A photoconductive switch for generating or detecting terahertz radiation (TR) is provided. The photoconductive switch may comprise at least a first and a second pair of electrodes (E.sub.V, E.sub.H, E.sub.GR) on a surface (SS) of a photoconductive substrate, wherein the electrodes of the first pair are separated by a first gap comprising at least a plurality of first rectilinear sections (G.sub.V) extending along a first direction (x) and the electrodes of the second pairs are separated by a second gap comprising at least a plurality of second sections (G.sub.H) extending along a second direction (y), different from the first direction. The photoconductive switch may further comprise a patterned opaque layer (PML) selectively masking portions of the gaps between the electrodes. Methods and devices for generating and detecting terahertz radiation comprising such photoconductive switches are also provided.

A wideband terahertz modulator based on gradual openings, which belongs to the technical field of electromagnetic functional devices, includes: a semiconductor substrate; an epitaxial layer provided on the semiconductor substrate; a modulation units array, a positive voltage loading electrode and a negative voltage loading electrode which are provided on the epitaxial layer; wherein each modulation unit in the modulation units array comprises a disconnected H-shaped structure, a metal electrode located below an end of the opening of the disconnected H-shaped structure, and a semiconductor doped heterostructure located below the opening of the disconnected H-shaped structure; wherein in the disconnected H-shaped structures, adjacent modulation units have different opening positions; in a same row, the opening positions are linearly distributed and have a certain slope, and inclination slopes of the opening positions of two adjacent rows are opposite.

A technique to generate terahertz radiation is disclosed, where a pump beam (12) is coupled into an optical element (50) made of a medium with non-linear optical properties having plane-parallel front and rear boundary surfaces (51, 52), wherein the pump beam (12) is split into a set of partial pump beams (121) by reflection and/or diffraction on a periodic relief structure (53) of said optical element (50). The partial pump beams travel along a direction at an angle γ that satisfies the velocity matching condition of v.sub.p,cs cos(γ)=v.sub.THz,f within the given medium, where v.sub.p,cs is the group velocity of the pump beam, v.sub.THz,f is the phase velocity of the terahertz radiation and the speed a planar envelope (212) travels toward the front boundary surface (51) of the optical element (50), and angle γ is the angle formed by the pulse front envelope and the phase front of the pump beam.

A high-electron mobility transistor (HEMT) array terahertz wave modulator loaded in a waveguide is provided, which belongs to the technical field of electromagnetic functional devices and focuses on fast dynamic functional devices in the terahertz band. The device comprises a waveguide cavity and a modulation chip. The modulation chip comprises a semiconductor material substrate, a heterostructure material epitaxial layer, an artificial microstructure, and a socket circuit. The applied voltage controls the distribution change of the two-dimensional electron gas in the HEMT, which in turn controls the resonance mode conversion in the artificial microstructure, thereby control the transmission of electromagnetic waves in the waveguide. The modulator has a modulation depth of up to 96% and a modulation rate above 2 GHz.

It remains a challenge to generate coherent radiation in the spectral range of 0.1-10 THz (“the THz gap”), a band for applications ranging from spectroscopy to security and high-speed wireless communications. Here, we disclose how to produce coherent radiation spanning the THz gap using efficient second-harmonic generation (SHG) in low-loss dielectric structures, starting from an electronic oscillator (EO) that generates coherent radiation at frequencies of about 100 GHz. The EO is coupled to cascaded, hybrid THz-band dielectric cavities that combine (1) extreme field concentration in high-quality-factor resonators with (2) nonlinear materials enhanced by phonon resonances. These cavities convert the input radiation into higher-frequency coherent radiation at conversion efficiencies of >10.sup.3%/W, making it possible to bridge the THz gap with 1 W of input power. This approach enables efficient, cascaded parametric frequency converters, representing a new generation of light sources extensible into the mid-IR spectrum and beyond.

A Tamm electromagnetic cavity (10, 20, 30, 40, 60) possessing a resonant frequency in the THz domain, comprising: an interference mirror that is reflective in the THz domain, this mirror consisting of a stack of dielectric layers (7) comprising an alternation, in a z-direction, of two different layers, a layer referred to as the layer of high refractive index (2) and a layer referred to as the layer of low refractive index (4), the index of the layer of low refraction being lower than that of the layer of high refractive index, and being manufactured by stacking layers mechanically or by joining dielectric layers to one another; an upper metal layer (5) deposited on or added to an upper dielectric layer of said interference mirror so as to form a structure that supports at least one Tamm mode in the THz domain, the upper metal layer (5) being structured so as to form an antenna possessing a resonant frequency equal to that of the electromagnetic cavity.

A nonlinear fiber interferometer is disclosed suitable for fiber sensor and other applications. A first nonlinear fiber section amplifies probe and conjugate sidebands of a pump through four-wave mixing. A second section introduces a phase shift to be measured, for example from a sensor. A third nonlinear fiber section amplifies with phase-sensitive gain to increase signal-to-noise ratio. Based on phase-sensitive output power of probe and/or conjugate components, the phase shift can be measured. Superior performance can be obtained by balancing gain between the (first and third) nonlinear sections. Non-fiber, for example photonic integrated circuit, embodiments are disclosed. Differential sensing, alternative detection schemes, sensing applications, associated methods, and other variations are disclosed.

Disclosed are a terahertz signal generation apparatus and a terahertz signal generation method using the same. The terahertz signal generation apparatus includes first and second resonators configured to respectively output an optical signal of a first resonant frequency and an optical signal of a second resonant frequency from an optical signal input through a gain medium, an optical modulator configured to optically modulate the output optical signal of the second resonant frequency, an optical combiner configured to combine the CW optical signal of the first resonant frequency and the modulated optical signal of the second resonant frequency, and a signal generator configured to generate a terahertz signal using heterodyne beating between the CW optical signal of the first resonant frequency and the modulated optical signal of the second resonant frequency, wherein the first resonant frequency and the second resonant frequency are processed to have a predetermined frequency difference.

A waveguide for time-domain integration of THz pulses, comprising two wires extending from an input gap g.sub.in to an output gap g.sub.out at a tapering angle θ relative to a longitudinal axis, a gap of the waveguide decreasing linearly from the input gap g.sub.in to the output gap g.sub.out, wherein a size of the output gap is at least one order of magnitude smaller than a central wavelength λ.sub.THz in a spectrum of the THz pulses, and a method for time-domain integration of THz pulses, comprising confining input THz pulses in the waveguide.

It remains a challenge to generate coherent radiation in the spectral range of 0.1-10 THz (“the THz gap”), a band for applications ranging from spectroscopy to security and high-speed wireless communications. Here, we disclose how to produce coherent radiation spanning the THz gap using efficient second-harmonic generation (SHG) in low-loss dielectric structures, starting from an electronic oscillator (EO) that generates coherent radiation at frequencies of about 100 GHz. The EO is coupled to cascaded, hybrid THz-band dielectric cavities that combine (1) extreme field concentration in high-quality-factor resonators with (2) nonlinear materials enhanced by phonon resonances. These cavities convert the input radiation into higher-frequency coherent radiation at conversion efficiencies of >10.sup.3%/W, making it possible to bridge the THz gap with 1 W of input power. This approach enables efficient, cascaded parametric frequency converters, representing a new generation of light sources extensible into the mid-IR spectrum and beyond.