JPS5946602A - Flat plate prism - Google Patents

Abstract

PURPOSE:To attain simplification in positioning and a reduction in thickness and size and to enable the control of dividing characteristics according to diffusion conditions by forming prisms in a transparent substrate by an ion diffusion method and forming and averaging refractive index distributions. CONSTITUTION:In figure, 12 is a flat plate microprism, 11, 13 are flat plate microlenses by a refractive index distribution, having respectively functions as a lens for input and a lens for output. 10 is an optical fiber for input and 14, 15, 16 are optical fibers for output. The focal length (f) of the lens 11 and the thickness of the substrate are beforehand made coincident in order to bring the end face of the fiber on a transmission side into tight contact with the lens 11 taking charge of the function as a lens for input. The same holds true for the lens 13 for output. An embodiment of the production method consists of masking the side face of an isotropic glass block 20 with an Au-Cr film or Ti film 21, putting a molten salt 23 of the metallic ions to be diffused in a vessel 22 of ceramics, etc., heating the same up to the molten state, dipping said glass block therein and performing a diffusion treatment until the intended profile of the refractive index is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flat prism having a light dispersion function using a distributed refractive index formed in a transparent substrate. More specifically, the present invention relates to a flat prism characterized in that the transparent substrate is made of synthetic resin or inorganic glass, and a refractive index distribution is formed in the transparent substrate mainly by a diffusion method.

There are two types of prisms; one is for the function of reflecting a beam of light to change its direction, and the other is for spectroscopy, which uses dispersion to separate light into monochromatic light.
A transparent body with two or more optical planes, at least one set of which is not even approximately parallel. Therefore, most common shapes are triangular prisms, which are important as basic optical components.

The present invention aims to provide a micro flat prism with a transparent substrate having a refractive index distribution, in contrast to conventional triangular prisms, in response to the recent demands for thinner and smaller optical devices for optical communications. .

One of the optical transmission systems is the wavelength division multiplexing transmission system. This transmission method multiplexes light of a plurality of different wavelengths, and after transmission, separates the light of each wavelength using an optical demultiplexer, and receives each light.

The optical demultiplexer required for this transmission method has been proposed and researched by combining existing optical components (for example, prisms and lenses).

FIG. 1 is a diagram showing an example of a conventional prism optical demultiplexer. (1) is an input optical fiber, (2) is an input lens,
(3) is a prism, (4) is an output lens, (5), (
6) and (7) are output optical fibers.

An example of multiplexing three channels (wavelengths λ1, λ2, λ3) will be described. The end face of the input optical fiber (1) is placed at the focal point f of the input lens (2). Lights with wavelengths λ1, λ2, and λ3 sent from the transmitting side to the input fiber (1) are output from the input optical fiber (1), and are converted into parallel light by the input lens (2), which then passes through the prism (3). to go into.

The light emitted from the prism (3) passes through the output lens (4) due to the dispersion of the prism, and the lights with wavelengths λ1, λ2, and λ3 are focused at different positions on the focal plane f of the output lens (4). be illuminated. Optical demultiplexing is performed by arranging optical fibers (5), (6), and (7) at positions where the lights of wavelengths λ1, λ2, and λ3 are focused.

Since the optical demultiplexer as explained above is a combination of individual optical components, there are problems such as difficulty in positioning accuracy, lack of stability against vibration of the optical thread, and difficulty in making it smaller and thinner. There are drawbacks.

In order to eliminate these drawbacks, the present invention forms a refractive index distribution in a transparent substrate and flattens the prism to simplify alignment, make it thinner and smaller, and at the same time, optical fibers can be attached as needed. A flat microlens was placed on the end face and brought into close contact with the end face to ensure stability against mechanical vibrations.

This will be explained below with reference to the drawings. FIG. 2 is a sectional view of one embodiment of the present invention. (12) is a flat plate microprism, (1
1) and (13) are flat plate microlenses with refractive index distribution, which function as input lenses and output lenses, respectively. (10) is an input optical fiber, (14), (15),
(16) is an output optical fiber. The moving body function is the same as described in the explanation of FIG. In order to bring the end face of the input fiber (10) on the transmitting side into close contact with the flat plate microlens (11) that shares the function of the input lens, the focal length f of the flat plate microlens (11) and the substrate thickness are made to match in advance. It is necessary to keep The same applies to the flat microlens (13) which shares the function of the output lens.

Note that instead of the flat microlenses (11) and (13), it is also possible to use a rod-shaped so-called selfoc lens.

Some application examples of optical devices using flat prisms have been described above, and now a method for manufacturing them will be described.

FIG. 3(a) shows an embodiment of the method for manufacturing a flat prism according to the present invention.

The side surfaces of the isotropic glass block (20) are masked with an Au-Cr film or a Ti film (21), and a ceramic container (
A molten salt (23) of metal ions to be diffused is placed in 22), the temperature is raised to a molten state, and the glass block is immersed for diffusion treatment until the desired refractive index distribution profile is obtained.

A specific example is soda-based BK on a glass block.
-7, thallium sulfate was used as the diffusion molten salt, and Au-Cr films were used as masks on the four peripheral sides of the glass block.55
When naturally diffused at 0° C. for about 160 hours, a glass block with a refractive index distribution at a depth of 2 to 3 mm can be obtained.

After the diffusion treatment, the Au--Cr mask on the side surface is dissolved with hydrochloric acid, and sliced and polished as shown in FIG. 3(b) to complete the intended flat plate microprism.

FIG. 4 shows an embodiment of another method for manufacturing a flat prism according to the present invention. (a) shows a mask pattern applied to the side surface of a glass block, in which slits (26) with continuously varying intervals are provided in a metal vapor-deposited film (25) of Ti, Au-Cr, etc. .

Immersed in the same molten salt of thallium sulfate as described above,
After natural diffusion at 0° C. for about 150 hours, the Tl ions diffused from the slit portion of the mask have a concentration distribution as shown in Figure (b), and a corresponding refractive index distribution profile is completed. According to the manufacturing method shown in FIG. 4, a relatively large flat prism can be manufactured.

In addition, in the manufacturing methods of the above two examples, when natural diffusion is performed, it takes a long time of 150 to 160 hours, so in consideration of workability, an electric field is applied in the diffusion direction to shorten the diffusion process time by a tenth. It is also possible to shorten it to a certain degree.

In addition to the above-mentioned inorganic glass, organic transparent substrates in which methyl methacrylate monomer is diffused and polymerized to a semi-polymerized synthetic resin made by adding several percent of benzoyl peroxide to diallyl inphthalate are also within the scope of the present invention. It is something that can be entered.

As explained above, the flat prism of the present invention having a light dispersion function using a distributed refractive index formed in a transparent substrate is easy to manufacture, and the branching characteristics can be controlled by adjusting the diffusion conditions. Also, since both end surfaces are parallel,
For example, it is easy to align with optical fibers, and above all, it has the advantage of being able to be made smaller and thinner.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional optical demultiplexer. FIG. 2 is a sectional view showing an applied embodiment of the present invention. FIG. 3 shows an embodiment of the method for manufacturing a flat prism of the present invention. FIG. 4 shows an embodiment of another method of manufacturing a flat prism of the present invention.

Claims (3)

[Claims] (1) A flat prism that has a light dispersion function using a refractive index distribution formed in a transparent substrate. (2) The flat prism according to claim 1, wherein the transparent substrate is made of synthetic resin or inorganic glass. (3) The flat prism according to claim 1, wherein the refractive index distribution formed in the transparent substrate is formed by an ion diffusion method.