JPH05203825A - Optical ring filter - Google Patents

Abstract

PURPOSE:To prevent a frequency jump of output light from being caused even when ambient temperature varies greatly and abruptly. CONSTITUTION:Directional coupling parts 8A and 8B are formed nearby the straight parts 21 of a ring light guide 2 in parallel and extending input/output light guides 3 and 4 are provided. A heater 5 which heats part of the ring light guide 2 and a temperature sensor 6 which detects the temperature of the ring light guide 2 are provided. A heater energizing circuit 7 controls the energizing quantity to the heater 5 so that the sum of the optical distance of the part of the ring light guide 2 where the heater 5 is provided and the optical distance of the part of the right light guide 2 where the heater 5 is not provided becomes equal to the overall optical distance of the ring light guide 2 below the upper limit value of the ambient temperature. Even if the ambient temperature varies, the overall optical distance of the ring light guide 2 is held constant, so the resonance frequency of the ring light guide 2 varies and no frequency jump is caused.

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 whose characteristics do not change depending on the ambient temperature.

[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, the optical distance of the ring optical waveguide may fluctuate due to disturbances, particularly changes in the ambient temperature, and the intensity of the demultiplexed light waves obtained in the input / output optical waveguide may decrease.

Therefore, in Japanese Patent Laid-Open No. 62-100706, a mirror is provided at the output port of the input / output optical waveguide to feed back a part of the output light so that the output light intensity is maximized. It is disclosed that the heater provided in the above is energized to adjust the optical distance of this portion.

[0005]

However, in the above-mentioned conventional optical ring filter, when the adjustment of the optical distance cannot be followed when the ambient temperature changes rapidly and greatly, the resonance frequency of the ring optical waveguide changes. When the frequency of the light of another wavelength coincides with the frequency of the light of another wavelength, the output light intensity also shows a peak, which causes a problem of frequency jump. Also,
Since most of the mirror reflected light returns to the ring optical waveguide, the feedback efficiency of the feedback light is poor, and it is difficult to maintain the control certainty.

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 does not cause frequency jump of output light even when the ambient temperature changes abruptly and largely.

[0007]

The structure of the present invention will be described. A ring optical waveguide 2 and a plurality of input / output optical waveguides 3 that extend by forming directional coupling portions 8A and 8B in the vicinity thereof.
In the optical ring filter in which 4 and 4 are provided on the same substrate 1, a heater 5 for heating at least a part of the ring optical waveguide 2 and a means 6 for detecting the temperature of the ring optical waveguide 2 are provided.
And the sum of the optical distance of the ring optical waveguide portion provided with the heater 5 and the optical distance of the ring optical waveguide portion not provided with the heater 5 of the entire ring optical waveguide at the upper limit of the ambient temperature. The heater 5 so that it is equal to the optical distance
It is provided with a means 7 for controlling the amount of electricity supplied to the device.

[0008]

In the above structure, the energization amount control means 7 controls the energization amount to the heater 5, and the optical distance of the ring optical waveguide portion provided with the heater 5 and the optical distance of the ring optical waveguide portion not provided with the heater 5. Is maintained to be always equal to the optical distance of the entire ring optical waveguide 2 under the upper limit value of the ambient temperature, regardless of the variation of the ambient temperature. Therefore, the resonance frequency of the ring optical waveguide 2 does not fluctuate and the frequency jump does not occur.

Further, since the control is performed so as to match the optical distance under the upper limit value of the ambient temperature, only the amount of electricity to the heater 5 is adjusted with respect to the variation of the ambient temperature, and cooling is unnecessary. ..

As in the conventional case, since the feedback light intensity is low, the problem that the reliable controllability cannot be maintained does not occur.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a straight line portion 2 parallel to a substrate 1 is formed.
1, an elliptical ring optical waveguide 2 is formed, and linear input / output optical waveguides 3 and 4 are formed in parallel to sandwich the ring optical waveguide 2. 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 optical waveguides 2, 3 and 4 are formed by an ion exchange method 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 process. 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 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 8A and 8B 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.

[0014]

## 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.

However, when an optical signal in which light waves of frequencies f1, f2 and f3 are mixed is input from the input port of the input / output optical waveguide 3 as shown by an arrow in the figure, only the light wave of frequency f1 is input to the directional coupling section 8A. Is propagated to the ring optical waveguide 2, and an optical signal containing only light waves of frequencies f2 and f3 is output from the output port of the optical waveguide 3.

A light wave of frequency f1 which is selectively input to the ring optical waveguide 2 and resonates propagates to the input / output optical waveguide 4 through the directional coupling portion 8B and is output from the output port 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.

[0018]

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

On the ring optical waveguide 2, a temperature sensor 6 is formed on one side of the curved portion, and a heater 5 is formed on the other side. The temperature sensor 6 is composed of a semiconductor thin film such as amorphous silicon, and the heater 5 is composed of a high resistance conductor thin film such as Ni-Cr or ITO. The output signal of the temperature sensor 6 is input to the heater energizing circuit 7, and the circuit 7 determines the energizing amount to the heater 5 based on this temperature signal.

That is, when the atmosphere temperature on which the substrate 1 is placed changes between 0 ° C. and 50 ° C., the refractive index of the ring optical waveguide portion provided with the heater 5 is nv, and the length is Lv. When the refractive index of the ring optical waveguide portion not provided is nr-v and the length thereof is Lr-v, the heater energization amount is determined so as to satisfy the following equation.

[0021]

## EQU3 ## nr (50) Lr (50) = nv (Tc) Lv
(Tc) + nr-v (Ta) Lr-v (Ta) ... Here, nr (T) and Lr (T) are the refractive index and the length of the ring optical waveguide 2 at the temperature T ° C., respectively, and
c is the heater temperature, and Ta is the temperature detected by the temperature sensor.
Note that nr (50) and Lr (50) are constants and nv
(Tc) and Lv (Tc) are related to the heater energization amount by nr
The relationship between -v (Ta) and Lr-v (Ta) and the detected temperature can be mapped in advance.

Thus, the optical distance nv (Tc) Lv (Tc) of the ring optical waveguide portion provided with the heater 5 and the optical distance nr-v (Ta) L of the ring optical waveguide portion not provided with the heater 5 are obtained.
The sum of rv (Ta) is the upper limit of atmospheric temperature (50 ° C)
The optical distance nr (50) L of the entire ring optical waveguide 2 below
By controlling the energization amount to the heater 5 so as to be equal to r (50), the resonance frequency of the ring optical waveguide 2 does not change even if the ambient temperature changes, and the frequency jump problem does not occur.

Further, in the present invention, since the optical distance of the ring optical waveguide is controlled so as to match the optical distance under the upper limit value of the ambient temperature, the amount of electricity supplied to the heater 5 is adjusted with respect to the variation of the ambient temperature. By itself, no cooling is required and the temperature control system is simplified.

It is also possible to provide a temperature sensor at the heater installation portion to directly obtain the temperature signal of this portion.

[0025]

Second Embodiment In FIG. 2, a Y-branch optical waveguide 41 for extracting a part of a light wave is formed at the output end of the input / output optical waveguide 4, and the light intensity obtained at the output port is detected by the light receiving element 9. The detection signal is input to the heater energization circuit 7, and the heater energization amount is corrected so that the detection signal maintains the peak value. With this configuration, a better demultiplexing function is realized.

In each of the above embodiments, a heater may be provided over the entire ring optical waveguide to maintain the temperature at the upper limit of the atmosphere.

[0027]

As described above, according to the optical ring filter of the present invention, it is possible to always obtain a good filtering function irrespective of changes in the ambient temperature.

[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 5 heater 6 temperature sensor (temperature detecting means) 7 heater energizing circuit (energizing amount controlling means) 8A, 8B directional coupling section

Claims (1)

[Claims] 1. An optical ring filter comprising a ring optical waveguide and a plurality of input / output optical waveguides formed adjacent to the ring optical waveguide and extending on the same substrate, wherein at least one of the ring optical waveguides is provided. A heater for heating the portion and a means for detecting the temperature of the ring optical waveguide, and the sum of the optical distance of the ring optical waveguide portion provided with the heater and the optical distance of the ring optical waveguide portion not provided with the heater. An optical ring filter comprising means for controlling the amount of electricity to the heater so as to be equal to the optical distance of the entire ring optical waveguide under the upper limit of the ambient temperature.