JPS61284707A - Optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To permit the substantial allowance for crosstalk attenuation even if a light signal having a narrow inter-wavelength space is used and to suppress the deterioration on quality by the interference between channels by providing an optical waveguide for suppressing an unnecessary leak signal to the optical waveguide on the demultiplexing side. CONSTITUTION:The tapered waveguide 5 is used for a port 3 on a demultiplexing side and in this case the wavelength lambda1 is larger than the wavelength lambda2. The width or thickness of the tapered optical waveguide and further the refractive index are so set that the tapered waveguide 5 satisfies a cut off condition for the wavelength lambda1; for example, if the above-mentioned width is designated as W, W is set as shown by equation 1, where nf is the refractive index of the optical waveguide, nc is the refractive index of the clad enclosing the optical waveguide. The light signal of the wavelength lambda1 is cut off in the waveguide 5 and is radiated in the form of a leak mode from the optical waveguide according to equation 1. Only the light signal of the wavelength lambda2 is propagated in an arrow 8 direction.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an optical device that multiplexes or demultiplexes light, particularly an optical multiplexer, optical demultiplexer, or Regarding optical multiplexer/demultiplexer.

[Background of the invention]

Optical wavelength division multiplexing transmission technology in optical fiber communications is important for economicalization. In the above optical wavelength division multiplexing transmission,
Optical multiplexer/demultiplexer is an essential device.

Conventionally, for the purpose of simplicity and miniaturization, a filter using the wavelength characteristics of a three-dimensional waveguide directional coupler was proposed by Kimoto et al.
a 389 (Fig. 1). This utilizes the fact that the wavelength characteristics of the directional coupler change gradually, and is effective as a branching layer with a wide wavelength interval. However, when demultiplexing optical signals having a plurality of wavelengths with a narrow wavelength interval, there is a problem in that quality deterioration due to crosstalk occurs because the stopband attenuation of the demultiplexer cannot be made sufficiently large.

[Purpose of the invention]

An object of the present invention is to solve the above problems.

That is, it is an object of the present invention to provide an optical multiplexer/demultiplexer that can provide a sufficiently large amount of crosstalk attenuation even when optical signals with narrow wavelength intervals are used, and can suppress quality deterioration due to inter-channel interference.

[Summary of the invention]

The present invention provides an optical waveguide for suppressing unnecessary leakage signals in the demultiplexing side optical waveguide of a directional coupler type optical multiplexer/demultiplexer.

Optical waveguides for suppressing unnecessary leakage signals include (1) an optical waveguide that uses a tapered waveguide and has a configuration in which unnecessary leakage signals are radiated from the optical waveguide according to the cutoff condition of the propagation mode, and (2) an optical waveguide that uses a grating to emit unnecessary leakage signals. (3) an optical waveguide configured to use a ring resonator type optical waveguide and trap unnecessary leakage signals in the ring resonator; (4) the above (
Various combinations of 1) to (3) are used. In addition to the ridge type shown in FIG. 1, the structure of the optical waveguide may be a conventional three-dimensional optical waveguide structure such as a buried type, a diffused type, a loaded type, or an embankment type.

Can be used.

[Embodiments of the invention]

Embodiments of the optical demultiplexer or optical multiplexer/demultiplexer of the present invention are shown in FIGS. 2 to 7. Note that these figures show only a top view of the optical waveguide viewed from above.

First, FIG. 2 shows an embodiment in which a tapered waveguide 5 is used in the port 3 on the branching side. In this case, the wavelength λ1 is larger than the wavelength λ2. For example, λ1=1.3 μm.

Let λ = 1.2 μm. The width, thickness, and refractive index of the tapered waveguide 5 are set so as to satisfy the cutoff condition for the wavelength λ1. For example, if this width is W, then W is.

Set it like this. However, n is the refractive index of the optical waveguide,
n8 is the refractive index of the cladding surrounding the optical waveguide. According to the above equation (1), the optical signal of wavelength λ1 is transmitted through the tapered waveguide 5.
It is cut off at , becomes a leaky mode, is radiated from the optical waveguide, and only the optical signal of wavelength λ2 propagates in the direction of arrow 8. Here, the shape distribution of the tapered waveguide 5 may be a shape distribution that changes parabolically, a shape distribution that changes linearly, an arbitrary curved shape distribution, or a shape distribution that changes stepwise.

FIG. 3 shows various configuration examples of the tapered waveguide. (a) is a top view, (b) and (c) are left side views, (d
) and (e) are front views. The front view may have a tapered distribution 14 in the thickness direction as shown in (d), and (e
) may have a tapered distribution 5 in the width direction. In addition, the left side view shows the waveguide 11 as shown in (b).
．． The cladding portion may have a 10° substrate 9 configuration, or the right and left waveguides 12 and 13 of the ridge-shaped waveguide may have different thicknesses as shown in (c).

FIG. 4 shows an embodiment in which unnecessary leakage signals are diffracted by using a grating waveguide to reduce quality deterioration due to crosstalk. The grating 15 is set to have a grating constant given by λ2 for an optical signal having a wavelength λ2. However, θ is the incident angle of the optical signal. The optical signal with wavelength λ, which has been demultiplexed to the boat 2 side, and the unnecessary leakage signal λ2 enter the grating 15, but since the unnecessary leakage signal with wavelength λ2 satisfies Bragg's condition, the grating of the above grating It is diffracted in a direction with a reflection angle θ with respect to the surface and radiated from the waveguide 2. On the other hand, the optical signal of wavelength λ1 passes through grating 15 and is propagated in the direction of arrow 7.

On the port 3 side, unnecessary leakage signals are suppressed by the tapered waveguide 5, and an optical demultiplexer with very little crosstalk can be constructed. As the grating 15, a grating with a periodic change in structure (for example, sawtooth structure, 9-phase grating type, etc.) or a grating with a periodic change in refractive index (for example, a micro grating) can be used. Furthermore, chirp gelating may be used.

FIG. 5 shows an embodiment using a ring resonator type optical waveguide. The ring length of the ring resonator type optical waveguide 16 is determined, the effective refractive index is n, the speed of light is Q, m is an arbitrary integer, and the resonant wavelength is set to λ2. Here, λ2 is given by nL λ2=□ (3) C. With this setting, the unnecessary leakage signal λ2 leaked to the port 2 side is coupled to the ring resonator type optical waveguide 16 and circulates therein.

As a result, only the optical signal of wavelength λ1 is propagated in the direction of arrow 7.

The embodiments so far have been related to duplexers, but the sixth embodiment
The figure shows an embodiment of a multiplexer/demultiplexer for bidirectional transmission. That is, a branch waveguide 18 is provided at port 1, and an optical signal of wavelength λ is transmitted through this branch waveguide 18 from the direction of arrow 17.

Note that the wavelengths are assumed to be λ1>λ2>λ.

The width W3 of the branch waveguide 18 is selected as follows. If the equation (4) is satisfied, the wavelength λ0. The signal of λ2 does not propagate within the branch waveguide 18 (because it satisfies the cutoff condition). In addition, in the direction of arrow 19, not only the optical signal of wavelength λ3 but also the optical signal of wavelength λ, , λ9
．． ...You can also increase your throat. That is, branch waveguides may be added accordingly. The number of branch waveguides may be 2 or 3 in addition to port 1. In addition, in order to realize an optical demultiplexer for three or more waves, wavelength-dependent parameters (for example, L g 2 W, Hy not n
This can be easily realized by cascading optical demultiplexers with different values (x, etc.). An example in this case is shown in FIG. From the direction of arrow 20, wavelengths λ□, λ2. λ3. An optical signal of wavelength λ4 is input, and the first directional coupler 21 transmits the optical signal of wavelength λ1. The optical signal of wavelength λ2 is transmitted in the direction of arrow 25 at wavelength λ1.
The optical signal of λ4 is demultiplexed. 5a is the wavelength λ0. This is a tapered waveguide that cuts off the optical signal of λ2. The directional coupler 22 outputs the wavelength λ1. The optical signal of wavelength λ2 is demultiplexed, and the directional coupler 23 separates the optical signal of wavelength λ3. The optical signal of λ4 is demultiplexed. 1
5a is a grating that allows an optical signal of wavelength λ to pass through and diffracts an optical signal of wavelength λ2. 5b is a tapered waveguide that cuts off the optical signal of wavelength λ□. 15b
is a grating that passes an optical signal of wavelength λ and diffracts an optical signal of wavelength λ4. 5c is a tapered waveguide that cuts off the optical signal of wavelength λ.

It goes without saying that the optical multiplexer/demultiplexer of the present invention may use the directional coupler shown in FIG. 8 instead of the directional coupler shown in FIG.

〔Effect of the invention〕

According to the present invention, it is possible to construct an optical multiplexer/demultiplexer with a very small amount of crosstalk even when a plurality of optical signals with narrow wavelength intervals are used. Furthermore, since it has a simple configuration and there are no adjustment points, it can be expected to significantly reduce costs through mass production. Furthermore, it can be made monolithic with a single chip.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional directional coupler type optical demultiplexer, FIGS. 2.4 and 5.7 are plan views showing embodiments of the optical demultiplexer of the present invention, and FIG. FIG. 6 is a plan view showing an embodiment of the optical multiplexer/demultiplexer of the present invention, and FIG. 8 is a directional view applicable to the optical multiplexer/demultiplexer of the present invention. FIG. 3 is a plan view of the coupler. 1.2, 3.4... Directional coupler ports, 5, 5a
. 5b, 5c, 14-tapered waveguide, 6,7
, 8° 17.20, 24.25... Arrow indicating the propagation direction of light, 9... Substrate, 10... Clad part, 11,
12゜13... Optical waveguide, 15, 15a15b...
Grating, 16... Ring resonator type optical waveguide, 18... Branch waveguide, 21, 22.23... Directional coupler.

Claims (1)

[Scope of Claims] 1. In a directional coupler type optical multiplexer/demultiplexer, an optical waveguide for suppressing unnecessary signals is provided on the side of the optical waveguide where the optical waveguide has been demultiplexed, causing an optical signal having a wavelength other than the optical waveguide that has been demultiplexed to be emitted from the optical waveguide. An optical multiplexer/demultiplexer characterized by having a wave path. 2. The optical multiplexer/demultiplexer according to item 1, wherein a tapered waveguide in which the width, thickness, or refractive index of the optical waveguide is tapered is used as the optical waveguide for suppressing unnecessary signals. 3. The optical multiplexer/demultiplexer according to item 1, wherein a grating that diffracts unnecessary signals and passes demultiplexed signals is used as the optical waveguide for suppressing unnecessary signals. 4. The optical multiplexer/demultiplexer according to item 1, wherein the optical waveguide for suppressing unnecessary signals is a ring resonator type optical waveguide that combines unnecessary signals by resonance and allows a demultiplexed signal to pass through. 5. The optical multiplexer/demultiplexer according to item 1, characterized in that the optical multiplexer/demultiplexer is comprised of various combinations of the unnecessary signal suppression optical waveguides described in items 2 to 4. 6. A branching waveguide for cutting off the demultiplexed signal is provided in either or both of the optical waveguides of the input terminal and the output terminal of the directional coupler, and the wavelength of the demultiplexed signal is lower than the wavelength of the demultiplexed signal from the branching waveguide. 6. The optical multiplexer/demultiplexer according to any one of items 1 to 5, wherein an optical signal with a short wavelength is inputted and bidirectional transmission is performed.