JPH06273705A - Acousto-optic modulating element - Google Patents

Abstract

PURPOSE:To prevent the change in the diffraction efficiency regardless of long- time use with respect to the acousto-optic modulating element produced by joining an acousto-optic medium and a piezoelectric oscillator. CONSTITUTION:Peltier elements 11 are closely fixed to two faces facing each other except an optical face 9, the junction face of a piezoelectric oscillator 13, and a polished part 10 in the acousto-optic modulating element produced by joining an acousto-optic medium 8 and the piezoelectric oscillator 13, thus fixing the temperature of the acousto-optic medium at the time of ultrasonic driving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acousto-optic modulator used in laser printers, laser scanners, laser facsimiles, optical switches and the like for optical deflection, optical switching, optical modulation and the like.

[0002]

2. Description of the Related Art With the development of optoelectronics, its practical application has been progressing at a rapid pace. Among them, an acousto-optic modulator is one of the devices for electrically controlling light.

The acousto-optic modulator shown in FIG. 1 is a high-frequency power source including an acousto-optic modulator made by joining an acousto-optic medium 6 and a piezoelectric vibrator 5 and a resonance circuit for driving the piezoelectric vibrator 5. 7 is used to apply a high-frequency voltage to the acousto-optic modulator, and the photoelastic effect in which the refractive index is periodically changed in the acousto-optic medium is used to change the path of the light, modulate the frequency of the light, That is, it is possible to utilize that the diffracted light undergoes a kind of Doppler effect by the moving ultrasonic wave and its frequency shifts by the frequency of the ultrasonic wave. These optical modulation effects are widely used in laser printers, laser scanners, laser facsimiles, etc. that use gas lasers, and with the recent increase in the speed of electronic computers, the speedup, noise reduction, and high-speed switching of computer peripheral devices have been achieved. Plays an important role in

In the light modulation effect, there are two phenomena, light refraction and diffraction, depending on the relationship between the wavelength of ultrasonic waves and the beam diameter of incident light. That is, in the case of a low frequency ultrasonic wave in which the wavelength of the ultrasonic wave is sufficiently longer than the beam diameter, the light gradually changes its refractive index and passes through the acousto-optic medium, which causes the refraction phenomenon. Occurs. On the other hand, in the case of a high frequency ultrasonic wave whose wavelength is sufficiently shorter than the beam diameter, light is diffracted because the periodic refractive index change in the acoustooptic medium acts as a diffraction grating. Generally, the latter diffraction phenomenon is used in an acousto-optic modulator.

The diffraction phenomenon by the acousto-optic modulator utilizing the light modulation effect includes Raman-Nass diffraction, in which a plurality of diffracted lights appear, and Bragg diffraction, in which only first-order diffracted light appears.
And the diffraction in the intermediate region, but Bragg diffraction is most widely used because of its high diffraction efficiency. In Bragg diffraction, light incident at an angle given by equation (1), that is, at a Bragg diffraction angle, is diffracted only in the direction forming the same angle as the wavefront. The phenomenon of 2θ deflection is shown. θ = sin ⁻¹ (λf _a / 2v) (1) θ: Bragg diffraction angle (deg), λ: wavelength of light (m),
v: Ultrasonic speed of sound in acousto-optic medium _{(m / s), f a} :
Ultrasonic frequency (Hz)

That is, the first-order diffracted light is generated when the electric input is turned on, and is not diffracted in the off state. Therefore, if only the first-order diffracted light is taken out through a slit or a pinhole, it is possible to switch a laser beam having an extremely high extinction ratio. Here, the level of the extinction ratio is expressed as the diffraction efficiency shown in the following equation (2). Diffraction efficiency (%) = {(first-order diffracted light intensity) / (transmitted light intensity)} × 100 (2) Practically, in order to realize laser beam switching with a high extinction ratio, the diffraction efficiency should be 60% or more. Is desired.

Generally, by increasing the ultrasonic input power, the diffraction efficiency also increases accordingly. However,
When the ultrasonic input power is increased, heat generated from the piezoelectric vibrator part and the ultrasonic collision part causes non-uniformity of the refractive index in the acousto-optic medium, which causes fluctuation of the diffraction angle and intensity of the light beam. . Furthermore, it also caused a decrease in diffraction efficiency due to heat. Therefore, conventionally, a metal block having good thermal conductivity such as aluminum is adhered to the acousto-optic modulation element to improve the heat dissipation effect to prevent uneven refractive index in the acousto-optic medium, but this is not always sufficient. There wasn't.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the non-uniform refractive index in an acousto-optic medium caused by heat generation from a piezoelectric vibrator and an ultrasonic wave collision section, and to deteriorate diffraction efficiency.
Another object of the present invention is to provide an acousto-optic modulator that does not have a diffraction angle of a light beam or intensity fluctuation.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention adheres Peltier elements to both side surfaces of an acousto-optic medium in order to keep the internal temperature of the acousto-optic medium constant, and uses the Peltier element for acousto-optics. The solution was achieved by cooling the medium and controlling the temperature of the acousto-optic medium.

That is, according to the present invention, in an acousto-optic modulation element in which an acousto-optic medium and a piezoelectric vibrator are bonded, an optical surface, a piezoelectric vibrator bonding surface, and an oblique polishing portion (for preventing ultrasonic reflection).
The acousto-optic modulator is characterized in that a Peltier element is brought into close contact with two surfaces opposite to each other except to control the inside temperature of the acousto-optic medium to 20 ± 2 ° C.

[0011]

Function: It is generally known that the diffraction efficiency depends on the ultrasonic input power. That is, it is possible to increase the diffraction efficiency by increasing the ultrasonic input power. However, when the ultrasonic input power is increased, the temperature inside the acousto-optic medium rises, which causes the diffraction angle and intensity fluctuation of the light beam. Moreover, the diffraction efficiency is further lowered.
In particular, these phenomena are remarkable when the refractive index changes greatly with temperature.

Based on these facts, the present inventor has found that the problem can be solved by controlling the internal temperature of the acousto-optic medium within 20 ± 2 ° C. by the Peltier device. That is,
The Peltier element is joined to the side surface of the acousto-optic medium to cool the acousto-optic medium, and the heat generated in the acousto-optic medium is cooled by the Peltier element to reduce the non-uniformity of the refractive index in the acousto-optic medium, It is possible to suppress fluctuations in the diffraction angle and intensity of, and reduction in diffraction efficiency.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An acousto-optic modulator of the present invention will be described with reference to the drawings. In FIG. 2, the arsenic selenide (A
s ₂ Se ₃ ), the piezoelectric vibrator 13 and lithium niobate (LiNb
Using O ₃ ), the piezoelectric vibrator 13 is bonded to the base electrode 12 formed on the end surface of the acousto-optic medium with an epoxy resin adhesive to form an acousto-optic modulator having a size of 10 mm × 8 mm × 5 mm. Next, except for the optical surface 9 on which a thin silicon oxide multilayer film is formed to which light is incident, the surface on which the base electrode 12 to which the piezoelectric vibrator is adhered, and the oblique polishing portion 10 are provided.
20mm × 10 on the surface to be joined to the acousto-optic modulator surface
A Peltier element 11 having a thickness of 2 mm and a thickness of 2 mm and manufactured by Thermobox Co., Ltd. shown in FIG. 3 was adhered by inserting a thermal compound having excellent thermal conductivity between the acousto-optic medium and the Peltier element. FIG. 2 is a schematic configuration diagram of the acousto-optic modulator manufactured in this example. The acousto-optic modulator manufactured as described above is incorporated in a high-frequency oscillation circuit, and the optical system shown in FIG. The acousto-optic modulator is installed between the optical power meter 20 and the
Ultrasonic signals of 0.5MHz and 0.5W are transmitted by the piezoelectric vibrator LiNbO.
Input was made between the _three electrodes, and a current-carrying test was conducted for 100 hours.
At this time, the temperature of the acousto-optic medium is increased to 18 by the Peltier element.
The temperature was controlled to -22 ° C. As a result, as shown in FIG. 5, the diffraction efficiency did not decrease, and neither beam drift nor deformation of the acousto-optic modulator was observed.

[0014]

[Comparative Example] Except that the Peltier device of the example was removed,
An acousto-optic modulator was produced in the same manner as in the example. The acousto-optic device produced above was incorporated into a resonance circuit, and an ultrasonic signal of 140 MHz and 0.5 W was input and an energization test was conducted for 100 hours using the optical system shown in FIG. The temperature of the acousto-optic medium with respect to the energization time at this time was measured by an acousto-optic element using an infrared thermometer (TVS-200) manufactured by Nippon Avionics. The acousto-optic element inputs ultrasonic waves as shown in FIG. After 50 hours, the temperature changed from 20 ° C to 55 ° C. As a result, as shown in FIG. 7, the temperature within the acousto-optic modulator increases 1 hour after the start of the test as shown in FIG. 6 to change the refractive index of light, and the temperature distribution inside the acousto-optic medium. Became non-uniform and the diffraction efficiency became unstable, and the diffraction efficiency decreased after 50 hours. Furthermore, the diffraction phenomenon did not occur after 100 hours.

In the embodiment of the present invention, the wavelength is 1.3 μm, and a large diffraction efficiency can be obtained with a low driving power of the piezoelectric vibrator. On the other hand, the acousto-optic medium whose diffraction efficiency is easily changed by the change of the element temperature. Although it is shown only for arsenic selenide which is, a Peltier element is bonded to the acousto-optic medium of the present invention for the lead molybdate single crystal and tellurium dioxide single crystal which are practically used as other acousto-optic media, and the temperature control is performed. It is natural that an acousto-optic modulator with no reduction in diffraction efficiency can be obtained by carrying out.

[0016]

As described above, according to the present invention, it is possible to remove the unevenness of the refractive index due to the heat generated in the acousto-optic medium by driving the high frequency ultrasonic wave, and drive for a long time. Even now, it has become possible to provide a high-performance acousto-optic modulator that does not cause the diffraction angle and fluctuation of the light beam and the reduction of diffraction efficiency.

[Brief description of drawings]

FIG. 1 is a front view showing the principle of the configuration of an acousto-optic modulator.

FIG. 2 is a side view showing a schematic configuration of an acousto-optic modulator manufactured according to this example.

FIG. 3 is a side view showing the structure of a Peltier device.

FIG. 4 is a layout view of an optical system for an electric current test used in this example and a comparative example.

FIG. 5 is a characteristic diagram showing changes in diffraction efficiency of an acousto-optic modulator manufactured according to the present example with respect to energization time.

FIG. 6 is a characteristic diagram showing measurement results of medium temperature with respect to energization time of an acousto-optic modulator manufactured according to a comparative example.

FIG. 7 is a characteristic diagram showing changes in diffraction efficiency with respect to energization time of an acousto-optic modulator manufactured according to a comparative example.

[Explanation of symbols]

 1 Incident Light 2 1st-Order Diffracted Light 3 Non-Diffracted Light 4 Ultrasonic Traveling Wave 5 Piezoelectric Vibrator 6 Acousto-Optical Medium 7 High-Frequency Power Source 8 Acousto-Optical Medium 9 Optical Surface 10 Oblique Polishing Part (for Ultrasonic Reflection Prevention) 11 Peltier Element 12 Base Electrode 13 Piezoelectric vibrator 14 Upper electrode 15 Lead wire 16 Light source (1.3 μm) 17 Acousto-optic modulator 18 Coaxial cable 19 High frequency power source (140 MHz) 20 Optical power meter 21 Optical path 22 Electronic cooling element 23 Copper electrode 24 Copper plate (Surface nickel) Plating) 25 Substrate (alumina ceramics) 26 Solder layer A → A Heat flow B → B Current flow

Claims (1)

[Claims] 1. An acousto-optic modulator including an acousto-optic medium and a piezoelectric vibrator, which are opposed to each other except an optical surface, a piezoelectric vibrator-bonding surface, and an oblique polishing portion (for preventing ultrasonic reflection). An acousto-optic modulator, wherein a Peltier element is brought into close contact with the surface and the internal temperature of the acousto-optic medium is controlled to 20 ± 2 ° C.