JPS6377171A - Optical receiver - Google Patents

Abstract

PURPOSE:To be able to directly monitor a photodetecting power thereby to be able to optimally control the magnification of an avalanche photodiode without influence of temperature by dividing the photodiode into a signal photodetecting region and a photodetecting power monitoring region, and at least forming the former in an avalanche photodiode structure. CONSTITUTION:An optical signal from an optical fiber 12 is mostly irradiated to a photodetecting region 10 for signal photodetecting of an avalanche photodiode, and the remaining light is irradiated to a photodetecting power monitoring region 11. A bias voltage is applied by a bias controller 15 to the region 10. An output from the region 11 is directly proportional to the photodetecting power. An optimum signal value generator 13 is so set as to output a signal of the same amplitude as the output current of the photodetecting region 10 at the optimum amplification factor from the value of the output current. A comparator 14 compares the output with the output from the region 10 to raise the bias voltage of the region 10 through the controller 10 when the latter is smaller, and to lower it if it is larger.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to an avalanche system used in the field of optical communications.
This invention relates to an optical receiver using a photodiode.

2. Description of the Related Art An example of an optical receiver using a conventional avalanche photodiode as a light receiving element is shown in FIG. In FIG. 3, 20 is a conventional avalanche 0 photodiode, 21 is a preamplifier, 22 is a variable gain amplifier, 23 is an amplitude detector, and 24 is an AGC (Auto
matic Gain Control) circuit.

The amplitude of the output electrical signal of the optical receiver is detected by the amplitude detector 23, and the AGC circuit 2
By changing the gain of the variable gain amplifier 22 and the multiplication factor of the avalanche photodiode 2Q, the output electric signal is controlled to be constant even with respect to fluctuations in received light power and other factors.

Problems to be Solved by the Invention However, in the above configuration, it is difficult to determine whether the amplitude of the output electrical signal is due to a change in the received light power, the gain of the variable gain amplifier 22, or the avalanche photodiode 20.
It is difficult to determine whether this is due to a change in the multiplication factor M. Therefore, in a normal optical receiver, only one of the gain of the variable gain amplifier 22 and the multiplication factor M of the avalanche photodiode 2o is often changed, rather than at the same time.

On the other hand, the multiplication factor of the avalanche photodiode 2o has an optimum value that maximizes the S/N ratio of the output electrical signal. This optimum multiplication factor is determined by the received light power and is obtained from the output current of the avalanche photodiode when the multiplication factor is 1. However, in the optical receiver configured as described above, the output current when the multiplication factor is 1 cannot be known in real time, so it is difficult to always obtain the optimum multiplication factor for any received light power. In addition, it is known that the breakdown voltage and quantum efficiency of avalanche photodiodes change depending on the ambient temperature, and the magnitude of the output signal changes accordingly.9 This also explains why avalanche photodiodes are used. This is one of the factors that makes optimal control of optical receivers difficult.

In view of the above, it is an object of the present invention to provide an optical receiver that can directly monitor the magnitude of received light power and realize control that takes the multiplication factor of an avalanche photodiode to an optimal value without being affected by temperature. .

Means for Solving the Problems The present invention has an avalanche photodiode, and has two parts that are irradiated with an optical signal from an optical fiber or a light source.
each region exists independently on the same substrate, and at least one region includes a photodiode having the structure of the Ano(Ransier photodiode). This is an optical receiver characterized in that it is used as a light receiving element.

According to the above-described configuration, the present invention uses the first region having an avalanche photodiode structure among the two regions of the photodiode as a signal light receiving region, and the second region as a light receiving region. It is used as a power monitoring area and controlled so that the multiplication factor of the signal light receiving area can be optimally set using the output current of the received light power monitoring area.

Embodiment FIG. 1 shows a perspective view of an avalanche photodiode used in an optical receiver according to an embodiment of the present invention, and FIG. 2 shows a block diagram of an optical receiver using this avalanche photodiode.

In FIG. 1, 1o is a signal receiving area, 11 is a receiving power monitoring area, and 12 is an optical fiber. Further, in FIG. 2, 13 is an optimum signal value generator that outputs a signal corresponding to the output current value of the photodiode power monitoring area 11, and 14 is an optimum signal value generator 13.
A comparator 15 compares the magnitude of the output from the signal light receiving region 10 with the magnitude of the output from the signal light receiving region 10, and a bias control section 15 controls the bias voltage applied to the signal light receiving region 1o based on the comparison result of the comparator 14.

Regarding the optical receiver of this embodiment configured as above,
The operation will be explained below.

The structure is such that most of the optical signal from the optical fiber or light source is applied to the signal receiving area 10 of the photodiode, and the rest is applied to the received light power monitoring area 11. A bias voltage is applied to the signal light receiving area 10 by a bias control section 16 .

On the other hand, the output from the received light power monitoring area 11 is received by an extremely small resistor or a transimpedance type amplifier in order to maintain linearity between the received light power and the output current. Since the output current from the received light power monitoring area 11 increases or decreases in direct proportion to the received light power, the magnitude of the received light power can be directly determined by monitoring this value. The optimum signal value generator 13 is configured to output a signal having the same magnitude as the output current of the signal light receiving area 1o at the optimum multiplication factor from this output current value. Then, the comparator 15 compares this output with the actual output from the signal light receiving area 10, and if the latter is smaller, the signal light receiving area 10 is
In contrast, if the latter is large, the bias voltage is lowered so that the two become equal.

With such a configuration, it is possible to realize control that always optimizes the multiplication factor of the avalanche photodiode in the signal light receiving area 10.

In addition, by optimally controlling the magnitude of the output signal of the signal light receiving region 1o as described above, it is possible to solve cases where the temperature variation of the breakdown voltage is dominant in the temperature change of the output signal, or the quantum efficiency of the two regions. When the temperature characteristics of the two are the same, it is possible to obtain an output electrical signal that is completely unaffected by changes in the multiplication factor due to changes in temperature.

On the other hand, the output from the received light power monitoring area 11 does not require a very fast response, so the light can be received over a sufficiently wide light receiving surface, and the output from the received light power monitoring area 11 does not require a very high signal-to-noise ratio. Only a small amount of signal is required, and most optical signals can be transmitted to the signal receiving area 1o.
can be irradiated with less loss.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, the magnitude of the received light power can be directly monitored by forming the second region in a part of the avanche photodiode, and this photodiode can be used to monitor the temperature. It is possible to realize an optical receiver that outputs a signal when the multiplication factor takes an optimum value without any influence.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a photodiode used in an optical receiver according to an embodiment of the present invention, FIG. 2 is a block diagram showing the overall configuration of the optical receiver, and FIG. 3 is a conventional avalanche
FIG. 2 is a block diagram of an optical receiver using a photodiode. 1o... Area for signal light reception, 11... Area for monitoring received light power, 12... Optical switch,
13...Optimum signal value generator, 14...
Comparator, 15...bias control section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2

Claims (2)

[Claims] (1) It has an avalanche photodiode, and the part to which the optical signal from the optical fiber or light source is irradiated is divided into two regions, and each of the two regions exists independently on the same substrate. and a photodiode in which at least one region (referred to as a first region and the other region is referred to as a second region) has an avalanche photodiode structure is used as a light receiving element. receiver. (2) The optical receiver according to claim 1, characterized in that it has at least a function of controlling the multiplication factor of the first region based on the output current value from the second region of the photodiode.