JP2016122066A - Semiconductor device for phase control of light propagating in semiconductor optical waveguide and method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device achieving long term stability by suppressing the influence due to a variation with time of phase control characteristics at the time of element deterioration, and a method for the same.SOLUTION: A semiconductor device for phase control of light propagating in a semiconductor optical waveguide comprises: a semiconductor optical waveguide; a phase adjustment electrode for performing current injection to the semiconductor optical waveguide; a monitor PD part which receives natural emission light emitted from the semiconductor optical waveguide by the current injection and generates a light absorption current in proportion to the intensity of the received natural emission light; a light absorption current extraction part which extracts the light absorption current generated by the monitor PD part.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a semiconductor device and a method thereof for controlling the amount of phase change of light propagating through a semiconductor optical waveguide by current injection, and more specifically, suppressing temporal variation of phase control characteristics at the time of element degradation, The present invention relates to a semiconductor device and a method for realizing long-term stability.

  Semiconductor optical modulators have greatly improved the characteristics of optical waveguides due to recent advances in crystal growth technology and high-precision processing technology, so high refractive index, which has been difficult with conventional optical modulators based on glass materials. Development of miniaturization and low operating voltage by control is progressing. Among these, in order to cope with various light modulation schemes and future promotion of high speed and large capacity, not only conventional intensity modulation schemes but also phase modulators using the phase and polarization of light are expected.

  As an example of such a phase modulator, a schematic diagram of a basic Mach-Zehnder (MZ) type modulator is shown in FIG. 1 includes an input waveguide 1, a branching section 2, first and second arm waveguides 3 and 4, a combining section 5, and first and second output waveguides 6 and 7. An MZ type optical modulator is shown. As shown in FIG. 1, the signal light input to the input waveguide 1 is bifurcated by the branching unit 2, and the phase of the branched signal light is controlled by the first and second arm waveguides 3 and 4, respectively. Later, by combining each signal light by the multiplexing unit 5, intensity-modulated light and phase-modulated light can be obtained from the first and second output waveguides 6 and 7.

  Such a multi-function optical phase modulator includes an optical waveguide portion for using an interaction with an electric signal, an optical waveguide portion for adjusting the phase, and an optical multiplexing / demultiplexing device. . Therefore, when these functional components are integrated and manufactured in the element, there arises a problem that the element is enlarged and the power consumption is increased. Since these optical waveguide components constituting the optical phase modulator are guided by confining light by the refractive index difference of the material, it is possible to reduce the size by increasing the refractive index difference.

  Compared to conventional glass materials, semiconductor materials can be set in a wide range of refractive indexes, so that it is possible to produce optical waveguide components using semiconductor materials. (For example, refer nonpatent literature 1). A waveguide structure formed of a semiconductor is formed by sandwiching a core layer, which is a center through which light is guided, with a material having a large refractive index. At this time, the sandwiched semiconductor layer is formed by the p layer and the n layer, and by applying a reverse electric field to both the conductive layers, an electric field can be efficiently applied to the i layer as the core layer, Thereby, the refractive index difference between the p layer, the n layer, and the i layer can be effectively increased. As a result, when a semiconductor material is used, the size can be reduced by about 1/10 compared to when a glass material is used.

Kikuchi et al., “80-Gb / s Low-Driving-Voltage InP DQPSK Modulator With an n-p-i-n Structure”, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.21, NO.12, p.787-789, June 15, 2009

  For the refractive index control of the semiconductor pin structure, in addition to applying the reverse electric field as described above, a forward current is injected into the pin junction structure to inject majority carriers from the p layer and the n layer into the i layer. It is also possible to control the refractive index of this portion by confining in the i layer. The refractive index controlled here is determined by the density of carriers accumulated in the i layer, and the carrier density per unit time based on the carrier decrease amount per unit time based on the carrier decrease rate determined by the carrier recombination lifetime and the injected carrier density. It becomes a value determined by an equilibrium state with the carrier increase amount.

  The injected carrier density into the semiconductor pin junction is determined by the injected current density, but the injected current density is controllable, but the value of the carrier decrease rate determined by the carrier recombination lifetime cannot be controlled. Therefore, when the carrier decrease rate fluctuates, the carrier density fluctuates even if the injection current density is constant, and the refractive index fluctuates. As a result, the phase change amount determined by the refractive index is stably controlled over a long period of time. Can be difficult.

  If the refractive index can be controlled to be constant based on the measured value by finding a method for measuring a physical quantity that reflects the carrier density, the semiconductor can be used regardless of the temporal variation of the phase control characteristics when the element deteriorates. It becomes possible to maintain the phase control characteristics of the element stably over a long period of time.

  In view of the above, it is an object of the present invention to provide a semiconductor device and a method thereof for suppressing long-term stability by suppressing the influence of temporal variation in phase control characteristics at the time of element degradation.

  In order to solve the above problem, a semiconductor device according to claim 1 is a semiconductor device for phase control of light propagating in a semiconductor optical waveguide, and includes a semiconductor optical waveguide having a pn junction structure or a pin junction structure; A phase adjusting electrode for injecting current into the semiconductor optical waveguide; and spontaneous emission light emitted from the semiconductor optical waveguide by the current injection; and a light absorption current proportional to the intensity of the received spontaneous emission light. A monitor PD unit to be generated and a light absorption current extraction unit that extracts the light absorption current generated by the monitor PD unit are provided.

  The semiconductor device according to claim 2 is the semiconductor device according to claim 1, wherein the value of the light absorption current extracted by the light absorption current extraction unit is set to a predetermined value from the phase adjustment electrode. A constant current circuit unit for controlling the injected current is further provided.

  A semiconductor device according to a third aspect is the semiconductor device according to the first or second aspect, wherein the semiconductor device is a Mach-Zehnder optical modulator.

  A semiconductor device according to a fourth aspect is the semiconductor device according to any one of the first to third aspects, wherein the monitor PD portion is manufactured in the same manufacturing process as the semiconductor optical waveguide. Or a composition having a light absorption edge wavelength longer than that of the semiconductor optical waveguide.

  The method according to claim 5 is a method for phase control of light propagating in a semiconductor optical waveguide in a semiconductor device, and current is injected from a phase adjustment electrode into a semiconductor optical waveguide having a pn junction structure or a pin junction structure. Receiving spontaneous emission light emitted from the semiconductor optical waveguide by the current injection, generating a light absorption current proportional to the intensity of the received spontaneous emission light in the monitor PD unit, and the monitor And extracting the light absorption current generated in the PD unit.

  The method according to claim 6 is the method according to claim 5, wherein the step of controlling the current injected from the phase adjustment electrode so that the value of the extracted light absorption current becomes a predetermined value. Is further included.

  A method according to a seventh aspect is the method according to the fifth or sixth aspect, wherein the semiconductor device is a Mach-Zehnder optical modulator.

  The method according to claim 8 is the method according to any one of claims 5 to 7, wherein the monitor PD portion is manufactured in the same manufacturing process as the semiconductor optical waveguide and is the same as the semiconductor optical waveguide. Or a composition having a light absorption edge wavelength longer than that of the semiconductor optical waveguide.

  According to the present invention, even when the carrier recombination lifetime at the time of device deterioration varies, it is possible to always maintain a constant carrier density, and it is possible to easily realize stable phase control over a long period of time.

It is a schematic diagram of an MZ light modulator. It is a figure which illustrates the relationship between a spontaneous emission light spectrum and injection current. It is a figure which illustrates the apparatus for controlling the phase of the light which propagates the semiconductor optical waveguide concerning this invention. It is a figure which illustrates the apparatus structure for controlling an injection current based on the light absorption current, and controlling a carrier density to a predetermined value based on this invention. It is a figure which illustrates the MZ type | mold optical modulator which concerns on the Example of this invention. It is a figure which illustrates the MZ type | mold optical modulator which concerns on the Example of this invention.

  Hereinafter, the principle of the present invention will be described. In order to maintain the phase control characteristics of the semiconductor element stably over a long period of time, it is important to make the amount of phase change determined by the refractive index constant. Here, since the refractive index is determined by the carrier density, if this carrier density can be directly measured, the carrier density can be controlled by controlling the injection current density even when the carrier recombination lifetime fluctuates. Can be kept constant, and the amount of phase change determined by the refractive index can be stably controlled over a long period of time.

  As a characteristic depending on the carrier density, there is spontaneous emission light intensity. Spontaneous emission is a phenomenon in which spontaneously emitted light is emitted with an intensity proportional to the injected carrier density in a state where carriers are always injected in a direct transition type semiconductor pn junction structure.

  Hereinafter, spontaneous emission will be described. When a forward current is passed through the pn junction, holes and electrons are injected from the p layer side and the n layer side, respectively, and flow into the pn junction interface or the i layer of the pin junction structure. Is converted into energy. At the time of carrier recombination, light emission recombination occurs at a certain rate, and the wavelength of the light generated at this time is distributed centering on the wavelength corresponding to the band gap energy, and its intensity is proportional to the carrier density.

  Therefore, when the refractive index control by current injection is used to control the phase of light propagating through the semiconductor optical waveguide formed with the pin structure, the desired refractive index is based on the intensity of spontaneous emission light generated from the i layer. It becomes possible to detect whether or not. An example of the relationship between the spontaneous emission spectrum and the injection current is shown in FIG. 2, 201, 202, and 203 indicate the emission intensity of spontaneous emission light with respect to the wavelength at each injection current, 204 indicates the signal light intensity with respect to the wavelength, and 205 indicates the light absorption sensitivity with respect to the wavelength in the photodiode. As indicated by 201, 202 and 203 in FIG. 2, the emission intensity increases as the current value increases. Further, as indicated by 205 in FIG. 2, the light absorption sensitivity is drastically reduced after the wavelength of 1400 nm, and spontaneous emission light is absorbed, but signal light is transmitted. Therefore, it is possible to monitor without affecting the signal light.

  FIG. 3 shows an apparatus configuration for controlling the phase of light propagating through the semiconductor optical waveguide according to the present invention. FIG. 3 shows a semiconductor optical waveguide 101 having a semiconductor pn or pin structure, a phase control electrode 102 for injecting current into the phase control region of the semiconductor optical waveguide 101, and the semiconductor optical waveguide 101 by current injection by the phase control electrode 102. A semiconductor comprising a monitor photodiode (PD) unit 103 that generates a light absorption current proportional to the emitted spontaneous emission light, and a light absorption current extraction unit 104 that extracts the light absorption current generated by the monitor PD unit 103 An apparatus 100 is shown.

  The monitor PD unit 103 is manufactured by forming a semiconductor pn or pin structure capable of detecting light of a specific wavelength. The semiconductor layer structure constituting the monitor PD unit 103 can be realized by the same layer structure as the semiconductor structure forming the semiconductor optical waveguide 101. In this case, when the semiconductor optical waveguide 101 is formed by etching from the uniformly formed semiconductor epitaxial layer, a region that becomes the monitor PD portion 103 is formed at the same time, so that the chip manufacturing process can be realized without any change. is there.

  The light absorption current extraction unit 104 can be manufactured, for example, by forming an electrode for extracting the light absorption current generated by the monitor PD unit 103. In this case, the light absorption current extraction unit 104 can also be realized with the same structure and process as the phase control electrode 102 is formed.

  Using the monitor PD unit 103 and the light absorption current extraction unit 104 thus formed, the value of the light absorption current proportional to the intensity of the spontaneous emission light emitted from the semiconductor optical waveguide 101 is held at a predetermined value. In this way, controlling the injection current from the phase control electrode 102 to the semiconductor optical waveguide 101 is equivalent to maintaining the carrier density at a predetermined value, so that the amount of phase change can be kept constant. Become.

  FIG. 4 shows an apparatus configuration for controlling the injection current based on the extracted light absorption current to control the carrier density to a predetermined value. FIG. 4 shows a semiconductor device 200 including a semiconductor optical waveguide 101, a phase control electrode 102, a monitor PD unit 103, a light absorption current extraction unit 104, and a constant current circuit 105.

  The constant current circuit 105 controls the current applied to the semiconductor optical waveguide 101 by the phase adjustment electrode 102 so that the carrier density becomes a predetermined value based on the light absorption current extracted by the light absorption current extraction unit 104. .

(Example)
Examples of the present invention are shown below. Here, in the following embodiment, an MZ type optical modulator is exemplified, but the present invention is not limited to this, and the present invention can be applied to any configuration that performs phase control of light propagating through a semiconductor optical waveguide.

  5 shows an embodiment of a semiconductor phase modulator in which a monitor PD section for detecting spontaneous emission light emitted from a semiconductor optical waveguide is provided in the vicinity of the semiconductor optical waveguide into which current is injected for phase control. Will be explained. FIG. 5 illustrates the configuration of an MZ type optical modulator according to an embodiment of the present invention. 5 includes an input waveguide 301, a branching section 302, first and second arm waveguides 303 and 304, a combining section 305, and first and second output waveguides 306 and 307. The MZ type optical modulator 300 modulates light propagating through the first arm waveguide 304 and the first modulation signal electrode 308 for modulating light propagating through the first arm waveguide 303. A second modulation signal electrode 309 for controlling the phase of light propagating through the first arm waveguide 303, and a phase of the light propagating through the second arm waveguide 304. The second phase adjusting electrode 311 for controlling the phase and the spontaneous emission light emitted from the first arm waveguide 303 are received and a first light absorption current proportional to the intensity of the spontaneous emission light is output. The first monitor PD unit 312 and the second A second monitor PD unit 313 that receives spontaneously emitted light emitted from the waveguide 304 and outputs a second light absorption current proportional to the intensity of the spontaneously emitted light, and is output from the first monitor PD unit 312. MZ type light provided with a first light absorption current extraction unit 314 for extracting the light absorption current and a second light absorption current extraction unit 315 for extracting the light absorption current output from the second monitor PD unit 313 A modulator 300 is shown.

  As shown in FIG. 5, the signal light input to the input waveguide 301 is bifurcated by the branching section 302 and output to the first and second arm waveguides 303 and 304, respectively, and the first and second arms The signal light propagating through the waveguides 303 and 304 is modulated by the first and second modulation signal electrodes 308 and 309, respectively, and a current is injected into the first arm waveguide 303 using the first phase adjustment electrode 310. Thus, after controlling the phase of the signal light propagating through the first arm waveguide 303, the signal light is multiplexed by the multiplexing unit 305, thereby being output from the first and second output waveguides 306 and 307, respectively. Light is output. Spontaneously emitted light is generated in the first arm waveguide 303 due to current injection in the first phase adjustment electrode 310, and the spontaneously emitted light is received by the first monitor PD unit 312 and is proportional to the intensity of the spontaneously emitted light. Light absorption current is generated. The first light absorption current extraction unit 314 can extract the light absorption current generated by the first monitor PD unit 312.

  Here, in the above description, a configuration example in which current is injected into the first arm waveguide 303 and the spontaneous emission light emitted from the first arm waveguide 303 is detected by the first monitor PD unit 312 is shown. Needless to say, the second monitor PD unit 313 may detect the spontaneous emission light emitted from the second arm waveguide 304 by injecting a current into the second arm waveguide 304. The same applies to the following.

  Hereinafter, a manufacturing process of the MZ type optical modulator 300 according to the embodiment of the present invention shown in FIG. 5 will be described. First, a pin layer structure or a pn layer structure is epitaxially grown on the entire surface of the semiconductor substrate, and an optical waveguide mask pattern is formed by photolithography. When this mask pattern is formed, a mask pattern in the form of a PD region for spontaneous emission detection is also formed. Thereafter, the optical waveguide structure and the PD structure are formed by selectively etching away portions not covered with the mask pattern using a method such as reactive ion etching. After planarization with a resin material or the like, an electrode is formed on the surface using photolithography. Again, by including the PD structure portion in the electrode mask pattern, the electrode portion can be formed simultaneously with the optical modulator portion. In particular, if the photodiode has the same layer configuration as that of the optical waveguide, it can be manufactured on the same substrate in a lump so that the crystal growth process can be omitted and the photodiode portion is the same semiconductor layer as the optical waveguide portion. Since it has a structure, spontaneous emission light emitted from the optical waveguide portion can be received. Here, in order to receive spontaneous emission light emitted from the optical waveguide part, the photodiode part has a longer light absorption edge wavelength than the optical waveguide part, even though the photodiode part does not have the same composition as the optical waveguide part. I just need it.

  Although there may be signal light leakage components as an input component to the photodiode region, the wavelength of the signal light reduces the absorption loss in the semiconductor as much as possible. Set short. Therefore, absorption due to leakage components of signal light to the photodiode region does not occur.

  In addition, two photodiodes are usually arranged to form two interference optical waveguides, but current injection into the phase adjustment region in the same interference system is performed only on one optical waveguide, so the other Spontaneously emitted light is not emitted from this optical waveguide, and spontaneously emitted light emitted from the optical waveguide provided on one side is not mixed into the photodiode provided on the other side.

  Furthermore, in a multilevel modulation or polarization multiplexing optical modulator in which a plurality of MZ optical modulators are integrated, light is emitted simultaneously from a plurality of spontaneous emission light generation sources. Since the monitor PD section for monitoring the emitted light is formed in the immediate vicinity of the phase control electrode and absorbs the spontaneous emission light, it affects the monitor PD section of the adjacent MZ light modulator formed further ahead. There is no. The spontaneous emission light emitted to the opposite side is absorbed by the opposite monitor PD part because the phase adjustment electrode on the side where current injection is not performed and the monitor PD part adjacent thereto are formed. It does not affect other MZ light modulators.

  Thus, in this embodiment, it is possible to directly measure the carrier density by measuring the spontaneous emission light intensity.

  A method for stably controlling the operating point over a long period of time in a semiconductor phase modulator having a monitor PD section in the vicinity of the optical waveguide will be described below with reference to FIG. 6 further includes a constant current circuit 316 connected to the first and second phase adjustment electrodes 310 and 311 and the first and second monitor PD units 312 and 313 in the configuration shown in FIG. An MZ type optical modulation circuit 350 is shown.

  The constant current circuit 316 receives the light absorption current extracted from the first monitor PD unit 312 via the first light absorption current extraction unit 314, and performs the first operation so that the received light absorption current becomes a predetermined value. The injection current in the phase adjustment electrode 310 can be controlled.

  The intensity of the spontaneous emission light detected by the first monitor PD unit 312 is detected based on the light absorption current output from the first monitor PD unit 312. This value reflects the carrier density of the current injection region emitting spontaneous emission light. Therefore, the carrier density can be held at a predetermined value by controlling the current value to the current injection region so that the light absorption current output from the first monitor PD unit 312 is held at a predetermined value. It becomes possible.

  Since the wavelength of the spontaneous emission light is a value that matches the band gap wavelength, it is shorter than the signal propagation light. Therefore, leak light or scattered light of the signal propagation light itself is hardly detected by the monitor PD.

  Here, FIG. 6 illustrates a configuration in which the constant current circuit 316 is connected to the first and second phase adjustment electrodes 310 and 311 and the first and second monitor PD units 312 and 313. It is good also as a structure connected only to the phase control electrode and light absorption current extraction part of the side to control.

  In this embodiment, the monitor PD units are provided on both sides of the two optical waveguides. However, the monitor PD unit may be provided only on one optical waveguide side.

  As described above, by forming the monitor PD portion in the vicinity of the phase control region of the optical waveguide, the intensity of spontaneous emission light emitted from the phase control region is monitored in this portion, and the intensity of spontaneous emission light is kept constant. By controlling the current injection into the phase control region using the constant current circuit, it is possible to always maintain a constant carrier density even when the carrier recombination lifetime fluctuates when the element deteriorates. Thus, stable phase control can be easily realized.

Input waveguide 1, 301
Branch part 2,302
Arm waveguide 3, 4, 303, 304
Multiplexing unit 5,305
Output waveguide 6, 7, 306, 307
Semiconductor device 100, 200
Semiconductor optical waveguide 101
Phase control electrode 102, 310, 311
Monitor PD 103, 312, 313
Light absorption current extraction unit 104, 314, 315
Constant current circuit 105, 316
MZ type optical modulator 300, 350
Modulation signal electrode 308, 309

Claims (8)

A semiconductor device for phase control of light propagating in a semiconductor optical waveguide,
a semiconductor optical waveguide having a pn junction structure or a pin junction structure;
A phase adjusting electrode for injecting current into the semiconductor optical waveguide;
A monitor PD unit that receives spontaneously emitted light emitted from the semiconductor optical waveguide by the current injection and generates a light absorption current proportional to the intensity of the received spontaneously emitted light;
A light absorption current extraction unit for extracting the light absorption current generated by the monitor PD unit;
A semiconductor device comprising:   The constant current circuit unit for controlling the current injected from the phase adjustment electrode so that the value of the light absorption current extracted by the light absorption current extraction unit becomes a predetermined value. 2. The semiconductor device according to 1.   The semiconductor device according to claim 1, wherein the semiconductor device is a Mach-Zehnder optical modulator.   The monitor PD unit is manufactured in the same manufacturing process as the semiconductor optical waveguide and has the same composition as the semiconductor optical waveguide, or has a composition having a light absorption edge wavelength longer than that of the semiconductor optical waveguide. The semiconductor device according to claim 1. A method for phase control of light propagating in a semiconductor optical waveguide in a semiconductor device,
injecting a current from a phase adjustment electrode into a semiconductor optical waveguide having a pn junction structure or a pin junction structure;
Receiving spontaneous emission light emitted from the semiconductor optical waveguide by the current injection, and generating a light absorption current proportional to the intensity of the received spontaneous emission light in the monitor PD unit;
Extracting the light absorption current generated by the monitor PD unit;
A method comprising the steps of:   The method according to claim 5, further comprising controlling a current injected from the phase adjustment electrode so that a value of the extracted light absorption current becomes a predetermined value.   The method according to claim 5, wherein the semiconductor device is a Mach-Zehnder optical modulator.   The monitor PD unit is manufactured in the same manufacturing process as the semiconductor optical waveguide and has the same composition as the semiconductor optical waveguide, or has a composition having a light absorption edge wavelength longer than that of the semiconductor optical waveguide. The method according to any one of claims 5 to 7.