JP2620776B2 - Laser diode stabilization circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for devices such as laser communication and optical disks, and has both the stability of optical output and the stability of pulse output obtained by photoelectric conversion, and The present invention relates to a laser diode stabilization circuit capable of operating at high speed.

[Conventional technology]

Conventionally, the current-optical output characteristics of a laser diode are such that the threshold current value fluctuates within a certain range in accordance with the quality standard as the break point is approached, and the slope of the characteristic curve has a large temperature dependence. laser·
There has been a problem that the light output of the diode and the amplitude of the photoelectrically converted pulse output are difficult to stabilize.

For this reason, in practical use of a laser diode, it is necessary to compensate for these by providing a stabilizing circuit for stabilizing the light output before use.

Thus, in a laser diode stabilization circuit, for example, as described in Japanese Patent Publication No. 59-22525, an optical signal proportional to the optical output of the laser diode is received and converted into an electric signal. in order to detect the peak value and the bottom value of the photoelectric conversion output, as shown in FIG. 7, the sample-and-hold circuit SH _b, it is used SH _p are known.

That is, this type of laser diode stabilization circuit has a light output control loop SH _b , A _b , CC _b
And the light output control loop SH _p , A _p , and CC _p that operate at the time of maximum light emission, the extinction ratio of the laser diode can be kept constant, stabilizing the light output and the pulse output photoelectrically converted. The configuration is such that the amplitude can be stabilized at the same time.

[Problems to be solved by the invention]

By the way, high-speed sample-and-hold circuits currently on the market and in practical use have a high response speed, but the response speed is limited to around 150 nS. In this field, for example, a response speed of about 5 nS is required, so that the conventional laser diode stabilization circuit as described above cannot be used.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a laser diode stabilizing circuit having a faster response.

[Means for solving the problem]

In order to achieve the above object, a laser according to the present invention
The diode stabilization circuit is a laser diode pulse modulation circuit that generates laser light corresponding to the input pulse signal, and a photoelectric conversion element that receives an optical signal proportional to the optical output of the laser diode and converts it into an electric signal. A post-amplifier unit for amplifying a signal from the photoelectric conversion element to detect the peak value and the bottom value of the photoelectric conversion output, and then dividing the amplified signal into two systems of signals; A demodulator unit having an analog switch that outputs two systems of a value signal, and inputting a single system divided signal from a post-amplifier unit to a linear input of the analog switch to detect a peak value and a bottom value; And another one-system divided signal from the post-amplifier section is AC-coupled and converted from a unipolar signal to a bipolar signal to generate a zero-cross signal. A strobe extraction unit that generates a strobe signal that is a control timing signal of an analog switch that inputs a low-cross signal to a comparator and detects a peak value and a bottom value, and corresponds to a peak value signal output from a demodulator unit. A drive circuit for driving a laser diode, comprising a drive circuit for maximum emission and a drive circuit for minimum emission corresponding to the bottom value signal.

An ECL switch may be used for the differential amplifier in the demodulator section. Further, the photoelectric conversion element includes a photo
It is better to use a diode.

[Action]

According to the present invention, since the peak value and the bottom value of the photoelectric conversion output are detected as the maximum current and the minimum current in the demodulator using the differential amplifier, the stability of the optical output is improved. And the stability of the pulse output obtained by photoelectric conversion, and enables a high-speed operation of about 5 nS which could not be used conventionally.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a schematic configuration of the present invention.
For example, the circuit is configured as shown in FIG. The signal from the photodiode PD is amplified by the stabilizing pre-amplifier 1 and applied to the post-amplifier 2 in the next stage. post·
The amplifier section 2 is an ST operation instruction input signal for extracting an _IMAX value corresponding to the peak value of the signal from the stabilized preamplifier section 1.
Through the strobe signal extraction circuit, _IN prepares an output signal that satisfies the input condition to the next-stage demodulator unit 3 and also controls ON / OFF of the peak value extraction operation of the demodulator unit 3.
Then, the output signal waveform of the post-amplifier unit 2 is as shown in FIG. 6, and when a write pulse comes in as shown in the write operation of FIG. Becomes The output signal waveforms at the time of reading and erasing do not include the AC component.
Further, the demodulator section 3 is provided with an output terminal so that the peak value and the bottom value of the input signal are output separately from each other, and when the write pulse WP is not input to the post-amplifier section 2. Operates to stop the peak value extraction operation. In the next stage I _MIN / I _MAX holding circuit 4, the bottom / peak output signal from the demodulator 3 is converted to the minimum current I
Converts extracted as _MIN / maximum current I _MAX, added to the next stage of the drive circuit section 5.

Upon receiving the write signal _SIN , the high-speed switching circuit 6 generates a high-speed pulse necessary for the laser diode LD to perform a pulse operation, and supplies the pulse to the drive circuit 5. In the drive circuit section 5, the drive circuit 5a which operates at the time of minimum light emission by the I _MIN signal from the I _MIN / I _MAX extraction circuit section 4
And a drive circuit 5b that operates at the time of maximum light emission by the / I _MAX signal and the high-speed pulse signal from the high-speed switching circuit section 6, and controls the extinction ratio of the laser diode LD based on these drive outputs. I do.

By the way, since the output signal waveform of the post-amplifier unit 2 is unipolar, the demodulator unit 3 converts it into a bipolar signal by using an A-coupling circuit, obtains a zero-cross signal as shown in FIG. 5, and gives it to a comparator. I _MAX extraction operation is to be controlled by the set value of the power supply V _R.

In the case the demodulator section 3 as constructed of FIG. 2, the comparator A _C which controls the switch SW _1, SW ₂ of the demodulator unit power V _R becomes "Low" state for the High, the switch B Since the position is ON, only the _IMAX extraction does not operate.

Similarly, since the comparator and the switch network coexist, the demodulator unit 3 is of a type in which the comparator is omitted.
As shown in the drawing, the current switching operation may be performed using the ECL switch A _ECL to detect the peak value and the bottom value.

〔The invention's effect〕

As described above, according to the present invention, the drive circuit for driving the laser diode is composed of the drive circuit that operates during the minimum light emission and the drive circuit that operates during the maximum light emission. Since the extinction ratio of the diode can be kept constant, the light output can be stabilized, and therefore, the amplitude of the photoelectrically converted pulse output can be stabilized at the same time.

Further, since the extinction ratio does not change with temperature, it can be used for a laser diode drive circuit such as an ultra-high-speed optical communication system that requires a high-speed operation of about 5 nS.

[Brief description of the drawings]

1 is a block diagram of the present invention, FIG. 2 is a first specific circuit diagram of the demodulator section of FIG. 1, and FIG. 3 is a second specific circuit diagram of the demodulator of FIG. 4 is a specific circuit diagram shown as an example of the embodiment of FIG. 1, FIG. 5 is an explanatory diagram of the operation of FIG. 2, FIG. 6 is an explanatory diagram of the operation of FIG. 3 and FIG. Seventh
The figure shows a conventional example. LD: Laser diode PD: Photo diode.

Claims (3)

(57) [Claims] 1. A laser diode pulse modulation circuit for generating a laser beam corresponding to an input pulse signal, a photoelectric conversion element for receiving an optical signal proportional to the optical output of the laser diode and converting the signal into an electric signal; In order to detect the peak value and the bottom value of the output, a post-amplifier unit that amplifies the signal from the photoelectric conversion element and divides the amplified signal into two systems of signals, and the output side of the peak value signal and the bottom value signal A demodulator section having an analog switch that outputs two systems, and inputting a single system divided signal from a post-amplifier section to a linear input of the analog switch to detect a peak value and a bottom value; Another one-system divided signal from the amplifier unit is AC-coupled and converted from a unipolar signal to a bipolar signal to generate a zero-cross signal. A strobe extraction unit that generates a strobe signal that is a control timing signal of an analog switch that inputs a comparator to detect a peak value and a bottom value, and a drive circuit for maximum light emission corresponding to the peak value signal output from the demodulator unit And a laser diode drive circuit comprising a minimum light emission drive circuit corresponding to the bottom value signal. 2. The laser diode stabilizing circuit according to claim 1, wherein the differential amplifier in the demodulator uses an ECL switch. 3. The laser diode stabilizing circuit according to claim 1, wherein the photoelectric conversion element is a photodiode.