JPH04273219A - Acoustooptic element - Google Patents

Abstract

PURPOSE:To shorten the response time. CONSTITUTION:The acoustooptic element is equipped with an optical medium 10 which is formed in a rectangular prism shape and an electrooptic transducer 11 which is fixed to the joined surface 10A of the optical medium and transduces a high-frequency signal. This electrooptic transducer 11 decreases in thickness gradually from a laser light incidence side 11A to a laser light projection side 11B. In concrete, the thickness of the acoustooptic element 11 varies in a wedge shape having an angle theta (thetanot equal to 0, pi/2) in the length direction of the joined surface between the optical medium 10 and electrooptic transducer 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acousto-optic element used in an acousto-optic modulator that deflects or modulates a light beam using an acousto-optic effect.

0002

2. Description of the Related Art Generally, the acousto-optic effect refers to an effect in which light is diffracted, refracted, reflected, and scattered due to the density and density of the refractive index produced in a medium by sound waves (particularly ultrasonic waves). Substances that show this effect prominently include fused silica, water, TiO2
, P6 Mo O 4 , Te O 2 , and AS 2 S 3 glasses are known and are used for light modulation, deflection, and the like.

As shown in FIG. 2, an acousto-optic device that has been proposed in the past includes an optical medium 1 processed and formed into a rectangular parallelepiped shape, and a bonding surface 1A of this optical medium 1 having a uniform thickness t. The structure also includes an electroacoustic transducer 2 that converts high frequency signals into mechanical vibrations.

0004

However, in the conventional acousto-optic device described above, since the thickness t of the electroacoustic transducer 2 is constant, f(MH2)=3360/t(μm
), and can diffract the laser beam 3 (wavelength λ) incident on the optical medium 1. This diffraction angle θd is the velocity of the ultrasonic wave propagating in the crystal, V
Then, it is approximated by the following formula.

[0005]

[Equation 1] θd ≒ λf/v

Therefore, in order to vary the diffraction angle θd, the driving frequency f, the laser wavelength λ, or the ultrasonic propagation velocity V
One of these must be made variable. However, in devices such as laser printers in which AO modulators are actually used, it is almost impossible to change the laser wavelength λ or ultrasonic propagation velocity V, so the driving frequency f is adjusted and the diffraction angle θd
must be adjusted.

However, an acousto-optic deflector (A
O deflector) is provided. However, in order to vary the diffraction angle θd, for example, tellurium dioxide is used as the optical medium 1, and transverse wavelength sound waves (ultrasonic propagation speed≈600 m/s) are propagated in a certain specific direction. For this reason, the response time (rise/fall time) of the diffracted light is several μs, resulting in a problem that high-speed response cannot be achieved.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide an acousto-optic device capable of increasing the response time.

[0009]

[Means for solving the problem] The invention according to claim 1 includes:
In an acousto-optic element comprising an optical medium and an electroacoustic transducer fixed to the optical medium and converting a high-frequency signal into mechanical vibration, the thickness of the electroacoustic transducer varies from the laser light incident side to the laser light output side. It is formed so that it gradually becomes smaller towards the end.

[0010] The invention according to claim 2 has a structure in which the thickness of the electroacoustic transducer changes in a wedge shape having an angle θ (θ≠0, π/2) from the laser beam incidence side to the laser beam output side. It is.

[0011]

According to the present invention, since the thickness of the electroacoustic transducer is gradually decreased from the laser beam incidence side to the laser beam output side, the diffraction angle can be varied by changing the driving frequency. Furthermore, since longitudinal ultrasound can be used, the material of the optical medium is not limited. Therefore, the response time can be considerably faster than in the past.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a perspective view of an ultrasonic optical modulator using an acousto-optic device according to the present invention. The acousto-optic element is
An optical medium 10 formed in the shape of a rectangular parallelepiped, and this optical medium 10
The structure includes an electroacoustic transducer 11 that is fixed to the joint surface 10A of and converts a high frequency signal into mechanical vibration. In this example, lead molybdate with an ultrasonic propagation velocity V of 3630 m/s was used for the optical medium 10, while lithium niobate was used for the electroacoustic transducer 11. Further, a high frequency signal generator 12 is connected to the electroacoustic transducer 11.

The electroacoustic transducer 11 is formed so that its thickness gradually decreases from the laser light incident side 11A toward the laser light output side 11B. More specifically, the thickness of the electroacoustic transducer 11 is the same as that of the optical medium 10 and the electroacoustic transducer 1.
The angle θ (θ≠0, π/2
) has changed into a wedge shape.

In this embodiment, the length of the electroacoustic transducer 11 is 10 mm, and the thickness of the side closer to the laser beam incidence side 11A is 30 μm so that the driving frequency f is at least 100 MH2 ≦f≦200 MH2. The thickness of the side closer to the laser beam emission side 11B was set to 15 μm. That is, the thickness of the laser beam incident side 11A and the laser beam output side 11
This is equivalent to providing an inclination of θ≈0.09 rad between the thicknesses of B.

Now, the electroacoustic transducer 11 of the present acousto-optic device
A high frequency signal generator 12 is connected to 100, 150, 2
Each was driven at a driving frequency of 00 MH2, and the diffraction angle θ and response time tr (rise time) at the angular frequency were measured. The incident laser beam 13 is He-N with a wavelength λ=633 nm.
An e-laser was used and the beam was incident on the optical medium 10 with a beam diameter of 1 mm. As a result, the diffraction angle θ was as follows. Note that FIG. 1 shows a state in which a transmitted light 14 is emitted from the emission side corresponding to the incident laser light 13, and diffracted lights 15 and 16 are emitted at a predetermined angle with the transmitted light 14.

[0017]

[Formula 2] θ100=0.013 (rad) θ150=0
．． 020 (rad) θ200=0.027 (rad)

[0018] This proves that the driving frequency can be varied.

The response time tr was also as follows.

[0020]

[Math. 3] tr100=210ns tr150=200ns tr200=195ns

[0021] From the above, it was confirmed that the time was significantly improved compared to the conventional one on the order of several μs.

[0022]

As explained above, according to the acousto-optic device of the present invention, the thickness of the electroacoustic transducer is gradually decreased from the laser beam incidence side to the laser beam output side, and the thickness of the electroacoustic transducer is changed by changing the driving frequency. Diffraction angle can now be changed. Furthermore, since longitudinal ultrasound can be used, the material of the optical medium is not limited at all. Therefore, according to the present invention, an excellent effect is achieved in that the response time can be increased from the conventional μs order to several tens of ns order.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an ultrasonic light modulator using an acousto-optic element according to the present invention.

FIG. 2 is a perspective view showing an example of a conventional acousto-optic device.

[Explanation of symbols]

10 Optical medium 10A joint surface 11 Electroacoustic transducer 11A Laser light incident side 11B Laser light emission side

Claims (2)

[Claims] 1. An acousto-optic element comprising an optical medium and an electroacoustic transducer fixed to the optical medium and converting a high frequency signal into mechanical vibration, wherein the thickness of the electroacoustic transducer is from the laser light incident side. An acousto-optic element characterized in that it is formed so as to become gradually smaller toward a laser beam emission side. 2. The thickness of the electroacoustic transducer described above is determined by the angle θ (θ≠0
, π/2).