JPH06230331A - Acousto-optic element - Google Patents

Abstract

(57) [Abstract] [Purpose] In an acousto-optic device in which an acousto-optic medium and a piezoelectric vibrator are joined, deformation of the beam and displacement of the beam are suppressed by suppressing heat generation in the acousto-optic medium due to ultrasonic waves.
Provided is an acousto-optic device without deterioration of diffraction efficiency. [Structure] An In (indium) film 11 is formed to a thickness of several μm on all surfaces except the optical surface of the acousto-optic device and the bonding surface of the piezoelectric vibrator by a vapor deposition method, a sputtering method or an ion plating method, and the heat sink 10 is adhered thereto. The structure will be changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustooptic device used for optical modulation, optical switching, optical frequency shifter and the like.

[0002]

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

An acousto-optic modulator is composed of an acousto-optic element formed by joining an acousto-optic medium and a piezoelectric vibrator and its resonance circuit. By applying a high frequency voltage to the acousto-optic element, the refractive index in the acousto-optic medium is increased. The photoelastic effect that changes periodically is used. By utilizing this effect, for example, optical path change of light, control of light traveling direction by frequency modulation, frequency modulation of light (diffracted light receives a kind of Doppler effect due to moving ultrasonic waves and its frequency is It is possible to use (shifting only the frequency). Therefore, these optical modulation effects are widely used in laser printers, laser scanners, and laser facsimiles that use gas lasers, and speed up output, noise reduction, and speed switching with the increase in speed of electronic computers in recent years. Play 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, when the wavelength of the ultrasonic wave is sufficiently longer than the beam diameter (low frequency ultrasonic wave), the light passes through the acousto-optic medium in which the refractive index gradually changes, and a refraction phenomenon occurs. . On the other hand, when the wavelength is sufficiently shorter than the beam diameter (high-frequency ultrasonic wave), light is diffracted because the periodic refractive index change in the acousto-optic medium acts as a diffraction grating. Generally, the latter diffraction phenomenon is used in an acousto-optic device.

The diffraction phenomenon by the acousto-optic element utilizing the light modulation effect is divided into Raman-Nass diffraction, in which a plurality of diffracted lights appear, Bragg diffraction, in which only first-order diffracted light appears, and diffraction in the intermediate region. Bragg diffraction is most widely used because of its high diffraction efficiency.

In Bragg diffraction, light incident at an angle (Bragg diffraction angle) given by equation (1) is diffracted only in a direction forming the same angle as the wavefront, and the diffraction angle can be deflected by 2θ.

Θ = sin ⁻¹ (λ / 2Λ) = sin ⁻¹ (λf _a / 2v) (1)

Θ: Bragg diffraction angle (degree), λ: wavelength of light (m), Λ: wavelength of ultrasonic wave (m) v: sound velocity of ultrasonic wave 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 extracted 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 equation (2).

Diffraction efficiency (%) = {(first-order diffracted light intensity) / (transmitted light intensity)} × 100 (2)

Practically, it is desired that the diffraction efficiency be 60% or more in order to realize laser beam switching with a high extinction ratio. By the way, the bonding state of the acousto-optic medium and the piezoelectric vibrator is mentioned as the largest factor in manufacturing that influences the diffraction efficiency, and a uniform bonding technique is required.

For this reason, for bonding the acousto-optic medium and the piezoelectric vibrator, metal adhesion such as indium and tin, or organic adhesive is used. However, in both cases, when a high-frequency voltage is applied, the temperature inside the acousto-optic medium rises with energization time, causing non-uniformity of the refractive index in the acousto-optic medium, causing beam deformation / position shift, and deterioration of diffraction efficiency due to heat. It was Therefore, conventionally, a metal block having a high heat dissipation property such as aluminum is bonded to the acousto-optic element with silicon rubber to improve the heat dissipation effect to prevent the non-uniform refractive index in the acousto-optic medium. It wasn't enough.

[0013]

Therefore, the technical problem of the present invention is to suppress the heat generation in the acousto-optic medium due to ultrasonic waves. By solving this technical problem, the deformation of the beam An object of the present invention is to provide an acousto-optic device that is free from misalignment and deterioration of diffraction efficiency.

[0014]

In order to solve the above problems, the present inventor measured the temperature distribution in an acousto-optic medium when a high frequency voltage was applied (Japan Avionics TVS-2
00). As a result, they have found that heat is generated at the collision part of ultrasonic waves (traveling waves). Based on these facts, the present inventor believes that it is possible to solve the above problems by installing a material excellent in both ultrasonic wave absorption and heat conduction in the collision part of ultrasonic waves and adhering a heat sink to it. As a result of examining the material, it was found experimentally that indium (In) was most suitable. That is, In is deposited on the entire surface of the acousto-optic device excluding the optical surface and the piezoelectric vibrator bonding surface by several μm by vapor deposition, sputtering or ion plating.
The problem of heat generation in the acousto-optic medium was solved by forming a film and adhering a heat sink. The present invention relates to an acousto-optic device in which an acousto-optic medium and a piezoelectric vibrator are bonded, and In is deposited in a thickness of 1 μm or more by physical vapor deposition on all surfaces except the optical surface and the bonding surface of the piezoelectric vibrator, and a heat sink is used. It is an acousto-optic device characterized by having a structure in which is adhered.

[0015]

[Function] In, which is excellent in ultrasonic wave absorption and heat conduction, is deposited to a thickness of several μm on all surfaces except the optical surface of the acousto-optic element and the bonding surface of the piezoelectric vibrator by a vapor deposition method, a sputtering method, or an ion plating method to radiate heat. By bringing the plates into close contact,
It is possible to suppress the temperature rise in the acousto-optic medium.

[0016]

[Examples] Arsenic selenide (As ₂ Se ₃ ) was used as the acousto-optic medium.
Lithium niobate (LiNb)
An O ₃ ) single crystal is used and both are bonded with an epoxy adhesive to form an acousto-optic device. Next, In was deposited to a thickness of 1 μm by a vacuum deposition method on the three surfaces of the acousto-optic device excluding the optical surface and the piezoelectric vibrator bonding surface, and an aluminum radiator plate was adhered thereto. FIG. 1 shows a schematic diagram of the configuration of the acoustooptic device (with a heat dissipation plate) manufactured in this example. The produced acousto-optic element was incorporated in a resonance circuit, an ultrasonic wave (140 MHz) signal was input (0.5 W) using the optical system shown in FIG. 2, and a current-carrying test was conducted for 100 hours. As a result, as shown in FIG. 3, the diffraction efficiency did not decrease. Neither beam drift nor deformation was observed. When the temperature inside the medium was measured by a thermal video system, the temperature rise was extremely low, and the temperature inside the medium was 25 to 28 ° C.

[0017]

Comparative Example An acousto-optic device was manufactured in the same manner as in the example, except that In was replaced with silicon rubber. The produced acousto-optic device was incorporated into a resonance circuit, and an ultrasonic (140 MHz) signal was input (0.
5W), and the energization test was performed for 100 hours. As a result, as shown in FIG. 4, the diffraction efficiency became unstable after 30 hours and decreased after 80 hours. Beam drift and deformation were also observed. Then, when the temperature in the medium was measured by a thermal video system, the temperature was increased by about 10 ° C as compared with the products manufactured in the examples, and the temperature in the medium was 38 to 42 ° C.

[0018]

As described above, according to the present invention, the temperature rise of the acousto-optical element can be suppressed, the deformation / positional deviation of the beam and the deterioration of the diffraction efficiency can be prevented, and the reliability and durability are high. An acousto-optic device can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an acoustooptic device manufactured according to this example.

FIG. 2 is an explanatory diagram showing an outline of a current-carrying test optical system used in Examples and Comparative Examples.

FIG. 3 is a diagram showing changes in diffraction efficiency with respect to energization time of the acousto-optic element manufactured according to this example.

FIG. 4 is a diagram showing a change in diffraction efficiency with respect to an energization time of an acoustooptic device manufactured according to a comparative example.

FIG. 5 is an explanatory diagram showing the operating principle of the acousto-optic device.

[Explanation of symbols]

 1 Incident Light 2 First-Order Diffracted Light 3 Non-Diffracted Light 4 Ultrasonic Traveling Wave 5 Piezoelectric Vibrator 6 Acousto-Optical Medium 7 High Frequency Voltage 10 Heat Sink 11 In Film 12 Sample Stage (Heat Sink) 13 Oblique Polishing Part (Ultrasonic Reflection Prevention 14 lead wire 15 light source (wavelength 1.31 μm) 16 acousto-optic modulator (resonance circuit and acousto-optic element) 17 coaxial cable 18 high-frequency power supply (140 MHz) 19 optical power meter a arrow indicating the traveling direction of light

Claims (1)

[Claims] 1. An acousto-optic device formed by joining an acousto-optic medium and a piezoelectric oscillator, wherein In is deposited to a thickness of 1 μm or more by physical vapor deposition on all surfaces except the optical surface and the piezoelectric oscillator joining surface, and heat is radiated. An acousto-optic device having a structure in which plates are closely attached.