JPH1010589A - Optical demultiplex/multiplex element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate type ADM(add and drop wavelength multiplexer) element with high wavelength resolution with 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, and 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 an MQW(multiple quanta well) structure in the part of the diffraction grating 21, and by applying a voltage to an electrode 24 provided on the surface, the refractive index of the part of the MQW structure of the waveguides 12, 14 is changed, and an ADD&DROping wavelength is controlled optionally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical demultiplexing / multiplexing device for extracting light of a specific wavelength from an optical waveguide and adding the light in reverse order, and in particular, to an ADM (Add and Drop Wavelength).
gth Multiplexer).

[0002]

2. Description of the Related Art In recent years, WDM (wavelength multiplexing technology) has been actively used as a technology for increasing the capacity for constructing a long-distance, large-capacity optical fiber transmission system. In brief, this is to transmit information by transmitting a signal to transmission light whose wavelength is gradually changed in one optical fiber, and to increase the transmission capacity according to the number of wavelengths. However, when trying to multiplex 8 waves, 16 waves or 64 waves within a limited wavelength band, for example, 1.55 μm band, the interval between adjacent wavelengths is inevitably narrowed, and the emission wavelength source and the specific wavelength are separated. The specifications of the devices that are waved or multiplexed (taken out or added), couplers, etc. will also be quite strict.

[0003] As a device for demultiplexing or multiplexing a specific wavelength, a filter-type device using a dielectric multilayer film has been conventionally used, and can be used sufficiently when the interval between adjacent wavelength peaks is as large as about 20 nm. However, in an actual WDM, the interval is about 2 nm, which is almost one tenth, so that the filter method is no longer suitable for WDM.

Therefore, at present, research and development of a fiber-type device utilizing wavelength selectivity by a diffraction grating called a fiber grating (FG) is being conducted. This is a structure having a periodic refractive index change by irradiating a high-output light such as an excimer laser with a high-power light, such as an excimer laser, after applying a phase shift mask to an optical fiber in which the core is highly doped with Ge. It is a built-in one. Further, a substrate type waveguide having a periodic structure having a similar refractive index has also been proposed (M

[0005]

However, in the FG or the substrate type waveguide having the periodic structure of the refractive index, there is a problem that only a specific wavelength can be added and dropped. In these, ADD & D is performed by Bragg reflection determined by the refractive index difference between (the period of) the periodic structure and the core / clad.
The wavelength for ROP is determined. However, once the periodic structure itself is created, the period cannot be changed, and the wavelength for ADD & DROP is fixed. Therefore, it is necessary to make a device having a periodic structure corresponding to several wavelengths each time, or to prepare a device in advance.
Tuning to DROP is impossible.

[0006] 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 improved so that the wavelength for DD & DROP can be arbitrarily tuned.

[0007]

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. It is characterized by having a waveguide layer having a structure, a primary diffraction grating formed along the light propagation direction of the waveguide layer, and an electric field application electrode.

The wavelength for ADD & DROP is determined by the period of the diffraction grating and the equivalent refractive index of the waveguide. However, since the waveguide layer has a multiple quantum well structure in which the equivalent refractive index changes greatly when an electric field is applied, ADD & DR is applied by the voltage applied to the electrode.
It is possible to tune the wavelength for OP.

[0009]

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.

[0010] These waveguides are bent so as to overlap each other at the center, and at the overlap, as shown in FIG. 2, a filter region having a two-story structure sandwiching a separation layer (InP layer) 13. . 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 portion, a first-order diffraction grating 21 having a periodic structure of a change in refractive index is formed between the separation layer 13 and the upper waveguide layer 14 along the light wave propagation direction. 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.

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. For example, if the equivalent refractive index of the MQW layers 22 and 23 is 3.25 to 3.30, ± 5 V to ± 1
± 5 nm to ± 10 nm due to applied voltage change of about 0V
The wavelength for ADD & DROP can be changed as the distance increases. That is, by changing the applied voltage, an arbitrary wavelength can be extracted or added from 5 to 10 waves.

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 guided 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.

[0016]

As described above, the ADM of the present invention is
According to the element, M which causes a large change in the refractive index when an electric field is applied
By employing the QW structure, the Bragg wavelength can be arbitrarily controlled by voltage control. Since such an optical demultiplexing / multiplexing device having a wavelength control function can be obtained, an optical signal of an arbitrary wavelength can be added or extracted in a WDM optical communication system, which is very effective.

[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;

[Explanation of symbols]

 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 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 and an electric field application electrode.