JPS5931044B2 - optical deflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical deflector for scanning or deflecting a laser beam or the like.

Optical deflectors include those based on mechanical methods, electricity, and acousto-optic effects, and an outline thereof will be explained below. Mechanical method: This method uses holographic technology to create diffraction gratings of different types with different diffraction angles, and mechanically switches these gratings sequentially. The disadvantage is that it is not suitable for high-speed, high-precision scanning, such as poor accuracy.

Methods using electric and acousto-optic effects: The electro-optic effect, which utilizes the deformation of the refractive index ellipsoid of the medium by an electric field, is mainly used for digital light deflection; Methods that use the interaction between sound waves and light utilize the photoelastic effect (change in the refractive index of the medium due to strain), and due to the change in the refractive index, the medium acts similar to a diffraction grating, thereby suppressing the diffraction of light. This method controls by changing the wavelength of the sound wave, but it has been difficult to satisfy all the conditions of deflecting the incident light beam at a faster speed than resolution over a wide deflection angle range and radiating it efficiently.

The present invention overcomes the above-mentioned drawbacks, and its purpose is to provide an optical deflection system that allows high-velocity beam scanning, provides a large deflection angle, and is structurally simple and inexpensive to manufacture. It is to provide the equipment. Next, embodiments of the present invention will be described with reference to the drawings.

1 is made of a material such as an X-cut crystal plate that has reverse piezoelectricity and is transparent to light, and electrodes 2 made of a conductive material are placed on the upper and lower surfaces of the material.
, 3 are provided by appropriate means such as vapor deposition.

Further, an entrance surface 1a of the inverse piezoelectric material 1, into which the opposing light beams are incident, and a radiation surface lb, from which the light beams are emitted, are optically polished to be smooth. Further, lead wires 4 and 5 for supplying power are connected to the electrodes 2 and 3 described above.
The whole of these will be referred to as a deflector A. X= seen in the example
The cut crystal resonator performs thickness longitudinal vibration in the X-axis direction, and elastic waves are formed inside the resonator.

The displacement distribution associated with the elastic vibration of the crystal resonator in the X-axis direction due to the primary vibration is as shown in Fig. T.

As can be seen from the same figure, it becomes a node at the center and does not displace, but at both ends (
t/2) indicates the maximum displacement. Vibration displacement in the X-axis direction (Y
x) is here {j:linit=t.

Perform standing wave vibration shown in equation 1.

The strain (S○) in the X-axis direction at a certain time can be expressed as follows.The refractive index change due to the photoelastic effect is an effect where the refractive index of the medium is caused by elastic strain in the medium, and the change (Δn) causes a change in the refractive index, where P is the photoelastic constant.

From this, the refractive index gradient becomes. This is COS2πγT
When T=1, the maximum value is shown (FIG. 8). As a result,
The refraction gradient (Dn) is Oゝ D at the vibration node.
x, and no polarization occurs.

The maximum refraction gradient occurs when X=±t/2.

Therefore, if we change the position of the incident beam from O to t/2, we get
The polarization angle corresponding to the φ-2L chopsticks can be obtained from the corresponding refraction gradient. The optical deflector A is used in electrical connection with a high frequency power supply device B consisting of a high frequency generator and its amplifier, and a high frequency ammeter or a high frequency power meter C or the like is installed as necessary.

A light beam D' emitted from a laser D is incident on a light deflector A, and the deflected light beam D' is emitted onto a screen E, for example. As is well known, when an inverse piezoelectric material is formed into a fixed geometric shape, it generally has a unique resonant frequency corresponding to that shape.

The optical deflector A according to the present invention operates best when the frequency of the high frequency supplied from the high frequency power supply device B is the resonant frequency of the inverse piezoelectric material 1. Above deflector A
The inverse piezoelectric material 1 used for
．． An X-cut quartz crystal plate having a resonant frequency of 0.0107 MHz is used, and electrodes 2 and 3 of thin silver films are formed on the X plane of the quartz plate by vacuum evaporation.

FIG. 4 shows the direction of deflection when the device is operated by high frequency power having a frequency of 1.0107 MHz via the single-wire wires 4 and 5 between the electrodes 2 and 3. In the figure, a black circle represents a light beam D' that is incident approximately perpendicularly to the incident surface 1a, and a white circle represents the deflection direction of the light beam D' on the incident surface 1a in a plan view. In this case, the deflection of the light beam D' is caused by a refractive index gradient 8 generated inside the crystal plate caused by a standing elastic wave generated inside the X-cut crystal plate that vibrates longitudinally in its thickness at its resonant frequency. The deflection direction of the light beam D' as a periodic function of the position of the incident light beam D' on the incident surface 1a is caused by It can be interpreted as a Lissage figure in which an elastic wave and a standing elastic wave in the Y-axis direction induced by the vibration are synthesized.

A practically desirable deflection direction can be easily set by appropriately adjusting the incident position of the light beam D' on the light beam entrance surface 1a. The deflection of the light beam D' as shown in FIG. 4 is caused by the change 8 in the refractive index occurring inside the inverse piezoelectric material 1 as described above.
Magnitude of Deflection (DX) There is generally a relationship Dx between the deflection angle φ and the force.

Here, L is the length of the optical path when the light beam D' passes through the interior of the inverse piezoelectric material 1. As is well known, in practice, it is desirable that the deflection angle φ is sufficiently large. As is clear from the above equation, the first means to increase the deflection angle φ is to increase Dx by 8. The increase by 5 is achieved by increasing the supplied high-frequency power and adjusting the frequency to 0dx. be done.

A second means of increasing the deflection angle φ is to increase L.

Taking FIGS. 1 and 2 as an example, L corresponds to the distance between the entrance surface 1a and the emission surface 1b. Therefore, an increase in L can be achieved by increasing the geometry of the inverse piezoelectric material 1. However, the shape and dimensions of the optically high-quality inverse piezoelectric material 1 are usually limited to some extent. Therefore, in order to further substantially increase L, as shown in FIGS. 5 and 6, a part of the entrance surface 1a and the emission surface 1b may be coated with a metal such as silver by vacuum evaporation or the like. Reflecting mirrors 1c and 1d made of thin films are provided, and the light beam D' incident on the incident surface 1a of the inverse piezoelectric material 1 is reflected by the reflecting mirror 1d and then reaches the reflecting mirror 1c, where the reflection is repeated again. The beam is emitted from the radiation surface 1b as a synchrotron radiation beam, so the distance between the incidence surface 1a and the radiation surface 1b is set to 10 to 20 m.
It can be made about m. Therefore, even when using the inverse piezoelectric material 1 having a shape and size that is usually easy to handle, the size of L can be substantially made sufficiently large, and as a result, a sufficiently large deflection angle can be obtained. In fact, for example, X
When operating optical deflector A using a cut crystal plate,
A deflection angle of about 1 degree can be easily achieved by supplying a small amount of power, usually a few watts or less, and a high speed corresponding to the frequency of the supplied high frequency, such as the embodiments described above. In this case, the optical beam D' can be scanned at a speed of 1 MHz. In the embodiments shown in FIGS. 5 and 6, the light beam D' is reflected twice between the reflecting mirrors 1c and 1d, but the number of reflections may be less than or more than two times. Of course, it is fine if it is something. As described above, the present invention enables higher-speed optical beam scanning than known, for example, rotating mirror type or vibrating mirror type optical deflectors, and also enables higher speed optical beam scanning than known electro-optic effect type optical deflectors. Furthermore, compared to known so-called conventional acousto-optic optical deflectors, it is structurally simpler and therefore easier to manufacture and less expensive. It has excellent features that make it possible to reduce costs.

[Brief explanation of the drawing]

The figures show an embodiment of the optical deflector according to the present invention, FIG. 1 is a perspective view of the optical deflector of the first embodiment, FIG. 2 is a side view of the same as above,
No. Figure 3 is a block diagram of a circuit for operating the optical deflector of the present invention, and Figure 4 is an explanation showing the relationship between the position of the light beam incident on the optical deflector of the present invention and the polarization direction of the light beam at that time. 5 is a perspective view of the optical deflector of the second embodiment, FIG. 6 is a plan view of the same as above, and FIG. 7 is a diagram showing the displacement distribution accompanying elastic vibration of the crystal resonator in the X-Z axis direction. FIG. 8 is a characteristic diagram similar to the above. 1...Inverse piezoelectric material, 1a...Incidence surface, 1b...Emission surface, 1c, 1d...Reflector, 2, 3... ...electrode, D'...light beam.

Claims (1)

[Scope of Claims] 1. An inverse piezoelectric material that has an optically smooth surface for incident and emitting a light beam and is transparent to light;
and a pair of electrodes for supplying power to the inverse piezoelectric material. 2. Having an optically smooth surface for incident and emitting a light beam, and arranging the smooth surfaces to face each other, and using a part of each smooth surface as a reflective surface, so as to be transparent to light. An optical deflector comprising an inverse piezoelectric material having an inverse piezoelectric material and a pair of electrodes for supplying power to the inverse piezoelectric material.