JPS6251441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the construction of optical filters, and more particularly to the construction of directional optical filters formed by single mode fibers.

Optical filters used in demultiplexers, etc. in optical communications using single-mode fibers are multilayer filters that allow light containing various wavelengths to pass through a dielectric multilayer film to separate light of desired wavelengths. Conventionally, a membrane transmission method or a Littrow method in which light of a desired wavelength is separated by reflection on a diffraction grating have been used, but these conventional methods all involve a condensing device as a filter structure, so the structure is The problem is that it is complicated and large, and that it is difficult to form narrow band filters with wavelengths that are very close to each other due to the structure.

In view of the above-mentioned problems, the present invention provides an optical filter having a simple structure, which can be formed in an extremely small size with high precision, and which allows formation of a narrow band filter with wavelengths that are very close to each other. .

That is, the present invention is made by contacting and fixing the extremely thin cladding surfaces of two parallel optical fibers to a sawtooth grating surface formed on a plate made of a translucent material. The grating surface of the first optical fiber, which has a sawtooth grating made of a translucent material on the optical filter formed extremely thinly, and the grating surface of the second optical fiber. An optical filter is characterized in that it is formed by contacting and fixing a thinly formed cladding surface in parallel, and a sawtooth-shaped grating made of a translucent substance is provided on an extremely thinly formed cladding layer. An optical filter is characterized in that two optical fibers are arranged and fixed in parallel with their grating surfaces in contact with each other. The present invention relates to an optical filter characterized in that a saw-toothed grating is interposed therebetween, and an optical path is formed by the grating.

The present invention will be explained below with a functional explanatory diagram shown in FIG. 1, a sectional view taken along the line A-A' of the first embodiment shown in FIG. 2a, and B-B' of the first embodiment shown in FIG. 2b. A cross-sectional view along the fiber of the second embodiment shown in FIG. 3, an explanatory diagram of the grating fiber forming process shown in FIGS. 4a and b, and a third embodiment shown in FIG. This will be explained in detail using a cross-sectional view taken along the fiber.

In principle, the optical filter of the present invention, as shown in the functional diagram of FIG. 2a, 2b, 2c
For example, fiber 1
In order to separate the light of wavelength λ ₁ from the light of wavelengths λ ₁ and λ ₂ in the air propagated in the transmission direction shown by arrow A in the functional diagram, optical paths 2a, 2b, 2c are
For the optical fiber wavelength λ ₁ ' of the wavelength λ ₁ to be separated, the pitch (distance l) between nλ ₁ '+1/
4 λ ₁ ' (n is 0 or a positive integer), and fiber 1
The distance D between the optical axes of a and 1b is formed as nλ ₁ ″+1/4λ _{1 ″ (n is 0 or a positive integer) with respect to the optical path wavelength λ 1 ″} of light with wavelength λ ₁ (however, the distance D between the optical axes of The refractive index and the optical refractive index of the optical path are assumed to be approximately equal).

When the optical filter is formed in this way, the wavelength λ ₁ propagated in the direction of arrow A within the optical fiber 1a
Among _the lights _of
a, 2b, 2c, etc., and is transmitted to the optical fiber 1b. The light that has passed through the optical paths 2a, 2b, 2c, etc. is divided into two by the fiber 1b in the direction opposite to the direction of the arrow A.
The light transmitted to b and traveling in the direction opposite to arrow A is in opposite phase to the light traveling in the direction of arrow A, transmitted by optical path 2a in front, and moreover, the light traveling in the direction of arrow A, transmitted by optical path 2a, is in opposite phase. It's weak, so it's canceled out.

Therefore, the light of wavelength λ ₁ that passes through each optical path in the optical filter and is collected into the fiber 1b is shown by the arrow A.
In addition, in the filter, the light of wavelength λ ₁ transmitted from each optical path is sequentially added, so the efficiency of the filter can be increased as the number of optical paths increases.

The present invention, which will be shown in the following embodiments, forms the above function by interposing a light-transmitting sawtooth grating between the single mode fibers. is the wavelength of the air transmitted through the fiber λ ₁
A case will be explained in which the light with wavelength λ ₁ is separated from the light with wavelength λ ₂ .

That is, one embodiment corresponding to the second term of the present invention is the second embodiment.
As shown in Figures a and _b , it is made of plastic or the like that is translucent and has _a higher optical refractive index than the core 3 of the fiber _.
nλ ₁ ″+1/4 λ ₁ ″ (λ ₁ ″ is the wavelength of light inside the grating. n is 0
Two fibers 1a and 1b are arranged in parallel with an optical axis spacing D of (or a positive integer), and the optical refractive index is approximately equal to that of the cladding layer 6 of the fiber so that light does not leak outside on the grating region. Silicon with
It has a structure in which it is sealed and fixed with a matching material 7 made of oil, glycerin, specific plastics, or the like. In this structure, the cladding layer in the region of the optical fibers 1a and 1b that is brought into contact with the grating 4 is etched or the like in order to increase the amount of light that passes through the cladding layer and reaches the grating 4 and to increase the coupling efficiency. A thin cladding layer 6' having a thickness close to 0 is formed in advance using the method. Furthermore, the grating plate 5 is manufactured to a predetermined pitch by precision machining. A fine grating with a predetermined pitch and depth using a metal plate, etc. on which a finely precise grating surface with a specific depth and shape is formed, or a fine grating with a predetermined pitch and depth using a microfabrication technique such as a V-groove formation method using anisotropic etching. A secondary matrix is formed by pouring a plastic, such as silicone rubber, etc., which has extremely weak adhesion to other substances onto a matrix made of a single crystal silicon plate or the like with a surface formed thereon. A grating material such as plastic having a desired optical refractive index is injection molded using a molding machine, and the molded body is peeled off from the secondary matrix. It is also possible to use the silicone rubber secondary matrix as it is as a grating plate.

In the optical filter having the above structure, light propagation from the fiber 1a to 1b is carried out from the contact point between the fiber 1a and the grating to the fiber 1b through the endmost path, that is, the top end surface of the grating. By changing the angle at which the gratings intersect, the optical path length can be changed and the wavelength of the separated light can be changed, and therefore, using this means, it is possible to accurately fine-tune the separated wavelength.

Further, in an embodiment corresponding to item 3 of the present invention, as shown in FIG.
A thin cladding layer 6' having a thickness close to that of
On the thin cladding layer 6' of the fiber 1a, a saw-toothed grating 4 made of plastic or the like having a higher optical refractive index than the core 3 of the fiber and having good translucency is adhesively formed. Another fiber 1b is placed on the top of the grating 4.
The parts of the thin cladding layer 6' are placed in contact with each other in parallel, and the region of the thin cladding layer 6' where the grating 4 is interposed is sealed with a matching material 7 in plastic or the like having approximately the same optical refractive index as the cladding layer. It has a fixed structure.

In this structure as well, the pitch L of the grating 4 is formed to be nλ ₁ '+1/4λ ₁ ', and the height of the grating 4 is such that the distance D between the optical axes of the fibers 1a and 1b is nλ ₁ ''+1/4λ. ₁ '', light with a wavelength λ ₁ is waved by the optical path formed by the grating. and,
In order to form a fiber having the grating, as shown in FIG. For example, a portion of the fiber 1a having a thin cladding layer 6' is placed across the fiber 1a
A solution 9 made of, for example, plastic, which has good translucency and a higher optical refractive index than the fiber core 3, is dropped from above and solidified, and then the fiber 1a is peeled off from the secondary matrix 8, as shown in FIG. 4b. A sawtooth-shaped grating 4 made of, for example, plastic is formed as shown in FIG.

FIG. 5 shows an embodiment corresponding to item 4 of the present invention. That is, in this example, the cladding layer 6 of a predetermined length is formed into a thin cladding layer 6' close to 0 by a method such as etching, and the optical refractive index higher than that of the fiber core 3 is formed on the thin cladding layer 6'. Two optical fibers 1a and 1b are formed by adhering saw-blade-shaped gratings 4 made of plastic or the like with good translucency using the method described above.
are arranged in parallel with the surfaces of the gratings 4 in contact with each other, and the region of the thin cladding layer 6' where the grating 4 is interposed is covered with a matching material such as plastic having an optical refractive index approximately equal to that of the cladding layer 6. It has a structure in which it is sealed and fixed at 7.

Therefore, in this structure, the distance between the optical axes of the two optical fibers is such that the top part 10 of the grating 4 disposed on each of the two optical fibers 1a and 1b is in contact with the grating 4 of the other optical fiber. An optical path is formed where the distance is the shortest, and the light is separated. Therefore, the pitch (distance) L' of the top part 10 of the grating can be formed smaller than the pitch L of the grating of one of the optical fibers, so the optical path can be formed with a narrow pitch that exceeds the machining accuracy of the grating. becomes possible. Therefore, in this structure, it is possible to form a narrow band optical filter with wavelengths closer to each other than in a structure in which one layer of grating is interposed between the optical fibers.

As explained above, the optical filter of the present invention can be easily and precisely formed in an extremely small size, and in the filter structure, it is possible to form a narrow band filter with wavelengths that are very close to each other. By applying this, it is possible to miniaturize narrowband demultiplexers, narrowband multiplexers, wideband demultiplexers, wideband multiplexers, directional couplers, or optical modulators, improve performance, and improve precision. The degree of integration can be improved, and at the same time, the cost of the device can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a functional explanatory diagram of the present invention, Fig. 2a is a sectional view taken along the line A-A' of the first embodiment of the invention, and Fig. 2b is a sectional view taken along the line B-B'. 3 is a sectional view taken along the fiber of the second embodiment of the present invention, FIGS. 4a and 4b are explanatory diagrams of the process of forming the fiber with grating, and FIG. 5 is a cross-sectional view of the fiber of the third embodiment of the present invention. FIG. In the figure, 1a and 1b are optical fibers, 2a and 2
b, 2c are optical paths, 3 is a fiber core, 4 is a grating, 5 is a grating plate, 6
is the fiber cladding layer, 6' is the thin cladding layer, 7 is the matting material, 8 is the secondary matrix, 9 is the plastic solution, 10 is the top of the grating,
A is the light transmission direction arrow, D is the distance between the optical axes, l is the distance (pitch) of the optical path, L is the pitch (distance) of the grating, and L' is the pitch (distance) of the top of the grating.

Claims (1)

[Scope of Claims] 1. A sawtooth-shaped grating having translucency is interposed in contact with each extremely thin clad surface of two parallel optical fibers,
An optical filter characterized in that an optical path is formed by the grating. 2. It is characterized by having extremely thinly formed cladding surfaces of two parallel optical fibers contacted and fixed to a sawtooth grating surface formed on a plate made of a translucent substance. An optical filter according to claim 1. 3 The grating surface of the first optical fiber is formed by providing a sawtooth grating made of a translucent material on the extremely thinly formed cladding layer, and the grating surface of the second optical fiber is formed extremely thinly. 2. The optical filter according to claim 1, wherein the optical filter is formed by contacting and fixing the cladding surface in parallel with the cladding surface. 4. Two optical fibers each having a saw-toothed grating made of a translucent material on an extremely thin cladding layer are arranged and fixed in parallel with the grating surfaces in contact with each other. An optical filter according to claim 1, characterized in that: