Abstract: A detector for terahertz electromagnetic waves includes a terahertz optomechanical transducer to transform an incident electromagnetic wave, having a terahertz frequency within a terahertz frequency band, into a measurable mechanical response; and a detection device for detecting an output signal. The terahertz optomechanical transducer includes a first element and an opposite element forming with the first element a capacitive gap.

Abstract: The invention relates to a three-dimensional LC electrical resonator device having a given resonant frequency of 100 gigahertz or more, comprising: a separating layer; a first track made of a conductor and comprising two overlapping portions; and a second track made of a conductor, the second track comprising two overlapping portions and an inductive loop connecting the two overlapping portions, the first track and the second track respectively being formed on either side of the separating layer, each overlapping portion of the first track being placed facing a respective overlapping portion of the second track so as to form two capacitors that are spatially spaced apart from each other.

Abstract: A detector for terahertz electromagnetic waves includes a terahertz optomechanical transducer to transform an incident electromagnetic wave, having a terahertz frequency within a terahertz frequency band, into a measurable mechanical response; and a detection device for detecting an output signal. The terahertz optomechanical transducer includes a first element and an opposite element forming with the first element a capacitive gap.

Abstract: The invention relates to a three-dimensional LC electrical resonator device having a given resonant frequency of 100 gigahertz or more, comprising: a separating layer; a first track made of a conductor and comprising two overlapping portions; and a second track made of a conductor, the second track comprising two overlapping portions and an inductive loop connecting the two overlapping portions, the first track and the second track respectively being formed on either side of the separating layer, each overlapping portion of the first track being placed facing a respective overlapping portion of the second track so as to form two capacitors that are spatially spaced apart from each other.

Abstract: A photodetector for the detection of a light beam, comprising: a metal layer acting as a ground plane, a semiconductor layer covering the metal layer, wherein the semiconductor layer is made of at least two different materials forming an heterostructure, an array of metal pads covering the semiconductor layer, collecting the light beam and directing it towards the semiconductor layer, each of the metal pads, together with the semiconductor layer and the metal layer underneath it, the metal pads being interconnected by metal connection strips for conducting the detection current, wherein the semiconductor layer is completely etched in areas of the semiconductor layer that are neither covered by the metal pads nor by the connection strips, and wherein each metal pad forming an antenna for collecting incident photons of the light beam on an effective collection surface (??) of the light at least twice larger than a physical collection surface (A) of the semiconductor layer covered by said metal pad.

Abstract: The method of the invention consists of implanting ions into the surface of multilayer optical waveguides, in the highly doped layer, in a defined pattern so as to modify the refractive index of this layer.

Abstract: The field of the invention is that of the detection of high frequency electromagnetic waves. The invention can be applied to a very wide range of bandwidths, but the preferred field of application is the terahertz frequency domain. The core of the detection device involves a so-called active material with an absorption coefficient in the optical domain that depends on the intensity of the terahertz signal to be detected. By measuring the variations of the absorption coefficient by means of an optical probe, the intensity of the terahertz signal is thus determined. By this means, a frequency translation is performed in a frequency domain where the measurement no longer poses technical problems. It is notably possible to improve the sensitivity of the detector by having antennas suited to the active medium, by using semiconductor or quantum well materials.

Abstract: The method of the invention consists of implanting ions into the surface of multilayer optical waveguides, in the highly doped layer, in a defined pattern so as to modify the refractive index of this layer.

Abstract: The present invention relates to a system for optical transmission in free propagation mode of one digital data signal in the atmosphere, with autocompensation of the turbulence effects. It applies especially to optical telecommunications. According to the invention, the system comprises light emission means and optoelectronic detection means suitable for detection around one given non-zero detection frequency. The emission means simultaneously emit, for each signal to be transmitted, two light waves at least one of said waves being intensity-modulated by said signal. Detection then takes place at a detection frequency equal to the difference between said frequencies of the light waves emitted.

Abstract: A method of controlling a unipolar semiconductor laser in the 4-12 &mgr;m mid-infrared range. This is an optical control method, unlike a purely electrical, power control method which injects a relatively large flux of electrons. The optical control method may advantageously include two optical beams of the same wavelength and a device for making those beams interfere in the active layer of the laser, the optical control beams having a much shorter wavelength than the wavelength of the unipolar laser and having a frequency capable of being modulated more rapidly than that of the laser.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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<0.5 .epsilon..sub..infin..sup.1/2 and k<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.