases.

  As the semiconductor laser multiple quantum well active layer 27 of the LD section 20, a multiple quantum well structure having a band gap wavelength of 1.3 μm is used, and as the active layer 12 of the multiple quantum well structure of the EAM section 10, a total insulating layer is formed. A six-fold multiple quantum well having a thickness of 350 nm was used. The insulating layer is a layer which is not doped with impurities, and is the entire well and barrier of the quantum well and the whole non-doped layer sandwiched between p and n outside this. Further, as the quantum well layer, a mixed crystal whose band gap wavelength is 50 nm detuning from the input wavelength is used at room temperature.

Here, a manufacturing method of the optical semiconductor device (modulator integrated light source) having the above-described configuration will be described.
First, on the n-type InP substrates 11, 21, 31, n-InP cladding portions 14, 24, 34 and a semiconductor laser multiple quantum well active layer 27 are grown. Except for the necessary portion of the LD portion 20 by wet etching, the active layer 12 and the passive layer 38 having a multiple quantum well structure are regrown.

  Subsequently, after forming the diffraction grating 29 in the LD portion 20, the p-InP cladding portions 13, 23, 33 are grown by 2 μm, and a p-InGaAs contact layer (not shown) is further formed on the p-InP cladding portions 13, 23. ) Is completed, a wafer on which a semiconductor laser, an electroabsorption modulator, and an optical waveguide device are formed is completed.

  Next, after a mesa formation process with a width of 2 μm, a BCB embedding process, and an electrode formation process on the completed wafer, a modulator integrated light source having a length of 400 μm to 1000 μm is formed by cleavage to complete the process.

  Therefore, according to the optical semiconductor device according to the present embodiment, the optical waveguide device 30 is provided between the LD unit 20 and the EAM unit 10 in addition to the same effects as the optical semiconductor device according to the first embodiment. Can control the extinction ratio in the EAM section 10 and modulate the signal at high speed while controlling the chirp by controlling the injection current to the LD section 20. it can.

[Third embodiment]
An optical semiconductor device according to the third embodiment will be described with reference to FIGS.
The optical semiconductor device according to the present embodiment is a device in which only the passive layer of the optical waveguide device 30 is changed in the optical semiconductor device according to the second embodiment described above. Additional description is omitted.

  As in the optical semiconductor device according to the second embodiment, the optical semiconductor device according to the present embodiment has an LD section 20, an EAM section 10, an LD section 20, and an EAM, as shown in FIGS. And a ridge-type modulator integrated light source including an optical waveguide device 30 provided between the units 10.

  The optical waveguide device 30 has a passive layer 38 different from the active layer 12 of the multiple quantum well structure of the EAM unit 10 and has no upper electrode for insulation. That is, the optical waveguide device 30 has a structure for guiding light and has a passive layer 38 made of bulk InGaAsP. Note that an n-type InP substrate 31 is provided below the passive layer 38 via an n-InP clad portion 34 (lower clad portion). A ridge mesa portion 35 obtained by etching the p-InP clad portion 33 (upper clad portion) to a desired width and both sides of the ridge mesa portion 35 are embedded in an upper portion of the passive layer 38 with an organic material (for example, polyimide or BCB). A buried portion (not shown) is provided.

  The band gap wavelength of the passive layer 38 is 1.2 μm. If the band gap wavelength of the passive layer 38 is too close to the oscillation wavelength of the laser, the loss due to absorption increases. Therefore, it is necessary that the band gap wavelength is sufficiently shorter than that, and this absorption loss is about 100 nm shorter than the oscillation wavelength. Is not a problem. In the present embodiment, since the oscillation wavelength is 1.3 μm, the band gap wavelength of the passive layer 38 needs to be shorter than about 1.2 μm. However, if the wavelength is too short, a difference in refractive index from the substrate cannot be obtained, making it difficult to produce a small optical waveguide structure. The band gap wavelength of the passive layer 38 capable of forming an optical waveguide having the same size as that of an ordinary InP substrate is usually 1.1 μm or more, and the laser having an oscillation wavelength of 1.3 μm in this embodiment is used. The optimum band gap wavelength of the passive layer 38 is about 1.1 μm to 1.2 μm. In the present embodiment, the band gap wavelength of the passive layer 38 is set to 1.2 μm, but the same effect can be obtained if it is 1.1 μm or more.

  In the present embodiment, as in the optical semiconductor device according to the second embodiment, a multiple quantum well structure having a band gap wavelength of 1.3 μm is used as the active layer 27 of the LD unit 20, and the EAM unit 10 A 6-fold multiple quantum well having a total insulating layer thickness of 350 nm was used as the active layer 12. The insulating layer is a layer which is not doped with impurities, and is the entire well and barrier of the quantum well and the whole non-doped layer sandwiched between p and n outside this. Further, as the quantum well layer, a mixed crystal whose band gap wavelength is 50 nm detuning from the input wavelength is used at room temperature.

Here, a manufacturing method of the optical semiconductor device (modulator integrated light source) having the above-described configuration will be described.
In the method of manufacturing an optical semiconductor device according to the present embodiment, after the active layer 12 having the multi-quantum well structure of the EAM portion 10 is regrown, unnecessary portions are removed again by wet etching, and then the InGaAsP bulk (passive layer 38). The process of regrowth is performed. Other steps are the same as those in the second embodiment.

  Therefore, according to the optical semiconductor device according to the present embodiment, the same operational effects as those of the optical semiconductor devices according to the first and second embodiments can be obtained, and the active layer 27 of the LD section 20 and the EAM can be obtained. Since the joint surface with the active layer 12 of the part 10 is scraped and the passive layer 38 is newly regrown, the shape of the joint end surface can be made beautiful. Since the shape of the joint end face greatly affects the light transmittance from the LD portion 20 to the EAM portion 10, it is better as it is more beautiful, and the decrease in the light transmittance can be suppressed.

  Further, unlike the case of the second embodiment, the band gap energy of the passive layer 38 is made larger than that of the quantum well layer of the EAM unit 10, so that carriers generated by absorbing light in the EAM unit 10 are generated. Since it does not enter the passive layer 38, it is advantageous for high-speed modulation.

[Fourth embodiment]
An optical semiconductor device according to the fourth embodiment will be described with reference to FIG.
The optical semiconductor device according to this embodiment is a device in which only the composition of the multiple quantum well structure is changed in the optical semiconductor device according to the first embodiment described above, and the same device is denoted by the same reference numeral. To do.

The optical semiconductor device according to the present embodiment is a device having a ridge type electroabsorption modulator (EAM), and as shown in FIG. 1, an In _1-x Ga _x As _y P _1-y barrier, It has an active layer 12 having a multiple quantum well structure composed of In _1-x Ga _x As _y P _1-y quantum wells. The x represents an index of Ga (gallium), and the y represents an index of As (arsenic). A substrate 11 made of n-type InP is provided below the active layer 12 having a multiple quantum well structure via an n-InP cladding portion 14 (lower cladding portion). A p-InP cladding portion 13 (upper cladding portion) is etched to a desired width above the active layer 12 having a multiple quantum well structure to produce a ridge waveguide structure having a ridge mesa portion 15. An embedded portion 16 is provided in which both sides are embedded with an organic material (for example, polyimide or BCB). An electrode is provided on the ridge mesa 15 via a contact layer or the like.

  The active layer 12 having a multiple quantum well structure is composed of a six-fold multiple quantum well having a total insulating layer thickness of 350 nm. Here, the insulating layer is a layer that is not doped with impurities, and is the whole well and barrier of the quantum well and the whole non-doped layer sandwiched between p and n outside this. Thereby, the quantum well in the active layer 12 of the multiple quantum well structure has a strain that achieves a wavelength such that the peak wavelength of photoluminescence is 1.1 μm to 1.3 μm, or 1.4 μm to 1.55 μm, It will have a thickness. Further, as the quantum well layer, a mixed crystal whose band gap wavelength has a difference (detuning) from the input light wavelength of 50 nm at room temperature is used.

  Therefore, according to the optical semiconductor device according to the present embodiment, even if the well layer and the barrier layer of the active layer 12 having the multiple quantum well structure are made of InGaAsP, as in the optical semiconductor device according to the first embodiment described above, By changing the intensity of the input light to the modulator, the temperature in the modulator can be raised and the extinction ratio can be increased. In addition, by adopting a ridge-type waveguide structure embedded with an organic material instead of the conventional semiconductor embedded type, it is possible to increase the temperature efficiently and increase the extinction ratio. That is, an electroabsorption modulator having a high extinction ratio, a high light output, and a high modulation band can be configured without changing the number of well layers and the modulator length.

[Fifth embodiment]
The optical semiconductor device according to the fifth embodiment will be described with reference to FIGS.
The optical semiconductor device according to the present embodiment is the same as the optical semiconductor device according to the second embodiment described above, in which the barrier layer and quantum well layer of the semiconductor laser multiple quantum well active layer of the LD portion, and the active layer of the EAM portion The barrier layer and the quantum well layer are changed to InGaAsP, and the passive layer of the optical waveguide device is changed to the same composition as the active layer of the EAM part. To do.

  As in the optical semiconductor device according to the second embodiment, the optical semiconductor device according to this embodiment includes an LD unit 20 that outputs light by an injection current and an EAM unit 10 as illustrated in FIGS. And a ridge-type modulator integrated light source in which the optical waveguide device 30 provided between the LD unit 20 and the EAM unit 10 is integrated on the same semiconductor substrate. The LD unit 20, the optical waveguide device 30, and the EAM unit 10 are configured to guide light.

  The EAM unit 10 includes an active layer 12 having a multiple quantum well structure including an InGaAsP barrier and an InGaAsP quantum well. Note that an n-type InP substrate 11 is provided below the active layer 12 having a multiple quantum well structure via an n-InP cladding portion 14 (lower cladding portion). On the active layer 12 having a multiple quantum well structure, a ridge mesa portion 15 obtained by etching the p-InP cladding portion 13 to a desired width, and both sides of the ridge mesa portion 15 are made of an organic material (for example, polyimide or BCB). An embedded portion (not shown) is provided. An electrode is provided on the ridge mesa portion 15 via a contact layer or the like.

  The LD unit 20 includes a semiconductor laser multiple quantum well active layer 27 including an InGaAsP barrier and an InGaAsP quantum well. Note that the semiconductor laser multiple quantum well active layer 27 is provided on the n-type InP substrate 21 via the n-InP clad portion 24 (lower clad portion). A diffraction grating 29 having a predetermined period Λ is provided on the semiconductor laser multiple quantum well active layer 27, and a p-InP clad portion 23 (upper clad portion) is provided thereon. Similar to the EAM unit 10, the p-InP clad unit 23 includes a ridge mesa unit 25 etched to a desired width, and an embedded unit in which both sides of the ridge mesa unit 25 are embedded with an organic material (for example, polyimide or BCB) (see FIG. Not shown). An electrode is provided on the ridge mesa 25 via a contact layer or the like.

  The optical waveguide device 30 has a configuration similar to that of the EAM unit 10, but has a configuration without an upper electrode for insulation. That is, the optical waveguide device 30 has a structure for guiding light, and has a passive layer (multiple quantum well active layer) 38 composed of an InGaAsP barrier and an InGaAsP quantum well. An n-type InP substrate 31 is provided below the passive layer 38 via an n-InP clad part 34 (lower clad part). A ridge mesa portion 35 obtained by etching the p-InP clad portion 33 (upper clad portion) to a desired width and both sides of the ridge mesa portion 35 are embedded in an upper portion of the passive layer 38 with an organic material (for example, polyimide or BCB). A buried portion (not shown) is provided.

  As the semiconductor laser multiple quantum well active layer 27 of the LD unit 20, a multiple quantum well structure having a band gap wavelength of 1.3 μm is used, and as the active layer 12 of the multiple quantum well structure of the EAM unit 10, the total insulating layer thickness A 6-fold multiple quantum well having a thickness of 350 nm was used. The insulating layer is a layer which is not doped with impurities, and is the entire well and barrier of the quantum well and the whole non-doped layer sandwiched between p and n outside this. Further, as the quantum well layer, a mixed crystal whose band gap wavelength is 50 nm detuning from the input wavelength is used at room temperature.

  Therefore, according to the optical semiconductor device according to the present embodiment, the barrier and quantum well of the semiconductor laser multiple quantum well layer of the LD unit 20, the barrier of the active layer 12 of the multiple quantum well structure of the EAM unit 10, the quantum well, and the optical waveguide Even if the active layer barrier and quantum well of the multi-quantum well structure, which is the passive layer 38 of the device 30, are each made of InGaAsP, as in the optical semiconductor device according to the second embodiment described above, the LD unit 20 and the EAM unit 10 A ridge-type modulator integrated light source provided with an optical waveguide device 30 between them and controlling the injection current to the LD unit 20 to control the extinction ratio in the EAM unit 10 and to control the chirp The signal can be modulated at high speed.

[Other Embodiments]
In the above description, the optical semiconductor device in which the number of wells in the active layer is six has been described. However, the number of wells in the active layer is not limited to six, and an optical semiconductor device having 1 to 20 can be used. is there. Even such an optical semiconductor device has the same effects as the above-described optical semiconductor device.

  In the above description, an optical semiconductor device having a diffraction grating having a uniform periodic structure is described. However, an optical semiconductor device having a structure in which a phase shift region is included in the diffraction grating may be used.

  According to the present invention, a method for controlling an optical semiconductor device having a high extinction ratio, a high optical output, and a high modulation band can be obtained without changing the number of well layers and the modulator length. be able to.

DESCRIPTION OF SYMBOLS 10 Optical semiconductor device 11 Substrate 12 Active part 13 of multiple quantum well structure Upper clad part 14 Lower clad part 15 Ridge mesa part 16 Embedded part 20 Semiconductor laser part 27 Semiconductor laser quantum well active layer 30 Optical waveguide device 38 Passive layer

Claims (6)

A substrate made of a semiconductor mixed crystal, an active part of a multiple quantum well structure including a quantum well layer and a barrier layer formed on the substrate, and an upper and lower cladding part covering the upper and lower sides of the active part, An electric field having a structure in which a part of the upper cladding part is etched to produce a ridge waveguide structure having a ridge mesa part with a width of about the optical wavelength, and both sides of the ridge mesa part are embedded with an organic material having a low thermal conductivity. An absorption light modulator;
A semiconductor laser that outputs light by an injection current;
An optical semiconductor device control method comprising: an optical waveguide device that is provided between the semiconductor laser and the electroabsorption optical modulator and guides light output from the semiconductor laser,
A method for controlling an optical semiconductor device, wherein the extinction ratio of the electroabsorption optical modulator is controlled by changing an injection current into the semiconductor laser. In the control method of the optical semiconductor device according to claim 1,
The method of controlling an optical semiconductor device, wherein a width of the ridge mesa portion is 0.5 μm or more and 2.5 μm or less, and a height of the ridge mesa portion is 1 μm or more and 3 μm or less. In the control method of the optical semiconductor device according to claim 1 or 2,
The method for controlling an optical semiconductor device, wherein the organic material is polyimide or benzocyclobutene. In the control method of the optical semiconductor device given in any 1 paragraph of Claims 1-3,
The semiconductor mixed crystal of the substrate is InP,
The well layer and barrier layer of the active part of the multiple quantum well structure are In _1-xy Al _x Ga _y As or In _1-x Ga _x As _y P _1-y , and the number of wells in the active part is 1 20. A method for controlling an optical semiconductor device, comprising: In the control method of the optical semiconductor device given in any 1 paragraph of Claims 1-4,
The quantum well layer in the active part of the multiple quantum well structure has a strain and thickness that achieves a wavelength such that the peak wavelength of photoluminescence is 1.2 μm to 1.3 μm, or 1.4 μm to 1.55 μm. A method for controlling an optical semiconductor device, comprising: In the control method of the optical semiconductor device according to any one of claims 1 to 5,
The optical waveguide device includes a substrate made of a semiconductor mixed crystal and an active portion of a multiple quantum well structure including a quantum well layer and a barrier layer formed on the substrate, or a bulk mixed crystal, and light is guided. And a method of controlling an optical semiconductor device, comprising: a passive layer that covers the upper and lower clads that respectively cover the upper and lower sides of the passive layer.

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