JP2008245118A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical level detection circuit capable of detecting an optical level input to a VOA (variable optical attenuator) on the basis of a driving current of the VOA and a photo-current flowing through a photodetector for a main signal in an optical receiver including the VOA and the photodetector. <P>SOLUTION: In the optical receiver, the VOA 101 is electrically connected with a driving circuit 104, and a photodetector 102 is electrically connected with a bias application circuit 105. Current detection circuits 106, 107 are connected to the VOA 101 and the photodetector 102, and the current detection circuits 106, 107 are connected with an arithmetic circuit 108. The output of the current detection circuits 106, 107 is converted from an analog signal to a digital signal by A/D converters 109a, 109b and input to a microprocessor 110 that performs digital operation. The microprocessor 110 calculates an optical input level value from the driving current value of the VOA 101 and the photo-current value of the photodetector 102. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical receiver having an input optical level detection circuit, and more particularly to an optical receiver having an optical input level detection circuit using an attenuation amount of a variable optical attenuator and a photocurrent value of a light receiving element.

  In general, an optical receiving apparatus includes a light receiving element such as an APD (Avalanche Photodiode) or PIN-PD (P-Intrinsic-N Photodiode), a transimpedance amplifier (TIA), a clock data reproduction (CDR) circuit, and the like. In some cases, a variable optical attenuator (VOA) is mounted in the input stage for the purpose of expanding the dynamic range of the optical input level. In general, an optical receiving apparatus needs to detect an optical input level in order to realize a function such as detecting an optical input being interrupted and raising an alarm. Optical input level detection methods include a method in which a part of the input light is branched and detected by a monitor photodetector other than the main signal photodetector, or a method in which detection is performed by the photocurrent of the main signal detection photodetector. Yes. (Non-Patent Document 1)

Takagi, Horio, Harada, Umezawa: “Multiplexing / demultiplexing function integrated 10 Gb / s optical transceiver”, Oki Technical Review, Vol. 190, Vol. 69 No. 2. April 2002

  However, the method of branching a part of the input light and detecting it with a monitor photodetector different from the main signal photodetector further requires an optical branch circuit and a photodetector only for detecting the optical level, which is complicated by the receiver. There has been a problem in that the performance is deteriorated due to the increase in size, the size, the cost, and the lowering of the main signal level. Also, the method of detecting by the photocurrent of the main signal detecting photo detector is not dependent only on the optical input level, but also greatly depends on the optical attenuation of the VOA in an optical receiver equipped with a VOA function. Therefore, there has been a problem that it is practically not applicable to optical input level detection.

  The present invention has been made in view of such problems, and an object thereof is based on the driving state of the VOA and the photocurrent flowing through the photodetector for the main signal in the optical receiver having the VOA and the photodetector. The purpose is to detect the light level input to the optical receiver.

  In order to achieve such an object, the present invention as claimed in claim 1 is an optical receiver, wherein variable optical attenuating means capable of adjusting a level of an input optical signal, and light output from the variable optical attenuating means. An optical receiver comprising: a photoelectric conversion unit that converts a signal into an electric signal; and an optical input level detection unit that is capable of detecting a level of the input optical signal. It has a function of detecting the level of the input optical signal from the attenuation amount of the variable light attenuating means and the light level input to the photoelectric conversion means.

  According to a second aspect of the present invention, in the optical receiver according to the first aspect, the optical input level detecting unit includes a first monitoring unit that monitors a driving current value or a driving voltage value of the variable optical attenuating unit. A second monitoring means for monitoring a bias current value, a photocurrent value of the photoelectric conversion means or a voltage value corresponding to them, an output of the first monitoring means, and an output of the second monitoring means, And calculating means for calculating at least a light input level value using the

  According to a third aspect of the present invention, in the optical receiver according to the second aspect, the first monitor means can be considered to be proportional to or proportional to a logarithmic (dB) display value of the attenuation amount of the variable optical attenuator. A value is output, and the second monitor means outputs a value that is proportional to or can be considered to be proportional to a logarithm (dBm) display of the light level incident on the photoelectric conversion means.

  According to a fourth aspect of the present invention, in the optical receiver according to the third aspect, at least one of the first monitor unit and the second monitor unit includes a log amplifier.

  According to a fifth aspect of the present invention, in the optical receiver according to any one of the second to fourth aspects, the calculating means includes an adding means or a subtracting means.

  According to a sixth aspect of the present invention, in the optical receiver according to any of the second to fifth aspects, the calculation means includes a level comparison means.

  According to a seventh aspect of the present invention, in the optical receiver according to any one of the second to sixth aspects, the computing means outputs an output of the first monitor means and an output of the second monitor means, respectively. An AD conversion means for converting an analog signal into a digital signal and a digital calculation means for inputting a digital signal output from the AD conversion means and performing a digital calculation are provided.

  According to an eighth aspect of the present invention, in the optical receiver according to the seventh aspect, the calculation unit corrects at least one of the output of the first monitoring unit and the output of the second monitoring unit. A correction table or a correction function, and the digital operation means corrects at least one of the output of the first monitor means and the output of the second monitor means by the correction table or the correction function. It is characterized by doing.

  According to a ninth aspect of the present invention, in the optical receiver according to the seventh or eighth aspect, the arithmetic means converts DA output means for converting the output of the digital arithmetic means from a digital signal to an analog signal, and the DA conversion. Voltage level comparing means for comparing the voltage level of the reference voltage level given by the output of the means and the output of the second monitoring means.

  A tenth aspect of the present invention is the optical receiver according to any one of the first to ninth aspects, further comprising a temperature detection unit, and the optical input level according to a temperature value detected by the temperature detection unit. The light input level detected by the detecting means is corrected.

  According to an eleventh aspect of the present invention, there is provided the optical receiver according to any one of the first to ninth aspects, further comprising an optical wavelength setting unit, wherein the light is set in accordance with a wavelength value set by the optical wavelength setting unit. The optical input level detected by the input level detecting means is corrected.

  A twelfth aspect of the present invention is the optical receiver according to any one of the first to ninth aspects, further comprising an optical wavelength detection unit, wherein the light is detected according to a wavelength value detected by the optical wavelength detection unit. The optical input level detected by the input level detecting means is corrected.

  According to the present invention, in an optical receiver having a VOA and a photodetector, it is possible to detect the optical level input to the optical receiver based on the driving state of the VOA and the photocurrent flowing through the photodetector for main signals. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1A shows an optical level detection method in a conventional optical receiver, and FIG. 1B shows an optical level detection method in the optical receiver according to the embodiment of the present invention. The VOA 101 and the photodetector 102 are optically connected, and the photodetector 102 and the CDR 103 are electrically connected. The VOA 101 is electrically connected to the drive circuit 104 and the amount of attenuation of the input optical signal is controlled by the drive circuit 104. The photodetector 102 is electrically connected to the bias application circuit 105 and is applied with a reverse bias voltage from the bias application circuit 105.

  The conventional optical receiver has a configuration in which an input optical signal is branched before the VOA 101 and the optical level of the branched light is monitored (FIG. 1A). On the other hand, according to the present invention, the optical level detection circuit 100 is connected so as to be able to monitor the drive current (or drive voltage) of the VOA 101 and the APD current flowing through the photodetector 102 (FIG. 1B), and controls the VOA 101. The light level is detected from the drive current or drive voltage and the bias current flowing through the photodetector 102. That is, in the present invention, the optical level can be measured without using the branched light of the input optical signal.

  FIG. 2 shows a configuration example of an optical level detection circuit according to the embodiment of the present invention. The VOA 101 and the photodetector 102 are optically connected, and the photodetector 102 and the CDR 103 are electrically connected. The VOA 101 is electrically connected to the drive circuit 104 and the amount of attenuation of the input optical signal is controlled by the drive circuit 104. The photodetector 102 is electrically connected to the bias application circuit 105 and is applied with a reverse bias voltage from the bias application circuit 105.

  A current detection circuit 106 is inserted between the VOA 101 and the drive circuit 104, a current detection circuit 107 is inserted between the photodetector 102 and the bias application circuit 105, and the current detection circuits 106 and 107 are connected to the arithmetic circuit 108. ing. The current detection circuits 106 and 107 may be voltage detection circuits. In this case, the current values detected by the current detection circuits 106 and 107 are read as voltage values.

  Outputs of the current detection circuits 106 and 107 are converted from analog signals to digital signals by the AD converters 109a and 109b, and input to the microprocessor 110 that performs digital calculation. In the microprocessor 110, the attenuation amount of the VOA 101 and the light level incident on the photodetector 102 from the outputs of the current detection circuits 106 and 107 are treated as logarithmic values.

  The microprocessor 110 performs logarithmic display by calculating on at least one of the drive current value of the VOA 101 and the photocurrent value of the photodetector 102 based on the correction table or the correction function stored in the storage device 111. Convert to Then, the microprocessor 110 calculates an optical input level value from the drive current value and the photocurrent value that are arranged in units. Note that variations due to individual differences can be corrected by using a correction table or a correction function.

  Further, in the present embodiment, the comparator 113 is connected without passing through the current detector 107 and the AD converter 109b, and is connected through the microprocessor 110 and the DA converter 112. The comparator 113 compares the current value signal from the current detector 107 with the reference level signal generated by the microprocessor 110 based on the current value of the current detector 106, and determines whether the intensity of the input optical signal satisfies a predetermined standard. Promptly determine whether or not. When speed is required for determination such as issuing an alarm due to light input interruption or releasing an alarm due to input recovery, a configuration using an analog circuit is desirable.

  Such a determination of the input optical signal level can also be made in the microprocessor 110. FIG. 5 shows a configuration example of an optical level detection circuit according to an embodiment of the present invention in which a microprocessor has a function of determining an input optical level. In this embodiment, functions such as an optical input level monitor, an alarm issuance, and an alarm release are realized by digital output from a microprocessor without using a DA converter.

  In addition, when at least one of the attenuation amount of the VOA 101 detected by the current detection circuit 106 and the input level to the photodetector 102 detected by the current detection circuit 107 is a linearly displayed value, the linearly displayed value is By connecting a log amplifier to at least one of the output of the current detection circuit 106 and the current detection circuit 107 to be output, the logarithmic display value can be converted before AD conversion. A configuration example of this embodiment is shown in FIG. Since the photocurrent value of the photodetector 102 is generally a linear value with respect to the input light level, it is effective to insert the log amplifier 116 at the output of the current detection circuit 107. Since it is assumed that the attenuation amount of the VOA 101 detected by the current detection circuit 106 is a logarithmic value, the log amplifier 116 is not inserted in the output of the current detection circuit 106. In the present embodiment, logarithmic conversion in the digital arithmetic circuit is unnecessary, and the load on the digital arithmetic circuit can be reduced.

  FIG. 3 shows a configuration in which the optical receiver according to the embodiment of the present invention includes a temperature detector. If the arithmetic circuit 108 is further provided with a temperature detector 114, the optical input level value can be corrected in accordance with the detected temperature based on the temperature characteristics of the optical receiver previously examined. The level value detection accuracy can be increased.

  If the wavelength setting means 117 is provided in addition to the temperature detector 114, the optical input level value is corrected by correcting the optical input level value according to the wavelength value if the wavelength of the input optical signal is known. The detection accuracy can be further increased. A configuration example of this embodiment is shown in FIG. Only the wavelength setting means may be used without using the temperature detection means.

  FIG. 4 shows a configuration in which the optical receiver according to the embodiment of the present invention includes the wavelength detector 115. If the wavelength detector 115 including the wavelength setting means is provided, correction can be performed according to the detected wavelength value even if the wavelength of the input optical signal is not known in advance. The present embodiment may include a temperature detection unit as in the embodiment shown in FIG.

  Another configuration example is shown in FIG. In the present embodiment so far, the digital circuit is used as the circuit for calculating the optical input level value in the arithmetic circuit 108. However, this may be assembled by an analog circuit 118 including an addition circuit or a subtraction circuit.

(A) is a figure which shows the structure of the conventional optical receiver, (b) is a figure which shows the structure of the receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the optical receiver which concerns on embodiment of this invention.

Explanation of symbols

100 Optical input level detection means 101 VOA
102 Photo detector 103 CDR
104 Driving circuit 105 Bias voltage application circuit 106, 107 Current detection circuit 108 Arithmetic means 109a, 109b AD converter 110 Microprocessor 111 Storage device 112 DA converter 113 Comparator 114 Temperature detector 115 Wavelength detector 116 Log amplifier 117 Wavelength setting means 118 Addition Circuit including subtractor or subtractor

Claims (12)

Variable optical attenuation means capable of adjusting the level of the input optical signal;
Photoelectric conversion means for converting an optical signal output from the variable optical attenuation means into an electrical signal;
Optical input level detection means capable of detecting the level of the input optical signal;
In an optical receiver comprising:
The optical receiving device, wherein the optical input level detecting means has a function of detecting the level of the input optical signal from the attenuation amount of the variable optical attenuating means and the optical level input to the photoelectric converting means. . The optical input level detection means is
First monitoring means for monitoring a driving current value or a driving voltage value of the variable light attenuating means;
Second monitoring means for monitoring a bias current value, a photocurrent value of the photoelectric conversion means, or a voltage value corresponding to them;
A computing means for computing at least a light input level value using the output of the first monitoring means and the output of the second monitoring means;
The optical receiver according to claim 1, further comprising:   The first monitoring means outputs a value proportional to or proportional to the logarithmic (dB) display value of the attenuation of the variable optical attenuator, and the second monitoring means is incident on the photoelectric conversion means. 3. The optical receiver according to claim 2, wherein a value that is proportional to or can be regarded as proportional to a value expressed in logarithm (dBm) as an optical level is output.   4. The optical receiver according to claim 3, wherein at least one of the first monitor unit and the second monitor unit includes a log amplifier.   5. The optical receiver according to claim 2, wherein the calculating means includes an adding means or a subtracting means.   6. The optical receiver according to claim 2, wherein the arithmetic means includes a level comparison means. The computing means is
AD conversion means for converting the output of the first monitoring means and the output of the second monitoring means from an analog signal to a digital signal, respectively;
Digital operation means for inputting a digital signal output from the AD conversion means and performing digital operation;
The optical receiver according to claim 2, further comprising: The calculation means includes a correction table or a correction function function for correcting at least one value of the output of the first monitor means and the output of the second monitor means,
8. The digital arithmetic means corrects at least one value of the output of the first monitor means and the output of the second monitor means by the correction table or the correction function. Optical receiver. The computing means is
DA conversion means for converting the output of the digital operation means from a digital signal to an analog signal;
Voltage level comparison means for comparing the voltage level of the reference voltage level given by the output of the DA conversion means and the output of the second monitoring means;
The optical receiver according to claim 7 or 8, further comprising:   10. The light input level detected by the light input level detecting means is corrected according to a temperature value detected by the temperature detecting means. 10. The optical receiver described in 1.   10. The optical input level detected by the optical input level detecting means is corrected according to a wavelength value set by the optical wavelength setting means. Any one of the optical receivers.   10. The optical input level detected by the optical input level detecting unit is corrected according to a wavelength value detected by the optical wavelength detecting unit. Any one of the optical receivers.

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