JP2000305055A - Electroabsorption optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro-absorption optical modulator which enhances electron confinement, obtains an efficient quantum effect, and lowers a valence band barrier to prevent hole pile-up. I do. SOLUTION: The quantum well layer 2 is sandwiched between a barrier layer I having a forbidden bandwidth wider than the forbidden bandwidth of the quantum well layer and a barrier layer II having a forbidden bandwidth wider than the forbidden bandwidth of the barrier layer I. An electro-absorption type optical modulator including a light absorption layer 4 having a structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-absorption optical modulator, and more particularly to an electro-absorption optical modulator which operates by driving with a low bias voltage and modulates a high-frequency input signal without signal deterioration. .

[0002]

2. Description of the Related Art With the development of thin film growth technology, the era has come in which a semiconductor heterojunction interface showing a steep composition change at a monoatomic layer thickness level can be formed. The multiple quantum well structure formed by stacking thin films by this thin film growth technique has been applied to optical devices such as optical modulators and optical switches.

In a quantum well structure, exciton absorption occurs at room temperature, and when an electric field is applied in a direction perpendicular to the quantum well layer,
A quantum confined Stark effect occurs in which the absorption peak shifts in proportion to the square of the electric field strength to the longer wavelength side, which is the lower energy side. In an electro-absorption type optical modulator, this is necessary to obtain a high efficiency and equivalent extinction ratio compared to the conventional Franz-Keldysh effect using a bulk. Capacity is reduced,
High-speed modulation characteristics can be obtained by low-voltage driving.

Referring to FIG. 1, a conventional example of an electroabsorption type optical modulator is a metal organic chemical vapor deposition (MOVPE).
Alternatively, it is formed in the following order by employing a molecular beam epitaxy method (MBE). The surface of the n-InP substrate 6 has n
An n-InP cladding layer 3 doped with a mold is formed. Next, InGa is deposited on the surface of the n-InP cladding layer 3.
An AsP barrier layer II is formed. This InGaAsP barrier layer
An InGaAsP quantum well layer 2 is formed on the surface of II. I
An InGaAsP barrier layer I is formed on the surface of the nGaAsP quantum well layer 2. Further, a p-type doped p-InP cladding layer 1 is formed on the surface of the InGaAsP barrier layer I. Next, the surface of the p-InP cladding layer 1 and the n-
An electrode is formed on the back surface of the InP substrate 6. A DC power supply is connected to these electrodes with opposite polarities, and a reverse bias electric field is applied vertically to the InGaAsP quantum well layer 2 and the light absorption layer 4 composed of the InGaAsP barrier layer I and the InGaAsP barrier layer II. A signal source is also connected in series to the DC power supply.

This electro-absorption type optical modulator makes light incident on one surface 41 of the light absorption layer 4 in a direction perpendicular to the plane of the drawing. Light incident on the light absorbing layer 4 from one surface 41 of the light absorbing layer 4 propagates through the light absorbing layer 4 and is emitted from the other surface. Since the region of the light absorption layer 4 sandwiched between the electrode and the electrode on the back surface of the n-InP substrate 6 operates as a modulation layer, propagating light is modulated by an applied electric field in this process, and the other side of the light absorption layer 4 is modulated. Radiated from the surface.

Here, the energy band of the conventional example is as shown in FIG. FIG. 3A shows the case where the electric field = 0, and FIG. 3B shows the case where the reverse bias electric field is applied. That is, InGaP sandwiching the InGaAsP quantum well layer 2
The energy bands of the AsP barrier layer I and the InGaAsP barrier layer II are equal. And InGaAs (P) / In
In the P system, the band offset ΔE _c of the conduction band is small, and the band offset ΔE _v of the valence band is large.

From the above, the electron-hole of the current generated when light is incident on the light absorbing layer 4 is InG
The confinement of electrons in the aAsP quantum well layer 2 is weak, and the quantum effect deteriorates. Then, when an electric field is applied to the quantum well structure, the electrons easily move out of the quantum well structure by a tunnel phenomenon, so that the absorption edge broadens and the quenching characteristics are degraded. In addition, heavy holes are difficult to cross the barrier because of a large band offset ΔE _v of the valence band. When the intensity of incident light is high, the heavy holes accumulate in the quantum well, and the frequency response characteristics deteriorate.

[0008]

An electroabsorption optical modulator having a quantum well structure as described above is made of InGaAs.
(P) / In InP system, the band offset Delta] E _c of the conduction band is small, the band offset Delta] E _v of the valence band is large. Therefore, the confinement of electrons is weak, the quantum effect is degraded, and the quenching characteristic is degraded due to the easy tunnel phenomenon when an electric field is applied. When the intensity of incident light is large, heavy holes are piled up and the frequency response characteristics are deteriorated.

An object of the present invention is to provide an electro-absorption type optical modulator which has low-voltage driving and high-speed modulation characteristics and which solves the above-mentioned problem.

[0010]

Means for Solving the Problems Claim 1: Quantum well layer 2
A light absorption layer 4 having a quantum well structure sandwiched between a barrier layer I having a forbidden bandwidth wider than the forbidden bandwidth of the quantum well layer and a barrier layer II having a forbidden bandwidth wider than the forbidden bandwidth of the barrier layer I.
An electro-absorption type optical modulator comprising Claim 2: In the electroabsorption type optical modulator according to claim 1, the forbidden band facing the barrier layer I constituting one surface of the light absorbing layer 4 and wider than the forbidden band width of the barrier layer I. It has a width and a p-type doped cladding layer 1 and faces the barrier layer II constituting the other surface of the light absorbing layer 4 and has a wider bandgap than the bandgap of the barrier layer II. Thus, an electroabsorption optical modulator including the cladding layer 3 doped with n-type was formed.

[0011] Claim 3: Claims 1 and 2
In the electroabsorption type optical modulator described in any one of the above, electrodes are formed on the surfaces of both cladding layers 1 and 3, and a direct current power supply is connected to both electrodes in opposite polarities to reversely bias the light absorption layer vertically. An electro-absorption optical modulator for applying an electric field was constructed.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a light absorption layer of an electro-absorption type optical modulator, comprising: a quantum well layer; a barrier layer I having a wider forbidden band width than the quantum well layer; And a quantum well structure composed of a barrier layer II having a wide bandgap.
By providing the light absorbing layer as described above, the electron confinement can be strengthened, an efficient quantum effect can be obtained, and the valence band barrier can be reduced, and the hole pile can be reduced. Up can be prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an embodiment of the present invention also employs metal organic chemical vapor deposition (MOVPE) or molecular beam epitaxy (MBE) to form each layer in the same manner as in the prior art. They are formed in the following order. First, the n-InP clad layer 3 doped with n-type is formed on the surface of the n-InP substrate 6. Next, an InGaAsP barrier layer II is formed on the surface of the n-InP cladding layer 3. This InGaAs
The composition of the sP barrier layer II is 1.1 μm at the photoluminescence peak wavelength. An InGaAsP quantum well layer 2 is formed on the surface of the InGaAsP barrier layer II. This In
The composition of the GaAsP quantum well layer 2 is 1.55 μm in photoluminescence peak wavelength. An InGaAsP barrier layer I is formed on the surface of the InGaAsP quantum well layer 2.
The composition of the InGaAsP barrier layer I is 1.33 μm at the photoluminescence peak wavelength. Further, InGaAs
P-InP doped p-type on the surface of the P barrier layer I
The clad layer 1 is formed.

Next, electrodes are formed on the front surface of the p-InP clad layer 1 and the back surface of the n-InP substrate 6. A DC power supply is connected to these electrodes with opposite polarities, and the InGaAsP quantum well layer 2, the InGaAsP barrier layer I and the InGaAsP
A reverse bias electric field is applied vertically to the light absorption layer composed of the barrier layer II. A signal source is also connected in series to the DC power supply.

In the above-described electroabsorption type optical modulator, the quantum well layer 2 is made to have a barrier layer I having a band gap wider than the band gap of the quantum well layer 2 and a band gap wider than the band gap of the barrier layer I. The light absorption layer 4 having a quantum well structure sandwiched by the barrier layers II is provided. This electro-absorption type optical modulator faces the barrier layer I which constitutes one surface thereof and has a p-type doped clad layer 1 having a band gap wider than the band gap of the barrier layer I. A cladding layer 2 which faces the barrier layer II constituting the other surface of the light absorption layer 4 and has an forbidden band width larger than the forbidden band width of the barrier layer II and is doped with n-type. I have.

In this electro-absorption type optical modulator, electrodes are formed on the surfaces of both cladding layers 1 and 2, and a DC power supply is connected to both electrodes with opposite polarities to apply a reverse bias electric field vertically to the light absorption layer. Apply. Here, FIG. 2 is an energy band diagram of the embodiment. FIG. 2A shows a case where the electric field is 0, and FIG.
(B) shows a case where a reverse bias electric field is applied.

As shown in FIG. 2, the n-
InGaAsP barrier layer II facing InP clad layer 3
The band offset ΔE _c of the conduction band at
Electrons are strongly confined, and an efficient quantum effect can be obtained. Then, the In facing the p-InP clad layer 1
The band offset ΔE _v of the valence band in the GaAsP barrier layer I is reduced, and the movement of holes having a high mass can be performed smoothly, thereby preventing the pile-up of holes in the InGaAsP quantum well layer 2.

[0018]

As described above, the electroabsorption optical modulator according to the present invention has an InGaAsP quantum well layer 2 as a light absorbing layer, and an InGaAsP barrier having a wider bandgap compared with the quantum well layer 2. Layer I and an InGaAsP barrier layer II having a wider bandgap compared to the InGaAsP barrier layer I
Having a quantum well structure consisting of
-InP clad layer 1 faces barrier layer I, and n-In
A P cladding layer 3 is formed so as to face the InGaAsP barrier layer II, and the surface of the p-InP cladding layer 1 and the n-In
An electrode is formed on the back surface of the P substrate 6 and a reverse bias electric field is applied vertically to the light absorbing layer. By providing the above structure, electron confinement can be strengthened, an efficient quantum effect can be obtained, and the valence band barrier can be reduced. Can be blocked.

Thus, an electro-absorption optical modulator driven at a low voltage and exhibiting high-speed modulation characteristics can be constructed.

[Brief description of the drawings]

FIG. 1 illustrates an electro-absorption optical modulator.

FIG. 2 is an energy band diagram of the embodiment.

FIG. 3 is an energy band diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cladding layer 2 Quantum well layer 3 Cladding layer 6 Substrate I Barrier layer II Barrier layer

Claims (3)

[Claims] 1. A quantum well comprising a quantum well layer sandwiched between a barrier layer I having a forbidden bandwidth wider than the forbidden bandwidth of the quantum well layer and a barrier layer II having a forbidden bandwidth wider than the forbidden bandwidth of the barrier layer I. An electro-absorption type optical modulator comprising a light absorption layer having a structure. 2. The electro-absorption type optical modulator according to claim 1, which faces the barrier layer I which constitutes one surface of the light absorption layer, and has a forbidden band width wider than the forbidden band width of the barrier layer I. A cladding layer doped with p-type, and facing the barrier layer II constituting the other surface of the light absorbing layer,
An electroabsorption optical modulator comprising an n-type doped cladding layer having a band gap wider than the band gap II. 3. The electro-absorption optical modulator according to claim 1, wherein electrodes are formed on both clad layer surfaces, and a DC power supply is connected to both electrodes in opposite polarities. An electroabsorption optical modulator characterized in that a reverse bias electric field is applied vertically to the light absorbing layer.