JP2008113387A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a compact waveform equalizing circuit in optical space transmission using a plurality of light receiving elements. <P>SOLUTION: This waveform equalizing circuit comprises: N-pieces of avalanche photodiodes for converting incident optical signals into electric signals; N-pieces of power sources for supplying bias voltages to the N-pieces of avalanche photodiodes; a delay portion for delaying (N-1)-pieces of electric signals out of electric signals outputted from the N-pieces of avalanche photodiodes; a compositor for compositing the electric signals outputted from the N pieces of avalanche photodiodes; and a waveform monitor for monitoring a waveform of the electric signal outputted from the compositor. The waveform equalizing circuit controls output voltages of the N pieces of power sources based on waveform information in the waveform monitor, and controls multiplication factors of the N pieces of avalanche photodiodes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical space transmission technology that uses light as a radio signal, and more particularly to waveform equalization of a received waveform at the time of optical reception.

  In optical space transmission, since an optical signal is transmitted wirelessly in free space, the waveform equalization method is used for waveform distortion caused by atmospheric fluctuations, intersymbol interference generated in the optical transmitter and optical receiver, etc. It is conceivable to perform waveform equalization on the optical receiving side.

  As a prior art, an automatic equivalent circuit that performs waveform equalization based on intersymbol interference after light reception has been proposed. FIG. 7 shows an automatic equivalent circuit. In FIG. 7, 11 is a photodiode, 12 is an amplifier, 13 is an equalizer, 14 is a comparator, 15 is an intersymbol interference extraction circuit, 16 is a frequency band characteristic control circuit, 17 is a threshold control circuit, and 18 is a peak. A detector, 19 is a comparator, and P is an optical signal.

  The received binary optical signal P is converted into a binary electrical signal by the photodiode 11, and then the frequency band characteristic control circuit 16 based on the intersymbol interference amount extracted by the intersymbol interference amount extraction circuit 15. The frequency characteristic of the electric signal waveform is corrected. In order to reduce the code, it is effective to widen the transmission frequency band, but there is a problem that the amount of noise increases if it is too wide. Therefore, it is important to maintain a frequency band condition that can reduce the effects of intersymbol interference and noise.

  On the other hand, the optimum threshold level at which the code error rate characteristic is minimized changes in the direction in which it increases in comparison with the case where there is no intersymbol interference, so that the code extracted by the intersymbol interference extraction circuit 15 Based on the amount of interference, an optimum threshold level is set by the threshold control circuit 17.

  As described above, the frequency band characteristic of the received binary optical signal is controlled by the frequency band characteristic control circuit 16 according to the configuration based on the amount of intersymbol interference extracted by the intersymbol interference amount extraction circuit 15, and the threshold control is performed. Since the circuit 17 makes the determination at the optimum threshold level, the code error rate characteristic can be kept good.

As a waveform equivalent circuit, there is a configuration using a tap filter. FIG. 8 is a schematic diagram showing a tap delay line filter used for waveform equalization. After receiving light with a light receiving element (not shown), the received electrical signal is branched into multiple parts with different delay time differences, multiplied by a tap coefficient, and then added to realize a filter with an arbitrary frequency characteristic can do. The waveform equalization using the tap delay line filter is a technique that has already been put to practical use in microwave radio communication and the like, and is considered to have high reliability. By adopting this configuration, it is possible to equalize waveforms that have received intersymbol interference or the like. An example of using this filter to compensate for degradation due to polarization mode dispersion during optical fiber transmission is described in J. Pat. H. Winters and M.C. A. Santoro, “Experimental Equalization
of Polarization Dispersion ", IEEE Phototoni
cs Technology Letters, Vol. 2, no. 8, pp. 591-593, 1990.
Japanese Examined Patent Publication No. 62-21419 IEEE Photonics Technology Letters, Vol. 2, no. 8, pp. 591-593, 1990

  However, when performing optical space transmission, it is very important to improve received light power in order to ensure transmission quality. Therefore, it is desirable to secure a light receiving area as large as possible as the light receiving portion. However, there is a trade-off between the light receiving area of the light receiving element and the high speed response, and it is necessary to use a light receiving element having a small light receiving area in order to realize high speed transmission. Therefore, in optical space transmission, light may be received using a plurality of light receiving elements. In this case, it is necessary to perform band equivalence for each light receiving element, which causes a problem that the circuit scale increases. It was. Further, in order to use a light receiving element having a light receiving area as large as possible in order to secure the received light power, it is necessary to sacrifice the frequency band. In this respect, it is desired to realize a waveform equivalent with a small circuit scale.

In the case of receiving an optical signal using a plurality of light receiving elements in optical space transmission or the like,
An object of the present invention is to provide an optical receiver that realizes a waveform equivalent function without increasing the circuit scale.

  In order to solve the above-described conventional problems, the first optical receiver of the present invention outputs N light attenuating units that change the amount of incident light with respect to an incident optical signal, and is output from the light attenuating unit. N light receiving units that convert optical signals into electric signals; a delay unit that delays (N-1) electric signals out of the electric signals output from the N light receiving units; and the N light receiving units. Based on the waveform information in the synthesis unit that synthesizes the electrical signal output from the light receiving unit, the waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit, and the waveform monitor unit, the N optical attenuations It is characterized by controlling the light attenuation amount of the part.

  Further, the second optical receiver of the present invention includes (N−1) of N optical attenuators that change an incident amount with respect to an incident optical signal and an optical signal output from the optical attenuator. ) Optical delay units that delay optical signals, N light receiving units that convert optical signals output from the N optical attenuation units into electrical signals, and N light receiving units that are output from the N light receiving units Based on the waveform information in the synthesis unit that synthesizes the electrical signal, the waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit, and the waveform monitor unit, the optical attenuation amount of the N light attenuation units is calculated. It is characterized by control.

  The third optical receiver of the present invention includes two optical attenuators that change an incident amount with respect to an incident optical signal, and two optical signals that are output from the optical attenuator. A light receiving unit; a delay unit that delays one of the electric signals output from the two light receiving units; and a differential amplifier that differentially amplifies the electric signal output from the two light receiving units. A waveform monitor unit that monitors an electrical signal waveform output from the differential amplifier unit, and the light attenuation amount of the two light attenuating units is controlled based on waveform information in the waveform monitor unit. Yes.

  In addition, the fourth optical receiver of the present invention delays one optical signal among two optical attenuating sections that change the incident amount with respect to an incident optical signal and an optical signal output from the optical attenuating section. An optical delay unit, two light receiving units that convert optical signals output from the two optical attenuating units into electrical signals, and differential amplification that differentially amplifies the electrical signals output from the two light receiving units An optical signal waveform output from the differential amplifier, a waveform monitor that monitors the waveform of the electric signal output from the differential amplifier, and controlling the optical attenuation of the two optical attenuators based on the waveform information in the waveform monitor. It is a feature.

  According to a fifth optical receiver of the present invention, in the first to fourth aspects of the present invention, the optical attenuator is a MEMS mirror.

  The sixth optical receiver of the present invention includes N avalanche photodiodes that convert incident optical signals into electric signals, N power supply units that apply bias voltages to the N avalanche photodiodes, Of the electrical signals output from the N avalanche photodiodes, a delay unit that delays (N-1) electrical signals and a synthesis unit that combines the electrical signals output from the N avalanche photodiodes. A waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit; and, based on the waveform information in the waveform monitor unit, controls the output voltage of the N power supply units, and the N avalanche units It is characterized by controlling the multiplication factor of the photodiode.

  The seventh optical receiver of the present invention outputs (N−1) optical delay units and (N−1) optical delay units that respectively delay incident optical signals. Combining N avalanche photodiodes that convert optical signals into electrical signals, N power supply units that apply bias voltages to the N avalanche photodiodes, and electrical signals output from the N avalanche photodiodes The optical attenuation amount of the N light attenuating units based on the waveform information in the waveform monitoring unit and the waveform monitoring unit that monitors the electric signal waveform output from the differential amplifying unit. It is characterized by doing.

  Further, an eighth optical receiver of the present invention includes two light receiving units that convert an incident optical signal into an electric signal, and at least one of the two light receiving units is an avalanche photodiode, At least one power supply unit that applies a bias voltage to the diode, a delay unit that delays one of the electric signals output from the two light receiving units, and an electric signal output from the two light receiving units A differential amplifier for differential amplification, a waveform monitor for monitoring an electrical signal waveform output from the differential amplifier, and an output of the at least one power source based on waveform information in the waveform monitor The voltage is controlled, and the multiplication factor of the at least one avalanche photodiode is controlled.

  The ninth optical receiver of the present invention includes an optical delay unit that delays an incident optical signal, two light receiving units that convert an incident optical signal into an electrical signal, and the two light receiving units, At least one is an avalanche photodiode, and an optical signal received by one of the two light receiving units is an optical signal delayed by the optical delay unit, and is biased to the avalanche photodiode. At least one power supply unit for applying a voltage; a differential amplification unit for differentially amplifying electrical signals output from the two light receiving units; and a waveform monitor unit for monitoring an electrical signal waveform output from the differential amplification unit And controlling the output voltage of the at least one power supply unit based on the waveform information in the waveform monitor unit, and controlling the multiplication factor of the at least one avalanche photodiode. It is characterized in.

  With this configuration, when an optical signal is received using a plurality of light receiving elements, it is possible to provide an optical receiver that realizes a waveform equivalent function without increasing the circuit scale.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of an optical receiver according to Embodiment 1 of the present invention. In FIG. 1, 111 is an avalanche photodiode (APD), 112 is a variable output power source, 113 is a control unit, 114 is a light receiving element, 115 is a power source, 116 is a delay unit, 117 is a differential amplifier, 118 is a waveform monitor, 119 Is a discriminator, and 120 is an optical receiver. The light receiving element is a photodiode (PD) or APD.

  Next, the operation of the optical receiver will be described with reference to FIG. The input received optical signal is converted into an electric signal by the APD 111 to which a bias voltage is applied by the variable output power source 112 and the light receiving element 114 to which a voltage bias is applied by the power source 115, respectively. In general, the APD 111 has a multiplication characteristic depending on a given bias voltage, and has better light receiving sensitivity than a photodiode. Thereafter, the converted electric signals are input to the differential amplifier 117. Here, before being input to the differential amplifier 117, a delay is given to one of the electrical signals (here, the electrical signal output from the light receiving element 114). The differentially amplified electrical signal is input to the discriminator 119, and the data transmitted as the discrimination result is output. The waveform monitor 118 monitors the electrical signal waveform output from the differential amplifier 117, measures the degree of waveform deterioration such as intersymbol interference and eye opening from the waveform information, and outputs the result to the control unit 113. The control unit 113 controls the power source of the variable output power source 112 based on the output from the waveform monitor 118 and controls the multiplication factor of the APD 111.

  Assuming that the delay amount given by the delay unit 116 is T, when the electrical signal output from the APD 111 and the electrical signal output from the light receiving element 114 are respectively input to the differential amplifier 117, two shifts shifted by T are provided. It is differentially amplified as a waveform. Therefore, although the amplitude component decreases during the time when two electrical signals overlap, the waveform shaping is performed because the rising / falling portion of the waveform is emphasized.

  The APD 111 has a multiplication characteristic. By changing the multiplication factor by changing the bias voltage of the APD 111, a difference can be appropriately generated between the two signal levels. Thereby, the emphasis degree of the rising / falling portion of the waveform can be changed, and it is possible to appropriately cope with a situation where the waveform deterioration is different.

  As described above, the APD having a multiplication factor is used, the waveform after differential amplification is monitored, and the APD bias voltage is made variable according to the waveform deterioration, which has been conventionally required. Waveform equalization that does not require a variable amplifier can be realized.

(Embodiment 2)
FIG. 2 is a configuration diagram of an optical receiver according to Embodiment 2 of the present invention. 2, those having the same functions as those in FIG. 1 are given the same numbers, and descriptions thereof are omitted. In FIG. 2, 111-1 to N are avalanche photodiodes (APD), 112-1 to N are variable output power sources, 113-1 to N are control units, 116-1 to (N-1) are delay units, 211 Is a synthesis part. The main difference from the configuration shown in FIG. 1 is that the number of light receiving elements is N and all are APD configurations, and a variable output power source is provided for each APD so that the multiplication factor can be varied. ) Delay units are provided, and different delay times are given to the electrical signals output from all APDs to synthesize them.

Next, the operation of the optical receiver will be described with reference to FIG. The input received optical signals are converted into electric signals in the APDs 111-1 to N, to which the bias voltages V _{b1 to} V _bN are given by the variable output power sources 112-1 to 112-N, respectively. Thereafter, (N−1) electrical signals, excluding one of the converted N electrical signals, are converted into different delay amounts T˜ (N−1) by the delay units 116-1 to (N−1), respectively. -1) Receive T Thereafter, N electrical signals are combined by the combining unit 211. The synthesized electric signal is input to the discriminator 119, and the data transmitted as the discrimination result is output. Further, the waveform monitor 118 monitors the electrical signal waveform output from the synthesizing unit 211, measures the degree of waveform deterioration such as intersymbol interference and eye opening from the waveform information, and sends the result to the control units 113-1 to 113-N. Output. The control units 113-1 to 113 -N control the power sources of the variable output power sources 112-1 to 112 -N based on the output from the waveform monitor 118 and control the multiplication factors of the APDs 111-1 to N.

  In the configuration of the second embodiment, N APDs 111-1 to 111 -N are provided, and the bias voltage applied to each APD is made variable using the variable output power sources 112-1 to 112 -N. The delay units 116-1 to (N-1) are provided for synthesizing the output N electrical signals with different delay times. By adopting this configuration, a transversal filter configuration that is an optical signal input is provided, and waveform equalization with higher accuracy can be realized as compared with the first embodiment.

  As described above, using N APDs having multiplication factors, N electrical signals after photoelectric conversion are multiplexed with different delay amounts, and APDs are added according to waveform deterioration after the multiplexing. By making the bias voltage variable, it is possible to realize waveform equalization that is conventionally required and that does not require N variable amplifiers.

(Embodiment 3)
FIG. 3 is a configuration diagram of an optical receiver according to Embodiment 3 of the present invention. In FIG. 3, those having the same functions as those in FIG. The main difference from FIG. 1 is that the bias voltage applied to the APD 111 is applied from the power supply 115 instead of the variable output power supply 112, and a variable optical attenuator 311 for attenuating the optical signal power incident on the APD is provided. It is a point.

  Next, the operation of the optical receiver will be described with reference to FIG. The operation of the third embodiment is different from that of the first embodiment in that the variable output power source 112 makes the bias voltage applied to the APD variable so that the gain can be changed, and the optical power incident on the APD itself Is realized by changing the attenuation of the variable optical attenuator 311.

  Therefore, the control unit 113 can change the attenuation amount of the variable optical attenuator 311 based on the waveform information monitored by the waveform monitor 118, thereby realizing the same operation as in the first embodiment. .

  An example in which a variable mirror is used as the variable optical attenuator 311 is shown in FIG. FIG. 4 is a configuration diagram of the optical space transmission method according to Embodiment 3 of the present invention. FIG. 4 shows a configuration in which a variable mirror 411 is added, focusing on only the optical coupling to the APD 111. The variable mirror 411 is configured to reflect an incident received optical signal and couple the optical signal to the light receiving element, and the mirror direction is variable according to the direction of the incident received optical signal. A configuration in which the reflection direction of the mirror is made variable according to the direction of the incident optical signal is a common optical axis adjustment method in optical space transmission.

  By making the reflection direction of the variable mirror 411 variable, the amount of the optical signal incident on the APD 111 is also variable, so that it can be used as a variable optical attenuator.

  As shown in FIG. 4, the control unit 113 shown in the first embodiment controls the reflection direction of the variable mirror 411 to adjust the amount of the optical signal incident on the light receiving element, thereby changing the variable optical attenuation. Functions can be realized. Therefore, the control unit 113 controls the optical axis adjustment configuration that is used as an optical axis adjustment method in optical space transmission, so that it can also be used as a variable optical attenuation function. In addition, by using a variable mirror that is generally used as an optical axis adjustment configuration, it can be realized with a very small configuration.

  As described above, the waveform equalization function can also be realized by providing a variable optical attenuator instead of the variable output power source shown in the first embodiment to attenuate the optical signal power input to the APD. In addition, by using a reflection mirror that has been used for the purpose of optical axis adjustment in conventional optical space transmission as a variable optical attenuator, a variable amplifier that has been necessary in the past can be obtained without a new additional configuration. Unnecessary waveform equalization can be realized.

(Embodiment 4)
FIG. 5 is a configuration diagram of an optical receiver according to Embodiment 4 of the present invention. 5, those having the same functions as those in FIG. 3 are given the same numbers, and descriptions thereof are omitted. The main difference from FIG. 3 is that an optical delay unit 511 is provided instead of the delay unit 116 that delays the electrical signal output from the light receiving element 114.

  Next, the operation of the optical receiver will be described with reference to FIG. The operation of the fourth embodiment is different from the third embodiment in that instead of delaying the electrical signal using the delay unit 116, the optical signal is delayed using the optical delay unit 511. is there. As the optical delay unit 511, there is a method of generating a desired delay time once coupled to an optical fiber, an optical waveguide or the like. In addition, although there are technically unfinished parts, it is possible to vary the propagation speed in the crystal by using the photonic crystal structure. A desired delay time can be obtained not by adjusting the transmission distance but by controlling the propagation speed.

  FIG. 6 shows an example in which an optical filter 611 is used as the optical delay unit 511 in FIG. In FIG. 6, it is assumed that the incident optical signals are wavelength-multiplexed optical signals that are modulated with the same data (not shown). The input wavelength-multiplexed optical signal is input to the optical filter 611, and if a diffraction grating type optical filter is used, it is separated in a different direction for each wavelength. Accordingly, different delay amounts can be provided by installing the APDs 111-1 to 111 -N at different distances from the optical filter 611.

  As described above, the waveform equalization function can be realized only by synthesizing in the electric signal region and by providing a delay in the optical signal region. Thereby, it is possible to perform high-speed processing compared to the electrical signal.

  An optical receiver according to the present invention uses an APD having a multiplication factor, monitors a waveform after synthesizing a plurality of electric signals, and makes a bias voltage of the APD variable according to waveform deterioration. Thus, it is possible to realize waveform equalization that is conventionally required and does not require a variable amplifier. Accordingly, it is possible to provide an optical receiver or the like that is strong against fluctuations in the optical space and waveform distortion in the optical transceiver, and that is small and that realizes good transmission quality.

Configuration diagram of optical receiver in Embodiment 1 of the present invention Configuration diagram of optical receiver in Embodiment 2 of the present invention Configuration diagram of optical receiver according to Embodiment 3 of the present invention Example of variable optical attenuator according to Embodiment 3 of the present invention Configuration diagram of optical receiver in Embodiment 4 of the present invention Example of optical delay unit in embodiment 4 of the present invention Conventional automatic equivalent circuit that performs waveform equalization based on intersymbol interference after receiving light Schematic diagram showing a conventional tap delay line filter used for waveform equalization

Explanation of symbols

111-1 to N Avalanche Photodiode (APD)
112-1 to N Variable output power supply 113-1 to N Control unit 114 Light receiving element 115-1 to N power supply 116-1 to (N-1) Delay unit 117 Differential amplifier 118 Waveform monitor 119 Discriminator 120 Optical receiver 311 Variable optical attenuator 411 Variable mirror 511 Optical delay unit 611 Optical filter

Claims (9)

N light attenuators that change the amount of incident light with respect to an incident optical signal;
N light receiving units that convert an optical signal output from the light attenuating unit into an electrical signal;
Of the electrical signals output from the N light receiving units, a delay unit that delays (N-1) electrical signals;
A combining unit that combines the electrical signals output from the N light receiving units;
The optical attenuation amount of the N optical attenuation units is controlled based on the waveform information in the waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit and the waveform monitor unit, Receiver. N light attenuators that change the amount of incident light with respect to an incident optical signal;
Among the optical signals output from the optical attenuating unit, an optical delay unit that delays (N-1) optical signals;
N light receiving units that convert optical signals output from the N light attenuating units into electrical signals;
A combining unit that combines the electrical signals output from the N light receiving units;
The optical attenuation amount of the N optical attenuation units is controlled based on the waveform information in the waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit and the waveform monitor unit, Receiver. Two light attenuators that change the amount of incident light with respect to an incident optical signal;
Two light receiving units for converting an optical signal output from the light attenuating unit into an electrical signal;
A delay unit that delays one of the electrical signals output from the two light receiving units;
A differential amplifier for differentially amplifying electrical signals output from the two light receivers;
Based on the waveform information in the waveform monitor unit and the waveform monitor unit that monitors the electrical signal waveform output from the differential amplifier unit, the optical attenuation amount of the two optical attenuation units is controlled, Optical receiver. Two light attenuators that change the amount of incident light with respect to an incident optical signal;
An optical delay unit that delays one of the optical signals output from the optical attenuation unit;
Two light receiving sections for converting the optical signals output from the two light attenuating sections into electrical signals;
A differential amplifier for differentially amplifying electrical signals output from the two light receivers;
Based on the waveform information in the waveform monitor unit and the waveform monitor unit that monitors the electrical signal waveform output from the differential amplifier unit, the optical attenuation amount of the two optical attenuation units is controlled, Optical receiver.   The optical receiver according to claim 1, wherein the optical attenuator is a MEMS mirror. N avalanche photodiodes that convert incident optical signals into electrical signals;
N power supply units for applying a bias voltage to the N avalanche photodiodes;
A delay unit that delays (N−1) electrical signals among electrical signals output from the N avalanche photodiodes;
A combining unit that combines the electrical signals output from the N avalanche photodiodes;
Based on the waveform information in the waveform monitor unit and the waveform monitor unit that monitors the electrical signal waveform output from the synthesis unit, the output voltage of the N power supply units is controlled, and the N avalanche photodiodes An optical receiver characterized by controlling a multiplication factor. (N−1) optical delay units that respectively delay incident optical signals;
N avalanche photodiodes that convert optical signals output from the (N-1) optical delay units into electrical signals;
N power supply units for applying a bias voltage to the N avalanche photodiodes;
A combining unit that combines the electrical signals output from the N avalanche photodiodes;
A waveform monitor unit that monitors an electrical signal waveform output from the differential amplifier unit, and a light attenuation amount of the N light attenuating units is controlled based on waveform information in the waveform monitor unit. , Optical receiver. Two light receiving sections for converting an incident optical signal into an electrical signal;
Of the two light receiving parts, at least one is an avalanche photodiode,
At least one power supply for applying a bias voltage to the avalanche photodiode;
A delay unit that delays one of the electrical signals output from the two light receiving units;
A differential amplifier for differentially amplifying electrical signals output from the two light receivers;
A waveform monitor unit for monitoring an electrical signal waveform output from the differential amplifier unit; and, based on waveform information in the waveform monitor unit, controlling an output voltage of the at least one power supply unit, and the at least one avalanche photo An optical receiver characterized by controlling a multiplication factor of a diode. An optical delay unit that delays an incident optical signal;
Two light receiving sections for converting an incident optical signal into an electrical signal;
Of the two light receiving parts, at least one is an avalanche photodiode,
The optical signal received by any one of the two light receiving units is an optical signal delayed by the optical delay unit,
At least one power supply for applying a bias voltage to the avalanche photodiode;
A differential amplifier for differentially amplifying electrical signals output from the two light receivers;
A waveform monitor unit for monitoring an electrical signal waveform output from the differential amplifier unit; and, based on waveform information in the waveform monitor unit, controlling an output voltage of the at least one power supply unit, and the at least one avalanche photo An optical receiver characterized by controlling a multiplication factor of a diode.

Images