JPS6142981A - Optoelectronic integrated circuit device - Google Patents

Abstract

PURPOSE:To obtain the laser light source of high function and compactness by providing a drive circuit which modulates semiconductor laser beams at high speeds and an automatic photo output control circuit which keeps the photo output level constant not by changes in ambient temperature. CONSTITUTION:A differential type transistor is switched into the modulation of semiconductor laser beams by applying modulation signals to the bases of transistors Q3 and Q4. Besides, in order to prevent the photo output from changing by the variation in threshold value of a semiconductor laser LD with temperature changes, the laser photo output is monitored by means of a photo diode PIN, the difference between its output and the set voltage is amplified in an OP amplifier A, and the output is fed back to a laser drive transistor Q2, thereby carrying out automatic control so that the average photo output may become constant. Of such a circuit, for example the parts of the semiconductor laser, photo diode, and electronic circuit surrounded with a dot line are integrated into a laser light source including the chip of the photoelectronic IC and the chip of an integration of the part of the OP amplifier A within the same package.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optoelectronic integrated circuit element used as a light source for optical communications and optical information processing equipment.

Conventional Structures and Problems Semiconductor lasers have established a very important position as key devices in optical information processing systems such as optical communications, pickups for optical disk drives, and light sources for laser printers.

゛ When using a semiconductor laser as a light source in these systems, it is necessary to keep the laser light output constant and modulate it at high speed. In semiconductor lasers, the optical output can be easily modulated by modulating the drive current, which is a major feature not found in other lasers. Therefore, integrating a semiconductor laser and its driving transistor is extremely advantageous for high-speed laser modulation.

By the way, semiconductor lasers use light emission associated with electronic transition between the conduction band and the valence band for laser oscillation, so the threshold current for laser oscillation varies greatly with temperature, even if the semiconductor laser is operated at a constant current. Light output increases or decreases with changes in temperature. FIG. 1 shows the current-optical output characteristics of a semiconductor laser. It can be seen that the threshold value increases as the temperature rises, and that the operating current must be increased in order to obtain a constant optical output.

In order to control the optical output to a constant level, it is conceivable to keep the temperature of the semiconductor laser constant. Figure 2 shows a method of keeping the temperature of the laser constant using a thermoelectric cord. Here, (1) is a semiconductor laser, (2) is a temperature sensor, (3) is a thermoelectric element, (4) is a heat sink, (5) is a temperature control circuit, and (6) is
This is a laser drive circuit. In this way, it is highly desirable to keep the temperature of the semiconductor laser constant not only from the viewpoint of optical output control but also from the viewpoint of stabilizing one oscillation wavelength and improving reliability. However, the thermoelectric element (3), temperature control circuit (5)
), etc., making it impossible to take full advantage of the small size and light weight of semiconductor lasers.

Therefore, it is considered unsuitable for optical pickup, etc., and is limited to special uses.

Another way to control the light output is to sense the laser light output and feed it back into the drive current to provide a constant light output. This method requires fewer additional elements,
Generally widely used.

In this case, as shown in Fig. 3, the rear end facet output of the semiconductor laser (7) is received by the photodetector (8), it is amplified by the ○P amplifier (9), and the current control circuit of the laser drive circuit ( 1
0) to control the drive current. A photodiode that detects the backward light output is usually built into the semiconductor laser package, and this output is used.

When integrating a semiconductor laser and its driving element,
Considering the optical output control function mentioned above, it is considered essential to integrate a photodetector element and an automatic control circuit to realize a more highly functional 0EIC, and the impact it will have on the miniaturization of optical information processing equipment will be expected to be very large.

OBJECTS OF THE INVENTION The present invention is directed to the realization of an optoelectronic integrated circuit device having high-speed modulation and automatic optical power control (APC) functionality.

Implantation of the Invention To achieve this objective, the present invention provides a semiconductor laser,
An optoelectronic integrated circuit (OEIC) monolithically integrates a photodetector and electronic elements such as transistors that drive them on the same substrate, and a monitor electrical output from the photodetector is amplified and fed back to the electronic element. The amplifier circuit that controls the optical output is installed in the same package, and only the modulation electrical signal and optical output setting signal are applied externally.This configuration allows for stable output modulation against changes in ambient temperature. An optical signal is obtained, and a modulation function and an APC function are obtained.

Description of examples An embodiment of the present invention will be described in detail below.

First, Figure 4 shows a circuit made up of individual elements used to control the optical output of a semiconductor laser and perform high-speed modulation.
In this circuit configuration, a modulation signal is applied to the bases of transistors Q, Q, to switch the differential transistors and modulate the semiconductor laser light. In order to prevent the threshold value of the semiconductor laser LD from changing due to temperature changes and the optical output changing, the laser optical output is monitored by the photo diode PIN, and the differential amplification between the output and the set voltage is amplified by the ○P amplifier A. By feeding back the output to the laser drive transistor Q2, automatic control is performed so that the average optical output is constant.
In a first embodiment of the invention.

The semiconductor laser, photodiode, and electronic circuit parts surrounded by dotted lines in Figure 4 are integrated into an optoelectronic integrated circuit (O
A laser light source that includes a chip in which an EIC (EIC) chip and an OF amplifier A part are integrated in the same package will be described. Next, as a second embodiment, an O'EIC in which all the circuits shown in FIG. 4 are monolithically integrated on the same substrate will be described.

Figure 5 shows the ○P amplifier chip and ○E according to the first embodiment.
The circuit configuration of the IC chip and the wiring between the two are shown. The monitor output voltage of the 0EIC chip is applied to the inverting input terminal IN- of the oP amplifier chip, and the set voltage divided by an external resistor P□ is applied to the non-inverting input terminal IN. The control signal output from the ○P amplifier chip is input to the base of the transistor circuit of the 0EIC chip, and the laser drive current is controlled. On the other hand, the modulation signal is transmitted by transistor Q3 of the 0EIC chip. It is added to the base of Q. The signal level is a TTL level, and the peak value of the modulated optical output is set by changing the base voltage of the transistor Q using an external resistor P2. Figure 6 shows how the above ○P amplifier chip and 0EIC chip are assembled in the same package.6 Figure 6 shows the cap (12).
FIG. 2 is a partially cutaway perspective view. 0EIC chip (13
) are arranged and bonded so that laser light can be extracted through the transparent window (11). 0EIC chip (1
3) and the OP amplifier chip (14) are bonded onto a substrate (15) (16) made of SiC, etc., which has good thermal conductivity and is an electrical insulator, and is connected to an external lead wire (17) through a wiring pattern. Ru. (18) is a heat sink, and (19) is a stem body.

Next, in a second embodiment of the present invention, the OP amplifier circuit and the OEIC circuit shown in FIG. 5 are monolithically integrated on the same substrate. In this case, the manner in which it is assembled into the package is similar to that shown in FIG. 6, and there is only one chip, indicated by (13).

Effects of the Invention The optical integrated circuit of the present invention has a drive circuit that modulates semiconductor laser light at high speed and an automatic light output control circuit that keeps the light output level constant regardless of changes in ambient temperature. High-performance, compact laser light sources have great effects on downsizing and increasing reliability of optical communications and optical information processing equipment.

[Brief explanation of drawings]

Figure 1 is a current-optical output characteristic diagram of a semiconductor laser, Figure 2 is an example diagram showing a method of controlling the temperature of a semiconductor laser to a constant level, and Figure 3 is a diagram of a method of controlling the optical output of a semiconductor laser to a constant level. An example diagram, FIG. 4, is a circuit diagram for modulating a semiconductor laser while applying APC. FIG. 5 is an 0EIC circuit diagram showing an embodiment of the present invention. FIG. 6 is a diagram showing how 0EIC: is assembled into a package. (11) - Translucent window, (12) -Ki'v 7p, (
13) ・OE IC chip, (14)...oP amplifier chip, (15)...substrate, (16)...substrate,
(17)... Lead wire first factor 0 50 to. Current (tnA) Figure 2 Factor 15

Claims (1)

[Claims] 1. An optoelectronic integrated circuit (OEIC) in which electronic elements such as a semiconductor laser, a photodetector, and a transistor for driving them are monolithically integrated on the same substrate, and monitor electricity from the photodetector. An opto-electronic integrated circuit element that includes an amplifier circuit that amplifies the output and controls the optical output by feeding it back to the electronic element in the same package, and applies only a modulated electric signal and an optical output setting signal from the outside. 2. The opto-electronic integrated circuit device according to claim 1, wherein the opto-electronic integrated circuit and the amplifier circuit are integrated on the same substrate and constituted as a single chip.