JPH0426234B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a photoelectric converter, and more specifically, a semiconductor laser and a method for integrating and assembling the same on the same substrate in order to make the output light constant. Regarding photoelectric converters.

[Conventional technology]

Generally, a laser light emitting element that generates laser light tends to have a temperature rise due to internal heat generation. This is because the optical output part of a semiconductor laser, that is, the active layer, has a narrow width of generally 1 μm or less.
This is because it produces a high output of 80mW or more despite its small optical output cross-sectional area, and its high energy density generates a large amount of heat. The amount of heat dissipated from this heat generated by laser oscillation changes depending on the ambient temperature, and the temperature of the active layer itself also changes. This changes the thermal equilibrium state, changes the number of electrons and holes injected into the conduction band and valence band, and changes the frequency of recombination.
This changes the level of the optical output of the semiconductor laser. Furthermore, the optical output of the semiconductor laser changes greatly due to fluctuations in the semiconductor laser drive voltage. These factors cause instability in the optical output.

Conventionally, to solve this problem, a material with good thermal conductivity, such as diamond, was used as a heat sink. However, it is expensive and has the drawbacks of increasing the wafer process and bonding process due to the use of In as an adhesive.

Conventionally, in order to stabilize unstable output light, the optical output of a semiconductor laser is reflected and transmitted by a half mirror, the reflected light is detected by a photoelectric conversion element, etc., and the detection signal is sent to a current/voltage control drive circuit. A method was used to stabilize the optical output of the semiconductor laser by providing feedback to the semiconductor laser. but,
By using a half mirror, skill is required to adjust the angle of transmitted light and reflected light.
Moreover, due to the unevenness of the reflectance distribution of the half mirror itself, it is difficult to separate the transmitted light and the reflected light at a constant ratio.

Furthermore, such conventional devices, namely:
When configuring a constant output semiconductor laser output device using a semiconductor laser as a laser emitting element, a half mirror as an optical demultiplexer, a photodiode as a light receiving element, and an FET (field effect transistor) as a drive circuit, each interface is required. They were connected by optical and electrical circuits through the FACE. The process of aligning the optical axis and the like at this time was complicated and difficult, and the apparatus had drawbacks such as an increase in size. The instability of the optical output in conventional semiconductor laser output devices has determined the limit of accuracy as a laser measuring device. For example, when measuring the propagation loss of an optical fiber, if the optical output of a semiconductor laser entering the fiber is unstable, the output light from the fiber will also change as the intensity of the incident light changes. Even if the sensitivity of the detector is stable, there have been cases where it is not possible to accurately detect propagation loss of the optical fiber.

Therefore, in order to eliminate the above drawbacks, as shown in FIGS. 1 to 3, on the same substrate, a semiconductor laser is used as a laser emitting element, an optical waveguide branch is used as an optical demultiplexer, and a photodiode drive circuit is used as a light receiving element. A device including an FET (field effect transistor) and an impedance element, in other words, an integrated constant output semiconductor laser device is being considered.

Specifically, FIG. 1 is a diagram showing a constant output semiconductor laser device using a conventional photoelectric converter, FIG. 2a is a cross-sectional view taken along line A-A, and FIG. is a functional schematic representation of the plan view. In FIG. 1, first, a part of the step is provided on an insulating substrate 1, and a semiconductor laser 2 is provided as a laser emitting element. The optical output of the semiconductor laser is guided to an optical demultiplexer 4 through an optical waveguide 3 made of a thin film. Although a ferroelectric substrate such as LiNbO ₃ is an optical nonconductor, it becomes a good optical conductor by diffusing impurities such as Ti, so the optical waveguide 3 is formed by forming a Ti diffusion region in a part of the ferroelectric material. be able to. Furthermore, the optical waveguide 3 can be formed by depositing a chalcogenide amorphous thin film (As-Se-S-Ge), which is a good optical conductor, on a part of a ferroelectric substrate made of an optical nonconductor or various dielectric substrates. can. As shown in FIG. 3, a conventional optical demultiplexer 4 is formed by arranging Ti diffusion waveguides close to each other on a dielectric material such as LiNbO ₃ .

A part of the optical output of the semiconductor laser demultiplexed here is also sent through the optical waveguide 3 to a light receiving element 5 composed of a photodiode or the like. Light receiving element 5
Then, an electric signal corresponding to the amount of light received is sent to the control drive circuit 6. Photodiodes are made using conventional semiconductor integrated circuit technology. Here, the control drive circuit 6 compares the electrical signal with a reference electrical signal inputted from the reference electrical signal input terminal 7 to determine the magnitude thereof, and controls the optical output of the semiconductor laser so that it is always at a constant level. Control is performed by controlling laser drive voltage and current.

That is, the photoelectric converters that are the gist of this conventional example are listed as follows.

(a) Using an optical waveguide branch as an optical demultiplexer, a part of the optical output of the semiconductor laser is demultiplexed for detection. The extracted optical output is guided to a light-receiving element using an optical waveguide, where it is photoelectrically converted.

(b) Optical waveguides are constructed on the same substrate using semiconductor circuit manufacturing technology, photoetching, etc.

[Problem to be solved by the invention]

However, in the optical demultiplexer 4 shown in FIGS. 1 to 3, it is difficult to appropriately set the ratio of the optical output of the semiconductor laser to be demultiplexed. Further, since the optical demultiplexer 4 and the light receiving element 5 are formed individually, the optical output of the semiconductor laser demultiplexed by the optical demultiplexer 4 is propagated to the light receiving element 5 through the optical waveguide 3. Therefore, there is a limit to miniaturizing the photoelectric converter.

[Means to solve the problem]

In the present invention, a part of the optical output of a semiconductor laser propagating through an optical waveguide is converted using a photoelectric converter with an ultra-small structure that has both the functions of an optical demultiplexer and a photodetector as in the conventional example and can be integrated and integrated. Convert to electrical signal.

[Effect]

In the photoelectric converter configured in this manner, the wavelength of the laser beam and the amount of light to be absorbed can be configured by a combination of the composition of the p-type amorphous silicon thin film 13 and the length of the recess 20 in the optical waveguide. It is also possible to convert optical energy into electrical signals according to the amount of absorbed light.

〔Example〕

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

FIG. 4 is an embodiment of the present invention, and is a diagram showing a photoelectric converter for an optical integrated circuit (hereinafter referred to as optical IC) having the function of combining the optical demultiplexer 4 and the light receiving element 5. It is.

That is, FIG. 4 is a diagram showing a photoelectric converter 19 that utilizes the thermoelectric effect accompanying absorption of light energy and heat generation. In FIG. 4, 1 is an insulating substrate (ferroelectric substrate), 3 is an optical waveguide, 13 is a p-type amorphous silicon thin film, 14 is an n-type amorphous silicon thin film, 15 and 16 are electrodes, 17 is the input light of the semiconductor laser, and 8 is the output light of the semiconductor laser. The p-type amorphous silicon thin film 13 in FIG. 4 absorbs light and generates heat, and forms a thermoelectric body with the n-type amorphous silicon thin film 14 provided as a pair. In this example, a buried optical waveguide (for example, formed on a LiNbO ₃ substrate by Ti diffusion) is used.
Since a part of the optical waveguide 3 is removed by etching, the removed recess 20 is a p-type amorphous silicon thin film 1 deposited on a ferroelectric substrate.
Embedded in 3. The p-type amorphous silicon thin film 13 has wavelength dependence in light absorption characteristics, and has an absorption coefficient of approximately 10 ¹ to ^{10 3} cm ⁻¹ . Therefore, if the length of the recess 20 of the optical waveguide 3 is set to 1 to 10 μm, the amount of laser light absorbed in the region of the p-type amorphous silicon thin film 13 will be 0.1 to 100%. In this case, once the wavelength of the laser beam and the amount of light to be absorbed are determined, it can be configured by combining the composition of the p-type amorphous silicon thin film 13 and the length of the recess 20 in the optical waveguide.
P-type amorphous silicon thin film 13 in recess 20
generates heat due to absorption of laser light and becomes high temperature. P-type amorphous silicon thin film 13 near the recess 20
The n-type amorphous silicon thin film 14 provided in contact with a part of the p-type amorphous silicon thin film 13 constitutes a thermocouple, and the vicinity of the recess serves as a hot junction.
Each amorphous silicon thin film 13, 14 and electrodes 15, 16 provided separately from each other form a cold contact. Generally, amorphous silicon thin films have good thermal conductivity, so in order to increase detection sensitivity, each amorphous silicon thin film 13, 14 has a strip shape as shown in FIG.

As for the method of forming an amorphous silicon thin film with high conductivity and Seebeck coefficient, the method described in "Thermocouple Element" (Japanese Patent Application No. 108728/1982) is used.

As described above, in this example, the thermoelectric effect, the photovoltaic effect, the photoconductive effect in a broad sense, which the junction part formed of the semiconductor has, and the optical multiplication effect of the P-i-n structure, and the optical By combining the light absorption properties of transparent semiconductors, a portion of the light energy incident on the semiconductor is absorbed by the semiconductor and photoelectrically converted, converting the light energy into an electrical signal, while the large portion that is not absorbed is It uses a new type of photodetector that detects the magnitude of incident light energy by passing the incident light energy through a portion.

〔Effect of the invention〕

As mentioned above, according to the photoelectric converter of the present invention,
Once the wavelength of the laser beam and the amount of light to be absorbed are determined, the amount of light can be configured by a combination of the composition of the p-type amorphous silicon thin film 13 and the length of the recess 20 in the optical waveguide 3. Furthermore, recess 2
The n-type amorphous silicon thin film 14 provided in contact with a part of the p-type amorphous silicon thin film 13 near 0 is the p-type amorphous silicon thin film 13.
and constitute a thermocouple. Therefore, the optical energy of the amount of absorbed light can be converted into an electrical signal, and it can have the functions of an optical demultiplexer and a light receiving element.

[Brief explanation of drawings]

Figure 1 is a diagram showing a constant output semiconductor laser device using a conventional photoelectric converter, Figure 2a is a sectional view taken along line AA in Figure 1, and Figure 2b is a functional plan view of Figure 1. Figure 3 shows the conventional light
Optical demultiplexer for IC, FIG. 4a is a diagram showing an embodiment of the present invention, and FIG. 4b is an enlarged view of part a of FIG. 4a. 1... Insulating substrate, 2... Laser emitting element (semiconductor laser), 3... Optical waveguide, 4... Optical demultiplexer,
5... Light receiving element, 6... Control drive circuit, 7... Reference electric signal input terminal, 8... Optical output, 9... Separated optical output, 13... P-type amorphous silicon thin film, 14... ...N-type amorphous silicon thin film, 15, 16... Electrode, 17... Light input, 19
...Photoelectric converter, 20 ... recess.

Claims (1)

[Claims] 1 An insulating substrate 1, an optical waveguide 3 formed integrally with the substrate, a light-transmissive p-type amorphous silicon thin film 13, a light-transmissive n-type amorphous silicon thin film 14, and the p-type amorphous silicon thin film 14. The electrode 15 provided on the amorphous silicon thin film and the n
Electrode 1 provided on amorphous silicon thin film
6, and a recess 20 provided in a part of the optical waveguide.
and the p-type amorphous silicon thin film and the n-type amorphous silicon thin film are integrated on the substrate so that at least a portion thereof overlaps in the recess and crosses the optical waveguide.