JPS5814115A - Thick film optical circuit - Google Patents

Abstract

PURPOSE:To provide plural optical processing functions to a single thick film optical guide with a good efficiency, and match the coupling with optical fibers by providing a refractive index distribution to the core of the thick film optical guide thereby providing a focusing effect of light to the core. CONSTITUTION:The refractive index distribution of a semicircular columnar core 2 is uniform in the propagation axis direction of light, decreases in proportional to the square of the distance from the central axis of the column 2 within the section perpendicular to the propagation axis and is the same as that of a near parabolic circular columnar lens which is bisected at the plane inclusive of its central axis. Therefore, the ray from an input optical fiber 6 is bent of the optical path by the refractive index distribution of the core 2, repeats total reflection on the surface of a waveguide 1 (once in the figure), focuses again and is made incident to an output optical fiber 11. It is possible to provide plural optical processing functions in the single thick film optical guide by disposing optical function elements such as diffraction grating and filters in every surface position of the waveguide 1 where said ray reflects totally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multimode optical circuit that combines a thick film optical waveguide and a functional element.

Conventionally, optical demultiplexers and directional couplers as shown in FIGS. 1 and 2 have been realized as multimode optical circuits using thick film optical waveguides. However, in the thick-film optical waveguide 1 used there, since the core 2 has a uniform refractive index distribution, the guided light is geometrically and optically uniform at the interface between the core 2 and the cladding 3. The light is totally reflected, and is evenly distributed within the cross section of the core 2.

Therefore, in order to configure an optical circuit using this waveguide, the functional element 4 must be provided at a position perpendicular to the propagation axis of the waveguide, as shown in FIG. like,
It was necessary to utilize the wide portion 5 of the total reflection surface of the core 2. Therefore, in order to construct an optical circuit using multiple functional elements such as an optical integrated circuit, in the case of the configuration shown in Fig. 1, only the end face of the waveguide can be used, and reflective functional elements must be used. 4 can be used, but disadvantages include the difficulty of producing transparent functional elements in Europe, and the need to precisely manufacture a core with a complex shape in the case of the configuration shown in Figure 2. was there.

In addition, since the above-mentioned core does not have a light focusing effect, when considering coupling with a fiber, direct coupling will result in a large coupling loss, and a lens is required to reduce coupling loss. The matching of the coupling with the fiber is
There was a drawback that it was not good.

The present invention aims to solve these drawbacks, and by creating a refractive index distribution in the core of a thick-film optical waveguide and making the core concentrate light, the coupling with the fiber can be matched and the inside of the core can be adjusted. By periodically totally reflecting the light beam propagating on the surface of the thick-film optical waveguide, and arranging various functional elements at each total reflection position, multiple optical processing functions can be implemented within one thick-film waveguide. The drawings will be described in detail below.

FIG. 3 shows the structure of the thick film optical waveguide 1 used in the present invention, in which 2 is a core, 3 is a cladding, and 6.11 is a coupling fiber.

Figure 4 shows the refractive index distribution of a thick film optical waveguide.
The refractive index is uniform in the direction of the light propagation axis, and in a cross section perpendicular to the propagation axis, the refractive index decreases in proportion to the square of the distance from the origin 0. The part B here is the outside world, the part B is the inside of the waveguide, and the part O of the ear axis is the waveguide surface. This refractive index distribution is the same as that obtained by dividing a focusing cylindrical lens into two along a plane including the central axis of the cylinder. Therefore, the shape of the core is approximately semicircular in cross section as shown in FIG. 3, and the refractive index of the exposed surface becomes large even if it is located close to the central axis X.

A thick film optical waveguide having such a refractive index distribution can be manufactured as follows. A multicomponent glass plate of appropriate thickness is prepared, and a tinned film is formed on its surface.

Next, using photolithography technology on the surface,
The tinned film is removed in the shape of a single narrow groove narrower than the width of the core 2. Next, when this glass plate is placed in some kind of salt solution and reacted for a long time, salt diffuses into the multicomponent glass plate from the narrow grooves where the tinned film has been removed due to ion exchange.
This results in the formation of the necessary core refractive index distribution in the multicomponent glass plate. Thereafter, all the tinned films are removed to obtain the desired thick film optical waveguide.

Next, explain the waveguide principle. FIGS. 5(a) to 5(d) show ray trajectories when the thick film optical waveguide 1 is excited by the fiber 6 from the side. Here, (b) is a top view, (c
) shows a cross-sectional view, and (d) shows a side view. Input optical fiber 6
The optical path of the light beam that enters the thick-film optical waveguide 1 is bent by the refractive index distribution within the core 2. When the position of the input optical fiber on the side surface is r, and the core diameter of the thick film optical waveguide is a, the following condition is satisfied: (numerical aperture of input optical fiber) 2 < (-X (numerical aperture of thick film optical waveguide)) 2 In this case, the incident light beam becomes a nearly parallel beam, undergoes total reflection on the angulation on the surface of the thick film optical waveguide 10, and propagates inside the thick film optical waveguide 1 again. From the light incident position from the input optical fiber 6, 0.5P-πa/[
1-The light converges on one point after traveling the distance of (no)zuuma. Therefore, when a fiber is placed at that condensing position, the light enters the fiber as it is. As an example, the input optical fiber has a core diameter/cladding diameter −= 50Iim/G of 1251in.

(2) Using an optical fiber (relative refractive index difference -1 factor), r=0.
9Xa, a=1mm, n=1.602, n241.5
36, no==1.0, θoz14.6°
, θ, ; 49.4°, 0.5P=11.0mm
, 2A: 3.3mm.

2 B:; 1.8im. In addition, in order to establish the ray trajectory shown in FIG. 5, it is desirable that the core diameter a of the thick film optical waveguide is approximately 500 Am or more. This shows the case where light is incident from the surface of the thick film optical waveguide 1. 8 is prism,
9 is a lens. In FIG. 6fa), the light beam emitted from the input optical fiber 6 is expanded into a substantially parallel light beam by a lens 9, passes through a prism 8, and enters the thick film optical waveguide 1. The rest of the waveguiding situation is the same as in the case of FIG. In FIG. 6 (1)), a fiber whose end face is canted obliquely is used as the input optical fiber 6, and after traveling a distance of 0.5P from the input point, it converges again at one point on the surface of the thick-film optical waveguide. Shine. At this time, if the oil tangent of the thick-film optical waveguide is greater than the refractive index of the outside world 7, all or a portion of the light is totally reflected and propagates within the thick-film optical waveguide again.

Figures 5 (a) to (d) and Figure 6 (a) and (b)
) uses the output of the optical fiber as the input light to the thick film optical waveguide, but the same effect can be obtained by placing a light emitting diode or semiconductor laser directly at the input optical fiber 6. . Also, on the output side, since reciprocity is established in the thick film optical waveguide 1, if the direction of the light rays in the thick film optical waveguide 1 is reversed, the output optical fiber or photodiode is placed at the position of the input optical fiber 6. It is obvious that you can also put

In order to construct an optical circuit using a thick film optical waveguide with
The optical functional element may be placed at a position where the light beam is totally reflected as shown in FIGS. 5 and 6.

As examples of thick film optical circuits, FIGS. 7a to 7e show an optical demultiplexer using a diffraction grating 10, and FIGS. 8a to d show an optical demultiplexer using an interference film filter 12. Showing wave equipment. In FIGS. 7 and 8, 10 is a diffraction grating, 11 is an output optical fiber, 12 is an interference film filter, and 13 is a reflection plate.

The configuration of FIG. 7(a) will be explained. A light beam composed of a plurality of (two in this case) wavelengths that enters the core 2 from the input optical fiber 6 is converted into a parallel light beam while propagating through the core 2 and enters the diffraction grating 10 . These light beams consisting of multiple wavelengths are reflected by the diffraction grating 1 ( ) at slightly different angles for each wavelength and propagate through the core 2 again, during which parallel light beams are focused and exit the thick film optical waveguide at the end face. The light rays of each wavelength focus on different positions on the end face as points.

When the output optical fiber 11 is placed at a position where this image is focused, light beams having different wavelengths are coupled to the different output optical fibers 11 and extracted, thereby operating as an optical demultiplexer.

As a calculation example, the core diameter a = 1 mm, and the interval between the output optical fibers 11 is 8071771. The wavelength interval for demultiplexing is 3
0 nm, and the blaze wavelength is 850 nn+, the number of grating grooves of the diffraction grating 10 is approximately 1100/mm, and the grating groove angle is 125°, which are fully achievable values. Although the optical demultiplexer shown in FIG. 7(a) has been described, if the input optical fiber 6 and the output optical fiber 11 are interchanged, the optical path is simply reversed, so that this operates as an optical multiplexer.

7(a), 7(b), and 7(d) use a reflection type diffraction grating 10, and FIGS. 7(C) and 7(d) use a transmission type diffraction grating. The operations in FIGS. 7(b) to 7(e) are almost the same as those in FIG. 7(a).

The interference film filters used in FIGS. 8(a) to 8(e) transmit or reflect light of wavelengths λ1 and λ2 according to their wavelength characteristics. In Figure 8.

Light with a wavelength of λ1 is transmitted, and light with a wavelength of λ2 is reflected. The locus of light transmitted or reflected by the interference film filter is the same as in the case of FIG. Naturally, the optical demultiplexer shown in FIG. 8 also operates as an optical multiplexer.

In addition, in FIGS. 8(a) to (d), the interference film filter 1
If you use a transparent plate instead of 20, it will depend on the branching ratio!
5, it is possible to configure a branching/coupling system for branching/coupling optical power.

Next, FIGS. 9(a) to 9(d) show examples of thick film optical circuits having an ultrasonic element disposed on the thick film optical waveguide surface.

14 is a surface ultrasound generating element, and 15 is a bulk ultrasound generating element.

The operations shown in FIGS. 9(a) and 9(b) will be explained. The light from the input optical fiber 6 becomes a parallel beam and reaches the surface of the thick film waveguide. On the surface, a surface acoustic wave is generated by a surface ultrasound generating element, and this acts as a traveling wave diffraction grating. Then, the light that hits this elastic wave is split at a certain power ratio, reflected in different angular directions (so-called Raman-Nass scattering), and focused at different positions at the end of the thick-film optical waveguide. By adjusting the power and frequency of surface acoustic waves, power branching, reflection angle direction (
In other words, the end face condensing position) can be changed.

This indicates that this optical circuit works as an optical modulator and an optical switch.

The operations in FIGS. 9(C) and 9(d) are also similar to those in FIGS. 9(a) and (1), except that the direction in which the output optical fiber is arranged is different.

FIGS. 9(e) and 9(f) show examples of optical deflectors 1-.

By tilting the direction of propagation of surface acoustic waves at a certain angle with respect to the propagation direction of light, the propagation direction of light can be changed (Bragg reflection). By connecting the elements shown in FIG. 9('e) (in this case, fibers may be used), a matrix optical switch can be constructed. FIGS. 9(g) and (11) are examples using an ultrasonic generating element 15 that generates bulk elastic waves.
This method uses Ramannus scattering. If a thick film optical waveguide with a length of 1.0P is used, the light will be focused at a position of 0.5P, so if an ultrasonic elastic wave is made incident at this position,
Light travels through a wider angle than before without the incidence of elastic waves. Therefore, the numerical aperture of incidence on the output optical fiber 11 changes at the focal point of the end face of the thick-film optical waveguide. Therefore, this optical circuit works as an input numerical aperture variable device. This can be applied to optical modulators, mode modulators, optical speckle cancelers, etc.

FIG. 10 shows an example in which a diffraction grating 16 is placed obliquely with respect to the light propagation direction on the surface of a thick film optical waveguide. This is an example in which a layer (for example, liquid crystal) is attached to the surface of a thick film optical waveguide. Due to the external field θ
. 〉θ, -5in-1(1-(-!l!-Q-)2]'
The light 2 escapes to the film layer 18 without being totally reflected at the surface. Therefore, it operates as an optical switch.

In FIG. 12, a Parctz crystal 18 exhibiting various optical properties is placed on the surface.If the crystal does not need to be very thick, it can operate as a small optical circuit element that does not require an input/output coupling lens.

Additionally, if a resistive film is attached to the surface, it can also function as a fixed attenuator.

It is also possible to realize an optical integrated circuit having multifunctional characteristics by cascading several stages of the above-mentioned optical circuits or connecting them in a plane.

As explained above, by giving an appropriate distribution to the refractive index of the core of a thick-film optical waveguide, the light beam propagating inside the thick-film optical waveguide is periodically totally reflected on its surface, and various By arranging optical functional elements, it is easy to provide multiple optical processing functions to a single thick-film optical waveguide, and since the thick-film optical waveguide itself has focusing properties, it is possible to easily connect input and output to the thick-film optical waveguide. An optical system such as a lens is not required in the coupling system with the optical fiber. Therefore, it must be small and have low loss.
It has advantages such as high reliability and low cost because each circuit component can be easily adjusted.

Further, the thick film optical waveguide itself also has the advantage that it can be manufactured in large quantities and at low cost by ion exchange of multi-component glass.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an optical demultiplexer using a conventional thick-film optical waveguide, Fig. 2 is a block diagram of a directional coupler using a conventional thick-film optical waveguide, and Fig. 3 is a block diagram of a directional coupler using the conventional thick-film optical waveguide. Fig. 4 is a diagram showing the refractive index distribution of the thick film optical waveguide according to the present invention, and Fig. 5 (a) to (d) show the optical path of the thick film optical waveguide according to the present invention. Figures 6(a) to 6(1) are diagrams showing a method of coupling the thick film optical waveguide with the input light beam according to the present invention.
Figures (a) to (e) are configuration diagrams of the optical multiplexer/optical demultiplexer according to the present invention, and Figures 8 (a) to (d) are other configurations of the optical multiplexer/optical demultiplexer according to the present invention. 9(a) to 9(h) show the optical modulator, optical switch, optical polarizer, N, and Ai according to the present invention.
A block diagram of a transformer, FIG. 10 is a block diagram of an optical branching circuit according to the present invention, FIG. 11 is a block diagram of an optical switch according to the present invention, and FIG. 12 is a block diagram of a lens-free optical crystal optical circuit according to the present invention. It is a diagram. ■... Thick film optical waveguide, 2... Core, 3... Clad, 4... Functional element, 5... Total reflection Wide area, 6... Input optical fiber, 7... Outside world, 8... Prism, 9...
Diffraction grating, 11...
... Output optical fiber, 12 ... Interference film filter, 13 ... Reflection plate, 14.15 ...
・Ultrasonic generation element, 16... Diffraction grating,
17...Refractive index change film layer, 18... Bulk optical crystal. Patent Applicant Nippon Telegraph and Telephone Public Corporation Patent Application Agent Megumi Yamamoto - Ll1 Figure 79122 Procedural Amendment (Spontaneous) January 27, 1980 Commissioner of the Patent Office Shima 1) Haruki Tono 1, Display of the Case 1982 Patent Application No. 110872 2, Title of Invention Thick Film Optical Circuit 3, Relationship with the Amendment Case Name of Patent Applicant (422) Nippon Telegraph and Telephone Public Corporation Specification 1, Page 9, Line 5 - Page 9 of the same The 12th line [- is shown. -Song: Same as IMJ in Figure 7. 8-1 is corrected as shown below. I'm talking. In FIG. 7(1)), the number of grating grooves and the grating groove angle of the diffraction grating 10 are set to values different from those used in FIG. 7(a), and the light rays incident on the diffraction grating 10 are It has the advantage of being compact because the input and output optical fibers can be installed on the same end face of the thick film optical waveguide because the angle of reflection is set in the same direction as the incident light beam. FIG. 7(C) shows λ1. which is also input to the input optical fiber 6. λ
The light beam consisting of two wavelengths is converted into parallel light beam by lens 9,
This is made incident on a transmission type diffraction grating 10 and transmitted at different angles for each wavelength.By this, each wavelength is focused at a different position on the end face of the thick film optical waveguide, and each wavelength is separated and outputted from a different output optical fiber 11. Take it out. The characteristics of this configuration are
The lens 9 converts the light rays incident from the input optical fiber 6 into any one of parallel rays, diverging rays, and convergent rays, and converges the light rays through the thick-film optical waveguide and couples them to the output optical fiber 11. The numerical aperture of the light beam coming out of the prism 8 and the numerical aperture of the core 2 that passes through the prism 8 and enters the core 2 can be made to almost match,
The light beam emitted from the input optical fiber 6 can be efficiently coupled to the thick film waveguide. Therefore, there is an advantage that the insertion loss of this thick film optical circuit can be reduced. As the lens used here, a lens combination consisting of a convergent cylindrical lens, a spherical lens, and an aspherical lens can be considered. 7th
FIG. 6(d) shows an example constructed using the method of coupling the thick film waveguide and the input/output optical fiber shown in FIG. 6(b). The operating principle is almost the same as the configuration shown in FIGS. 7(a) and 7(b). FIG. 7 (el shows two thick-film waveguides of the present invention installed through a transmission type diffraction grating so that their cores 2 coincide.The light rays emitted from the input source fiber 6 are The core 2 of the thick film waveguide converts the beam into almost parallel light, which passes through the transmission type diffraction grating 10 at different angles for each wavelength. Focus at different positions on the end face and output from different output optical fibers 11 for each wavelength.In the configuration shown in Fig. 7, the wavelength λ1
Although the case of separating two wavelengths, λ and λ2, has been described, it is also possible to separate two or more wavelengths by installing the necessary number of output optical fibers. The interference film filters used in FIGS. 8(a) to (1) transmit or reflect light with wavelengths of λ1 and λ2 according to their wavelength characteristics. In FIG.
It transmits light with a wavelength of λ2 and reflects light with a wavelength of λ2. FIG. 8(a) shows the first grid 10 of FIG. 7(21).
0, an interference film filter 12, a prism 8, and a fouling plate 1;
3. The light beam emitted from the input optical fiber 6 is converted into a nearly parallel light beam by the core 2, and the incident angle θ is determined from the refractive index distribution of the core 2. and enters the interference film filter 12. The light beam with wavelength λ2 has an incident angle θ here. The light is reflected in the same angular direction, converged by the core 2, focused on the end face of the thick-film optical waveguide, and output from the output optical fiber 11. On the other hand, the light beam having the wavelength λ1 that has passed through the interference film filter 12 (1 - passed through the prism 8 and has the reflection plate 1
3 and passes through the circular interference film filter 12 and passes through the core 2.
The light is converged and output from the output optical fiber 11. In this operation, it is desirable to set the wavelength λ to the same value as the incident angle (θ0) when the light ray enters the interference film filter 12 for the second time.The reason is that the wavelength characteristics of the interference film filter This is because the light beam with wavelength λ and the light beam with wavelength λ2 are reflected and enter the core 2 at the same angle of incidence θ.However, they are focused at different positions on the end face of the thick-film optical waveguide. The reason for this connection is that the two light rays enter from different positions on the core 2.
1)) In the configuration shown in FIG. 8(a), a light beam of wavelength λ is connected to the output optical fiber 1 using a lens as in FIG. 7(C).
1, and the operations, effects, and types of lenses used are the same as in each case. FIG. 8(C) shows the diffraction grating 10 in FIG. 7(e).
is replaced with an interference film filter 12, and the basic configuration is the same as that shown in FIG. 7(e). In addition, the operating principle and the trajectory of the light beam are the same as those in Fig. 7(e) and Fig. 8(bl). Fig. 8(d) shows the interference film filter in place of the diffraction grating 100 in Fig. 12. Prism 8
, using a reflecting plate 13, and the operation and trajectory of the light beam are the same as the corresponding parts in FIG. 7(di) and FIG. 8(a). (4) FIGS. 8(a)-( In d), interference film filters are bandpass filters that transmit a single wavelength and reflect other wavelengths, short wavelength pass filters that transmit short wavelengths and reflect long wavelengths, and long wavelength pass filters that have the opposite characteristics. Filters and combination filters that are a combination of these can be used.Also, as a reflection plate, a total reflection surface, a metal vapor deposited surface, and an interference film filter having wavelength characteristics that reflect all wavelengths of light rays incident on the reflection plate can be used. Can be used. No. 8” (5)

Claims (1)

[Claims] A thick film optical waveguide having a flat plate structure having a core portion in which at least a portion of light guided is exposed to the outside, and a rad portion having a uniform refractive index that substantially surrounds the core portion, and an exposed portion i of the core portion.
In a thick film optical circuit having an active functional element or a passive functional element to be produced, and a means for coupling an input/output optical fiber to the thick film optical waveguide, the refractive index distribution of the core portion affects the propagation of the guided light ray. In a cross section that is uniform in the axial direction and perpendicular to the propagation axis, it is approximately 2 mm away from a given point on the surface of the thick film waveguide.
1. A thick film optical circuit characterized in that the active functional element or the passive functional element is formed at a period determined by the refractive index distribution of the core portion.