A method of generating THz radiation includes the steps of generating optical input radiation with an input radiation source device (10), irradiating a first conversion crystal device (30) with the optical input radiation, wherein the first conversion crystal device (30) is arranged in a single pass configuration, and generating the THz radiation having a THz frequency in the first conversion crystal device (30) in response to the optical input radiation by an optical-to-THz-conversion process, wherein a multi-line frequency spectrum is provided by the optical input radiation in the first conversion crystal device (30), and the optical-to-THz-conversion process includes cascaded difference frequency generation using the multi-line frequency spectrum. Furthermore, a THz source apparatus being configured for generating THz radiation and applications thereof are described.

Embodiments of the invention provide apparatuses and methods for generating frequency combs. A non-linear optical medium may generate new optical waves centered at frequencies differing from the input waves, while retaining the input wave properties. In the case when a parametric mixer is used to generate frequency combs with small frequency pitch, the phase correlation of the input (seed) waves can be achieved by an electro-optical modulator and a single master laser. In the case when a frequency comb possessing a frequency pitch that is larger than frequency modulation that can be affected by an electro-optic modulator, the phase correlation of the input (seed) waves is achieved by combined use of an electro-optical modulator and injection locking to a single or multiple slave lasers.

A system for optical comb carrier envelope offset frequency control includes a mode-locked oscillator. The mode-locked oscillator produces an output beam using an input beam and one or more control signals. The output beam includes a controlled carrier envelope offset frequency. A beat note generator produces a beat note signal using a portion of the output beam. A control signal generator produces the one or more control signals to set the beat note signal by modulating the intensity of the input beam within the mode locked oscillator. Modulating the intensity comprises using a Mach-Zehnder intensity modulator or using an intensity modulated external laser to affect a gain medium within the mode-locked laser.

A microwave imaging system is provided. The microwave imaging system comprises a dual-comb transceiver module and a processing module. The dual comb transceiver module comprises a transmitter module for transmitting an output signal, at least one receiver module for receiving the output signal from the transmitter via a channel and for generating a first output signal, and a reference receiver module for receiving a portion of the output signal transmitted by the transmitter module via an attenuator module and for generating a second output signal. Further, one or more channel parameters associated with the microwave imaging are determined based on the first output signal and the second output signal.

A planar optical resonator capable of parametrically generating frequency combs includes two optical waveguide cores forming inner and outer loops, the resonator having two sections, in which laterally adjacent segments of the cores are resonantly optically coupled to each other at two separate wavelength regions causing separate peaks in the second order dispersion. The resonator sections may be configured to suppress integrated dispersion of the resonator in a broad spectral range favorably for generating a spectrally uniform frequency comb.

The invention relates to a method for modulating the resonant frequency of an optical resonator (1) in accordance with a periodic, not necessarily harmonic, modulation signal (U.sub.mod(t)). Fast modulation of an optical resonator is intended to be made possible in which the current resonant frequency follows the modulation signal (U.sub.mod(t)) as precisely as possible, and specifically at a fundamental frequency of the modulation signal in the kHz range. To do this, the invention proposes the following method steps: deriving an error signal (E(t)) from a light field circulating in the resonator (1), wherein the error signal (E(t)) indicates the deviation of the optical frequency of the light field from a target value, deriving a first actuating signal (S.sub.1(t)) from the error signal (E(t)) by means of a controller (6), generating a second actuating signal (S.sub.2(t)), which has actuating-signal components at one or more harmonics (f.sub.mod, 2f.sub.mod, . . . ) of the fundamental frequency (f.sub.mod) of the modulation signal (U.sub.mod(t)), and applying a superposition signal made up of the first and the second actuating signal (S.sub.1(t), S.sub.2(t)) to an actuator (3) that changes the optical path length of the resonator (1). In other words, the invention makes use of a combination of control and narrow-band feed-forward control tuned to the spectrum of the modulation signal (U.sub.mod(t)) and of the error signal (E(t)) to modulate the resonant frequency. Preferably, the feed-forward control used for generating the second actuating signal (S.sub.2(t)) is automatically adapted in accordance with the error signal (E(t)). In addition, the invention relates to an accordingly configured optical system.

Systems and methods for soliton microcomb-based precision dimensional metrology via spectrally-resolved interferometry are described. In an embodiment, the system includes a dual-pumped soliton microcomb generator comprising a pump, a microresonator, and an auxiliary pump and that generates a single-soliton microcomb, an erbium-doped fiber amplifier that amplifies a C-band section of the soliton microcomb and a non-polarizing beam splitter that divides the soliton microcomb pulses into a reference arm pulse and a measurement arm pulse for an interferometer and recombines the reference arm pulse and the measurement arm pulse into a recombined beam upon their return.

Optical frequency combs and related methods, devices, and systems are described. An example device can comprise a waveguide configured to optically couple to an optical source and at least one optical resonator optically coupled to the waveguide. The one or more of the at least one optical resonator can be tuned such that an optical frequency comb is generated based on mode interaction between two different modes of the at least one optical resonator. The device can comprise an output coupled to the waveguide and configured to output the optical frequency comb.

An optical parametric oscillator and method for generating coherent signal light involve a resonant optical cavity for coherent signal light, and in the cavity a non-parametric gain element for amplifying the coherent signal light to only partially compensate for passive optical roundtrip losses, thereby obtaining lower effective roundtrip losses. A parametric gain element is arranged in the cavity, for converting coherent pump light into coherent signal light through an instantaneous nonlinear optical interaction. The parametric oscillator has means for adjusting an intracavity optical power of the coherent pump light above a threshold value, where the parametric gain is balancing the effective roundtrip losses, thus inducing sustained oscillations of the signal light in the optical cavity. The non-parametric gain element is configured to have a limited non-parametric gain over a gain bandwidth of the parametric gain element, which is less than the passive optical roundtrip losses in the gain bandwidth.

An integrated electro-optic frequency comb generator based on ultralow loss integrated, e.g. thin-film lithium niobate, platform, which enables low power consumption comb generation spanning over a wider range of optical frequencies. The comb generator includes an intensity modulator, and at least one phase modulator, which provides a powerful technique to generate a broad high power comb, without using an optical resonator. A compact integrated electro-optic modulator based frequency comb generator, provides the benefits of integrated, e.g. lithium niobate, platform including low waveguide loss, high electro-optic modulation efficiency, small bending radius and flexible microwave design.