JPH02253239A - Acousto optical switch - Google Patents

Abstract

PURPOSE:To eliminate the dependency on polarization by the polarization state of incident light by providing polarization beam splitters on the optical axis between a single mode optical fiber for output and an acoustooptical element and inclining the polarization direction of the incident light to the acoustooptical element with the progressing direction of the ultrasonic wave propagating in the acoustooptical element. CONSTITUTION:The acoustooptical element 1 consisting of lead molybdate is provided between lenses 3 and 5 for condensing. Prisms 15, 16 and the polarization beam splitters 14, 17 are provided between the acoustooptical element 1 and the condenser lens 3. Exit light is a piece of beam and is so adjusted as to have the two polarization components orthogonal with each other and to maintain + or -45 deg. angle from the progressing direction of the ultrasonic wave propagating in the acoustooptical element 1. As a result, the perpendicular component and horizontal component with respect to the progressing direction of the ultrasonic wave are always 1:1. The dependency of diffraction efficiency on the polarization is eliminated in this way.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an acousto-optic optical switch, and more particularly to an acousto-optic optical switch that eliminates the polarization dependence of diffracted light by an acousto-optic element in the acousto-optic switch.

[Conventional technology]

FIG. 5 shows a typical configuration example of a conventional acousto-optic switch. The acousto-optic optical switch according to the present invention is particularly used in a measuring instrument called 0TDR (optical pulse tester). 0TDR is a comprehensive evaluation device for optical communication networks made up of optical fibers, which detects optical fiber break points, optical fiber-specific transmission losses, optical fiber connection losses, etc. The laser pulse emitted from the input single mode optical fiber 7 is transmitted to the undriven acousto-optic element 1.
and enters the output single mode optical fiber 6. In this case, the optical fiber to be inspected is connected to the output optical fiber. The components of the laser pulse reflected or scattered in the single mode optical fiber under test are:
The light travels back through the single-mode optical fiber to be inspected, enters the driven acousto-optic element 1, undergoes Bragg diffraction by the ultrasonic diffraction grating, is guided by the prism 9, and then enters the diffracted light output fiber 8. , guided to a light sensor. The condensing lenses 3, 4.5 collimate or converge the light beams. The matching circuit 2 performs impedance matching between the drive circuit 12 and the acousto-optic element 1. The drive circuit 12 drives the acousto-optic element 1 at a predetermined frequency. power terminal l
O is an input terminal for the DC power supply of the drive circuit 12, and the control signal input terminal 11 is used to input a signal for controlling the drive of the drive circuit 12 with an external circuit. , a matching circuit 2, and a drive circuit 12 are built in, and an optical fiber, a control signal input terminal 11, and a power terminal 10 are installed through holes. Reflection from the optical fiber to be inspected includes Fresnel reflection from a break point, etc., and photons of the transmitted light collide elastically with molecules or atoms of the optical fiber to be inspected, and the transmitted light is reflected in the optical fiber to be inspected. , there is Rayleigh scattering that undergoes continuous scattering. The component of this Rayleigh scattering that completely returns in the direction of incidence is called backscattered light, and the transmission loss specific to the optical fiber can be evaluated based on the strength of the backscattered light. Furthermore, the fracture location can be evaluated by measuring the intensity and transit time of Fresnel-reflected light. Generally, the above-mentioned acousto-optic optical switch is a tellurium oxide (T
era), an acousto-optic element made of lead molybdate (PbMoO4), etc. is used, but the acousto-optic element has different photoelastic constants in the vertical and horizontal directions with respect to the direction of the ultrasound propagating within the acousto-optic element. It is known that diffraction efficiency varies depending on the polarization state of incident light. In order to solve this drawback, Japanese Patent Application Laid-Open No. 63-115144 and Japanese Patent Application Laid-open No. 62
-246017 was proposed. However, by injecting circularly polarized light into the optical fiber to be inspected, the optical beam is made to travel backwards through the optical fiber to be circularly polarized. In some cases, the polarization of the returning light beam is disturbed and linearity occurs in an arbitrary direction.This is unsatisfactory in that the diffraction efficiency in the acousto-optic element changes. An object of the present invention is to solve the above-mentioned drawbacks of the prior art. [Means for solving the problems] The present invention aims to solve the above-mentioned problems. The first invention provides an acousto-optic element, a drive circuit for driving the acousto-optic element through a matching circuit, and a drive circuit for guiding diffracted light diffracted by the acousto-optic element to a diffracted light detection means. The acousto-optic system has a light guiding means built into a housing, a light input means for inputting a laser pulse to the optical fiber to be inspected through an output single mode optical fiber, and an output single mode optical fiber and a diffracted light detection means attached to the housing. In an optical switch, a polarizing beam splitter is provided on the optical axis between the output single-mode optical fiber and the acousto-optic element, and the polarization direction of the light incident on the acousto-optic element is changed from the traveling direction of the ultrasonic wave propagating within the acousto-optic element. The present invention provides an acousto-optic optical switch characterized by being tilted by 45 degrees.Thereby, the polarized light incident on the acousto-optic element is divided into two components at ±45 degrees with respect to the traveling direction of the ultrasonic wave. is incident.If you divide this into a vertical component and a horizontal component, it will always be l:1.Even if a light beam is incident with any polarization, it will be divided into a vertical component and a horizontal component by 1=1, so the polarization of diffraction efficiency The second invention includes an acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide that guides diffracted light diffracted by the acousto-optic element to a diffracted light detection means. an acousto-optic light including an optical means built into a housing, a light input means for inputting a laser pulse to the optical fiber to be inspected through an output single mode optical fiber, and an output single mode optical fiber and a diffraction light detection means attached to the housing; The present invention provides an acousto-optic optical switch characterized in that a polarizing beam splitter and a local wavelength plate are provided on the optical axis between an output single mode optical fiber and an acousto-optic element. A polarizing beam splitter and a wavelength plate are provided between the mode optical fiber and the acousto-optic element, and the polarization is adjusted so that the polarized light is tilted accurately by 45 degrees from the traveling direction of the ultrasonic wave propagating within the acousto-optic element. As a result, the polarized light incident on the acousto-optic element has two components at an angle of ±45° with respect to the traveling direction of the ultrasonic wave. When this is divided into a vertical component and a horizontal component, the ratio is always 1:1. Even if a light beam is incident with any polarization, the vertical and horizontal components are divided into 1=1, so the polarization dependence of diffraction efficiency is eliminated. As a third invention, an acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are housed in a housing. In an acousto-optic optical switch that has a built-in light input means for injecting a laser pulse into the optical fiber to be inspected through a single mode optical fiber for output into the housing, a single mode optical fiber for output and a diffraction light detection means, The present invention provides an acousto-optic optical switch characterized in that a polarizing beam splitter and a wavelength plate are provided on the optical axis between a mode optical fiber and an acousto-optic element. A polarizing beam splitter and a quarter wavelength plate are installed between the output single mode optical fiber and the acousto-optic element.
Adjustment is made so that a circularly polarized light beam is incident on the acousto-optic element. In this case, even if light of any polarization is incident, the light beam becomes circularly polarized light in front of the acousto-optic element, so there is no polarization dependence of the diffraction efficiency. , a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are built into the housing, and the housing is used for output. In an acousto-optic optical switch equipped with a light input means for injecting a laser pulse into an optical fiber to be inspected through a single mode optical fiber, an output single mode optical fiber and a diffracted light detection means, between the output single mode optical fiber and the acousto-optic element. The present invention provides an acousto-optic optical switch characterized in that a polarizing beam splitter and a depolarizing plate are provided on the optical axis of the acousto-optic optical switch.A polarizing beam splitter and a depolarizing plate are provided between the output single mode optical fiber and the acousto-optic element. A plate is provided and adjusted so that an unpolarized light beam enters the acousto-optic element.In this case,
Even if light of any polarization is incident, the light beam becomes unpolarized in front of the acousto-optic element, so the polarization dependence of diffraction efficiency disappears. [Function] Functions of the acousto-optic switch according to the present invention are shown in FIGS. 1 to 4.
This will be explained using figures. In the case of FIG. 1, a laser pulse guided by an input single-mode optical fiber 7, which is a light input means, is transmitted to an undriven acousto-optic element 1, a polarizing beam splitter 14,
The light is transmitted or reflected through the prisms 15 and 16 and the polarizing beam splitter 17 and enters the output single mode optical fiber 6. The reflected component of the incident laser pulse is split into two light beams with orthogonal polarization by the polarization beam splitter 17, reflected by the prisms 15 and 16, and combined into one light beam by the polarization beam splitter 14. . At this time, the polarization of the light beam has two orthogonal components. The orthogonal components of this light beam are incident on the acousto-optic element 1 at an angle of 45 degrees with respect to the traveling direction of the ultrasonic wave propagating within the acousto-optic element 1. Driving acousto-optic element 1
The diffracted light is guided by a prism 9 and enters a multimode optical fiber 8 for outputting diffracted light. In the case of FIG. 2, the light guided by the input single mode optical fiber 7 passes through the undriven acousto-optic element l, the wavelength plate 18, the polarizing beam splitter 14, and the prism 15.
．． 16, it is transmitted or reflected through the polarizing beam splitter 17 and enters the output single mode optical fiber 6. The reflected component of the incident laser pulse is split into two light beams with orthogonal polarization by the polarization beam splitter 17, reflected by the prisms 15 and 16, and combined into one light beam by the polarization beam splitter 14. At this time, the polarization of the light beam will have two orthogonal components. The orthogonal components of this light beam are tilted at 45 degrees to the acousto-optic element 1 with respect to the traveling direction of the ultrasonic wave propagating within the acousto-optic element 1.
It is rotated by a 1/2 wavelength plate 18 so that the light is incident on the inside. The following is the same as in Figure 1. In the case of FIG. 3, the light guided by the input single mode optical fiber 7, which is the light input means, passes through the undriven acousto-optic element 1, the wavelength plate 19, and the polarizing beam splitter 1.
4. Prism 15.16, polarizing beam splitter 17
Single mode optical fiber 6 for transmission or reflection and output
incident on the The reflected component of the incident laser pulse is split into two light beams with orthogonal polarization by a polarization beam splitter 17, reflected by a prism 15, 16, and combined into one light beam by a polarization beam splitter 14. 1/4 wavelength plate 1
9, it becomes circularly polarized light. The following is the same as in Figure 1. In the case of FIG. 4, the light guided by the input single mode optical fiber 7, which is the light input means, passes through the undriven acousto-optic element 1, the depolarizing plate 20, the polarizing beam splitter 14, the prism 15, 16, and the polarizing beam. splitter 1
7 is transmitted or reflected and enters the output single mode optical fiber 6. The reflected component of the incident laser pulse is split into two light beams with orthogonal polarization by a polarization beam splitter 17, reflected by a prism 15, 16, and combined into one light beam by a polarization beam splitter 14. Depolarizing plate 20
The light becomes unpolarized. The following is the same as in Figure 1. Note that the depolarizing plate is composed of one or two wedge-shaped crystalline crystals, and has the effect of converting the light into a pseudo non-polarized state. [Example] A first example of the present invention will be described with reference to FIG. The input single mode optical fiber 7 and the output single mode optical fiber 6 had a core diameter of 11 μm and a wavelength of 1.3 μm, and were optically coupled in the same housing 13. Condensing lenses 3 and 5 were used for the coupling. Lead molybdate (PbMo04) is placed between the condensing lenses 3 and 5.
A prism 15, 16 and polarizing beam splitters 14, 17 are installed between the acousto-optic element l and the condenser lens 3, so that the emitted light is orthogonal to one beam. It has two polarized wave components, and is adjusted to maintain an angle of ±45° from the direction of propagation of the ultrasonic wave propagating within the acousto-optic element 1. The light diffracted by the acousto-optic element 1 is guided by a prism 9, and then entered by a condensing lens 4 into a multimode optical fiber 8 for outputting diffracted light having a core diameter of 50 μm. A circuit for driving the acousto-optic element 1 is a matching circuit 2.
and a drive circuit 12, and the matching circuit 2 includes an acousto-optic element l.
Impedance matching between the drive circuit 12 and the drive circuit 12 is performed. The drive circuit 12 drives the acousto-optic element 1. A power supply terminal IO and a control signal input terminal 11 for controlling driving of the drive circuit are attached to the drive circuit 12,
It can be connected to the outside through a hole drilled in the housing 13. Here, as mentioned above, since the polarization of the light beam entering the acousto-optic element 1 is tilted by 45 degrees from the traveling direction of the ultrasonic wave traveling inside the acousto-optic element 1, the vertical component with respect to the traveling direction of the ultrasonic wave, The horizontal component is always 1. This eliminates the polarization dependence of diffraction efficiency. In this case, a semiconductor laser may be provided as the light input means instead of the input single mode optical fiber 7. Furthermore, if an optical sensor is provided as a diffracted light detection means instead of the multimode optical fiber 8 for outputting diffracted light, detection efficiency can be increased. A second embodiment of the invention will be described with reference to FIG. The single mode optical fiber 7 for input and the single mode optical fiber 6 for output have a core diameter of 11 tLm and a wavelength of 1.3 μm.
They were optically coupled and provided in the same housing 13. A condensing lens 3.5 was used for coupling. Lead molybdate (PbMo04
) between the acousto-optic element 1 and the condensing lens 3, a wavelength plate 18 and a prism]5.16
and polarization beam splitters 14 and 17 are provided, and the emitted light has two orthogonal polarization components in one beam, and the angle is ±45° from the traveling direction of the ultrasonic wave propagating within the acousto-optic element 1. It is adjusted to maintain the angle of The other parts are the same as the embodiment shown in FIG. in this case,
A Faraday rotator may be used instead of the local wavelength plate 14. A third embodiment of the invention is shown in FIG. The input single mode optical fiber 7 and the output single mode optical fiber 6 have a core diameter of l11. Lm and those for wavelengths of 1 and 3 μm were provided in the same housing 13 by optically coupling them. A condensing lens 3.5 was used for coupling. Focusing lens 3.5
An acousto-optic element 1 made of lead molybdate (PbMo04) is placed between the acousto-optic element 1 and the condenser lens 3, and a prism 15, 16 and a polarizing beam splitter 14 are placed between the acousto-optic element 1 and the condenser lens 3.
, 17 are provided, and the output light is one beam having two orthogonal polarization components, and is adjusted by a wavelength plate 19 so that it becomes circularly polarized light. The other parts are the same as the embodiment shown in FIG. Here, since the polarization of the beam entering the acousto-optic element 1 is always adjusted to be circularly polarized as described above, the polarization dependence of the diffraction efficiency is eliminated. A fourth embodiment of the invention is shown in FIG. The input single mode optical fiber 7 and the output single mode optical fiber 6 have a core diameter of 111 Lm and a wavelength of 1.3 μm, and are optically coupled in the same housing 13. A condensing lens 3.5 was used for coupling. An acousto-optic element 1 made of lead molybdate (PbMoO4) is placed between the focusing lens 3.5, and a prism 15.16 and a polarizing beam splitter 14 are placed between the acousto-optic element 1 and the focusing lens 3.
, 17 are provided, and the output light is one beam having two orthogonal polarization components, and is adjusted by a depolarization plate 20 so that it becomes non-polarized light. The other parts are the same as the embodiment shown in FIG. Here, since the polarization of the beam entering the acousto-optic element 1 is adjusted to always be non-polarized as described above, the polarization dependence of the diffraction efficiency is eliminated. In this case, as the depolarization plate 17, a two-piece crystal depolarization plate (DEQ-2S manufactured by Sigma Koki) is used, but any material having a depolarization function can be used. [Effects of the Invention] The present invention has an excellent effect of being able to eliminate polarization dependence due to the polarization state of light incident on an acousto-optic element of an acousto-optic switch.

[Brief explanation of drawings]

1 to 4 are sectional views of four embodiments of the present invention, and FIG. 5 is a sectional view of a conventional example. 1... Acousto-optic elements 14, 17... Polarizing beam splitters 15, 16
... Prism 18... Wave plate 19... Percent wave plate 20... Depolarization plate Figure 2. S'J? ,%6h Figure 3! ? Furusaki official J self-centered r5'I butt scolding] R1 stick) Hayabusa 19 cans r

Claims (4)

[Claims] (1) An acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are built into a housing. In the acousto-optic optical switch, the acousto-optic optical switch is equipped with a light input means for injecting a laser pulse into the optical fiber to be inspected through the output single mode optical fiber, an output single mode optical fiber, and a diffraction light detection means in the housing, A polarizing beam splitter is provided on the optical axis between the acoustooptic device and the acousto-optic device, and the polarization direction of the light incident on the acousto-optic device is tilted by 45 degrees from the direction of propagation of the ultrasonic wave propagating within the acousto-optic device. Acousto-optic light switch. (2) An acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are built into the housing. an acousto-optic optical switch in which a light input means for inputting a laser pulse to an optical fiber to be inspected through an output single mode optical fiber, an output single mode optical fiber and a diffracted light detection means are attached to the housing,
An acousto-optic optical switch characterized in that a polarizing beam splitter and a half-wave plate are provided on the optical axis between an output single mode optical fiber and an acousto-optic element. (3) An acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are built into the housing. an acousto-optic optical switch in which a light input means for inputting a laser pulse to an optical fiber to be inspected through an output single mode optical fiber, an output single mode optical fiber and a diffracted light detection means are attached to the housing,
An acousto-optic optical switch characterized in that a polarizing beam splitter and a quarter-wave plate are provided on the optical axis between an output single mode optical fiber and an acousto-optic element. (4) An acousto-optic element, a drive circuit that drives the acousto-optic element through a matching circuit, and a light guide means that guides the diffracted light diffracted by the acousto-optic element to the diffracted light detection means are built into the housing. an acousto-optic optical switch in which a light input means for inputting a laser pulse to an optical fiber to be inspected through an output single mode optical fiber, an output single mode optical fiber and a diffracted light detection means are attached to the housing,
An acousto-optic optical switch characterized in that a polarizing beam splitter and a depolarizing plate are provided on the optical axis between an output single mode optical fiber and an acousto-optic element.