Showing papers by "Philip St. J. Russell published in 2002"

Demonstration of ultra-flattened dispersion in photonic crystal fibers

Abstract: We demonstrate photonic crystal fibers with ultra-flattened, near zero dispersion. Two micro-structured fibers showing dispersion of 0 ± 0.6 ps/nm.km from 1.24 μm-1.44 μm wavelength and 0 ± 1.2 ps/nm.km over 1 μm-1.6 μm wavelength have been measured.

Supercontinuum generation by stimulated Raman scattering and parametric four-wave mixing in photonic crystal fibers

Abstract: Supercontinuum generation is investigated experimentally and numerically in a highly nonlinear index-guiding photonic crystal optical fiber in a regime in which self-phase modulation of the pump wave makes a negligible contribution to spectral broadening. An ultrabroadband octave-spanning white-light continuum is generated with 60-ps pump pulses of subkilowatt peak power. The primary mechanism of spectral broadening is identified as the combined action of stimulated Raman scattering and parametric four-wave mixing. The observation of a strong anti-Stokes Raman component reveals the importance of the coupling between stimulated Raman scattering and parametric four-wave mixing in highly nonlinear photonic crystal fibers and also indicates that non-phase-matched processes contribute to the continuum. Additionally, the pump input polarization affects the generated continuum through the influence of polarization modulational instability. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate the importance of index-guiding photonic crystal fibers for the design of picosecond and nanosecond supercontinuum light sources.

Extruded soft glass photonic crystal fiber for ultrabroad supercontinuum generation

Abstract: We report the fabrication and properties of soft glass photonic crystal fibers (PCF's) for supercontinuum generation. The fibers have zero or anomalous group velocity dispersion at wavelengths around 1550 nm, and approximately an order of magnitude higher nonlinearity than attainable in comparable silica fibers. We demonstrate the generation of an ultrabroad supercontinuum spanning at least 350 nm to 2200 nm using a 1550 nm ultrafast pump source.

Microstructured optical fibre

Abstract: A method of manufacturing an optical fibre comprises: (a) providing an elongate element comprising (i) a core region 310, (ii) a cladding region 320 that surrounds the core region and that includes a plurality of elongate holes 315, (iii) a higher-index zone that comprises dielectric material having a first, higher refractive index and (iv) a lower-index zone that surrounds the higher-index zone and comprises dielectric material having a second, lower refractive index. (b) at least partially collapsing the holes in a length of the element to provide a collapsed portion comprising a core region, formed from the higher-index zone of the elongate element, and a cladding region, formed from the lower-index zone of the elongate element, such that the core region in the collapsed portion has a refractive index that is higher than the refractive index of the cladding region in the collapsed portion. Collapse of the elongate holes in a microstructured optic fibre may cause a spot size of a guided mode to change by more than 20%. More than 90% of the power of a guided mode may propagate in an inner core region.

Femtosecond optical clock

Abstract: An experimental scheme of femtosecond optical clock is described. The characteristics of the elements and blocks of the setup are given. Possible application areas of the optical clock described are discussed.

Femtosecond optical clock with the use of a frequency comb

Abstract: The principles of precision measurement of frequency intervals in optical range with the help of femtosecond lasers are described. An experimental scheme of femtosecond optical clock is described. The characteristics of the basic elements and units of the setup are presented. The results of a broadened spectrum researches with the help of tapered fibers are reported.

Nonlinear effects in microstructured fibers

Abstract: Control of nonlinear processes in optical fibers can provide the foundation for future all-optical signal processing applications which would impact a number of basic and applied fields. An ideal setting to study these phenomena is provided by microstructured optical fibers (or photonic crystal fibers –PCFs). The enhanced nonlinear effects in these structures has attracted considerable attention and has been the focus of intense research activity spanning a variety of applications [1,2]. We report here on a variety of effects which are observed experimentally by propagating 160 fs, λ=1550 nm pulses in a short segment of microstructured fiber. By operating at low average powers (up to 25 mW) and varying the input pulse polarization we can observe fundamental (N=1) soliton formation, higher order (N=2) formation in combination with a large self-frequency shift, visible harmonic generation and optical bistability in dependence of the input pulse polarization state.

Spectral shaping of SC in a photonic crystal fibre: polarization, pulse duration and chirp properties

Abstract: Summary from only given. We present results of experiment aiming to generate smooth spectrum in the range 500-1100 nm with the use of chirp and polarization adjustments of the incident pulse as well as its duration. No numerical simulations are known on this subject mainly because of the difficulties in 3D modelling the complex PCF-structure; as well as no systematical experimental results are known. The polarization dependence can be explained with the multifrigency of the PCF, due to its broken azimuthal symmetry.