The invention relates to a terahertz dual-comb spectrum stabilization system, including an optical loop for coupling a first optical frequency comb signal (OFCS) to a second OFCS; and a frequency mixer for performing frequency mixing on the coupled first OFCS and second OFCS to generate a dual-comb signal. A local oscillator signal end of the frequency mixer is connected to a multi-chain frequency multiplication chain, the multi-chain frequency multiplication chain is used for performing frequency multiplication processing on a radio frequency signal, a local oscillator frequency in terahertz frequency range is generated the local oscillator frequency in terahertz frequency range is respectively mixed with the first OFCS and the second OFCS in the frequency mixer, and two down-converted OFCSs are generated in microwave frequency range. One line of comb teeth of the two down-converted OFCSs are respectively locked to obtain a stable multi-heterodyne dual-comb spectrum.

In some embodiments, a device for generating mid-infrared radiation is provided. The device may include a thin film quadratic nonlinear waveguide formed on a mid-infrared transparent cladding by a thin film material of a predetermined film thickness, the waveguide having a predetermined etch depth and a predetermined top width. At least one of the predetermined film thickness, the predetermined etch depth, and the predetermined top width may be tuned for the device to generate a coherent idler wave as a mid-infrared radiation from a fixed pump wave and a tunable signal wave.

Bright entangled photon sources including an alignment-free, fiber-based, mechanically-rugged and generic interferometric module are disclosed. The inherent phase-stability of a Sagnac interferometer is deployed. High down-conversion efficiency of periodically poled nonlinear-waveguides is combined with the optical gain of semiconductor optical amplifiers and immunity of fiber optics. A single compact interferometric engine combines these attributes, allowing highly stable, integrable and bright polarization entangled-photon sources operating at room temperature. Using a minimum number of in-line optical parts, the compact module is based on a novel method that enhances the long-term stability and efficiency without compromising the entanglement quality. Besides energy entanglement, polarization entanglement is presented and set through the operational conditions. An optional periodically poled nonlinear waveguide can be hosted to achieve the desired spectral bandwidth and photons generation rate. The result is a zero-maintenance, lightweight, low-power consumption engine of compact and fully-integrable bright polarization-entangled photon sources.

A system and method for correcting environmental phase drift between signal and reference branches of a photonic analog-digital converter (pADC) with passive remote sampler (PRS) sends a continuous-wave (CW) laser from a base unit through the PRS in a reverse optical path to measure the phase drift. The CW optical signal is converted to an electrical signal from which a phase-error signal indicative of the phase drift is filtered out and sent to a phase shifter. The pADC sends an optical pulse through the PRS in a forward optical path; the signal pulse is phase-modulated according to a received radio frequency (RF) signal of interest. The phase-modulated optical pulses (e.g., signal and reference) are received at the base unit and the phase drift corrected out of the optical pulses via the phase shifter. The corrected optical pulses are demodulated to provide a digital counterpart to the RF signal of interest.

A system and method for correcting environmental phase drift between signal and reference branches of a photonic analog-digital converter (pADC) with passive remote sampler (PRS) sends a continuous-wave (CW) laser from a base unit through the PRS in a reverse optical path to measure the phase drift. The CW optical signal is converted to an electrical signal from which a phase-error signal indicative of the phase drift is filtered out and sent to a phase shifter. The pADC sends an optical pulse through the PRS in a forward optical path; the signal pulse is phase-modulated according to a received radio frequency (RF) signal of interest. The phase-modulated optical pulses (e.g., signal and reference) are received at the base unit and the phase drift corrected out of the optical pulses via the phase shifter. The corrected optical pulses are demodulated to provide a digital counterpart to the RF signal of interest.

In semiconductor inspection using second-harmonic generation within an object, a weak second-harmonic is detected at high sensitivity. In a semiconductor inspecting apparatus which irradiates a pulsed laser with a very short pulse width to a surface of a semiconductor device as the object, and measures the second-harmonic generated within the semiconductor device, a second-harmonic generation element is disposed between a light source and the object to generate a first second-harmonic. Further, the apparatus modulates a phase of only the first second-harmonic using an electric optical crystal, and then, a fundamental wave is irradiated onto the object. When the fundamental wave is irradiated onto the semiconductor device, the second-harmonic is generated therefrom. The first second-harmonic interferes with the second second-harmonic on a detector, and an intensity of the light obtained by the interfering is modulated at the same period as that of the phase modulation of the first second-harmonic. An amplitude of the second second-harmonic may be obtained from a modulated amplitude thereof, and a phase of the second second-harmonic may be measured from a modulated phase thereof.

For adapting optical properties of a continuous body arranged in a resonator cavity and comprising a nonlinear optical material to light of two different wavelengths passing through the continuous body along an optical axis, the continuous body having a total length along the optical axis, a spatially constant temperature is adjusted in a first region of the continuous body, the first region extending over at least 20% of the total length, and a temperature gradient is adjusted in a second region of the continuous body, the second region neighboring the first region and extending over at least 10% of the total length. The temperature gradient may be selected such as to achieve resonance of the light of both wavelengths in the resonator cavity.

Embodiments can include a photonic structure comprising: a substrate; a waveguide formed over the substrate; an insulator layer formed over the waveguide, wherein the waveguide is formed of nonlinear optical material; and a tuning structure integrally formed on the photonic structure with the waveguide, the tuning structure configured for tuning the waveguide.