Lucent Technologies Inc.

At+t Corp.

At&t Bell Laboratories

Georgia Tech Research Corporation

At&t Ipm Corp.

Jerome Faist

Federico Capasso

Alfred Yi Cho

Deborah Lee Sivco

Albert Lee Hutchinson

Carlo Sirtori

Claire F Gmachl

James Nelson Baillargeon

Alessandro Tredicucci

Gaetano Scamarcio

Sung-Nee George Chu

Serge Luryi

Boris Mizaikoff

Evgueni E Narimanov

Alfred Douglas Stone

Jens Uwe Noeckel

Mattias Beck

Christy Charlton

Marcella Giovannini

Briefly described, embodiments of this disclosure, among others, include solid state, thin film waveguides, detection systems including waveguides, and methods of detecting target compounds.

Film thin waveguides, methods of fabrication thereof, and detection systems

A long wavelength (e.g., mid-IR to far-IR) semiconductor laser comprises an active region and at least one cladding region characterized in that the cladding region includes a light guiding interface between two materials which have dielectric constants opposite in sign. Consequently, the guided modes are transverse magnetic polarized surface waves (i.e., surface plasmons) which propagate along the interface without the need for a traditional dielectric cladding. In a preferred embodiment, the interface is formed between a semiconductor layer and a metal layer. The complex refractive index of the metal layer preferably has an imaginary component which is much larger than its real component. In an illustrative embodiment, our laser includes a QC active region sandwiched between a pair of cladding regions one of which is a guiding interface based on surface plasmons and the other of which is a dielectric (e.g., semiconductor) structure.

Long wavelength semiconductor lasers incorporating waveguides based on surface plasmons

The quantum cascade (QC) photon source according to this invention can emit simultaneously at two distinct wavelengths, typically both in the mid-infrared. This is accomplished through provision of a semiconductor layer structure in which, at the proper bias voltage, electrons are injected into an energy level E.sub.3 and then forced to cascade through an intermediate level E.sub.2 before reaching the ground state E.sub.1 of the active region. In the process, photons of energy E.sub.3 -E.sub.2 (wavelength .lambda..sub.1) and E.sub.2 -E.sub.1 (wavelength .lambda..sub.2) are emitted. Dual wavelength photon sources according to this invention can be used in a variety of ways, e.g., to determine the absorption of a gaseous sample at wavelengths .lambda..sub.1 and .lambda..sub.2, exemplarily to determine the concentration of a particular chemical compound in the sample.

Article comprising a dual-wavelength quantum cascade photon source

A solid state laser comprises a cavity resonator in the form of a generally cylindrical body and, located within the resonator, an active region which generates lasing light when suitably pumped. The resonator has a relatively high effective refractive index (n&gt;2 and typically n&gt;3) is sufficiently deformed from circularity so as to support at least one librational mode (e.g., a V-shaped or a bow-tie mode, the latter being presently preferred for generating relatively high power, directional outputs). Specifically described is a Group III-V compound semiconductor, quantum cascade (QC), micro-cylinder laser in which the resonator has a flattened quadrupolar deformation from circularity. This laser exhibits both a highly directional output emission and a three-order of magnitude increase in optical output power compared to conventional semiconductor micro-cylinder QC lasers having circularly symmetric resonators.

Solid state laser for operation in librational modes

A novel superlattice quantum cascade (SLQC) laser has undoped SL active regions, with the dopant concentration in the injector region being selected, such that, under an appropriate electrical bias, the SL active region is substantially electric field free. The absence of dopant atoms in the SL active region results in reduced carrier scattering and reduced optical losses, with consequent low threshold current and/or room temperature operation. The novel laser emits in the mid-IR spectral region and can be advantageously used in measurement or monitoring systems, e.g., in pollution monitoring systems.

Article comprising an improved superlattice quantum cascade laser

A QC laser comprises first and second optical confinement (i.e., cladding) regions, and an In-based, Group III-V compound, QC active region disposed between the confinement regions. At least the first confinement region and the active region having the shape of an elongated mesa. An i-type InP layer covers the sidewalls to provide efficient heat transport and effective low loss mode confinement. A metal layer makes ohmic contact with the top surface of the mesa and a rectifying contact with the i-InP layer.

Quantum cascade laser

A quantum cascade (QC) laser has a multilayer core region comprising alternating layers of a first and a second semiconductor material, with lattice constants a.sub.1 and a.sub.2, respectively. The first material is selected such that a.sub.1 &gt;a.sub.0, where a, is the lattice constant of the substrate (typically InP), and the second material is selected such that a.sub.2 &gt;a.sub.0. The materials are also selected such that the conduction band discontinuity .DELTA.E.sub.c between the first and second materials is greater than 520 meV in absolute value. The multilayer core comprises a multiplicity of essentially identical multilayer repeat units. The layer thicknesses and materials of the repeat units are selected to substantially provide strain compensation over a repeat unit. QC lasers according to this invention preferably comprise a distributed feedback feature, (e.g., a Bragg grating) selected to ensure single mode laser emission, and can be designed for operation at a wavelength in the first atmospheric window, typically about 3-5 .mu.m. Such lasers can advantageously be used for absorption spectroscopy, e.g., for emission monitoring.

Article comprising a strain-compensated QC laser

In a novel tunable semiconductor laser, the lasing transition is a non-resonant tunneling transition, with the frequency of the emitted photon depending on the electrical bias across the multi-period active region of the laser. The laser can be designed to emit in the mid-IR, and can advantageously be used for, e.g., trace gas sensing.

Article comprising an electric field-tunable semiconductor laser

The core of the disclosed novel quantum cascade (QC) laser comprises a multiplicity of nominally identical repeat units, with a given repeat unit comprising a superlattice active region and a carrier injector region. Associated with the superlattice active region is an upper and a lower energy miniband, with the lasing transition being the transition from the lower edge of the upper miniband to the upper edge of the lower miniband. The injector facilitates carrier transport from the lower miniband to the upper miniband of the adjacent downstream repeat unit. QC lasers according to this invention can be designed to emit in the infrared, e.g., in the wavelength region 3-15 .mu.m, and can have high power.

It has been found that previously known quantum cascade (QC) lasers have a shortcoming that substantially decreases their usefulness as radiation sources for pollution monitoring and other potential applications that involve absorption measurements. Except at cryogenic temperatures, these lasers have to be driven in pulse mode and are inherently multimode. We have now established that this shortcoming can be overcome by provision of appropriate distributed feedback. Resulting lasers (QC-DFB lasers) can have single mode mid-IR output at or near room temperature, can have significant optical power, and be continuously tunable over a significant spectral region.

Article comprising an improved QC laser

The novel unipolar laser resembles a quantum cascade laser but utilizes radiative transitions between upper and lower minibands of superlattices, with injection of charge carriers from the lower miniband into the upper miniband of the adjacent downstream superlattice facilitated by a multilayer injector region. The lasing wavelength is typically in the mid-infrared, selectable by choice of the superlattice parameters. The novel laser is potentially well suited for high power operation, since it utilizes carrier transport in minibands, as opposed to tunneling between discrete energy states.

Article comprising a unipolar superlattice laser

The disclosed improved quantum cascade (QC) laser comprises features that facilitate lasing at temperatures above 260 K, preferably above 300 K. Among the features is a wavefunction-increasing feature that enhances the amplitude of the lasing level wavefunction in the adjacent upstream barrier layer, thereby increasing carrier injection efficiency into the lasing level. Exemplarily, the wavefunction-increasing feature is an approximately disposed thin quantum well. Among the features typically is also a chirped superlattice in the injection/relaxation region that acts as a Bragg reflector to suppress escape of carriers from the lasing level in the continuum, while facilitating carrier extraction from the ground state into a miniband, with the energy width of the miniband decreasing over at least a portion of the thickness of the injection/relaxation region.

Article comprising an improved quantum cascade laser

The disclosed unipolar quantum cascade (QC) laser comprises a multiplicity of essentially identical active regions, with adjacent active regions separated by a superlattice carrier injection/relaxation region. A given active region contains a single quantum well with at least two electron states. Lasing is obtained without global intersubband population inversion. Instead, there is believed to exist local population inversion in a small region of k-space near k=0, corresponding to electron energies approximately within an optical phonon energy (.about.35 meV) from the bottom of the lower subband. A novel design feature that can be used to improve the thermal characteristics of substantially any QC laser is also disclosed.

Semiconductor laser

This application discloses, to the best of our knowledge, the first unipolar laser. An exemplary embodiment of the laser was implemented in the GaInAs/AlInAs system and emits radiation of about 4.2 .mu.m wavelength. Embodiments in other material systems are possible, and the lasers can be readily designed to emit at a predetermined wavelength in a wide spectral region. We have designated the laser the 'quantum cascade' (QC) laser. The QC laser comprises a multilayer semiconductor structure that comprises a multiplicity of essentially identical undoped 'active' regions, a given active region being separated from an adjoining one by a doped 'energy relaxation' region. In a currently preferred embodiment each active region comprises three coupled quantum wells designed to facilitate attainment of population inversion. In the currently preferred embodiment the energy relaxation regions are digitally graded gap regions. However, other energy relaxation regions are possible. Disclosed are also embodiments that rely primarily on 'vertical' transitions in a given quantum well. Such lasers preferably comprise superlattice Bragg reflectors. The unipolar plasma in a unipolar laser can be manipulated by means of an electric 'control' field, facilitating, for instance, beam steering or external control of the modal gain of the laser. Means for accomplishing this are discussed.

Unipolar semiconductor laser

Articles according to the invention include a semiconductor waveguide having a core and a cladding, with the cladding including doped semiconductor material. The doping level is selected such that both the real part n and the imaginary part k of the complex refractive index of the doped material are relatively low, exemplarily n&lt;0.5 .epsilon..sub..infin..sup.1/2 and k&lt;1, where .epsilon..sub..infin. is the high frequency lattice dielectric constant of the material. Appropriate choice of the doping level can result in improved confinement of the guided radiation without undue increase in the attenuation of the guided radiation. The invention exemplarily is embodied in a long wavelength (.about.8.5 .mu.m) quantum cascade laser. Other embodiments are contemplated.

Growing community of inventors

Scotch Plains, NJ, United States of America

Jerome Faist