JPH01149031A - Acoustooptic device - Google Patents

Abstract

PURPOSE:To perform accurate measurement which is not affected by the polarized state of light by providing a pulse modulator in a driving part operated to obtain the diffracted light from the incident light and setting a prescribed power so that the diffraction efficiency of vertical linear polarization and that of horizontal linear polarization are equalized. CONSTITUTION:An acoustooptic medium 1, a piezoelectric element 2, a driving part 3 of this element 2, and a modulation input terminal of the pulse modulator are provided. In this case, the output of the driving part 3 is set to a prescribed power so that a diffracted light 5a has the same diffraction efficiency whether an incident light 5 is a vertically linearly polarized light or a horizontally linearly polarized light. Thus, the same diffraction efficiency is obtained in the case of the same intensity of light though the polarized state of the incident light like a laser light is changed, and accurate measurement is possible at the time of trouble point detection of an optical fiber or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an acousto-optic device that utilizes the diffraction of light caused by ultrasonic waves, that is, the acousto-optic effect.

Conventional technology Acousto-optic elements have a basic structure in which a piezoelectric element is attached to an acousto-optic medium made of single crystal or glass such as tyl dioxide (TeO2) or lead molybdate (PbMo, 04). A diffraction grating is formed, and light such as laser light that is incident thereon at a certain angle (Black angle) can be diffracted. The diffraction angle is determined by the frequency of the ultrasonic wave, and the intensity of the diffracted light is determined by the intensity of the ultrasonic wave, so this can be used to modulate light.

The operating principle of the acousto-optic device is shown in FIG. In FIG. 4, a stain completion signal is input from the drive unit 6 to the piezoelectric element 2 provided on one surface of the acousto-optic medium 1, and the piezoelectric element 2 converts the electrical signal into an ultrasonic signal. The beam propagates through an acousto-optic medium l, and diffracts light 5 such as a laser beam. Here, 5a is diffracted light and 5b is transmitted light.

Conventionally, this type of acousto-optic device uses a constant linear polarization state of incident light such as a laser beam, and sets the input power from the drive section 6 so that the diffraction efficiency is maximized.

That is, in Figure 2, which shows the relationship between input power and diffraction efficiency of an acousto-optic element, in the case of linearly polarized light perpendicular to the plane created by the incident light and diffracted light (hereinafter referred to as vertical linear polarized light), the input power of A, the incident light and direct M polarized light parallel to the plane created by the diffracted light (
In the case of horizontal linearly polarized light (hereinafter referred to as horizontal linear polarization), an input power of C was used. Further, when using incident light 5 other than vertically linearly polarized light and horizontally linearly polarized light, a material with little polarization dependence on the wavelength of the incident light 5 is used as the material for the acousto-optic medium 1.

Problems to be Solved by the Invention In such a conventional configuration, if the polarization state of incident laser light or other light changes, the diffraction efficiency will change even if the input power from the drive unit 6 is constant. When using an acousto-optic device for 0TDR to detect fault points in optical fibers, there is a problem in that accurate measurements cannot be made.

In addition, when using a material for the acousto-optic medium 1 that has little polarization dependence depending on the wavelength of the incident light, for example, lead molybdate is used for the acousto-optic medium 1 and laser light with a wavelength of 633 nm is incident on the acousto-optic medium 1. Since the material of the acousto-optic medium 1 and the wavelength of the incident light 5 are limited, such as by using chil dioxide ρ for l and injecting a laser beam with a wavelength of 1.3 μm, the degree of freedom of the device is small, which is a problem. Ta.

The present invention solves these problems, and aims to provide an acousto-optic device that has excellent measurement accuracy and can alleviate restrictions on the material of the acousto-optic medium and the wavelength of incident light.

Means for Solving the Problem In order to solve this problem, the present invention provides an acousto-optic element, a driving section for driving the acousto-optic element to obtain diffracted light from incident light, and a driver for driving the acousto-optic element to obtain diffracted light from incident light. a pulse modulator provided in the drive unit, and the output of the drive unit is configured such that the polarization state of the incident light of the acousto-optic element is a linearly polarized light parallel to a plane formed by the incident light and the diffracted light, and a straight line perpendicular to the plane. This is set to a predetermined power that allows the same diffraction efficiency to be obtained with polarized light.

Effect With the above configuration, even if the polarization state of light such as a laser beam incident on the acousto-optic element changes, as long as the light intensity is the same, the same diffraction efficiency can be obtained. In this case, accurate measurements can be made without being affected by the polarization state of the light, and furthermore, restrictions on the material of the acousto-optic medium and the wavelength of the incident light used can be relaxed. At this time, the driving section can be operated to diffract only the reflected light from the failure point, such as the optical fiber, by its Varne modulation output.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing the principle configuration of an acousto-optic device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between input power and diffraction efficiency of an acousto-optic element. In FIG. 1, 1 is an acousto-optic medium, 2 is a piezoelectric element, 5 is incident light, 5a is diffracted light, 5
b is transmitted light, which is the same as in FIG. 3 is a drive section for the piezoelectric element 2, and is provided with a pulse modulator. 4 is a modulation input terminal.

The output of the drive unit 3 is set to a predetermined power so that the diffraction efficiency of the diffracted light 5a is the same whether the incident light 5 is vertically linearly polarized light or horizontally linearly polarized light. In other words, from FIG. 2, it can be seen that in order to make the diffraction efficiency of vertically linearly polarized light and horizontally linearly polarized light the same, the acousto-optic element should be driven at the input power B, so the output of the driving section 3 is set to a predetermined voltage that provides such input power.

On the other hand, the pulse modulator of the drive unit 3 uses a pulse modulation signal, and the acousto-optic element diffracts and transmits the incident light 5.

FIG. 3 shows an example of a flaw detection device using the acousto-optic device of the present invention. The incident light from the light source 11 is transmitted through the acousto-optic element 12 and enters the optical fiber 13 when not driven by the pulse modulation signal, and the reflected light from the failure point of the optical fiber 13 is reflected from the acousto-optic element driven by the pulse modulation signal. 12
This diffracted light is reflected by a mirror 14, received by a light receiver 15, and measured. At this time, even if the reflected light from the fault point has an uneven polarization state, the fault point can be detected accurately.

Effects of the Invention As described above, according to the present invention, even if the polarization state of incident laser light or other light changes, as long as the intensity of the light is the same, the same diffraction efficiency can be obtained, and it is possible to detect fault points in optical fibers. Accurate measurements are possible when using an acousto-optic device for 0TDR. Furthermore, the conventional limitations on the material of the acousto-optic medium and the wavelength of the incident light due to polarization dependence can be alleviated.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle configuration of an acousto-optic device according to an embodiment of the present invention, Figure 2 is a diagram showing the relationship between input power and diffraction efficiency of an acousto-optic element, and Figure 3 is a diagram showing the relationship between the input power and diffraction efficiency of an acousto-optic device. FIG. 4 is a block diagram showing an example of a flaw detection device, and FIG. 4 is a diagram showing the principle structure of a conventional acousto-optic device. l... Acousto-optic medium, 2... Piezoelectric element, 3... Drive unit, 4... Modulation input terminal, 5... Incident light, 5a...
... Diffracted light, 5b... Transmitted light. Representative Yoshihiro Morimoto Figure 1 Figure '2

Claims (1)

[Claims] 1. An acousto-optic element, a drive unit that drives the acousto-optic element to obtain diffracted light from incident light, and a pulse modulator provided in the drive unit, and the output of the drive unit is An acousto-optic device in which the polarization state of the incident light of the acousto-optic element is set to a predetermined power such that equivalent diffraction efficiency can be obtained for linearly polarized light parallel to a plane formed by the incident light and diffracted light and linearly polarized light perpendicular to the plane.