Hybrid optical fibers, i.e. optical fibers that combine, in the same structure, glass with crystal, metal, polymer or a second type of glass, open access to a wide range of optical properties or optical functions not accessible to common single-glass-made optical fibers. Silicon-core fibers are one type of hybrid fibers that have been intensively studied since 2006 with the aim to take benefit of the mid-infrared transparency of silicon or to implement opto-electrical functions in the optical fiber itself. Some of the unique optical properties of these semiconductor-core fibers have been demonstrated but it is admitted that optical losses are still today a drag on the rise of performances and hence devote specific attention. Post-processing based on laser or thermal annealing can be applied on the as-drawn fibers to improve core crystallinity and then reduce optical losses. However, such processing techniques have been demonstrated on centimeter-long fibers only. In the present paper, we demonstrate as-drawn silicon-core fiber with loss level below 0.2 dB/cm on the 1250-1650nm wavelength range, this fiber being continuously manufactured over length exceeding one hundred of meters. Several fibers have been fabricated from a rod-in-stack approach and different core dimensions ranging from about 0.8 to 3.4 μm have been successively realized and extensive characterizations (XRD, micro-Raman spectroscopy, TEM and ToF-SIMS analysis) have been conducted on the 3.4 μm core fiber. The crystalline state of the core, the absence of oxygen contamination and the optical transmission from 1.1 to 4 μm will be presented.
We report on the time-resolved measurement of the full transmission matrix (TM) of a short length of specialty annularcore few-mode fiber which guides 10 vector modes. We show how our method can isolate the fiber TM from "misalignment" contributions from free space optics upstream and downstream of the fiber. From measurements spanning two days, we extract the drift of the fiber TM. We show that drifts in the TM elements are mostly described as correlated phase variations rather than amplitude variations. We show that an empirical model of the fiber TM parametrized in one parameter can successfully account for the drift.
We demonstrate broadband supercontinuum generation from 560 nm up to 2350 nm by coupling a Q-switched picosecond microchip laser at 1064 nm into a 15 μm-core step-index germanium-doped silica fiber, designed to support five spatial modes at 1064 nm. It is further shown that multiple cascaded intermodal four-wave mixing and Raman processes take place in the fiber with large frequency detuning up to 150 THz. The multimode properties of this fiber yield a number of intermodal nonlinear coupling terms and the parametric sideband wavelengths have been obtained from the phasematching condition for intermodal four-wave mixing.
A new few-mode fiber design taking advantage of a micro-structured core consisting of 19 secondary cores embedded in a pedestal geometry is presented. This design offers the possibility of precisely tailoring the rare earth ion distribution in the core in order to manage the differential modal gain. An optimized configuration of an erbium-doped few-mode fiber supporting 10 modes in the C-band with a theoretical low gain excursion is designed and realized. Preliminary optical characterizations of this fiber are presented.
We report on the first polarization maintaining single-mode fiber that delivers a flat-top intensity profile at 1050 nm. A high quality fundamental flat mode was obtained. We showed that our fiber can be considered as single-mode in practice with low confinement losses. Its birefringence was measured to be 0.6x10-4, and the PER was measured at more than 20 dB even for a 20 m fiber long. Strategies to enhance this birefringence preserving the flat top profile and the singlemode behaviour as well are also discussed.
Compactness, long term stability and no free-space alignment are important advantages of fiber lasers over bulky systems. These fiber lasers have also demonstrated their capability to deliver high-power pulses and are thus suitable for numerous applications. Nevertheless the intensity profile delivered usually has a Gaussian-like shape, which most of the time is sufficient, but it could be interesting, for many applications (laser-biological tissues interactions, heat treatment, industrial laser processing or for seeding large-scale laser facilities like Laser MegaJoule) to obtain a homogeneous intensity profile at the fiber laser output. Moreover several of these applications required a linearly polarized output beam. In order to achieve all these requirements we have developed and realized a new fiber design. This fiber is the first polarization maintaining single-mode fiber delivering a flat top intensity. A high quality flat mode was obtained at 1.05μm through the use of a well-tailored index profile and single-mode behavior was verified by shifting the injection and using the S² imaging. Moreover, boron Stress Applying Parts (SAPs) including in the cladding led to a birefringence of 0.6x10-4 and a measured PER better than 20dB even for a long fiber length (~20 m). Alongside the fabrication, we developed a simulation code, using Comsol Multiphysics®, to take into account the stress dependency induced by the SAPs. Further modeling allows us to present an effectively single-mode fiber design, delivering a top-hat mode profile and exhibiting a polarizing behavior.
We report on the design and the fabrication of a new design of an all-solid Bragg fiber based on the pixelization and heterostructuration of a cladding made of only two high index rings. The thickness of the low index ring as well as the geometry of the heterostructuration (its symmetry and the number of removed pixels) have been chosen to maximize the confinement losses of the Higher Order Modes (HOM) (above 10 dB/m) while keeping the Fundamental Mode (FM) losses low (below 0.1 dB/m). The proposed geometry allows having access to different Mode Field Diameter (MFD) from 54 μm to 60 μm at 1 μm wavelength by drawing the same stack to different fiber (and hence, core) diameters. As a result, a record MFD of 60 μm is reported for a Solid Core Photonic Bandgap Fiber (SC-PBGF) and single-mode behavior is obtained experimentally even for a short fiber length (few tens centimeters) maintained straight.
Solid-Core Photonic BandGap Fibers (SC-PBGF) belongs to the family of microstructured optical fibers whereby the cladding is made of high refractive index inclusions as compared to that of the fiber core. In such fibers, light is confined to the core by an anti-resonant mechanism and several high transmission windows separated by high loss regions compose the transmission spectrum. Guiding mechanism is then identical to the one observed in Hollow-Core PBGF (HC-PBGF) except that a solid core can be exploited. Such PBGFs have proven to be good candidates for single-mode high power delivery and for controlling the spectral extension of supercontinuum generation. Mixing different types of resonators in the cladding or mixing PBG with modifed-Total Internal Reection (m-TIR) mechanism also lead to original and more exible fiber designs. Recent developments in the design and realization of Large Mode Area (LMA) and Highly NonLinear (HNL) fibers are presented, including single-mode ring-structured Bragg _bers, LMA fibers exhibiting a fundamental mode with a flat-top profile, and hybrid fibers for supercontinuum generation or frequency conversion.
We present a new passive air/silica microstructured optical fiber designed to be single mode and which delivers a flat-top
intensity profile at 1 μm. By inclusion of a raised index ring surrounding the central core, the refractive index profile of
the fiber flattens the intensity distribution of the fundamental mode. Experimental results clearly demonstrate the
feasibility of all-fibered top-hat beam delivery systems with one spatial mode suitable for many applications.
We report the first experimental demonstration of an optical fiber supporting a fundamental mode with flattened intensity
profile around 1050 nm. The design has been defined through intensive numerical simulations by paying a special
attention to the constraints imposed by the fabrication process. We show that the fabricated fiber presents a single-mode
We report recent advances in the domain of Highly Non-Linear Photonic Crystal Fibers (HNL-PCFs) especially designed as gain medium for Raman fiber lasers. Indeed, a fiber Raman coefficient as high as 42 W-1.km-1 at 1.12μm has been obtained, while keeping optical losses moderate, below 6 dB/km at this wavelength. We have calculated that only 2 meters of such a germanium doped HNL-PCF is required to obtain an output power in the order of 10W at 1.12 μm with an efficiency of 90%. Experimental output optical spectra of multi-cascades cavities are finally given.
Fiber Bragg gratings with strong resonance peaks for both Bragg and cladding modes are made in photonic crystal fiber
modified with a germanium doped core. Experimental results for strain, temperature and refractive index sensitivities of
fiber Bragg gratings are reported. We show the existence of an inner cladding mode that has the largest coupling from
the core mode and that is insensitive to surrounding index changes. The core mode, inner cladding mode and outer
cladding modes all have the same temperature sensitivity. By tracking the cladding mode resonances shifts relative to
the core mode, a temperature and index insensitive strain sensor can be made.