Riccardo Pennetta

Self-alignment of glass fiber nanospike by optomechanical back-action in hollow-core photonic crystal fiber

A topic of great current interest is the harnessing and enhancement of optical tweezer forces for trapping small objects of different sizes and shapes at relatively small powers. Here we demonstrate the stable trapping, inside the core of a hollow-core photonic crystal fiber (HC-PCF), of a mechanically compliant fused silica nanospike, formed by tapering a single-mode fiber (SMF). The nanospike is subwavelength in diameter over its ∼50  μm insertion length in the HC-PCF. Laser light, launched into the SMF core, adiabatically evolves into a mode that extends strongly into the space surrounding the nanospike. It then senses the presence of the hollow core, and the resulting optomechanical action and back-action results in a strong trapping force at the core center. The system permits lens-less, reflection-free, self-stabilized, and self-aligned coupling from SMF to HC-PCF with a demonstrated efficiency of 87.8%. The unique configuration also provides an elegant means of investigating optomechanical effects in optical tweezers, especially at very low pressures.

Flying particle microlaser and temperature sensor in hollow-core photonic crystal fiber

Whispering-gallery mode (WGM) resonators combine small optical mode volumes with narrow resonance linewidths, making them exciting platforms for a variety of applications. Here we report a flying WGM microlaser, realized by optically trapping a dye-doped microparticle within a liquid-filled hollow-core photonic crystal fiber (HC-PCF) using a CW laser and then pumping it with a pulsed excitation laser whose wavelength matches the absorption band of the dye. The laser emits into core-guided modes that can be detected at the endfaces of the HC-PCF. Using radiation forces, the microlaser can be freely propelled along the HC-PCF over multi-centimeter distances-orders of magnitude farther than in previous experiments where tweezers and fiber traps were used. The system can be used to measure temperature with high spatial resolution, by exploiting the temperature-dependent frequency shift of the lasing modes, and may also permit precise delivery of light to remote locations.

Broadband, Lensless, and Optomechanically Stabilized Coupling into Microfluidic Hollow-Core Photonic Crystal Fiber Using Glass Nanospike

We report a novel technique for launching broadband laser light into liquid-filled hollow-core photonic crystal fiber (HC-PCF). It uniquely offers self-alignment and self-stabilization via optomechanical trapping of a fused silica nanospike, fabricated by thermally tapering and chemically etching a single mode fiber into a tip diameter of 350 nm. We show that a trapping laser, delivering ∼300 mW at 1064 nm, can be used to optically align and stably maintain the nanospike at the core center. Once this is done, a weak broadband supercontinuum signal (∼575–1064 nm) can be efficiently and close to achromatically launched in the HC-PCF. The system is robust against liquid-flow in either direction inside the HC-PCF, and the Fresnel back-reflections are reduced to negligible levels compared to free-space launching or butt-coupling. The results are of potential relevance for any application where the efficient delivery of broadband light into liquid-core waveguides is desired.

Dissipative optomechanical cooling of a glass-fiber nanospike coupled to a bottle resonator

Optical cooling of mechanical degrees of freedom is one of the biggest achievements of cavity optomechanics. Although it has mostly been demonstrated in the dispersive coupling regime, where the mechanical motion modulates the cavity frequency, in the dissipative coupling regime, i.e., when the mechanical motion changes the decay rate of the cavity, cooling can be achieved outside the stringent “good cavity” limit. In the most common experimental configurations of cavity optomechanics, however, where free-standing waveguides are evanescently coupled to an optical micro-cavity, low mechanical Q-factors have so far prohibited observation of dissipative cooling. Recently we reported that glass-fiber nanospikes, fashioned by tapering single-mode fibers, support high-Q flexural resonances (Q > 105) in the few kHz range, at the same time providing low loss, adiabatic guidance of light. Here we report the use of a silica nanospike to demonstrate dissipative cooling and amplification, by coupling it to an ultra-high-quality bottle resonator. In particular an effective temperature of 1.8 K can be inferred from the measurement of the mechanical power spectrum for a launched optical power of only ~200 µW. We believe this system could open the door to optomechanical cooling of low frequency mechanical resonators beyond the sideband-resolved regime.Optical cooling of mechanical degrees of freedom is one of the biggest achievements of cavity optomechanics. Although it has mostly been demonstrated in the dispersive coupling regime, where the mechanical motion modulates the cavity frequency, in the dissipative coupling regime, i.e., when the mechanical motion changes the decay rate of the cavity, cooling can be achieved outside the stringent “good cavity” limit. In the most common experimental configurations of cavity optomechanics, however, where free-standing waveguides are evanescently coupled to an optical micro-cavity, low mechanical Q-factors have so far prohibited observation of dissipative cooling. Recently we reported that glass-fiber nanospikes, fashioned by tapering single-mode fibers, support high-Q flexural resonances (Q > 105) in the few kHz range, at the same time providing low loss, adiabatic guidance of light. Here we report the use of a silica nanospike to demonstrate dissipative cooling and amplification, by coupling it to an ultra-h...