JPS62283302A - Optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To form a simple and inexpensive optical multiplexer and demultiplexer by constituting the same of waveguides formed on a semiconductor substrate and an n-type doped layer which is formed in the waveguides by doping a donor impurity at a high concn. and has the refractive index different from the refractive index of the waveguide part. CONSTITUTION:The waveguides are formed of an intrinsic semiconductor core layer 1 and clad layer 4. The n<+> doped layer 2 exists within the plane having a half angle theta of an intersection angle 2theta. The semiconductor material includes GaAs or InP and mixed crystal of GaXAl1-xAs or mixed crystal of InxGa1- xAsyP1-y are used for the material of the clad layer 4. These materials are selected by the desired wavelength desired to be multiplexed and demultiplexed. The n<+> type doped layer 2 is formed by doping the donor impurity at a high concn. into the mixed crystal of the intrinsic semiconductor core layer 1.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a multiplexer/demultiplexer used in optical wavelength division multiplexing communication.

(Prior Art) FIG. 8 shows an example of a conventional duplexer that has been often used as a duplexer. This is called a multi-reflection interference film duplexer. In FIG. 8, 10a is an input optical fiber, 1
0b is an output optical fiber that extracts only a specific wavelength, 11
1 is a dielectric multilayer film, and 12 is a sheet of glass.

Each of the six dielectric multilayer films 11 has the property of transmitting only light of a certain wavelength and reflecting all the rest. The dielectric multilayer film is made by alternating a material with a high refractive index (mainly Zn5) and a material with a low refractive index (mainly MgFz) at a thickness of approximately λ/4 for the wavelength λ of the light to be transmitted. 2
It has a structure with 0 layers stacked on top of each other.

A multiplexer/demultiplexer with this structure requires very high precision alignment of the axes between the optical fibers, which necessitates a more precise structure, making it expensive.

(Problems to be Solved by the Invention) An object of the present invention is to provide a simple and inexpensive optical multiplexer/demultiplexer.

(Means for Solving the Problems) The present invention includes a waveguide formed on a semiconductor substrate and doping with a donor impurity at a high concentration.

An n-type doped layer having a refractive index different from that of the waveguide portion formed in the waveguide.

That is, for example, a first semiconductor waveguide consisting of a true shareholder core (or no '1 core) provided on a semiconductor substrate and a cladding layer, and a first semiconductor waveguide that diagonally intersects the first semiconductor waveguide. an n3-type doped layer (
or) is composed of −゛′).

Unlike conventional multiplexers/demultiplexers, this structure of multiplexer/demultiplexer does not require alignment of the optical fibers and can be monolithically integrated on a semiconductor substrate, making it possible to manufacture small and inexpensive products. The difference is in what you can do.

FIG. 1 is a perspective view of a two-wavelength optical multiplexer/demultiplexer representing an embodiment of the present invention. In the semiconductor substrate, 4 represents a cladding layer.

The intrinsic semiconductor core layer 1 and the craft layer 4 form a waveguide. The n-type doped layer 2 lies within a plane forming a half angle θ of the intersection angle 2θ, as shown in FIG.

The semiconductor material is GaAs-based or InP-based, and the material for the cladding layer 4 is GaAl, □As-based mixed crystal, or InXGa+-XASYP-ly-based mixed crystal. The choice is made depending on the desired wavelength of the wave.

The n-type doped layer 2 is formed by doping donor impurities into the mixed crystal of the intrinsic semiconductor core layer 1 at a high concentration.

Next, the operating principle of this multiplexer/demultiplexer will be explained. Here, the material of the waveguide is GaAs and AI!
We will explain the method using .

FIG. 2 is a diagram showing the absorption coefficients of intrinsic GaAs and GaAs doped with a high concentration of donors, in which the curve a
is the absorption coefficient (α) of intrinsic GaAs obtained from experiments. This absorption coefficient α is the complex electric susceptibility χ(ω)=χ′
It has the following relationship with the imaginary part χ″(ω) of (ω)−4χ−(ω).

and However, K is the wave number vector of light, ε is the dielectric constant at ω→(3).

Substituting equation (1) into the Kramers-Kronisohi relation gives the following equation. Since the refractive index n(ω) at the frequency ω is the square root of the real part of the complex permittivity ε (ω), when χ is small, the refractive index n(ω) becomes
(ω) can be calculated. The refractive index of intrinsic GaAs was determined from equation (4) and α shown in FIG. 2, and the result is shown by curve a in FIG.

Next, consider the case where GaAs is doped with a donor impurity at a high concentration. At this time, the absorption coefficient α(ω) is approximately (
EF-EC-4KIT) to the high energy side, that is, to the short wavelength side. However, Er is a doped G
The Fermi level of aAs, E is the energy at the bottom of the conduction band, K is Boltzmann's constant, and T is the absolute temperature.

FIG. 4 is a diagram showing the relationship between the conduction electron concentration in GaAs and the amount of Burstein shift. According to this, if the conduction electron concentration is doped to about 8X10''/cm', 0
．． It can be seen that a shift of α(ω) of 1ev is possible. FIG. 3 shows the results of calculating the refractive index using equation (4) for an n° type Todo-1 layer in which α(ω) has been shifted by 0.1 ev to the shorter wavelength side.

Now, let us consider the case in which light with wavelength λ2 in FIG. 3 enters the n-type Todo-1 layer refractive index nD2°) from the waveguide (refractive index n2°) (n, □ + n Da).

Next, the light with the wavelength λ1 in Fig. 3 enters the n゛ type doped layer from the waveguide (refractive index n, 21), is totally reflected in the type doped layer, and the light with the wavelength λ1 travels straight. can. for example! 1.0.83μm.

For light with λz=0.85pm, n #3.41
．． nDλ, λl =3. ．． 39. n, =3.47. nDλ2=3
．． 37, so if 6.2° and θ<13.8°, demultiplexing is possible.

If λ, 1 and λ2 are made incident on separate waveguides using exactly the same method, multiplexing is also possible.

FIG. 5 is a perspective view of a two-wavelength multiplexer/demultiplexer according to another embodiment of the present invention, and the shape is the same as that in FIG. The n゛゛ semiconductor core layer 6 is a high resistance semiconductor layer in which protons and the like are injected into the n゛゛ semiconductor core layer to compensate carriers. n°
° Since the higher the donor concentration of the semiconductor core layer, the lower the level of deterioration, the core layer located far from the high-resistance semiconductor layer is doped more heavily than the core layer near the high-resistance semiconductor layer.

In this case, in FIG. 3, the curve a is the high resistance semiconductor N
6, and the curve represents the refractive index of the semiconductor core N5. This light is totally reflected in a layer with high resistance, and it is possible to cause light with a wavelength of λ to travel straight. For example, λ. =0.81μm1λ, =0.83
For μm light, nλ.

=3.35, nDλo=3.425, nλ
1=3.41, nDλ,=3.39, 6.2
If °<θ<12.0', these two waves of light can be separated.

FIG. 6 shows another embodiment of the present invention, and shows an example in which a three-wavelength optical demultiplexer is constructed based on the embodiment shown in FIG. The same reference numerals as in FIG. 1 are the same. 2b is an n-type TODO-1 layer doped more highly than 2a.

The boundary between the n-type Todo-1 layer 2a and the core layer 1 on the total reflection side is
The n-type TODO-1 layer 2a is formed to have a steep refractive index change, but the boundary on the opposite side (the shaded area in FIG. 6) is formed to have a gradual increase in refractive index. The reason for this will be explained later.

In FIG. 7, a curve a represents the refractive index of the intrinsic semiconductor core layer 1, a curve a represents the refractive index of the n-type doped N2a,
Curve C shows the refractive index of even higher concentration n-type doped JiJ2b.

Now, as shown in FIG. 7, λ3. λ2. When λ (λ, λ2 × λ,) is incident on the n° type doped layer 2a, λ,
is totally reflected at 2a, and λ1. λ2 goes straight. To achieve this, θ1 in FIG. 6 may be set as follows.

At this time, the n° type doped layer 2a and the intrinsic semiconductor core layer 1
The refractive index must change smoothly at the boundary on the transmission side. This is because if the boundary on the transmission side has a steep refractive index change, light with a wavelength λ will be totally reflected at the boundary on the transmission side.

The remaining λ9. For demultiplexing λ2, the aforementioned two-wavelength demultiplexer may be used as is.

At this time, θ2 in FIG. 6 is a three-wavelength optical demultiplexer as shown below; similarly, a three-wavelength optical demultiplexer based on the embodiment shown in FIG. The composition is also possible. Furthermore, although demultiplexing has been explained here as an example, multiplexing is also possible by operating in the opposite direction.

(Effects of the Invention) As explained above, the present invention makes it possible to construct a simple and inexpensive optical multiplexer/demultiplexer.

Furthermore, this multiplexer/demultiplexer can multiplex/demultiplex two wavelengths that are very close to each other.

Therefore, by applying this to optical wavelength division multiplexing communication,
It has the advantage of providing an inexpensive communication network.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a two-wavelength optical multiplexer/demultiplexer representing an embodiment of the present invention. FIG. 2 is a diagram showing the absorption coefficients of intrinsic GaAs and GaAs doped with a high concentration of donors. Figure 2 shows the refractive index of intrinsic GaAs and n-type GaAs shown by curves a and b in Figure 2. Figure 4 shows the relationship between the carrier (electron) concentration of GaAs and the amount of Burstein shift. A perspective view of a two-wavelength multiplexer/demultiplexer according to another embodiment of the invention, FIG. 6 is a plan view of a three-wavelength multiplexer/demultiplexer according to another embodiment of the present invention, and FIG. 7 shows the refractive index of intrinsic GaAs. (Curve a) and the refractive index of GaAs doped with a high concentration of donors (Curves a and b). Figure 8 is a diagram showing a multi-reflection interference film duplexer that has been put into practical use in the past. . 1... Intrinsic semiconductor core layer 2, 2a, 2b--N'' type doped layer 3... Semiconductor substrate 4... Clad layer 5... N'' type semiconductor core layer 6... High resistance semiconductor Layer Fig. 4 Carrier (electron) concentration (cm-'') Refractive index n Fig. 6 7. Enter 2. Input ■ 2a, 2b--n+ type F°-bu A Fig. 7

Claims (1)

[Claims] 1. A first semiconductor waveguide formed of an intrinsic semiconductor core layer and a cladding layer provided on a semiconductor substrate, and a second semiconductor waveguide diagonally intersecting the first semiconductor waveguide. It is characterized by being constituted by a waveguide and an n^+ type doped layer formed by doping an impurity into the waveguide in a plane forming a half angle of the intersection angle of the first and second semiconductor waveguides. Optical multiplexer/demultiplexer. 2. A first semiconductor waveguide comprising an n^+ type semiconductor core layer and a cladding layer provided on a semiconductor substrate, and a second semiconductor waveguide diagonally intersecting the first semiconductor waveguide;
An optical multiplexer/demultiplexer comprising: a high-resistance semiconductor layer formed in a waveguide in a plane forming a half angle of the intersection angle of the first and second semiconductor waveguides. 3. A first semiconductor waveguide formed of an intrinsic semiconductor core layer and a cladding layer provided on a semiconductor substrate, a second semiconductor waveguide that diagonally intersects the first semiconductor waveguide, and a second semiconductor waveguide that intersects the first semiconductor waveguide obliquely; A third semiconductor waveguide that intersects at a different position from the first and second semiconductor waveguides is formed by doping impurities into the waveguide in a plane that forms a half angle of the intersection angle of the first and second semiconductor waveguides. A second n^+ type doped layer formed by doping an impurity into the waveguide in a plane forming a half angle of the intersection angle between the first n^+ type doped layer and the first and third semiconductor waveguides. An optical multiplexer/demultiplexer comprising a doped layer. 4. A first semiconductor waveguide comprising an n^+ type semiconductor core layer and a cladding layer provided on a semiconductor substrate, and a second semiconductor waveguide diagonally intersecting the first semiconductor waveguide;
a third semiconductor waveguide that intersects at a different position from the intersecting position; and a first waveguide formed in a plane that forms a half angle of the intersection angle of the first and second semiconductor waveguides. It is characterized by being composed of a high-resistance semiconductor layer and a second high-resistance semiconductor layer formed in the waveguide in a plane forming a half angle of the intersection angle of the first and third semiconductor waveguides. Optical multiplexer/demultiplexer.