JP4291006B2 - Optical receiver - Google Patents

Description

[0001]
BACKGROUND 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 electrical 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 if the light reception level in the optical receiver changes. In order to achieve this, the 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 becomes constant, thereby changing the light reception level in the optical receiver. Even so, the output electrical signal was constant.
[0003]
However, the transmitter has to be provided with a separate pilot signal transmission means for transmitting the pilot signal superimposed on the transmission signal, and the receiver needs a pilot signal extraction means for extracting the pilot signal. there were. Furthermore, 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 the optical signal received by the light receiving element is monitored by a monitor terminal provided in the light receiving element, and the electric signal output from the light receiving element is monitored by the monitor signal from the monitor terminal. It has been proposed to control the level (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 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 the light receiving element and gain-controls an electric signal output from the light receiving element based on this detection 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 source (+ Vcc) by a resistor R101 and a resistor R100. Then, the photocurrent flowing through the photodiode PD becomes 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 with a predetermined amplification degree. The amplified electrical signal is supplied to the second amplifying unit 113 via the variable attenuating unit 111 and amplified with a predetermined amplification degree. The electrical 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 attenuation amount of the variable attenuation unit 111 according to the detected intensity of the optical signal, so that the level of the electric signal output from the variable attenuation unit 111 becomes constant.
[0006]
Here, the characteristic of the photocurrent Ipd [mA] flowing through the photodiode PD with respect to the optical input power [dBm] of the photodiode PD is shown in FIG. Referring to FIG. 8, the photocurrent Ipd has a non-linear characteristic that increases exponentially with respect to the optical input power. In addition, since the variable attenuation unit 111 controls the passing amount with a PIN diode, the variable attenuation unit 111 has a nonlinear characteristic in which the attenuation amount changes logarithmically with respect to the control amount. As described above, even if the control amount output from the control unit 112 becomes an exponential non-linearity with respect to the optical signal power received by the photodiode PD, the attenuation amount of the variable attenuation unit 111 with respect to the control amount. Since it changes to a logarithmic non-linear, there is a problem that it is difficult to keep the output constant even if gain control is performed. That is, the frequency characteristic of the output level in the receiver shown in FIG. 7 is shown in FIG. 9. The frequency characteristic of the output level shown in FIG. 9 is a characteristic 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 understood that the output level is not gain-controlled at a constant level.
[0007]
Therefore, an object of the present invention is to provide an optical receiver that can perform 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 is provided between a power source and a ground including a photodiode and a resistor, and a Zener diode means whose voltage-current characteristic for applying a bias to the photodiode exhibits a logarithmic function characteristic. A series circuit connected to the control circuit; a control unit that receives an electrical signal that is extracted from one end of the photodiode and that changes in accordance with the magnitude of the light input; and a control signal from the control unit that controls the photodiode. Logarithmic function characteristic level varying means for controlling the level of the received signal output from the signal to be constant.
[0009]
Further , in the optical receiver of the present invention, the control means has a noise removing means, and the electric power that changes according to the magnitude of the light input taken out from one end of the photodiode by the noise removing means. You may make it remove the noise contained in a signal.
Further , in the optical receiver of the present invention, temperature compensation of the Zener diode means is applied to the control means to which an electric signal that is taken out from one end of the photodiode and changes according to the magnitude of the optical input is input. A temperature compensating means for performing may be provided .
[0010]
According to the present invention, since the bias is applied to the photodiode by the diode means having a non-linear voltage-current characteristic, it is possible to perform gain control that can keep the output level constant. Become. Further, since the noise included in the electric signal that 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 noise generated from the diode means or the like. Furthermore, by performing temperature compensation of the diode means whose voltage-current characteristics are non-linear, gain control can be performed while suppressing level fluctuations with respect to temperature changes.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a circuit configuration of the optical receiver according to the 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 becomes 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 with a predetermined amplification degree. The amplified electric signal is gain-controlled in the variable attenuating unit 11 and supplied to the second amplifying unit 13 to be amplified with a predetermined amplification degree. 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 so that the level of the electric signal output from the variable attenuation unit 11 is constant by controlling the attenuation amount of the variable attenuation unit 11 according to the detected intensity of the optical signal. Yes. Here, FIG. 3 shows an example of voltage-current characteristics when a reverse voltage is applied to the Zener diode ZD. As shown in FIG. 3, when a reverse voltage is applied to the Zener diode ZD, even if the current Id changes, the voltage Vd has a logarithmic function characteristic that is substantially constant. Therefore, when the photocurrent Ipd that flows through the photodiode PD that receives the optical signal changes according to the optical signal power, the bias voltage Vd of the photodiode PD changes with a logarithmic function characteristic. Therefore, when a bias is applied to the photodiode PD by the Zener diode ZD, the electrical signal converted in the photodiode PD due to the nonlinear characteristic of the Zener diode ZD changes with 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 also to the control unit 12. Then, the variable attenuation unit 11 is controlled according to the light intensity detected by the control unit 12. The variable attenuating unit 11 is configured by using, for example, a PIN diode, and the attenuation amount of the variable attenuating unit 11 changes in a logarithmic non-linear manner with respect to the control amount. Then, as described above, the electric signal that changes with the 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 amount of attenuation changes logarithmically. From the attenuator 11, an electric signal having a substantially constant level is output.
Here, the frequency characteristic of the output level when the optical input power in the optical receiver of the present invention shown in FIG. 1 is changed is 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. The deviation of the output level is within about 1 dB, and it can be seen 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 of 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 is provided. , Input to the amplifying unit 10 is prevented. Furthermore, an electric signal converted by the photodiode PD may be supplied to the control unit 12 through a low-pass filter to prevent the influence of noise generated in the Zener diode ZD.
[0015]
By the way, the voltage-current characteristic in the Zener diode ZD is a function of temperature, and changes according to the ambient temperature. FIG. 5 shows the frequency characteristics of the output level when the ambient temperature changes in the optical receiver having the circuit shown in FIG. The frequency characteristics of the output level shown in FIG. 5 are frequency characteristics when the ambient temperature is −10 ° C., 20 ° C., and 50 ° C. Referring to FIG. 5, when the ambient temperature is changed from −10 ° C. to 20 ° C., the output level deviation is about 1.5 dB. When the ambient temperature is changed from −10 ° C. to 50 ° C., the output level deviation is expanded to about 3 dB. Therefore, gain control is not performed 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 that can solve this problem.
The optical receiver shown in FIG. 2 includes the temperature compensation unit 20 in the optical receiver shown in FIG. Therefore, the temperature compensation unit 20 will be described. A resistor R3 is connected in series with a parallel circuit of a thermistor TH and a resistor R2 between the power supply (+ Vcc) and the ground. The connection point between the parallel circuit and the resistor R3 is connected to the inverting input terminal of the amplification unit 14, and the connection point between the Zener diode ZD and the photodiode PD is connected to the non-inverting input terminal of the amplification unit 14. . As a result, an output based on the difference between the inputs from the amplifier 14 to both input terminals can be obtained. Since this resistance decreases as the temperature of the thermistor TH increases, the output decreases as the ambient temperature increases. Since the variable attenuation unit 11 is controlled in accordance with this output, the control amount output from the control unit 12 decreases as the ambient temperature increases, and the variable attenuation unit 11 is controlled to increase the attenuation amount. become.
[0017]
On the other hand, when the ambient temperature is low, the reverse is true, and the control amount output from the control unit 12 is increased, and the attenuation amount of the variable attenuation unit 11 is controlled to be small. As a result, gain control is performed so that the output level from the variable attenuation section 11 is 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 frequency characteristics when the ambient temperature is −10 ° C., 20 ° C., and 50 ° C. Referring to FIG. 6, the output level deviation is about 0.5 dB even when the ambient temperature is changed from −10 ° C. to 20 ° C., and the output level deviation is not changed even when the ambient temperature is changed from −10 ° C. to 50 ° C. The gain is controlled so that the output level is constant within about 1 dB. The resistor R2 connected in parallel to the thermistor TH is a resistor that adjusts the temperature characteristics of the thermistor TH.
[0018]
Further, 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 and the inverting input terminal of the amplifying unit 14 in the control unit 12, a low-pass filter is configured by the action of the resistor R5 connected to the non-inverting input terminal. The control signal from which noise is 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 of 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 this low-pass filter , Input to the amplifying unit 10 is prevented.
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 end of the resistor R5 is grounded, and the control unit 12 shown in FIG. Removal has been done.
[0019]
In the above description, a stable gain control can be 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 Zener diode ZD can be used instead. One or a plurality of general diodes may be connected in series, and a semiconductor element having a characteristic capable of correcting the nonlinearity of the photodiode PD can be used in place of the Zener diode ZD.
[0020]
【The invention's effect】
As described above, in the present invention, since the bias is applied to the photodiode by the diode means having a non-linear voltage-current characteristic, it is possible to perform gain control capable of keeping the output level constant. Become. Further, since the noise included in the electric signal that 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 noise generated from the diode means or the like. Furthermore, by performing temperature compensation of the diode means whose voltage-current characteristics are non-linear, gain control can be performed while suppressing level fluctuations with respect to temperature changes.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of an optical receiver according to an embodiment of the present invention.
FIG. 2 is a diagram showing 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 illustrating a frequency characteristic of an output level when optical input power changes in the optical receiver of the present invention.
FIG. 5 is a diagram showing a frequency characteristic of an output level when the ambient temperature changes in the optical receiver of the present invention.
FIG. 6 is a diagram illustrating frequency characteristics of an output level when an ambient temperature changes in an optical receiver including a temperature compensation 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 graph showing the characteristics of the photocurrent flowing in the photodiode PD with respect to the optical input power of the photodiode.
FIG. 9 is a diagram showing frequency characteristics of an output level when optical input power changes in a conventional optical receiver.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Amplification part, 11 Variable attenuation part, 12 Control part, 13 Amplification part, 14 Amplification part, 20 Temperature compensation part, 110 Amplification part, 111 Variable attenuation part, 112 Control part, 113 Amplification part, 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 (3)

A series circuit connected between a power source and a ground including a photodiode and a resistor, and a Zener diode in which a voltage-current characteristic for applying a bias to the photodiode exhibits a logarithmic function characteristic; and
Control means for receiving an electrical signal taken out from one end of the photodiode and changing according to the magnitude of the light input;
Logarithmic function characteristic level variable means for controlling the level of the reception signal output from the photodiode to be constant by a control signal from the control means;
An optical receiver comprising:   The control means has noise removal means, and removes noise contained in an electrical signal that is taken out from one end of the photodiode by the noise removal means and changes according to the magnitude of light input. The optical receiver according to claim 1.   Temperature compensation means for compensating temperature of the Zener diode is provided in the control means to which an electrical signal that is taken out from one end of the photodiode and changes according to the magnitude of light input is input. The optical receiver according to claim 1.

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