Microstructured optical fibres (MOFs), also known as Photonic Crystal Fibres (PCFs) or Holey Fibres (HFs), play an important role in supercontinuum generation because of their high nonlinearity and ability to tailor the dispersion profile. Nowadays, studies have extended to the multimode environment to enhance spectral broadening by taking advantage of various intermodal nonlinear effects. Recently, it has been shown that these types of fibres can also be able to provide spatially cleaned output beams through a novel nonlinear spatial effect called Kerr-induced beam self-cleaning (KBSC), which makes these fibres suitable for a variety of multimode-based applications. In this paper, a full modal analysis of germanium (Ge)-doped graded-index multimode PCFs with different geometrical sizes is provided. The influence of fibre size on modal properties, such as effective refractive index, birefringence and dispersion, was investigated using the finite element method. It was found that the changes in the geometric parameters can significantly affect the modal properties and then the frequency generation and spectral broadening. Experimentally, high-efficiency frequency generation with different frequency detunings was obtained in a short length of each PCF by launching input pulses at 1064 nm pump wavelength. For longer fibre length and high input power, supercontinuum generation with improved broadening from visible to near IR by intermodal four-wave mixing and stimulated Raman scattering was observed in all PCFs. A study of the effect of input peak power, input polarization axis and fibre length on supercontinuum spectrum is presented. Experimental evidence of the KBSC effect as a function of various fibre and laser parameters is also reported. The evolution of spatial output beam pattern from higher-order mode to fundamental mode with low-peak-power self-cleaning threshold was observed for all the fibres by launching a 1064 nm pump laser with 1 ns pulse duration.
The mid-infrared spectral region is a great technical and scientific interest in numerous research field and applications. Among these studies, the generation of mid-infrared supercontinuum in fibers has attracted strong interest in the last decade, because of unique properties such as broad wavelength-coverage and brightness. In this work, a cascaded supercontinuum generated in a fluoride and a chalcogenide fiber spanning from 2 to 10 µm has been used for the detection of infrared signatures of organic compounds. Those results open a new way for remote sensing and spectroscopy in the mid-IR.
Supercontinuum (SC) generation towards the mid-infrared (MIR) range is an active field of research and development motivated by a wide range of applications including optical coherence tomography (OCT), material processing, optical sensing and absorption spectroscopy. In this work, we investigate mid-IR SC generation in a cascaded silica and soft-glass fiber system directly pumped with a commercially-available picosecond fiber laser operating in the telecommunications window at 1.55 μm. This all-fiber system is shown to generate a flat broadband mid-IR-SC covering the entire range from 2 to 10 μm with several tens of mW of output power. This technique paves the way for practical and robust broadband SC sources in the mid-IR without the requirement of mid-infrared pump sources or Thulium-doped fiber amplifiers. We also describe a fully-realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system and use our numerical results to discuss the physical processes underlying the spectral broadening in the cascaded system.
We report on a 3 W Mid-IR supercontinuum extended up to 4.6 μm based on an all-PM thulium doped fiber gainswitched laser seeding an InF3 fiber. This innovative fiber presents a specific design that increases non-linear effects and shows very weak background losses. Thanks to the versatility of our gain-switched laser, all the pulse parameters have been widely optimized to generate a supercontinuum emission with the highest average power and the largest spectrum.
This paper introduces a supercontinuum (SC) laser source emitting from 400 nm to beyond 1750 nm, with
adjustable pulse repetition rate (from 250 kHz to 1 MHz) and duration (from ~200 ps to ~2 ns). This device
makes use of an internally-modulated 1.06 μm semiconductor laser diode as pump source. The output radiation
is then amplified through a preamplifier (based on single-mode
Yb-doped fibres) followed by a booster (based
on a double-clad Yb-doped fibre). The double-clad fibre output is then spliced to an air-silica microstructured
optical fibre (MOF). The small core diameter of the double-clad fibre allows reducing the splice loss. The strongly
nonlinear propagation regime in the MOF leads to the generation of a SC extending from the violet to the nearinfrared
wavelengths. On the Stokes side of the 1.06 μm pump line, i.e., in the anomalous dispersion regime, the
spectrum is composed of an incoherent distribution of quasi-solitonic components. Therefore, the SC source is
characterised by a low coherence length, which can be tuned by simply modifying pulse duration, that is closely
related to the number of quasi-solitonic components brought into play. Finally, the internal modulation of the
laser diode permits to achieve excellent temporal stability, both in terms of average power and pulse-to-pulse
period.
Optical Coherence Tomography is an emerging technique for biomedical diagnostic help. This is a non-invasive, high resolution, non-destructive mean for some optical biopsy. Since a few years new developments have been undergone in the field of OCT trying to functionalize OCT measurements. One of them is Spectroscopic OCT where simultaneous access to depth resolution as well as spectral features depth resolved in the media are obtained. These spectroscopic OCT system are mainly based on post processing of classical OCT signals what is time consuming and which add numerical noise. We propose an 'all optical' system for real-time direct display of depth-frequency analysis of media.
Following the first demonstration of an all guided two-beam stellar interferometer designed for space missions, we report an experiment recombining the beams coming from three telescopes using only guided optics or integrated optics components. This additional aperture could give us the possibility to achieve an image reconstruction using the phase-closure technique. We focus these calibration experiments on the interference fringe contrast measurements and the evolution of the phase-closure term versus the differential dispersion effects induced by the stretching of fiber delay lines.
The phase closure is well known to remove the phase biases in a three-arm interferometer. This property is very useful to avoid the phase effect of the atmosphere in stellar interferometry. In this paper we theoretically investigate the effect of differential dispersion in a three-arm interferometer. We demonstrate that phase closure is corrupted by this spectral behavior. This theoretical analysis is illustrated by experimental results on a fiber version of a stellar interferometer. The good accordance between the numerical simulations and the experimental results valid this model.
We describe a preliminary experimental study of an interferometer built with two 500-meters-long arms made of polarization maintaining optical fibers. The control of the field polarization state along the single-mode fiber arms enables to measure fringe contrast up to 93% with a laser source emitting a 1290nm carrier wavelength. Preliminary contrast measurements achieved with broadband spectrum sources exhibit differential dispersion effect resulting from fiber inhomogeneities. Partial compensation of this effect is achieved by introducing additional fiber pieces on one arm. Moreover, we experimentally characterize the differential chromatic dispersion evolution as a function of the various additional fiber sections. Using the channeled spectrum method, a spectral analysis of the interferometric mixing allows to accurately measure the differential effect of chromatic dispersion i.e. second and third order term of the spectral phase shift.
We report an experiment demonstrating the potential of optical fibers in the design of stellar interferometers for space missions. For the first time to our knowledge, only guided optics components are used to achieve the different basic functions of a stellar interferometer: optical field propagation from the telescope to the mixing station; delay line to synchronize the field to be mixed; and optical fiber couplers to split and recombine the beams.
We report the first technical results of the Integrated Optics Near-infrared Interferometric Camera developed and characterized at the Observatoire de Grenoble as well as the first tests carried out on the GI2T Interferometer (Observatoire de la Cote d'Azur, France). This near-infrared interferometric camera dedicated to astronomical observations is implemented in a single dewar, which hosts the planar integrated optics beam combiner and a cooled HgCdTe infrared detector, with optical interfaces reduced to optical fibers for signal injection in the component. Thanks to its versatility, this concept allows to combine any number of telescopes in the near infrared range (J, H and K bands). The compactness of the integrated optics components allows various combining schemes (co- and multi-axial ones) and observations in different spectral bands simultaneously. Finally, a camera upgrade with a PICNIC chip is also described. This new set-up under integration at the Observatoire de Grenoble would allow to reach limiting magnitudes of H equals 4 - 6 with the GI2T.
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