JPH0769550B2 - Acousto-optic switch - Google Patents

Description

TECHNICAL FIELD The present invention relates to an acousto-optic switch suitable for an optical pulse tester or the like.

[Conventional technology]

The progress of optical fiber communication technology has been remarkable, and many optical fiber communication systems have been put to practical use. Various measuring instruments are used to maintain the transmission quality of these optical fiber communications. In particular, searching for a fault point that locates a break point or a discontinuity point of an optical cable, a propagation loss of light,
The optical pulse tester that measures the connection point status is an important measuring instrument. This kind of optical pulse tester makes an optical pulse from a semiconductor laser driven by a pulse generator enter an optical fiber to be measured through an optical directional coupler, and generates backscattered light generated in the optical fiber or A method has been used in which the Fresnel reflected light generated at the end face of the optical fiber is again incident on the detector via the optical directional coupler and converted into an electric pulse.
However, in this method, especially when the fiber to be measured is a single mode, the level of backscattered light is small, the difference from the Fresnel reflected light level is large, the dynamic range is reduced, and the unobserved region is widened and the resolution deteriorates. It had the drawback of There was also the problem that an optical directional coupler with low loss and low crosstalk was required to separate the backscattered light from the light incident on the optical fiber from the light source.

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

Conventionally, as an acousto-optic switch of this type, as shown in FIG. 2, first and second fibers 10 and 20 facing each other with an acousto-optic element 50 such as PbMoO ₄ or TeO ₂ sandwiched between the first and second fibers 10 and 20, respectively. The second lens 41, 42 is coupled by a parallel beam system, and the acousto-optic device 50 is operated to diffract the incident light from the second fiber 20, and the third fiber 43 is used to diffract the incident light. The optical path was switched to 30 (Kanayama et al., National Technical Report, Vol.29, No.6
p.100, December 1983).

[Problems to be solved by the invention]

However, in the above-described acousto-optic switch, since Bragg diffraction due to the acousto-optic effect is used, in order to couple the fiber 20 and the fiber 30 in the optimum state with a small loss, the fiber 20 to the acousto-optic element 50 should be connected. The incident angle of light is
It is necessary to fix the optical system to a specific angle (Bragg angle) determined by the wavelength of light, the output sine wave frequency of the electric circuit 90 that drives the acousto-optic element, and the ultrasonic wave propagation velocity inside the acousto-optic element 50. There is.

On the other hand, in the conventional acousto-optic switch, since the output sine wave signal is fixed at a single frequency, the light from the fiber 20 to the acousto-optic element 50 can be used for light of a wavelength different from that when the optical system is set. The incident angle of the beam will deviate from the Bragg angle, and the diffraction efficiency will decrease and the optical axis will shift.
The disadvantage is that the coupling loss of light from 20 to fiber 30 is significantly increased. On the other hand, as an optical pulse tester, it is desirable to measure the transmission characteristics of an optical fiber with light of the same wavelength as when it is actually used as a transmission line. A tester is required.

However, when the above-described optical pulse tester is configured by the conventional acousto-optic switch, the acousto-optic switch as many as the light of the desired wavelength is required, and there is a problem that the configuration becomes complicated.

Therefore, in view of the above problems, the present invention provides an acousto-optic switch that does not reduce the diffraction efficiency and shifts of the optical axis even for lights of various wavelengths.

[Means for solving problems]

According to the present invention, the first and second fibers arranged to face each other, the first and second lenses for optically coupling the first and second fibers, and the first and second fibers An acousto-optic device provided on the optical axis between the lenses, a third lens and a third fiber for receiving a light beam incident from the second fiber and deflected in the acousto-optic device, and the acousto-optic device The optical system is configured to include an electric circuit for controlling the element using the output sine wave frequency f, and the optical system with respect to the wavelength λ _{o of} light used when setting the optical system and the output sine wave frequency f _{o of the} electric circuit. By switching the output sine wave frequency f of the electric circuit so that fλ = f _o λ _o when light having a wavelength λ different from that at the time of entering from the second fiber, the second fiber Setting of optical system for light of different wavelengths emitted from Without changing the incident angle of the light from said second fiber to said acousto-optic element, an acousto-optic switch is obtained diffraction efficiency is characterized in that equal to the Bragg angle becomes maximum. As a result, it is possible to operate the optical coupling state of the light from the second fiber to the third fiber in an optimum state.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of the acousto-optic switch according to the present invention. First fiber 10 and second fiber
20 is optically efficiently coupled through a converging rod lens 41 which is a first lens and a converging rod lens 42 which is a second lens. Focusing rod lens 4
An acousto-optic device 50 using As ₂ Se ₃ is provided on the optical axis between 1, 42. The light emitted from the second fiber 20 and diffracted by the acousto-optic device 50 has its optical path changed by the prism 70 and is incident on the third fiber 30 via the converging rod lens 43 which is the third lens. To do. The acousto-optic device 50 is set so that the incident angle of light having a wavelength of 1.3 μm from the fiber 20 to the acousto-optic device 50 satisfies the Bragg condition with respect to the output sine wave frequency of 140 MHz of the electric circuit. Electric circuit 90
Has a 140MHz and 117.42MHz crystal oscillator inside and has a function to switch the output frequency according to a signal from the outside. Further, the electric circuit 90 is incorporated in the same case as the acousto-optic device 50.

In Fig. 1, by switching the output sine wave frequency of the electric circuit 90 to 140MHz and 117.42MHz for light with wavelengths of 1.3μm and 1.55μm, respectively, fλ = 182 (Hz ・ m) is always maintained, and As a result, the acousto-optic switch can be operated in a state where the incident angle of light from the fiber 20 to the acousto-optic element 50 satisfies the Bragg condition without changing the optical system setting. That is, the optical path from the fiber 20 to the fiber 30 is connected in the optimal coupling state without the reduction of the diffraction efficiency and the deviation of the optical axis. The insertion loss from the fiber 20 to the fiber 30 in this embodiment is 2.0 dB when the wavelength 1.3 μm light source is used, and the wavelength 1.55 μ
It was 3.6 dB when using the m light source, and good insertion loss was obtained for both wavelengths of light.

On the other hand, when using the same single frequency electric circuit as the conventional acousto-optic switch, when using a light source with a wavelength of 1.3 μm
2.0 dB, 21 dB when using a 1.55 μm wavelength light source.

As a method of the electric circuit 90, a method of using a VC0 (Voltage controlled oscillator) may be used in addition to a method of switching a plurality of crystal oscillators to an amplifier of one system as in the present embodiment.

〔The invention's effect〕

As described above, the acousto-optic switch according to the present invention changes the output sine wave frequency of the electric circuit that drives the acousto-optic element in accordance with the wavelength of the light used, so that the acousto-optic switch is always able to detect light of various wavelengths. , The optical system can be used in an optimal state with no reduction in diffraction efficiency and optical axis shift, and there is no significant increase in insertion loss due to the difference in the wavelength of the light used. Therefore, if the acousto-optic switch according to the present invention is used, an optical pulse tester capable of measuring light with a plurality of wavelengths can be easily configured without adding an acousto-optic switch.

[Brief description of drawings]

FIG. 1 is a plan view showing the outline of an embodiment of the acousto-optic switch of the present invention, and FIG. 2 is a plan view showing the outline of a conventional acousto-optic switch. 10 ... First fiber, 20 ... Second fiber, 30 ... Third fiber, 41 ... First converging rod lens, 42 ...
2nd focusing rod lens, 43 ... 3rd focusing rod lens, 50 ... Acousto-optic element, 60 ... Matching circuit, 70
…… Prism, 90 …… Electric circuit.

Claims (1)

[Claims] 1. A first and a second fiber which are arranged to face each other, a first and a second lens which optically couple the first and the second fiber, and the first and the second lens. An acousto-optic element provided between the lenses, a third lens and a third fiber for receiving a light beam incident from the second fiber and deflected in the acousto-optic element, and an acousto-optic element that outputs an output sine And an electric circuit that controls using a wave frequency, and by driving the acousto-optic device by the electric circuit, an optical path from the second fiber to the first fiber is formed. An acousto-optic switch for switching an optical path from a fiber to the third fiber, wherein the output sine wave frequency of the electric circuit is changed according to a wavelength of light emitted from the second fiber,
For any wavelength, the second fiber and the third fiber
The acousto-optic switch characterized by being able to optimize the optical coupling state with the fiber.