JPH04142786A - Laser diode drive device - Google Patents

Abstract

PURPOSE:To enable a laser diode drive device to be simplified in component elements and to control a laser very accurately by a method wherein optical signal data are directly subjected to a digital signal process through a dividing circuit and input signals are subjected to a digital signal process through a dividing circuit, and analog data conversion is carried out through the comparison of the signals concerned. CONSTITUTION:The signal of an input terminal 1 is inputted into a laser diode drive circuit 3 and a first dividing circuit 9a. A laser diode 2 is connected to a laser diode bias circuit 4 which controls an offset bias, and signals are transmitted to an amplifier 8 located in the control loop of the bias circuit 4. The output optical signal is connected to an optical output 6. The signal amplified through the amplifier 8 are inputted into a second dividing circuit 9b, the output of the circuit 9b is inputted into an exclusive logic circuit 10 together with the output of the first dividing circuit, and the average level of the output of the logic circuit 10 is detected by an average value detection circuit 7. The DC level of the detected average level is compared with the DC level of a Vth adjustment terminal 5 through the laser diode bias circuit 4, whereby the offset bias current of the laser diode 2 is controlled.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a laser diode driving device.

[Conventional technology]

In the conventional laser diode driving device, as shown in FIG. 6, an input terminal 1 is connected to a laser diode driving circuit 3 and a mark rate detection circuit 17 that detects the mark rate of the input signal and converts it into an average DC level. are doing. The laser diode drive circuit supplies current to the laser diode 2 through voltage/current conversion, causing the laser diode 2 to emit light. Of the output light from the laser diode 2, the forward light goes to the optical output 6, and the backward light goes to the photodetector 20.
is irradiated. The output of this photodetector 20 is
The signal is input to the P, D, F circuit 19, where it undergoes current/voltage conversion and is converted to a DC level corresponding to the optical power. The output from the buffer circuit 19 is input to the comparison amplifier circuit 18 together with the output from the mark rate detection circuit 17 described above, where the difference in DC voltage is amplified and input to the laser diode bias circuit 4. The signal output from the comparison amplifier circuit is voltage-to-current converted in this bias circuit, superimposed on the output of the laser diode drive circuit, and supplied to the laser diode to drive the laser diode 2 with a bias current.

In this configuration, the optical output power changes depending on the mark rate of the input data signal. Therefore, in order to keep the optical output power according to the data signal constant, the mark rate of the data signal is detected by the mark rate detection circuit 17, and the optical power fluctuation detected by the P and D balance circuit 19 is sent to the comparison amplifier circuit 18. We are using a method to correct this.

[Problem to be solved by the invention]

This conventional laser diode driving device has a drawback that it requires a large number of adjustment steps because it has a complicated circuit configuration and requires multiple highly accurate analog data processes.

Also, for optical power control, voltage → current → light → light → current →
Since voltage, electrical, and optical signals are switched, there are many uncertainties (such as optical conversion efficiency), making highly accurate bias control difficult.

[Means to solve the problem]

The laser diode drive device of the present invention includes a laser diode drive circuit and a laser diode bias circuit that drive a laser diode, a first frequency divider circuit that branches the signal input section of the above-mentioned drive circuit, and uses the signal input section as an input section, and a drive circuit output. a second frequency divider circuit whose input section is the frequency divider circuit via an amplifier, an exclusive logic circuit whose inputs are the outputs of the first and second frequency divider circuits, and an average circuit which converts the output of the logic circuit to a DC level. It has a configuration in which a value detection circuit and the output of the detection circuit are fed back to the input of the bias circuit described above.

In addition, another invention provides a first device connected to a signal input terminal and frequency-dividing the signal from this input terminal by two via a delay element.
a frequency dividing circuit, a pulse width control circuit connected to the signal input terminal, a laser diode drive circuit that converts the signal from the pulse width control circuit into voltage/current and supplies it to the laser diode, and a laser diode drive circuit connected to the signal input terminal. a second frequency divider circuit connected to the cathode side; and a second frequency divider circuit connected to the cathode side;
an exclusive logic circuit that receives the output of the frequency dividing circuit as an input; an average value detection circuit that receives the output of the exclusive logic circuit as an input and outputs an average DC level to the pulse width control circuit; and is connected to the cathode side of the laser diode. The structure is characterized in that it includes at least a laser diode bias circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of a laser diode driving device according to an embodiment of the present invention. The signal at the input terminal 1 is input to the laser diode drive circuit 3 and the first frequency dividing circuit 9a. The laser drive circuit 3 has a voltage/current conversion function to cause the laser diode 2 to emit light. The laser diode 2 has a laser diode bias circuit 4 that controls the offset bias of the laser diode.
The bias circuit 40 is connected to the amplifier 8 in the control loop, and the output optical signal from the laser diode is connected to the optical output 6. The signal amplified by the amplifier 8 is input to the second frequency divider circuit 9b, and its output is input to the exclusive logic circuit 10 together with the output of the first frequency divider circuit described above, and the average level of the output is determined as an average value. The detection circuit 7 detects the DC level, and the laser diode bias circuit 4 converts the DC level to v7. The offset bias current of the laser diode 2 is controlled by comparing it with the DC level of the adjustment terminal 5.

Next, the operation timing in FIG. 1 will be explained using FIG. 2. Input signal and signal a driven by it
A slight difference occurs in the pulse width on the time axis and becomes a minute signal. This phenomenon will be discussed later. The signal a is amplified to a certain level in the amplifier circuit 8 of FIG. 1 and converted into a signal S, then transmitted to the frequency divider circuit 9b, converted into a signal C, and inputted into the exclusive logic circuit IO. A signal d obtained by directly frequency-dividing the input signal is also input to the exclusive logic circuit 10.

By applying exclusive logic to these signals C and d, a signal e having a pulse width equal to the time delay of the rise of the waveform is generated.

Generally, a laser diode emits light only when a current exceeding a bias I th flows therethrough, as shown in FIG. At this time, as shown in FIG. 4, the impedance (Zo) of the laser diode changes rapidly as the light is emitted. This phenomenon results in the generation of a signal a as shown in FIG.

Also, the delay time until the laser diode emits light ■: Laser diode drive pulse current Ib: ”
Bias current τ. : Since it is expressed by the interband transition time, it has the property that the closer the bias current is to the threshold current, the smaller it becomes. Therefore, the pulse width of the signal e output from the exclusive logic circuit IO is the difference between the bias current and the threshold current, and by detecting the average value of this signal e, the signal f is generated, and the signal f becomes smaller. By adjusting the voltages of the V and h adjustment terminals 5 as shown, the bias current can be controlled to be close to the threshold current.

The reason why this bias current is controlled to be near the threshold current is to prevent chirping on the transmission path due to a wavelength shift when the laser diode emits light.

FIG. 5 is a block diagram of the second embodiment, which is an example of a method for controlling the laser diode driving pulse width. The difference from the previous embodiment is that a pulse width control circuit 15 is inserted between the input terminal 1 and the laser diode drive circuit 3, and the output of the average value detection circuit 7 is connected to the control section of this pulse width control circuit 15. a delay element 16 that determines the offset between the laser diode pulse width and the driving waveform pulse width.
is the point inserted between the input terminal 1 and the first frequency dividing circuit 9a. Other than this, the configuration is the same as that of the previous embodiment.

In this embodiment, as explained in the first embodiment, the difference in pulse width between the drive waveform and the laser diode light emitting waveform is utilized, and this difference in pulse width is offset by the delay element 16, so that the laser diode The drive pulse width is directly controlled to obtain the same pulse width as the drive pulse at the input terminal 1.

[Effects of the Invention] As explained above, the present invention performs direct digital signal processing on optical signal information using a frequency dividing circuit and digital signal processing on an input signal using a frequency dividing circuit. Since analog information is converted, circuit adjustment is simplified. In addition, electricity is used for optical signal information →
Since there is no need for conversion from light to electricity, only a laser diode is required for the laser module (no monitor photodiode is required), simplifying the components.
Highly accurate control becomes possible.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a laser diode drive device according to an embodiment of the present invention, Fig. 2 is a timing chart, Fig. 3 is a diagram showing the relationship between optical output and drive current of laser diode characteristics, and Fig. 4 is a laser diode drive device. FIG. 5 is a diagram showing the relationship between impedance and current of diode characteristics, FIG. 5 is a diagram of the second embodiment, and FIG. 6 is a diagram showing a conventional laser diode bias control circuit. 1...Input terminal, 2...Laser diode, 3...Laser diode drive circuit,
4... Laser diode bias circuit, 5.
...vlゎ adjustment terminal, 6 ... light output, 7
...Average value detection circuit, 8...Amplifier,
9a, 9b... Frequency dividing circuit, 10... Exclusive logic circuit, 15... Pulse width control circuit, 16
... Delay element, 17 ... Mark rate detection circuit, 18 ... Comparison amplifier circuit, 19 ...
P, D balance circuit, 20...Photodetector agent Patent attorney

Claims (1)

[Claims] 1. A first frequency dividing circuit that is connected to a signal input terminal and divides the frequency of the signal from this input terminal by two; and a first frequency dividing circuit that converts the signal from the signal input terminal into voltage/current and supplies it to a laser diode. a laser diode drive circuit to supply, a second frequency divider circuit connected to the cathode side of the laser diode via an amplifier, and an exclusive logic circuit whose inputs are the outputs of the first and second frequency divider circuits. an average value detection circuit that receives the output of the exclusive logic circuit as an input and outputs an average DC level; and a laser diode bias circuit that receives the DC level as an input, performs voltage/current conversion, and outputs the voltage/current to the cathode of the laser diode. A laser diode drive device comprising: 2. A first frequency divider circuit that is connected to the signal input terminal and divides the signal from this input terminal into two via a delay element, a pulse width control circuit that is in contact with the signal input terminal, and a pulse width control circuit that a laser diode drive circuit that converts the signal into voltage/current and supplies the signal to the laser diode; a second frequency divider circuit connected to the cathode side of the laser diode via an amplifier; an exclusive logic circuit that receives the output of the circuit, an average value detection circuit that receives the output of the exclusive logic circuit and outputs an average DC level to the pulse width control circuit, and is connected to the cathode side of the laser diode. A laser diode drive device comprising at least a laser diode bias circuit.