Apparatus and methods for generating mid-IR frequency combs using intra-pulse DFG. A mode-locked pulse generation laser generates near-IR pulses which are amplified. The amplified pulses are spectrally broadened by a nonlinear element, for example a normal dispersion highly nonlinear fiber (ND-HNLF) to generate broadened pulses. The nonlinear spectral broadening element is a transparent dielectric material having a cubic nonlinear response. Broadened pulses are temporally compressed to generate short, high-power pulses which few-cycle conditioned pulses which are ready for the intrapulse DFG process. The DFG block generates a mid-IR comb by difference frequency generation. It might comprise an orientation patterned GaP (OP-GaP) crystal or a poled lithium niobate (PPLN) crystal.

Disclosed is an optical component, being configured to function as an optical frequency converter in a broadband radiation source device. The optical component comprises a gas cell, and a hollow-core photonic crystal fiber at least partially enclosed within said gas cell. The local cavity volume of said gas cell, where said hollow-core photonic crystal fiber is enclosed within the gas cell, comprises a maximum value of 36 cm.sup.3 per cm of length of said hollow-core photonic crystal fiber.

An optical parametric oscillator for producing idler coherent light and signal coherent light from pump coherent light by balanced parametric dispersion includes: substrate cladding; a microring resonator disposed on the substrate cladding and including: a broadly transparent Kerr nonlinear medium including a annulus with a radius R, a height H, and a width W that provides a balanced parametric dispersion; and that: receives pump coherent light from a waveguide; and produces idler coherent light and signal coherent light from the pump coherent light, the idler coherent light and signal coherent light produced according to the balanced parametric dispersion of the microring resonator; and the waveguide disposed on the substrate cladding in optical communication with the microring resonator and comprising a broadly transparent medium such as silicon nitride and that: receives pump coherent light; and communicates the pump coherent light to the microring resonator for production of the idler coherent light and the signal coherent light from the pump coherent light.

Disclosed is an optical component, being configured to function as an optical frequency converter in a broadband radiation source device. The optical component comprises a gas cell, and a hollow-core photonic crystal fiber at least partially enclosed within said gas cell. The local cavity volume of said gas cell, where said hollow-core photonic crystal fiber is enclosed within the gas cell, comprises a maximum value of 36 cm.sup.3 per cm of length of said hollow-core photonic crystal fiber.

This invention proposes to use a specially designed layered nonlinear optic (LNO) for intracavity harmonic generation. The LNO generates the harmonic and guides the generated harmonic beam to a different path from the fundamental beam path with total internal reflection, a phenomenon that all lights are reflected when lights in one (“internal”) optic strike sufficiently obliquely against the interface with a second (“external”) optic, in which the refractive index is lower than that in the internal optic. No coating is necessary for the harmonic inside the fundamental beam laser cavity. The generated harmonic beam does not travel through any surface inside the fundamental beam cavity, either. Hence this invention improves the reliability of intracavity harmonic generation laser especially if the harmonic is in the UV range.

An aspect of the present disclosure is related to a method for measuring and controlling linear chirp level of ultrafast laser pulse. The method includes steps as follows. A carrier-envelope phase-chirp (CEP-chirp) relation which serve as a chirp monitor is extracted, in which the CEP-chirp relation is generated from an ultrafast laser pulse. A linear chirp level of a target pulse is measured in response to the CEP-chirp relation. According to the measuring with respect to the linear chirp level of the target pulse, a dispersion element which the ultrafast laser pulse passes through is varied to control and stabilize the linear chirp level of the target pulse.

Disclosed is an optical component, being configured to function as an optical frequency converter in a broadband radiation source device. The optical component comprises a gas cell, and a hollow-core photonic crystal fiber at least partially enclosed within said gas cell. The local cavity volume of said gas cell, where said hollow-core photonic crystal fiber is enclosed within the gas cell, comprises a maximum value of 36 cm.sup.3 per cm of length of said hollow-core photonic crystal fiber.

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 is an optical component, being configured to function as an optical frequency converter in a broadband radiation source device. The optical component comprises a gas cell, and a hollow-core photonic crystal fiber at least partially enclosed within said gas cell. The local cavity volume of said gas cell, where said hollow-core photonic crystal fiber is enclosed within the gas cell, comprises a maximum value of 36 cm.sup.3 per cm of length of said hollow-core photonic crystal fiber.

Disclosed is an optical component, being configured to function as an optical frequency converter in a broadband radiation source device. The optical component comprises a gas cell, and a hollow-core photonic crystal fiber at least partially enclosed within said gas cell. The local cavity volume of said gas cell, where said hollow-core photonic crystal fiber is enclosed within the gas cell, comprises a maximum value of 36 cm.sup.3 per cm of length of said hollow-core photonic crystal fiber.