JPS63304231A - Acoustooptic switch - Google Patents

Abstract

PURPOSE:To eliminate preshooting and overshooting in the waveform of the diffracted light to be emitted by setting an acoustooptic element in such a manner that the once diffracted light in the element is diffracted to the transducer side of the acoustooptic element and guiding the twice diffracted light to a 3rd fiber. CONSTITUTION:The 1st fiber 10 and 2nd fiber 20 are coupled with good optical efficiency via a near parabolic rod lens 41 which is a 1st lens and a near parabolic rod lens 42 which is a 2nd lens. The acoustooptic element 50 formed by using As2Se3 is provided on the optical axis between the near parabolic rod lenses 41 and 42. The light which is emitted from the 2nd fiber 20 and is diffracted twice by the acoustooptic element 50 is changed in the optical path by a prism 70 and is entered via a near parabolic rod lens 43 which is a 3rd lens to the 3rd fiber 30. The preshooting and overshooting in the waveform of the diffracted light are eliminated without depending on the input power of the driving electricity into the acoustooptic element by diffracting the light twice in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an acousto-optic switch suitable for optical/lux testers and the like.

[Conventional technology]

There has been remarkable progress in optical fiber communication technology.

Many optical fiber communication systems are in use.

Nine different measuring instruments are used to maintain the transmission quality of these optical fiber communications, but they are particularly useful for detecting failure points to locate breaks and discontinuities in optical cables, optical propagation loss, Light to measure connection point status etc./? Lux tester is an important measuring instrument. This kind of optical 9 Luss tester is /
4 optical pulses from a semiconductor radar driven by a pulse generator.

The backscattered light or light generated within the optical fiber is incident on the optical fiber to be measured through the optical directional coupler.

The Fresnel reflected light generated at the end face of the optical fiber is made incident on the detector via the optical directional coupler again.

It used a method of converting it into electrical pulses.

However, with this method, especially when the fiber under test is single mode, the level of backscattered light is small and the difference between it and the Fresnel reflected light level is large, and the dynamic range is reduced, which increases the unobservable region and reduces the resolution. The problem was that it worsened.

Another problem is that an optical directional coupler with low loss and low crosstalk is required to separate the light incident on the optical fiber from the light source and the backscattered light.

In order to solve the above problems, a system using an acousto-optic switch instead of an optical directional coupler has been developed. In this case, since the Schiffresnel reflection can be masked by the optical switch, the unobserved area can be improved.

As shown in FIG. 2, a conventional acousto-optic switch of this type consists of single-mode first and second optical fibers (hereinafter referred to as fibers) that face each other with an acousto-optic element 50 such as sPbMo0a or Too□ in between. (abbreviated)) are coupled by a parallel beam system to the first and second focusing rod lenses 41 and 42, respectively, and the acousto-optic element 50 is operated.

The incident light from the second fiber 20 is diffracted once.

The optical path was switched to the third focusing multimode fiber 30 via the third lens 43 (Kanayama et al., National Technical Report Vol. 29, No. 6, 100).
Page (National Technical Repo
rt.

Vol-29, 46P-100), December 1983
[Problems to be Solved by the Invention] In general, acousto-optic materials used in acousto-optic modulators have different acousto-optic figures of merit depending on the polarization direction of incident light, as shown in Figure 3. The diffraction efficiency for two orthogonal polarized lights is different. FIG. 3 is a diagram showing the relationship between incident power and diffraction efficiency, in which (a) shows polarized light in the direction of propagation of the ultrasonic wave, and (b) shows polarized light in a direction perpendicular to the direction of propagation. Therefore, it is necessary to set the operating point at the intersection point P of the diffraction efficiency curve of orthogonally bipolarized light with respect to the high-frequency input power of the acousto-optic modulator.

In this case, for one polarized light, the high-frequency input power is larger than the power value that gives the maximum diffraction efficiency, so Figure 4a)
yb) As shown in K, the light P1. which has been once diffracted by S1. ．． P1
A part of b becomes pta again at 82 toward the propagation direction of the transmitted light.
/ l Plb' is diffracted. Since the geometrical centers of the two diffraction beams are at different distances from the transducer, the time it takes for the ultrasonic waves generated from the transducer to reach each diffraction center is shorter for one and longer for the other. Therefore, since the acousto-optic switch described above uses the one-time diffracted light within the acousto-optic element, the fourth
Figure C).

As shown in d), the diffracted light waveform has the disadvantage that oversheeting occurs at the rising edge or pre-shading occurs at the falling edge.

That is, in the case of FIG. 4a), when the acousto-optic element starts to be driven, the first diffraction center S1 turns on and the power of the diffracted light increases, and then the second diffraction center S2 turns on. # The diffracted light power at Sl among the diffracted light powers at Sl is P1. ' is lost.

Therefore, the diffracted light p1. emitted from the acousto-optic element. As shown in FIG. 4C, the waveform of P18' is over-done at startup. However, when the drive of the acousto-optic element ends, Sl is turned off before 82, so there is no waveform distortion of Pl.

On the other hand, in the case of FIG. 4 b), when the acousto-optic element starts to be driven, the first diffraction center S1 is turned on, and by the time the second diffraction light reaches the second diffraction center S2, 82 has already been turned on. Since it is turned on, there is no waveform distortion of the diffracted light P1b emitted from the acousto-optic element, but at the end of driving, Sl
Since 81 turns off before 81, the diffracted light ij 1b', which was lost due to the second diffraction, overlaps Plb and becomes P
There is a problem in that a pre-shade of P1b' occurs in the falling waveform of lb.

The present invention aims to solve these problems of the conventional switch, and provides an acousto-optic switch in which the waveform of emitted diffracted light is free of solezite and hypersheet.

[Means for solving problems]

According to the present invention, first and second fibers are arranged to face each other, first and second lenses optically couple the first and second fibers, and first and second lenses. one or two acousto-optic elements provided between, a third lens and a third fiber that receive a light beam incident from the second seven-eyeper and deflected within the acousto-optic element; an acousto-optic switch configured to include a drive circuit for operating an acousto-optic element, and for switching an optical path from the second fiber to the first fiber to an optical path from the second fiber to the third fiber; The incident angle of the light incident from the second fiber is set so that the light diffracted once within the acousto-optic element is diffracted to the transducer side of the acousto-optic element, and the light is diffracted twice within the acousto-optic element. An acousto-optic switch is obtained, which is characterized in that the light is guided to the third fiber.

〔Example〕

The present invention will be explained below with reference to the drawings.

FIG. 1 is a plan view showing one embodiment of the present invention.

The first fiber 10 and the second fiber 20 are optically efficiently coupled via a focusing rod lens 41 that is a first lens and a focusing rod lens 42 that is a second lens. On the optical axis between the focusing rod lenses 41 and 42, an acousto-optic element 50 using As□Se s is provided. Further, the light emitted from the second fiber 20 and diffracted twice by the acousto-optic element 50 has its optical path changed by the prism 70 and enters the third fiber 30 via the converging rod lens 43 which is the third lens. do.

Now, as shown in FIG. 5, the incident angle of the light incident on the acousto-optic element 50 from the second fiber 20 is such that the one-time diffracted light within the acousto-optic element is diffracted toward the transducer side of the acousto-optic element. Since the diffraction center S2 of the second diffraction light is closer to the transducer than the first diffraction center S1, the first time the acousto-optic element 50 starts to be driven is the point at which the first diffraction occurs. The ultrasonic wave at the second diffraction center S2 position is already in a steady state, and overshading of the waveform of the light incident on the third fiber does not occur.

That is, it becomes equivalent to the rising waveform of FIG. 4d). on the other hand.

This is because the second diffraction S2 ends before the first diffraction S1 when the driving of the acousto-optic element ends.

The waveform of the light incident on the third fiber is at the falling edge! I don't have a receipt. In other words, it is equivalent to the falling waveform of FIG. 4C).

This phenomenon is due to the difference in the spatial positions of the two diffraction centers and is not dependent on the drive force applied to the acousto-optic element. Therefore, even if the driving power is set so that the diffraction efficiency of the acousto-optic element does not depend on the polarization direction of the light incident from the second fiber, overshading and preshoot of the first diffracted light waveform will not occur. In addition, since the interaction distance between light and ultrasound within the acousto-optic element required from the first diffraction to the second diffraction depends on the driving power of the acousto-optic element, the driving The distance between the transmitted light and the twice-diffracted light can be changed by adjusting the power. Therefore, if an acousto-optic material with no polarization dependence of diffraction efficiency is used or if there is no need to consider the polarization dependence of diffraction efficiency, the optical axis of the first fiber and first lens and the third fiber and The accuracy of the distance between the third lens and the optical axis can be relaxed.

In the embodiment of FIG. 1, when the high-frequency output power of the drive circuit 9o is 0.4 W, the frequency is 300 MHz, and the transducer length of the acousto-optic element 50 is 30 g, the separation distance between the transmitted light and the second diffracted light is 1. It is 3 mm. In this example, the insertion loss from fiber 1o to fiber 20 is 1.2 d
B, insertion loss from fiber 20 to 30 is 3.5 dB
The polarization dependence of the insertion loss from the y eyeers 20 to 30 was 0.04 dB, and the overshoot and 7° receipt of the optical output waveform from the fiber 30 during /4 Luss driving were both ~OdB. Against this.

The preshoot of the diffracted light output waveform due to one-time diffraction is ~0.
It is 1 dB.

In this example, diffraction was performed twice within one acousto-optic element, but it is also possible to obtain the same waveform abnormality reduction effect even if diffraction is performed once using two acousto-optic elements. can.

〔Effect of the invention〕

As explained above, the acousto-optic switch according to the present invention allows the diffraction to occur twice within the acousto-optic element, so that the waveform of the diffracted light can be changed once without depending on the drive electric input or the It is possible to eliminate pre-sheets and over-sheets. Therefore, even if the driving power is set to compensate for the polarization dependence of the diffraction efficiency due to the difference in the acousto-optic figure of merit depending on the polarization direction of the incident light on the acousto-optic element, an abnormality in the waveform of the diffracted light does not occur. Furthermore, if the polarization dependence of the two-diffraction efficiency does not need to be taken into account, the distance between the transmitted light and the diffracted light can be adjusted depending on the driving power, so the positional accuracy of the optical input/output fiber can be relaxed.

This also has the effect of reducing the mechanical accuracy of the parts that hold the optical system and the optical axis adjustment accuracy of the lens.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the configuration of an embodiment of the acousto-optic switch of the present invention, FIG. 2 is a plan view showing the configuration of a conventional acousto-optic switch, and FIG. 3 is an acousto-optic switch used inside the acousto-optic switch. A characteristic curve diagram of the element, FIG. 4 is a principle explanatory diagram showing the principle of optical output waveform distortion of a conventional acousto-optic switch, and FIG. 5 is a principle explanatory diagram showing the operating principle of the acousto-optic switch of the present invention. 10.20,30...Fiber, 41,42°43.
... Focusing rod lens, 50... Acousto-optic element. 60... Matching circuit, 70... Prism, 90
...Drive circuit. Fig. 1 Focusing rod lens 43 Fig. 2 50 Acousto-optic element Fig. 3 P. Incident power Figure 5 (G)

Claims (1)

[Claims] 1. first and second optical fibers arranged oppositely;
first and second lenses that optically couple the first and second optical fibers; an acousto-optic element provided between the first and second lenses; a third light beam which is deflected within the acousto-optic element;
a lens, a third optical fiber, and a drive circuit for operating the acousto-optic element, and the optical path from the second optical fiber to the first optical fiber is connected from the second optical fiber to the first optical fiber. In an acousto-optic switch that switches the optical path to a third optical fiber, the incident angle of the light incident from the second optical fiber is changed so that the one-time diffracted light within the acousto-optic element is on the transducer side of the acousto-optic element. An acousto-optic switch characterized in that the light is set to be diffracted twice within the acousto-optic element and guided to the third optical fiber.