JPS60251732A - Optical transmitter - Google Patents

Abstract

PURPOSE:To attain stable optical pulse train and long range and high speed transmission line by generating a signal the same as an input signal when a sudden input exists and allowing the titled transmitter to generate a signal when no input exists so as to drive a semiconductor laser. CONSTITUTION:A drive signal generating circuit 1 uses an input signal presence or absence detecting signal from a control signal generating circuit 8, generates a signal equal to the input signal 10 while the input signal 10 is inputted suddenly and generates a pulse signal or a DC signal when no input signal 10 is inputted and inputs a drive signal 30 to a drive circuit 2. On the other hand, a part of the optical signal of a semiconductor laser 3 is fed back to the circuit 2 via an optical multiplexing device 4, a photodetector 5 and a level detector 6. Further, the optical signal of the semiconductor laser 3 driven by the output of the circuit 2 is outputted externally only when the signal 10 is inputted by an optical switch 7 controlled by the signal 20.

Description

[Detailed Description of the Invention] The present invention provides optical transmission in which optical transmission is performed in bursts using a semiconductor 1/- laser: <z:, +i? Regarding. , semiconductor
When constructing an optical transmitter using a semiconductor laser, it is necessary to take into account the temperature dependence of the emission characteristics of the semiconductor laser. ! shows an example of the drive current vs. output optical power characteristics of a single-body laser.
2) When driving this semiconductor laser, if it is driven with a constant current ■1, the vorticity T1
At temperature T2, the optical output is P+, and at temperature T2, the optical output is P2, which is a practical problem because the optical output fluctuates greatly depending on the temperature.

Conventionally, to solve this problem, the output light level of the semiconductor laser is detected, the detected level is compared with a preset optical output setting value, and the comparison result is fed back to the semiconductor laser drive circuit. Return Th1 by
A configuration is adopted in which a lJ I+1'J loop is formed and the optical output level is always kept constant. However, in lines where data is generated in bursts, such as data communication lines, conventional systems*l have the following drawbacks: 1. When signal pulses are generated in bursts, the transmitted pulses are transmitted over a long period of time. Since this does not occur, it becomes impossible for the return fE control loop to determine the optical output level -C and maintain that level, making it difficult to control the optical output level.

Furthermore, if a transmission pulse is suddenly applied after a long period of time without any transmission pulses being generated, a large current drive pulse will be instantaneously applied to the semiconductor laser, which may deteriorate or destroy the semiconductor laser. or

In order to eliminate the drawbacks of these conventional devices, the present invention uses an optical switch to perform Hr control of the optical output.

According to the present invention, in an optical transmitter that converts an input signal suddenly input using a semiconductor laser into an optical signal and transmits the signal, during the period when the input signal is input, a signal equal to the input signal is transmitted. a drive signal generation circuit that generates a pulse signal or a DC signal by itself during a period when no input signal is input; and a drive signal generation circuit that is connected to the drive signal generation circuit; and a semiconductor laser drive circuit configured to vary the level of this electrical signal, a photodetector that partially receives the optical signal of the semiconductor laser, and a photodetector that detects the output level of the optical emitter and detects the output level of the semiconductor laser. an optical level detection circuit that generates an optical level signal that varies the output level of the drive circuit; and an optical switch control signal that is applied from the outside to output other optical signals of the half- and single-body lasers; and an optical switch for shutting off the input signal, and the optical switch is controlled to be open during a period when the input signal is present and closed during a period when there is no input signal.3. Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing a first embodiment of the present invention. In the figure, 1 is a drive signal generation circuit that generates a semiconductor laser drive signal 30 from an input signal 10 and a control signal 20;
3 is a semiconductor laser drive circuit which takes the drive-1 signal 30 as input and generates a current signal 40k for driving the semiconductor laser at a necessary level controlled by the optical level signal 50; 3 converts the drive-1 signal 40 into an optical signal. 1"; 4 is an optical branching circuit for extracting a part of the output light of the semiconductor laser as monitor light; 5 is a photodetector for receiving the monitor light and converting it into a MIG signal; 6 is a light detector for monitoring MIG signal. a level detection circuit that detects a peak level and generates a level signal 50;
8 is an optical switch for switching the laser output light divided by the branch circuit 4, and 8 is an optical switch for detecting the presence of the input signal 10.
FIG. 3 shows an example of the signal waveforms of each part in FIG.

The input signal 10 is a signal that is suddenly input, and is a Janchester code in which the 10'' of the signal is continuous for at least 3 times.The optical switch control signal 20 uses the encoding rule of this input signal. 6. In other words, the first pulse rise of the input signal is detected and the control signal 20 is converted from "0" to 61", and the end of the input signal is 0" three times in a row. Therefore, at this time, the control signal is changed from "1" to "0". By doing so, when the control signal 20 is "1", the input signal 10 is being input. The drive signal generating circuit 1 outputs the same signal as the input signal 10 as the drive signal 30 when the control signal is 11'', and outputs a signal of 1'' when the depth is 60''. As a result, the output light from the semiconductor laser 3 outputs an optical output corresponding to the input signal 10 during the period when the input signal 1o exists, and the output light from the semiconductor laser 3 corresponds to the input signal 10 during the period when the input signal does not exist and the semiconductor laser does not emit light. It cannot exceed 4 bits of signal.

The level detection circuit 6 detects the peak level of the monitor electrical signal from the west detector 5, compares the level with a preset reference level, and transmits the comparison result to the optical level signal 5.
It is outputted as 0 to the semiconductor laser drive circuit 2, and is composed of a peak level detection circuit consisting of, for example, a diode and a capacitor, and a differential amplifier. In this embodiment, since the period of 60'' of the input signal to the level detection circuit 6 does not exceed 4 bits of the input signal, it responds well to the peak level of the signal even if the discharge time constant of the capacitor of the peak level detection circuit is shortened. peak value can be maintained.

Therefore, the semiconductor laser drive circuit 2, the semiconductor laser 3
, branch circuit 4, photodetector 5, and level detection circuit 6, the level of laser driving current signal 40 is kept constant regardless of the presence or absence of input signal 10.

On the other hand, the output light of the semiconductor laser 3 branched by the branch circuit 4 enters the optical switch 7. This optical switch is turned off when the control signal 20 is 61# and ONS is "0", but when the control signal 20 is 1" and the input signal 10 is being input, the input signal from the semiconductor laser 3 is The corresponding optical output enters via the branch circuit 4. Therefore,
Optical switch 7 generates an optical output that is identical to the input signal.

Note that in this embodiment, the output signal 30 of the drive signal generation circuit 1
If the sign of 01 is 01, the sign of 10 is A1, and the sign of control signal 20 is B, then C-AB-4-AB ・・・・・・・・・・・・・・・・・・
...(1), and the drive signal generation circuit 1 can be easily configured with only logic circuits, but as shown in FIG. 4, the input signal 10 is delayed by a delay time of 3 bits or less. It may be constructed of a delay circuit 9a and a multiplex circuit 9b that takes the sum of the inverted control signal 20 and the output (i) of the delay circuit 9a. However, when the circuit shown in FIG. 4 is used, The output timing of the external output optical signal 70 is delayed by the delay time of the delay circuit 9 compared to the case where the external output optical signal 70 is constructed using only logic circuits based on equation (1) (the case shown in FIG. 3).

In addition, in this embodiment, when there is no input signal 10, the semiconductor laser drive signal 30 is set to all "1", but 1#, "
'0'', 1''l'l□'', etc., or a signal pattern asynchronous to the input signal clock cycle. In this case, the control signal generation circuit 8 identifies the pattern and inputs it. All you have to do is detect the signal1
．． ! , if the maximum period of 0'' of the input signal 10 is specified, the period of 1'' of the control signal 20 is determined, so the presence or absence of the input signal can be detected.Furthermore, if the input signal 10 includes a synchronization signal, the control signal Since the presence or absence of an input signal can be detected by detecting this synchronization in the generation circuit 8, this embodiment does not depend on the type of the input signal 10.

As described above, according to the present invention, it is possible to construct an optical transmitter that stably transmits optical pulse trains generated in a burst pattern without deteriorating the semiconductor laser.

Therefore, a semiconductor laser with a high optical output level and a fast response speed can be used as a light source for optical signal transmission in a device such as a packet terminal that transmits data in packets. Therefore, the transmission path can be made longer and faster. In addition, since a semiconductor laser with a high optical output level can be used as a light source, it is possible to increase the number of connectable terminals and expand the system scale in optical systems that distribute optical signals to several terminals using optical star couplers. It can be measured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the output characteristics of a semiconductor laser as the intensity changes; FIG. 2 is a block diagram showing an embodiment of the present invention;
FIG. 3 is a time chart showing waveforms of various parts in FIG. 2, and FIG. 4 is a block diagram showing an example of a drive signal generation circuit used in FIG. 2. 1... Drive signal generation circuit 1, 2... Semiconductor laser drive circuit, 3... Semiconductor laser, 4...
... Optical splitter, 5 ... Photodetector, 6 ...
...Level detector, 7...Light switch, 8...
... Wariyoku 1 signal generation circuit, 9... Delay circuit,
10...Multiple circuit. Agent Patent attorney Uchihara Kita X-shi Hayabusa 7 Figure 1v 4th WJ 1st base b

Claims (1)

[Claims] MiJ
During the period when the input signal is input, a signal equal to the input signal is generated, and during the period -1 when no input signal is input, the drive signal generates a pulse signal and a Vi direct signal.
A semiconductor laser drive connected to the drive circuit and the drive circuit, and configured to generate an electric signal for driving the semiconductor laser and to vary the level of the electric signal. a photodetector that receives a portion of the optical signal of the semiconductor laser; and a source level detection unit that detects the output level of the photodetector and generates an optical level signal that varies the output level of the semiconductor laser drive circuit. circuit, and an optical switch for outputting or cutting off other optical signals of the semiconductor laser according to an optical switch control signal applied from the outside, and the optical switch outputs or cuts off other optical signals of the semiconductor laser during a certain period of the input signal. An optical transmitting device characterized in that it is controlled to be open and closed during a period when there is no input signal.