JPS59192225A - Optical circuit - Google Patents

Abstract

PURPOSE:To realize the mass production of an optical circuit and a small loss by forming a hollow glass tube or a columnar glass bar, which has a high- refractive index core layer and a low-refractive index clad layer, into a plane plate with wire drawing while rolling or stretching it. CONSTITUTION:A glass layer 6 which should become a core is formed on the surface of the inside wall of a hollow glass tube 5 by CVD, and a refractive index controlling dopant such as P, Ge, or the like is added to the glass film 6 to give a desired refractive index or refractive index distribution. This hollow glass tube is subjected to wire drawing while rolling or stretching it to obtain a plane plate-shaped optical waveguide. The glass film 6 and the hollow glass tube 5 become a core layer and a clad layer 7 of the optical waveguide respectively. Thus, the mass production and a small loss of the optical waveguide are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical circuit, particularly an optical circuit suitable for a waveguide type optical splitter (star coupler), an optical directional coupler, and the like.

[Background of the invention]

With the rapid progress of optical fiber transmission technology, optical CAT
Research and development of V-networks, optical local area networks, optical computer links, etc. has become active. In configuring these systems, optical directional couplers used for extracting monitor light to monitor the status of the light source and transmission line, and inserting inspection light to inspect the photodetector and transmission line, as well as multiple inputs, are required. An optical star coupler is an essential device that can mix optical signals from an output optical fiber and equally distribute the signal to multiple output optical fibers with low loss.

Conventionally, these devices have a lens s Mi7V,
C.This was achieved by combining individual parts, processing optical fibers, etc.
There were problems with mass production and economy. As a solution to this,
Recently, thick-film waveguide sections have been proposed.

FIG. 1 shows a conventional example of a thick IM single waveguide type optical star coupler.

This combines a core layer 1 with a high refractive index with a cladding layer 2 with a lower refractive index. At both ends of the slab waveguide with a sandwiched structure,
A long optical fiber array 3 and an output optical fiber array 4 are connected.

Slab waveguide manufacturing methods include (1) drawing a preform with a structure in which a glass plate with a high refractive index is sandwiched between glass plates with a low refractive index, and (2) forming a cladding layer and a core layer on a quartz substrate. There are two ways to make it: by growing it and sintering it into glass.

The equal wave path type optical star coupler thus obtained is superior in mass production compared to the individual component type or optical fiber processing type. However, transmission loss is not taken into consideration, and the problem of reducing loss remains.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art,
The object of the present invention is to provide an optical circuit that can be mass-produced and achieve low loss.

[Summary of the invention]

In order to achieve the above object, the optical circuit of the present invention is produced by rolling or drawing a hollow glass tube or cylindrical glass rod having a high refractive index core layer and a low refractive index cladding layer deposited with high purity, The present invention is characterized in that the high refractive index core layer and the low refractive index cladding layer are formed into a flat plate shape to form a flat low loss optical waveguide.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples.

2(a) and 2(b) are a perspective view and a side view of a hollow glass tube used in an embodiment of the present invention, and FIG. 2(c),
(d) shows the refractive index distribution in the A-A plane of FIG. 2(b).

Hollow glass tube 5 shown in FIGS. 2(a) and 2(b) (using quartz glass such as quartz glass and Vycor glass)
A glass film 6, which will become the core of the optical waveguide, is formed on the inner wall surface of the optical waveguide by a conventional internal CVD method (chemical vapor deposition method). In the internal CVD method, a mixture of raw material gas and 0□ passing through the hollow glass tube 5 is heated from outside the tube, and an oxidation reaction (SsCla+02→S 102 +2 C12) is carried out.
This method deposits a glass film 6 on the inner wall of the tube.This film is formed in a closed tube and uses a gas phase chemical reaction, so it has high purity and contains few impurities, so it reduces the absorption of light energy by impurities. transmission loss can be reduced to near the theoretical limit value. Further, the refractive index distribution of the glass film 6 with a refractive index value n1 can be arbitrarily realized by adding a refractive index control dopant such as P or Ge to the glass (Si02) film 6.

Furthermore, since a very dense glass film can be formed on the inner wall of the tube, scattering loss due to irregularities in the interface between the core and the cladding is extremely small. FIG. 2(C) shows a step index type in which the refractive index of the glass film 6 is uniform, and FIG. 2(d) shows a graded index type in which the refractive index becomes thicker toward the center. ing.

The thickness of the glass film 6 is several μm or more in the case of an optical waveguide for single mode transmission, and several tens of micrometers in the case of an optical waveguide for multimode transmission.
Deposit more than μm.

FIG. 3(a) shows an optical waveguide formed by rolling or stretching the hollow glass tube of FIG. 2(a) in its axial direction and drawing it into a flat plate, and FIG. 3(b) is a side view thereof. , Figure 3 (C
) and (d) show the refractive index distribution in the B-B' plane of FIG. 3(b). Even if it is formed into a flat plate shape in this way, the low transmission loss property is not impaired.

Glass film 6 in FIG. Hollow glass tubes 5 each form a core layer 8 of the optical waveguide. This becomes the cladding layer 7.

The thickness d of the core layer 8 is made approximately equal to the core diameter of the optical fiber so that it is well matched with the optical fibers connected to both end faces of this optical waveguide. For example, in the case of a single mode optical fiber, d is several μm, and in the case of a multimode optical fiber, d is several tens of μm.
It becomes μm. The width W of the core layer 80 is selected to be approximately equal to the width of the optical fiber array connected to this end face.

FIG. 4 shows an embodiment of an optical star coupler constructed using the optical waveguide 9 of FIG. 3.

This figure shows a case where the number of input and output ports are both 13. Note that in order to reduce excessive loss, the thickness of the cladding layer of the output optical fiber array may be made as thin as several micrometers. 3 is an input optical 7-eyebar array.

The optical waveguide 9 is formed by stretching and drawing the hollow glass tube 5 in FIG. 2 so that the thickness of the core layer 8 becomes a desired value d. If a large and long one is used and the thickness of the glass film 6 is sufficiently thick compared to the core diameter of the input/output optical fiber, a long leading wavepath can be realized at one time.On the other hand, as shown in FIG. The length of the optical waveguide 9 of the optical star coupler shown in the figure is from several α to several degrees, so it is possible to fabricate a large number of optical waveguides (several 10 or more) for the optical star coupler from the aforementioned long leading waveguide. In addition, by increasing the drawing ratio, it is possible to obtain an optical waveguide with extremely high dimensional accuracy and a uniform core and cladding interface, similar to drawing an optical fiber, and also to reduce absorption loss and scattering loss. It can be made extremely small.

5 shows a hollow glass tube used in another embodiment of the present invention, FIG. 5(a) is a perspective view, FIG. 5(b) is a side view,
(C) is a cross-sectional circular refractive index distribution diagram taken along line A-A in (b).

A glass film 6 serving as a core and a glass film 10 serving as a cladding are formed on the inner wall surface of the hollow glass tube 5 by an internal CVD method.
is formed with high purity. As is clear from FIG. 2(C), the refractive index of the glass film 6 is made larger than the refractive index of the glass film 10, so that the glass film 6 becomes a core and the glass film 10
is used as cladding. In this figure, the refractive index distribution of the core layer is of a step index type, but it may be of a graded index type. As shown in FIG. 5, forming a glass film 1o serving as a cladding has the following effects compared to that shown in FIG. In step 8 of FIG. 2, in which the hollow glass tube is rolled or stretched and drawn into a flat plate, the hollow glass tube is heated to near its melting temperature, so that the refractive index control dopant in the glass film 6 is An unfavorable phenomenon occurred in which the refractive index near the center of the core glass layer 8 decreased due to evaporation. The film 10 also has the effect of being able to function as a barrier layer and prevent a decrease in the refractive index of the core glass layer 6.Furthermore, after forming the core glass film 6 in a closed tube, the clad glass is immediately formed while maintaining high purity. Since it is covered with the film 1o, there is no need to worry about an increase in the insertion loss of the core due to the contamination of impurities during the step of forming it into a flat plate.It is also superior to the case shown in FIG. 2 in this respect.

FIG. 6 shows an optical waveguide formed by converting the hollow glass tube in FIG. 5 into a flat plate in the same manner as in FIG. 3; (a) is a perspective view, (b) is a side view, and (C) is a refractive index distribution map.

The glass film 6 in FIG. 5 becomes the core layer 12, and the glass film 1o
becomes the cladding layer 13. Here, when cutting in the length direction of the planar optical wave path along the planes CC' and D-D' shown in FIG.
A stage leading waveguide 14 can be realized. Then, a first optical fiber coupler having an input optical fiber array 3 and an output optical fiber array 2, and a second optical star coupler having an input optical fiber array g and an output optical fiber array 4 are constructed. be able to. In this way, by alternately depositing h layers of the core glass film 6 and the cladding glass film 1o, it is possible to realize a so-called stacked optical star coupler in which 2h optical star couplers are stacked.

Front views of the thus obtained connecting portion between the laminated optical waveguide and the optical fiber are shown in FIGS. 8(a), 8(b), and 8(c). (a) is stacked in two stages, (b) is stacked in three stages,
(C) is a case of 4 stages. 18, 18, 18, 18
are optical fibers, 15, 15', 17, 17', 20 &
'! Leading waveguide cladding layer, 16.16', 19.19
' is the core layer of the optical waveguide. The thickness of the core layer of the optical waveguide is set to be approximately equal to the core diameter of the optical fiber. Note that, as shown in (al), it may be cut along A-A/ to form one optical star coupler.

FIG. 9 is a diagram for explaining one embodiment of the method for manufacturing an optical waveguide according to the present invention.

The hollow glass tube 5 shown in FIG. 9(a) is inserted into the heat source 21 shown in FIG. 9(b) at a speed V, and the heated and melted hollow glass tube 5 is pulled out from the heat source 21. By rotating the rolling roller 22 in the direction of the arrow 23, a flat optical waveguide 25 can be obtained. Figure 9(C) is
FIG. 3 is a side view of an optical waveguide obtained by the above method.

In this method, the thickness of the core layer 8 of the optical waveguide can be perfectly adjusted by changing the ratio between the compression speed v1 and the drawing speed v2 of the hollow glass tube 50.

Also, one end of the hollow glass tube 5 is closed, and the arrow 24
If the pressure inside the hollow glass tube 5 is reduced by pulling the wall in the direction of
A flat plate-shaped four-wavelength optical wave path can be easily manufactured.

Since the material of the hollow glass tube 5 is usually quartz-based glass, the heating source 21 is made of a carbon electric furnace-like material (eg, ceramics, carbon, etc.).

Note that the method for manufacturing an optical waveguide described above can also be applied to the case where an optical waveguide is manufactured by rolling a cylindrical glass rod instead of the hollow glass tube 50. In addition, in FIGS. 2 and 3, if the cladding glass film is first formed on the inner wall of the hollow glass tube, then the core glass film 6 is formed.
It is possible to create products with lower absorption loss and scattering loss.

FIG. 10 shows a multi-distribution optical star coupler having a structure that is a modification of the laminated optical star coupler shown in FIG. 7, in which (a) is a front view and (b) is a bottom view.

This is made by elongating the center of the optical waveguide 26 longer than the other parts to form a tapered part 27, and as a result, the light enters one of the optical fibers of the input optical fiber arrays 3 and 3'. The resulting light is equally distributed to all the optical fibers of the output optical fiber arrays 4, 4'. The ratio of the output power distributed to each output optical fiber of the output optical fiber array 7 and the output power distributed to each output optical fiber array 4' can be controlled by the coupling state of the core layer 37 and δD. That is, the taper ratio of the tapered portion 27,
Depends on taper length. Furthermore, the core layer 37.37
For example, if this difference is kept small, the distribution ratio can be made uniform with a relatively small taper ratio and taper length. Further, the thickness of the cladding layer 38 may be made thinner. Furthermore, the glass film may be formed so as to curve the cladding layer 38 toward the center of the tapered portion.

In FIG. 11, the number of input optical fiber ports is 1, and the number of output optical fiber ports is m (>2).

That is, it shows a schematic diagram of the manufacturing method and structure of an 1:m optical star coupler. First, in (a),
Tensile stress is applied in the direction of arrow 30, 30' while heating the vicinity of the center of optical waveguide 28 with heating source 29, or tensile stress is applied in one of the directions of arrow 30, 30'. Then, as shown in (b), a tapered portion 31 is formed near the center. The tensile stress is applied so that the core shape in the A-A/cross section is approximately equal to the core diameter of the optical fiber.

Next, the structure shown in (C) is obtained by cutting the AA cross section. Here, the core layer 33 is approximately equal to the core diameter of the optical fiber connected to this end face, but the cladding layer 32 does not have to be particularly equal to the cladding diameter of the optical fiber. (d) is a schematic diagram of a 1:m optical star coupler, where m is 6. The light incident on the optical fiber 35 is expanded by the tapered optical waveguide 34 and output to the output optical fiber 36-1.36-.
Equally distributed to 2.36-3°36-4.36-5.36-6.

Figure 12 (a) shows the cylindrical original fiber base material, (b) shows its side view, (C) and (d) show the refractive index distribution in the A-A' plane of (b), and (C) shows the refractive index distribution in the A-A' plane of (b). A step index type is shown, and (d) shows a graded index type. 39 is a cladding layer, and 40 is a core layer.

Such a base material is manufactured by the conventional VAD (vapor phase axial growth) method, rod-in-tube method, external CVD method, etc., and is designed to achieve ultra-low loss. By stretching the cylindrical optical fiber base material of FIG. 12 while rolling or drawing it by the method shown in FIG.
A flat optical waveguide consisting of a cladding layer 41 and a core layer 42 as shown in the figure can be realized.

FIG. 14(a) shows a cylindrical optical fiber base material with a low loss made from a plurality of concentric glass layers, FIG. 14(b) is a side view thereof, (C), (d), (e), ( f) shows the refractive index distribution in the A-A' plane of (b). In this case, the cladding layer 43. Core layer 44. Cladding layer 45
However, a plurality of core layers and cladding layers may be alternately formed. It is clear from the above description that the refractive index value n, the refractive index distribution horn thickness, etc. of the core layer and the cladding layer can be arbitrarily selected. For example, in the case of the optical fiber base material shown in FIG. 14, the refractive index value n
For example, as well as being the highest in the core layer, (
In C), (d), the cladding layer 43.45 is equal;
In (e), the cladding layer 45 is higher than the cladding layer 43, and in (f), the cladding layer 45 is lower than the cladding layer 43.

A laminated optical waveguide as shown in FIG. 6 can be obtained by stretching such an optical fiber base material while rolling or drawing it in the manner described above.

Although several embodiments have been described above, the present invention is not limited to these embodiments. For example, in the hollow glass tube shown in FIG. 2, in addition to the internal CVD method, a glass film having a refractive index lower than that of the glass tube may be formed on the outside of the hollow glass tube using the external CVD method. Alternatively, hollow glass tubes with different diameters may be fitted together to realize the tube-in-tube method. Further, clad glass films may be formed on both side surfaces 46 and 46 of the stacked leading waveguide shown in FIG. 8 to prevent light leakage. In the optical waveguide manufacturing method shown in FIG. 9, instead of rolling with the rolling rollers 22, a hollow glass tube or a cylindrical optical fiber preform may be passed through a heated crucible and rolled. Further, the stretching direction may be a vertical direction, a horizontal direction, or an inclined direction. Furthermore, in the case of the hollow glass tube 2 and the cylindrical optical fiber having a low softening point, so-called multi-component glass, it may be manufactured by a normal glass press method. The multi-distribution optical star coupler shown in FIG. 10 is shown in FIG. 8(b).

It can also be realized using a laminated optical waveguide as shown in (C).

Although FIG. 11 shows a 1-to-In optical star coupler, it is clear that 41゜4 configurations such as 2-to-rn, 3-to-n1, etc. may also be used.

〔Effect of the invention〕

As explained above, the optical circuit of the present invention has excellent mass productivity and can realize low loss.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional thick film star coupler; FIGS. 2, 5, 12, and 14 are diagrams for explaining the materials used in the present invention; figure. 6 and 13 are diagrams showing examples of optical circuits (optical waveguides) of the present invention formed from the materials shown in FIGS. 2, 5, 14, and 12, respectively, and FIG. Figures 7, 8, 10, and 11 are diagrams for explaining examples of devices using the optical circuit of the present invention, and Figure 9 is for explaining a method of rolling the material used in the present invention. This is a diagram. 7, 13. 32.4.1: Cladding layer of the optical circuit (optical waveguide) of the present invention, 8, 12, 33, 42: Core layer-layer of the optical circuit (optical waveguide) of the present invention Fig. 1 Fig. 3 Fig. 2 ( a) (t)) (C)
(d) (a) (b) (
c) (d) l( Figure 5 (a) (b) (
c) Figure 6 (a) (b) No. 8
Figure 9 Figure 1○(a) Figure 11 0. 5el-Φ Figure 12 (a) (b) (c
) (d) Figure 13 Figure 14 (b) (c) (d)

Claims (5)

[Claims] (1) A hollow glass tube or cylindrical glass rod having a high refractive index core layer and a low refractive index cladding layer deposited with high purity is drawn while rolling or stretching, and the high refractive index core layer and low refractive index cladding layer are An optical circuit characterized by forming a flat, low-loss optical waveguide by folding the layers into a flat plate. (2) A patent characterized in that the low-loss optical waveguide is a borrowed one in which the high refractive index core layer and the low refractive index cladding layer are formed on all front, rear, left, and right end faces through which light can be transmitted. An optical circuit according to claim 1. (3) The optical circuit according to claim 1, wherein the low-loss optical waveguide has a tapered shape near its center. (4) The optical circuit according to claim 1, wherein the low-loss optical waveguide has a narrow tapered width at one end and a wide width at the opposite end. (5) The optical circuit according to claim 1, wherein the low-loss optical waveguide has an optical fiber connected to the high refractive index core layer on both opposing end faces thereof, and has an optical distribution function. .