Guillaume Vienne

High-power air-clad large-mode-area photonic crystal fiber laser

We report on a 2.3 m long air-clad ytterbium-doped large-mode-area photonic crystal fiber laser generating up to 80 W output power with a slope efficiency of 78%. Single transverse mode operation is achieved with a mode-field area of 350 /spl mu/m/sup 2/. No thermo-optical limitations are observed at the extracted /spl sim/35 W/m, therefore such fibers allow scaling to even higher powers.

Demonstration of optical microfiber knot resonators

We demonstrate optical resonance from microfiber knots obtained by manipulating freestanding silica microfibers. Q factors as high as 57 000 with finesse of 22 are observed in knots with sizes less than 1mm. The free spectral range of the resonator can be easily tuned by tightening the knot structure in air. The knot resonators are highly stable in water with Q factors up to 31 000 and finesse of 13. The possibility of supporting the knot resonator with a solid MgF2 substrate is also demonstrated.

Demonstration of microfiber knot laser

The authors demonstrate a 1.5 mu m wavelength microfiber laser formed by tightening a doped microfiber into a knot in air. The 2-mm-diameter knot, assembled using a 3.8-mu m-diameter microfiber that is directly drawn from Er:Yb-doped phosphate glass, serves as both active medium and resonating cavity for lasing. Single-longitudinal-mode laser with threshold of about 5 mW and output power higher than 8 mu W is obtained. Their initial results suggest a simple approach to highly compact lasers based on doped microscale optical fibers. (c) 2006 American Institute of Physics.

All-fiber add-drop filters based on microfiber knot resonators

We demonstrate an all-fiber add-drop filter composed of a microfiber knot (working as a resonator) and a fiber taper (working as a dropping fiber). The dropping taper can be either parallel or perpendicular to the input port of the filter. A quality factor (Q factor) of 13,000 is obtained from a parallel-coupling 308 microm diameter microknot add-drop filter with a free spectral range (FSR) of 1.8 nm. A Q factor of approximately 3300 is obtained from a cross-coupling 65 microm diameter microknot add-drop filter with a FSR of 8.1 nm. This device is particularly easy to fabricate and to connect to fiber systems.

Ultra-large bandwidth hollow-core guiding in all-silica bragg fibers with nano-supports

We demonstrate a new class of hollow-core Bragg fibers that are composed of concentric cylindrical silica rings separated by nanoscale support bridges. We theoretically predict and experimentally observe hollow-core confinement over an octave frequency range. The bandwidth of bandgap guiding in this new class of Bragg fibers exceeds that of other hollow-core fibers reported in the literature. With only three rings of silica cladding layers, these Bragg fibers achieve propagation loss of the order of 1 dB/m.

Air-guiding photonic bandgap fibers: spectral properties, macrobending loss, and practical handling

For development of hollow-core transmission fibers, the realizable fibers lengths, bandwidth, characterization, and compatibility with standard technology are important issues. We report record-length air-guiding fiber, spectral properties, splicing, and optical time domain reflectometer (OTDR) measurements. Furthermore, spectral macrobending loss measurements for two different designs of air-core photonic bandgap fibers are presented. While bending loss is observed, it does not limit operation for all practical bending diameters (>5 mm).

Observation of a nonlinear microfiber resonator

Measurements of the intensity transfer function of a silica microfiber resonator are shown to follow a wide variety of hysteresis cycles, depending on the cavity detuning and the scanning frequency of the range of input powers. We attribute these observations to a nonlinear phase shift of thermal origin and provide a simple model that reproduces well our measurements. The response time is found to be around 0.6 ms.

Effect of Host Polymer on Microfiber Resonator

We observe that changing the surrounding material from air to a low refractive index polymer can considerably alter the transmission spectrum of a microfiber knot around a given wavelength. We report on a silica microfiber knot resonator about 180 m in diameter. Using a supercontinuum source, we study its transmission when air and when a low index polymer are used as cladding. The resonator shows similar extinction ratio and Q-factor for both cladding materials. However, embedding the resonator in the polymer down-shifts the optimal operating wavelength by about 20%.

Demonstration of a reef knot microfiber resonator

We propose a new way to realize a microfiber optical resonator by implementing the topology of a reef knot using two microfibers. We describe how this structure, which includes 4 ports and can serve as an add-drop filter, can be fabricated. Resonances in an all-silica reef knot are measured and good fits are obtained from a simple resonator model. We also show the feasibility of assembling a hybrid silica-chalcogenide reef knot structure.

Theoretical study of microfiber resonator devices exploiting a phase shift

Phase shifts within microfiber resonators can be exploited to demonstrate compact and fast-responding devices. Two examples, a sensor and a bistable device, where the origins of the phase shift are fundamentally different, are investigated. In the sensor the phase change originates from the change of refractive index of the medium surrounding the microfiber ring. This is a linear mechanism which translates into a change of resonance wavelength. Calculations of a silica microfiber ring immersed in an aqueous solution and operating at a wavelength of 1550 nm show that with a fiber 550 nm in diameter the sensitivity approaches a maximal value of about 1137 nm/RIU. In contrast to the sensitivity, the detection limit is critically dependent on the Q factor of the microfiber resonator, and with state of the art microfiber resonators we predict a detection limit of the order of 10 −7 RIU. In the bistable device the phase shift is assumed to originate from the nonlinear optical Kerr effect. In contrast to the sensor, the nonlinearity affects the shapes of the resonances, a phenomenon responsible for bistability. Analytical formulae are derived to evaluate the main parameters at play. We investigate the suitability of several glass materials to realize a microfiber bistable device in air operating at a wavelength of 1550 nm. While the threshold for bistability is predicted to be of the order of tens of watts for silica, it drops to less than 30 mW for G2S2, an easily processed chalcogenide glass.