JP3149671B2 - Method for manufacturing mode-field-diameter enlarged optical waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to an optical waveguide formed on a glass substrate or a Si substrate, a method of manufacturing a topically optical waveguide path of the enlarged mode field diameter, especially for improving the optical coupling characteristics Things.

[0002]

2. Description of the Related Art In addition to light emitting / receiving elements and optical fibers, optical directional couplers, optical star couplers, optical multiplexers / demultiplexers, optical switches, etc. There is a need for optical passive components with optical signal processing and control functions.

[0003] Optical passive components can be classified into a bulk type, an optical fiber type, and an optical waveguide type. Among these, the optical waveguide type component is a component that can be expected to be most compact, economical, and complex and integrated in function, and is being actively developed.

[0004] As one of the optical waveguide type components, a buried optical component formed by forming a slit in an optical waveguide and inserting an optical element into the slit has been studied. In such an embedded optical component, not only can the performance of the optical waveguide component be improved, but also a function (for example, an isolator) that has been difficult with the optical waveguide alone can be added.

[0005]

In order to reduce the size and increase the functionality of an optical waveguide component, it is important to increase the relative refractive index difference Δ of the optical waveguide to improve the bending loss characteristics of the optical waveguide. It is. However, when Δ is increased, the mode field diameter is reduced, so that the connection loss is increased due to the mismatch of the mode field diameter between the optical waveguide and the optical fiber, and there is a problem that the characteristics of the optical waveguide cannot be sufficiently extracted to the outside. . An example is shown below.

[0006] and the mode field diameter of the optical waveguide and 2 [omega _1, when the mode field diameter of the optical fiber was 2 [omega _2, the optical coupling loss η caused by mismatch of the mode field diameter is known to be expressed by the following formula I have.

[0007] As _{η = -20log (2ω 1 ω 2} / (ω 1 2 + ω 2 2)) (1) an example, the calculation result of the coupling loss between the optical waveguide and the optical fiber when 2 [omega ₁ is 7μm and 10μm As shown in FIG.
From the figure, the mode field diameter 2ω ₂ of the optical fiber is 1
In the case of 0 μm, when 2ω ₁ becomes 7 μm, the optical coupling loss becomes about 0.5 dB.

On the other hand, a slit is formed in the optical waveguide, and
Examination of a buried optical component in which an optical element is inserted and fixed in the slit has revealed that when the width of the slit is increased, the diffraction loss increases, so that the practically practicable slit width is at most about 30 μm. With such a narrow slit, there is a problem that the types of optical elements that can be inserted are very limited.

As a method for solving these problems, a local mode field conversion technique of an optical waveguide by a thermal diffusion method has been reported (Yanagisawa et al., 1993 IEICE Spring Conference C
-240). If the mode field diameter at an arbitrary position in the optical waveguide can be increased, the coupling loss with the optical fiber can be reduced, and the diffraction loss caused by forming the slit can also be reduced.

However, in this method, even if the mode field diameter 2ω is increased from 5 μm to 10 μm, it is necessary to heat the optical waveguide at a temperature of 1300 ° C. for 10 hours, which causes a problem in work efficiency.

In order to reduce the diffraction loss, it is necessary to increase the mode field diameter to 20 μm or more.
When it was attempted to further increase 2ω by this method, a problem occurred in that the clad glass layer was deformed and the loss of the optical waveguide was increased. In addition, this method
Since the position where the optical waveguide can be enlarged is limited to both ends of the optical waveguide, there is a problem that the mode field diameter of the optical waveguide at the position where the slit is formed cannot be enlarged.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method of manufacturing a mode-field-diameter enlarged optical waveguide having good optical coupling characteristics and low loss.

[0013]

Means for Solving the Problems In order to achieve the above object, a method of manufacturing a mode-field-diameter enlarged optical waveguide according to the present invention comprises forming a core on a substrate, and
Core surface after melting locally by heating and deforming flat
A cladding layer is formed on the substrate.
The ratio of the major axis to the minor axis of the core section of the flat shaped portion is 0.12.
It is desirable to be less than.

[0014]

[Function] By locally heating and melting the middle of a core formed on a substrate and deforming it flat, a cladding layer is formed on the core surface, so that the mode field diameter can be reduced without thermally deforming the cladding layer. Can be expanded. CO ₂ as a heating source for locally heating the middle of the core
If a laser, a micro heater, or the like is used, an arbitrary place on the substrate can be heated, and the heating range can be arbitrarily controlled.

It is known that the diffraction loss caused when a slit having a width d without a waveguide effect is formed in the middle of a waveguide can be obtained by the following equation.

Η = 1 / (1 + z ² ) (2) where z = λd / (2πnω ₁ ² ) (3) where λ is a wavelength, n is a refractive index of an optical element inserted into the slit, and 2ω ₁ is This is the mode field diameter of the optical waveguide.

FIG. 2 shows the calculated value of the diffraction loss with respect to the slit width when 2ω is a parameter (λ = 1.5
5 μm, n = 1.0). From the figure, it can be seen that the diffraction loss decreases as 2ω increases.

FIG. 3 shows a calculation result of a mode field shape when an optical waveguide having a core size of 8 μm × 8 μm is deformed to have a constant cross-sectional area (64 μm ² ) and a flat shape in cross-section. Marcatili's theory was applied for the calculation.
The relative refractive index difference of the core was set to 0.3%. The figure shows one quadrant obtained by dividing the mode field into four parts.
Is the ratio of the major axis to the minor axis (ε = minor axis diameter / major axis diameter), a is the radius on the major axis side of the mode field, and b is the radius on the minor axis side. From the figure, it is understood that the diameter on the long axis side of the mode field can be increased by decreasing the long axis ratio ε of the core.

FIG. 4 shows the relationship between the major / minor axis ratio ε of the core and the radius b on the minor axis side of the mode field in detail. From the figure, it can be seen that by setting ε <0.12, b also becomes larger than before deformation.

[0020]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 3 shows an outline of a manufacturing process of a mode field diameter enlarged optical waveguide according to one embodiment of the present invention.

First, a core glass film (composition: TiO ₂ —SiO ₂ , relative refractive index difference Δ = 0.
3%), and this film is patterned into a core 2 having a size of 8 μm × 8 μm by photolithography and dry etching (step 1). The core pattern of this embodiment has a wavelength of 1.31 μm from the first port P1 into the core 2.
When light of 1.55 μm is incident on the third port P3, light of 1.55 μm is emitted from the second port P2.
Is a pattern having a directional coupler type optical demultiplexer 3 designed at the center of the substrate 1 so as to emit 1.31 μm light. Next, the middle of the core 2 near the second port P2 (portion where the slit is formed) on the substrate 1 was locally heated with a CO ₂ laser (carbon dioxide laser) 5 for 5 minutes (step 2). As a result, the core 2 of the laser irradiation section (heating section) 4 was melted, the diameter was increased in the horizontal direction and the diameter was reduced in the vertical direction, and the section was flattened. As another heating source, for example, a micro heater, an oxyhydrogen flame heater, or the like can be used.
By using these heating sources, any place on the quartz glass substrate 1 can be heated. Further, the heating range can be arbitrarily controlled. Subsequently, the quartz glass substrate 1
A soot to be the clad layer 6 was deposited thereon by the flame volume method, and then sintered and vitrified (step 3). A slit 8 having a width of 100 μm was formed in the optical waveguide with cladding 7 so as to cut the core 2 of the laser irradiation section 4 almost vertically (step 4). The slit 8 is machined by, for example, a mechanical cutting method using a diamond saw or RIE.
A chemical technique such as (reactive ion etching) can be used. The reflection characteristics can be changed by changing the angle between the slit 8 and the optical axis of the optical waveguide. Finally, optical fibers 10, 11, and 12 were fusion-spliced to the ports P1 to P3 of the optical waveguide 7 to obtain a mode-field-diameter enlarged optical waveguide 9 with slits. Further, for comparison, an optical waveguide with a slit was manufactured with the same core dimensions and the conventional method without performing the heat treatment.

After the above step 3, the loss of the optical waveguide of this embodiment was measured and compared with the conventional optical waveguide without heat treatment. The loss difference between the two was as small as 0.1 dB or less, and it was confirmed that there was almost no increase loss due to the heat treatment. When the optical waveguide was cut and the mode field diameter of the portion was measured by the far field pattern method, the mode field diameter of the portion subjected to the heat treatment by laser irradiation was longer than that of the portion not subjected to the heat treatment. The side was magnified 3 times and the minor axis side was magnified 1.4 times.

In this embodiment, the case where quartz glass is used for the optical waveguide substrate 1 has been described.
The present invention can be applied to i or multi-component glass.

When the insertion loss of the optical waveguide of the present embodiment after the slit processing is formed and the insertion loss of the conventional optical waveguide with a slit are compared, the optical waveguide of the present embodiment has a lower loss of 2.5 dB than the conventional optical waveguide with a slit. there were. This can be said to be the effect of increasing the mode field diameter.

Further, 1.31 μm transmission / 1.55 μm was transmitted through the slit 8 of the optical waveguide 9 with a slit manufactured in this embodiment.
A μm cut-off optical filter (thickness: 90 μm) was inserted and fixed with an adhesive to produce a filter-embedded duplexer. 1.
31 band transmission loss 1 dB or less, isolation 50 d
The characteristic of B or more was obtained. As compared with the conventional optical waveguide type duplexer, the isolation is improved by 20 dB or more.

In addition to this embodiment, an optical attenuator, an optical splitter, an optical multiplexer / demultiplexer, an optical isolator, an optical circulator, etc. are manufactured by changing the optical element inserted into the slit. It has been confirmed that these are also effective.

The end of the core 2 (ports P1, P2,
P3) was subjected to a heat treatment to produce an optical waveguide whose mode field diameter was enlarged, and the coupling characteristics between the optical fibers 10, 11, and 12 were evaluated. The result that the loss due to the optical axis shift was also reduced was obtained.

[0028]

In summary, the mode feel of the present invention is as follows.
According to the manufacturing method of the optical waveguide with enlarged diameter, the core is placed on the substrate.
Formed, locally heated in the middle of this core and deformed flat
After that, a cladding layer was formed on the core surface.
Therefore, the core can be formed without thermally deforming the cladding layer.
The mode field diameter can be enlarged at a position where the

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a calculation result of a connection loss due to mode field diameter mismatch.

FIG. 2 is a graph showing an example of a result obtained by calculating a relationship between a slit width and a diffraction loss by using a mode field diameter as a parameter.

FIG. 3 is a graph showing an example of a result obtained by calculating a change in a short-axis side mode field shape when a long-axis ratio of a core is changed.

FIG. 4 is a graph showing an example of a result obtained by calculating a change in a minor axis side mode field diameter when a major axis ratio of a core is changed.

FIG. 5 is a series of process charts showing a method for manufacturing a mode-field-diameter enlarged optical waveguide of the present invention.

[Explanation of symbols]

1 substrate 2 core 4 laser irradiation portion (heating portion) 5 CO ₂ laser beam (heating means) 6 cladding layer 7 optical waveguide 8 slits

Continuation of the front page (56) References JP-A-64-49004 (JP, A) JP-A-6-43330 (JP, A) JP-A-6-174954 (JP, A) JP-A-4-220609 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/12-6/14 JICST file (JOIS)

Claims (1)

(57) [Claims] A core is formed on a substrate.
Core surface after melting locally by heating and deforming flat
A cladding layer is formed on the
A method for manufacturing an optical waveguide having an expanded field field diameter .