JP2600201B2 - Optical deflection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical deflecting device, and more particularly to an optical deflecting device using an acousto-optic effect.

(Prior Art) Techniques using acousto-optics for two-dimensional light deflection are regarded as important in optical signal processing, display devices, and the like. In order to control the light spot to an arbitrary position on a plane, a pair of deflectors is usually used in the horizontal and vertical directions. When an acousto-optic light deflection device is used for light deflection, Bragg diffraction is often used to increase the light deflection angle.

(Problems to be Solved by the Invention) However, since the angle of incidence of light incident on the optical deflecting device depends on the deflecting effect, such an acousto-optical optical deflecting device requires the It was necessary to adjust each polarization angle independently. In addition, an optical deflecting device based on anisotropic Bragg diffraction requires an optical system for correcting the deflecting state of incident light, and thus has a disadvantage in that the entire optical deflecting device becomes complicated.

In order to realize horizontal and vertical two-dimensional deflection with a one-element optical deflection device, an optical deflection device using Raman-Nath diffraction, and a transducer on the adjacent side surface of a cubic TeO ₂ crystal are used. There are also Bragg reflection-type ones provided, but these have a problem that the deflection angle cannot be increased.

In the Bragg reflection type, light incident on the ultrasonic diffraction grating from the direction of θ _BH ｛= sin ⁻¹ (light waveform)｝ is reflected at an angle of 2θ _{BH in} the traveling direction of the ultrasonic wave. Therefore, the wavefront of the ultrasonic wave is shifted from the vertical direction by an angle θ _BH so that the angle of incidence on the second-stage ultrasonic grating satisfies the Bragg condition.
Optical media must be provided. Therefore, there is a problem that such a Bragg reflection type is disadvantageous in terms of deflection efficiency.

Now, a theoretical explanation of light polarization according to the present invention will be given. It has been found that an optical deflection device using an interdigital transducer and using a liquid as an optical medium has almost the same properties as an optical deflection device using a solid medium. As shown in FIG. 2, a transducer of the type that excites a leaky surface acoustic wave (LSAW) at the boundary between a solid and a liquid has an ultrasonic radiation direction of α ｛= sin ^-1 (phase velocity of LSAW / phase velocity of longitudinal wave in liquid)｝. This enables two-dimensional light deflection by a pair of interdigital transducers arranged on the same plane.

As shown in FIG. 2, U _H and U indicated by circles along the optical path horizontally and vertically polarized by ultrasonic waves.
_U represents the wavefronts of two ultrasonic diffraction gratings that intersect each other. In order to efficiently perform two-dimensional light deflection, the interdigital transducers 2a and 2b must be arranged so that the wavefronts U _H and U _U have an appropriate incident angle. Therefore, such interdigital transducers 2a and 2b must have a geometrical positional relationship satisfying the following expression.

δθ = θ _BH · sin α (1) δ _a = (L / 2) · θ _BU · sin α (2) where θ _BH and θ _BU are the center frequencies of the ultrasonic diffraction grating for horizontal axis and vertical light deflection. and the distance a of the Bragg angle, L is the interaction length of the ultrasound and light (see FIG. 1), [delta] _a from the center line of the substrate 1 corresponding to the optical path of the light to the center position of the interdigital transducer 2a in, The difference between the center line of the substrate 1 and the distance (a + δ _a ) from the center position of the interdigital transducer 2b.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an optical deflection device having a simple structure and excellent deflection efficiency.

(Means for Solving the Problems) The light deflecting device according to the present invention reduces the incident light to 2
A substrate made of a piezoelectric material to deflect in a three-dimensional manner; and one surface of the substrate separated by a predetermined distance from the optical path so as to transmit ultrasonic waves for horizontally deflecting light incident along the optical path. A first interdigital transducer formed at an upper position; and a first interdigital transducer with respect to a centerline opposite to the optical path for transmitting ultrasonic waves for vertically deflecting the light.
A second surface formed on a surface of the substrate at a predetermined distance away from the interdigital transducer and at a predetermined angle with respect to the center line.
And a pair of drive circuits for driving the first and second interdigital transducers with a drive signal that changes the frequency in accordance with the amount of light deflection in the horizontal and vertical directions, respectively. It is characterized by the following.

(Operation) According to the optical deflection device of the present invention, the first and second interdigital transducers formed on the same surface of the substrate transmit ultrasonic waves to the optical medium at an angle such that they intersect each other. The light incident on the optical medium is deflected in the X and Y directions.

(Embodiment) FIG. 1 is a plan view of an optical deflection device showing an embodiment of the present invention. The substrate 1 of the piezoelectric body has a rotation angle of 128 ° Y-X
Consisting of LiNbO _3. On the substrate 1, interdigital transducers (IDT) 2a and 2b for transmitting ultrasonic waves to deflect light in the horizontal direction and the vertical direction, respectively, come into contact with pure water, and the upper left corner and the lower right corner at the positions shown in the drawing. Is formed. IDTs 2a and 2b have an electrode pitch (λ / 2) of 10 to 20.
μm linear chirp type, electrode index is 32 pairs, gradient δθ between them is 24 m rad, ultrasonic and light action length L is 5.0 × 5.0 ×
0.5 mm. Furthermore, [delta] _a is the distance a from the center of the opposed substrate 1 in the optical path showing the traveling direction of light by an arrow to the central position of IDT2a, the difference between the distance from the center position to the center position of IDT2b Show.

FIG. 2 is a path diagram of polarized light. In FIG. 2, α is the angle of the radiation direction of the ultrasonic wave with respect to the normal line of the substrate 1, and is represented by α = sin ⁻¹ (phase velocity of LSAW / phase velocity of longitudinal wave in liquid).

FIG. 3 is a block diagram of a measuring circuit for measuring light deflection by the IDTs 2a and 2b. The Ne-Ne laser 3 emits and emits light of 633 nm. This light enters the optical deflection device 1 of the present invention via the collimator 4.

On the other hand, voltage controlled oscillators (VCOs) 6 and 7 receive control signals 6a and 7a for linearly deflecting the light of the Ne-Ne laser 3 in the horizontal and vertical directions, respectively, and thereby control the oscillation frequency. Signals 6b and 7b are applied to drive circuits 8 and 9 respectively.
Is being entered. The drive circuits 8 and 9 amplify the frequency signals of the voltage controlled oscillators 6 and 7 and apply the amplified signals to the IDTs 2a and 2b of the optical deflection device 5 of the present invention as deflection signals 8a and 9a.

The IDTs 2a and 2b of the optical deflecting device 1 convert the light incident from the Ne-Ne laser 3 via the collimator 4 into deflection signals 8a and 8b.
The light is deflected in the horizontal and vertical directions according to 9a, and the deflected light is incident on the CCD array 11 via the lens 10. However, when the deflection amount is 0, the light goes straight through the optical deflection device 1 and enters the slit 13. The drive of the CCD array 11 is controlled by a stage 11a, and the incident light is converted into an electric signal and input to an amplifier. This allows
The amplifier 14 inputs the amplified electric signal to the monitor 15. The monitor 15 also receives the frequency signals 6b and 7b of the voltage controlled oscillators (VCOs) 6 and 7, and synchronizes with the frequency signals 6b and 7b.
The deflection state of the light of the Ne-Ne laser 3 is output so as to be monitored via the 13 output signals, for example, displayed on a CRT.

FIG. 4 is a characteristic diagram showing the deflection frequency versus the deflection position of the optical deflection device 1 measured by the measurement circuit shown in FIG. In FIG. 4, the x-axis indicates the x position of the deflected light of the Ne—Ne laser 3, and the y axis indicates the y position. Also, f
_{H (MHz), f V (} MHz) is horizontal, a vertical deflection frequency. ○ marks in the drawing by way each IDT2a, showing the measured values of the (CCD array 11 in this case) deflection signal 8a applied to 2b, 9b of deflection frequency f _H, the screen away 20cm to changes in f _V There is a 1: 1 correspondence with the control signals 6a and 7a.
As is clear from FIG. 4, the positions of the light after being two-dimensionally deflected by the light deflecting device 1 of the present invention are the IDTs 2a and 2b.
Corresponding to the vector sum of the respective deflection amounts, and changes linearly with the change in frequency. When the light transmission medium in the light deflecting device 1 is a combination of lithium niobate and pure water, the deflection by the IDTs 2a and 2b is about 2
2.5 degrees, and the deflection directions cross each other.

FIG. 5 is a characteristic diagram showing an intensity distribution of light two-dimensionally deflected by two-dimensional display on a screen. Where x
The axis indicates the vertical position (mm / div), the y axis indicates the position in the horizontal direction, and the z axis indicates the light intensity (dB). As is clear from the figure, the difference in light intensity within the range of 30 MHz is within -3 dB. The number of resolution points of the optical deflecting device 1 (approximately equal to the diameter of the light beam / the speed of sound in the medium × the frequency bandwidth of the deflection) is 10 mm
Is 200 × 200 with respect to the incident beam diameter, and the deflection speed (light beam diameter / sound speed in the medium) is 6.6 μs. This indicates that the optical deflection device 1 has a relatively high response as an acousto-optic deflection device and can be used as an optical deflection device for laser scanning.

(Effect of the Invention) As described above in detail, according to the present invention, 1
By providing a pair of optical deflecting IDTs on a single piezoelectric substrate, the structure as an optical deflecting device can be simplified, and light deflecting can be performed with respect to one light incidence, so reflection This has the effect of reducing the effects of

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the optical deflecting device of the present invention, FIG. 2 is an optical path diagram of polarized light, FIG. 3 is a block diagram of a measuring circuit for measuring optical deflection by IDT, FIG. FIG. 5 and FIG. 5 are characteristic diagrams showing characteristics of the optical deflection device measured by the measuring circuit shown in FIG. 1 ... board, 2a, 2b ... IDT, 8, 9 ... drive circuit.

Claims (1)

(57) [Claims] 1. An optical deflecting device for two-dimensionally deflecting incident light, comprising: a substrate made of a piezoelectric material; and an ultrasonic wave for deflecting light incident along an optical path in a horizontal direction. A first interdigital transducer formed at a position on one surface of the substrate at a predetermined distance from the optical path; and It is formed at a position on the one surface of the substrate at a predetermined distance away from the opposing center line on a side opposite to the first interdigital transducer and at a predetermined angle with respect to the center line. The first and second interdigital transducers are driven by a drive signal that changes the frequency in accordance with the amount of light deflection in the horizontal and vertical directions, respectively. An optical deflecting device, comprising: a pair of drive circuits for driving a digital transducer.