JPH05203826A - Optical ring filter - Google Patents

Abstract

PURPOSE:To obtain the optical ring filter which is easily mass-produced and has excellent frequency selectivity. CONSTITUTION:A ring light guide 2 and plural input/output light guides 3 and 4 which extend while directional coupling parts 5A and 5B are formed nearby the ring light guide 2 in parallel are formed on the same substrate. Input/output ports 32 and 33, and 42 and 43 at the respective end parts of the input/output light guides 3 and 4 are tapered gradually increasing in sectional area toward the light guide ends, so a large diameter optical fiber can be connected. The input/output light guides 3 and 4 can be formed having the same large specific refractive index difference with the ring light guide 2, so they can be formed in the same process with the light guide 2 and the mass-production efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical ring filter, and more particularly to an optical ring filter which has good frequency selectivity and is easy to manufacture.

[0002]

2. Description of the Related Art Optical ring filters are used for demultiplexing, multiplexing, etc. in optical multiplex communication, in which a ring optical waveguide having a predetermined optical distance is interposed between parallel input / output optical waveguides. Thus, the light waves resonating in the ring optical waveguide are selectively demultiplexed or combined.

In such an optical ring filter, unless the spacing between the resonance frequencies of the ring optical waveguide is set larger than the frequency range used for multiplex communication, only the light wave of the desired frequency cannot be selected satisfactorily. Therefore, it is necessary to make the optical distance of the optical ring waveguide sufficiently small.

In view of this, in Japanese Unexamined Patent Publication No. Sho 62-100706, the outer diameter is reduced (and therefore the optical distance is short) by increasing the relative refractive index difference of the ring optical waveguide and decreasing the waveguide cross-sectional area. It is disclosed that a single mode condition at the time of resonance is satisfied while preventing loss due to light leakage in a large ring optical waveguide.

[0005]

However, in the above-mentioned conventional optical ring filter, the input / output optical waveguide and the ring optical waveguide, which have a small relative refractive index difference and a large waveguide cross-sectional area in consideration of matching with the optical fiber, are separated from each other. Since it needs to be formed on the substrate in a process, this may be a bottleneck in mass production.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical ring filter which can be easily mass-produced and has good frequency selectivity.

[0007]

To explain the constitution of the present invention, a ring optical waveguide 2 and a plurality of input / outputs extending in the vicinity of the ring optical waveguide 2 by forming directional coupling portions 5A and 5B therein. In the optical ring filter in which the optical waveguides 3 and 4 are provided on the same substrate 1, the input / output ports 32, 33, 42 and 43 at the respective ends of the input / output optical waveguides 3 and 4 are directed to the optical waveguide ends. The taper shape has a gradually increasing cross-sectional area.

[0008]

In the above structure, since the input / output ports 32, 33, 42, 43 at the ends of the input / output optical waveguides 3, 4 are tapered, a large-diameter optical fiber is connected to the input / output optical waveguides 3, 4. However, the main body portions 31 and 41 of the input / output waveguides 3 and 4 excluding the both end portions can have a small cross-sectional area with the same relative refractive index difference as the ring optical waveguide 2. Therefore, both optical waveguides 3 and 4 can be formed in the same process, and mass production efficiency is improved.

In this case, the tapered input / output port 32,
Although the relative refractive index difference between 33, 42, and 43 also becomes large, this portion can be made very short, so that the single mode condition is not impaired.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a straight line portion 2 parallel to a substrate 1 is formed.
An elliptical ring optical waveguide 2 having a line 1 is formed, and linear input / output optical waveguides 3 and 4 are formed in parallel with the ring optical waveguide 2 sandwiched therebetween. The substrate 1 and the optical waveguides 2, 3, 4 are made of a dielectric material such as quartz or multi-component glass, and the optical waveguides 2, 3, 4 have a refractive index higher than that of the substrate 1.

The linear portion 21 of the ring optical waveguide 2 and the portions of the input / output optical waveguides 3 and 4 adjacent thereto are directional coupling portions 5A and 5B for propagating a light wave from one to the other,
In the ring optical waveguide 2 set to a predetermined optical distance, a light wave having a frequency f1 satisfying the following expression is in a resonance state.

[0012]

## EQU1 ## Nc / f1 = nr Lr Here, N is an integer, c is the speed of light, nr is the refractive index of the optical waveguide 2, Lr is its length, and nr Lr is an optical distance.

As a result, the frequencies f1, f2, f3 from the input port 32 of the input / output optical waveguide 3 as shown by the arrows in the figure.
When an optical signal obtained by mixing the light waves of
At A, only the light wave of frequency f1 propagates to the ring optical waveguide 2, and the frequency f2 is output from the output port 33 of the optical waveguide 3.
, F3, an optical signal containing only the light waves of f3 is output.

An optical wave of frequency f1 which is selectively input to the ring optical waveguide 2 and resonates propagates to the input / output optical waveguide 4 via the directional coupling portion 5B and is output from the output port 43 of the optical waveguide 4.

In order to secure the frequency selectivity of the ring optical waveguide 2, it is necessary that the resonance frequency interval be equal to or greater than the interval between f1 and f3. Therefore, the length Lr is within the range that satisfies the following equation. Need to be kept to.

[0016]

## EQU2 ## Lr <c / (f3 -f1) nr ...

When (f3-f1) is large, it is necessary to make the length Lr of the ring optical waveguide 2 sufficiently small, and the curvature of the curved portion becomes large. Therefore, in the ring optical waveguide 2, the relative refractive index difference is increased to reduce the loss due to light leakage at the curved portion, and the waveguide cross-sectional area is made small so as to satisfy the single mode condition.

In each of the input / output optical waveguides 3 and 4, the body portions 31 and 41 except the input and output ports 32, 33, 42 and 43 at both ends have the same small cross-sectional area as the ring optical waveguide 2, and The difference in optical refractive index is also set to the same size.
And its input and output ports 32, 33, 42,
43 is formed in a taper shape whose cross-sectional area gradually increases toward the edge of the substrate 1 so that it can be connected to a large-diameter optical fiber.

The optical waveguides 2, 3 and 4 are formed in the same step by ion exchange or by forming an optical waveguide material by a CVD method or a sputtering method and then forming it into a predetermined shape through a photolithography step. When the refractive index of the substrate 1 is larger than that of the optical waveguides 2, 3 and 4, a buffer layer having a small refractive index is provided between the substrate 1 and the optical waveguides 2, 3 and 4. In this case, a semiconductor material such as silicon can be used as the substrate 1.

The tapered input and output ports 3
The difference in relative refractive index between 2, 33, 42, and 43 is also caused by the ring optical waveguide 2.
However, this part is short enough that the single mode condition is not compromised.

[0021]

[Embodiment 2] In FIG. 2, one curved portion of the ring optical waveguide 2 is provided as an optical distance control region 22, and by changing the optical distance of this portion, the optical waveguide 2 can be calculated from the following equation.
The resonance frequency f can be selected.

[0022]

Nc / f = nv Lv + nr-v Lr-v ... where c is the speed of light, nv is the refractive index of the control region, Lv is the length of the region, and nr-v is the refractive index of the non-control region. , Lr-v is the length of the region, and N is an integer.

The resonance frequency f is selected, for example, by providing a heater in the control region 22 to heat by energization and changing the nv Lv.

[0024]

As described above, since the ring optical waveguide having good frequency selectivity and the input / output optical waveguide can be formed in the same process, mass production efficiency can be greatly improved.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical ring filter according to an embodiment of the present invention.

FIG. 2 is a perspective view of an optical ring filter according to another embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 ring optical waveguide 3,4 input / output optical waveguide 31,41 body part 32,42 input port (input / output port) 33,43 output port (input / output port) 5A, 5B directional coupling part

Claims (1)

[Claims] 1. An optical ring filter in which a ring optical waveguide and a plurality of input / output optical waveguides that extend in the vicinity of the ring optical waveguide by forming directional coupling portions therein are provided on the same substrate. An optical ring filter, wherein an input / output port at each end of the output optical waveguide is tapered so that the cross-sectional area gradually increases toward the optical waveguide end.