JPS6144295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light control device used as a light propagator having active functions such as light modulation and light branching.

Conventionally, when modulating or branching light propagating through an optical fiber, an optical coupler has been used to couple the optical fiber with another waveguide. Since this type of optical coupler is required to have high optical coupling efficiency, the device must be sophisticated and complicated. For example, the thickness of thin-film optical waveguides used for modulating and branching light is only a few microns, and requirements for alignment and end face flatness for optical coupling are extremely strict, making practical complications and work difficult. There are many problems in terms of sexuality.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical control device that eliminates the above-mentioned disadvantages by giving an active function to the optical fiber itself, which conventionally only played the role of propagating light.

In order to achieve this object, the present invention provides an ultrasonic transducer that is disposed on the end face of an optical fiber or on one end face of a joint between optical fibers, and arranged substantially parallel to the propagation direction of light waves propagating in the optical fiber. By propagating ultrasonic waves into an optical fiber and arranging another optical fiber very close to the ultrasonic propagation part by a suitable distance, one optical fiber can be connected to the other optical fiber according to the ultrasonic signal. It is designed to selectively optically couple the two.

Hereinafter, the present invention will be explained in further detail with reference to embodiments shown in the drawings.

FIG. 1 shows an example of a structure in which an ultrasonic transducer 2 is attached to the end face of an optical fiber 1.
The ultrasonic transducer 2 consists of a piezoelectric material layer 3 and transparent electrodes 4 and 5 placed on both sides so as to sandwich this layer. Piezoelectric material layer 3 is a ZnO thin film,
It can be composed of LiNbO ₃ crystal flakes or the like. ZnO does not have very good light transmittance, but 1~
A thin film of about 3 microns can be used practically without any problem. The transparent conductive layers 4 and 5 only need to be transparent to the light used, and their materials include Au, SnO ₂ ,
In ₂ O ₃ etc. can be used.

Figure 2 shows a transmission type ultrasonic transducer 12.
This shows an example of a structure in which the optical fibers 11 are arranged to surround the optical fiber 11. This ultrasonic transducer 12 is composed of a piezoelectric cylinder 13 made of LiNbO ₃ crystal and annular electrodes 14 and 15 arranged on both end faces of the piezoelectric cylinder 13 . In this case, the annular electrode 14,
Electrical power is applied to the piezoelectric cylinder 13 via the piezoelectric cylinder 15 to generate ultrasonic waves, which are propagated through the optical fiber 11 substantially parallel to the propagation direction of the light waves propagating therein. The piezoelectric cylinder 13 and the optical fiber 11 must be bonded with structural care so that ultrasonic waves can be efficiently transmitted between them, that is, so that acoustic impedance can be matched. Of course, it goes without saying that the structure between the optical fiber 11 and the piezoelectric cylinder 13 must be configured so that light propagation can be carried out efficiently.

As the optical fibers 1 to 11, those having a core diameter of 10 to 150 microns are usually used. Optical fibers include a graft type (refractive index stepped type), a graduated index type (focusing type), etc.
In terms of mode selectivity, fibers can be divided into single mode fibers and multimode fibers. Although any type of optical fiber may be used in the device of the present invention depending on the purpose, it is preferable to use a single mode fiber or graded-integrated type fiber in order to provide the function of an optical frequency filter.

FIG. 3 shows an embodiment of the overall configuration of the device of the present invention. Ultrasonic transducer 2
The main optical fiber 21 to which 0 is attached and the auxiliary optical fiber 22 to which it is not attached are very close to each other within the coupling length L, and the optical fiber is arranged so that it can be transmitted well, but it is difficult to transmit ultrasonic waves. The ultrasonic transducer 20 is positioned and arranged so that the ultrasonic wave U excited when electric energy is supplied from the ultrasonic oscillator 24 to the transducer 20 through both electrodes propagates at least to the area of the coupling portion 23. be done.

It is assumed that input light P is incident on the main optical fiber 21 in FIG. 3 from the side opposite to the ultrasonic transducer 20 with the coupling portion 23 as the center. Here, the ultrasonic transducer 20 propagates the ultrasonic wave into the main optical fiber 21 in a direction facing the input light P. At that time, the main optical fiber 21
In the coupling part 23 between the optical fiber 22 and the sub optical fiber 22, the propagation constant k of the optical wave changes due to the interaction between the optical wave and the ultrasonic wave.
is k=k ₁ ±K (1). However, k ₁ is the propagation constant of the main optical fiber 21, and K is the propagation constant of the ultrasonic wave. Therefore, when the propagation constant k ₂ of the auxiliary optical fiber 22 satisfies k ₂ =k (2), a phase matching condition is obtained between both optical fibers 21 and 22, and the coupling length L becomes the perfect coupling length. L ₀ =
When π/2c (where c is the coupling constant between both optical fibers), all the light waves input to the main optical fiber 21 are transmitted to the sub-light 22, and the output light Q ₂ is output from the output end of the sub-optical fiber 22. is output as
According to the above principle, by changing the output of the ultrasonic wave or changing its frequency, the output light Q ₂ of the sub optical fiber 22 is transmitted to the sub optical fiber.
can be changed arbitrarily.

To change the ultrasonic output according to the transmission signal, an electric circuit like the one shown in Figure 4 can be used, and to change the ultrasonic frequency according to the transmission signal, an electric circuit like the one shown in Figure 5 can be used. You can use

In the control shown in FIG. 4, the ultrasonic output signal of the oscillator 30 is modulated by the mixer 32 by the transmission signal from the transmission signal generator 31, and the output is applied to the ultrasonic transducer 20 via the amplifier 33 to generate ultrasonic waves. Change the output of sound waves. Further, in the circuit shown in FIG. 5, the output frequency of the voltage controlled oscillator 34 is changed by the transmission signal from the transmission signal generator 31, and the ultrasonic excitation frequency of the ultrasonic transducer 20 is changed via the amplifier 33.

When light waves of many modes or frequencies are propagating in the main optical fiber 21, only light waves of propagation modes or frequencies that satisfy the condition of equation (2) can be transmitted to the sub optical fiber 22. Also,
By configuring the ultrasonic transducer 20 to be a light transmission type, the main optical fiber 21 can be used as a main line for transmitting light waves (carrier waves) in many modes, and the sub optical fiber 22 can be used to transmit only specific light waves. can be used to selectively transmit. That is, the device of the present invention can be used as (a) a modulation and branching device for a single light wave, and (b) a mode selection device that extracts only a light wave of a specific frequency or propagation mode from a large number of light waves.

As described above, according to the present invention, the optical control having the functions (a) and (b) above is achieved by the interaction between the ultrasonic waves excited in the main optical fiber and the light waves propagating in the main optical fiber. Therefore, unlike conventional methods that use optical couplers, optical coupling efficiency is high, and there is no need to worry about the complexity of optical arrangement and poor workability. The problem can essentially be avoided. Note that since the optical fiber has a fine structure, the excitation power for ultrasonic waves is small, and it is clear that this also contributes to improving the efficiency of optical coupling.

[Brief explanation of the drawing]

1 and 2 are side views and perspective views showing different embodiments of the attachment configuration of the ultrasonic transducer to the optical fiber, and FIG. 3 is a layout diagram showing one embodiment of the optical control device according to the present invention. , Figures 4 and 5
The figure is a block diagram showing different embodiments of electrical circuitry for an ultrasound transducer. 20... Ultrasonic transducer, 21... Main optical fiber, 22... Sub optical fiber, 23... Coupling unit, 24... Oscillator.

Claims (1)

[Claims] 1 a pair of optical fibers placed very close to each other by an appropriate distance so that they can be optically coupled to each other;
The ultrasonic wave is placed on one end face of the pair of optical fibers or on one end face of the joint between the two optical fibers, and is applied to the optical fiber in substantially parallel to the propagation direction of the light wave propagating in the one optical fiber. Equipped with an ultrasonic transducer that propagates
An optical control device characterized in that the one optical fiber and the other optical fiber are selectively optically coupled in accordance with an ultrasonic signal.