JPH05183240A - Optical signal receiving circuit - Google Patents

Abstract

PURPOSE:To narrow the dynamic range required for an electric range required for an electric circuit such as a preamplifier, an AGC, etc., to be arranged in the rear stage of a photodetector for actualizing the wider range in the equivalent circuit. CONSTITUTION:The title optical signal receiving circuit using semiconductor lasers 1-1, 2-1 as photodetectors of the optical signals is provided with the photodetecting sensitivity control means 1-5, 2-5 of semiconductor lasers 1-1, 2-1 by adjusting the current running in the semiconductor lasers during the signal receiving step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor laser (hereinafter,
The present invention relates to an optical receiving circuit for converting a received optical signal into an electric signal in an optical transmission system using an LD as a light receiving element.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing a configuration example of a conventional optical transmission / reception circuit using an LD as a light receiving element, in which 1 is a first
2 is a second transmission device, and 3 is a transmission line.
The first transmission device 1 includes LD1-1 and LD drive circuit 1-
2, the preamplifier 1-3, and the AGC amplifier 1-4. Similarly, the second transmission device 2 is LD2-1
, LD drive circuit 2-2, preamplifier 2-3, AG
LD of the first transmission device 1, which is composed of a C amplifier 2-4 and
The optical transmission / reception circuit is configured by disposing the transmission line 3 between 1-1 and the LD2-1 of the second transmission device 2. S-1 is the transmission signal of the first transmission device 1, R-1 is the reception signal of the first transmission device 1, S-2 is the transmission signal of the second transmission device 2, and R-2 is the second signal. 2 is a reception signal of the transmission device 2.

In such a configuration, the transmission signal S-1 of the transmission device 1 is input to the LD drive circuit 1-2 and LD1-
It is converted into an optical signal at 1 and sent to the transmission line 3. In the transmission device 2, the optical signal received via the transmission line 3 is LD2-1
After being converted into an electric signal by the preamplifier 2-3 and amplified by the preamplifier 2-3, the gain control is further performed by the AGC amplifier 2-4 to obtain the reception signal R-2. In addition, the transmission signal S-2 of the transmission device 2
Is transmitted to the transmission device 1 by the same operation as above, and the reception signal R-1 is obtained.

Since LD1-1 and 2-1 cannot perform transmission / reception at the same time, as shown in the time chart of FIG. 3, when the transmission device 1 sends out an optical signal, the transmission device 2 receives it. When the transmission apparatus 2 is in the state and the optical signal is transmitted by the transmission apparatus 2, the transmission apparatus 1 uses the time axis compression bidirectional transmission method in which the transmission apparatus 1 is in the reception state and transmits the optical signal.

In such an optical transmission system, the difference between the minimum transmission distance and the maximum transmission distance, that is, the transmission loss difference corresponding to the transmission distance difference becomes the dynamic range required for the optical receiving circuit. Further, since intensity modulation is used for ordinary optical transmission, the dynamic range of twice the transmission loss difference is required in the electric circuit portion of the optical receiving circuit. For example, assuming that the minimum transmission distance is 0 km and the maximum transmission distance is 20 km, and the transmission loss of the optical fiber is 1 dB / km, the transmission loss difference is 20 dB, and this value is the dynamic range required for the receiving circuit. The preamplifiers 1-3 and 2-3 and the AGC amplifiers 1-4 and 2-4 require a dynamic range of 40 dB.

[0006]

In the prior art, the gain control by the light receiving element is not performed, and the preamplifier or AGC is used.
There are drawbacks such that the transmission distance difference is limited by the dynamic range of the amplifier, and expensive parts are required to realize the required transmission distance difference.

The present invention has been made in view of the above circumstances, and an object thereof is to reduce a dynamic range required for an electric circuit section such as a preamplifier or an AGC amplifier which is provided in a subsequent stage of a light receiving element, and an equivalent circuit. The purpose of the present invention is to provide an economical optical receiver circuit that can realize a wider dynamic range.

[0008]

In order to achieve the above object, according to a first aspect of the present invention, in a light receiving circuit using a semiconductor laser as a light receiving element of an optical signal, the light receiving of the semiconductor laser is adjusted by adjusting a current flowing through the semiconductor laser during reception. A means for controlling the sensitivity was provided.

According to a second aspect of the present invention, in an optical receiving circuit using a semiconductor laser as a light receiving element for an optical signal, a means for detecting the receiving level of the semiconductor laser and a semiconductor laser which flows according to the detection result of the level detecting means. Means for controlling the light receiving sensitivity of the semiconductor laser by adjusting the current.

Further, in claim 3, an automatic gain control amplifier for amplifying the electric signal received by the semiconductor laser is provided.

[0011]

According to the first aspect, the current flowing through the semiconductor laser at the time of reception is adjusted, and the light receiving sensitivity of the LD is controlled to a desired level.

According to the second aspect, the current flowing through the semiconductor laser is adjusted by the negative feedback of the electric signal level after the light is received by the LD, and the light receiving sensitivity of the LD is automatically controlled.

According to the third aspect of the invention, the electric signal after being received by the LD is subjected to a predetermined amplifying action by the automatic gain control amplifier.

[0014]

1 is a block diagram showing a first embodiment of an optical receiving circuit according to the present invention, and the same components as those in FIG. 2 showing a conventional example are designated by the same reference numerals. That is, 1a is the first
Transmission device, 2a is a second transmission device, 3 is a transmission line, S-1
Is a transmission signal of the first transmission device 1, R-1 is a reception signal of the first transmission device 1, S-2 is a transmission signal of the second transmission device 2, R-
2 is a received signal of the second transmission device 2.

The first transmission device 1a transmits an optical signal to the transmission line 3
LD1-1, which emits to the optical signal from the transmission line 3 and receives it as an electrical signal according to the received light level, an LD drive circuit 1-2 that drives the LD1-1 during transmission, and amplifies the received electrical signal. Preamplifier 1-3 and AGC amplifier 1-4, and an LD that flows to LD1-1 in response to an external control signal CTL input.
It consists of a bias circuit 1-5 that regulates the current.

Similarly, the second transmission device 2a emits an optical signal to the transmission line 3, receives the optical signal from the transmission line 3 and converts it into an electrical signal corresponding to the received light level LD2-1, and at the time of transmission, L
LD drive circuit 2-2 for driving D2-1, preamplifier 2-3 and AGC amplifier 2-4 for amplifying received electric signal
And a bias circuit 2-5 for adjusting the LD current flowing through LD2-1 in accordance with the input of the control signal CTL from the outside.

Bias circuits of these transmission devices 1a and 2a
As described above, 1-5 and 2-5 adjust the LD currents of LD1-1 and 2-1 based on the control signal CTL.
L is generated so that the LD current is kept near zero when the optical signal level received by LD1-1 and 2-1 is low, and a large amount of LD current flows when the optical signal level is high. To be done.

FIG. 4 shows that the LD current and the received optical signal are LD
2 shows an example of the relationship of the voltage generated between the terminals of the LD, the horizontal axis represents the LD current, and the vertical axis represents the voltage generated between the terminals of the LD. As is clear from FIG. 4, the voltage generated between the terminals is almost constant up to the LD current of 0.5 [mA], but when the voltage exceeds 0.5 [mA], the voltage between the terminals rapidly decreases. It becomes a constant value again in the vicinity of 2 [mA].
This tendency has various LDs though there are some differences in the current value.
Is a common phenomenon. Therefore, when the level of the received optical signal is low, the LD current is set near zero, and when the level of the optical signal is high, the level of the received optical signal is set near 2 [mA]. A constant electric signal can be obtained regardless of. That is, by adjusting the LD current, the light receiving sensitivity when the LD converts the received optical signal into an electric signal can be controlled, so that the gain control by the LD can be performed without using the preamplifier or the AGC amplifier.

Next, the operation of the above configuration will be described.

For example, the transmission signal S-1 of the transmission device 1a is L
It is input to the D drive circuit 1-2, converted into an optical signal by the LD 1-1, and sent out to the transmission line 3.

In the transmission device 2a, the received optical signal is LD
Converted to electrical signal in 2-1. At this time, bias circuit 2-
The LD current of LD2-1 is adjusted by 5 based on the control signal CTL. Specifically, when the level of the received optical signal is low, a current near zero is adjusted so as to flow to LD2-1, and when the level of the optical signal is high, a large amount of current is L.
It is adjusted to flow to D2-1. This makes LD2-
The light receiving sensitivity when 1 converts the received optical signal into an electric signal is controlled.

The optical signal thus received is the LD
After being converted into an electric signal by 2-1 and amplified by the preamplifier 2-3, gain control is further performed by the AGC amplifier 2-4 to obtain a reception signal R-2.

The transmission signal S-2 of the transmission device 2a is also sent to the transmission device 1a by the same operation as above, and the reception signal S-2 is received.
R-1 is obtained.

As described above, according to this embodiment,
Since the gain control using the LD can be performed, the dynamic range necessary for the electric circuit can be reduced, the preamplifier and the AGC amplifier can be configured with inexpensive parts, and the cost of the optical receiving circuit can be reduced. Also, the preamplifier and A
When the GC amplifier has a dynamic range equivalent to that of the conventional one, the gain control by the LD can be used together to widen the dynamic range of the entire optical receiving circuit, so that a larger transmission distance difference can be accommodated. ..

FIG. 5 is a block diagram showing a second embodiment of the optical receiving circuit according to the present invention. This embodiment is different from the first embodiment in that the bias circuits 1-5 and 2-5 are connected to the LD1-1, 2-1 LDs according to the input of the control signal CTL from the outside.
Instead of configuring to regulate the current, LD1-1,2-
LD by negative feedback of the received electric signal level after receiving 1
This is because the current is adjusted to control the photosensitivity of LD1-1 and 2-1.

Specifically, as shown in FIG. 6, LD1-1
, 2-1 output side (preamplifier input side) is equipped with level detection circuits 1-6, 2-6 that AC-couple the preamplifier input to detect the peak voltage value, and level detection circuits 1-6, 2-6 The output of the peak voltage value detection circuit 61 of the bias circuit 1-5, 2-
5, and the voltage-current conversion circuit 51 performs voltage-current conversion to adjust the LD current.

Further, in this configuration, since the automatic gain control which is performed by the AGC amplifier of the electric circuit is performed by the above-mentioned automatic control by the negative feedback, it is not necessary to provide the AGC amplifier of the electric circuit. Therefore, in this embodiment, fixed gain amplifiers 1-7 and 2-7 are arranged instead of the AGC amplifiers 1-4 and 2-4 in FIG.

Next, the operation of the above configuration will be described.

For example, the transmission signal S-1 of the transmission device 1a is L
It is input to the D drive circuit 1-2, converted into an optical signal by the LD 1-1, and sent out to the transmission line 3.

In the transmission device 2a, the received optical signal is LD
Converted to electrical signal in 2-1. This electric signal is level-detected by the level detection circuit 2-6. This detection result is input to the bias circuit 2-5, and the LD current of LD2-1 is adjusted by this. Specifically, the LD current is increased when the detected level is high, and the LD current is decreased when the detected level is low. That is, when the detected level is high, the light receiving sensitivity of the LD is low, and when the detected level is low, the light receiving sensitivity of the LD is high, and automatic control by negative feedback is performed.

The optical signal thus received is the LD
The signal is converted into an electric signal in 2-1 and amplified by the preamplifier 2-3 and the amplifier 2-7 to obtain the reception signal R-2.

The transmission signal S-2 of the transmission device 2a is also sent to the transmission device 1a by the same operation as described above, and the received signal S-2 is received.
R-1 is obtained.

As described above, according to this embodiment,
Since the automatic gain control using the LD can be performed, the dynamic range required for the preamplifier can be reduced, and the AGC amplifier, which has been an essential component in the related art, can be a fixed gain amplifier. Therefore, the electric circuit can be configured with inexpensive parts,
The cost of the optical receiving circuit can be reduced.

FIG. 7 is a block diagram showing a third embodiment of the optical receiving circuit according to the present invention. This embodiment is different from the second embodiment in that instead of the fixed gain amplifiers 1-7 and 2-7 on the output side of the preamplifiers 1-3 and 2-3, as in the case of FIG.
This is due to the placement of the GC amplifier.

With such a configuration, the automatic gain control using the LD can be performed in addition to the automatic gain control by the conventional AGC amplifier, so that the dynamic range of the optical receiving circuit as a whole can be widened, which is larger. It is possible to cope with the difference in transmission distance.

In the second and third embodiments, the level detection circuits 1-6 and 2-6 are connected to the preamplifiers 1-3 and 2-.
Although it is connected to the input side of 3, it is not limited to this, and may be connected to the output side of the preamplifiers 1-3 and 2-3.

[0037]

As described above, according to the first aspect, the LD light receiving sensitivity can be controlled by adjusting the bias voltage of the LD, so that the gain can be controlled during light reception.
Therefore, the dynamic range required for the electric circuit can be reduced, the preamplifier and the AGC amplifier can be configured with inexpensive parts, and the cost of the optical receiving circuit can be reduced. Also, when the preamplifier or AGC amplifier has a dynamic range equivalent to the conventional one, it is possible to expand the dynamic range of the optical receiving circuit as a whole by using the gain control by the LD, so that a larger transmission distance difference can be accommodated. It will be possible.

Further, according to the second aspect, the LD light receiving sensitivity can be controlled by adjusting the current flowing in the LD by using the negative feedback of the electric signal after the light receiving, so that the automatic gain control can be performed at the time of light receiving. As a result, the dynamic range required for the preamplifier can be reduced, and the AG
The C amplifier can be a fixed gain amplifier. Therefore, the electric circuit can be composed of inexpensive parts, and the cost of the optical receiving circuit can be reduced.

According to the third aspect, in addition to the automatic gain control by the conventional AGC amplifier, the dynamic range of the entire optical receiving circuit is improved by the automatic gain control when receiving light by adjusting the current flowing through the LD. Since it can be widened, it is possible to cope with a larger transmission distance difference.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical receiving circuit according to the present invention.

FIG. 2 is a diagram showing a configuration example of a light receiving circuit using a conventional LD as a light receiving element.

FIG. 3 is a time chart for explaining a time axis compression bidirectional transmission system.

FIG. 4 is a diagram showing an example of a relationship between a current flowing through an LD and a voltage generated by a received optical signal between terminals of the LD.

FIG. 5 is a configuration diagram showing a second embodiment of an optical receiving circuit according to the present invention.

FIG. 6 is a diagram showing a configuration example of a level detection circuit and a bias circuit according to the present invention.

FIG. 7 is a configuration diagram showing a third embodiment of an optical receiving circuit according to the present invention.

[Explanation of symbols]

1a ... 1st transmission apparatus, 1-1 ... LD, 1-2 ... LD drive circuit, 1-3 ... Preamplifier, 1-4 ... AGC amplifier, 1-5
... Bias circuit, 1-6 ... Level detection circuit, 1-7 ... Fixed gain amplifier, 2a ... Second transmission device, 2-1 ... LD, 2-2
… LD drive circuit, 2-3… Preamplifier, 2-4… AGC
Amplifier, 2-5 ... Bias circuit, 2-6 ... Level detection circuit,
2-7 ... Fixed gain amplifier, 3 ... Transmission line, s-1 ... Transmission signal of first transmission device, R-1 ... Reception signal of first transmission device,
S-2: Transmission signal of the second transmission device, R-2: Reception signal of the second transmission device.

Claims (3)

[Claims] 1. An optical receiving circuit using a semiconductor laser as a light receiving element for an optical signal, comprising a means for controlling the light receiving sensitivity of the semiconductor laser by adjusting a current flowing through the semiconductor laser during reception. .. 2. An optical receiving circuit using a semiconductor laser as a light receiving element for an optical signal, wherein: means for detecting a receiving level of the semiconductor laser; and adjusting a current flowing through the semiconductor laser according to a detection result of the level detecting means. And a means for controlling the light receiving sensitivity of the semiconductor laser. 3. The optical receiving circuit according to claim 2, further comprising an automatic gain control amplifier for amplifying an electric signal received by the semiconductor laser.