JPH01149024A - Acoustooptic element - Google Patents

Abstract

PURPOSE:To obtain an acoustooptic element of low cost and high reliability requiring no reflection preventing film by setting angles of light incidence and emission of an acoustooptic medium in the vicinity of Brewster angle and making light incidence and emission faces parallel with each other and forming the acoustooptic medium so that the the wave surface of an ultrasonic wave coincides with an average direction of the incident light and the diffracted light in the acoustooptic medium. CONSTITUTION:An acoustooptic medium 1 having a first face 1a to which a piezoelectric element 3 is attached and second and third faces 1b and 1c for light incidence and emission which intersect the first face 1a and are parallel with each other is so formed that the angle of intersection between second and third faces 1b and 1c and the first face 1a approximates theta=90 deg.-sin<-1>[cos{tan(n)}] [(n) is the refractive index of the acoustooptic medium), and the light is made incident with an angle approximating theta1=tan<-1> [(n) to the normal of light incidence and emission faces. Thus, the reflection preventing film is not used to realize light incidence of less reflection, and a sufficient acoustooptic effect is obtained in this state, and the reflection of the diffracted light is very reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an acousto-optic element that modulates light such as a laser beam by an acousto-optic effect.

Conventional technology An acousto-optic device has a basic configuration in which a piezoelectric element is attached to an acousto-optic medium.When an electrical signal is input to the piezoelectric element, it becomes an ultrasonic signal that propagates through the acousto-optic medium, passing through the acousto-optic medium at a certain angle. It diffracts the incident light. Glass or single crystal materials are used for the acousto-optic effect, and the front input and output surfaces are optically polished, but if left as is, a considerable amount of light is reflected due to the difference in refractive index with air, so an antireflection coating is required. is applied. As the antireflection film, a single layer or multilayer film of fluoride or oxide is used, which is deposited to a certain thickness by vapor deposition or the like.

Problems to be Solved by the Invention In such a conventional configuration, it is necessary to select the material of the antireflection film depending on the material of the acousto-optic medium, and in order to form a durable film, heating is required. However, there was a problem in that the cost was extremely high and the productivity was poor. Furthermore, when the intensity of the incident light increases, the antireflection film lacks durability, resulting in short lifespan and lack of reliability.

The present invention solves these problems and aims to provide a low-cost, highly reliable acousto-optic device that does not require an antireflection film.

Means for Solving the Problems In order to solve the above problems, the acousto-optic element of the present invention includes:
The second and third surfaces of the acousto-optic medium have a first surface on which a piezoelectric element is mounted, and second and third surfaces for light input and output that intersect the first surface and are parallel to each other.
The intersection angle between the surface and the first surface is θa=90°−sin'
(cos(tan 1(n))) (where n is the curvature index of the acousto-optic medium), and the light is held at an angle near θ1=tan(n) with respect to the normal to the light incident surface. It is made so that it is incident at an angle.

Effect: With this configuration, it is possible to achieve light incidence with extremely low reflection without using an anti-reflection film, and in this state, a sufficient acousto-optic effect can be obtained by the ultrasonic signal, and the diffracted light is similar to the incident light. This results in extremely low reflection. Therefore, an antireflection film is not required. Further, the direction of the emitted light is near the incident optical axis.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

The gist of the acousto-optic element according to the present invention is to make the light input and output from the acousto-optic medium near Brewster's angle, to make the light input and output surfaces almost parallel to each other, and to make the incident light and the incident light in the acousto-optic medium It is formed so that the wavefront of the ultrasonic wave coincides with the average direction of the diffracted light.

That is, in FIG. 1, 1 is an acousto-optic medium, and a piezoelectric element 3 connected to a high frequency electric signal source 2 is attached to a first surface la of the medium using an organic adhesive or metal.

At both ends of this first surface 1a, second and third surfaces 1b intersect with the first surface 1m at a predetermined angle θa and are light input/output surfaces.

1c are parallel to each other. Then, the incident light is incident on the second surface 1b at a predetermined angle θ1 with respect to the normal a, and this angle θ1 is calculated as follows, where n is the refractive index of the acousto-optic medium l, θs=tan ( n)
--- It is assumed to be near the angle that satisfies the condition (1).

For example, if a tellurium dioxide crystal is used as the acousto-optic medium and a helium neon laser beam (wavelength 63λ8mm) is used as the incident light, n=Z26 and θ1''36&1'.The light reflectance in this vicinity is shown in Figure 2. It will be as shown.

By the way, the refraction angle θ of incident light is determined by Snell's law and (
1) The following equation is obtained.

+! 12=sin'((sinθt)/n)=s
in-1 (cos θ1) ・−・−・(2) In order to match the wavefront of the ultrasound to this angle θ2, the first surface 1
The predetermined angle θa between a and the second surface lb is θa=9
0°-1. n=. That is, θa=90°−si
n-1(cosθ1)=90°-sin'(cos(
tan-1(n)))...(3) neighborhood.

On the other hand, light diffraction due to the acousto-optic effect occurs when the wavelength of light in vacuum is λ, the frequency of ultrasound is f1, and the propagation speed of ultrasound in an optical medium is V, then the angle of 1 degree (Bragg angle) that satisfies the light incidence condition is θb is θb = sin-' (λo ・f/2nv)
...(4). λ in the example above. =63
λ8 nm, f=100!1iHz, n=2
．． 26, V = 42eorry's, θ
b=0.19°.

In light diffraction, diffracted light is generated symmetrically with the incident light with respect to the wavefront of the ultrasonic wave, and the separation angle from the incident light is 2θb.

Therefore, even if the angle can be moved to set the Bragg angle, it is possible to maintain a state in which the light reflectance is sufficiently low. Third surface 1c that is the light exit surface of the acousto-optic medium 1
The conditions for emitting the diffracted light in the second.
Since the third 1b and 1( are parallel, the influence of the acousto-optic medium on the output direction of the diffracted light can be canceled out due to the symmetry. Even if the 2nd and 3rd light input/output surfaces are reversed, It's exactly the same.

By the way, the front shadow optical medium 1 is made of tellurium dioxide (Te
When using an Ox) crystal, the first plane 1a is the (0013 plane), and the normal to the second and third planes 1b and 1( is (11
The surface exists on the 03 plane or the [1〒0] plane, and the electric field vibration plane of the incident light is linearly polarized light parallel to the [001] axis. When using PbMoO4) crystal, the first surface 1a is
0013 page, and the second page. The third surfaces 1b and lc are surfaces whose normal lines lie on the [100] plane or the [010] plane, and the electric field vibration plane of the incident light is linearly polarized light parallel to the (001) axis.

Effects of the Invention As described above, according to the present invention, the substantially parallel light input/output surface and the 90°-sin' [cos(jan 1(n)))
By attaching a piezoelectric element to a nearby angled surface and allowing the light to enter at an angle near jan=(n) with respect to the normal to the light incident surface, an antireflection film is not required. A highly reliable acousto-optic device can be obtained at low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram illustrating the operation of an acousto-optic device according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between light incidence angle and light reflectance. 1... Acousto-optic medium, 1a... First surface, 1b...
- Second surface, 1c...Third surface, 3... Piezoelectric element.

Claims (1)

[Claims] 1. An acousto-optic device having a first surface on which a piezoelectric element is mounted, and second and third surfaces for light input and output that intersect the first surface and are parallel to each other. The intersection angle between the second and third surfaces of the medium and the first surface is θa=90°-sin
^-^1 [cos {tan^-^1(n)}] (n is the refractive index of the acousto-optic medium), and
θ_1=tan^-^1(
n) an acousto-optic element which allows the incident to be incident at a tilted angle; 2. A tellurium dioxide (TeO_2) crystal is used as the acousto-optic medium, the first plane is the [001] plane, and the normals of the second and third planes are the [110] plane or the [1@1@0] plane. The electric field vibration surface of the incident light is [001]
The acousto-optic element according to claim 1, wherein the light is linearly polarized parallel to the axis. 3. Lead molybdate (PbMoO_4) as acousto-optic medium
Using a crystal, the first plane is the [001] plane, and the second and third planes are the [001] plane.
Let the plane be a plane whose normal lies on the [100] plane or the [010] plane, and the electric field vibration plane of the incident light should be the [001] plane.
] The acousto-optic element according to claim 1, wherein the acousto-optic element emits linearly polarized light parallel to the axis.