JPS62272711A - Photoelasticity displacement transducer - Google Patents

Abstract

PURPOSE:To convert an optical signal into an elastic displacement effectively with simple constitution by mounting both converting functions of the photoelectric conversion and electroacoustic conversion on one and same element. CONSTITUTION:A semiconductor layer 2 is formed while being adhered to a piezoelectric medium 1. The semiconductor layer 2 is formed so as to have the photovolatic effect by means of the pn junction. In receiving an incident light 6, the upper/lower face of the semiconductor layer 2 has a potential difference. since the upper face of the semiconductor layer 2 is connected electrically to an electrode 6 adhered to the lower face of the piezoelectric medium through a transparent electrode 3 and a lead wire 5, the voltage produced between the upper/lower faces of the semiconductor layer 2 is applied to the upper/lower face of the piezoelectric medium 1 and converted into the elastic displacement through the piezoelectric medium and the thickness of the medium 1 is changed slightly. That is, the incident light 6 is converted into the elastic displacement.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a converter having the function of converting an optical signal into elastic displacement.

(Prior Art and its Problems) In various electronic devices, elements that function to convert one type of signal into another type of signal, that is, conversion elements, are often used. Typical examples include piezoelectric transducers that convert electrical signals into elastic waves, and photodiodes that convert optical signals into electrical signals.

Despite the progress and development of these various conversion elements, an effective element for converting optical signals into elastic displacement has not been realized, and its development has been awaited.

(Objective of the Invention) The present invention provides an optical system that can effectively convert an optical signal into elastic displacement with a simple configuration by mounting both optical-electrical conversion and electro-acoustic conversion functions on the same element. - provides an elastic displacement transducer;

(Structure of the Invention) The present invention forms a semiconductor photovoltaic element by adhering it to a piezoelectric medium, and applies a voltage obtained by irradiating the photovoltaic element with light to the piezoelectric medium. The first feature of the configuration is that it converts into displacement, and as a result,
An extremely small photo-elastic displacement conversion element is realized. In addition to this feature, the conversion element of the present invention has the feature that a piezoelectric filter can be formed on the element at the same time, so that when pulsed input light is irradiated, a light beam with a repetition period corresponding to the passing frequency of the piezoelectric filter is generated. It is also possible to have both an optical-to-electrical conversion function and a filter function, in which only the pulse sequence is extracted as an electrical signal.

(Example) FIG. 1 is a diagram illustrating a first example of the present invention.
is a piezoelectric medium, 2 is a semiconductor layer, 3 is a transparent electrode, 4 is an electrode,
5 is a lead wire that electrically connects the transparent electrode 3 and the electrode 4, and 6 is incident light. In this embodiment, the semiconductor layer 2
is formed so as to have a photovoltaic effect by a method such as a pn junction, and specifically, the structure is as shown in FIG. 2, for example. In FIG. 2, 21, 22, and 23 are amorphous silicon thin films, which are designated as a p layer, an i layer, and an n layer, respectively.

When the semiconductor layer 2 is irradiated with the incident light 6 through the transparent electrode, a potential difference is generated between the p layer 21 and the n layer 23 due to the photovoltaic effect. Similarly, when the incident light 6 is irradiated in FIG. 1, a potential difference is generated between the upper and lower surfaces of the semiconductor layer 2. The upper surface of the semiconductor layer 2 includes a transparent electrode 3 and a lead wire 5.
The voltage generated on the upper and lower surfaces of the semiconductor layer 2 is applied to the upper and lower surfaces of the piezoelectric medium 1, and is further converted into elastic displacement through piezoelectricity. The piezoelectric medium 1 changes its thickness very slightly. That is, the incident light 6 is converted into elastic displacement. If the intensity of the incident light 6 is constant, the amount of displacement will also be a constant value, and if the intensity of the incident light 6 changes, the amount of displacement will also change according to the intensity. With such a conversion function, the element of this embodiment can be used as an actuator element for finely controlling the position using light or as a speaker for directly converting light into sound.

Here, when considering elastic waves, it is clear that the element of the embodiment shown in FIG. 1 can form a piezoelectric resonator. As mentioned above, the amount of elastic displacement changes depending on the intensity of the incident light, so
Periodic elastic strain occurs in incident light that is periodically intensity-modulated. Therefore, if the modulation frequency fM of the incident light matches the piezoelectric resonance frequency fr, strong elastic resonance will occur, and this fact can be utilized to provide a filtering effect as well.

FIG. 3 shows an example of this. In this embodiment, a piezoelectric resonator consisting of a light-acoustic wave conversion means having the same configuration as that shown in FIG. Output terminals 51 and 52 are provided which are connected to each other.

In such a configuration, in terms of elastic waves, a so-called monolithic crystal filter (MCF) is formed, so that the incident light is intensity-modulated at a frequency that matches the passing frequency determined by the thickness of the piezoelectric plate of the MCF. It is possible to electrically extract the conversion output corresponding to .

FIG. 3 fbl and (C1 are side views of signal waveforms for explaining the above-mentioned filter action, (bl is the incident light, and tc+ is the electric output appearing at the output and output terminals 51 and 52.The incident light has a period T “0” or “1” in a pulse code string having
It is assumed that the optical pulse is intensity-modulated as shown in FIG. If it matches the passing frequency of the MCF, an electrical output with a frequency f is obtained at the output terminals 51 and 52 as shown in FIG. 3 (C1).

Since the MCF has a finite Q value, “
Even if 0'' continues for a while, a continuous electrical output can be obtained. Therefore, the element of the embodiment shown in FIG. 3 can also be used as a timing extraction filter in an optical communication device.

FIG. 4 shows a third embodiment of the present invention, in which 1a is a piezoelectric medium;
2 is a semiconductor layer, 3 is a transparent electrode, 4a is an electrode, 5 is a lead wire, 6 is incident light, 7 is an elastic wave propagation medium made of quartz or the like, and 8 is an elastic wave converted from the incident light. In this embodiment, the elastic waves converted through the photovoltaic effect and the piezoelectric effect propagate through the propagation medium 7, so that they can be used as delay elements. Further, the elastic waves generated in this way may be extracted as electrical output by providing a piezoelectric transducer at the right end of the propagation medium 7, or
Alternatively, it is also possible to use a material with a large photoelastic effect for the propagation medium 7 and irradiate the propagation medium 7 with another light beam to deflect it.

In each of the embodiments shown in FIG. 1, FIG. 3, and FIG. ,1
A configuration in which the light is irradiated from the side a is also possible. In this case, the electrode 4 or 4a may be a transparent electrode.

Furthermore, it goes without saying that if a piezoelectric semiconductor such as GaAs is used as the piezoelectric medium 1, 1a, the structure of the semiconductor layer 2 does not depend on that shown in FIG. 2, and it is possible to provide a photovoltaic effect with a single semiconductor layer. Nor.

The light-acoustic wave conversion element according to the present invention is capable of generating not only bulk acoustic waves but also surface acoustic waves. FIG. 5 is a diagram showing an example thereof, in which 10 is a piezoelectric medium, 2 is a piezoelectric medium;
0 is a semiconductor layer, 30 is a transparent electrode, 40 is an electrode, 50 is a lead wire connecting each electrode, 60 is incident light, and 80 is a converted surface acoustic wave. In this embodiment, semiconductor/transparent electrode layers and electrode layers having a photovoltaic effect are alternately arranged on a piezoelectric medium, and the arrangement period is L. As explained in the embodiment of FIG. 1, by irradiating the incident light 60, a potential difference is generated between the upper and lower surfaces of each semiconductor layer 20 due to the photovoltaic effect, but the transparent electrode 30 attached to the upper surface of the semiconductor layer Since it is connected to the electrode 40, an electric field as shown by the arrowed curve in the figure is applied near the surface of the piezoelectric medium 10, so that periodic elastic strain appears on the surface of the piezoelectric medium. That is, the configuration shown in FIG. 5 also has the same effect as an interdigital electrode transducer (IDT) for surface acoustic wave excitation, and surface acoustic waves 80 are transmitted to both sides of the interdigital electrode transducer (IDT). In IDT, the frequency f3-V is generally determined by the electrode period and the surface acoustic wave propagation speed V of the piezoelectric medium.
The conversion efficiency to elastic waves is maximum for 3/L.

Therefore, even in the configuration shown in FIG. 5, when the incident light 60 is intensity-modulated, the surface acoustic wave 8 is most efficient when the modulation frequency f matches the above-mentioned frequency f.
Converted to 0.

In the structure for converting into surface acoustic waves, as shown in FIG. 6, if an IDT for wave reception is provided on either the left or right side of the conversion element of the embodiment shown in FIG. 5, or on both sides, the structure shown in FIG. Of course, a filtering effect can be provided in the same manner as described in the embodiment. In the embodiment shown in FIG. 6, 40a is an electrode, and 51a and 52a are output terminals.

(Effects of the Invention) As explained above, since the light-elastic displacement converter according to the present invention can convert optical input into elastic displacement with a simple configuration, it can be used as an actuator element or a speaker that can be controlled by light. . Furthermore, since it is easy to filter the intensity-modulated incident light at its modulation frequency, it can be used as a signal processing component in various electronic devices such as optical communication devices. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
A sectional view showing an example of the configuration of the photovoltaic element part in the embodiment shown in the figure, FIG. FIG. 4 is a sectional view showing an embodiment of the present invention having delay characteristics, and FIGS. 5 and 6 are sectional views showing an embodiment of the present invention for surface acoustic wave excitation.・Piezoelectric medium, 2.20...
Semiconductor layer, 3.30...Transparent electrode, 4.4a, 4
0.40a, 41°42...electrode, 5.50...
・Lead wire, 51, 52.51a, 52a... Output terminal, 6.60... Incident light, 7... Elastic wave propagation medium, 8... Elastic wave, 80... Surface acoustic wave ,
21... Amorphous 99179 layer, 22... Amorphous 99171 layer, 23... Amorphous silicon n layer.

Claims (5)

[Claims] (1) A light comprising, on a piezoelectric medium, a photovoltaic element and an electrode for applying a potential difference generated on both sides of the photovoltaic element by incident light to the piezoelectric medium.・Elastic displacement transducer. (2) The photo-elastic displacement converter according to claim 1, wherein the photovoltaic element is made of a semiconductor layer. (3) A plurality of the photovoltaic elements and the electrodes are alternately arranged in an interdigital pattern at regular intervals on the piezoelectric medium. Optical-elastic displacement converter. (4) A photo-elastic displacement conversion means having a photovoltaic element and an electrode for applying a potential difference generated on both sides of the photovoltaic element by incident light to the piezoelectric medium on a piezoelectric medium. A light-elastic displacement converter further comprising: a piezoelectric resonator on the piezoelectric medium that couples with the elastic wave excited by the light-elastic displacement converting means. (5) A plurality of photovoltaic elements and a plurality of electrodes for applying a potential difference generated on both sides of the photovoltaic element by incident light to the piezoelectric medium are arranged on a piezoelectric medium at a constant rate. The piezoelectric medium further includes optical-elastic displacement converting means arranged in an interdigital pattern at intervals, and further receives surface acoustic waves transmitted by the optical-elastic displacement converting means. 1. A light-elastic displacement converter comprising a surface acoustic wave transducer for