JPS6044647B2 - Light-controlled electro-optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light-controlled electro-optical element, and the drive of an optical switch using the electro-optic effect, which was conventionally performed by applying a voltage, is now possible by simply irradiating light. go there,
The aim is to realize an all-light controlled optical switch that eliminates the need for power supply lines to supply voltage.

There have been several previous attempts to control the electro-optic effect using light.

FIGS. 1, 2 and 3 show these systems. In FIG. 1, reference numeral 1 denotes an electro-optic effect element having electrodes on its upper and lower surfaces, and including reflecting mirrors 2 and 2', constitutes a Fabry-Perot optical resonator.

Now, the light 3 incident from the left side of the drawing appears or does not appear on the 3' side depending on whether the resonator satisfies the resonance condition. The resonance conditions are controlled by photoelectrically converting the light beam 3'' by a photodetector 4, amplifying it by an amplifier 5, and applying a voltage to the electro-optic effect element 1. 6 is a beam splitter, and a resonator This is to use a part of the light beam 3' as bias light.In this device, the light beam 3'
However, the detector 4 and amplifier 5 require power supply lines to apply voltage, and are not an optical control system that does not require any electric wires. Figure 2a shows an application of an optical waveguide. The structure of the optical switch is shown, and FIG. 2B is an equivalent circuit diagram.

In the figure, reference numerals 11 and 11' denote waveguides having an electro-optic effect, through which lights 12 and 12' are guided, respectively. 13, 13'
are electrodes for applying voltage to the waveguides 11, 11'.

A photoconductive film (for example, a CdS film) 14 is provided on the electrode 13 . Light 12 incident on the waveguide path 11 is absorbed by the photoconductive film 14, lowering its resistance. As a result, the voltage divided into the waveguide 11' increases (see the equivalent circuit in the figure), and the output light 12'' changes.However, in this case as well, the light to the photoconductive film 14 is 2″
Although the amount of light is controlled, it is necessary to supply the voltage from the power source VB of the voltage applied to the waveguides 11 and 11' through a power supply line, and it cannot be said to be an all-optical type. FIG. 3 shows the configuration of an optical switch that does not require a power supply line. In the figure, 21 is a waveguide 5 having an electro-optic effect, and 22 and 22' are incident light and output light, respectively. The voltage applied to the waveguide 21 is obtained by irradiating the pyroelectric effect element 23 with light 24, 24''.The polarization direction of the light in the waveguide 21 is controlled by this voltage, and the amount of change in light intensity is measured by the analyzer 25. This method eliminates the need for a power supply line, but the light to obtain voltage due to the pyroelectric effect must be intermittent light.In addition, short wavelength light (for pyroelectric material LiTaO3:Cr It is necessary to use a 4600A dye laser (4600A dye laser irradiation), which causes a large loss and is not practical when transmitting control light using an optical fiber.Furthermore, approximately 7mJ of optical energy is required to drive the switch. However, it would be impossible to transmit the light from a semiconductor laser or light emitting diode through a fiber due to the wavelength and optical power. A fully optically controlled optical switch is constructed by combining a ■-■ group compound film or a ■-■ group compound film that generates an electromotive force, and other Si films, e-films, etc., and solves the above-mentioned problems. be.

Hereinafter, embodiments of the present invention will be explained using FIG. 4. Although a directional coupling type waveguide switch is taken as an example here, the present invention can be applied to any element that uses an electro-optic effect. In FIG. 4a, 31 is a waveguide substrate (for example, LlNbO3, circle 1T, etc.), 32,
32'' is a waveguide provided on the substrate 31, which constitutes a directional coupler type switch.When no voltage is applied to the electrode 34, the light 33 incident on the waveguide 32 passes through the waveguide 32. During propagation, the light moves to the waveguide 32'', becomes light 33'', and is emitted.On the other hand, when a voltage is applied to the electrode 34, the light 33 travels straight and is emitted as light 33''. Whether or not this voltage is applied is controlled by the photovoltaic layer 35 shown in FIG. b. The photovoltaic layer 35 is made of, for example, CdTe, GaAs,
It is constructed using Sl and Ge. FIG. 5 shows the relationship between each illuminance and photovoltaic force. In order to clarify the arrangement relationship of the waveguides 32, 32'', the electrode 3, the photovoltaic layer 35, etc., a cross section taken along line AA'' in FIG. 4b is shown in FIG. 4c.

The photovoltaic layer 35 is provided in contact with the electrode 34, and a glass film 36 is provided between the waveguides 32, 32'', the substrate 31, and the photovoltaic layer 35.
serves as the cladding layer of the waveguides 32, 32'' and as the substrate glass of the photovoltaic layer 35.The photovoltaic layer 3
In addition to using a direct spatially propagating light beam, a good method for supplying light to the optical system 5 is to use an optical fiber. Note that 37 in the figure is a rod lens tangential to the fiber 38, and the light from the fiber 38 becomes a parallel beam of light as shown by the broken line in the figure, and enters the photovoltaic layer 35. Note that a fiber bundle may be used instead of the rod lens 37.
Next, specific examples of the present invention will be explained using numerical values.

FIG. 5 shows the relationship between illuminance and photovoltaic force of obliquely deposited films of CdTe, GaAs, Si, and Ge. Cd
In the case of Te, a voltage of 450V or more is shown at 5×101'x. (Temperature: 20° C.), 5×101 eX of light corresponds to an optical power of 120 pW per 1 d of red light. In the case of CdTe, an electromotive force is generated by light with a wavelength shorter than 850 r1m. On the other hand, the photovoltaic force of CdTe is about 1
Corresponds to the voltage between electrodes spaced 0 nm apart, 1? When the distance is about 45 cm. Currently, the most common material is L.
There are 4 directional coupler type switches using iNbO3 substrate.
Since it operates at a voltage of about 10V, the dimensions are 100~
A 200 pm wide CdTe layer would allow the switch to be driven by light.

Furthermore, if PLn is used as the waveguide material, the electro-optical constant of PLET is more than 3 times that of LjNbO3, so if an optical switch under the same conditions is manufactured, it will be LiNlO3.
It is possible to operate with a voltage of 113 degrees when using.

In this case, a photovoltaic layer such as GaAs may also be used. Furthermore, if the required area of the photovoltaic layer is larger than the electrode spacing of the waveguide, an electrode structure as shown in FIG. 6 may be used. That is, the interval between the electrodes 34 is widened in the vertical direction in the drawing, and a photovoltaic layer (roughly hatched portion) 35 is provided thereon. The black portion of the electrode 34 is insulated from the photovoltaic layer 35, and the finely hatched portion is connected to the photovoltaic layer 35. Although the embodiments of the directional coupler type optical switch have been described above, the present invention can be applied to all cases where the electro-optic effect is applied, as described above, and other examples are shown in FIG. Shown below.

In FIG. 7, 41 is a substrate, 42 is a waveguide, which has a Y-shaped branch path, and a diffraction grating 45 is provided at the branch point.

When voltage is applied through the electrode 44, the flag condition of the diffraction grating 45 is relaxed, and the light 43 travels straight and is emitted as light 43''.When no voltage is applied, the light 43 is reflected by the flag grating 45 and becomes the light 43''. ”. Regarding this structured optical switch as well, by providing a photovoltaic layer on the electrode, an optically controlled switch can be constructed in the same manner as in the above example. The optically controlled electro-optical element having the structure of the present invention as described above does not require a power supply or a power supply line for applying voltage, and can operate only with light, and requires less optical power to drive it. I'll try it.

Furthermore, the wavelength of light used to generate electromotive force in the photovoltaic layer can be in the region of low loss in optical fibers, and the fiber can drive optical switches by transmitting light from light emitting diodes and semiconductor lasers. becomes. Furthermore, since it does not use electricity at all, it has the advantage of being safe even in highly flammable atmospheres.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are diagrams each showing the configuration of a typical example of a conventional optically controlled optical switch. FIG. 4 shows the configuration of an optical switch that can be controlled only by light, which is an embodiment of the present invention. FIG. Figure c
Figure 5 is a diagram showing the A-A'' section in Figure b and the arrangement of the lens and fiber for supplying light. Figure 5 is a diagram showing the relationship between illuminance and photovoltaic force of obliquely deposited films of various materials. .6th
The figure shows a method of widening the electrode spacing and increasing the photovoltaic force in the present invention. FIG. 7 is a diagram showing the configuration of a waveguide switch according to another embodiment of the present invention. 31...
・Waveguide substrate, 32, 32″...Waveguide, 34
... Electrode, 35 ... Photovoltaic layer, 36
... Glass film, 37 ... Rod lens, 38 ... Fiber, 41 ... Waveguide substrate, 42 ... Waveguide, 44 ... ·····electrode,
45...Diffraction grating.

Claims (1)

[Claims] 1. An optical switch that uses an electro-optic effect, and a photovoltaic film that is formed on the same substrate as the optical switch and that generates a voltage by light, the voltage that is generated in the photovoltaic film. is applied to the optical switch. 2. The optically controlled electro-optical element according to claim 1, wherein the optical power supplied to the photovoltaic film is transmitted through an optical fiber.