An assembly including a non-linear element configured for generating broadband radiation from input radiation coupled into the non-linear element. The assembly further includes an optical element positioned downstream of the non-linear element configured to reflect a fraction of the broadband radiation back into the non-linear element. The non-linear element can be a nonlinear fiber, such as a hollow-core photonic crystal fiber (HC-PCF).

An optical source including a supercontinuum generation apparatus including a pump light source, a twisted photonic crystal fibre, PCF, and a wideband quarter-wave retarder. The pump light source is arranged to provide circularly polarised pump light. The twisted PCF is arranged to receive the pump light and to convert the pump light into circularly polarised supercontinuum light. The wideband quarter-wave retarder is arranged to convert the circularly polarised supercontinuum light into linearly polarised supercontinuum light. The optical source may additionally include a wavelength tunable bandpass optical filter arranged to transmit the linearly polarised supercontinuum light at wavelengths within a selected range.

A supercontinuum source may include a seed source providing seed light, where the seed source includes one or more seed lasers to generate the seed light and a seed controller to adjust at least one of a temporal pulse profile or a wavelength of the seed light. The supercontinuum source may further include an optical fiber to receive the seed light, where the seed source pumps the optical fiber to induce the generation of supercontinuum output light, and where a spectrum of the supercontinuum output light is controllable by adjusting at least one of the temporal pulse profile or the wavelength of the seed light with the seed controller.

An apparatus includes a first photonic crystal fiber. The first photonic crystal fiber includes a first dispersion at a pump wavelength. The first photonic crystal fiber includes a zero dispersion. The pump wavelength is within 100 nm of the zero dispersion. The first dispersion is normal. The first photonic crystal fiber includes a first mode field diameter at the pump wavelength. The apparatus also includes a second photonic crystal fiber coupled to the first photonic crystal fiber and outputs a broadband spectrum. The second photonic crystal fiber includes a second dispersion at the pump wavelength. The second dispersion is anomalous. The second dispersion is negative, and the first dispersion is positive. The second photonic crystal fiber includes a second mode field diameter at the pump wavelength. The second mode field diameter is smaller than the first mode field diameter.

A system and method for providing a radiation source. In one arrangement, the radiation source includes an optical fiber that is hollow, and has an axial direction, a gas that fills the hollow of the optical fiber, and a plurality of temperature setting devices disposed at respective positions along the axial direction of the optical fiber, wherein the temperature setting devices are configured to control the temperature of the gas to locally control the density of the gas.

A microstructured optical fiber having a length and a longitudinal axis along its length, the finer including a core region capable of guiding light along the longitudinal axis and a cladding region which surrounds the core region, the cladding region comprising a cladding background material and a plurality of cladding features within the cladding background material, the cladding features being arranged around the core region, wherein the cladding region comprises an inner cladding region comprising an innermost ring of cladding features and an outer cladding region comprises outer cladding rings of outer cladding features, the innermost ring consisting of those cladding features being closest to the core region, wherein the rings of cladding features each comprise bridges of cladding background material separating adjacent features of the ring, wherein the bridges of the innermost ring have an average minimum width (w1), the minimum width of a bridge of a ring being the shortest distance between two adjacent features of the ring; and wherein at least one outer cladding ring has an average minimum width (w2) of bridges that is larger than the average minimum width (w1) of the bridges of the innermost ring. Also described are a cascade optical fiber with at least one fiber as described, as well as a source of supercontinuum radiation.

A broadband radiation source device, including a fiber assembly having a plurality of optical fibers, each optical fiber being filled with a gas medium, wherein the broadband radiation source device is operable such that subsets of the optical fibers are independently selectable for receiving a beam of input radiation so as to generate a broadband output from only a subset of the plurality of optical fibers at any one time.

A microstructured optical fiber including a core region and a cladding region which surrounds the core region. The cladding region includes a plurality of cladding features within a cladding background material, wherein the cladding region includes an inner cladding region with at least one inner ring of cladding features and an outer cladding region with at least three outer cladding rings of outer cladding features. The inner cladding features have a first characteristic diameter and the outer cladding region includes a plurality of outer cladding features having a characteristic diameter smaller than the first characteristic diameter. The first characteristic diameter is at least about 10% larger than an average diameter of the outer cladding features and the core region has a diameter of at least about 2 μm. A cascade optical fiber with at least one fiber as described, as well as a source of optical supercontinuum generation.

A broadband light source device for creating broadband light pulses includes a hollow-core fiber and a pump laser source device. The hollow-core fiber is configured to create the broadband light pulses by an optical non-linear broadening of pump laser pulses. The hollow-core fiber includes a filling gas, an axial hollow light guiding fiber core configured to support core modes of a guided light field, and an inner fiber structure surrounding the fiber core and configured to support transverse wall modes of the guided light field. The pump laser source device is configured to create and provide the pump laser pulses at an input side of the hollow-core fiber. The transverse wall modes include a fundamental transverse wall mode and second and higher order transverse wall modes.

A waveguide including: a first section, the first section configured to generate, by a non-linear optical process, a broadened wavelength spectrum of pulsed radiation provided to an input end of the waveguide; a second section, the second section including an output end of the waveguide, the second section configured to exhibit a larger absolute value of group velocity dispersion than the first section; wherein a length of the second section is configured to reduce a peak intensity of one or more peaks in the broadened wavelength spectrum by at least 20%.