At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

American Telephone and Telegraph, Co.

Daniel S Chemla

David A Miller

Peter W Smith

Israel Bar-Joseph

Tao-Yuan Chang

Thomas Huntington Wood

Arthur C Gossard

Theodoor Charlouis Damen

Stephan Schmitt-Rink

Stefan N Schmitt-Rink

Resonant tunneling devices having an improved device switching speed are realized by including an optical control element rather than an electrical control element for switching the device from one stable state to the other. The resulting optoelectronic device including at least one double barrier quantum well semiconductor heterostructure is controllably switched from an active state to an inactive state and vice versa by impinging optical signals from an optical control element having a mean photon energy less than the bandgap energy of the double barrier quantum well semiconductor heterostructure, wherein the active state of the device exhibits conduction of charge carriers by resonant tunneling. Improvement in the switching speed occurs because the optical processes initiated by the optical control element are condsiderably faster than the electronic processes induced by prior art electrical control elements.

Optically controlled resonant tunneling electronic devices

Modulation-doped quantum well heterostructures are cascaded in a semiconductor device to achieve high speed operation while obtaining large index of refraction or absorption coefficient changes for modulating lightwave signals without significant increases in the operating potentials over prior quantum well structures. Each modulation-doped quantum well heterostructure exhibits substantially equal boundary conditions in an unbiased condition for efficient cascading or stacking. Each quantum well has associated with it a barrier layer to minimize leakage current. As a result, each quantum well has associated with it a separate charge reservoir. This aspect contributes to the speed of the cascaded structure. When incorporated within a waveguide structure, cascaded modulation-doped quantum well heterostructures can act as an external modulator, or as an intra-cavity wavelength tuning element, or as an intra-cavity modulator, or even as an optically-pumped laser.

Semiconductor device including cascaded modulation-doped quantum well

The invention is a controlled laser having an optical resonator, a laser gain medium placed inside the optical resonator, the laser gain medium being capable of emitting light and of lasing with the light, a multiple layer heterostructure placed inside the optical resonator, and means for varying an optical absorption of the multiple layer heterostructure for the light in order to control an optical gain of the optical resonator, and thereby control lasing of the laser gain medium. Passive mode locking is achieved by the light emitted by the gain medium controlling the optical absorption of the multiple layer heterostructure. Active mode locking and modulation are achieved by controlling the optical absorption of the multiple layer heterostructure by applying an electric field to the multiple layer heterostructure. Control of laser gain by an external light source is achieved by controlling the optical absorption of the multiple layer heterostructure by illuminating it with light from the external light source. An embodiment of the multiple layer heterostructure fabricated as a GaAs-AlGaAs multiple quantum well with a Type I superlattice band structure is a passive mode locker for a semiconductor diode laser.

Laser controlled by a multiple-layer heterostructure

Information borne by an optical signal at a first wavelength is transferred intact to another optical signal at a second wavelength and vice versa via an optoelectronic circuit employing quantum well devices connected serially to facilitate self electrooptic effects therein. The optoelectronic circuit accepts two input signals and provides two output signals wherein an input signal and its corresponding output signal are at the same wavelength. Bidirectional information transfer with bidirectional wavelength conversion is permitted by the optoelectronic circuit.

Wavelength conversion using self electrooptic effect devices

Optical apparatus is disclosed wherein narrow line width light from a source is directed through the substrate of a semiconductor structure and reflected from the gate electrode of a field effect transistor element fabricated on the surface of the semiconductor structure. A quantum well layer serves as the current channel for the field effect transistor, and charge carries from a doped semiconductor layer provide high mobility carriers in the quantum well layer. Changes in the potential between the gate and source electrodes of the field effect transistor causes the normal pinchoff of carriers in the quantum well layer thereby causing changes in the absorption characteristic presented by the quantum well layer. By directing light from the source at the gate electrode through the substrate of the semiconductor structure, a photodetector can be positioned so as to detect a change in light which has passed twice through the quantum well layer, thereby detecting a change in the electrical state of the field effect transistor.

Optical reading of quantum well device

In response to ultrafast optical signal pulses, it is now possible to generate correspondingly ultrafast electrical signal pulses by employing semiconductor apparatus including at least one quantum well layer electrically biased by a static electric field. Optical signal pulses incident on the quantum well are at a wavelength substantially less than the absorption edge of the quantum well layer or layers. In other words, the incident optical pulses have a means photon energy less than the bandgap energy of the quantum well layer or layers. The electrical signal pulse generated subsists for a period of time substantially equal to the duration of the optical signal pulses incident on the quantum well layer or layers.

High speed quantum well optical detector

A nonlinear optical device includes a layered semiconductor structure having layers of different energy band gap materials. Alternate layers of the structure are arranged for containing trapped charge. An input light beam is applied to the layers. A control light beam varies the trapped charge for controlling propagation of the input light beam through the structure.

Light beam applied to a layered semiconductor structure is controlled by

A nonlinear optical apparatus is provided with a multiple layer heterostructure made from alternate layers of a charge carrier semiconductor material having a narrow bandgap energy, and a charge barrier material having a wider bandgap energy than the charge carrier material. The layers are deposited one upon the other in substantially flat planes forming a series of potential barriers. The potential barriers are capable of confining charge carriers which arise within the layers of the charge carrier semiconductor material to remain substantially therein. The optical absorption coefficient of the multiple layer heterostructure exhibits at least one sharp resonant optical absorption peak near the semiconductor material bandgap absorption. A light source is restricted to provide a beam of light photons of energy near the energy of the sharp resonant optical absorption peak for promoting production of charge carriers within the charge carrier semiconductor material. The light photons are directed into the multiple layer heterostructure so that the light photons may saturate the optical absorption coefficient and thereby cause the index of refraction of the multiple layer heterostructure to vary with incident light intensity.

Nonlinear optical apparatus

An optical device includes a layered semiconductor structure having a variable input light beam applied to the structure with an E field component polarized normal to the layers. Intensity of the input light beam controls charge trapped in the layers, the dielectric constant of the layers containing the trapped charge, and the propagation of the input light beam within the device.

Intensity of a light beam applied to a layered semiconductor structure

A four-wave mixer which uses a multiple quantum well structure as a nonlinear optical material is provided. There are provided means for providing a first beam of light which propagates through said multiple quantum well structure, and means for providing a second beam of light which also propagates through said multiple quantum well structure and substantially overlaps said first beam of light within said MQW structure. At least one ouput phase conjugate beam of light is produced by interaction of said first and said second beams of light with said multiple quantum well structure. An alternate embodiment has two counterpropagating pump beams and a probe beam of light which produce a backward scattered phase conjugate beam of light.

Degenerate four-wave mixer using multiple quantum well structures

A semiconductor apparatus is provided. The apparatus has a multiple layer heterostructure having first and second material layers having first and second bandgaps, respectively and a semiconductor layer of a third bandgap being fabricated between said material layers, the bottom of the conduction band of said semiconductor layer is below the bottom of the conduction band of said material layers, and the top of the valence band of said semiconductor layer is above the top of the valence band of said material layers, the thickness of said semiconductor layer is chosen sufficient for carrier confinement effects within said semiconductor layer to influence the optical properties of said multiple layer heterostructure, and means for applying an electric field to the multiple layer heterostructure in order to vary an optical absorption coefficient and an index of refraction of the multiple layer heterostructure in response to the electric field. The apparatus is adapted for use as an optical absorption modulator or optical phase modulator, or as an electrically tuned Fabry-Perot cavity or as a polarization modulator, or as a nonlinear or bistable apparatus in which the operating point is varied by application of an electric field.

Growing community of inventors

Rumson, NJ, United States of America

Daniel S Chemla