JPH02253238A - Acousto optical switch - Google Patents

Abstract

PURPOSE:To eliminate the dependency on polarization by the polarization state of incident light by inclining the main axis of a polarization plane maintaining optical fiber consisting of a single mode optical fiber for output with the progressing direction of the ultrasonic wave progressing in an acoustooptical element. CONSTITUTION:The light guided by the single mode optical fiber 7 for input which is a light incident means is made incident through the undriven acoustooptical element 1 on the polarization plane maintaining optical fiber 6'. The reflected component of the incident laser pulses is divided to the component orthogonal with the main axis direction by the polarization plane maintaining optical fiber 6' for output. The main axis of the polarization plane maintaining optical fiber 6' is inclined 45 deg. from the progressing direction of the ultrasonic wave propagating in the acoustooptical element 1, by which the perpendicular component and horizontal component are always made into 1:1 in the progressing direction of the ultrasonic wave. The dependency of the diffraction efficiency on the polarization is eliminated in this way.

Description

Detailed Description of the Invention [Industrial Application Field] 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. Regarding.

[Prior Art] FIG. 5 shows a typical configuration example of a conventional acousto-optic optical 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 l.
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 laser pulse component reflected or scattered in the single-mode optical fiber to be inspected travels back through the single-mode optical fiber to be inspected and enters the driven acousto-optic element l, where it is subjected to Bragg diffraction by the ultrasonic diffraction grating. After being guided by the prism 9, the light enters the diffracted light output fiber 8 and is guided to the optical 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.The power supply terminal 10 is an input of the DC power supply of the drive circuit 12. The control signal input terminal 11, which is a terminal, inputs a signal for controlling the drive of the drive circuit 12 with an external circuit.
A prism 9, 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 supply 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
eam), lead molybdate (PbMo04), etc., but the acousto-optic element has a photoelastic constant in the vertical and horizontal directions with respect to the direction of the ultrasound propagating within the acousto-optic element. It is known that the diffraction efficiency varies depending on the polarization state of the incident light. In order to eliminate this drawback, JP-A-63-115144 and JP-A-6
2-246017 was proposed. However, since circularly polarized light is incident on the optical fiber to be inspected, the light beam that returns inside the optical fiber to be inspected is brought closer to circularly polarized light, so it depends on the condition of the optical fiber to be inspected. In this case, the polarization of the returning light beam is disturbed and linearity occurs in any direction. For this reason, the diffraction efficiency of the acousto-optic element changes, which is unsatisfactory.

[Problems to be Solved by the Invention] The object of the present invention is to solve the above-mentioned drawbacks of the prior art.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and as a first invention, it provides an acousto-optic element and a drive circuit that drives the acousto-optic element through a matching circuit. and a light guiding means for introducing the diffracted light diffracted by the acousto-optic element to the diffracted light detecting means are built into the housing, and an optical fiber to be inspected 9- is connected to the housing through an output single mode optical fiber.
In an acousto-optic optical switch equipped with a light input means for inputting a laser pulse, an output single mode optical fiber, and a diffracted light detection means, the output single mode optical fiber is a polarization maintaining optical fiber, and the main axis of the polarization maintaining optical fiber is The present invention provides an acousto-optic optical switch characterized in that it is tilted by 45 degrees from the direction of propagation of ultrasonic waves traveling within an optical element. As a result, the polarized light incident on the acousto-optic element 1 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, 1=1 always holds. Even if a light beam is incident with any polarization, 1 = 1 for vertical and horizontal components.
Since it can be divided by 1, the polarization dependence of diffraction efficiency is eliminated.

As a second 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 diffracted light diffracted by the acousto-optic element to a diffracted light detection means are housed. In an acousto-optic optical switch, a light input means for inputting an optical fiber laser pulse to be inspected through a single mode optical fiber for output is built into the housing, and a single mode optical fiber for output and a diffraction light detection means are attached. The present invention provides an acousto-optic optical switch characterized in that the single mode optical fiber is a polarization-maintaining optical fiber, and a wavelength plate is provided on the optical axis between the polarization-maintaining optical fiber and the acousto-optic element. A wavelength plate is provided between the polarization-maintaining optical fiber and the acousto-optic element, and the wavelength plate is adjusted so that the polarized light is more accurately tilted by 45@ than the direction of propagation of the ultrasonic wave traveling within the acousto-optic element. As a result, the polarized light incident on the acousto-optic element has two components of ±45@ with respect to the traveling direction of the ultrasonic wave. If you divide this into a vertical component and a horizontal component, it is always 1:l
becomes. Even when a light beam is incident with any polarization, it is perpendicular.
Since the horizontal component is divided 1:1, the polarization dependence of the diffraction efficiency is eliminated. As a third invention, a drive circuit for driving an acousto-optic element through a matching circuit and a light guide means for guiding diffracted light diffracted by the acousto-optic element to a diffracted light detection means are built in a housing, In an acousto-optic optical switch, the acousto-optic optical switch is equipped with seven light input means for inputting an optical fiber laser pulse to be inspected through a single mode optical fiber for output into a 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 it is a polarization-maintaining optical fiber and a wavelength plate is provided on the optical axis between the polarization-maintaining optical fiber and an acousto-optic element. A wavelength plate is provided between the polarization-maintaining optical fiber and the acousto-optic element, and adjusted so that a circularly polarized light beam enters the acousto-optic element. In this case, even if light of any polarization is incident, it becomes a circularly polarized light beam in front of the acousto-optic element, so there is no polarization dependence of diffraction efficiency.

A fourth invention includes an acousto-optic element, a drive circuit for driving the acousto-optic element through a matching circuit, and a light guide means for guiding diffracted light diffracted by the acousto-optic element to a diffracted light detection means. In an acousto-optic optical switch, which is built in a housing and has a light input means for inputting a laser pulse into an optical fiber to be inspected through an output single mode optical fiber into the housing, an output single mode optical fiber and a diffracted light detection means, an output Provided is an acousto-optic optical switch characterized in that a single mode optical fiber for use in the present invention is a polarization-maintaining optical fiber, and a depolarization plate is provided on the optical axis between the polarization-maintaining optical fiber and an acousto-optic element. . A depolarization plate is provided between the polarization-maintaining optical fiber and the acousto-optic element, and adjustment is made 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] The functions of the acousto-optic optical 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, 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 and enters the polarization maintaining optical fiber 6'. The reflected component of the incident laser pulse is divided into components perpendicular to the principal axis direction by the output polarization-maintaining optical fiber 6'. Furthermore, an output polarization-maintaining optical fiber 6'
The main axis of
The reflected component of the incident laser pulse is ±45° from the direction of propagation of the ultrasonic wave within the acousto-optic element l.
The incident light is shifted.

The diffracted light diffracted by the driven acousto-optic element 1 is
The 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 single mode optical fiber 7, which is the light input means, passes through the undriven acousto-optic element 1 and the local wavelength plate 14, and enters the polarization maintaining optical fiber 6'.

The reflected component of the incident laser pulse is divided into two orthogonal polarized waves by the output polarization-maintaining optical fiber 6'. These two orthogonal polarized waves are tilted by 45° with respect to the traveling direction of the ultrasonic wave within the acousto-optic element l by the wavelength plate 14,
The light is incident on the acousto-optic element that is being driven. The following is the same as in Figure 1.

In the case of FIG. 3, the light guided by the single mode optical fiber 7, which is the light input means, passes through the undriven acousto-optic element l and the storm wave plate 16, and enters the polarization maintaining optical fiber 6'.

The reflected component of the incident laser pulse is divided into two orthogonal polarized waves by the output polarization-maintaining optical fiber 6'. These two orthogonal polarized waves are turned into circularly polarized light by the wavelength plate 16 and are incident on the acousto-optic element being driven. below,
Same as in Figure 1.

In the case of FIG. 4, the light guided by the single mode optical fiber 7, which is the light input means, passes through the undriven acousto-optic element 1 and the depolarization plate 17, and enters the polarization maintaining optical fiber 6'.

The reflected component of the incident laser pulse is divided into two orthogonal polarized waves by the output polarization-maintaining optical fiber 6'. These two orthogonal polarized waves are turned into unpolarized light by the depolarization plate 17 and are incident on the acousto-optic element being driven. 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 has a core diameter of 11 μm and a wavelength of 1.3 μm, and the output polarization-maintaining optical fiber 6′ has a core diameter of 9 μm and a wavelength of 1.3 μm. It was set up in conjunction with. A condensing lens 3.5 was used for coupling. An acousto-optic element 1 made of lead molybdate (PbMoO4) is provided between the condensing lenses 3 and 5. An acousto-optic element 1 made of lead molybdate (PbMoO4) is provided, and an output beam is directed at 45 degrees to the ultrasonic wave traveling inside the acousto-optic element 1. The polarization-maintaining optical fiber 6' for output was set so that the main axis of the polarization-maintaining optical fiber 6' was aligned. 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. The circuit number for driving the acousto-optic element 1 consists of a matching circuit 2 and a driving circuit 12. The matching circuit 2 performs impedance matching between the acousto-optic element 1 and the driving circuit 12. The driving circuit 12 is an acoustic The drive circuit 12 that drives the optical element 1 is attached with a power terminal 1O and a control signal input terminal 11 that controls the drive of the drive circuit, and can be connected to the outside through a hole made in the housing 13. It looks like this.

Here, as mentioned above, since the main axis of the polarization maintaining optical fiber 6' is tilted at 45 degrees from the direction of propagation of the ultrasonic wave traveling inside the acousto-optic element 1, the vertical component and the horizontal component with respect to the direction of propagation of the ultrasonic wave are The components are always 1=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 is shown in FIG. A wavelength plate 14 is provided between the acousto-optic element 1 and the condensing lens 3,
The orthogonally polarized light emitted from the output polarization-maintaining optical fiber 6' is rotated so that it is tilted by 45 degrees from the direction of the ultrasonic wave traveling inside the acousto-optic element 1. Other parts are the same as those of the embodiment shown in FIG. In this case, a Faraday rotator may be used instead of the wavelength plate 14.

A third embodiment is shown in FIG. A wavelength plate 16 is provided between the acousto-optic element 1 and the condensing lens 3,
The orthogonally polarized light emitted from the output polarization-maintaining optical fiber 6' is adjusted to be circularly polarized and incident on the acousto-optic element 1. This eliminates the polarization dependence of diffraction efficiency. Other parts are the same as those of the embodiment shown in FIG.

A fourth embodiment is shown in FIG. 4. A depolarization plate 17 is provided between the acousto-optic element 1 and the condensing lens 3.
It is adjusted so that the orthogonally polarized light emitted from the output polarization-maintaining optical fiber 6' enters the acousto-optic element 1 in a non-polarized state. As a result, the polarization dependence of the diffraction efficiency is eliminated (the other parts are the same as those in the embodiment shown in FIG. 1). Elimination board (DE made by Sigma Koki)
Q-2S), but any device that has a depolarization function can be used.

[Effects of the Invention] The present invention has the excellent effect of being able to eliminate polarization dependence due to the polarization state of light incident on the 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 element 6'... Polarization maintaining optical fiber 14... Local wavelength plate 16... Residual liquid length plate 17... Depolarization plate l' Illustration scolding, cotton) Hayabusa eyes! r ikanso χf3 44th + Paste jJ circuit 1 key figure figure figure figure figure! 3 Self-centered circuit investigation;

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. 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 the output single mode optical fiber is a polarization-maintaining optical fiber, and the main axis of the polarization-maintaining optical fiber is inclined by 45 degrees from the direction of propagation of ultrasonic waves within an acousto-optic element. (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,
1. An acousto-optic optical switch characterized in that the output single mode optical fiber is a polarization-maintaining optical fiber, and a wavelength plate is provided on the optical axis between the polarization-maintaining optical fiber and the 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 the output single mode optical fiber is a polarization-maintaining optical fiber, and a quarter-wave plate is provided on the optical axis between the polarization-maintaining optical fiber and the 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,
1. An acousto-optic optical switch, characterized in that the output single mode optical fiber is a polarization-maintaining optical fiber, and a depolarization plate is provided on the optical axis between the polarization-maintaining optical fiber and an acousto-optic element.