FR3114887A1 - TRAVELING WAVE OPTICAL AMPLIFIER WHOSE AMPLIFICATION IS CONTROLLED BY FIELD-EFFECT TRANSISTORS - Google Patents

Abstract

The present invention relates to an optical amplification device in particular in the frequency range from 1 to 800 THz using a traveling wave principle and whose gain and operating range can be controlled by field effect transistors. tricks

Description

Traveling wave optical amplifier whose amplification is controlled by field effect transistors.

The present invention relates to an optical amplification device and more particularly in the frequency range from 1 to 800 THz; using the principle of traveling waves and amplification controlled by field effect transistors.

The gain of the amplifier is stabilized by making it oscillate at a wavelength which can be variable and not used for the amplification of the input signal.

State of the art:

The invention relates to an optical amplifier using a principle of traveling waves and whose amplification is controlled by field effect transistors. Such an amplifier can be used in the field of telecommunications by optical fiber, in particular for amplifying an optical signal before transmitting it over a long distance.

Currently there are several types of optical amplifier for this application including: the semiconductor amplifier and the fiber amplifier doped with a rare earth.

For infrared transmission, the erbium-doped fiber amplifier is most commonly used. The gain recovery time in an erbium-doped fiber amplifier is greater than 0.1 ms. This high recovery time provides gain stabilization for the modulation frequencies used in the field of telecommunications which are of the order of 100 MHz to 10 GHz. On the other hand, because of a very short recovery time, semiconductor amplifiers exhibit significant gain non-linearity up to modulation frequencies of several gigahertz, when the amplifier operates in saturation mode.

Conventionally, a semiconductor optical amplifier comprises an active optical guide into which an electric current is injected transversely. The input signal, to be amplified, is injected at one end of the guide, and the amplified optical signal is collected at the other end of the guide. The gain of a conventional semiconductor amplifier is, to a first approximation, a linear function of the density of electric charge carriers in the active guide. However, it has non-linearities.

Solutions have been proposed to overcome the nonlinear behavior of a semiconductor amplifier:

- The use of an electric feedback acting on the intensity of the electric current injected into the amplifier, depending on the amplitude of the amplified signal leaving this amplifier.

- The use of quantum well semiconductor materials.

Japanese patent JP-A-01 143 382 describes a semiconductor optical amplifier comprising a semiconductor laser, the latter emitting on a first wavelength. The optical signal to be amplified has a second wavelength, different from the first. The gain is stabilized but this amplification is not satisfactory because it is resonant on the resonance peaks of the cavity, the signal to be amplified being partially reflected on the split faces and creating standing waves in the cavity. Patent EP 0 639 876 A1 describes a semiconductor optical amplifier comprising a laser. The gain is stabilized but this amplification operates on a single cavity resonance frequency.

The object of the invention is to provide an optical amplifier in which the gain is constant over a wide frequency band and where the amplification is traveling wave.

The object of the invention is an optical amplifier using a principle of traveling waves and whose gain and operating range can be controlled by field effect transistors, having reduced non-linearity, characterized by an optical guide and resonant means coupled to this guide to cause this amplifier to oscillate at a wavelength different from the wavelength of the signal to be amplified.

The amplifier thus characterized has, for any wavelength different from the oscillation wavelength, a constant progressive wave gain with respect to the variations of the amplified signal. In the amplifier according to the invention, the gain is stabilized at a wavelength not used for the amplification of the input signal.

The amplification is progressive wave, because the resonant means used resonate at a wavelength different from the signal to be amplified. The amplifier according to the invention does not present any disturbing effects of non-linearity.

According to one embodiment, the resonant means comprise a network of field effect transistors.

In some embodiments, the amplifier may have at least one resonant cavity wavelength that overlaps the gain spectrum of the amplifier, such that the gain provided by the amplifier is greater than the losses, in this case, the device becomes a source of highly polarized coherent optical radiation (possibly a plasmon-polariton laser).

The invention will be better understood using the description below:

- there shows the block diagram of an amplifier according to the invention (1000);

- there shows the block diagram of an embodiment of an amplifier according to the invention, seen in longitudinal section;

- there shows a cross section of this embodiment of an amplifier according to the invention.

- Figure 4 shows another embodiment of an amplifier according to the invention.

Description of the invention:

An optical amplifier is an optical device capable of coherently amplifying optical radiation (eg photons). The device (1000) consists of an optical structure that incorporates a medium with optical gain, which enables an optical amplification process. The gain medium must be excited to provide optical gain. It involves a transfer of energy from an energy source to the gain medium by an optical, electrical or chemical process. An optical amplifier has input and output ports (100, 101). In such a device, an optical signal is introduced into the input port (100) so that it propagates through the structure interacting with the gain medium and undergoes optical amplification before being extracted from the device via the output port (101). The gain of an optical amplifier, G, is simply defined as the ratio of the output signal power to the input signal power. Noise is usually quantified by the optical noise figure, F which is the ratio of the signal-to-noise ratio at the output port to the signal-to-noise ratio at the input port.

There schematically represents the entire amplifier according to the invention:

- an optical amplifier adapted to amplify optical radiation (1000);

- an input coupling configured to receive an optical signal having a wavelength within a predetermined range (100);

- a cleaved face entrance mirror, anti-reflective treatment, perpendicular to the longitudinal axis of the guide (200);

- an optical waveguide (500) having one end optically coupled to the input coupling (100), and to the output coupling (101), the optical waveguide (500) comprises one or more materials having a permittivity relative complex and dimensioned such that the optical radiation of the optical signal couples to the field-effect transistors and propagates along the main axis of the guide;

- a field effect transistor network surrounding the guide and made of a material which may have a complex relative permittivity (600, 60n);

- a cleaved face output mirror, antireflection treated, perpendicular to the longitudinal axis of the guide (201);

- an output coupling optically coupled to the optical waveguide (101).

There represents an embodiment of the amplifier according to the invention.

It comprises :

- electrodes (660, 680, 690), making it possible to inject an electric current I;

- a semiconductor substrate 630 consisting of a first N-type semiconductor material, included between the electrodes 660, 680, 690;

- a confinement layer 620, made of the same first material, but with a P+ doping opposite to that of the substrate 630;

- an optical guide 500, active over its entire length, and whose longitudinal axis is parallel to the electrodes 660, 680, 690; consisting of a second semiconductor material whose mesh is matched with that of the first material and which has a greater refractive index than that of the first material;

- A field effect transistor network extending all along the guide 500; and periodically etched into a portion of the thickness of layer 620;

- two cleaved faces, 200 and 201, anti-reflective treatment, terminating the substrate 630, perpendicular to

the longitudinal axis of the guide 500.

The length of the guide 500 is less than that of the substrate 630, so that the two ends of the guide 500 constitute two windows buried in the substrate 630 at a certain distance from the faces 200 and 201 respectively.

Guide 500 is made by a conventional method for making a semiconductor optical amplifier. It is made, for example, of InGaAsP for use in infrared.

The substrate 630 is for example made of In-P.

They can be produced by a conventional method of epitaxy by molecular beam, or in the vapor phase.

An input optical signal denoted Pi is applied to the end of guide 500 through face 200. An amplified optical signal denoted Ps emerges from face 201.

The pitch of the network of field effect transistors is chosen such that the operation of the amplifier is in the spectral amplification range of the semiconductor material of the active guide 500. The network of field effect transistors reflects any wave propagating along the guide 500. The dimensions of the network of field effect transistors and its distance vis-à-vis the guide 500 determine the coupling coefficient between the mode guided by the guide 500 and said network. This coupling coefficient is chosen such that there is oscillation, and that the gain necessary for the oscillation has a high value, for example 30 dB (expected value for the gain).

The faces 200 and 201 are treated with antireflection to eliminate Fresnel losses. In addition, the faces 200 and 201 must be anti-reflection treated so that the amplifier operates in traveling waves, outside the band of the oscillation line. To obtain low reflectivity values of the faces 200 and 201, less than 1. It may be necessary to interrupt the active guide 500 before the faces 200 and 201, to form buried windows.

The embodiment shown in the comprises such buried windows, the length of the guide 500 being chosen to be less than the length of the substrate 630 so that the two ends of the guide 500 are buried in the substrate 630 at a certain distance from the faces 200 and 201 respectively.

The total length of the guide is less than that of the substrate, such that the ends of the guide are inside the substrate and constitute windows buried in the substrate at a certain distance from the cleaved faces.

The fact that the field generated by the field effect transistor network is more uniform makes it possible to improve the constancy of the gain of the amplifier.

There shows a cross-sectional view of a first embodiment.

FIG. 4 represents another embodiment of the amplifier according to the invention.

It comprises :

- electrodes (660, 680, 690), making it possible to inject an electric current I;

- a semiconductor substrate 630 made of a P-type semiconductor material;

- a confinement layer 620, consisting of a material, but with an N doping opposite to that of the substrate 630;

- an optical guide 500, active over its entire length, and whose longitudinal axis is parallel to the electrodes 660, 680, 690; consisting of a second semiconductor material whose lattice is matched with that of the first material and which has a greater refractive index than that of the first material;

- A field effect transistor network extending all along the guide 500; and periodically etched into a portion of the thickness of layer 620;

- two cleaved faces, 200 and 201, anti-reflective treatment, terminating the substrate 630, perpendicular to

the longitudinal axis of the guide 500.

The length of the guide 500 is less than that of the substrate 630, so that the two ends of the guide 500 constitute two windows buried in the substrate 630 at a certain distance from the faces 200 and 201 respectively. Guide 500 is made by a conventional method for making a semiconductor optical amplifier. The substrate 630 is for example made of p-Si. They can be produced by a conventional method of epitaxy by molecular beam, or in the vapor phase.

An input optical signal denoted Pi is applied to the end of guide 500 through face 200. An amplified optical signal denoted Ps emerges from face 201.

This example of an amplifier with a network of field effect transistors of this composition has the particularity of comprising a 2D electron gas. These electrons have a very high electronic mobility and can interact with photons or plasmons or phonons.

The pitch of the network of field effect transistors is chosen such that the operation of the amplifier is in the spectral amplification range of the semiconductor material of the active guide 500. The network of field effect transistors reflects any wave propagating along the guide 500. The dimensions of the network of field effect transistors and its distance vis-à-vis the guide 500 determine the coupling coefficient between the mode guided by the guide 500 and said network. This coupling coefficient is chosen such that there is oscillation, and that the gain necessary for the oscillation has a high value, for example 30 dB (expected value for the gain).

Manufacturing process of the invention:

Several methods can be used in forming the enhancer in conjunction with the present invention. Specific details regarding an etching process can be found in U.S. Patent No. 5,484,740 issued January 16, 1996 and U.S. Patent No. 5,619,064, issued April 8, 1997, both of which are incorporated herein by reference only.

Other methods of making the enhancer can be VLS (vapor-liquid-single-phase) growth or vapor-phase epitaxy (CVD). For example, based on hydrogen gas, 2% silane gas and 2% germane gas can be used as raw material. As a doping gas, a phosphine gas diluted with 100 ppm hydrogen can be used to obtain an n-type. Arsine can be used as a dopant. The substrate can be heated to approximately 300-500°C, and silane gas can be supplied in a reduced pressure state of 5 Torr. The growth rate can be on the order of 2 nm/s. Each layer has a thickness of 10 to 150 nm.

Claims (5)

Optical amplifier using a traveling wave principle and whose gain and operating range can be controlled by field effect transistors, having reduced non-linearity, characterized in that it comprises an optical guide (500) and resonant means (620, 630, 660, 670, 680, 690) coupled to this guide to cause this amplifier to oscillate at a wavelength different from the wavelength of a signal to be amplified, and to provide amplification traveling wave, of the signal to be amplified. Amplifier according to Claim 1, characterized in that the resonant means comprise at least one network of field-effect transistors (660, 670, 680, 690), each network being coupled to the optical guide (500) and having a length of wave chosen for the oscillation. Amplifier according to Claim 2, characterized in that the resonant means comprise a network of field effect transistors (660, 670, 680, 690) coupled to the guide (500). Amplifier according to Claim 3, characterized in that the guide comprises an active part (500) between the two split faces (200, 201). Amplifier according to Claim 1, characterized in that it comprises a substrate (630) terminated by cleaved faces (200, 201) treated with anti-reflection.