JPS643351B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the integration of optical bistable devices and to an integrated optical bistable device that can be operated at a higher temperature.

FIG. 1 is a diagram showing the structure of a conventional optical bistable device. In this Figure 1, 1 is a GaAs layer, and this GaAs layer 1 is about 4 to 5 μm in thickness.
An optical bistable element is fabricated using a molecular beam epitaxy cell with a structure in which Al _0.42 Ga _0.58 As2, 3 is used as a sandwich arch, and furthermore, the outside is coated with dielectric reflective films 4, 5 with a reflectance R = 0.9. .

The name optical bistable device refers to a structure in which a medium whose absorption or dispersion changes nonlinearly with the light intensity is inserted into a Fabry-Perot resonator. It originates from the fact that it can take any of the following states.

The characteristics of such optical bistable devices include nonlinearity and hysteresis effect in the light input/output intensity characteristics, and optical bistable devices are used in optical memories, switches, logic operations, triode operations, image contrast control, etc. can be used.

In addition, by utilizing its transient characteristics, regenerative oscillation,
Generation of pulse examples, monostable and bistable multivibrator operation, etc. are possible.

Next, the operation will be explained. Shown in Figure 1
A GaAs optical bistable device uses the exciton state of GaAs as a medium, and on both sides Al _0.42 Ga _0.58 As2,
Layer 3 forms a heterojunction to better trap electrons. In addition, the dielectric reflective films 4 and 5
forms an optical resonator.

When this optical bistable element is irradiated with light with a wavelength slightly shorter than the energy gap of the exciton state of GaAs and the intensity of the irradiated light (hereinafter referred to as incident light Ii) is gradually increased, the light intensity of a certain input light Ii The intensity of transmitted light (hereinafter referred to as output light It) increases rapidly with respect to the value of .

On the other hand, when the light intensity of the input light Ii is gradually decreased, the intensity of the output light It remains strong until the input light intensity is lower than that (the light intensity corresponding to the rise of the optical power light when the input light intensity increases). That is, there are two stable output light states for a certain amount of input light, and a history effect appears in the output light as the input light increases or decreases.

Figure 2 shows this state, with the input light amount on the horizontal axis and the output light amount on the vertical axis.Characteristic a in Figure 2 shows the case without a medium, and characteristic b shows the case. The case with a medium is shown.
As is clear from this characteristic b, it can be seen that the history effect appears as described above.

Furthermore, from FIG. 1, it can be seen that there is nonlinearity with respect to the amount of input and output light.

As described above, conventional optical bistable devices are composed of plates, so they are suitable for forming two-dimensional arrays for spatial image processing, but when used as optical logic operation devices, it is difficult to integrate the devices. It is necessary to In addition, conventional elements have low temperatures (up to ~120〓)
It is desired to create a device that can operate at room temperature (~300℃).

The present invention has been made in consideration of the above points, and an object of the present invention is to provide an integrated optical bistable device that can be integrated and operate at room temperature.

Embodiments of the integrated optical bistable device of the present invention will be described below with reference to the drawings. FIG. 3 is a sectional view showing the configuration of one embodiment. In FIG. 3, a superlattice optical waveguide 14 is formed on a substrate 19. Further, on the superlattice optical waveguide 14, there is an input optical waveguide 11 that guides the input light 12 and an output optical waveguide 18 that guides the input light 12.
An output optical waveguide 17 is formed to be separated by a desired distance, and a taper coupler 13 is provided at the opposing line portions of the input optical waveguide 11 and the output optical waveguide 17.
a and 13b are formed respectively.

The taper coupler 13a is connected to the input optical waveguide 1.
1 and the superlattice optical waveguide 14, and the taper coupler 13
b is for realizing optical coupling between the output optical waveguide 17 and the superlattice optical waveguide.

Further, on the upper surfaces of the input optical waveguide 11 and the output optical waveguide 17, a Bragg reflection diffraction grating 15 is provided.
a, 15b are respectively formed, and the portion of the superlattice optical waveguide 14 located between the Bragg reflection diffraction gratings 15a, 15b is formed by both the Bragg reflection diffraction gratings 15a, 15b and the taper couplers 13a, 13b. The light 16 is subjected to multiple reflections, thereby confining the light within the superlattice optical waveguide 14.

Next, the operation of the integrated optical bistable device of the present invention configured as described above will be explained.

Input light 12 entering from input optical waveguide 11 is partially reflected by Bragg reflection diffraction grating 15a, but the remaining light is guided to taper coupler 13a and coupled to superlattice optical waveguide 14. The light 16 incident on the superlattice optical waveguide 14 undergoes multiple reflections within the optical waveguide 14 and travels, and is guided to the output optical waveguide 17 from the taper coupler 13b provided on the other side. Here again, the Bragg reflection diffraction grating 15b
A part of the light is reflected, retraces the original optical path, and undergoes multiple reflections with the incident diffraction grating 15a. In other words, the diffraction gratings 15a and 15b have the same function as the reflective films 4 and 5 of the conventional optical bistable element. A part of the light multiple-reflected between the diffraction gratings 15a and 15b passes through the output side diffraction grating 15b and becomes output light 18. The input/output optical waveguides 11 and 17 are made of, for example, an Al _x Ga _1-x As layer, and x is selected so as to have an absorption edge with higher energy than the optical absorption edge of the superlattice optical waveguide. Bragg reflection diffraction grating 15a
and 15b, a photoresist is patterned on a part of this Al _x Ga _1-x As layer using the holographic interference of laser light and the photoresist method, and the Al _x Ga _1-x As layer is etched using this as a mask. and form it. Also, taper couplers 13a, 13b
The formation of the microscopic gap is performed many times using focused ion beam etching.

The superlattice optical waveguide 14 is made of, for example, GaAs and Al _y
A multilayer superlattice layer in which layers of Ga _1-y As (50 to 500 Å each) are stacked alternately using the molecular beam epitaxy (MBE) method and Al _z Ga _1-z As sandwiched between the layers are stacked alternately using the molecular beam epitaxy (MBE) method.
One possibility is to form it from layers. The GaAs layer of the multilayer superlattice layer functions to confine carriers (exciton), and the Al _z Ga _1-z As layers on both sides function to confine photons.

In addition, in the superlattice optical waveguide 4, the coupling energy of excitons is theoretically lower than that of a normal bulk optical waveguide.
It is known to increase by up to 2 times. From this, the exciton state is preserved even in a large thermal energy state (that is, at a higher temperature), so there is a possibility of changing from the conventional low-temperature (~120°) operation to normal-temperature operation.

In such an integrated optical bistable device of the present invention, when the intensity of the input light 12 is increased or decreased, input/output optical characteristics similar to characteristic b in FIG. 2 can be obtained.

In the above embodiment, an optical bistable device that operates purely optically was explained, but as shown in FIG. can be a multifunctional device, as it can be operated not only by light but also by electrical signals. That is, the electrode 20
When the current injected into a and 20b is zero, it naturally has the same function as the integrated optical bistable device shown in FIG. 3, and when the current injected exceeds a certain value, it operates as a laser oscillator.

Furthermore, for intermediate injection currents, when input light 2 is present, the device operates as an optically coupled laser bistable device.

Next, an integrated optical bistable device having a Bragg reflection grating formed on a superlattice optical waveguide will be described.

FIG. 5 is a configuration diagram of one embodiment. In FIG. 5, 15 is a Bragg reflection diffraction grating formed on the superlattice optical waveguide. Diffraction grating 15
is formed, for example, by holographic methods or ion beam etching. The incident light 12 is guided from the taper coupler 13a to the superlattice optical waveguide. A part of this light is the taper coupler 13b
While traveling in the direction, it is diffracted by the diffraction grating 15,
Generates a light wave that travels backwards in the direction of incidence. This diffraction wave is again diffracted by the diffraction grating 15 and added to the original incident light. In other words, the diffraction grating 15 has the function of a so-called optical resonator, confining the incident light in this region, similar to the diffraction gratings 15a and 15b in FIGS. 3 and 4. Therefore, as in FIG. 3, when the intensity of the incident light 12 is increased or decreased, an optical bistability characteristic as shown in characteristic b in FIG. 2 is obtained.

Furthermore, by providing an electrode similar to that shown in FIG. 4 and applying a reverse bias to this electrode, the exciton state can be changed, thereby controlling the optical bistability characteristic.

As described above, according to the integrated optical bistable device of the present invention, the input optical waveguide and the output optical waveguide are disposed on the upper part of the superlattice optical waveguide which exhibits nonlinearity in absorption, dispersion, or both with respect to input light intensity on the substrate. In addition to forming an optical waveguide, a taper coupler is provided to connect the input optical waveguide and the output optical waveguide to the superlattice optical waveguide, and the input light from the input optical waveguide is guided to the superlattice optical waveguide through the taper coupler. After confining it there, it is guided to the output optical waveguide through a taper coupler, making it possible to integrate it and operate at room temperature.

Furthermore, due to the inherent multifunctionality of optical bistable elements such as optical memory, optical switches, and optical calculation, they can be expected to have a wide range of applications as basic components of various optical information processing devices.

[Brief explanation of drawings]

Figure 1 shows the structure of a conventional optical bistable device.
2 is a diagram showing the input/output characteristics of the optical bistable device shown in FIG. 1, FIG. 3 is a diagram showing the configuration of an embodiment of the integrated optical bistable device of the present invention, and FIG. FIG. 5 is a diagram showing the structure of another embodiment of the bistable device. FIG. 5 is a diagram showing the structure of still another embodiment of the integrated optical bistable device of the present invention. 11... Input optical waveguide, 13a, 13b... Taper coupler, 14... Superlattice optical waveguide, 15
a, 15b...Diffraction grating for black reflection, 17...
...Output optical waveguide, 19...Substrate, 20a, 20b
……electrode. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A superlattice optical waveguide formed on a substrate and exhibiting nonlinearity in absorption and/or dispersion with respect to input light intensity, an input optical waveguide and an output optical waveguide formed on the superlattice optical waveguide. a taper coupler for coupling the input optical waveguide and the output optical waveguide with the superlattice optical waveguide for input light on the superlattice optical waveguide, and a taper coupler on the input optical waveguide and the output optical waveguide or the superlattice optical waveguide. An integrated optical bistable device comprising a formed Bragg reflection diffraction grating. 2. The integrated type according to claim 1, characterized in that an electrode for carrier injection into the superlattice optical waveguide is provided on the back side of the substrate and the superlattice optical waveguide, so that it can also function as a laser oscillator. Optical bistable element.