JP3060731B2 - Optical circuit manufacturing apparatus and manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circuit manufacturing apparatus and method for manufacturing a mode conversion circuit of a glass optical circuit used for optical communication and optical information processing.

[0002]

2. Description of the Related Art Glass optical waveguides are very difficult to manufacture various optical components because of their features such as low loss, high stability, good workability, and good matching with optical fibers. Useful for Recently, research on optical circuits with higher functions and higher integration utilizing these characteristics has been advanced. Here, in order to further downsize and highly integrate optical components,
Specific refractive index difference Δ between core and clad in glass optical waveguide
It is very effective to take a large value. However,
When the refractive index difference is increased, the mode diameter in the optical waveguide is reduced, and the matching with the optical fiber is deteriorated, and the relative refractive index difference Δ of the optical waveguide and the matching with the optical fiber have a trade-off relationship. Has become. Here, as a method for solving this problem, it is promising to manufacture a mode conversion circuit at the input / output end to increase the mode diameter of the optical waveguide.

In a mode conversion circuit using an optical waveguide,
There are currently two methods of making. One is a method in which the core is formed in a tapered shape in advance, and the other is a method in which the dopant in the core is locally thermally diffused in post-processing to increase the mode diameter.

[0004]

However, in the method of forming the core in a tapered shape in advance, a double core structure in which two kinds of tapered cores are overlapped has been proposed, but the manufacturing method is complicated. There are problems such as points.
As for the method of expanding the mode diameter by locally diffusing the dopant in the core in the post-processing, a method of locally diffusing the heat using a thin film heater formed on the upper part of the waveguide has been proposed. However, considering the case where the heating temperature is high, there remain problems such as the heat resistance and the temperature distribution of the thin film heater. Both are in the research stage at present, and a practical optical waveguide mode conversion circuit has not been realized.

On the other hand, although not an optical waveguide, in an optical fiber, a TEC (Thermally-diffused Expanded Core) is used.
A technique is used, and is currently used effectively. In this technique, a burner or an electric furnace is used to locally heat an optical fiber. Here, the heat treatment is performed without any cooling mechanism due to the low thermal conductivity of the optical fiber (glass). However, when the TEC technology in the optical fiber is applied to the optical waveguide as it is, the heat conduction in the substrate is not performed. In particular, in the case of thermal diffusion processing at a high temperature or when applied to an optical waveguide made of a material having a high thermal conductivity, the entire optical waveguide is heated, thereby changing the characteristics of the optical circuit body. Problems such as rounding and an increase in taper length occur.

An object of the present invention is to provide an optical circuit manufacturing apparatus capable of favorably obtaining a mode conversion circuit necessary for connecting optical circuits having different mode diameters or an optical waveguide having a small mode diameter to an optical fiber. And a manufacturing method.

[0007]

According to the present invention, a temperature gradient is forcibly formed in the optical waveguide by locally heating the end face or the inside of the glass optical waveguide by a heater and cooling the opposite side. The main feature is that a mode conversion (enlargement) circuit is manufactured by thermal diffusion of the dopant in the core. The main feature is that a mode conversion circuit is manufactured at one end, both ends, and in the plane of the optical waveguide by the configuration of various heaters, heat shielding slits, and holders.

In the prior art, TEC in optical fiber
In the technology, a cooling mechanism was unnecessary because of the low thermal conductivity of the optical fiber. However, as for the optical waveguide, the heat conduction by the substrate could not be neglected.
EC technology cannot be applied. Here, in the present invention,
In order to expand the mode diameter only at the local portion, in addition to the heater, a heat shield slit and a holder with a cooling mechanism are installed, so that local heating only at the waveguide end face or near the input / output end in the plane is performed. And a mode conversion circuit having a short taper length can be manufactured. This method is particularly useful for a silica-based waveguide in which dopant diffusion must be performed at a high temperature or a waveguide using a material having a high thermal conductivity (eg, silicon) as a substrate.

In addition, since it is a simple manufacturing method in which a heat diffusion process is performed only on a desired portion in a subsequent step, complicated processing such as processing into a tapered shape in a core forming step in manufacturing a mode conversion circuit using an optical waveguide is required. The process is unnecessary and can be said to be a practical process technology.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, a mode conversion (enlargement) circuit fabrication process by local heating of an optical waveguide end face will be described below.
Examples of the present invention will be specifically described in detail.

(Embodiment 1) FIG. 2 is a view showing the structure of a silica-based optical waveguide used for confirming the effect of the present invention, wherein 1 is a core, 2 is a clad, and 3 is a silicon substrate. A flame deposition method was used for fabrication. Here, the dopant of the core is germanium (Ge), and the core shape is 6 × 6 μm.
² rectangle, relative refractive index difference Δ between core and cladding 0.75%
And In the following examples, quartz optical waveguides having the same structure were used.

Next, using an electric furnace as shown in FIGS. 1A and 1B, one end face of the optical waveguide is locally heated to enlarge the mode diameter near the end of the optical waveguide. Here, 4a is a quartz-based optical waveguide (frequency multi-wavelength duplexer), 5a is a heater such as a carbon heater or a tungsten heater, 6a is a heat shield slit, and 7a is a holder for the optical waveguide and circulating cooling water can be introduced. It is a holder with a cooling mechanism. The heating conditions were such that the heating temperature at the end face was 1300 ° C. and the heating time was 5 hours. As a result, in the optical waveguide 4a after the heat treatment, the core expands in a tapered shape near the end face, and a mode conversion circuit is formed. The connection loss between the converted optical waveguide 4a and the optical fiber was 0.1 dB or less, which was significantly reduced as compared with the connection loss of 0.5 dB when the mode diameter was not enlarged. Also, the tolerance of positional accuracy on connection loss has been expanded. Here, the tapered shape can be controlled by the heating temperature, the cooling temperature, and the position of the heat shielding slit.

The present method is very effective for an optical waveguide having a large relative refractive index difference. For example, in an optical waveguide having a Δ of 2%, a connection loss with an optical fiber is about 2.5 dB.
However, by applying this method, Δ can be reduced to 0.1 dB or less as in 0.75%.

(Embodiment 2) In Embodiment 1, a method of manufacturing a mode conversion circuit at one end of an optical waveguide has been described.
Next, a method for manufacturing a mode conversion circuit at both ends of the optical waveguide will be described with reference to FIGS. By using an electric furnace having a cooling mechanism holder 7b at the center and a heater 5b at both ends thereof, the mode diameter at the input and output ends can be simultaneously increased as in the case of one end, and the optical waveguide (4 × 4 optical switch) Total connection loss 1d at both ends of 4b
B was reduced to 0.1 dB or less. Here, 6b is a heat shielding slit.

The mode conversion length can be further reduced by adding a heat insulating material or the like for heat shielding in addition to the heat shielding slit 6b.

(Embodiment 3) FIGS. 4A and 4B show a method of manufacturing a mode conversion circuit in the plane of an optical waveguide. In order to perform local heating in the plane of the optical waveguide, a heater 5c is arranged above and below the optical waveguide 4c, and a holder 7c with a cooling mechanism is arranged at the end of the optical waveguide 4c. FIG. 4 (a),
In (b), 6c is a heat shielding slit, and 7c is a holder with a cooling mechanism. Here, using this method, FIG.
This is applied to the insertion of a narrow band filter into the optical waveguide 4d as shown in FIG. First, local mode expansion was performed in the plane of the optical waveguide 4d to increase the mode diameter from 8 μm to 15 μm. Next, a groove was formed in the mode expansion portion, and the narrow band filter 8 was inserted. At this time, the excess loss due to the insertion of the filter 8 could be reduced from about 2 dB without the mode expansion to about 0.5 dB by expanding the mode diameter.

A convex heater 5d as shown in FIGS. 6A and 6B is used at the center of the optical waveguide 4e.
By cooling the periphery of the optical waveguide 4e, it is possible to manufacture a mode conversion circuit in an arbitrary local region in the plane. 6 (a) and 6 (b), 6d is a heat shield slit, and 7d is a holder with a cooling mechanism.

[0018]

As described above, the mode conversion circuit is formed by locally heating the end face or the inside of the optical waveguide by using the electric furnace constituted by the heater, the heat shield slit and the holder with the cooler. According to the present invention, the optical circuit body is made compact and highly integrated by using an optical waveguide having a high refractive index difference, and an optical circuit or an optical circuit having a different mode diameter at an optical waveguide end face or an in-plane input / output end. A mode conversion circuit matched to the fiber can be manufactured. In addition, since a local mode conversion circuit can be manufactured only in a desired portion in the final step without changing the conventional glass optical circuit manufacturing method, an efficient optical circuit can be manufactured. Become.

[Brief description of the drawings]

1A is a side view showing an example of a method for manufacturing a mode conversion circuit at one end of an optical waveguide according to the present invention, and FIG. 1B is a top view of the same.

FIG. 2 is a cross-sectional view illustrating an example of the structure of a silica-based optical waveguide according to the present invention.

3A is a side view showing an example of a method for manufacturing a mode conversion circuit at both ends of the optical waveguide according to the present invention, and FIG. 3B is a top view of the same.

4A is a side view showing an example of a method for manufacturing a mode conversion circuit in the plane of an optical waveguide according to the present invention, and FIG. 4B is a top view of the same.

FIG. 5A is a side view showing an example of an optical circuit according to the present invention in which a narrow band filter is inserted in a mode expansion portion, and FIG.
Is also a top view.

FIG. 6 (a) shows an optical waveguide according to the present invention,
FIG. 7B is a side view showing an example of a method for manufacturing a mode conversion circuit for an arbitrary local portion, and FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Clad, 3 ... Silicon substrate, 4a, 4
b, 4c, 4d, 4d... quartz optical waveguides, 5a, 5b,
5c, 5d: heater, 6a, 6b, 6c, 6d: heat shielding slit, 7a, 7b, 7c, 7d: holder with cooling mechanism, 8: narrow band filter.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/10-6/138 G02B 6/14

Claims (4)

(57) [Claims] 1. An apparatus for manufacturing an optical circuit, wherein an electric furnace for locally heating an end face of a glass optical waveguide comprises a holder having a heater, a heat shield slit and a cooling mechanism. 2. An optical circuit according to claim 1, wherein the electric furnace comprises a holder having a cooling mechanism arranged at the center, a heater and heat shielding slits arranged at both ends. apparatus. 3. An electric furnace for locally heating the surface of a glass optical waveguide includes a heater disposed on the surface of the optical waveguide, and a holder having heat insulating slits and a cooling mechanism disposed on both sides thereof. An optical circuit manufacturing apparatus, characterized in that: 4. The mode diameter of the optical waveguide is tapered by locally heating the end face or the surface of the glass optical waveguide by using the electric furnace according to claim 1, 2 or 3. A method for manufacturing an optical circuit, comprising: