JPS60175025A - Optical demultiplexer - Google Patents

Abstract

PURPOSE:To make demultiplexing without insertion loss, easy integration, easy tuning of a center wavelength, etc. possible by using a grating due to a p-n junction waveguide to which a current lower than an oscillation threshold is charged. CONSTITUTION:When the charging current is flowed in the forward direction to a p-n junction wavelength having a periodic structure LAMBDA=lambda0/2N (N is an equivalent refractive index), an inverted distribution of electrons and positive holes due to a carrier is formed, and the waveguide 1 becomes a gain medium. Consequently, if signal lights having wavelengths lambda1, lambda2...lambda0...lambdan are made incident while keeping the charging current lower than the oscillation threshold, only the wavelength lambda0 is amplified and reflected, and signal lights having the other wavelengths pass through because their phases do not coincide with the phase of the grating period. The reflected signal light having the wavelength lambda0 is demultiplexed by a beam splitter 4 and is discharged. When the charging current is changed, the refractive index is changed by the carrier, and thereby, the center wavelength is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a compact optical demultiplexer with sharp wavelength selectivity.

(Background Art) As a conventional optical demultiplexer of this type, there is a directional coupler type optical demultiplexer that utilizes the fact that the coupling characteristic between two optical waveguides has wavelength selectivity. The wavelength selectivity of this optical demultiplexer is determined by the degree of coupling between the two optical waveguides, and in order to sharpen the selectivity, the degree of coupling must be weakened. As a result, there are drawbacks such as a long element length, increased insertion loss, and a requirement for high manufacturing precision. Furthermore, since the wavelength selection characteristic has periodicity, it is difficult to selectively extract light of a single wavelength with a single element.

In addition, Pantono! dielectric multilayer film can be used as a wavelength selective element. There are optical demultiplexers that use filters, but they have drawbacks such as difficulty in forming a leading waveguide and integrating them, difficulty in later tuning the center wavelength, and large insertion loss.

(Problem of the Invention) The present invention utilizes the characteristics of an active type optical filter in order to solve these drawbacks, and will be described in detail below with reference to the drawings.

(Structure and operation of the invention) FIG. 1 is an embodiment of the present invention, and is a schematic diagram of the structure. 1 is a waveguide composed of a pn junction and has a structure with a period A. 2 and 3 are claddings of the waveguide 1, and these structures are similar to those realized as an embedded DFB radar. Reference numeral 4 is a beam splitter, which has a function of separating and extracting reflected light. Therefore, although a beam sinter is used here for the sake of simple configuration, an optical circulator may also be used. Also, the incidence of signal light,
Although the extraction is simply indicated by an arrow in the drawing, it goes without saying that a waveguide structure may also be used.

The grating of periodic structure Δ is now long! In a certain case, the maximum reflectance, the center wavelength λ, and the wavelength width Δλ are expressed as shown below for each plate.

nM = tanh (Kl) (1) λo = 2N-
A (2) However, K is the coupling coefficient, N is the isolateral refractive index of the waveguide, and Ng
roup is an isolateral group refractive index and is approximately equal to N.

FIG. 2 shows the RM, λ0. expressed by equations (1), (2), and (3). It shows the wavelength dependence of reflectance explaining Δλ. For example, λO=1.5μm, A=
0.214 When composed of Jim's GaAtAs/GaAs material, tiRM≧0.4. The characteristic of Δλ≦IOX can be easily obtained. When an injection current flows in the forward direction through this pn junction waveguide, an inverted distribution of electrons and holes due to carriers is formed, and the waveguide 1 becomes a gain medium. Therefore, when the injection current is kept below the oscillation threshold, λ1. λ2・
...λ0. ...If the signal light of λn is incident, then λ.

Only the signal light of the wavelength is amplified and reflected, and the signal light of other wavelengths is passed because the phase of the grating period and the wavelength do not match. The reflected signal light of λ0 can be emitted and split by the beam splitter 4. Note that when the injection current is changed, the refractive index changes due to carriers, and the center wavelength can also be changed using equation (2). In addition, if there is reflection at the incident surface of the pn junction waveguide, the signal light emitted from the beam snoritzer 4 will have a wavelength of λ. It is desirable to apply an anti-reflection coating to prevent light of other wavelengths from leaking.

Needless to say, these structures can be integrated using semiconductor process technology.

(Effect of the invention) As explained above, the pn in which the current is injected below the oscillation threshold
Demultiplexing using a grating with a junction waveguide has the following advantages.

(1) Since there is a gain ', it is possible to perform demultiplexing and further amplification without insertion loss.

(2) Very sharp wavelength selectivity can be obtained.

(3) It has a switching function by turning the injection current on and off.

(4) It is possible to monitor the selected signal wavelength light by changing the terminal voltage of the pn junction waveguide.

(5) Long life.

(6) It is inexpensive because it can be mass-produced.

(7) Compact integration is possible.

[Brief explanation of drawings]

Figure 1 is a diagram showing the configuration of an embodiment of the present invention, and Figure 2 is a diagram showing the wavelength dependence of reflectance. 1... A waveguide composed of a pn junction in which a grating with a period Δ is formed, 2, 3... Cladding of the waveguide 1, 4... Beam silicate. Figure 1 Figure 2

Claims (1)

[Claims] In an optical demultiplexer that selects and extracts light λ0 of a specific wavelength from input signal light containing a plurality of wavelengths, there is a beam splitter that receives the input signal light, and A=λo/2 disposed after the beam splitter.
It is characterized by having a pn junction waveguide having a periodic structure of N (where N is an equal refractive index), and controlling the demultiplexing center wavelength λ0 by injecting a current below the oscillation threshold into the pn junction waveguide. optical demultiplexer.