JPH0325765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a novel optical bistable device that can be applied to optical logic circuits and the like.

Conventional structure and its problems ELECTRONICS is one of the conventional optical bistable circuits that perform logical operations and storage using light.
There is a semiconductor laser described in an article published in LETTERS, Vol. 17, No. 4, pp. 167-168, 1981. In this semiconductor laser, an excitation region and a non-excitation region are formed on a stripe electrode in the direction of the cavity, and since the non-excitation region operates as a saturable absorption region, it has bistable optical characteristics (i.e., one It has been experimentally shown that it can be obtained with two optical output states for one excitation current value. This operating principle is explained as follows. As the current injected into the excitation region increases, the light injection from the excitation region into the non-excitation region, which is a saturable absorption region, becomes stronger. When a certain light injection level is reached, the absorption coefficient in the saturable absorption region becomes zero, and laser oscillation begins.

On the other hand, when the value of the injection current is decreased from the threshold current or more, the light injection from the excitation region to the non-excitation region becomes weaker. When the light injection level decreases to a certain level, the non-excited region becomes no longer transparent and laser oscillation is stopped. At this time, the value of the injected current takes a value smaller than the oscillation threshold, so the relationship between the optical output and the injected current exhibits hysteresis. Such characteristics are
It can also be obtained by inputting light from the outside while keeping the injection current constant.

That is, light with a wavelength shorter than the absorption edge of the non-excited region is incident, electric power and holes are excited in the active region, and the light intensity is increased to create the negative temperature state necessary for oscillation.

According to such a method, operations such as light switching can be performed using optical signals, and since the electrical system is only a bias, it is possible to perform extremely high-speed signal processing. When considering an optical arithmetic circuit that combines a large number of units that operate optical elements using light, the most important problem is the exchange of light between the elements. Since such arithmetic circuits are naturally integrated, unit elements that can emit light in all directions are required. However, conventional lasers can only provide optical output in two directions, which poses a major barrier to integration.

Purpose of the Invention The present invention provides a semiconductor laser having the above-mentioned optical bistable function, and also makes it possible to obtain optical output in eight directions, and provides an extremely effective element particularly for integrating optical arithmetic circuits, etc. It is intended for this purpose.

Structure of the Invention The present invention provides first and second optical waveguide layers on the front and back surfaces of a semiconductor substrate, respectively, and
A reflective surface is formed at each end of the optical waveguide layer at an angle of 45 degrees with respect to the waveguide layer so that the light guided through the waveguide layer is reflected into the substrate, and a surface between the reflective surfaces is formed. A resonator is formed in an optical path composed of the first and second optical waveguide layers and the substrate, and the first or second optical waveguide layer, which is a part of the optical path, is used as an excitation region in the optical path. The other part is set as a non-excitation region, and an output surface is formed on the reflection surface to output the light of the optical path in the direction of the optical waveguide layer and the front and back sides of the substrate, and the injected current is lower than the laser oscillation threshold. Light having a wavelength shorter than the absorption edge of the non-excitation region is injected into the optical waveguide layer in a state where the absorption edge is lowered. In such a structure, one reflective surface emits light in two directions, light from the substrate direction and light from the light guide path, and in the laser of the present invention, four reflective surfaces emit light from the front and back surfaces. Since the waveguides are coupled, it is possible to obtain optical output in eight directions. It goes without saying that for reflective surfaces that do not require light output to the outside, the reflectance may be increased as much as possible. Light is injected into the optical waveguide in the non-excitation region, for example, while the current injected into the semiconductor laser having such a structure is kept slightly lower than the laser oscillation threshold. In this case, the wavelength of the light is assumed to be shorter than the absorption edge of the non-excited waveguide layer. Under such conditions,
When the light intensity of the incident light is increased until it reaches a certain level (called the optical threshold), the absorption coefficient in the non-excited waveguide becomes almost zero, and laser oscillation begins, and the light intensity increases in the direction of the incident light. It is possible to obtain optical output from eight directions, including the

DESCRIPTION OF EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor laser according to an embodiment of the present invention. n-InP2, n
-InGaAsP3 (E _g 0.95eV), p-InP4, p-
InGaAsP5 (E _g 1eV) is sequentially grown by liquid phase epitaxial method. This grown layer is etched into stripes to form mesas, and then a current blocking layer is grown by a second epitaxial method. Next, the substrate 1 is polished until it has a thickness of around 100 μm,
n− by a third epitaxial growth on the polished surface.
InP6, n-InGaAsP7 (E _g ~0.95eV), n-InP
8. Sequentially grow n-InGaAsP9.

In addition, p-InGaAsP5 and n-InGaAsP9
does not have to be for making it easier to take the ohmic electrode. After forming the third growth layer, a mesa is formed by etching to match the surface stripe that has already been formed, and is filled with an n-InP layer by the fourth growth. The back surface embedding need not be a front flow blocking layer since it is sufficient to confine only the light. Second
The figure is a sectional view taken along the line A-A' of the grown layer in FIG. The optical waveguide layers 3 and 7 are precisely aligned. Ohmic electrodes 10 and 11 are attached to such an epitaxially grown wafer, and etched at an angle of about 45° so that light from the active layer penetrates through the substrate 1, and then the wafer is etched at an angle of about 45° so that light from the active layer penetrates through the substrate 1. Deposit a coating film. The reflective coating film is formed of SiO ₂ 12, 14, 16, 18 and Si 13, 15, 17, 19, each having a thickness of, for example, SiO ₂ ~2240 ÅSi ~ 900 Å, and can be laminated to freely adjust the reflectance. As we all know, things can change. The reflectance in this example is approximately 50%.

In such a structure, the light emitted from the optical waveguide 3, which is an excitation region, is guided into the substrate by the reflective ends 12 and 18, and into the optical waveguide 7, which is a non-excitation region, via the reflective ends 16 and 14. It will be destroyed. That is, since an optical resonator is formed in which a pair of optical waveguides are coupled through the substrate, laser oscillation can be achieved by increasing the excitation intensity of the excitation region 3.

In the semiconductor laser device according to the present invention shown in FIG. 1, as shown in FIG. 3, when a positive electrode 11 and a negative electrode are attached to the electrode 10 and a current is applied,
Oscillation started at approximately 120mA. It was also found that the optical output at this time could be obtained from the eight directions shown in the figure. Next, when the current was set just before the start of oscillation and light was input from the direction A into the active layer 7, which is the non-excited region, it was found that optical bistable characteristics were obtained.

In this embodiment, for convenience, a buried structure is used as the semiconductor laser structure, but other structures such as a buried heterostructure semiconductor laser, a distributed feedback semiconductor laser, and a planar semiconductor laser may also be used.

Effects of the Invention As described above, according to the semiconductor laser of the present invention, it is possible to obtain optical output in eight directions instead of the conventional two-direction optical output, and optical bistable operation is also possible. It is.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a semiconductor laser according to an embodiment of the present invention, FIG. 2 is a sectional view of FIG. 1, and FIG. 3 is a configuration diagram for explaining the light emission direction of the semiconductor laser shown in FIG. 1. It is. 1... n-InP substrate, 2... n-InP, 3...
n-InGaAsP, 4...p-InP, 5...p-
InGaAsP, 6...n-InP, 7...n-
InGaAsP, 8...n-InP, 9...n-
InGaAsP, 10, 11...ohmic electrode.

Claims (1)

[Claims] 1. First and second layers on the front and back surfaces of the semiconductor substrate, respectively.
A second optical waveguide layer is provided at each end of the first and second optical waveguide layers, and the light guided through the waveguide layer is processed at an angle of 45 degrees with respect to the waveguide layer, and the light guided through the waveguide layer is formed within the substrate. a resonator is formed in an optical path composed of the first and second optical waveguide layers and the substrate between the reflective surfaces, and the optical path is a part of the optical path; The first or second optical waveguide layer is used as an excitation region, the other part of the optical path is used as a non-excitation region, and the light of the optical path is emitted to the reflective surface in the direction of the optical waveguide layer and the front and back directions of the substrate. 1. An optical bistable element, characterized in that an output surface is formed, and light having a wavelength shorter than the absorption edge of the non-excitation region is injected into the optical waveguide layer while the injection current is lower than a laser oscillation threshold.