JP2004236259A - Optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve gain control of high linearity without using a pilot signal. <P>SOLUTION: A photo-diode PD is biased by a Zener diode ZD. The intensity of an optical signal photo-detected by the photo-diode PD is detected by a control part 12 and on the basis of a detecting signal, gain control of an electric signal resulting from converting the optical signal is performed by a variable attenuation part 11. Non-linear characteristics of the photo-diode PD are corrected by non-linear characteristics of the Zener diode ZD, thereby obtaining an approximately constant output from the variable attenuation part 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical receiver that can perform stable gain control without using a pilot signal.
[0002]
[Prior art]
When the light receiving level of the optical receiver changes in the optical transmission system, the level of the electric signal output from the optical receiver changes. However, in the optical transmission system, it is required that the output electric signal has a constant output level even when the light receiving level in the optical receiver changes. To achieve this, a pilot signal is added to the optical signal and transmitted, and the gain control is performed so that the level of the pilot signal extracted in the optical receiver is constant. Even so, the output electric signal is kept constant.
[0003]
However, the transmitter has a problem that a pilot signal transmitting means for superimposing a pilot signal on a transmission signal and transmitting the signal must be provided separately, and a pilot signal extracting means for extracting the pilot signal is required in the receiver. there were. Further, there is a system that cannot use a pilot signal, and there is a problem that gain control cannot be performed in such a system.
In order to solve this problem, the level of an optical signal received by the light receiving element is monitored by a monitor terminal provided on the light receiving element, and the monitor signal from the monitor terminal allows the electric signal output from the light receiving element to be monitored. It has been proposed to control the level (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-8-56200
[Problems to be solved by the invention]
FIG. 7 shows a circuit example of a conventional optical receiver that detects the level of an optical signal received by a light receiving element and controls the gain of an electric signal output from the light receiving element based on the detected signal.
In FIG. 7, an optical signal input from an optical fiber or the like is received by a photodiode PD. A bias is applied to the photodiode PD from a power supply (+ Vcc) by the resistors R101 and R100. Then, the photocurrent flowing through the photodiode PD has a magnitude corresponding to the intensity of the optical signal, and the optical signal is converted into an electric signal. This electric signal is supplied to the first amplifying unit 110 via the capacitor C100 that extracts only the signal component, and is amplified at a predetermined amplification degree. The amplified electric signal is supplied to the second amplifying unit 113 via the variable attenuating unit 111 and is amplified at a predetermined amplification degree. Further, the electric signal converted by the photodiode PD is supplied to the control unit 112, and the intensity of the optical signal is detected. The control unit 112 controls the amount of attenuation of the variable attenuator 111 in accordance with the intensity of the detected optical signal so that the level of the electric signal output from the variable attenuator 111 becomes constant.
[0006]
Here, FIG. 8 shows the characteristic of the photocurrent Ipd [mA] flowing through the photodiode PD with respect to the optical input power [dBm] of the photodiode PD. Referring to FIG. 8, the photocurrent Ipd has non-linear characteristics that increase exponentially with respect to the optical input power. Further, since the variable attenuation unit 111 controls the passing amount by the PIN diode, the variable attenuation unit 111 has a non-linear characteristic in which the attenuation amount varies logarithmically with respect to the control amount. As described above, even if the control amount output from the control unit 112 becomes exponentially non-linear with respect to the optical signal power received by the photodiode PD, the attenuation of the variable attenuator 111 does not increase with respect to the control amount. There is a problem that it is difficult to keep the output constant even when the gain is controlled because the output changes nonlinearly in a logarithmic function. That is, FIG. 9 shows the frequency characteristics of the output level in the receiver shown in FIG. 7, and the frequency characteristics of the output level shown in FIG. 9 are the characteristics when the optical input power of the photodiode PD is +1 dBm and -5 dBm. Referring to FIG. 9, when the optical input power increases from -5 dBm to +1 dBm, the output level also increases by 4 to 5 dB, and it can be seen that the output level is not constantly controlled in gain.
[0007]
Therefore, an object of the present invention is to provide an optical receiver capable of performing stable gain control without using a pilot signal.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an optical receiver according to the present invention comprises a diode means for applying a bias to a photodiode, the voltage-current characteristic of which exhibits a non-linear characteristic, and an optical input taken out from one end of the photodiode. A control unit to which an electric signal that changes according to the magnitude is input, and a level of a non-linear characteristic that controls a level of a reception signal output from the photodiode by a control signal from the control unit. Variable means.
[0009]
Further, in the optical receiver according to the present invention, the diode may be a Zener diode, and a bias may be applied to the photodiode by using a non-linear characteristic of the Zener diode.
Further, in the above-mentioned optical receiver of the present invention, the control means has a noise removing means, and the electricity removed from one end of the photodiode by the noise removing means changes according to the magnitude of the optical input. The noise included in the signal may be removed.
Further, in the optical receiver according to the present invention, the electric signal extracted from one end of the photodiode and changing according to the magnitude of the optical input is transmitted through the temperature compensating means for performing temperature compensation of the diode means. You may make it input into the said control means.
[0010]
According to the present invention, the bias is applied to the photodiode by the diode means having a non-linear voltage-current characteristic, so that the gain control that can keep the output level constant can be performed. Become. Further, since the noise included in the electric signal which changes according to the magnitude of the light input is removed by the noise removing means included in the control means, it is possible to prevent the influence of the noise generated from the diode means and the like. Further, by performing temperature compensation of the diode means having a non-linear voltage-current characteristic, it is possible to perform gain control in which a level change with respect to a temperature change is suppressed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a circuit configuration of an optical receiver according to an embodiment of the present invention.
In FIG. 1, a series circuit of a Zener diode ZD, a photodiode PD, and a resistor R is connected between a power supply (+ Vcc) and the ground, and a bias is applied to the photodiode PD by the Zener diode ZD. An optical signal input from an optical fiber or the like is received by the photodiode PD. Then, the photocurrent flowing through the photodiode PD has a magnitude corresponding to the intensity of the optical signal, and the optical signal is converted into an electric signal. This electric signal is supplied to the first amplifying unit 10 via the capacitor C that extracts only the signal component, and is amplified at a predetermined amplification degree. The amplified electric signal is gain-controlled in the variable attenuator 11 and supplied to the second amplifier 13 where it is amplified at a predetermined amplification factor. Further, the electric signal converted by the photodiode PD is supplied to the control unit 12, and the intensity of the optical signal is detected.
[0012]
The control unit 12 controls the gain of the variable attenuator 11 by controlling the amount of attenuation of the variable attenuator 11 according to the intensity of the detected optical signal so that the level of the electric signal output from the variable attenuator 11 is constant. I have. Here, an example of the voltage-current characteristic when a reverse voltage is applied to the Zener diode ZD is shown in FIG. As shown in FIG. 3, when a reverse voltage is applied to the Zener diode ZD, the voltage Vd has a logarithmic function characteristic in which the voltage Vd is substantially constant even if the current Id changes. Therefore, when the photocurrent Ipd flowing through the photodiode PD that receives the optical signal changes according to the power of the optical signal, the bias voltage Vd of the photodiode PD changes with a logarithmic function characteristic. From this, when a bias is applied to the photodiode PD by the Zener diode ZD, the electric signal converted in the photodiode PD by the nonlinear characteristic of the Zener diode ZD changes in a logarithmic function characteristic with respect to the optical input power. Become.
[0013]
Such an electric signal is supplied to the amplifying unit 10 via the capacitor C and to the control unit 12. Then, the variable attenuator 11 is controlled according to the light intensity detected by the controller 12. The variable attenuator 11 is configured using, for example, a PIN diode, and the amount of attenuation of the variable attenuator 11 changes in a logarithmic non-linear manner with respect to the control amount. Then, as described above, the electric signal that changes in a logarithmic function characteristic with respect to the optical input power is amplified by the amplifying unit 10 and supplied to the variable attenuating unit 11, so that the variable whose attenuation amount changes in a logarithmic function. The attenuator 11 outputs an electric signal having a substantially constant level.
Here, FIG. 4 shows the frequency characteristics of the output level when the optical input power changes in the optical receiver of the present invention shown in FIG. The frequency characteristic of the output level shown in FIG. 4 is a frequency characteristic when the optical input power of the photodiode PD is +1 dBm and -5 dBm. Referring to FIG. 4, even if the optical input power increases from -5 dBm to +1 dBm. It can be seen that the deviation of the output level is within about 1 dB, and that the gain is controlled so that the output level becomes constant.
[0014]
Although not shown, a low-pass filter is provided between the connection point between the photodiode PD and the capacitor C and the Zener diode, and an electric signal on which noise generated in the Zener diode ZD is superimposed by the low-pass filter. , Are not input to the amplifying unit 10. Further, the electric signal converted by the photodiode PD may be supplied to the control unit 12 via a low-pass filter to prevent the influence of noise generated in the Zener diode ZD.
[0015]
Incidentally, the voltage-current characteristic of the Zener diode ZD is a function of temperature, and changes according to the ambient temperature. Therefore, FIG. 5 shows the frequency characteristics of the output level when the ambient temperature changes in the optical receiver of the circuit shown in FIG. The frequency characteristics of the output level shown in FIG. 5 are the frequency characteristics when the ambient temperature is −10 ° C., 20 ° C., and 50 ° C. Referring to FIG. 5, when the ambient temperature changes from −10 ° C. to 20 ° C., the output level deviation becomes about 1.5 dB, and when the ambient temperature changes from −10 ° C. to 50 ° C., the output level deviation expands to about 3 dB. And the gain is not controlled so that the output level becomes constant.
[0016]
FIG. 2 shows another circuit configuration of the optical receiver according to the embodiment of the present invention which can solve this problem.
The optical receiver shown in FIG. 2 includes the temperature compensator 20 in the optical receiver shown in FIG. The temperature compensator 20 will now be described. A resistor R3 is connected in series between a power supply (+ Vcc) and the ground in a parallel circuit of the thermistor TH and the resistor R2. A connection point between the parallel circuit and the resistor R3 is connected to an inverting input terminal of the amplifier 14, and a non-inverting input terminal of the amplifier 14 is connected to a connection point between the Zener diode ZD and the photodiode PD. . As a result, an output based on the difference between the inputs from the amplification unit 14 to both input terminals can be obtained. Since this output decreases as the temperature of the thermistor TH increases, the output decreases as the ambient temperature increases. Since the variable attenuator 11 is controlled in accordance with this output, the control amount output from the controller 12 decreases when the ambient temperature increases, and the control is performed such that the attenuation of the variable attenuator 11 increases. become.
[0017]
On the other hand, when the ambient temperature is low, the control is performed in such a manner that the control amount output from the control unit 12 increases and the attenuation amount of the variable attenuation unit 11 decreases. Thus, the gain is controlled so that the output level from the variable attenuator 11 becomes constant regardless of the change in the ambient temperature. Here, FIG. 6 shows the frequency characteristics of the output level when the ambient temperature changes in the optical receiver of the circuit shown in FIG. The frequency characteristics of the output level shown in FIG. 6 are the frequency characteristics when the ambient temperature is −10 ° C., 20 ° C., and 50 ° C. Referring to FIG. 6, even when the ambient temperature changes from −10 ° C. to 20 ° C., the deviation of the output level is about 0.5 dB. It is within about 1 dB, and the gain is controlled so that the output level becomes constant. The resistor R2 connected in parallel with the thermistor TH is a resistor for adjusting the temperature characteristics of the thermistor TH.
[0018]
In addition, since the zener diode ZD generates noise, the control unit 12 removes the noise. That is, by connecting the capacitor C2 between the output terminal of the amplifying unit 14 and the inverting input terminal of the control unit 12, a low-pass filter is formed by the action of the resistor R5 connected to the non-inverting input terminal. The control signal from which noise has been removed by the low-pass filter is output from the control unit 12, and noise is removed from the control signal supplied to the variable attenuation unit 11. Further, although not shown, a low-pass filter is provided between the connection point between the photodiode PD and the capacitor C and the zener diode, and the low-pass filter generates an electric signal on which noise generated in the zener diode ZD is superimposed. , Are not input to the amplifying unit 10.
The circuit configuration of the control unit 12 shown in FIG. 1 is the same as the circuit configuration of the control unit 12 shown in FIG. 2, but the input terminal of the resistor R5 is grounded, and the control unit 12 shown in FIG. Removal has been performed.
[0019]
In the above description, a stable gain control is performed by applying a bias to the photodiode PD using the Zener diode ZD. However, the present invention is not limited to this, and the present invention is not limited to this. One or more general diodes may be connected in series, and a semiconductor element having characteristics capable of correcting the nonlinearity of the photodiode PD can be used instead of the Zener diode ZD.
[0020]
【The invention's effect】
As described above, in the present invention, the bias is applied to the photodiode by the diode means having a non-linear voltage-current characteristic, so that the gain control that can keep the output level constant can be performed. Become. Further, since the noise included in the electric signal which changes according to the magnitude of the light input is removed by the noise removing means included in the control means, it is possible to prevent the influence of the noise generated from the diode means and the like. Further, by performing temperature compensation of the diode means having a non-linear voltage-current characteristic, it is possible to perform gain control in which a level change with respect to a temperature change is suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a circuit configuration of an optical receiver according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating another circuit configuration of the optical receiver according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating voltage-current characteristics of a Zener diode in the optical receiver according to the embodiment of the present invention.
FIG. 4 is a diagram showing a frequency characteristic of an output level when the optical input power changes in the optical receiver of the present invention.
FIG. 5 is a diagram illustrating a frequency characteristic of an output level when an ambient temperature changes in the optical receiver of the present invention.
FIG. 6 is a diagram illustrating a frequency characteristic of an output level when an ambient temperature changes in an optical receiver including a temperature compensating unit according to the present invention.
FIG. 7 is a diagram illustrating an example of a circuit configuration of a conventional optical receiver.
FIG. 8 is a diagram showing characteristics of a photocurrent flowing through the photodiode PD with respect to an optical input power of the photodiode.
FIG. 9 is a diagram showing a frequency characteristic of an output level in a conventional optical receiver when optical input power changes.
[Explanation of symbols]
Reference Signs List 10 amplifying section, 11 variable attenuating section, 12 control section, 13 amplifying section, 14 amplifying section, 20 temperature compensating section, 110 amplifying section, 111 variable attenuating section, 112 control section, 113 amplifying section, C capacitor, C2 capacitor, C100 Capacitor, PD photodiode, R resistor, R2 resistor, R3 resistor, R4 resistor, R5 resistor, R100 resistor, R101 resistor, TH thermistor, ZD Zener diode

Claims (4)

Diode means for applying a bias to the photodiode, wherein the voltage-current characteristic exhibits a non-linear characteristic;
A control unit to which an electric signal which is taken out from one end of the photodiode and changes according to the magnitude of the light input is inputted;
By a control signal from the control means, a non-linear characteristic level variable means for controlling the level of the received signal output from the photodiode to be constant,
An optical receiver comprising: 2. The optical receiver according to claim 1, wherein the diode is a Zener diode, and a bias is applied to the photodiode using a non-linear characteristic of the Zener diode. The control unit has a noise removing unit, and the noise removing unit removes noise included in an electric signal extracted from one end of the photodiode and changing according to the magnitude of light input. The optical receiver according to claim 1, wherein: An electric signal, which is extracted from one end of the photodiode and changes in accordance with the magnitude of light input, is input to the control unit via a temperature compensation unit that performs temperature compensation of the diode unit. The optical receiver according to claim 1, wherein

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