JPS62100706A - Optical ring filter - Google Patents

Abstract

PURPOSE:To couple/separate optical signals with a wide frequency interval under a low transmission by forming an input waveguide, an output waveguide, ring-like waveguides, and optical directional coupling parts for coupling respective waveguides mutually. CONSTITUTION:The input waveguide, output waveguide, ring-like waveguides, and optical directional coupling parts 16-18 are formed on the same dielectric base and an optical ring resonator includes a single or plural ring-like waveguides having large differences of specific refractive indexs for the input waveguide and the output waveguide and reducing its sectional area smaller than that of the input and output waveguides. The radius of curvature of the waveguides 14, 15 for the optical ring resonator can be reduced by using waveguides having a large difference of specific refractive indexes and a small value at the size for the waveguides 14, 15. Consequently, the optical ring resonator having a wide resonance frequence interval and reducing its loss can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to optical multiplexers and demultiplexers that multiplex couple or separate multiple optical signals with narrow frequency intervals in optical spectroscopy or optical frequency division multiplexing transmission systems. This invention relates to the optical ring filter used.

[Conventional technology]

FIG. 6 is a diagram showing an example of the configuration of an optical demultiplexer using a conventional optical ring filter, and is particularly an apparatus for examining the characteristics of an optical ring filter.

An optical ring filter includes a ring-shaped waveguide provided between an input waveguide and an output waveguide, and a ring-shaped waveguide provided in each direction that mutually couples the ring-shaped waveguide, the input waveguide, and the output thin waveguide. This is an optical ring resonator that transmits a specific optical signal having a resonant frequency corresponding to the link length of the ring-shaped waveguide among the input optical signals.

Note that in the prior art, a ring-shaped optical fiber is used in the ring-shaped waveguide.

In FIG. 6, reference number 31 is an input port of the input optical directional coupler 35, reference number 32 is an output port of the input optical directional coupler 35, and reference numbers 33 and 34 are output optical directional ports. This is an output port of the coupler 36.

Reference number 37 is a ring-shaped optical fiber, reference number 38 is a measurement light source to which input light is optically coupled to input boat 31, and reference number 39.40 is an output monitor to which output light from output ports 32 and 34 is optically coupled. It is a light-receiving element for Measurement light #3
8 and the output monitor light receiving elements 39 and 40 are as follows:
Observed using oscillographs, etc.

This prior art is described in (``Electronics Letter'', Vol.
9, No. 24, pp. 1027-1028).

Input optical directional coupler 35, output optical directional coupler 36
In the optical ring resonator constituted by the ring-shaped optical fiber 37, resonance appears periodically, and an optical signal having this resonant frequency is transmitted and emitted from the output port 34. The resonance conditions are the frequency f of the optical signal, the link length (the length of one circumference of the ring-shaped optical fiber 37), the relative refractive index n of the optical fiber 37, the propagation constant β of the light speed C1, and the constant N, L=N・2π/β ~Nc/nf ------
It is given by (1).

Moreover, the resonance frequency interval Δf is Δf~c/L n −・---
−+21.

Among the optical signals input to the input port 31, the optical signal having a frequency that satisfies the condition of equation (1) resonates in the optical ring resonator and is extracted from the output port 34.

Optical signals of other frequencies are taken out from the output port 32. In this way, optical signals of different frequencies can be separated. The same applies to wave combining.

FIG. 7 is a diagram showing an example of conventional optical filtering characteristics. Waveform a shows the intensity of the optical signal taken out from the output port 32, and waveform a shows the intensity of the optical signal taken out from the output port 34. Link length L of optical fiber 37 = 35
．． When 8CI+1 and relative refractive index n=1.5, the resonant frequency interval Δf is approximately 559 MHz.

[Problem that the invention seeks to solve]

However, although such a conventional optical demultiplexer using an optical ring filter has good matching with a single mode optical fiber, it has the following problems.

Since the resonator is constructed of optical fiber, it is susceptible to external mechanical or thermal disturbances.

Since the resonator is constructed of optical fiber, it is difficult to manufacture a structure with a short link length, that is, one with a large resonance frequency interval of GHz or more.

A device using a single optical ring resonator has a narrow pass band width, resulting in a large pass loss for modulated light.

In order to widen the passband width, manufacturing a multi-resonator structure using multiple optical fiber rings becomes even more difficult.

Furthermore, in order to multiplex or separate multiple optical signals with narrow frequency intervals, the frequency interval of the optical signals to be optically multiplexed and demultiplexed must be widened. An optical ring resonator is required, but as the link length becomes shorter, the radius of curvature of the bent waveguide generally becomes smaller, increasing radiation loss due to bending.

This bending radiation loss is a function of the relative index difference of the waveguide, the waveguide dimensions, and the radius of curvature.

FIG. 8 is a diagram showing an example of numerically calculating the relationship between relative refractive index difference and bending radiation loss using the waveguide radius of curvature as a parameter in a waveguide with a wavelength of 1.55 μm and a waveguide size of 1 μm.

When the relative refractive index difference of the waveguide is increased, the bending radiation loss is small even with a small radius of curvature. However, if the relative refractive index difference of the waveguide is increased, the size of the waveguide that becomes a single mode must be reduced, and therefore the matching between the waveguide and a normal optical fiber deteriorates.

The present invention solves these conventional problems,
The object of the present invention is to provide an optical ring filter that combines and separates optical signals with relatively wide frequency intervals with low loss.

[Means for solving problems]

The present invention includes an input four-wave product, an output waveguide, a ring-shaped waveguide, and an optical directional coupling part that couples each of the waveguides to each other. In the optical ring filter, the coupling part is an optical ring resonator that transmits an optical signal of a specific frequency that resonates in the ring-shaped waveguide among the input optical signals of the input waveguide. The output waveguide, the ring waveguide, and the optical directional coupling part are formed on the same dielectric substrate, and the optical ring resonator has a relative refractive index with respect to the input waveguide and the output waveguide. It is characterized by including a single or multiple ring-shaped waveguides with a large difference and a small waveguide cross-sectional area.

[For production]

The optical ring resonator waveguide that is coupled via the input/output waveguide and the optical directional coupler has a large relative refractive index difference and a small waveguide size. The radius of curvature of the waveguide can be reduced. Therefore, it is possible to realize an optical ring resonator with a wide resonance frequency interval and low loss.

In addition, the input/output waveguide has the same shape as a normal optical fiber (
By making the relative refractive index difference Δn ~ 0.3%), the compatibility with ordinary optical fibers for input and output is improved. By forming it on a substrate, it is possible to configure an optical ring filter that is less susceptible to external shadows.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. The first embodiment shows the configuration of an optical ring filter having a double resonator structure using two optical ring resonator waveguides. The present invention uses an optical ring resonator waveguide integrally formed on a dielectric substrate instead of a conventional ring-shaped optical fiber.

In FIG. 1, reference number 10 is a planar waveguide substrate, reference number 11 is an input boat, reference number 12.13 is an output boat, reference number 14.15 is an optical ring resonator waveguide,
Reference number 16 is an output optical directional coupler, reference number 17 is an intermediate optical directional coupler, and reference number 18 is an input optical directional coupler.

Here, input port H1, output port 12.13, 4
The relative refractive index difference of the waveguide (Δn=0.3%) and the waveguide dimension (D=8 μm) are almost the same as those of a normal optical fiber. The optical ring resonator Shikahaji 14.15 is connected to the input boat 1.
1. The structure has a larger relative refractive index difference and smaller waveguide dimensions than the waveguides of the output ports 12 and 13.

Planar waveguide substrate 10 is a dielectric substrate such as multi-component glass or quartz. The optical ring resonator waveguides 14 and 15 with a large relative refractive index difference have potassium (
A high refractive index portion is formed by diffusing K) ions or tantalum (Ta) ions.

Next, the four-wave path shape will be explained using an example in which five optical signals arranged at 5 GHz intervals are demultiplexed.

FIG. 2 is a diagram showing the arrangement of five optical signals arranged at 5 GHz intervals to be demultiplexed.

If the resonance frequency interval Δf is chosen to be 40 GHz, then in equation (2), ΔF = 40 x 109tlzXn =
1.5, C=3×10 μm/sec, so the ring length is about 5 mm (radius of curvature ~0.8 mm). Therefore, from the numerical calculation example in Figure 8, the waveguide size is 1 μm.
, if the waveguide relative refractive index difference Δn is selected to be about 5%, the radiation loss of the bent waveguide is negligibly small.

The filtering characteristic T of this double optical ring resonator is T [a − b ) = −j k,”−kz·exp
(-jφ) / [[1 ((1-+") (1-kz"))
""・exp(-jφ)]2+k%(Ik+)'
It is given by exp(-j2φ). Here, k is the coupling coefficient of the output optical directional coupler 16 and the input optical directional coupler 18, and k2 is the coupling coefficient of the intermediate optical directional coupler 17. Further, φ is the ring-circumference phase delay amount of the optical fiber ring 14, 15.

FIG. 3 is a diagram showing the optical filtering characteristics of the double optical ring resonator, and shows the optical filtering characteristics when the coupling coefficient of the intermediate optical directional coupler 17 is set to 2 as a parameter.

FIG. 4 is a diagram showing the optical filtering characteristics of a single optical ring resonator.

As shown in FIGS. 3 and 4, when a dual optical ring resonator is used, an optical ring filter with a wide passband width can be obtained.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

The feature of the second embodiment is that it basically has the same configuration as the first embodiment, but that means is provided for correcting changes in the optical filtering characteristics due to external disturbances. That is,
Distributed transition type reflection mirror 21 in the waveguide of the output port 12
and output port 12 and output port 22 on the opposite side.
is equipped with a light receiving element 23, and an optical ring resonator waveguide 14.1.
The current of the heating electrodes 24 and 25 provided in the photodetector 23
This configuration includes a phase adjustment circuit 26 that is controlled by the output of.

Part of the light toward the output port 12 is reflected by the distributed feedback reflection mirror 21, and most of the reflected light is received by the light receiving element 23, and the heating electrode 24 is adjusted by the phase adjustment circuit 26 so that the output is maximized. By controlling the current of .25 and the amount of propagation phase delay in the optical ring resonator waveguides 14 and 15, it is possible to correct changes in optical filtering characteristics due to external disturbances.

〔Effect of the invention] As explained above, the present invention has the following effects.

■ Since the optical ring resonator is constructed on the same dielectric substrate, it is stable and less susceptible to external mechanical and thermal disturbances.

■ To form an optical ring resonator on a dielectric substrate,
The ring length is short, that is, the resonance frequency interval is wide (G
tl z order) can be easily manufactured.

■ By increasing the relative refractive index difference of the optical ring resonator waveguide with a small radius of curvature and reducing the waveguide dimensions, it is possible to maintain the single mode property of the waveguide and reduce the bending radiation. .

■ Since it has a double resonator structure and can be easily manufactured, it has a wide passband width and can therefore realize an optical ring filter that can combine and separate optical signals with a wide frequency interval in a smart manner.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a diagram showing the arrangement of five optical signals arranged at intervals of 5 GIIz. FIG. 3 is a diagram showing optical filtering characteristics of a double optical ring resonator. FIG. 4 is a diagram showing the optical filtering characteristics of a single optical ring resonator. FIG. 5 is a block diagram showing a second embodiment of the present invention. FIG. 6 is a diagram showing an example of the configuration of an optical filter using a conventional optical ring filter. FIG. 7 is a diagram showing an example of optical filtering characteristics of a conventional optical ring resonator. FIG. 8 is a diagram showing an example of numerically calculating the relationship between the relative refractive index difference and the bending radiation loss using the waveguide radius of curvature as a parameter. 10... Planar waveguide substrate, 11... Input port,
12.13... Output port, 14.15... Optical ring resonator waveguide, 16... Output optical directional coupler, 1
7... Intermediate optical directional coupler, 18... Input optical directional coupler, 21... Distributed feedback reflection mirror, 22...
Output port, 23... Light receiving element, 24.25...
Heating electrode, 26... Phase adjustment circuit, 31, Input port, 32.33.34... Output port, 35...
- Optical directional coupler for input, 36... Optical directional coupler for output, 37... Optical fiber, 38... Light source for measurement,
39.4o... Light receiving element for output monitor. Patent Applicant: Nippon Telegraph and Telephone Corporation Representative, Patent Attorney Nao Takashi Ide Optical filtering characteristics of dual optical ring resonator Figure 3 Optical filter lettering characteristics of single optical link resonator Figure 4 Second embodiment of the present invention Figure 5 Conventional example Figure 6 Optical filtering characteristics Figure 7 Figure 8

Claims (1)

[Claims] (1) An input waveguide, an output waveguide, a ring-shaped waveguide, and an optical directional coupling section that couples each of the waveguides to each other, and the ring-shaped waveguide and the optical directional coupling section are provided. , an optical ring filter that is an optical ring resonator that transmits an optical signal of a specific frequency that resonates in the ring-shaped waveguide among the input optical signals of the input waveguide; The waveguide, ring waveguide, and optical directional coupling part are formed on the same dielectric substrate, and the optical ring resonator has a large relative refractive index difference with respect to the input waveguide and output waveguide. An optical ring filter comprising a single or plural ring-shaped waveguides each having a small waveguide cross-sectional area.