JPH1146032A - Optical transmitter - Google Patents

Abstract

(57) [Problem] To provide an optical transmission device capable of controlling so as to obtain a constant laser light output even when the input signal is restarted after the Low state of the input signal is continued. SOLUTION: While a control current supplied to a laser diode LD is on / off controlled in accordance with an input modulation signal, an optical output of an optical signal transmitted from the laser diode LD is detected by a monitor PD, and this optical output is detected. In response, the current supplied to the laser diode LD is controlled by the operational amplifier OP1, and an optical signal corresponding to the control current is transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter using a laser diode or the like, and more particularly, to an optical transmitter capable of automatically adjusting a current supplied to an optical transmitter and stabilizing an optical signal.

[0002]

2. Description of the Related Art As a first prior art, an optical transmitter capable of stabilizing an optical output by detecting output light from a laser diode and automatically adjusting a supply current to the laser diode. 101 are known. As shown in FIG. 3, in a laser diode driving system, an input signal is supplied to a signal on / off transistor Tr101 through a logic buffer IC 103, and the signal is switched by the signal on / off transistor Tr101. The laser light is output by directly modulating the LD.

Further, in a feedback loop system, a peak hold type APC (Automatic) is used.
A monitor control PD detects a part of the optical output of the laser diode LD using a power control circuit 105, and amplifies a light receiving signal from the monitor PD (Photodiode) by an amplifier 107. Next, the peak voltage value of the light receiving signal amplified by the amplifier 107 is held in the capacitor 111 in the peak hold circuit 109. Here, the operational amplifier OP101 outputs a difference between the reference voltage value VREF and the held peak voltage value as a feedback voltage value. Next, by applying the feedback voltage value to the base of the bias current control transistor Tr102 and controlling the current supplied to the laser diode LD, the current supplied to the laser diode LD is automatically adjusted to stabilize the laser light output. This has the advantage that Note that the resistor R101 is a current limiting resistor for limiting the current supplied to the laser diode LD.

[0004] As a second conventional technique, there is known an optical transmission apparatus 115 using an average value type APC circuit 113 in a feedback system. In this case, as shown in FIG. 4, a part of the laser light output of the laser diode LD is detected by the monitor PD, and the light receiving signal from the monitor PD is amplified by the amplifier 117. Next, the peak value of the light receiving signal amplified by the amplifier 117 is stored in the capacitor 1 in the integrating circuit 119.
The triangular wave voltage is obtained by periodically discharging the electric charge of the capacitor 121 while being held at 21, and further smoothed to obtain an average value. Here, the operational amplifier OP102 amplifies the difference between the average voltage and the reference voltage value (VREF), and
Output as feedback voltage value. Next, this feedback voltage value is applied to the bias current controlling transistor T.
By controlling the current supplied to the laser diode LD in addition to the base of r102, there is an advantage that the current supplied to the laser diode LD is automatically adjusted to stabilize the laser light output.

[0005]

Here, FIG. 5 is a schematic diagram of FIG.
6 is a timing chart for explaining the operation of the peak hold type APC circuit 105 shown in FIG. Operational amplifier O
P101 amplifies the difference between the voltage value applied to the inverting input terminal and the reference voltage value (VREF) applied to the non-inverting input terminal, and outputs the amplified value as a feedback voltage value. As a result, at the timing (b) shown in FIG. 11A, the capacitor 111 in the peak hold circuit 109 is in a ground level state because it has been sufficiently discharged, so that the reference voltage value applied to the non-inverting input terminal is (VREF) is a bias current control transistor Tr10
2 and is controlled to supply the maximum current to the laser diode LD.

On the other hand, the timing (a) shown in FIG.
Then, the input signal is set to Lo in the logic buffer IC 103.
w state, the signal on / off transistor Tr
Reference numeral 101 denotes an off state without performing a switching operation, and the laser diode LD is in a state in which a light emission waveform does not appear regardless of an output voltage from the operational amplifier OP101.

Next, as for the light emission waveform of the laser diode LD, the input signal is supplied to the base of the signal on / off transistor Tr101 via the logic buffer IC 103 as shown in the timing (c) shown in FIG. ,
In addition, since the bias current control transistor Tr102 is controlled to be able to supply the maximum bias current to the laser diode LD, the emission waveform becomes extremely large as compared with the steady state (d).

FIG. 6 shows the average value AP shown in FIG.
6 is a timing chart for explaining the operation of the C circuit 113. The operational amplifier OP102 amplifies the voltage value applied to the non-inverting input terminal, and outputs the amplified value as a feedback voltage value. As a result, at the timing (b) shown in FIG. 11A, the capacitor 121 in the integration circuit 119 and the capacitor 1 in the smoothing circuit 123
25 is in a ground level state because it is sufficiently discharged, so that the inverting input terminal and the non-inverting input terminal are in the ground level state. Accordingly, the feedback voltage value becomes 0 [V], and the bias current control transistor Tr
No voltage is applied to the base of 102 and the laser diode LD is controlled so as not to supply current.

On the other hand, the timing (a) shown in FIG.
Means that the input signal is Low in the logic buffer IC 103
State, the signal on / off transistor Tr1
01 is an off state without performing a switching operation, and the laser diode LD is a state in which no light emission waveform appears.

Next, the timing (c) shown in FIG.
Since the emission waveform of the laser diode LD is controlled so that the bias current control transistor Tr102 does not supply the bias current to the laser diode LD, the emission waveform is extremely small compared to the steady state (d).

As described above, in the conventional optical transmitting apparatus 101 shown in FIG. 3, when the low state of the input signal is continued, the capacitor 11 in the peak hold circuit 109
Since 1 is sufficiently discharged, the current value to the laser diode LD is set to the maximum at the time of re-operation, and as a result,
At the time of re-operation, since the light output from the laser diode LD becomes extremely large, there are problems that the laser diode LD is damaged, the life of the device is shortened, and the light receiving system using the present device is over-input.

The conventional optical transmitter 11 shown in FIG.
In the case of No. 5, when the low state of the input signal is continued, the capacitor 121 in the integrating circuit 119 is sufficiently discharged, so that the light output from the laser diode LD becomes small at the time of re-operation, and a stable laser There was a problem that an optical output could not be obtained.

The present invention has been made in view of the above,
It is an object of the present invention to provide an optical transmission device that can be controlled to obtain a constant laser light output even when the input signal is restarted after the Low state of the input signal is continued.

[0014]

According to the first aspect of the present invention,
In order to solve the above problem, a transmitting unit for transmitting an optical signal corresponding to a control current, a detecting unit for detecting an optical output of the transmitted optical signal, and supplying the transmitting unit to the transmitting unit according to the detected optical output An optical transmission device having a supply current control means for controlling a current to be supplied, a supply means for supplying a signal corresponding to an input modulation signal, and a control current supplied to the transmission means being turned on / off in accordance with the modulation signal The gist of the present invention is to provide switching means for controlling.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a circuit configuration of an optical transmission device 1 according to an embodiment of the present invention.

The optical transmitter 1 shown in FIG. 1 has a logic buffer IC 3, a switching diode 5, a bias current controlling transistor Tr1, and a laser diode L.
D, a monitor PD (Photodiode), and an operational amplifier OP.

The logic buffer IC 3 supplies an input signal to the switching diode 5 (a Schottky barrier diode of high speed and small reference voltage is suitable) and isolates the influence of the switching operation of the switching diode 5 on the input signal. It is. The laser diode LD outputs a laser beam according to the amount of current supplied.

The monitor PD is a light receiving diode for detecting and monitoring a part of the laser light output from the laser diode LD. The operational amplifier OP1 is a high-speed operational amplifier (slew rate: several hundred to several thousand V / μsec),
The detection voltage value corresponding to the light receiving signal from the monitor PD is subtracted from the reference voltage value (VREF), and the result of the subtraction is represented by a resistor R
1, and a predetermined amplification rate α determined by R2. The bias current control transistor Tr1 is connected to the laser diode L by a control voltage value applied to the base.
The current supplied to D is controlled. The resistance R
Reference numeral 3 denotes a current limiting resistor for limiting a current supplied to the laser diode LD.

Next, the operation of the optical transmitter 1 will be described with reference to the timing chart shown in FIG. The timing chart shown in FIG. 3A is an input signal to the logic buffer IC, and the timing chart shown in FIG. 3B is a light emission waveform by the laser diode LD. First, at the timings (a) and (c) shown in FIG.
Let it be in the w state. Here, the operational amplifier OP1
Calculates the difference between the control voltage value according to the light receiving signal from the monitor PD and the reference voltage value (VREF), and amplifies the difference. Then, the amplified value is output to the base of the bias current control transistor Tr1 as a control voltage value via the resistor R4.

At this time, since there is no laser light output from the laser diode LD, no light receiving signal is output from the monitor PD, and the inverting input terminal of the operational amplifier OP1 is in the ground level state. Therefore, the operational amplifier OP
1, the reference voltage (V) input to the non-inverting input terminal
REF) is output. On the other hand, at this time, since the input signal of the logic buffer IC 3 is in the low state, the output is also at the ground level, and the cathode side of the switching diode 5 is at the ground level to turn on the switching function. Then, the output from the operational amplifier OP1 flows to the switching diode 5 side, and the control voltage value applied to the base of the bias current control transistor Tr1 becomes the ground level state.

Therefore, when the input signal is in the low state, the laser diode LD is controlled so as not to output the laser light, as shown in timings (e) and (g) shown in FIG. Next, from the timing (a) rising from (b) to the timing (b) shown in FIG.
At the time of rising, the input signal becomes a high state, the logic buffer IC3 also becomes a high state,
A reverse voltage is applied to the switching diode 5. Therefore, the switching diode 5 is turned off in the switching operation. Therefore, the control voltage value applied to the base of the bias current control transistor Tr1 is:
The value is determined by the operational amplifier OP1 and the resistor R4. At this time, since the laser diode LD is not outputting laser light, the monitor PD does not output a light receiving signal. Therefore, the inverting input terminal of the operational amplifier OP1 is at the ground level, and the reference voltage value (VREF) is amplified and output from the operational amplifier OP1 and is applied to the base of the bias current control transistor Tr1. Therefore, when the input signal is switched to High, a predetermined laser light output corresponding to the reference voltage value (VREF) can be obtained.

On the other hand, the timing (b) shown in FIG.
When the laser light is output from the laser diode LD as in (d) and (d), the monitor PD outputs a light receiving signal corresponding to the laser light output. Therefore, the output voltage value from the operational amplifier OP1 is a value obtained by subtracting the light receiving voltage value corresponding to the light receiving signal from the reference voltage value (VREF) and amplifying the subtracted value by a predetermined amplification degree α. Operational amplifier O
When a light receiving voltage value is input to the inverting input terminal of P1, that is, when laser light is output from the laser diode LD, the light receiving voltage value applied to the inverting input terminal of the operational amplifier OP1 and the light receiving voltage value are applied to the non-inverting input terminal. A difference from the reference voltage value (VREF) is calculated, and the calculated value is amplified at a predetermined amplification factor α and output. This output voltage value is applied to the bias current controlling transistor Tr1 via the resistor R4.
Added to the base.

This bias current control transistor Tr
When a control voltage value is applied to one base, a current corresponding to the control voltage value applied to the base flows between the collector and the emitter. The laser diode L corresponds to the current flowing between the collector and the emitter.
D outputs a constant laser beam as shown in timings (f) and (h) in FIG.

As described above, the voltage supplied to the base of the bias current control transistor Tr1 is controlled on / off by the input signal, and the control voltage value controlled so as to obtain a constant laser light output is controlled by the bias current control transistor Tr1. By controlling to add to the base of the transistor Tr1, even when the state where there is no input signal is continued,
At the time of re-operation, the laser light output from the laser diode LD can be controlled so as to prevent the laser light output from becoming extremely large or small as compared with a normal state, so that even a burst signal can be controlled by one bit. A constant laser light output can be obtained from the eyes. In addition, since the switching diode 5 is used for signal switching and no transistor for turning on / off the signal is used, the circuit of the optical transmitter 1 can be simplified.

Further, unlike the average value control method and the peak hold method, there is no processing by charging the capacitor, so that it is not necessary to design according to the transmission speed and can be driven by a DC signal.

[0026]

As described above, according to the first aspect of the present invention, the control current supplied to the transmitting means is controlled on / off in accordance with the input modulation signal, while the control current is transmitted from the transmitting means. The optical output of the optical signal is detected by the detecting means, the current supplied to the transmitting means is controlled by the supply current control means in accordance with the optical output, and the optical signal corresponding to the control current is transmitted. Even if the operation is restarted after the absence state is continued, control can be performed so as to obtain a constant laser light output.

[Brief description of the drawings]

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

FIG. 2 is a timing chart for explaining the operation of the optical transmission device 1.

FIG. 3 is a diagram showing a circuit configuration of a first conventional technique.

FIG. 4 is a diagram showing a circuit configuration of a second conventional technique.

FIG. 5 is a timing chart for explaining the operation of a conventional optical transmission device.

FIG. 6 is a timing chart for explaining an operation of a conventional optical transmission device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical transmission device 3 Logic buffer IC 5 Switching diode LD Laser diode OP1 Operational amplifier PD Monitor PD R1, R2, R3, R4, R5 Resistance Tr1 Bias current control transistor

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/06 (72) Inventor Mitsuo Nakajima 1 Higashi-shinmachi, Higashi-ku, Nagoya-shi, Aichi Prefecture Inside Chubu Electric Power Co., Inc. (72) Inventor Shinichi Tanaka Aichi Prefecture 1 Higashi-Shinmachi, Higashi-ku, Nagoya City Chubu Electric Power Co., Inc.

Claims (1)

[Claims] A transmitting means for transmitting an optical signal corresponding to a control current; a detecting means for detecting an optical output of the transmitted optical signal; and a current supplied to the transmitting means in accordance with the detected optical output. An optical transmission device having a supply current control means for controlling the control signal, a supply means for supplying a signal corresponding to an input modulation signal, and an on / off control of a control current supplied to the transmission means in accordance with the modulation signal. An optical transmission device comprising switching means.