JPH1010590A - Optical demultiplex/multiplex element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate type ADM(add&drop wavelength multiplexer) element with low power consumption, high resolving power and a wavelength control function. SOLUTION: Upper part/lower part waveguides 12, 14 are superposed into a two-storied structure holding a separation layer 13 therebetween in a central part, a diffraction grating 21 by a periodical change in a refractive index is formed between the separation layer 13 and the upper part waveguide 14 in the central part, and the upper part/lower part waveguides 12, 14 are made to an MQW(multiple quantum well) structure in the part of the diffraction grating 21, and recessed parts 27 are provided on ridge parts on both ends of the part of the diffraction grating 21, and an electric field formed by applying a voltage to an electrode 24 provided on the surface is isolated by the recessed parts 27, and is centralized at the MQW(multiquanta well) structural part of the waveguides 12, 14, and the refractive index is changed efficiently, and an ADD&DROPing wavelength is controlled optionally, and the low power consumption is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a WDM (wavelet
The present invention relates to an optical demultiplexing / multiplexing element that extracts or adds light of a specific wavelength from an optical waveguide and is suitable for an optical transmission system or the like.
d Drop wavelength multiplexer).

[0002]

2. Description of the Related Art Conventionally, as a light demultiplexing / multiplexing element for extracting or adding light of a specific wavelength from an optical waveguide,
Filter type devices using a dielectric multilayer film have been used. This filter type optical demultiplexing / multiplexing device is suitable when the interval between adjacent wavelength peaks is as wide as about 20 nm.

However, when multiplexing with 8, 16 or 64 waves in a limited wavelength band, for example, a 1.55 μm band by the WDM technique, the interval between adjacent wavelengths is necessarily narrowed. In an actual WDM optical transmission system, the interval between adjacent wavelength peaks is extremely narrow, about 2 nm. In such a case, the conventional filter type optical demultiplexing / multiplexing device is not suitable.

Therefore, a substrate type ADM element or the like that uses a Bragg reflection by providing a first-order diffraction grating based on a periodic refractive index change has been proposed (M.

[0005]

However, the conventional substrate type ADM device has a problem that the wavelength for ADD & DROP cannot be tuned arbitrarily. In other words, the wavelength for ADD & DROP is determined by the Bragg reflection determined by the grating interval (period of refractive index change) of the primary diffraction grating and the refractive index difference between the core and the clad. Once a device is made, it becomes fixed, and eventually ADD &
This is because the wavelength for DROP is fixed.

It is conceivable to change the refractive index difference by applying an electric field, but it is difficult to efficiently change the refractive index by simply applying an electric field, and it is impossible to perform wavelength tuning with low power consumption.

[0007] In view of the above, the present invention provides an A
It is an object of the present invention to provide an optical demultiplexing / multiplexing device in which the wavelength for DD & DROP can be arbitrarily adjusted with low power consumption and improved.

[0008]

In order to achieve the above object, in an optical demultiplexing / multiplexing device according to the present invention, a multiple quantum well formed above and below a semiconductor substrate with a low-refractive-index separation layer interposed therebetween. A waveguide layer having a structure, a first-order diffraction grating formed along the light propagation direction of the waveguide layer, an electric field application electrode, and the upper waveguide layer for isolating an electric field. It is characterized by having a recess.

When a voltage is applied to the electrodes, an electric field is formed,
The equivalent refractive index of the waveguide layer having the multiple quantum well structure changes greatly. A concave portion is provided in the upper waveguide layer, and the electric field is isolated by the concave portion. Therefore, the electric field formed by voltage application is not formed in unnecessary portions,
It is formed efficiently only in the multiple quantum well structure waveguide layer near the diffraction grating where the refractive index needs to be changed.
As a result, the refractive index can be largely changed even at a low voltage, and the wavelength of ADD & DROP determined by the period of the diffraction grating and the equivalent refractive index of the waveguide can be controlled with low power consumption.

[0010]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, after forming a groove on an n-InP substrate 11, a high-refractive-index InGaAsP layer 12, a low-refractive-index InP layer 13, and a high-refractive-index InGaAsP layer 14 are sequentially formed. A ridge portion is formed on which an InP layer 15 having a low refractive index and an InGaAsP layer 16 having a high refractive index are stacked. The lower InGaAsP layer 12 is formed as a rib-type waveguide by the groove, and the upper InGaAsP layer 1 is formed.
Reference numeral 4 designates a ridge-type waveguide by the ridge portion thereon.

These waveguides are bent so as to overlap each other at the center, and at the overlapping portion, as shown in FIG. 2, a filter region having a two-story structure sandwiching a separation layer (InP layer) 13 therebetween. . The waveguide continuing to the filter region is bent to spatially separate the input / output ports 31 and 32 and the input / output ports 33 and 34. In this manner, the waveguide is continuous from end to end as a bent portion, a filter portion, and a bent portion in this order.

In this filter section, a first-order diffraction grating 21 having a periodic structure of refractive index change is formed between the separation layer 13 and the upper waveguide layer 14 along the propagation direction of the light wave. The primary diffraction grating 21 is coupled to the upper or lower waveguide layers 12 and 14, and these layers 12, 1
4, it is only necessary to follow the propagation direction of the light wave, so that the distance between the separation layer 13 and the lower waveguide layer 12, or between the lower waveguide layer 12 and the substrate 11, or between the upper waveguide layer 14 and the low refractive index It is also possible to form between the layer 15. However,
From the viewpoint of the coupling efficiency of the light wave propagating through the waveguide layers 12 and 14 with the diffraction grating 21, it is desirable that the distance between the separation layer 13 and the upper waveguide layer 14 or that the separation layer 13 and the lower waveguide layer 12 be between. .
Then, in the part of the diffraction grating 21, both the upper and lower waveguides have a multiple quantum well (MQW) layer 2 as shown in FIG.
2, 23. Further, an electrode 24 is provided so as to cover the ridge in the portion of the diffraction grating 21. The electrode 24 is continuous with the wire bonding pad 25 integrally. An electrode 26 paired with the electrode 24 is provided on the entire back surface of the n-InP substrate 11.

As shown in FIG. 3, the ridge portion is provided with a concave portion 27 for electric field isolation between the filter portion provided with the diffraction grating 21 and the bent portion. The recess 27 is provided by dry etching such as RIE (reactive ion etching), and has a depth of the upper waveguide (MQW layer 23, InGaAs).
The distance is set so as to reach the P layer 14), and the interval is set to 2 μm or less. Although the concave portion 27 is finally filled with a resin (polyimide or the like) covering the whole element, it may be left as an air layer.

The multiple quantum well layers 22, 2 of this filter section
3 is an InP barrier layer (composition wavelength 0.91 μm) and a well layer (composition wavelength 1.3 μm;
(1.3 μm band, 1.65 μm; 1.55 μm band) for about 10 cycles. To make this,
After the barrier layer and the well layer are alternately grown by metal organic chemical vapor deposition (MOCVD) on the entire surface of the n-InP substrate 11 provided with the groove to form the multilayer film 22, the bent portions other than the filter portion are formed. A so-called butt joint method or the like in which the multilayer film 22 is removed and the InGaAsP layer 12 is formed and embedded in the removed portion can be employed. After flattening the surface on which the multilayer film and the InGaAsP layer 12 are arranged, an InP layer (separation layer) 13 is provided on the entire surface thereof,
Further, on the entire surface of the InP layer 13, the upper multiple quantum well layer 23 and the I
An nGaAsP layer 14 is provided. That is, the InP layer 1
A barrier layer and a well layer are alternately grown on the entire surface of 3 to form a multilayer film 23. The multilayer film 23 is removed while leaving only the filter portion, and the removed portion is filled with the InGaAsP layer 14.

The wavelengths λ1, λ2,...
, .lambda.n, the wavelength .lambda.k can be extracted from the port 32 (DROP), and the wavelength .lambda.k 'incident from the port 34 is added (ADD), and the wavelengths .lambda.1, .lambda.2,. ', ..., λn. The wavelength λk for this ADD & DROP is λk =
It is determined by 2 · Λ · neff. Here, Λ is the pitch of the primary diffraction grating (period of refractive index change), and neff is the equivalent refractive index of the waveguide (MQW layers 22, 23).

When a voltage is applied between the electrodes 24 and 26 to form an electric field, a large change in the refractive index of the MQW layers 22 and 23 can be caused. In this case, the electric field formed by the voltage applied to the electrode 24 is isolated by the concave portion 27 and concentrates only on the filter portion where the diffraction grating 21 is formed. Therefore, the MQW layer 22 can be efficiently used at a low voltage.
23 can cause a change in the refractive index.

For example, assuming that the equivalent refractive index of the MQW layers 22 and 23 is 3.25 to 3.30, the wavelength of ADD & DROP is set to ± 5 by an applied voltage change of about ± 2 V to ± 5 V.
nm to ± 10 nm. That is, by changing the applied voltage, an arbitrary wavelength can be extracted or added from 5 to 10 waves, and the voltage can be low, so that power consumption can be reduced.

In this case, a part of the ridge portion is interrupted by the concave portion 27, but the propagating light is not affected at all by the guided mode. Therefore, only the electric field is isolated, and there is no hindrance to light propagation.

In the above description, the MQW layers 22 and 23 are formed by the butt joint method. However, in the bent portions other than the central filter portion, the equivalent composition wavelength is sufficiently shorter than the waveguide wavelength, and a low-loss conductive material is used. As long as it is a wave path,
Various manufacturing methods such as a selective growth method can be employed. According to the selective growth method, fabrication is easy, in which case,
A multilayer film having an MQW structure is provided on the entire surface so that the equivalent composition wavelength is long in the center filter portion and the equivalent composition wavelength is short in other bent portions. This includes MOCVD
If a mask (for example, a silicon dioxide film) that inhibits the growth is provided in the method, the characteristic that the inhibited component grows intensively around the mask (portion not covered by the mask) is used. I do. That is, by using a mask having an appropriate pattern, only the central filter portion is set as a growth inhibition region of the MOCVD method so that its equivalent composition wavelength becomes longer.

[0020]

As described above, the ADM of the present invention is
According to the element, since the electric field is concentrated on the MQW structure waveguide in the diffraction grating portion to cause a large refractive index change in this waveguide, the Bragg wavelength can be arbitrarily set efficiently by applying a low voltage. In the WDM optical transmission system, it is possible to add or extract an optical signal of an arbitrary wavelength with low power consumption,
A very large effect in the WDM optical transmission system can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line A-A ′ of FIG. 1;

FIG. 3 is a sectional view taken along line B-B ′ of FIG. 1;

DESCRIPTION OF SYMBOLS 11 Substrate 12, 14 High refractive index layer 13 Low refractive index layer 15, 16 Ridge part 21 Diffraction grating 22, 23 Multiple quantum well layer 24, 26 Electrode 25 Pad 27 Electric field isolation recess 31-34 Port

Claims (1)

[Claims] 1. A waveguide layer having a multiple quantum well structure formed above and below a semiconductor substrate with a low refractive index separating layer interposed therebetween, and a primary layer formed along a light propagation direction of the waveguide layer. An optical demultiplexing / multiplexing device comprising: a diffraction grating; an electric field application electrode; and a concave portion provided in the upper waveguide layer for isolating an electric field.