JPS62246017A - Acoustooptic switch - Google Patents

Abstract

PURPOSE:To reduce the polarization dependency of diffracted light by deviating the polarization direction of light beams incident on an optical fiber consisting of a single mode fiber and a polarization plane maintaining fiber from the principal axis of the polarization plane maintaining fiber. CONSTITUTION:The single mode fiber 21 and polarization plane maintaining fiber 22 are connected opposite each other by an adapter 110 to constitute an optical fiber 20, and an optical connector 101 is fixed so that projection light beams from the fiber 21 deviate from the principal axis of the fiber 22 by 45 deg.. The light projected beams from the optical fiber 20 is diffracted by an acoustooptic element 50 made of arsenic selenide and changes its principal axis in a prism 70 to be made incident on a graded index optical fiber 30 through a converging rod lens 43. In this constitution, the projection polarization light beams of the fiber 21 are linear polarized light beams and the projection light beams of the fiber 22 is close to circular polarization.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an acousto-optic switch suitable for source pulse test equipment, and more particularly to an acousto-optic switch for single mode fibers.

[Conventional technology]

Due to the rapid progress of fiber-optic communication technology, many fiber-optic communication systems are now in practical use. Various measuring instruments are used to maintain the transmission quality of these optical fiber communications, but in particular, they are used to locate failure points, such as locating break points and discontinuities in the original cable, and to measure optical fibers per unit length. An optical pulse tester that can determine loss, connection point evaluation, etc. is one of the most prestigious measuring instruments.

Other original pulse testers introduce the emitted light pulse from a semiconductor laser driven by a pulse generator into the fiber under test via a directional coupler, and the backscattered light generated within the optical fiber is In addition, the Fresnel reflected light generated at the end face of the original fiber is made to enter the detector again via the original directional coupler.
It used a method of converting it into electrical pulses. However, in this method, especially when the target eye is a single mode fiber, the level of backscattered light is small and the difference from the Fresnel reflection level becomes large, the dynamic range decreases and the invisible side area widens. This had the disadvantage that resolution deteriorated. First, there was also the problem that a low-loss, low-crosstalk optical directional coupler was required to separate the light emitted from the light source to the optical fiber and the backscattered light.

In order to solve the above problems, a method using an acousto-optic switch instead of an optical directional coupler has been developed. Since this optical switch can mask Fresnel reflection, it is possible to reconstruct the disfigured side area.

Conventionally, PbMo() is used as an optical switch in this book.
4 or T e U 2 etc. t41II element element? ! - By arranging the first and second source fibers facing each other with a pair of sides, and coupling them by a lens so that the source between each optical fiber becomes a parallel beam, and operating it with an acousto-optic element, the second source fiber is
The configuration was such that the total diffraction of the light emitted from the original fiber was switched to the third original fiber through a lens (
Domestic Technology Teleport (at
ional Technical Report ),
(See Volume 29, No. 6, page ioo).

[Problem that the invention seeks to solve]

However, in the pulse tester using the acousto-optic switch described above, tellurium oxide (+1te (J2)) and lead molybdate (PbAao 0
Since the acousto-optic elements such as 4) have different photoelastic constants in the direction of ultrasonic propagation and in the direction perpendicular thereto, the single diffraction efficiency changes depending on the polarization state of the original beam incident on the acousto-optic element. - Since the polarization of light propagating in a single mode fiber is disturbed by a slight external force and imperfections in the wandering inside the core or at the boundary between the core and cladding, the backscattered light also changes the propagation distance of the original fiber. The polarization state will change accordingly. Therefore, when backscattered light is incident on an acousto-optic switch, the diffraction efficiency of the acousto-optic element has polarization dependence, resulting in a disadvantage that the loss changes over time.

In other words, in a pulse tester using a conventional acousto-optic switch, waveform fluctuations occur due to the polarization characteristics of backscattered light, making it difficult to detect minute changes in loss distribution and connection loss. It had

[Means for solving problems]

The acousto-optic switch of the present invention includes first
's? a second optical fiber; first and second lenses that optically couple the first and second original fibers;
an acousto-optic element provided on the optical axis between the first and second lenses; and a third lens element for receiving the original beam emitted from the second original fiber and deflected within the acousto-optic element. the first original fiber is a single mode fiber, the second original fiber includes at least a mi plane-maintaining fiber, and the polarization direction of the original beam incident on the second original fiber is 7rlJ is located offset from the main axis of the holding fiber. With this configuration, the light emitted from the polarization-maintaining fiber can be in a state close to circularly polarized light. Therefore, when the acousto-optic switch according to the present invention is used in a pulse tester, the light emitted from the polarization-maintaining fiber can be The scattered light also becomes close to circularly polarized light,
- Since the light incident on the acousto-optic switch has a constant polarization, d waveform distortion due to the polarization characteristics of the fiber under test is hardly observed.

〔Example〕

Next, embodiments of the present invention will be described in detail using the drawings.

No. 11\1 is a plan view showing the first embodiment of the present invention.

In the figure, the first original fiber 10 and the second original fiber 20h are optically coupled via a t-th lens 41 and a second lens 42. Thirteenth second lens 41.
An acousto-optic element 50 made of arsenic selenide (As2Se3) is provided within the element axis of 42. Reference numeral 60 denotes a circuit that performs muving between a signal source that generates a frequency signal that drives the acousto-optic element 50 and the transducer of the element 50. Output from the second optical fiber 20 and the acousto-optic element 50
The optical path of the diffracted source is changed by the prism 70 and sent to the third source fiber 30 via the third lens 43! R′jru.

1st. An original connector is fixed to the tip of the third original fiber lO, 30. The first optical fiber IO is a single mode fiber with a core diameter of 10 μm, and the third original fiber 30 is a convergent fiber with a core diameter of 50 μm. 1st
．． Second. The third lens 41.42.43 has a length of 0.22
This is Birichi's focusing rod lens. The second original fiber 20 has a core diameter lOμ with the original connector 100 attached to the tip.
m second single mode fiber 21 and a polarization maintaining fiber 22 of length 50cIIL with original connectors ioi, 102 attached at both ends, υ, mutually duffed by 1.
Connected via lOk. Here, the original connector 101 is fixed so that the output polarized light of the second single mode fiber 21 is deviated from the main axis of the polarization maintaining fiber 22.

In other words, since the output polarization of the single mode fiber 21 in Fragment 2 is almost linearly polarized, the main axis of the polarization maintaining fiber 22 is inclined, for example, by 45 degrees with respect to the one spider polarization, so that the output light of the fiber 22 is Make it almost circularly polarized.

In this embodiment, the second single-mode fiber 21 and the polarization-maintaining seven-eye fiber 22 are connected by an all-optical connector, but they may also be connected by a splice. However, the length of the polarization maintaining fiber 22 is preferably longer than the beat length, and is not particularly limited.

When the waveform fluctuation due to the polarization characteristics of one fiber under test was observed using the acousto-optic suite TF full-pulse tester according to this embodiment, it was found to be about 0.02 dB, which was several tens of times lower than that of the conventional method.

FIG. 2 is a plan view showing a second embodiment of the present invention, which differs from the first embodiment shown above in that a polarization maintaining fiber 22' is used instead of the second original fiber 20. It is a point. Here, rather than the polarization-maintaining fiber 22' having a situation close to circularly polarized light at the output end, the end facing the second lens 42 is completely rotated and remains stationary.

〔Effect of the invention〕

As explained above, the acousto-optic switch according to the present invention has
The optical fiber on the input side includes a polarization-maintaining fiber, and the polarization plane that is likely to enter the polarization-maintaining 7-eye I (is shifted from the main axis of the polarization-maintaining fiber).
This has the effect of reducing the polarization dependence of diffracted light. Therefore, the pulse tester using the acousto-optic switch according to the present invention has the effect of sufficiently suppressing waveform fluctuations caused by the polarization dependence of backscattered light.

[Brief explanation of drawings]

1 and 2 are the first and second embodiments of the present invention, respectively.
A plan view showing an example of 010.20...
Single mode fiber, 22.22'... Polarization maintaining fiber, 30... Focusing multimode fiber, 41.42.43... Focusing c2 lens, 50 ...Acousto-optic element, 60...
Matching circuit, 70...Beam optical path changing frame, 80...Electric input terminal, 100.101
．． 102,103. 104... Original connector, 110... Adapter. Agent: Susumu Hara, Patent Attorney PI3. t<' , y \,

Claims (1)

[Claims] first and second optical fibers arranged oppositely; a first optical fiber that optically couples the first and second optical fibers;
and a second lens, an acousto-optic element disposed on the optical axis between the first and second lenses, and a light beam emitted from the second optical fiber and deflected within the acousto-optic element. a third optical fiber that receives the optical fiber, and by driving the acousto-optic element, the optical path from the second optical fiber to the first optical fiber is changed from the second optical fiber to the third optical fiber. In the acousto-optic switch, the first optical fiber is a single-mode fiber, the second optical fiber is at least a polarization-maintaining fiber, and the main axis of the polarization-maintaining fiber is directed to the polarization-maintaining fiber. An acousto-optic switch characterized in that the switch is provided in a direction different from the polarization direction of an incident light beam.