JPH03135235A - Optical receiver - Google Patents

Abstract

PURPOSE:To precisely detect a carrier by controlling a system in such a manner that a multiplication factor becomes constant regardless of input light power. CONSTITUTION:A dark current Id2 flowing in an avalanche photo diode 2 for reference is adjusted in such a manner that a voltage drop by a resistance 17 becomes equal to the non-inversion-side input voltage of an operational amplifier 14 by a field effect transistor 7 and the operational amplifier 14. At this time, the potential of a point A is detected by a high withstand voltage follower 5. A circuit consisting of an operation amplifier 8, a high withstand voltage follower 4 and a field effect transistor 6 adjusts the potential of the point A and that of a point B to be equal. Thus, the voltage drop of a resistance 18, which is detected in an operational amplifier 9, goes to be accurately proportional to light input for an avalanche photodiode for reception 1 and rapid carrier detection is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical receiver, and in particular to an optical receiver that uses an avalanche photodiode to detect an optical signal transmitted through an optical transmission line. be.

BACKGROUND OF THE INVENTION Conventionally, some optical receivers use avalanche photodiodes to detect and multiply optical signals, but avalanche photodiodes can achieve higher sensitivity than p1n photodiodes. However, on the other hand, it requires a high bias current, and in order to obtain the desired multiplication factor, it is necessary to precisely control the bias voltage.

This control method can be broadly classified into the following two methods.

(1) AGC method: The applied voltage is controlled so as to keep the amplitude of the detected optical signal constant.

(2) Reference detector method: In addition to the receiving avalanche photodiode, a separate avalanche photodiode or a normal diode is provided for reference, and a voltage proportional to the breakdown voltage of the reference diode is applied to the receiving avalanche photodiode. - applied to the

The AGC method described in item (1) above is the most widely used method for long-distance communication, but because of its limited response speed, it is used in applications that must support burst signals (optical LA).
N, computer system bus). Therefore, I will not specifically discuss it here, and I will not discuss the above (2).
The reference detector method in Section 2.2 is detailed below.

FIG. 4 of the accompanying drawings schematically shows an example of the configuration of a first receiver based on this reference detector method. As shown in FIG. 4, a reference avalanche photodiode 2 is provided on a heat sink in which a reception avalanche photodiode 1 is provided. The current flowing through the reference avalanche photodiode 2 is connected to the field effect transistor 7,
It is kept constant by the operational amplifier 14 and the resistor 17. At this time, since no optical signal is incident on the reference avalanche photodiode 2, a dark current ■ occurs.

However, if I is set appropriately, the voltage applied to the reference avalanche photodiode 2 will be:
This gives a constant multiplication factor.

By means of the operational amplifier 8 and the field effect transistor 6, the voltage applied to the receiving avalanche photodiode 1 is adjusted to be exactly the same as the voltage applied to the reference avalanche photodiode 2. Therefore, in this case, if the two avalanche photodiodes 1 and 2 have similar characteristics (for example, if they are taken from the same wafer) and have the same element temperature, then the multiplication factor of the receiving avalanche photodiode 1 is It is kept constant almost regardless of the optical input level. In other words, the optical receiver configured in this way can completely handle burst signals.

Furthermore, if the relationship between dark current and amplification factor does not strongly depend on the element temperature, such as when the multiplication factor is high (≧500) in a Si avalanche photodiode, it can also serve as temperature compensation.

Problems to be Solved by the Invention However, in InGaAs avalanche photodiodes, which have become mainstream in recent years in the long wavelength band (1.3 μm or more), the multiplication factor that provides the highest sensitivity as an optical receiver is approximately 50 at most. The magnitude of the dark current that provides this multiplication factor is not independent of temperature. Figure 5 shows
This is a graph showing an example of the temperature dependence of the multiplication factor versus dark current characteristic of this type of avalanche photodiode, and the above will be clear from this graph as well. In other words, when the optical receiver based on the conventional reference detector method as described above is applied to an InGaAs avalanche photodiode, a problem arises in that the multiplication factor is temperature dependent.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver that solves the conventional problems as described above.

Means for Solving the Problems According to the present invention, an optical receiver that detects an optical signal using an avalanche photodiode includes a receiving avalanche photodiode for receiving the optical signal, a reference avalanche photodiode, and the reference avalanche photodiode. dark current setting means for setting the dark current value of the avalanche photodiode; a first bias voltage applying means for applying to the photodiode; and a bias voltage that is the same as the bias voltage applied to the reference avalanche photodiode by the first bias voltage applying means to the receiving avalanche photodiode. a second bias voltage applying means for applying a bias voltage; an element temperature detecting means for detecting the element temperature of the receiving avalanche photodiode and the reference avalanche photodiode; and an element temperature detected by the element temperature detecting means. and control means for controlling the dark current setting value by controlling the dark current setting means so that the multiplication factor of the receiving avalanche photodiode becomes a predetermined value according to the multiplication factor. By controlling the dark current of the avalanche photodiode and controlling the set value of the dark current using the element temperature, the temperature dependence of the multiplication factor of the optical receiver is eliminated.

Embodiments Next, the present invention will be explained in more detail with reference to embodiments of the present invention based on FIGS. 1 to 3 of the accompanying drawings.

FIG. 1 schematically shows the configuration of an optical receiver as an embodiment of the present invention. As will be clear from what will be described later, in the first receiver of this embodiment, in accordance with the principle of the present invention, the multiplication factor is controlled by the dark current of the reference avalanche photodiode, and the set value of the dark current is controlled by the element temperature. This eliminates the temperature dependence of the multiplication factor. In order to eliminate the temperature dependence of the multiplication factor of this type of optical receiver, the present inventors controlled the multiplication factor using the dark current of a reference avalanche photodiode, and controlled the set value of the dark current using the element temperature. The present invention was obtained from the experimental results shown in FIG. 2, suggesting that this is effective. That is, the graph in FIG. 2 exemplifies the measurement results of the multiplication factor versus dark current characteristics of four avalanche photodiode elements having different manufacturing lofts and different characteristics such as breakdown voltage.

As is clear from the graph in FIG. 2, the avalanche photodiode APD-A and the avalanche photodiode ΔPD-B have different manufacturing ports.
Although their characteristics (especially breakdown voltage) are very different, the temperature dependence of the multiplication factor vs. dark current characteristics are both very similar.

This means that by controlling the multiplication factor using the dark current of the reference avalanche photodiode and controlling the set value of the dark current using the element temperature, it is possible to eliminate the temperature dependence of the multiplication factor of the optical receiver. It was convincing.

As shown in FIG. 1, in this embodiment, the reference avalanche photodiode 2 and the receiving avalanche photodiode 1 are mounted on the same heat sink. This reference avalanche photodiode 2 is selected to have the same characteristics as the reception avalanche photodiode 1 (for example, one taken from the same wafer). The field effect transistor 7 and the operational amplifier 14 adjust the dark current Id2 flowing through the reference avalanche photodiode 2 so that the voltage drop across the resistor 17 is equal to the non-inverting input voltage of the operational amplifier 14. At this time, in the circuit shown in FIG. 1, the potential at a point indicated by reference numeral A is detected by the high voltage follower 5, and a calculation is performed so that this potential becomes equal to the potential at a point indicated by reference numeral B. A circuit consisting of an amplifier 8, a high voltage follower 4 and a field effect transistor 6 performs the adjustment. Voltage supplied to the cathodes of receiving avalanche photodiode 1 and reference avalanche photodiode 2) (Since V0 is common, the voltage applied to both avalanche photodiodes is equal, and therefore the receiving avalanche photodiode The multiplication factor of diode l remains approximately constant regardless of the optical input from the optical fiber.

Trimmers 19 and 20 are for correcting characteristic distortion of both avalanche photodiodes.

A thermistor 3 is mounted on the same heat sink as the receiving avalanche photodiode 1 and the reference avalanche photodiode 2, and the thermistor 3 is mounted on the same heat sink as the receiving avalanche photodiode 1 and the reference avalanche photodiode 2 mounted on the heat sink. The resistance of the thermistor 3 changes according to changes in element temperature, and the change in resistance of the thermistor 3 is detected by an operational amplifier 10, and its output is sent to an operational amplifier 11.
12 and 13, the third
A given amplification factor as shown in the figure is converted into a dark current (corresponding voltage) given at that temperature. By such an operation, the multiplication factor of the reception avalanche photodiode 1 is kept constant regardless of changes in ambient temperature or changes in optical input. The voltage drop across the resistor 18 detected by the operational amplifier 9 is precisely proportional to the optical input to the receiving avalanche photodiode 1, allowing quick key detection.

Effects of the Invention As described above, according to the present invention, in an optical receiver that improves the dynamic range and reception sensitivity by controlling the amplification factor of an avalanche photodiode, the multiplication factor becomes constant regardless of the manual optical power. As a result, carrier detection, which is important in applications such as optical LAN, can be performed with high precision, and the relationship between dark current and amplification factor (including its temperature dependence) can be controlled for relatively small devices. Since there is no dependence, side effects such as easy adjustment or no adjustment can be obtained.

In short, the present invention provides an avalanche photodiode drive circuit in which (1) the amplification factor is constant regardless of the optical input, so it can handle burst signals, and (2) the amplification factor is less likely to fluctuate due to temperature. It becomes possible to configure. In addition, since a photocurrent that is accurately proportional to the optical input can be obtained, this can be used to (3) accurately and quickly detect carriers;
(4) AGCl can be realized using a simple circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of an optical receiver as an embodiment of the present invention, and FIG. 2 is an enlarged diagram of four avalanche photodiode elements that are manufactured in different manufacturing lots and have different breakdown voltage and other characteristics. Figure 3 shows an example of the output of the dark current setting circuit using the thermistor and function generator in the circuit of Figure 1. Figure 4 shows the reference detector method. FIG. 5 is a diagram schematically showing an example of the configuration of a conventional optical receiver according to the present invention. FIG. 1...Avalanche photodiode for reception,
2...Reference avalanche photodiode,
3...Temperature detection thermistor, 4.5...
...High breakdown voltage voltage follower, 6.7... Field effect transistor, 8-14... Operational amplifier, 15.16... Diode, 17.18...
...Resistance, 19.20...Trimmer. Figure 2 Ambient temperature (°C) Figure 3 Ambient temperature ('C) Figure Dark current (μA)

Claims (2)

[Claims] (1) In an optical receiver that detects an optical signal using an avalanche photodiode, set a receiving avalanche photodiode that receives the optical signal, a reference avalanche photodiode, and a dark current value of the reference avalanche photodiode. and a first bias for applying a bias voltage to the reference avalanche photodiode so that a dark current having a value set by the dark current setting means flows through the reference avalanche photodiode. a voltage applying means; and a second bias voltage applying means for applying the same bias voltage as the bias voltage applied to the reference avalanche photodiode by the first bias voltage applying means to the receiving avalanche photodiode. and an element temperature detection means for detecting the element temperature of the receiving avalanche photodiode and the reference avalanche photodiode, and an increase in the number of the receiving avalanche photodiodes depending on the element temperature detected by the element temperature detection means. An optical receiver comprising control means for controlling the dark current setting value by controlling the dark current setting means so that the magnification becomes a predetermined value. (2) The optical receiver according to claim 1, wherein the reception avalanche photodiode, the reference avalanche photodiode, and the element temperature detection means are attached to the same heat sink.