JP2000206352A - Optical waveguide with spot size changing core structure, and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide with a spot size changing core structure connected to a fiber at a low loss irrespective of a wave length and having a large process tolerance, and provide a manufacturing method therefor. SOLUTION: When cores 4, 6, 7 are film-formed on a substrate 5 by a flame deposition method, the core 6 of high refractive index, the core 4 changed in its refractive index and height, and the core 7 having a core height and a refractive index connected to a fiber at a low loss are formed integrally. In the cores 4, 6, 7, a shape of the core 4 changed in its refractive index and height is formed into a tapered shape by etching, a shape of the core 6 of the high refractive index is formed into straight or curved line, the core 7 connected to the fiber is worked into a straight line to form core structure 4 for changing a spot size, connection to the fiber is carried out thereby at a low loss irrespective of a wave length, and an optical waveguide with spot size changing core structure of a large process tolerance is provided thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical waveguide having a spot size conversion core structure and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a directional coupler has been used to connect an optical waveguide having a core having a relative refractive index difference of 0.8% or more to a single mode fiber with low loss.

[0003]

FIG. 7 is a diagram showing a structure for connecting a conventional optical waveguide having a core with a relative refractive index difference of 0.8% or more to a single mode fiber.

An optical waveguide 5-6 having a relative refractive index difference of 0.8% or more
The light 5-1 propagating through the core 5-7 is connected to the optical waveguide 5-11 that can be connected to the optical fiber with low loss by a length L and a width G. The light 5-1 propagating through the core 5-7 is transmitted to the light 5-2, 5-
3, 5-4 and gradually coupled to the core 5-10 to become light 5-4, and the spot size of the light 5-1 propagating in the core 5-7 is changed to the light 5 propagating in the core 5-10. Convert to -5 and couple with optical fiber with low loss.

In such a structure, since the complete coupling length L differs depending on the wavelength of the light, there is a problem that light other than a specific wavelength involves a loss at the coupling portion L and cannot be coupled to the fiber with low loss. . In addition, the width G and the coupling length L must be achieved with high precision, which requires advanced process technology and mounting technology, and causes a problem of deterioration in yield.

Accordingly, an object of the present invention is to solve the above-mentioned problems, to provide an optical waveguide having a spot size conversion core structure which can be connected to a fiber with low loss regardless of wavelength and has a large process tolerance, and a method of manufacturing the same. Is to do.

[0007]

In order to achieve the above object, an optical waveguide having a spot size conversion core structure according to the present invention comprises a linear waveguide core and a specific refractive index having a smaller width and height than the linear waveguide core. With other linear waveguide cores with a large difference,
Both ends are coupled to the two linear waveguides, and the tapered waveguide has a core width, a core height, and a refractive index of the core that gradually change.

In addition to the above configuration, the tapered waveguide of the optical waveguide having the spot size conversion core structure of the present invention has a large refractive index when the core width and height are small, and a refractive index when the core width and height are large. Is preferably small.

In addition to the above configuration, the tapered waveguide of the optical waveguide having the spot size conversion core structure of the present invention preferably has a refractive index gradient not only in the longitudinal direction of the core but also in the height direction.

[0010] In addition to the above structure, the relative refractive index difference of the optical waveguide having the spot size conversion core structure of the present invention is preferably 0.8% or more for a large one and 0.45% or less for a small one. .

It is preferable that the core of the optical waveguide having the spot size conversion core structure of the present invention be formed on a quartz substrate or a silicon substrate.

According to the method of manufacturing an optical waveguide having a spot size conversion core structure of the present invention, a linear waveguide core and other linear waveguide cores having a smaller width and height than the linear waveguide core and a large relative refractive index difference are gradually formed. A method of manufacturing an optical waveguide having a spot size conversion core structure coupled by a tapered waveguide having a variable core width, height, and refractive index, wherein the core is formed by a flame deposition method and the refractive index is changed. Is formed by changing the concentration of the source gas.

According to the present invention, when a core is formed on a substrate by a flame deposition method, a core having a large refractive index, a core having a changed refractive index and height, and a core height capable of being connected to a fiber with low loss. And a core having a refractive index are collectively formed,
The core whose refractive index and height have been changed by etching has a tapered shape, the core with a high refractive index has a straight or curved shape, and the core connected to the fiber has a linear shape. By forming a core structure that converts the spot size by processing, it can be connected to the fiber with low loss independent of wavelength, and has a large process tolerance, and has a spot size conversion core structure that can be manufactured with the current mounting technology. A wave path is obtained.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1A is a plan view showing an embodiment of an optical waveguide having a spot size conversion core structure according to the present invention, and FIG. 1B is a side sectional view of FIG. 1A. ,
FIG. 1C is a diagram showing the relative refractive index difference in the longitudinal direction of FIG. 1A.

The optical waveguide of the present invention has the following three features.

(1) The change in the relative refractive index was achieved by the change in the refractive index of the core (not the change in the refractive index of the clad).

(2) A waveguide whose relative refractive index changes is formed by a flame deposition method (not a waveguide formed by diffusion).

(3) The relative refractive index is changed by changing not only the refractive index of the core but also the height of the core (not a change only in the width of the core and the core width direction of the clad).

The present optical waveguide has a structure in which cores 4, 6, and 7 are embedded with a substrate 5 and a clad 3. The width W1 and the height T1 of the core 6 having the larger relative refractive index difference are smaller than the width W2 and the height T2 of the core 7 having the smaller relative refractive index difference. The core 6 and the core 7 are smoothly connected by the core 4 which expands in a tapered shape in the width direction and the height direction. Taper angles θ1, θ2 of the tapered core 4
Is an angle of 0.1 degrees or less.

The relative refractive index difference of the core 6 is 0.8% or more, and the core 6 of the waveguide element connected to the core 6 or the spot size of the light propagating through the optical fiber is substantially equal to the core. The relative refractive index difference, the width W1, and the height T1 are set. The relative refractive index difference of the core 7 is 0.45% or less, and the relative refractive index difference of the core 7 is substantially equal to the spot size of light propagating through the optical fiber connected to the core 7.
The width W2 and the height T1 are set. Core 6 and Core 7
The relative refractive index difference of the tapered core 4 connecting
From the relative refractive index difference of the core 7 to the relative refractive index difference of the core 7. Further, the refractive index also changes in the height direction of the core 4.

Here, in the optical waveguide shown in FIGS. 1A to 1C, since the refractive index of the core is changed, it can be made equal to the refractive index of the core to be connected. No reflection occurs due to the difference in the refractive index of the core.

If the change in the relative refractive index difference is taken by the cladding, the cores have different refractive indices and reflect. Further, in the present optical waveguide, since both the width and the height of the core are changed, a conversion waveguide that can be connected to a core having any shape can be obtained.

FIG. 2A is a longitudinal sectional view of the core when the refractive index of the core changes only in the longitudinal direction.
FIG. 2B is a longitudinal sectional view of the core when the refractive index of the core changes not only in the longitudinal direction but also in the height direction.

FIG. 3A shows that when the refractive index of the core C1 changes only in the longitudinal direction, light returns (reflection occurs) in the direction opposite to the incident direction (the direction of arrow 10).
As shown in FIG. 3B, when the refractive index of the core C2 changes not only in the longitudinal direction but also in the height direction, the incident direction (arrow 11)
Light does not return in the opposite direction (no reflection)
I understand.

That is, by changing the refractive index not only in the longitudinal direction of the core but also in the height direction, it is possible to suppress the reflected light returning from the layer whose refractive index is changing.

Next, a method of manufacturing an optical waveguide having a spot size conversion core structure shown in FIGS. 1A to 1C will be described.

FIG. 3 is an explanatory diagram for explaining a method of forming a spot size conversion core. FIG. 4A is an explanatory diagram for explaining a method for forming a tapered structure of the core and a change in the refractive index, and FIG. 4B is a view taken along the line AA in FIG.
It is a line sectional view. 5A to 5F are explanatory diagrams of a method of forming a tapered structure in the width direction of the spot size conversion core, and FIGS. 5A, 5C, and 5E show plan views.
(B), (d), and (f) show a sectional view taken along line DD, a sectional view taken along line EE, and a sectional view taken along line FF.

The core is formed on the substrate 2-1 by a flame deposition method as shown in FIG. The height of the core may be changed by changing the film thickness formed by flame deposition.
Raw material gas (SiCl ₄ , PCl
₃ , BCl ₃ , GeCl ₄ , TiCl ₃ ).

Next, referring to FIGS. 4A and 4B, FIG.
A method for manufacturing the optical waveguide shown in (a) to (c) will be described.

The flame 2-2 in which the flame hydrolysis reaction is caused by the input of the raw material gas is transferred from the line BB to the line C-B on the substrate 3-7.
The glass fine particles are formed by reciprocating between the -C lines along the lines 3-1 to 3-6. The flame 2-2 is BB
When a film is formed along the line 3-1 from the line CC to the line CC, the deposited film 3-9 in the section AA of the substrate 3-7 is formed.
Is assumed to have a height t, and
6 and the position of the flame 2-2, the flame 2-2
Is changed while gradually increasing the number of reciprocations on the lines 3-1 to 3-6, thereby forming a core film 3-10 having an inclination in the height direction on the substrate 3-8. Also,
The flame determines the concentration of the raw material gas put in the flame 2-2 as BB.
In this case, the refractive index in the longitudinal direction and the height direction is changed by changing the refractive index at the time of the line, the line CC. The glass particle film formed by the flame deposition method as described above is vitrified by performing an annealing process after the film formation.

Next, the steps after the formation of the core film will be described with reference to FIGS.

The core 4-2 formed in the steps shown in FIGS. 4A and 4B is patterned on the substrate 4-3 shown in FIGS. 5A and 5B, and the core 4-2 is formed by RIE. The cores 4-4 to 4-6 as shown in FIGS. 5C and 5D are formed on the substrate 4-3 by etching. The cores 4-4 to 4-6 are patterned so that the cores have a tapered structure in the width direction.

After the step shown in FIG. 5C, the substrate 4-3
By covering the upper cores 4-4 to 4-6 with the over cladding 4-7, the cores have a tapered structure in the width and height directions as shown in FIGS. Also, a spot size conversion core structure that changes in the height direction and the longitudinal direction is formed.

FIG. 6 shows an application example of the spot size conversion core structure. Core 6 of high refractive index portion 6-1 having a large refractive index
-5 to 6-8 are curved waveguides, and from the core pitch pa of the fiber array to the core pitch pb (of the optical waveguide to be connected)
The interval between the cores 6-5 to 6-8 is narrowed. By forming a bent portion with a waveguide core having a high refractive index, the element size L1
Becomes shorter.

[0036]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to obtain an optical waveguide which can be connected to a fiber with low loss irrespective of wavelength, has a large process tolerance, and has a spot size conversion core structure which can be manufactured by the current mounting technology.

[Brief description of the drawings]

FIG. 1A is a plan view showing an embodiment of an optical waveguide having a spot size conversion core structure according to the present invention,
(B) is a side sectional view of (a), and (c) is a diagram showing a relative refractive index difference in the longitudinal direction of (a).

FIG. 2A is a cross-sectional view in the longitudinal direction of the core when the refractive index of the core changes only in the longitudinal direction, and FIG. 2B is a diagram in which the refractive index of the core is not only in the longitudinal direction but also in the height direction. FIG. 7 is a cross-sectional view in the longitudinal direction of the core in a case where it has also changed.

FIG. 3 is an explanatory diagram for explaining a method of forming a spot size conversion core.

4A is an explanatory diagram for explaining a method of forming a tapered structure of a core and a change in refractive index, and FIG. 4B is a cross-sectional view taken along line AA of FIG.

FIGS. 5A to 5F are explanatory views of a method of forming a tapered structure in the width direction of the spot size conversion core.
(C), (e) shows a plan view, (b), (d),
(F) has shown the DD sectional view, the EE sectional view, and the FF sectional view.

FIG. 6 is an application example of a spot size conversion core structure.

FIG. 7 is a diagram showing a structure for connecting a conventional optical waveguide having a core with a relative refractive index difference of 0.8% or more to a single mode fiber.

[Explanation of symbols]

 3 Over clad 5 Substrate 4, 6, 7 core

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Seiichi Kashimura 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture F-term in Opto-Systems Research Laboratories, Hitachi Cable, Ltd. 2H037 AA01 BA31 CA34 2H047 KA04 KA13 MA05 PA01 PA21 PA24 QA04 TA32

Claims (6)

[Claims] 1. A linear waveguide core, another linear waveguide core having a smaller width and height than the linear waveguide core and a large relative refractive index difference, and both ends are coupled to both linear waveguides, and the core width is gradually increased. An optical waveguide having a spot size conversion core structure, comprising: a taper waveguide having a core height and a refractive index of the core that changes. 2. The spot size conversion core structure according to claim 1, wherein the tapered waveguide has a larger refractive index when the core width and height are smaller, and has a smaller refractive index when the core width and height are larger. Having an optical waveguide. 3. The optical waveguide having a spot size conversion core structure according to claim 1, wherein the tapered waveguide has a refractive index gradient not only in the longitudinal direction of the core but also in the height direction. 4. The larger relative refractive index difference is 0.8%.
2. The smaller value is 0.45% or less.
An optical waveguide having a spot size conversion core structure according to item 1. 5. The optical waveguide according to claim 1, wherein the core is formed on a quartz substrate or a silicon substrate. 6. A linear waveguide core and another linear waveguide core having a smaller width and height and a larger relative refractive index difference than the linear waveguide core have tapered waveguides whose core width, height and refractive index gradually change. A method for manufacturing an optical waveguide having a spot size conversion core structure coupled by a waveguide, wherein the core is formed by a flame deposition method, and a change in a refractive index is formed by a change in a concentration of a source gas. Of manufacturing an optical waveguide having a spot size conversion core structure.