JPS6144294B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light control device that is used as a light propagation medium and has active mechanisms 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 has a structure in which a plurality of optical fibers are arranged extremely close to each other by an appropriate distance and optically coupled, and ultrasonic waves of the same frequency or different frequencies are simultaneously transmitted through the plurality of optical fibers. is propagated approximately parallel to the propagation direction of the light wave propagating in the optical fiber, and light waves that satisfy a specific relationship determined from the propagation constants of the ultrasonic waves are selectively propagated to other optical fibers. This constitutes a light control device characterized by the following.

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

First, as an example, a configuration in which two optical fibers are optically coupled will be described. As shown in FIG. 1, two optical fibers 1 and 2 are placed sufficiently close together to provide proper coupling of the respective light waves. That is, the phase matching condition between both optical fibers 1 and 2 is obtained, and the coupling length L is the perfect coupling length L ₀ =
The structure is such that perfect optical coupling can be obtained when π/2C (where C is the coupling coefficient between both optical fibers). An ultrasonic transducer 4 is attached to one end of the optical coupling section 3 between the optical fibers 1 and 2 so that the ultrasonic wave propagates substantially parallel to the propagation direction of the light wave propagating in the optical fiber 1. In the optical coupling section 3, the optical fibers 1 and 2 must be sufficiently close to each other so that appropriate coupling of light waves can be obtained, and the mutual propagation of ultrasonic waves must not be hindered by the coupling of both optical fibers. For this purpose, the optical coupling section 3 must be
It is preferable to configure it as a thin film that has a relatively high refractive index and does not transmit ultrasonic waves.

The ultrasonic transducer 4 can be attached in both ways as shown in FIGS. 2 and 3.

In the system shown in Fig. 2, a common ultrasonic transducer 4A is provided to both optical fibers 1 and 2, and ultrasonic waves of the same frequency are simultaneously applied to both optical fibers. This method uses separate ultrasonic transducers 4B and 4B for both optical fibers 1 and 2.
4C so that ultrasonic waves of different frequencies can be applied to both optical fibers. In either method, the ultrasonic transducers 4A to 4B, 4C are constructed such that a piezoelectric material thin film 5 is sandwiched between transparent electrodes 6 and 7 from both sides. A fiber optical coupling portion 8 is configured adjacent to the transparent electrode 7 .

Now, the method shown in FIG. 2 in which ultrasonic waves of the same frequency are simultaneously applied to both optical fibers 1 and 2 will be explained as an example. Now let k ₁ be the propagation constant of optical fiber 1, k ₂ be the propagation constant of optical fiber 2, and let K be the propagation constant of ultrasonic waves. If k ₁ > k ₂ , then k ₁ -K=k ₂ +K... ...When the condition (1) is satisfied, a phase matching condition is obtained between the optical fibers 1 and 2, and for example, the light transmitted through the optical fiber 1 can be transferred to the optical fiber 2, and the optical fiber 1 can be transferred to the optical fiber 2. The output light Q from the optical fiber 2 can be obtained based on the input light P to the optical fiber 2. Note that when a large number of light waves with different propagation constants are propagating through the optical fiber 1, only light waves with an optical frequency or propagation mode that satisfies the condition of equation (1) can be obtained as the output light Q from the optical fiber 2. It will be done.

Next, when using the method shown in Fig. 3 in which ultrasonic waves of different frequencies are applied to both optical fibers 1 and 2, the relationship k ₁ ±K ₁ = k ₂ ±K ₂ ......(2) is satisfied. Light waves can be coupled between both optical fibers 1, 2.

By exciting ultrasonic waves in the optical fiber in this way, the optical fiber itself can have an active function, thereby configuring a light control device. More specifically, such a light control device can be widely applied as a device for light modulation, branching, mode selection, filter-type branching, coupling, etc.

FIG. 4 shows the ultrasonic transducer 4 of FIG.
This shows an example of an electric circuit for A. In this embodiment, an ultrasonic frequency signal f from an oscillator for generating ultrasonic waves 10 is modulated by a transmission signal S from a transmission signal source 11 by a mixer 12, and the output is transmitted between transparent electrodes 6 and 7 via an amplifier 13. is applied to excite ultrasonic waves of the same frequency between both optical fibers 1 and 2.

Although electric circuits similar to those shown in FIG. 4 can be used for the ultrasonic transducers 4B and 4C shown in FIG. 3, a different embodiment is shown in FIG. In the embodiment of FIG. 5, the transmission signal sources 11A, 11 are supplied as voltage signals, respectively.
The voltage controlled oscillator 1 is activated by the transmission signals S ₁ and S ₂ from B.
4A, 14B to generate ultrasonic frequency signals f ₁ , f ₂ , and apply them to the transparent electrodes of each ultrasonic transducer 4B, 4C via amplifiers 13A, 13B to connect both optical fibers 1, 2. This allows ultrasonic waves of different frequencies to be excited.

Of course, the circuit system shown in FIG. 5 may be applied to the device shown in FIG. 2, or both the circuit systems shown in FIGS. 4 and 5 may be used in combination as appropriate.

In the above embodiment, only the optical coupling between two optical fibers was explained, but a large number of optical fibers each having the above structure may be bundled together as shown in FIG. It is also possible to have a structure in which each of the surrounding optical fibers 21 is optically coupled via the optical coupling part 22, and each of them has the same optical coupling function as described above.

Furthermore, if it is desired to have the function of an optical frequency filter, it is generally desirable to use a single mode optical fiber as a focusing type optical fiber as the optical fiber.

As described above, according to the present invention, ultrasonic waves are excited in a plurality of optical fibers arranged extremely close to each other, and only specific light waves determined from the propagation constants of the light waves propagating in the optical fibers and the ultrasonic waves are selected. Because the signal is transmitted to another optical fiber, unlike conventional methods that use optical couplers,
The efficiency of optical coupling is high, and problems such as complicated optical arrangement and poor workability can be essentially avoided. Furthermore, since the optical fiber has a fine structure, the excitation power for ultrasonic waves is small.
It is clear that this also contributes to improving the efficiency of optical coupling.

[Brief explanation of the drawing]

FIG. 1 is a layout configuration diagram showing one embodiment of the optical control device according to the present invention, FIGS. 2 and 3 are configuration diagrams showing different embodiments of the ultrasonic transducer of FIG. 1, and FIGS. FIG. 5 is a block diagram showing an embodiment of the electric circuit for the ultrasonic transducers shown in FIGS. 2 and 3, respectively, and FIG. 6 is a perspective view of essential parts showing an example of a focusing type optical fiber device. 1, 2, 20, 21...Optical fiber, 3, 22
...Optical coupling part, 4, 4A, 4B, 4C... Ultrasonic transducer, 5... Piezoelectric material thin film, 6, 7
... Transparent electrode, 10 ... Oscillator for generating ultrasonic waves, 1
1, 11A, 11B...transmission signal source, 12...mixer, 14A, 14B...voltage controlled oscillator.

Claims (1)

[Claims] 1. A plurality of optical fibers arranged very close to each other by an appropriate distance so as to be optically coupled to each other;
An ultrasonic transducer attached to the optical fibers excites ultrasonic waves of the same or different frequencies and propagates the ultrasonic waves substantially parallel to the propagation direction of the light waves propagating in the optical fibers. an optical control device that selectively transmits only a specific light wave determined by the propagation constants of the light wave and the ultrasonic wave from an optical fiber to another optical fiber optically coupled to the optical fiber. .