JPH02106726A - Optical amplifier device - Google Patents

Abstract

PURPOSE:To enable amplification with good S/N ratio by utilizing the exciton- polariton mode arising from interaction of exciton in a semiconductor and light as a mechanism to lower the velocity of light than the velocity of electrons. CONSTITUTION:A light guide consisting of a clad layer 2, a core layer 3 forming multiple quantum well layers and a clad layer 4 is formed on a semi-insulating substrate 1 consisting of GaAs and after a secondary electron layer 5 and a cap layer 6 are formed thereon, ohmic electrodes 7, 8 are formed on the layer 5. Bias is impressed to this device in such a manner that secondary electrons 13 run at a satd. speed. Light is then made incident to the device. Exciton- polariton waves are generated by the coulone interaction of this light and the exciton if the multiple quantum wells are used for the core 3 of the light guide in such a manner and when the light of the wavelength corresponding to the exciton absorption peak is made incident thereto. The waves are then amplified by receiving the energy from the electrons propagating at the satd. speed. The S/N ratio is improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical amplification device. In particular, the present invention relates to a semiconductor device that amplifies traveling waves in an optical waveguide without using a stimulated emission mechanism.

[Conventional technology]

Optical amplifiers are important components in optical communication systems, and conventionally, those that utilize stimulated emission of light by carrier injection, as shown in FIG. 2, have been mainly studied. This uses the active layer 3 as a core, forms a leading wavepath with a p-type doped cladding layer 4 and an n-type doped cladding layer 2, and biases the pn junction in the forward direction to create electrons and holes in the active layer 3. It has a means to inject. When light enters the waveguide in this state, optical amplification occurs using the same stimulated emission mechanism as in semiconductor lasers. At this time, in order to prevent spontaneous laser oscillation, it is necessary to prevent the entrance surface 61 and the exit surface 62 from forming a resonator.

By the way, in this conventional device, the response time is determined by the electron-hole response time in the active layer, so the response time is 100 to 5.
Opsec is one limit. Furthermore, since the spontaneously emitted light in the waveguide always comes out on the output side, there is a problem that the S/N ratio deteriorates.

[Problem to be solved by the invention]

An object of the present invention is to provide an optical amplifier that improves the response speed of the optical amplifier and eliminates deterioration of the S/N ratio due to the contamination of spontaneous emission light.

[Means to solve the problem]

To achieve this, the present invention uses a well-known traveling waveform amplifier based on wave-particle interaction. in general,
When light (electromagnetic waves) and electrons that are spatially close to each other travel in the same direction and interact electrically, if the speed of the electrons is greater than the speed of the waves, part of the kinetic energy of the particles is transferred to the electromagnetic waves. light amplification occurs. In order to achieve this in a semiconductor, it is necessary to make electrons travel as fast as possible in the semiconductor, and at the same time, it is necessary to make light propagate at a speed slightly slower than the speed of the electrons through a leading waveguide close to the electrons.

As an example, T, nG lattice matched to GaAs or InP
The velocity of two-dimensional electrons in aAs is its maximum saturation velocity Vs
As, vs':: 1~2 x 107cm/
It has been actually measured that the vehicle is run at a speed of s. On the other hand, since the refractive index n of these semiconductors is about 3 to 4, the speed of light in a normal semiconductor waveguide is c'/=
co /n>vs (co is the speed of light in vacuum), and the above-mentioned interaction cannot occur. Therefore, a mechanism is required.

In the present invention, as a mechanism for making the speed of light slower than the speed of electrons, an exciton-polariton mo1- generated by the interaction between excitons in a semiconductor and light is used.

[Effect]

G' a As and GaA Q, multiple quantum wells made of As, InGaAs and InA lattice matched to InP
In a multiple quantum well made of QAs, strong two-dimensional exciton absorption is observed even at room temperature. When this multiple quantum well is used as the core of an optical waveguide and light with a wavelength corresponding to the exciton absorption peak is incident thereon, a wave called exciton-polariton is generated due to Coulomb interaction between this light and excitons. . In terms of image, this light is
When it propagates a little, it changes into an electron-hole pair and becomes an exciton, and after this exciton propagates a little, the electron-hole recombines and returns to light, so it can be seen as an intermediate entity between light and excitons. can. The propagation speed Vp of this wave is slightly slower than the saturation speed v5 of electrons, Vp~8×1,06
It is of the order of c+n/see. Therefore, the exciton-polar 1-wave is amplified by receiving energy from the electrons propagating at the saturation speed.

〔Example〕

The contents of the present invention described above will be explained in detail below based on examples.

FIG. 1 shows a conceptual diagram of an optical amplifier according to an embodiment of the present invention.

In this embodiment, a GaAs semi-insulating substrate 1 is used.
Undoped A'Q o, gGao, 7As cladding layer 2, Ga As 7' A Q, xG a
Core layer 3 forming a 5-xAs multiple quantum well layer, undoped A Q o, sGa O, 7As crat layer 4
A leading waveguide is formed, and a two-dimensional shield layer 5 and a cap layer 6 are then formed in the same manner as in HEMT.

Two-dimensional electrons exist in the annular GaAs layer 5, and electron supply donors for this exist at the interface of the Clarado layer 4 with the two-dimensional electron layer 5 or at the two-dimensional electron layer 6 of the cap layer 6. The interface with the dimensional electronic layer 5 is doped. After that, ohmic electrodes 7 and 8 are formed on the two-dimensional electronic layer 5. This electrode is usually A u G e / N i / A
An alloy electrode was prepared by alloying in H2 at 400'C for 5 minutes.

Thereafter, a DC bias is applied in a direction in which the two-dimensional electrons travel in the same direction as the light, so that the two-dimensional electrons travel at the saturation speed Vs. In this state, about 7
When light with a wavelength of 80 nm was incident, a light amplification effect was confirmed.

In the second embodiment, an undoped InAn As cladding layer 2 lattice-matched to the substrate is deposited on the semi-insulating LnP&plate 1.
An optical waveguide consisting of a core layer of an InGaAs/InA QAs multiple quantum well layer 3 and an undoped InA (l As cladding layer 4) is fabricated, and a HEMT is
A two-dimensional electronic layer 5 and a cap layer 6 are formed in the same manner as described above.

Two elementary electrons exist in the undoped InGaAs layer 5, and donors therefor exist in the cladding layer 4 or the carrier. After this, A u G e / N i / A u
The metal was heat treated in H2 at 300°C for 5 minutes to form an alloy electrode. In this state, the two-dimensional electron has a saturation velocity V5~2
After applying a bias so as to run at 107 .mu./sB, light having a wavelength of approximately 1.3 .mu.m corresponding to the exciton peak was incident, and light amplification was confirmed.

In both Examples 1 and 2 above, in order to increase the optical amplification factor, it was necessary to maintain the overlap ratio in which a part of the optical waveguide mode overlaps with the two-dimensional electron gas to at least 5 to 20%. .

Furthermore, as shown in the schematic diagram in FIG. 3, the light 12 in the optical waveguide propagates in a zigzag motion, so although it is originally transverse wave light, a part of the electric field is parallel to the traveling direction of the electrons 13. It comes to have a component.

The larger this component is, the stronger the interaction between electrons and polariton waves becomes. Therefore, by increasing the core thickness, increasing the refractive index difference between the cladding and the core, and increasing the angle of zigzag propagation, the interaction between electrons and polariton waves becomes stronger. In this optical amplifier, since spontaneous emission light does not originally exist in the optical waveguide, amplification with a good S/N ratio is possible.

Further, the wavelength used can be changed to some extent by changing the thickness Lw of the quantum well constituting the multiple quantum well and the thickness Ls of the barrier layer.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of an optical amplifier according to an embodiment of the present invention, Fig. 2 is a conceptual diagram of a conventional optical amplifier, and Fig. 3 is a conceptual diagram of the interaction between polariton mode light and two-dimensional electrons in a waveguide. It is a schematic diagram.

Claims (1)

[Claims] 1. Close to an optical waveguide whose core is a multi-quantum well layer with remarkable exciton absorption at room temperature and whose cladding layer is a semiconductor with a lower refractive index, within a distance that the optical mode in this waveguide can reach. An optical amplification device characterized by forming a two-dimensional electron layer and causing the two-dimensional electrons to travel at a saturation speed to amplify exciton-polariton mode light propagating in the optical waveguide.