JP2014107794A - Burst optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a burst optical receiver which, by reducing adjustment corresponding to a characteristic variation in the amplification factor of an avalanche photodiode (APD) and the bias voltage applied to the APD, can vary the amplification factor of the APD according to the intensity of an optical signal to be received.SOLUTION: The burst optical receiver comprises: an APD for converting an optical signal to an electric current; an APD output intensity determination unit for determining whether the output of the APD is strong or not; an APD power supply connection line for connecting the APD and a power supply for applying a bias voltage to the APD; a resistor connected in parallel with the APD power supply connection line between the APD and the power supply; and a path select switch for enabling or disabling the APD power supply connection line and the resistor, the select switch disabling the APD power supply connection line and enabling the resistor when the APD output intensity determination unit determines that the APD output is strong.

Description

  The present invention relates to a burst optical receiver that receives burst optical signals having different intensities. For example, the present invention is installed on a local company side of a passive optical network (hereinafter referred to as PON) system that is one of optical communication systems. The present invention relates to an optical signal receiver used for an optical line terminal (hereinafter referred to as an OLT).

  In an optical communication system or the like, an avalanche photodiode (hereinafter referred to as APD) is used as an element that converts a received optical signal into an electric signal. The APD receives an optical signal and outputs a current (photocurrent). The APD has a function of multiplying the photocurrent, and high reception sensitivity can be realized by setting the APD multiplication factor high when a weak optical signal is incident. On the other hand, if the multiplication factor is set high when a strong optical signal is incident, an overcurrent may flow and destroy the APD.

  In a PON system that is one of optical communication systems, an OLT installed on a local office side is shared by optical network units (optical subscriber premises equipment, hereinafter referred to as ONU) installed in a plurality of subscriber premises. In upstream signal transmission from the ONU to the OLT, optical signals transmitted from a plurality of ONUs are time-division multiplexed and transmitted to the OLT as burst optical signals. Since the ONUs are arranged at various positions as viewed from the OLT, and the distance between the OLT and the ONU is different for each ONU, the optical signal receiver of the OLT needs to receive optical signals having different intensities.

  When it is necessary to receive optical signals having different intensities as in the OLT of the PON system, it is desirable to change the multiplication factor of the APD according to the intensity of the received optical signal. However, in order to receive time-division multiplexed optical signals having different burst-like intensities, it is necessary to change the multiplication factor of the APD at a high speed on the order of nanoseconds.

  As a burst optical receiver that receives a burst-like optical signal by changing the multiplication factor of the APD at high speed, for example, there is a burst optical receiver disclosed in Patent Document 1. The burst optical receiver of Patent Document 1 includes an APD that converts an optical signal into a photocurrent, a preamplifier that converts and amplifies the generated photocurrent into a voltage, a level detection circuit that detects the output level of the preamplifier, and a constant output from the preamplifier. It comprises a limiter amplifier that converts to an output, an error correction signal determination circuit that performs error correction and signal determination of the output of the limiter amplifier, and an APD multiplication factor control circuit.

  The APD converts an incident optical signal into a photocurrent, which is input to a preamplifier. The preamplifier converts the current into a voltage, amplifies the voltage, and sends the output voltage to the limiter amplifier. A level detection circuit is provided between the preamplifier and the limiter amplifier, and the APD multiplication voltage control circuit switches the APD bias voltage based on the value of the level detection circuit.

  In the error correction signal determination circuit, the APD bias voltage can be adjusted so that the gain becomes the minimum optical input intensity that can achieve the bit error rate at the limit of error correction.

JP 2008-306250 A (FIG. 1)

  The conventional burst optical receiver has the configuration as described above. However, since the characteristics of the APD multiplication factor and the APD bias voltage vary greatly depending on the lot, the voltage value set by the APD multiplication factor control circuit is different for each lot. There is a problem that it is necessary to adjust, and it takes a lot of trouble in manufacturing the burst optical receiver.

  The burst optical receiver according to the present invention has been made to solve the above-described problems. In changing the APD multiplication factor according to the received optical signal, the APD multiplication factor and the APD bias voltage are provided. An object of the present invention is to realize a burst optical receiver capable of reducing the adjustment for optimizing the voltage value depending on the characteristic variation.

  A burst optical receiver according to the present invention includes an APD that converts an optical signal into a photocurrent, an APD output intensity determination unit that determines the strength of an APD output, and an APD power supply connection that connects a power source that applies a bias voltage to the APD and the APD. A line, a resistor connected between the APD and the power supply in parallel with the APD power connection line, and a path switch for enabling and disabling the APD power connection line and the resistor, When it is determined that the output of the APD is strong, the path switching unit disables the APD power supply connection line and enables the resistance.

  According to the present invention, in changing the APD multiplication factor according to the received optical signal, it is possible to reduce the adjustment for optimizing the voltage value depending on the characteristic variation of the APD multiplication factor and the APD bias voltage. A burst optical receiver can be obtained.

It is a block diagram of the burst optical receiver which concerns on Embodiment 1 of this invention. 3 is a correspondence table of path switch control performed by the logic circuit of the burst optical receiver shown in FIG. 1. It is a graph which shows the relationship between the bias voltage of APD and a multiplication factor. It is a graph which shows the difference of the relationship between the code error rate when a resistor is connected in series to an APD, and when there is no resistor, and the received light intensity. It is a block diagram of the burst optical receiver which concerns on Embodiment 2 of this invention. 6 is a correspondence table of path switching control performed by the logic circuit of the burst optical receiver shown in FIG. 5. It is a graph explaining the difference of the relationship between the photocurrent of APD and the bias voltage of APD at normal temperature and low temperature.

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals.
Embodiment 1 FIG.
A burst optical receiver according to Embodiment 1 of the present invention will be described. 1 is a configuration diagram of a burst optical receiver according to Embodiment 1 of the present invention. In FIG. 1, the burst optical receiver 100 is connected to a host board 104 that processes a signal received by the burst optical receiver 100 through an electric signal output line 102 and a reset signal line 103, and is also connected to a power source 200. . Next, the internal configuration of the burst optical receiver 100 will be described.

  In FIG. 1, the APD 1 receives an optical signal 101 and converts it into a photocurrent. The photocurrent output from the APD 1 is input to the amplifier 2, and the amplifier 2 converts the photocurrent into a voltage and outputs the voltage. The output of the amplifier 2 is input to the limiter amplifier 3, and the limiter amplifier 3 shapes the output of the amplifier 2 into a signal having a constant amplitude and outputs the signal to the electric signal output line 102.

  The output of the amplifier 2 is input to the APD output intensity determination unit 4, and the APD output intensity determination unit 4 determines whether or not the output of the APD 1 is equal to or higher than a specified value. A reset signal input from the reset signal line 103 initializes the APD output intensity determination unit 4.

  The APD output intensity determination unit 4 can be constituted by a peak detection circuit 4a and a comparator 4b as shown in FIG. 1, for example. Alternatively, the APD output intensity determination unit 4 may compare the output of the amplifier 2 with the threshold voltage, and may have other configurations such as holding this when the threshold voltage is exceeded. Here, a description will be given based on the configuration of the peak detection circuit 4a and the comparator 4b shown in FIG.

  The peak detection circuit 4a detects the peak value of the output of the amplifier 2 and outputs the peak value to the comparator 4b. The peak detection circuit 4a need not detect the true peak value in real time, and may be one that detects discretely with a certain step size, or one that is detected by smoothing with a past history.

  The comparator 4b compares the output of the peak detection circuit 4a with a predetermined voltage threshold (Vth), determines the output intensity of the APD 1, and outputs the determination result. When a reset signal is input from the reset signal line 103, the peak detection circuit 4a is initialized, and the output to the comparator 4b has an initial value lower than Vth.

  The APD power connection line 5 connects the APD 1 and the power source 200. The path switch 6 validates and invalidates the connection between the APD 1 and the power source 200 by the APD power source connection line 5. The path switch 6 can be configured by, for example, a MOS (Metal Oxide Semiconductor) switch or the like. The resistor 7 is inserted between the APD 1 and the power source 200 in parallel with the APD power source connection line 5 and the path switch 6. Here, when the APD power supply connection line 5 and the path switch 6 connect the APD 1 and the power supply 200, the resistance value is extremely smaller than the resistance value of the resistor 7. The logic circuit 8 controls the path switch 6 based on the determination result of the output intensity of the APD 1 in the APD output intensity determination unit 4.

  Next, the operation of the burst optical receiver according to the first embodiment of the present invention will be described.

  The host board 104 outputs a reset signal to the reset signal line 103 at a timing before the optical signal 101 is input to the burst optical receiver from the outside, such as when the burst optical signal 101 is interrupted or when the operation speed is switched. . Thus, the peak detection circuit 4a in the APD output intensity determination unit 4 is initialized before the reception of the optical signal 101 is started.

  When reception of the optical signal 101 is started and the optical signal 101 is incident on the APD 1, the APD 1 converts the optical signal 101 into a photocurrent and outputs it. The output photocurrent is input to the amplifier 2, and the amplifier 2 converts the input photocurrent into a voltage and outputs the voltage. The voltage output from the amplifier 2 is measured for a peak value by a peak detection circuit 4a in the APD output intensity determination unit 4.

  The peak detection circuit 4a is initialized before the start of optical signal reception, and outputs a value lower than the threshold voltage Vth in the initial state. After reception of the optical signal 101 is started, the comparator 4b in the APD output intensity determination unit 4 compares the peak value output from the peak detection circuit 4a with Vth, and the amplitude of the output voltage from the amplifier 2 is Vth or less ( That is, when the output of the APD 1 is smaller than a predetermined value), the logic value 0 is output, and when the amplitude of the output voltage from the amplifier 2 becomes Vth or more (that is, the output of the APD 1 is larger than the predetermined value). A logical value 1 is output.

  The logic circuit 8 controls the path switch 6 based on the output of the APD output intensity determination unit 4. FIG. 2 is a correspondence table of the control of the path switching unit 6 performed by the logic circuit 8. When the output of the APD output intensity determination unit 4 is a logical value 0, the path switcher 6 is turned ON, and when the output of the APD output intensity determination unit 4 is a logical value 1, the path switcher 6 is turned OFF. .

  When the control by the logic circuit 8 is ON, the path switch 6 connects the APD 1 and the APD power connection line 5, and the APD 1 and the power supply 200 are connected by the APD power connection line 5 and the path switch 6. At this time, since the resistance values of the APD power supply connection line 5 and the path switch 6 are extremely smaller than the resistance value of the resistor 7, the connection by the resistor 7 becomes invalid. On the other hand, when the control by the logic circuit 8 is OFF, the path switch 6 disconnects between the APD 1 and the APD power supply connection line 5 and the APD 1 and the power supply 200 are connected only via the resistor 7.

  FIG. 3 is a graph showing the relationship between the bias voltage and the multiplication factor for the APD characteristics. APD has a lower multiplication factor when the bias voltage is lowered.

  The operation principle of the present invention will be described with reference to the graph of FIG. In the present invention, the voltage of the power source 200 (the power source voltage in the graph of FIG. 3) is applied to the APD 1 when the path switch 6 is ON. In contrast, when the path switch 6 is in the OFF state, the resistor 7 is connected between the APD 1 and the power source 200, so that a voltage drop occurs due to the current flowing through the resistor 7 as shown in FIG. The bias voltage actually applied to the APD 1 (APD effective voltage in the graph of FIG. 3) is lower than the power supply voltage. Therefore, the multiplication factor of APD1 can be reduced.

  The amount of voltage drop due to the resistor 7 depends on the magnitude of the photocurrent. The larger the value of the photocurrent, the larger the voltage drop amount. Therefore, the multiplication factor is measured corresponding to individual variations of the APD 1 and the voltage setting value is set. There is no need to adjust.

  FIG. 4 is a graph showing the relationship between the code error rate of the received signal and the received light intensity with and without a resistor connected between the APD and the power supply. When a resistor is connected between the APD and the power source, the RC (resistive capacitor) time constant increases, and the code error rate may increase (deteriorate) when the photocurrent of the APD output changes at high speed.

  However, in the burst optical receiver according to the first embodiment, control is performed so that the resistor 7 is connected in series to the APD 1 only when the output of the APD 1 is strong, that is, when the received light intensity is strong. As shown in FIG. 4, in the region where the received light intensity is high, there is no difference in the code error rate due to the presence or absence of the resistance, and the deterioration of the code error rate due to the connection of the resistor 7 in series with the APD 1 hardly occurs.

  As described above, according to the burst optical receiver according to the first embodiment of the present invention, the APD output intensity determination unit is provided for the output of the amplifier that converts the photocurrent output from the APD into a voltage, and the APD output The strength determination unit determines whether or not the output of the amplifier is equal to or higher than a predetermined threshold value. When the output exceeds the predetermined threshold value, it is determined that the APD output is strong and a resistor is connected between the APD and the power source. By doing so, it is possible to obtain a burst optical receiver capable of reducing the adjustment corresponding to the variation in the characteristics of the APD and changing the multiplication factor of the APD according to the intensity of the received light.

  In addition, since the APD output intensity determination unit is initialized before the optical signal is incident, the APD output intensity determination unit is initialized before the next optical signal is incident even after it is determined that the APD output is strong once. Then, the APD can start the reception process from the state where the resistor is not connected.

In the burst optical receiver according to the first embodiment, the path switching unit enables and disables the connection between the APD and the power supply by the APD power connection line, and the resistor is always connected. It is possible to adopt a configuration in which connection by an APD power supply connection line and connection via a resistor are selected by a path switch.
Embodiment 2. FIG.
A burst optical receiver according to Embodiment 2 of the present invention will be described. 5 is a block diagram of a burst optical receiver according to Embodiment 2 of the present invention. 1 are the same as or equivalent to those of the burst optical receiver of FIG. Hereinafter, the internal configuration of the burst optical receiver 110 will be described focusing on the differences from FIG.

  In the burst optical receiver 110, the second resistor 9 is connected between the APD 1 and the power source 200 so as to be in parallel with the resistor 7. The second path switch 10 connects and disconnects the second resistor 9 and the APD 1. In FIG. 5, the second path switch 10 is provided between the second resistor 9 and the APD 1, but naturally, it may be provided between the second resistor 9 and the power source 200.

  The temperature determination unit 11 measures the ambient temperature and sets the temperature determination result in the logic circuit 12. The temperature determination unit 11 can be configured by, for example, a temperature sensor built-in CPU (Central Processing Unit) or a temperature sensor IC (Integrated Circuit). The logic circuit 12 performs ON / OFF control of the path switching unit 6 and the second path switching unit 10 based on the determination result of the APD output intensity determination unit 4 and the temperature determination result of the temperature determination unit 11.

  Next, the operation will be described. Since the same reference numerals as in FIG. 1 operate in the same manner as the burst optical receiver of the first embodiment, the difference will be mainly described.

  The temperature determination unit 11 measures the ambient temperature, and if the temperature is equal to or higher than a predetermined temperature threshold, the logical value is 1; Output to the circuit 12. FIG. 6 is a correspondence table of the control of the second path switching unit 10 performed by the logic circuit 12 according to the temperature determination result output from the temperature determination unit 11.

  When the output of the temperature determination unit 11 is a logical value 1, the second path switch 10 is turned off, and when the output is a logical value 0, the second path switch 10 is turned on. The second path switch 10 connects the second resistor 9 and the APD 1 when the switch is ON, and disconnects when the switch is OFF.

  When the output of the APD output intensity determination unit 4 is a logical value 0, the path switch 6 is turned on, and the APD 1 and the power source 200 are connected by the APD power source connection line 5. On the other hand, when the output of the optical signal intensity determination unit 4 is a logical value 1, when the output of the temperature determination unit 11 is a logical value 1, the APD 1 and the power source 200 are connected via the resistor 7 only. When the output of the APD output intensity determination unit 4 is a logical value 1 and the output of the temperature determination unit 11 is a logical value 0, the APD 1 and the power source 200 are connected via the resistor 7 and the second resistor 9.

  Since the resistor 7 and the second resistor 9 are connected in parallel, the resistance value between the APD 1 and the power source 200 becomes a combined resistance of the resistor 7 and the second resistor 9 in parallel, and the resistance value decreases, resulting in a voltage drop. The bias voltage actually applied to the APD 1 with the amount reduced becomes larger than that when the voltage is connected through one resistor 7.

  FIG. 7 is a graph showing the relationship between the APD bias voltage and the photocurrent at normal temperature and low temperature with respect to the APD characteristics. As shown in FIG. 7, the voltage range at which the APD operates normally is narrower at low temperatures than at normal temperatures.

  For this reason, when a resistor having the same resistance value is connected in series to the APD 1 at normal temperature and low temperature, the bias voltage (APD effective voltage in the graph of FIG. 7) actually applied to the APD 1 due to the voltage drop across the resistor is normal temperature. Sometimes, even if it falls within the normal operating range, it may fall outside the normal operating range at low temperatures.

  In the burst optical receiver according to the second embodiment of the present invention, as described above, the second resistor 9 is connected to the APD 1 and the power source 200 in parallel with the resistor 7 at a low temperature. It is possible to cause a voltage drop in value.

  As described above, according to the burst optical receiver according to the second embodiment of the present invention, the APD output intensity determination unit is provided for the output of the amplifier that converts the photocurrent output from the APD into a voltage, and the APD output The strength determination unit determines whether or not the output of the amplifier is equal to or higher than a predetermined threshold. If the output exceeds the predetermined threshold, it is determined that the APD output is high and a resistor is connected between the APD and the power source. By doing so, it is possible to obtain a burst optical receiver capable of reducing the adjustment corresponding to the variation in the characteristics of the APD and changing the multiplication factor of the APD according to the intensity of the received light.

  In addition, when the temperature determination unit determines that the temperature determination unit is in a low temperature state and the output of the amplifier is equal to or higher than a predetermined threshold value, the second resistance is added to the resistor used at room temperature. Is connected between the APD and the power supply in parallel with the resistor used at normal temperature, a burst optical receiver capable of changing the multiplication factor of the APD corresponding to low temperature with reduced voltage drop can be obtained.

  In addition, since the APD output intensity determination unit is initialized before the optical signal is incident, the APD output intensity determination unit is initialized before the next optical signal is incident even after it is determined that the APD output is strong once. Then, the APD can start the reception process from the state where the resistor is not connected.

  In the burst optical receiver according to the second embodiment, the second resistor for low temperature is connected in parallel with the normal resistor at the same time. However, the normal resistor and the second resistor can be connected at normal temperature by a selector. Use by switching at low temperatures, or connect two resistors in series, one resistor is provided with a bypass connection that bypasses the resistor, and the bypass connection is valid only at low temperatures, etc. It is also possible to do.

  In the burst optical receivers of the first embodiment and the second embodiment, the APD output intensity determination unit is configured to determine the intensity of the APD output based on the amplitude of the output voltage of the amplifier. You may make it determine by the electric current amount of the photocurrent to output. Or it is good also as a structure which determines indirectly by splitting received light and providing a separate photodetector.

1 APD, 2 amplifier, 3 limiter amplifier, 4 APD output intensity determination unit, 4a peak detection circuit, 4b comparator, 5 APD power supply connection line, 6 path switch, 7 resistor, 8 logic circuit, 9 second resistor, 10 second 2-path switch, 11 temperature determination unit, 12 logic circuit, 100 burst optical receiver, 101 optical signal, 102 electrical signal output line, 103 reset signal line, 104 host board, 110 burst optical receiver, 200 power supply

Claims (8)

An avalanche photodiode (hereinafter referred to as APD) that converts an optical signal into a photocurrent;
An APD output intensity determination unit that determines the strength of the output of the APD;
An APD power connection line for connecting the APD and a power source for applying a bias voltage to the APD;
A resistor connected between the APD and the power supply in parallel with the APD power connection line;
A path switcher that enables and disables the APD power connection line and the resistor, and the APD power connection line when the APD output intensity determination unit determines that the output of the APD is stronger than a predetermined value. A path switcher that disables and enables the resistance;
A burst optical receiver. The resistor is always connected to the APD and the power source,
The path switch enables the connection between the APD power connection line and the APD or the power source when the APD output intensity determination unit determines that the output of the APD is weaker than a predetermined value.
The burst optical receiver according to claim 1.   3. The burst optical receiver according to claim 1, wherein the APD output intensity determination unit determines the strength of the output of the APD based on a magnitude of a voltage amplitude obtained by converting the photocurrent.   The burst light according to claim 3, wherein the APD output intensity determination unit includes a peak detection circuit that detects a peak of the voltage, and a comparator that compares an output of the peak detection circuit with a predetermined voltage threshold value. Receiver.   The burst optical receiver according to any one of claims 1 to 4, wherein the APD output intensity determination unit is initialized before the optical signal is incident on the APD.   Connected in parallel with the resistor between the APD and the power source, connected to the second resistor that is enabled and disabled together with the resistor by the path switch, and connected to the second resistor, and around the APD 6. A second path switching device for disabling the second resistance when the temperature is higher than a predetermined temperature threshold and enabling the second resistance when the temperature is low. The burst optical receiver according to claim 1.   A second resistor connected in series with the resistor between the APD and the power source, and enabled and disabled together with the resistor by the path switch; a bypass connection line bypassing the second resistor; 6. The second path switching device according to claim 1, further comprising: a second path switching unit that invalidates the bypass connection line when the ambient temperature is higher than a predetermined temperature threshold and activates the bypass connection line when the ambient temperature is low. The burst optical receiver described in 1.   The burst optical receiver according to claim 6 or 7, further comprising a temperature determination unit that measures the ambient temperature and determines whether the measured temperature is higher or lower than the predetermined temperature threshold value.

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