JPS6032028A - Light control type optical switch - Google Patents

Abstract

PURPOSE:To improve the branching ratio and dimming ratio of the titled optical switch by forming PLZT thin film waveguides controlling waveguide light by using electric power generated by a photovoltaic film and transmitting the opti- cal wave reflected on a full reflection surface of a prism arranged on the waveguides to one waveguide. CONSTITUTION:An optical wave l5 reflected by the full reflection surface 41 formed by adhering the prism to the PLZT thin film waveguides 12, 13 is transmitted to the waveguide 12 by a TIR type switch constituted of the waveguides 12, 13 controlling the waveguide light by using electric power generated by the photovoltaic film 16. The optical wave l5 is sent to a taper-like gap 31 and then sent to a thin film 11 as evanescent light and the evanescent light is transmitted to a direction 42. Since the coupling method brings the prism 21 into contact with the thin film 11 at its thick point 43, a break or the like is not generated in the prism 21, so that proper contact is always obtained and high efficiency of transmission is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light-controlled optical switch, and more particularly to the structure of a prism-coupled light-controlled optical switch.

Conventional configurations and their problems Recently, optoelectronic components have become increasingly dense and sophisticated. In particular, optical circuit components using optical waveguides are attracting attention as a way to achieve high density and high reliability of components. Particularly in optical control systems, it goes without saying that optical switches that can switch an optical transmission line to any other optical transmission line are required everywhere, and even in these optical switches, there are mainly conventional moving parts. In place of mechanical optical switches, a solid-state optical circuit-based waveguide switch is desired. Various proposals and attempts have been made regarding optical waveguide type optical switches at the research level, and improvements in performance are being realized one after another. However, when these optical switches are evaluated from the viewpoint of being introduced into an actual optical system, their performance is insufficient. Further, in driving the above-mentioned optical switch, since the electro-optical effect is utilized, a power supply line is required to apply a voltage to the optical switch section.

On the other hand, switching optical transmission lines in flammable and explosive atmospheres is an essential technical element as one of the specific methods for realizing optical transmission and control in adverse environments for use in optical measurement and control systems, etc. be. In such an atmosphere, it is not desirable from a safety point of view to install a power supply line for voltage application, even though the voltage is low.

Based on the above background, the inventors have proposed a light-controlled optical switch shown in the main part of FIG. 1, which does not require a power supply line and can be driven only by supplying light through an optical fiber.

To explain the optically controlled optical switch according to the diagram, a PLZT thin film 1 with a large electro-optic effect is formed on a substrate 10.
A main waveguide 12 is formed in the main waveguide 1, and a sub-waveguide 13 connected to the main waveguide 12 is formed in the control electrode 14.14'.
constitutes a TIR type optical switch provided on the connection part 16,
A control optical fiber 1 is connected to a photovoltaic film 16 provided on the same substrate.
7 to generate a voltage and apply the voltage to the electrically coupled control electrodes 14, 14' to lower the refractive index of the waveguide under the electrode gap and form a low refractive index layer, The guided light propagating through the waveguide 12 is totally reflected at the interface with the low refractive index layer to change the propagation direction of the guided light. The specific operation is, for example, focused on deflecting the guided light traveling from 21° C. to 2° C. from 21° C. to 25° C. by applying a voltage. When implemented in a system, this optically controlled optical switch alone cannot be operated, so the optical fibers 18 and 19 must be coupled with an optical waveguide to form a fiber-coupled optically controlled optical switch.

However, with the above configuration, it is difficult to efficiently couple the transmitted light of the optical fiber 18 to the optical waveguide 12.

In order to satisfy this requirement, the cross-sectional shape of the optical waveguide 12 and the cross-sectional shape of the optical fiber 18 must be approximately matched, and the centers of the cross sections must be matched with high accuracy. Especially PLZ
Since the T-based thin film waveguide has a film thickness of 0.1 to 1 μm, even if a single mode fiber with a core diameter of 6 μm is used, the coupling loss is 30 dB or more, which is a practical problem. Furthermore, in the case of coupling from the optical fiber 18, it is usually difficult to couple only the guided light of a desired mode, and when the guided light of various modes propagates in the waveguide, the branching ratio of the TIR optical switch and There was a drawback that the extinction ratio decreased.

For this reason, a prism coupling shown in FIG. 2 can be considered to achieve high efficiency coupling even in a thin thin film waveguide.

Specifically, a prism 21 is provided on the waveguide 12° 13 to couple the transmitted light 24 incident on the prism 21 from the optical fiber 18 to the optical waveguide 12, and the prism 21
Due to the mode selectivity, only the guided light of the desired mode is excited, and the branching ratio and extinction ratio are improved, resulting in a good optically controlled optical switch. However, in Fig. 2, □ actually indicates that when the guided light passes through the right-angled ridge line 21' of the prism 21, if there is any disturbance due to a chip or the like in the right-angled ridge line 21', the guided light will be scattered and the mode will be converted. This resulted in the coupling efficiency not being very high, and the branching ratio and extinction ratio also decreased, making it impossible to put it into practical use.

In order to eliminate these drawbacks, the prism 21. As shown in FIG. 3, the air gear 31 between the thin films 11 was considered to have a cross-shaped shape.

This method eliminates the drawbacks of the above-mentioned coupling methods and has a very high ideal maximum coupling efficiency of 96%.

However, as a result of detailed study of this method, the present inventors determined that it has the following drawbacks and is not practical.

(1) Since the distance between the contact point 32 with the thin film 11 and the light transmission point 33 becomes large, surface accuracy of the substrate is extremely required.

(2) Since the point of contact 32 with the thin film is the front edge of the prism 21, a large pressure is applied to the extremely thin point of the prism wall, damaging the prism and making it impossible to obtain good contact.

The present inventors investigated various methods and found a highly efficient optically controlled optical switch structure by improving the structure between the fiber waveguides.

Purpose of the Invention The purpose of the present invention is to improve the coupling structure with the optical 7 fiber, improve the coupling efficiency, prevent mode conversion, and improve the branching ratio and extinction ratio of the TIR type optical switch section, thereby producing a light beam with excellent characteristics. A controlled optical switch is provided.

Structure of the Invention The optically controlled optical switch of the present invention is a TIR type optical switch composed of a PLZT thin film waveguide that controls guided light using electric power generated by a photovoltaic film, and a prism is closely attached on the waveguide. The optical wave reflected by the total reflection surface within the fixed prism is transmitted to the waveguide.

Description of examples The present invention will be explained in detail below based on Examples.

FIG. 4(a) is a perspective view of a light-controlled optical switch according to an embodiment of the present invention, and the same parts as in FIGS. 1 and 2 are given the same numbers. FIG. 5B is a sectional view of the main part of the light input section of FIG. 1A, and the gradient index lens is omitted. In the case of FIG. 4, a right angle prism is used. In the same figures (-) and (b), the optically controlled optical switch is a TIR type optical switch composed of PLZT thin film waveguides 12 and 13 that control guided light using the power generated by the photovoltaic film 16. A prism 21 is placed in close contact with the waveguide 12, 13 so that the light wave Q5 reflected by the total reflection surface 41 within the prism 21 is transmitted to the waveguide 12. In this configuration, the light wave transmitted through the optical fiber 18 is sent toward the total reflection surface 41, and the light wave 25 is reflected by the total reflection surface 41, sent to the tapered gap 31, becomes evanescent light, and is sent into the thin film 11. , the light is transmitted in direction 42.

As can be seen from FIG. 4, in this bonding method, since the thickest point 43 of the prism 21 is in contact with the thin film 11, no chips or the like occur on the prism 21, and good contact is always obtained. As a result, a good tapered air gap 31 is formed, resulting in extremely good transmission efficiency.

Furthermore, since it is possible to reduce the distance between the contact point 43 and the point 33 where the light wave is transmitted into the film, good coupling can be obtained even if the surface precision of the substrate is poor.

Note that the prism in this example used in the present invention is the second prism.
This prism is completely different from the prism shown in FIGS. This is because the prisms used in FIGS. 2 and 3 do not require the total reflection surface 41, so there is no problem in use regardless of the surface precision. However, the accuracy of the total reflection surface 41 of the prism 21 used in the present invention has extremely important significance as described above. Also, triangular prism 21
may be a shape cut along the group of broken lines 44 in FIG. 4 (daytime).

In this way, a prism having at least one reflective surface is used as a light coupling prism, and these reflective surfaces are used to connect the contact point 43 between the film and the prism to the light transmission point,
33 can be made smaller.

Therefore, (1) the required surface precision of the substrate is much more relaxed than in the past. (2) Optical member (prism)
Since sufficient contact between the optical member and the thin film can be made without adding a large burden to the optical member, and an ideal tapered air gap is formed, highly efficient coupling can be obtained.

This brings about great advantages such as:

In addition, as shown in Figure 4, if the coupling directions of the optical fibers are made to intersect with each other as shown in Figure 4(a), the system can be constructed with the same lengthwise dimensions as the optically controlled optical switch of the fiber direct coupling type. If it is incorporated into the system, it can be downsized. Furthermore, since it can be used even with multimode fibers, it has the advantage of being easy to handle and having high reliability.

Next, another embodiment of the present invention is shown in FIG. In FIG. 6, a hexagonal prism is used as the prism 21 to achieve even better coupling. That is, the triangular prism 21
In this case, a gradient index lens 4 shown in FIG. 4(a) is used.
6 (omitted in FIG. 5) and the prism 21 are performed at an angle, and since the prism surface and the lens surface are not parallel, it is difficult to fix and the joining is unstable.

This problem can be solved by using a pentagonal prism as shown in FIG. 6, in which the prism surface and lens surface can be arranged almost parallel to each other, and the gradient index lens 46 can also be positioned perpendicularly to the substrate 1o. Therefore, it is easy to fix, and a strong and stable joint can be obtained. By using such a hexagonal prism, it is possible to form an even better optical waveguide element.

In FIG. 6, the thin film 11 has a refractive index of 2.6° and a film thickness of 4.
Assuming that the substrate 10 has a refractive index of 1.78 and the prism has a refractive index of 3.31, the acute angle between the reflective surface 41 and the dielectric thin film 11 is 66° (the angle inside the prism 21 is 115°). becomes. Of course, if the above-mentioned conditions are changed - this angle will also change 0 By the way, a member with a refractive index of 1.6 to 3.6 is used as the prism 21, and the dielectric thin film 11
When a material with a refractive index of 1.6 to 3.0 is used as the prism, one corner of the prism described above takes an angle of 126° to 105°, so that light can be effectively transmitted within the thin film. Note that the reflective surface 41. The photoelectrically transparent surface facing the thin film 11 is optically polished. By using such a hexagonal prism, it is possible to form a good optical thin film element.

In all of the above examples, total reflection conditions are used for the total reflection surface 41 in the prism 21, but the present invention can also be carried out by applying a reflective material to a specific surface. Also,
In FIGS. 4(b) and 6, we have described the optical input section that transmits light to the thin film, but conversely, when the light is extracted from the thin film 11 to the prism 21, it goes through the reverse process in the same way and is connected to the fiber 19. In the light output part (the right part of FIG. 4(a)) which outputs light waves, the light waves travel along a path opposite to that of the light input part.

Further, the present inventors further investigated the structure of the prism coupling and found that it is effective as a light-controlled optical switch if a gradient index lens is provided between the optical fiber and the prism. That is, the transmitted light of the optical fiber naturally spreads while passing through a prism, and for example, when passing through a right-angled prism with a minus side of 6 g, the beam diameter of the transmitted light reaches the order of a square.

The width of the waveguide is usually 3 to 60 μm, and the coupling efficiency is reduced due to natural expansion. Therefore, Fig. 4 (
As shown in a), when the gradient index lens 46 is fixedly installed between the optical fiber 18 and the prism 21, the coupling efficiency is improved. In particular, the light transmission point 33 in the prism 21
It has been confirmed that it is particularly good to form a real image of the light output end of the optical fiber 18.

Furthermore, the present inventors have found that the coupling efficiency can be further improved by selecting the type of optical fiber. That is, it has been found that it is better to use a single mode fiber as the optical fiber 18 and a multimode fiber as the optical fiber 19. When a single-mode fiber is used as the input optical fiber 18, the light wave is normally transmitted through a single-mode core diameter of 6 to 10 μm, so it is finely focused and guided by the gradient index lens 46. It was confirmed that it was possible to focus the image almost on the wave path, and that the coupling efficiency was high. Further, when a multimode fiber was used as the output optical fiber 19, the output light from the waveguide having a width of 3 to 50 μm could be efficiently coupled with the gradient index lens.

Effects of the Invention As described above, the optically controlled optical switch according to the present invention can achieve high efficiency and miniaturization that could not be achieved with conventional structures, and has great practical value.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the structure of a conventional optically controlled optical switch, Figure 2 is a perspective view showing another structure of a conventional optically controlled optical switch, and Figure 3 is an optically controlled type switch according to Figure 2. 4(-) and 4(b) are perspective views showing the structure of a light-controlled optical switch according to an embodiment of the present invention; FIG. 6 is a sectional view showing the main structure of a light-controlled optical switch according to an embodiment of the present invention. 11...PLZT thin film, 12...Main waveguide, 13...Sub waveguide, 14...Control electrode, 16...Photovoltaic force Membrane, 17...
Control optical fiber, 18... Input optical fiber, 1
9... Output optical fiber, 21... Prism, 31... Air gap, 33...
...Transmission point, 41...Reflection surface.

Claims (3)

[Claims] (1) A PLZT thin film waveguide is formed to control guided light using the power generated by the photovoltaic film, a prism is installed on the waveguide, and the light wave reflected by the total reflection surface within the prism is A light-controlled optical switch characterized in that the light is transmitted through the waveguide. (2) Light control according to claim 1, characterized in that a light wave transmitted by an optical fiber is made incident on a prism, and a gradient index lens is provided between the optical fiber and the prism. type optical switch. (3) The optically controlled optical switch according to claim 1, wherein a single mode fiber is used for inputting light waves to the prism, and a multimode fiber is used for outputting light waves.