JP2001221925A - Light spot size transforming unit and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light spot size transforming unit capable of stably reducing a connection loss with an optical fiber and its manufacturing method. SOLUTION: In the light spot size transforming unit which is provided with an input waveguide 14, an output waveguide 15 having a fixed core width narrower than the width of the input waveguide 14, and a taper waveguide 16 smoothly connecting the input waveguide 14 to the output waveguide 15, falling down of the core of the output waveguide 15 owing to a heat treatment in the case of forming an upper clad 13 is restrained by providing a fall preventing core 17 which crosses with the core of the output waveguide 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical spot size converter using an optical waveguide and a method for manufacturing the same.

[0002]

2. Description of the Related Art A silica-based optical waveguide and a single mode fiber basically have the same mode field, and are directly connected to each other with an adhesive without using a lens. This direct connection method is widely used at present because it is simple and multi-core connection is possible.

However, recently, in order to realize a large-scale optical circuit, the relative refractive index difference Δ between the core and the clad of the silica-based optical waveguide is set to 1.5 to 2.0% and the single-mode fiber Δ
= 0.3% and the minimum bending radius is reduced to about 2 mm (for example, S. Suzu).
ki et al. , "High-densityin
graded 1 × 16 optical FDM
multi / demultiplexer ", LEO
S'94, IO 2.4, 1994).

In this case, in order to reduce the minimum bending radius, light is strongly confined in the core, the mode field becomes smaller than that of a single mode fiber, and the coupling loss between the two becomes large. Attempts have been made to reduce the core width at the fiber connection end of the silica-based optical waveguide to reduce light confinement, widen the mode field, and reduce the coupling loss with a single mode fiber.

The method of reducing the core size at the input / output end and expanding the mode field is a method widely used in LDs and the like (for example, TL Koche).
tal. , "Tapered waveguide I
nGaAs / InGaAsP multiple-qu
antum-well lasers ”, IEEEh
oton. Technol. Lett. , Vol. 2,
pp. 88-90, 1990).

[0006]

However, when actually manufacturing an optical spot size converter in which the core width of the silica-based optical waveguide is reduced, it was found that the coupling loss is high and the loss value varies. . In order to investigate the cause, the shape of the core on the end face was observed. As a result, it was found that the core was deformed, that is, collapsed when the core width was narrow as shown in FIG.

More specifically, when the ratio of the core height to the core width (hereinafter, the aspect ratio) is 2 or more, the frequency of deformation of the core becomes extremely high. In a quartz optical waveguide, after processing a core, an upper clad glass soot is deposited by a flame deposition method, and the soot glass is made transparent at a high temperature of 1000 ° C. or more. At this time, since the core was also soft, it is considered that the core was deformed by a slight force when the soot was sintered and contracted. In FIG. 1, 1
Denotes a lower clad, 2 denotes an upper clad, and 3 denotes a core.

An object of the present invention is to provide an optical spot size converter capable of stably reducing the coupling loss with an optical fiber and a method of manufacturing the same.

[0009]

According to the present invention, there is provided an optical waveguide comprising a core and a clad formed on a planar substrate, the input waveguide having a predetermined core width. An output waveguide having a constant core width narrower than the input waveguide, and a light spot size converter comprising at least a tapered waveguide for smoothly connecting the input waveguide and the output waveguide, wherein the output waveguide or A feature is provided in which a tilt prevention core intersecting with the core of the tapered waveguide is provided.

According to the above-described structure, the provision of the core for preventing the collapse of the core of the output waveguide due to the heat treatment during the formation of the clad can suppress the collapse of the core, thereby stabilizing the loss at the time of coupling with the optical fiber. It can be made smaller.

The light spot size converter includes a step of simultaneously forming a core constituting an input waveguide, an output optical waveguide, and a tapered waveguide, and a fall prevention core intersecting with the core of the output waveguide or the tapered waveguide. It can be obtained by the manufacturing method described above.

Further, according to the manufacturing method including the step of removing the output waveguide including the fall prevention core, it is possible to obtain an excellent light spot size converter having no radiation loss due to the fall prevention core. .

[0013]

FIG. 2 shows a first embodiment of an optical spot size converter according to the present invention, in which 11 is a silicon substrate, 12 is a lower clad, 13 is an upper clad, and 14 is a clad. An input waveguide (core), 15 is (output core), 16 is a tapered waveguide (core), and 17 is a fall prevention core.

The input waveguide 14 generally corresponds to a waveguide of an optical waveguide circuit manufactured on the same substrate, and is composed of a straight waveguide having a predetermined core width. The output waveguide 15 is for forming a connection with an optical fiber (here, a single mode fiber).
It consists of a straight waveguide with a constant core width smaller than 4.

The tapered waveguide 16 is connected to the input waveguide 14.
And the output waveguide 15 is connected smoothly, and the core width is smoothly reduced from the connection portion with the input waveguide 14 to the connection portion with the output waveguide 15.

The fall prevention core 17 is for preventing the output waveguide 15 having a narrow core width from falling.
The output waveguide 15 is formed integrally so as to intersect at a substantially right angle. The output waveguide 15 may be provided on the tapered waveguide 16 on the side where the core width is reduced.

In this embodiment, the relative refractive index difference Δ between the core and the clad of the quartz optical waveguide is 1.5%, the maximum core width of the tapered waveguide 16 is 4 μm, the minimum core width is 2 μm, and the height is 4 μm. , The width of the fall prevention core 17 is 10 μm and the length is 2
It was designed to be 0 μm and the height was 4 μm.

The effect of the present invention will be described.

When the fall prevention core 17 is not provided, the core shape at the end of the optical waveguide frequently falls down as shown in FIG. 1, and the coupling loss with the single mode fiber varies. However, by reinforcing with the fall prevention core 17, the fall is suppressed and the variation of the coupling loss can be suppressed.

This time, an optical spot size converter consisting only of an input waveguide, an output waveguide, a tapered waveguide, and a tilt-prevention core was prepared, and both ends of the optical spot size converter were directly connected with a single mode fiber, and the optical spot size converter was inserted. The loss was measured. Histograms of the insertion loss and frequency of the optical spot size converter with respect to the single mode fiber are shown in FIG. 3 when reinforced by the fall prevention core, and in FIG. 4 when not reinforced. Obviously, the provision of the fall prevention core can suppress the variation in the insertion loss of the optical spot size converter, and it can be seen that the present invention is more effective.

FIG. 5 shows a second embodiment of the light spot size converter according to the present invention, which is almost the same as the first embodiment, except that a fall prevention core is removed.
The core falls during the heat treatment for making the upper clad glass transparent, and the core does not fall after the upper clad glass is made transparent. Therefore, after the upper clad glass is made transparent, the fall prevention core is unnecessary. Further, when the light propagates through the fall prevention core, the optical waveguide structure changes discontinuously, so that light radiation loss occurs.

Therefore, after manufacturing a light spot size converter having a fall prevention core, the output waveguide side including the fall prevention core was removed to eliminate a factor that causes light radiation loss. Specifically, after the production of the waveguide circuit wafer, the output waveguide side including the fall prevention core was removed in a step of cutting into chips using a dicing saw. As a result, the insertion loss of the optical spot size converter with respect to the single mode fiber is 0.2 d on average compared with the case where the fall prevention core is not removed.
B improved. In FIG. 5, reference numeral 15 'denotes an output waveguide remaining after the removal.

In the first and second embodiments, the quartz glass waveguide has been described. However, the present invention is not limited to a silica glass waveguide. In the polymer waveguide, after core processing, an upper clad is formed by spin coating. In this case, the core having a high aspect ratio is easily deformed. The fall prevention core of the present invention is also effective in this polymer waveguide.

In the embodiment described above, a straight waveguide is used as an input waveguide. However, any optical waveguide such as an output waveguide of an N × 1 optical multiplexer can be used as an input waveguide.

[0025]

As described above, according to the present invention,
An optical spot size converter capable of stably reducing the coupling loss with an optical fiber and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a core shape of a waveguide end of a conventional light spot size converter.

FIG. 2 is a schematic configuration diagram showing a first embodiment of a light spot size converter according to the present invention.

FIG. 3 is a histogram of insertion loss and frequency of an optical spot size converter with respect to a single mode fiber reinforced with a fall prevention core.

FIG. 4 is a histogram of insertion loss and frequency of an optical spot size converter for a single mode fiber when not reinforced by a fall prevention core.

FIG. 5 is a schematic configuration diagram showing a light spot size converter according to a second embodiment of the present invention.

[Explanation of symbols]

11: Silicon substrate, 12: Lower clad, 13: Upper clad, 14: Input waveguide, 15, 15 ': Output waveguide, 16: Tapered waveguide, 17: Fall prevention core.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Saida 2-3-1, Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Yasuyuki Inoue 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 F-term in Nippon Telegraph and Telephone Corporation (reference) 2H047 KA04 KA13 LA23 MA05 QA04 TA32

Claims (3)

[Claims] 1. An optical waveguide comprising a core and a clad formed on a planar substrate, comprising: an input waveguide having a predetermined core width; and an output waveguide having a constant core width narrower than the input waveguide. A light spot size converter comprising at least a tapered waveguide that smoothly connects the input waveguide and the output waveguide, wherein a tilt prevention core that intersects the core of the output waveguide or the tapered waveguide is provided. A light spot size converter. 2. An optical waveguide comprising a core and a clad formed on a planar substrate, comprising: an input waveguide having a predetermined core width; and an output waveguide having a constant core width narrower than the input waveguide. A method of manufacturing a light spot size converter comprising at least a tapered waveguide for smoothly connecting the input waveguide and the output waveguide, wherein the input waveguide, the output optical waveguide and the core constituting the tapered waveguide are Forming a fall prevention core intersecting with the core of the output waveguide or the tapered waveguide at the same time. 3. The method of manufacturing an optical spot size converter according to claim 2, further comprising a step of removing an output waveguide side including a fall prevention core.