JP2010263601A - Optical receiving device and signal light conversion method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiving device capable of performing waveform shaping in a simple configuration. <P>SOLUTION: The optical receiving device 10 includes: a signal light irradiation means 13; a control light irradiation means 15; a photodetector 11 for receiving signal light; and a photodetector 12 for receiving control light. The photodetector 11 for receiving signal light receives signal light 14 irradiated by the signal light radiating means 13, and the photodetector 12 for receiving control light receives control light 16 irradiated by the control light radiating means 15. The photodetector 11 for receiving signal light and the photodetector 12 for receiving control light are connected in series to each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical receiver and a signal light conversion method of the optical receiver.

  In the fields of optical communication, optical information, optical measurement, etc., for example, signal light transmitted through a transmission path such as an optical fiber or optical waveguide or signal light transmitted by spatial propagation is received and converted into a signal current. A device (optical receiver) is used. It is known that the signal light transmitted through the transmission line or the like is deteriorated in quality, for example, the waveform width is widened due to characteristic distortion of the transmission line or the like. For example, when an optical fiber is used as the transmission line, signal light is dispersed due to the wavelength dependence of the optical fiber. Due to the dispersion of the signal light, the signal light is deteriorated. This deterioration of the signal light leads to a decrease in reception quality such as reception sensitivity. Examples of the decrease in reception quality include a decrease in signal S / N ratio.

Examples of the optical receiver that can prevent the reception quality from being deteriorated due to the deterioration of the signal light include, for example, a differential optical receiver (see, for example, Patent Documents 1 and 2) and a heterodyne optical receiver (for example, a patent). Reference 3), and an optical receiver that multiplexes PDs having PIN junctions to discriminate wavelengths (for example, refer to Patent Document 4).
The differential optical receiver includes two photodiodes (PD). The signal light and the excitation light emitted from the excitation light source are applied to one PD, and the other PD is irradiated with the excitation light, thereby generating an electrical signal from each PD. The phase of the signal generated from the other PD is reversed by the connection of the two PDs, so that the noise component of the semiconductor optical amplifier (SOA) is excluded by the inverting amplifier following both PDs. As a result, this apparatus can achieve high sensitivity.
In the heterodyne optical receiver, the signal light and the local light emitted from the local oscillation light source are multiplexed by an optical multiplexing circuit. This combined light is applied to the PD, and a beat signal generated from the PD is processed by a circuit. As a result, this apparatus can always demodulate a signal having the correct code polarity. In this apparatus, in order to perform heterodyne detection in the photodetector, as described above, both the signal light and the local light in the combined light are received by one PD.
In an optical receiving apparatus that multiplexes PDs having PIN junctions and discriminates wavelengths, the voltage generated in each PD is extracted by an electrode connected to each PD, and the wavelength component is specified by summing the voltages. Thereby, in this apparatus, the color component of incident light can be easily detected. Further, the sensitivity can be improved by connecting the PDs in series.

Further, as an optical receiver capable of preventing a reduction in reception quality due to the deterioration of the signal light, for example, an optical receiver shown in FIG. , Non-Patent Document 2), and the optical receiver shown in FIG. 16 (for example, see Non-Patent Document 3).
The optical receiver 1400 shown in FIG. 14 is used for the trunk line system. The optical receiver 1400 includes an optical fiber 1405 that exhibits inverse dispersion characteristics. The apparatus 1400 analyzes chromatic dispersion degradation of the signal light 1404 generated by the optical fiber 1403, and performs optical dispersion compensation using the optical fiber 1405 exhibiting the inverse dispersion characteristic. This optical dispersion compensated signal light is applied to the PD 1401.
The optical receiver 1500 shown in FIG. 15 performs optical correlation between the signal light and the reference light, and shapes the waveform. This optical receiver 1500 includes a phase comparator 1506 and an optical waveform shaper 1507. In this optical receiver 1500, first, the reference light 1505 modulated at high speed is introduced on the receiver side. Next, the signal light 1504 transmitted by the optical fiber 1503 and the reference light 1505 irradiated to the optical waveform shaper 1507 via the phase comparator 1506 are converted into light using the optical waveform shaper 1507. Waveform correlation at the waveform level. The PD 1501 is irradiated with this waveform-correlated light. Here, as the optical waveform shaper 1507, for example, a modulator or the like showing nonlinearity is used. Waveform shaping is performed by transmitting the signal light to the modulator.
An optical receiving apparatus 1600 illustrated in FIG. 16 is an optical receiving apparatus of an electrical dispersion compensation method in which dispersion compensation is electrically performed by an IC circuit. The optical receiver 1600 includes an amplification IC 1605 and an electrical dispersion compensation IC 1606. In this apparatus 1600, the signal light 1604 transmitted through the optical fiber 1603 is irradiated onto the PD 1601 and converted into an electric signal, and then the electric waveform is shaped by the amplification IC 1605 and the subsequent electric dispersion compensation IC 1606.

JP 2003-101480 A JP-A-5-183510 Japanese Examined Patent Publication No. 6-66732 Japanese Patent Laid-Open No. 61-115355

“Broadband dispersion compensating fiber module”, Fujikura Technical Review No. 103, published in October 2002, p. 56 M.M. Yoneyama et al. “40 Gbit / s optical gate using optical modulator driving by unity-travelling carrier photodiode”, ELECTRONICS LETTERS 34, p. 1607-1609 (1998) J. et al. Abe et al. , “Experimental Investigation of Adaptive Electric Dispersion Compensation Using Eye Monitoring LSI in 43 Gbit / s RZ-DPSK signal”, EcoC2008 p. 143-144 (2008)

However, the related art optical receiver requires special parts and devices for waveform shaping. As a result, there is a problem that the configuration becomes complicated. For example, in the optical receivers described in Patent Documents 1 and 2, the multiplexer or the optical waveguide for multiplexing the signal light and the pumping light to prevent the reception quality from being deteriorated due to the deterioration of the signal light, An inverting amplifier or the like is necessary.
Similarly, the optical receiver described in Patent Document 3 requires an optical multiplexing circuit, a photodetector, and the like.
Similarly, the optical receiving device described in Patent Document 4 requires an extraction electrode for each PD.
Similarly, the optical receiver 1400 shown in FIG. 14 requires an optical fiber 1405 having the inverse dispersion characteristic designed based on the analysis of the dispersion characteristic of the optical fiber 1403. Also, the design is difficult.
Similarly, the optical receiver 1500 shown in FIG. 15 requires the phase comparator 1506, the optical waveform shaper 1507, and the like.
Similarly, the optical receiver 1600 shown in FIG. 16 requires the amplification IC 1605, the electrical dispersion compensation IC 1606, and the like. Moreover, it is not easy to design a universal IC.

  An object of the present invention is to provide an optical receiver capable of waveform shaping with a simple configuration.

In order to achieve the above object, an optical receiver of the present invention comprises:
A signal light irradiation means, a control light irradiation means, a signal light receiving light receiving element, and a control light receiving light receiving element;
The signal light receiving element receives the signal light irradiated by the signal light irradiation means,
The control light receiving light receiving element receives the control light irradiated by the control light irradiation means,
The signal light receiving light receiving element and the control light receiving light receiving element are connected in series.

  The optical receiving apparatus of the present invention can perform waveform shaping with a simple configuration.

It is a block diagram which shows the structure of an example in Embodiment 1 of the optical receiver of this invention. (A) is sectional drawing which shows the structure of an example of PD used in Embodiment 1. FIG. (B) is sectional drawing which shows the structure of the other example of PD used in Embodiment 1. FIG. It is a figure which shows an example of the waveform shaping effect of the output signal obtained by Embodiment 1. It is a block diagram which shows the structure of an example in Embodiment 2 of the optical receiver of this invention. FIG. 6 is a cross-sectional view showing an example of the configuration of a multiplex PD used in Embodiment 2. FIG. 6 is a cross-sectional view showing a configuration of another example of a multiplex type PD used in Embodiment 2. (A) is sectional drawing which shows the structure of an example of PD used in Embodiment 3 of the optical receiver of this invention. (B) is sectional drawing which shows the structure of the other example of PD used in Embodiment 3. FIG. It is a figure which shows the example of a waveform of the control photocurrent with respect to the nonlinearity of PD for control light reception used for Embodiment 3. FIG. It is sectional drawing which shows the structure of an example of multiplex type PD used for Embodiment 4 of the optical receiver of this invention. It is a block diagram which shows the structure of an example in Embodiment 5 of the optical receiver of this invention. FIG. 9 is a cross-sectional view illustrating a configuration of an example of an integrated PD used in Embodiment 5. (A) is a top view which shows the structure of the other example of integrated PD used for Embodiment 5. FIG. (B) is sectional drawing seen in the II direction of integrated type PD which shows (a). It is sectional drawing which shows the structure of an example of integrated PD used for Embodiment 6 of the optical receiver of this invention. It is a block diagram which shows the structure of an example of the optical receiver of a nonpatent literature 1. 10 is a block diagram illustrating a configuration of an example of an optical receiver described in Non-Patent Document 2. FIG. It is a block diagram which shows the structure of an example of the optical receiver of a nonpatent literature 3.

  Hereinafter, the optical receiver of the present invention and the signal light conversion method of the optical receiver will be described in detail. However, the present invention is not limited to the following embodiments.

(Embodiment 1)
FIG. 1 shows an example of the configuration of the optical receiving apparatus of this embodiment. In the optical receiver of the present embodiment, as the signal light receiving light receiving element and the control light receiving light receiving element, a photodiode (PD) is used as the signal light irradiation means, and an optical fiber is used as the control light irradiation means. A case where a control light generation light source is used will be described as an example. As illustrated, the optical receiver 10 includes an optical fiber 13, a control light generation light source 15, a signal light receiving PD 11, and a control light receiving PD 12 as main components. The signal light receiving PD 11 and the control light receiving PD 12 are connected in series. Since the optical receiver according to the present embodiment is configured as described above, the configuration is simple. Furthermore, since the optical receiver of the present embodiment has a simple configuration, it can be reduced in size, for example. In the optical receiver according to the present embodiment, the signal light receiving PD is positioned upstream of the control light receiving PD in series connection, but the present invention is not limited to this example. For example, the signal light receiving PD may be positioned downstream of the control light receiving PD in series connection.

  In the optical receiver according to this embodiment, as described above, the PD is used as the light receiving element, but the present invention is not limited to this. Examples of the light receiving element include an element capable of converting an optical signal into a current signal, such as an avalanche photodiode (APD), a metal Schottky photodiode (MSM-PD), and a phototransistor, in addition to the PD.

  As the optical fiber, for example, a conventionally known optical fiber can be used. In the optical receiver of this embodiment, an optical fiber is used as the signal light irradiation means, but the present invention is not limited to this. As the signal light irradiation means, in addition to the optical fiber, for example, a transmission path such as an optical waveguide made of glass, resin, or semiconductor can be used. Further, the signal light irradiation means is not limited to the transmission path, and may be, for example, a space as long as the signal light can be transmitted. In the present invention, the “space” means a vacuum region where no substance exists and a place where a substance exists and a phenomenon occurs. The substance may be, for example, a gas such as the atmosphere; a liquid such as water; or a solid such as glass.

  As the control light generating light source, for example, a conventionally known light source can be used. The control light generation light source may be, for example, a light source that emits direct-current light or a light source that emits modulated light. In the optical receiver of this embodiment, the control light generation light source is provided inside the device, but the present invention is not limited to this example. The optical receiver of this embodiment, for example, transmits the control light emitted from a control light generation light source provided outside the apparatus into the apparatus through a transmission line such as an optical fiber disposed inside the apparatus. You may guide.

The signal light receiving PD 11 and the control light receiving PD 12 may be, for example, a PD having a PIN junction shown in FIG. FIG. 2A shows a configuration of an example of a PD having the PIN junction. FIG. 2B shows an example of the configuration when the PD having the PIN junction is used. In both the drawings and FIG. 1, the same reference numerals are given to the same portions. In this example, the light absorption region in the light receiving element is a light absorption layer i type. As shown in FIG. 2A, in the signal light receiving PD 11 having the PIN junction and the control light receiving PD 12 having the PIN junction, the semiconductor layer n-type 103 and the light absorption layer i are formed on the semiconductor substrate 107. The mold 102 and the semiconductor layer p-type 101 are stacked in the above order.
2B, the PDs 11 and 12 shown in FIG. 2A include an n-type electrode 201 on the surface of the semiconductor substrate 107 opposite to the semiconductor layer n-type 103. A p-type electrode 202 is provided on the surface of the semiconductor layer p-type 101 opposite to the light absorption layer i-type 102. In this example, the light absorption region is a light absorption layer i type, but is not limited to this example. In addition, the light receiving elements used in the optical receiving apparatus of the present embodiment are not limited to the PD having the PIN junction, and have, for example, a PN junction that does not have a low concentration I region (light absorption layer i type). PD may be sufficient. The two light receiving elements may be the same light receiving elements or different light receiving elements, for example.

  The material of the semiconductor substrate is not particularly limited, and examples thereof include an InP substrate. The material for forming the semiconductor layer n-type and the semiconductor layer p-type is not particularly limited, and examples thereof include an InP semiconductor. Examples of the material for forming the light absorption layer i-type include AlGaAs, InGaAsP, InAlGaAs, and AlGaAsSb.

  Next, based on FIG. 1 and FIG. 2B, the signal light conversion method of the optical receiver of this embodiment will be described.

  First, the signal light 14 transmitted through the optical fiber 13 is introduced into the optical receiver 10. By irradiating the introduced signal light 14 to the signal light receiving PD 11, the signal light 14 is absorbed (received) by the light absorption layer i-type 102 of the signal light receiving PD 11. As a result, a signal photocurrent is generated in the signal light receiving PD 11. That is, the signal light receiving PD 11 receives only the signal light 14 and does not receive control light. The same applies to the following embodiments. On the other hand, by irradiating the control light receiving PD 12 with the control light 16 from the control light generating light source 15, the control light 16 is absorbed (received by the light absorption layer i-type 102 of the control light receiving PD 12). ) Thereby, a control light signal is generated in the control light receiving PD 12. Here, the PDs 11 and 12 are connected in series by connecting the n-type electrode 201 and the p-type electrode 202 by electric wiring. As a result, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity, and the signal current (output signal) whose waveform width and signal level are defined at the minimum current level generated in both PDs. ) 19 is taken out to the outside. In the optical receiver of this embodiment, the signal photocurrent and the control photocurrent can be correlated by the signal light receiving PD and the control light receiving PD. The signal light can be converted into a waveform-shaped signal current without the need for a device. As a result, in the optical receiving apparatus of this embodiment, it is possible to prevent the reception quality from being lowered due to the waveform deterioration of the signal light. The same applies to the following embodiments.

  An example of waveform shaping based on the correlation between the signal photocurrent and the control photocurrent will be described with reference to FIG. Note that the waveform shaping effect achieved by the optical receiver of the present embodiment is not limited to this example.

  FIG. 3A shows a waveform shaping effect when light modulated at high speed, emitted from a light source that emits modulated light, is used as control light. As shown in the figure, for example, the signal light is irradiated to the signal light receiving PD in a state where a loss is caused by being transmitted through the optical fiber and the signal light is deteriorated due to the chromatic dispersion characteristic of the optical fiber. A current is generated (signal photocurrent waveform 34a). In this case, a control photocurrent is generated by irradiating the control light receiving PD with the optical signal (local light emission signal) modulated at high speed (control photocurrent waveform 36a). As described above, since the signal light receiving PD and the control light receiving PD are connected in series, a signal current (output signal) having a correlated waveform is extracted based on the principle of current continuity. That is, the waveform width is determined by control light having no waveform deterioration, the signal level is defined by signal light having a small signal current peak, and the signal current is waveform-shaped (signal current waveform 39a).

  FIG. 3B shows a waveform shaping effect when DC light emitted from a light source that emits DC light is used as control light. As shown in the figure, for example, when signal light (signal photocurrent waveform 34b) amplified by an optical amplifier or the like is transmitted to an optical receiving device, the control light receiving PD is irradiated with the direct-current light. Then, a control photocurrent is generated (control photocurrent waveform 36b). As described above, since the signal light receiving PD and the control light receiving PD are connected in series, the signal current (output signal) defined by the current level of the control light is extracted from the principle of current continuity. (Signal current waveform 39b). Such an effect indicates an optical limiter operation. In this way, by limiting the signal level, for example, it is possible to avoid an adverse effect on an IC or the like connected subsequently to the light receiving element.

(Embodiment 2)
FIG. 4 shows an example of the configuration of the optical receiver according to this embodiment. As shown in the figure, this optical receiver 40 includes an optical fiber 43, a control light generating light source 45, a multiplexing means 47, a signal light receiving PD, and a control light receiving PD provided on the same substrate. A mold PD41 is provided as a main component. In the optical receiver according to this embodiment, the composite PD 41 is a multiplex PD. Except for these points, the optical receiver of the present embodiment has the same configuration as the optical receiver of the first embodiment. Since the optical receiver of the present embodiment is configured as described above, it is possible to reduce the wiring distance for electrically connecting the signal light receiving PD and the control light receiving PD. High-speed correlation between light and control light is facilitated. As a result, the waveform shaping effect can be further improved. The multiplexing means is not particularly limited as long as the signal light and the control light can be combined, and examples thereof include an optical multiplexing circuit.

FIG. 5 shows a basic configuration of the multiplex PD used in the present embodiment. FIG. 6 shows a configuration example when the multiplex type PD is used. In both the drawings and FIG. 4, the same parts are denoted by the same reference numerals. As shown in FIG. 5, in this multiplex PD 41, control light receiving PD 412 having a PIN junction and signal light receiving PD 411 having a PIN junction are stacked on a semiconductor substrate 407 in the order described above. In the control light receiving PD 412, the semiconductor layer n-type 406, the light absorption layer i-type 405, and the semiconductor layer p-type 404 are arranged in the order from the semiconductor substrate 407 side to the signal light receiving PD 411 side. Are stacked. In the signal light receiving PD 411, the semiconductor layer n-type 403, the light absorption layer i-type 402, and the semiconductor layer p-type 401 are stacked in this order from the control light receiving PD 412 side.
Further, as shown in FIG. 6, the multi-type PD 41 shown in FIG. 5 includes an n-type electrode 601 on the surface of the semiconductor substrate 407 opposite to the semiconductor layer n-type 406, and the semiconductor layer p-type. A p-type electrode 602 is provided on the surface of 401 opposite to the light absorption layer i-type 402. In the multiplex type PD 41, the signal light receiving PD 411 can selectively receive signal light, and the control light receiving PD 412 can selectively receive control light. The signal light receiving PD 411 and the control light receiving PD 412 are electrically connected in series. The multiplex PD used in this embodiment is not limited to this example. For example, the signal light receiving PD having the PIN junction and the control light receiving PD having the PIN junction are arranged on the semiconductor substrate. In addition, they may be laminated in the above order.

  Next, a signal light conversion method of the optical receiver according to the present embodiment will be described with reference to FIGS.

  First, the signal light 44 transmitted through the optical fiber 43 and introduced into the optical receiver 40 is combined with the control light 46 from the control light generation light source 45 by the multiplexing means 47. As a result, a combined light 48 including the signal light 44 and the control light 46 is generated. The combined light 48 is applied to the semiconductor layer p-type 401 of the signal light receiving PD 411 in the multiplex type PD 41 (upper surface in FIG. 6). As described above, the signal light receiving PD 411 can selectively receive the signal light 44 of the combined light 48. For this reason, the signal light 44 included in the irradiated combined light 48 is absorbed (received) by the light absorption layer i-type 402 of the signal light receiving PD 411. As a result, a signal photocurrent is generated in the signal light receiving PD 411. On the other hand, the control light receiving PD 412 can selectively receive the control light 46 of the combined light 48 transmitted through the signal light receiving PD 411. Therefore, the control light 46 included in the irradiated combined light 48 is absorbed (received) by the light absorption layer i-type 405 of the control light receiving PD 412. As a result, a control photocurrent is generated in the control light receiving PD 412.

  As described above, the signal light receiving PD 411 and the control light receiving PD 412 are electrically connected in series. For this reason, the optical carrier generated in both PDs drifts due to the reverse electric field applied by the external power supply connected to both PDs, and is collected as a current. Here, also in the optical receiver of the present embodiment, as in the first embodiment, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity and are the minimum current generated in both PDs. The signal current (output signal) 49 specified by the level is taken out to the outside. That is, the optical receiver of this embodiment can perform temporal correlation between the signal photocurrent and the control photocurrent in the multiplex PD. This temporal correlation is defined by the dielectric relaxation time of the optical carrier, and is performed at a very high speed in the optical receiver of this embodiment. For this reason, when the control light is an optical signal modulated at high speed, the signal light can be converted into a signal current having a further waveform shape. Thereby, it is possible to further prevent the reception quality from being lowered due to the waveform deterioration of the signal light. When the control light is direct current light, the peak level of the signal current (output signal) can be defined by the current level of the control light, as in the first embodiment. That is, it shows an optical limiter operation.

In the optical receiver according to the present embodiment, as described above, the signal light receiving PD having the PIN junction can selectively receive signal light, and the control light receiving PD having the PIN junction can receive the control light. Can be selectively received. In order to enable both the PDs to selectively receive the signal light and the control light, for example, the wavelength of the signal light, the wavelength of the control light, and the two PDs are set so as to satisfy the following formula (I): The i-type band gap energy of the light absorption layer may be set. However, the optical receiver of this embodiment is not limited to this example.

(1.23 / λ1)>Eg1> (1.23 / λ2)> Eg2 (I)

In the formula (I), the meaning of each symbol is as follows.
λ1: Wavelength of the signal light (μm)
λ2: wavelength of the control light (μm)
Eg1: Band gap energy (eV) of the light absorption layer i-type of the signal light receiving PD
Eg2: i-type band gap energy (eV) of the light absorbing layer of the control light receiving PD

  An example of satisfying the formula (I) will be specifically described. When the wavelength λ1 of the signal light is, for example, 1.3 μm, the wavelength λ2 of the control light emitted from the control light generation light source is, for example, 1.5 μm, which is longer than the wavelength λ1 of the signal light. Set to. By making the both light absorption layers i-type into, for example, an InGaAsP layer, the band gap energy Eg1 of the light absorption layer i-type of the signal light receiving PD is 0.92 eV, and the control light receiving PD The light absorption layer i-type band gap energy Eg2 is set to 0.77 eV. By setting in this way and satisfying the formula (I), the signal light receiving PD can selectively receive the signal light of the combined light, and the control light receiving PD The control light of wave light can be selectively received. Thereby, the effect of this embodiment can be acquired.

Further, when the wavelength of the control light is set to be shorter than the wavelength of the signal light, for example, the wavelength of the signal light, the wavelength of the control light, and the both PDs are set so as to satisfy the following formula (II): What is necessary is just to set the band gap energy of each said light absorption layer i type. In this case, the multiplexed PD may be, for example, a form in which the signal light receiving PD and the control light receiving PD are stacked in the order on the semiconductor substrate.

(1.23 / λ2)>Eg2> (1.23 / λ1)> Eg1 (II)

In the formula (II), the meaning of each symbol is as follows.
λ1: Wavelength of the signal light (μm)
λ2: wavelength of the control light (μm)
Eg1: Band gap energy (eV) of the light absorption layer i-type of the signal light receiving PD
Eg2: i-type band gap energy (eV) of the light absorbing layer of the control light receiving PD

(Embodiment 3)
In the optical receiver of this embodiment, the light absorption region of the control light PD used in the optical receiver of Embodiment 1 shown in FIG. 1 is the intensity of incident control light and the photocurrent generated by the control light. It is a light absorption region showing a nonlinear relationship with intensity. Except for this point, the optical receiver of the present embodiment has the same configuration as the optical receiver of the first embodiment. The control light PD may be, for example, a PD 72 having a PIN junction shown in FIG. FIG. 7A shows an exemplary configuration of a PD having the PIN junction. FIG. 7B shows an example of the configuration when the PD having the PIN junction is used. In both the drawings, FIG. 1 and FIG. 2, the same parts are denoted by the same reference numerals. In this example, the light absorption region in the light receiving element is a light absorption layer i type. As shown in FIG. 7A, in the control light receiving PD 72 having this PIN junction, the semiconductor layer n-type 103, the light absorption layer i-type 702, and the semiconductor layer p-type 101 are formed on the semiconductor substrate 107. They are stacked in the above order. In the light absorption layer i-type 702, the intensity of the incident control light and the intensity of the photocurrent generated by the control light have a non-linear relationship.
Also, as shown in FIG. 7B, the control light receiving PD 72 shown in FIG. 7A has an n-type electrode 201 on the surface of the semiconductor substrate 107 opposite to the semiconductor layer n-type 103. A p-type electrode 202 is provided on a surface of the semiconductor layer p-type 101 opposite to the light absorption layer i-type 702. Note that the control light receiving PD used in the optical receiver of the present embodiment is not limited to the PD having the PIN junction, for example, a PN junction having no low-concentration I region (light absorption layer i type). It may be a PD having

  The material of the semiconductor substrate is not particularly limited, and examples thereof include an InP substrate. The material for forming the semiconductor layer n-type and the semiconductor layer p-type is not particularly limited, and examples thereof include an InP semiconductor.

The light absorption layer showing the nonlinear relationship can be formed by, for example, the following three methods.
The first method is a method of introducing crystal defects when forming the light absorption layer. By doing in this way, the generated optical carrier is captured by the defect and non-linearity is generated. The defects can be generated by, for example, forming a light absorption layer at a low temperature during the lamination of the crystal structure. Depending on the degree of this defect, the nonlinearity of pattern 1 and pattern 2 shown in FIG.
The second method is a method in which an impurity capable of forming a deep level in a semiconductor crystal such as iron or oxygen is added to the light absorption layer. The “deep level” means, for example, a level existing between a donor level and an acceptor level in the forbidden band. By doing so, deep levels (deep impurity levels) are formed, and optical carriers are captured to generate nonlinearity. The non-linearity shown in FIG. 8 described later is obtained depending on the identity of the impurity level to be formed, that is, the energy level in the forbidden band and the amount added.
The third method is a method of forming a light absorption layer with a superlattice structure. The superlattice structure is formed by repeatedly laminating thin film semiconductor structures made of two or more kinds of semiconductor materials. The band structure differs depending on the semiconductor material forming the superlattice structure. That is, there are a structure in which electrons and holes are confined in the same well layer (TYPEI type), a structure in which electrons and holes are not confined (TYPEII type), and the like. Both TYPEs exhibit different nonlinearities with respect to the input light intensity. In the TYPEI type, when the light intensity increases, the light absorption coefficient decreases in the absorption edge wavelength region due to the internal electric field effect of the optical carrier generated in the superlattice. For this reason, the nonlinearity of the pattern 1 shown in FIG. 8 mentioned later is obtained. In the TYPE II type, when the light intensity increases, the light absorption coefficient tends to increase, and the nonlinearity of the pattern 2 shown in FIG. Examples of the material for forming the TYPEI superlattice structure include combinations of AlGaAs / GaAs, InP / InGaAsP, InAlAs / InGaAlAs, and the like. Examples of the material forming the TYPE II type superlattice structure include a combination of InAlGaAs / InGaAsP, InAlGaAs / InGaAsSb, and the like.

  Next, a signal light conversion method of the optical receiver according to the present embodiment will be described with reference to FIGS. 1, 3, 7 (b), and 8.

  First, the signal light 14 transmitted through the optical fiber 13 is introduced into the optical receiver 10 and irradiated to the signal light receiving PD 11. As a result, a signal photocurrent is generated in the signal light receiving PD 11. On the other hand, by irradiating the control light receiving PD 72 with the control light 16 from the control light generating light source 15, the control light 16 is absorbed (received) by the light absorption layer i-type 702. As a result, a control photocurrent is generated in the control light receiving PD 72. Here, the PDs 11 and 72 are connected in series by connecting the n-type electrode 201 and the p-type electrode 202 by electrical wiring. Thus, as in the first embodiment, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity, and the waveform width and signal level are defined at the minimum current level generated in both PDs. The signal current (output signal) 19 is taken out to the outside. Note that the current waveform shaping in the optical receiver of the present embodiment is the same as that of FIG. 3 illustrated in the first embodiment, for example.

The optical receiver of this embodiment is characterized by the waveform of the control photocurrent. As described above, in the light absorption layer i-type 702 of the control light PD 72, the intensity of the incident control light and the intensity of the photocurrent generated by the control light show a non-linear relationship. An example of the nonlinearity will be described with reference to FIG. The nonlinearity is not limited to this example.
As shown in the figure, in the pattern 1, the photocurrent is suppressed with respect to the increase of the light input intensity. When control light is incident on the control light receiving PD 72 having such characteristics, a control photocurrent having saturation characteristics is obtained. In this case, the signal current can be shaped into a waveform defined in the control photocurrent waveform by the waveform shaping principle shown in FIG. As a result, for example, a limiter effect in which the peak of the current waveform is suppressed is achieved.
On the other hand, in the pattern 2, the photocurrent is exaggerated with respect to the increase of the light input intensity. When the control light is incident on the control light receiving PD 72 having such characteristics, a steep peak control photocurrent can be obtained. In this case, the signal light waveform deteriorated by the principle of waveform shaping shown in FIG. 3 can be shaped.

In the light receiving element, the intensity P of incident light and the photocurrent I generated by this light usually show a linear proportional relationship represented by the following formula (III).

I = A × η × P (III)

In the formula (III), the meaning of each symbol is as follows.
A: Constant determined by optical wavelength (A / W)
η: conversion efficiency determined by element structure P: intensity of incident light (W)
I: Generated photocurrent (A)

  In the optical receiver of this embodiment, the nonlinearity is not particularly limited. For example, when the intensity of the incident control light changes 10 times, the absolute value of the photocurrent shows a nonlinear change of 20% or more, for example. For example, when a photocurrent of 0.1 mA is generated at an input light intensity of 0.1 mW, the photocurrent generated by increasing the input light intensity to 1 mW is, for example, 0.8 mA or less (corresponding to pattern 1 in FIG. 8). ), Or 1.2 mA or more (corresponding to pattern 2 in FIG. 8). It is preferable that the absolute value of the photocurrent exhibits a non-linear change of 50% or more with respect to the change.

  In the optical receiver of this embodiment, as described above, the light absorption region of the control light PD has a light absorption in which the intensity of the incident control light and the intensity of the photocurrent generated by the control light have a non-linear relationship. It is an area. For this reason, for example, the waveform of the control photocurrent can be easily controlled without using a control light generating light source having modulation performance. Note that the non-linearity exhibited by the optical receiving apparatus of the present embodiment and the waveform shaping effect associated therewith are not limited to this example.

(Embodiment 4)
In the optical receiver of this embodiment, the light absorption region of the control light PD in the multiplex PD used in the optical receiver of Embodiment 2 shown in FIG. 4 is generated by the intensity of the incident control light and the control light. It is a light absorption region showing a non-linear relationship with the photocurrent. Except for this point, the optical receiver of the present embodiment has the same configuration as the optical receiver of the second embodiment. FIG. 9 shows an example of the configuration of the multiplex type PD 91. In this figure, the same parts as those in FIGS. 4 and 5 are denoted by the same reference numerals. As shown in the figure, in this multi-type PD 91, a control light receiving PD 912 having a PIN junction and a signal light receiving PD 411 having a PIN junction are stacked on the semiconductor substrate 407 in the order described above. In the control light receiving PD 912, the semiconductor layer n-type 406, the light absorption layer i-type 905, and the semiconductor layer p-type 404 are arranged in the order from the semiconductor substrate 407 side to the signal light receiving PD 411 side. Are stacked. In the signal light receiving PD 411, the semiconductor layer n-type 403, the light absorption layer i-type 402, and the semiconductor layer p-type 401 are stacked in this order from the control light receiving PD 912 side. In the light absorption layer i-type 905, the intensity of the incident control light and the intensity of the photocurrent generated by the control light show a non-linear relationship. The light absorption layer i-type 905 is the same as the light absorption layer i-type 702 in the third embodiment, for example.

  In the optical receiver of this embodiment, the effect that the light absorption layer exhibits the nonlinearity is the same as that of the third embodiment shown in FIG. That is, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity, and are externally output as a signal current (output signal, reference numeral 49 in FIG. 4) defined by the minimum current level generated in both PDs. It is taken out. In the optical receiver of this embodiment, as described above, the light absorption region of the control light PD has a light absorption in which the intensity of the incident control light and the intensity of the photocurrent generated by the control light have a non-linear relationship. It is an area. For this reason, in addition to the effect exhibited in the second embodiment, for example, the waveform of the control photocurrent can be easily controlled without using a control light generation light source having modulation performance.

(Embodiment 5)
FIG. 10 shows an example of the configuration of the optical receiving apparatus of this embodiment. As shown in the figure, this optical receiving device 100 includes an optical fiber 43, a control light generating light source 45, a multiplexing means 47, a signal light receiving PD, and a control light receiving PD provided on the same substrate. A mold PD111 is provided as a main component. In the present embodiment, the composite PD 111 is an integrated PD. Except for these points, the optical receiver 100 has the same configuration as the optical receiver 40 described above. Since the optical receiver of the present embodiment is configured as described above, it is possible to reduce the wiring distance for electrically connecting the signal light receiving PD and the control light receiving PD. High-speed correlation between light and control light is facilitated. As a result, it is possible to further improve the waveform shaping effect of the present invention.

FIG. 11 shows a basic configuration of an integrated PD used in this embodiment. FIG. 12 shows a configuration example when the integrated PD is used. FIG. 12A is a plan view of the integrated PD. FIG.12 (b) is sectional drawing seen in the II direction of Fig.12 (a). 10 to 12, the same parts are denoted by the same reference numerals. As shown in FIG. 11, in this integrated PD 111, a signal light receiving PD 1011 having a PIN junction and a control light receiving PD 1012 having a PIN junction are arranged in parallel on a semiconductor substrate 1007. The signal light receiving PD 1011 and the control light receiving PD 1012 are separated by an isolation groove 1008. In the signal light receiving PD 1011, a semiconductor layer n-type 1003, a light absorption layer i-type 1002, and a semiconductor layer p-type 1001 are stacked in the order from the semiconductor substrate 1007 side. In the control light receiving PD 1012, a semiconductor layer n-type 1006, a light absorption layer i-type 1005, and a semiconductor layer p-type 1004 are stacked in the order from the semiconductor substrate 1007 side. In the integrated PD 111, the signal light receiving PD 1011 can selectively receive signal light, and the control light receiving PD 1012 can selectively receive control light. In this integrated PD 111, since PDs having two PIN junctions are integrated by a waveguide structure, for example, integration with other waveguide elements is easy.
Also, as shown in FIG. 12, the integrated PD 111 shown in FIG. 11 includes a p-type electrode 1202a on the surface of the semiconductor layer p-type 1001 opposite to the light absorption layer i-type 1002. An n-type electrode 1201 a is provided on the surface of the semiconductor layer n-type 1003 opposite to the semiconductor substrate 1007. A p-type electrode 1202b is provided on the surface of the semiconductor layer p-type 1004 opposite to the light absorption layer i-type 1005. An n-type electrode 1201b is provided on the surface of the semiconductor layer n-type 1006 opposite to the semiconductor substrate 1007. The signal light receiving PD 1011 and the control light receiving PD 1012 are electrically connected in series by an interelectrode wiring 1203. The n-type electrodes 1201a and 1201b and the p-type electrodes 1202a and 1202b are, for example, laminated electrodes containing gold (Au).

  Next, a signal light conversion method of the optical receiver according to the present embodiment will be described with reference to FIGS.

  First, the signal light 44 transmitted by the optical fiber 43 and introduced into the optical receiver 100 and the control light 46 by the control light generation light source 45 are combined by the multiplexing means 47, and the signal A combined light 48 including the light 44 and the control light 46 is generated. The combined light 48 is applied to the signal light receiving PD 1011 in the integrated PD 111 (left surface in FIG. 12B). As described above, the signal light receiving PD 1011 can selectively receive the signal light 44 of the combined light 48. Therefore, the signal light 44 included in the irradiated combined light 48 is absorbed (received) by the light absorption layer i-type 1002 of the signal light receiving PD 1011. As a result, a signal photocurrent is generated in the signal light receiving PD 1011. On the other hand, as described above, the control light receiving PD 1012 can selectively receive the control light 46 of the combined light 48 transmitted through the signal light receiving PD 1011. Therefore, the control light 46 included in the irradiated combined light 48 is absorbed (received) by the light absorption layer i-type 1005 of the control light receiving PD 1012. As a result, a control photocurrent is generated in the control light receiving PD 1012.

  As described above, the signal light receiving PD 1011 and the control light receiving PD 1012 are electrically connected in series. For this reason, the optical carrier generated in both PDs drifts due to the reverse electric field applied by the external power supply connected to both PDs, and is collected as a current. Here, also in the optical receiver of the present embodiment, as in the first embodiment, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity and are the minimum current generated in both PDs. The signal current (output signal) 109 specified by the level is taken out to the outside. That is, the optical receiver of this embodiment can perform temporal correlation between the signal photocurrent and the control photocurrent in the integrated PD. This temporal correlation is defined by the dielectric relaxation time of the optical carrier, and is performed at a very high speed in the optical receiver of this embodiment. For this reason, when the control light is an optical signal modulated at high speed, the signal light can be converted into a signal current having a further waveform shape. Thereby, it is possible to further prevent the reception quality from being lowered due to the waveform deterioration of the signal light. When the control light is direct current light, the peak level of the signal current (output signal) can be defined by the current level of the control light, as in the first embodiment. That is, it shows an optical limiter operation. The points other than those described above are the same as in the second embodiment, and for example, it is preferable to satisfy the formula (I) or the formula (II).

(Embodiment 6)
In the optical receiver of this embodiment, the light absorption area of the control light PD in the integrated PD used in the optical receiver of Embodiment 5 shown in FIG. 10 is generated by the intensity of the incident control light and the control light. It is a light absorption region showing a non-linear relationship with the intensity of the photocurrent. Except for this point, the optical receiver of the present embodiment has the same configuration as the optical receiver of the fifth embodiment. FIG. 13 shows an example of the configuration of the integrated PD 131. In this figure, the same parts as those in FIGS. 10 and 11 are denoted by the same reference numerals. As shown in FIG. 13, in this integrated PD 131, a signal light receiving PD 1011 having a PIN junction and a control light receiving PD 1312 having a PIN junction are arranged in parallel on a semiconductor substrate 1007. The signal light receiving PD 1011 and the control light receiving PD 1312 are separated by an isolation groove 1008. In the signal light receiving PD 1011, a semiconductor layer n-type 1003, a light absorption layer i-type 1002, and a semiconductor layer p-type 1001 are stacked in the order from the semiconductor substrate 1007 side. In the control light receiving PD 1312, a semiconductor layer n-type 1006, a light absorption layer i-type 1305, and a semiconductor layer p-type 1004 are stacked in this order from the semiconductor substrate 1007 side. In the light absorption layer i-type 1305, the intensity of the incident control light and the intensity of the photocurrent generated by the control light show a non-linear relationship. The light absorption layer i-type 1305 is the same as the light absorption layer i-type 702 in the third embodiment, for example.

  In the optical receiver of this embodiment, the effect that the light absorption layer exhibits the nonlinearity is the same as that of the third embodiment shown in FIG. That is, the signal photocurrent and the control photocurrent are synchronized in time according to the principle of current continuity, and are externally output as a signal current (output signal, reference numeral 109 in FIG. 10) defined by the minimum current level generated in both PDs. It is taken out. In the optical receiver of this embodiment, as described above, the light absorption region of the control light PD has a light absorption in which the intensity of the incident control light and the intensity of the photocurrent generated by the control light have a non-linear relationship. It is an area. For this reason, in addition to the effects achieved in the fifth embodiment, for example, the waveform of the control photocurrent can be easily controlled without using a control light generation light source having modulation performance.

  As described above, the optical receiver of the present invention can perform waveform shaping with a simple configuration. As a result, it is possible to prevent a decrease in reception quality due to waveform deterioration of the signal light. Applications of the optical receiver of the present invention include, for example, an optical communication device, an optical information processing device, an optical measurement device, and the like. However, its use is not limited and can be applied to a wide range of fields.

10, 40, 100 Optical receiver 11 PD for receiving signal light (PD for receiving signal light having a PIN junction)
12, 72 PD for receiving control light (PD for receiving control light having PIN junction)
13, 43 Optical fiber (signal light irradiation means)
14, 44 Signal light 15, 45 Control light generation light source (control light irradiation means)
16, 46 Control light 19, 49, 109 Signal current (output signal)
34a, 34b Signal photocurrent waveform 36a, 36b Control photocurrent waveform 39a, 39b Signal current waveform 41 Composite PD (Multiple PD)
47 Multiplexing means 48 Combined light 101, 401, 404, 1001, 1004 Semiconductor layer p-type 102, 402, 405, 702, 905, 1002, 1005, 1305 Light absorption layer i type (light absorption region)
103, 403, 406, 1003, 1006 Semiconductor layer n-type 107, 407, 1007 Semiconductor substrate 111, 131 Composite PD (integrated PD)
201, 601, 1201a, 1201b n-type electrodes 202, 602, 1202a, 1202b p-type electrodes 411, 1011 PD for receiving signal light having PIN junction
412, 912, 1012, 1312 Control light receiving PD having PIN junction
1008 Isolation groove 1203 Inter-electrode wiring 1400, 1500, 1600 Optical receivers 1401, 1501, 1601 PD
1403, 1503, 1603 Optical fibers 1404, 1504, 1604 Signal light 1405 Dispersion compensation optical fiber 1505 Reference light 1506 Phase comparator 1507 Optical waveform shaper 1605 Amplifier IC
1606 Electrical dispersion compensation IC

Claims (20)

A signal light irradiation means, a control light irradiation means, a signal light receiving light receiving element, and a control light receiving light receiving element;
The signal light receiving element receives the signal light irradiated by the signal light irradiation means,
The control light receiving light receiving element receives the control light irradiated by the control light irradiation means,
The light receiving device, wherein the signal light receiving light receiving element and the control light receiving light receiving element are connected in series. And further comprising a multiplexing means for multiplexing the signal light and the control light,
The signal light receiving light receiving element and the control light receiving light receiving element are a composite light receiving element in which the signal light receiving light receiving element and the control light receiving light receiving element are provided on the same substrate,
The signal light receiving element is capable of selectively receiving the signal light of the combined light,
The optical receiver according to claim 1, wherein the light receiving element for receiving control light is capable of selectively receiving the control light of the combined light.   The composite type light receiving element is a multiple type light receiving element in which the signal light receiving light receiving element and the control light receiving light receiving element are stacked, or the signal light receiving light receiving element and the control light receiving light receiving element. 3. The optical receiver according to claim 2, wherein the optical receiver is an integrated integrated light receiving element. The wavelength of the signal light, the wavelength of the control light, the band gap energy of the light absorption region of the light receiving element for receiving signal light, and the band gap energy of the light absorption region of the light receiving element for receiving control light are expressed by the following formula (I ) Or (II)
The signal light receiving element is capable of selectively receiving the signal light of the combined light,
4. The optical receiver according to claim 2, wherein the light receiving element for receiving control light is capable of selectively receiving the control light of the combined light.

(1.23 / λ1)>Eg1> (1.23 / λ2)> Eg2 (I)
(1.23 / λ2)>Eg2> (1.23 / λ1)> Eg1 (II)

λ1: Wavelength of the signal light (μm)
λ2: wavelength of the control light (μm)
Eg1: Band gap energy (eV) of the light absorption region of the light receiving element for receiving signal light
Eg2: band gap energy (eV) of the light absorption region of the light receiving element for receiving control light
  5. The optical receiving apparatus according to claim 1, wherein at least one of the light receiving element for receiving signal light and the light receiving element for receiving control light is a light receiving element having a PIN junction. 6. .   The light absorption region of the light receiving element for receiving control light is a light absorption region in which the intensity of incident control light and the intensity of photocurrent generated by the control light exhibit a non-linear relationship. The optical receiver according to any one of 1 to 5.   The light receiving device according to claim 1, wherein a light absorption region of the light receiving element for receiving control light includes an impurity that forms a deep level in a semiconductor.   8. The optical receiver according to claim 1, wherein a light absorption region of the light receiving element for receiving control light includes a superlattice structure. 9.   8. The material for forming a light absorption region of the light receiving element having the PIN junction includes at least one selected from the group consisting of AlGaAs, InGaAsP, InAlGaAs, and AlGaAsSb. The optical receiver described in 1.   9. The material for forming the superlattice structure includes at least one combination selected from the group consisting of AlGaAs / GaAs, InP / InGaAsP, InAlAs / InGaAlAs, InAlGaAs / InGaAsP, and InAlGaAs / InGaAsSb. Optical receiver.   11. The optical receiver according to claim 1, wherein the control light irradiation unit includes a light source that emits modulated light or a light source that emits direct-current light. Using the optical receiver according to claim 1,
By irradiating the signal light to the signal light receiving light receiving element by the signal light irradiation means, a signal photocurrent is generated in the signal light receiving light receiving element,
By irradiating the control light receiving light receiving element by the control light irradiating means, a control photocurrent is generated in the control light receiving light receiving element,
A signal light conversion method for an optical receiver, wherein the signal light is converted into a waveform-shaped signal current by correlating the signal photocurrent and the control photocurrent. Using the optical receiver according to any one of claims 2 to 4,
The signal light and the control light are multiplexed by the multiplexing means,
Irradiating the combined light to the signal light receiving light receiving element and the control light receiving light receiving element,
In the light receiving element for receiving signal light, the signal light of the combined light is selectively received to generate a signal photocurrent,
In the light receiving element for receiving control light, the control light of the combined light is selectively received to generate a control photocurrent,
A signal light conversion method for an optical receiver, wherein the signal light is converted into a waveform-shaped signal current by correlating the signal photocurrent and the control photocurrent.   14. The signal light conversion method for an optical receiver according to claim 12, wherein at least one of the light receiving element for receiving signal light and the light receiving element for receiving control light is a light receiving element having a PIN junction.   The light absorption region of the light receiving element for receiving control light is a light absorption region in which the intensity of incident control light and the intensity of photocurrent generated by the control light exhibit a non-linear relationship. The signal light conversion method of the optical receiver according to any one of 12 to 14.   16. The signal light conversion of the optical receiver according to claim 12, wherein a light absorption region of the light receiving element for receiving control light includes an impurity that forms a deep level in the semiconductor. Method.   17. The signal light conversion method for an optical receiver according to claim 12, wherein a light absorption region of the light receiving element for receiving control light includes a superlattice structure.   The material for forming a light absorption region of the light receiving element having the PIN junction includes at least one selected from the group consisting of AlGaAs, InGaAsP, InAlGaAs, and AlGaAsSb. A signal light conversion method for the optical receiver according to claim 1.   The material for forming the superlattice structure includes at least one combination selected from the group consisting of AlGaAs / GaAs, InP / InGaAsP, InAlAs / InGaAlAs, InAlGaAs / InGaAsP, and InAlGaAs / InGaAsSb. Signal light conversion method of the optical receiver of the present invention.   The signal light conversion method for an optical receiver according to claim 12, wherein the control light is modulated light or direct current light.

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