Natalie V. Wheeler

Low loss broadband transmission in hypocycloid-core Kagome hollow-core photonic crystal fiber

We report on the fabrication of a seven-cell-core and three-ring-cladding large-pitch Kagome-lattice hollow-core photonic crystal fiber (HC-PCF) with a hypocycloid-shaped core structure. We demonstrate experimentally and theoretically that the design of this core shape enhances the coupling inhibition between the core and cladding modes and offers optical attenuation with a baseline of ∼180 dB/km over a transmission bandwidth larger than 200 THz. This loss figure rivals the state-of-the-art photonic bandgap HC-PCF while offering an approximately three times larger bandwidth and larger mode areas. Also, it beats the conventional circular-core-shaped Kagome HC-PCF in terms of the loss. The development of this novel (to our knowledge) HC-PCF has potential for a number of applications in which the combination of a large optical bandwidth and a low loss is a prerequisite.

Mid-infrared gas filled photonic crystal fiber laser based on population inversion

We demonstrate for the first time an optically pumped gas laser based on population inversion using a hollow core photonic crystal fiber (HC-PCF). The HC-PCF filled with 12C2H2 gas is pumped with ~5 ns pulses at 1.52 μm and lases at 3.12 μm and 3.16 μm in the mid-infrared spectral region. The maximum measured laser pulse energy of ~6 nJ was obtained at a gas pressure of 7 torr with a fiber with 20 dB/m loss near the lasing wavelengths. While the measured slope efficiencies of this prototype did not exceed a few percent due mainly to linear losses of the fiber at the laser wavelengths, 25% slope efficiency and pulse energies of a few mJ are the predicted limits of this laser. Simulations of the lasers behavior agree qualitatively with experimental observations.

10 kHz accuracy of an optical frequency reference based on (C2H2)-C-12-filled large-core kagome photonic crystal fibers

Saturated absorption spectroscopy reveals the narrowest features so far in molecular gas-filled hollow-core photonic crystal fiber. The 48-68 mum core diameter of the kagome-structured fiber used here allows for 8 MHz full-width half-maximum sub-Doppler features, and its wavelength-insensitive transmission is suitable for high-accuracy frequency measurements. A fiber laser is locked to the (12)C2H2 nu(1); + nu(3) P(13) transition inside kagome fiber, and compared with frequency combs based on both a carbon nanotube fiber laser and a Cr:forsterite laser, each of which are referenced to a GPS-disciplined Rb oscillator. The absolute frequency of the measured line center agrees with those measured in power build-up cavities to within 9.3 kHz (1 sigma error), and the fractional frequency instability is less than 1.2 x 10(-11) at 1 s averaging time.

Double photonic bandgap hollow-core photonic crystal fiber

We report on the design, fabrication and characterization of hollow-core photonic crystal fiber with two robust bandgaps that bridge the benchmark laser wavelengths of 1064 nm and 1550 nm. The higher-order bandgap arises due to the extremely thin struts of the silica cladding and their fine-tuning relative to the apex size. The optimum strut thickness was found to be approximately one hundredth of the cladding pitch.

Acetylene frequency references in gas-filled hollow optical fiber and photonic microcells

Gas-filled hollow optical fiber references based on the P(13) transition of the ν1+ν3 band of 12C2H2 promise portability with moderate accuracy and stability. Previous realizations are corrected (<1σ) by using proper modeling of a shift due to line-shape. To improve portability, a sealed photonic microcell is characterized on the 12C2H2 ν1+ν3 P(23) transition with somewhat reduced accuracy and stability. Effects of the photonic crystal fiber, including surface modes, are explored. Both polarization-maintaining (PM) and non-PM 7-cell photonic bandgap fiber are shown to be unsuitable for kilohertz-level frequency references.

Large-core acetylene-filled photonic microcells made by tapering a hollow-core photonic crystal fiber

We report on kagomé-lattice photonic microcells with low losses, large outer diameters, and large cores. The large (40-70microm) cores are accommodated by tapering the fibers and splicing the reduced ends to a single-mode fiber. We demonstrate the repeatability of this process and obtain splice losses of 0.6dB by optimizing the taper transition length. Narrow electromagnetically induced transparencies and saturable absorption are demonstrated in an acetylene-filled photonic microcell.

Matched cascade of bandgap-shift and frequency-conversion using stimulated Raman scattering in a tapered hollow-core photonic crystal fibre.

We report on a novel means which lifts the restriction of the limited optical bandwidth of photonic bandgap hollow-core photonic crystal fiber on generating high order stimulated Raman scattering in gaseous media. This is based on H(2)-filled tapered HC-PCF in which the taper slope is matched with the effective length of Raman process. Raman orders outside the input-bandwidth of the HC-PCF are observed with more than 80% quantum-conversion using a compact, low-power 1064 nm microchip laser. The technique opens prospects for efficient sources in spectral regions that are poorly covered by currently existing lasers such as mid-IR.

Mid-IR laser emission from a C 2 H 2 gas filled hollow core fiber

We demonstrate what we believe is the first hollow fiber gas laser based on population inversion. A single-cell-defect Kagome fiber with a core diameter of about 40 microns was filled with a few torr of acetylene (12C2H2). Acetylene has absorption transitions in the attractive telecommunication C band region and recently lasing was observed at about 3 microns from a gas cell when optically pumped. Pumping the gas filled fiber (1.65 m) with micro Joule pulses from a 5-ns OPO resulted in the emission of two laser lines at 3123.2 nm and 3162.4 nm. The pump (-1521 nm) was in the guiding regions of the fiber (loss ∼ 0.75 dB/m) while the laser output occurred in weakly guided modes (∼ 20 dB/m). This laser combines attractive features of both fiber and gas lasers, such as the confinement of the pump and laser over long interaction lengths in a compact configuration, the many possible emission wavelengths of various gases, high damage threshold, and the potential for coherent beam combining of mutually incoherent pump sources. While this first laser demonstration used a pulsed pump, the gas filled fiber laser is particularly attractive for pumping with CW laser sources.

Multipass Hollow Core-PCF Microcell Using a Tapered Micromirror

We demonstrate the insertion of a micromirror into the core of a hollow core photonic crystal fiber (HC-PCF). The micromirror is formed from a single mode fiber that has been tapered to fit into the hollow core and fixed in place using a fusion splicer. A large range of reflectivities higher than 4% was also achieved by silver-coating the silica tapered-fiber end-face using thermal evaporation. The current micromirror provides two key advantages over using a full-sized fiber splice to create a reflective interface. First, the tapered fiber tip can be coated to increase the reflectivity without degradation due to heating during the splicing process. Second, increased efficiency of input and output coupling is possible because of improved mode-field overlap with the fundamental mode of the HC-PCF. We show potential applications of micromirrors for the formation of microcavities in hollow-core fibers and for gas saturated absorption spectroscopy.

Portable acetylene frequency references inside sealed hollow-core kagome photonic crystal fiber

A continuous-wave diode laser is stabilized to a near-infrared acetylene transition inside a sealed kagome photonic crystal fiber. Stability and absolute frequency are measured with a frequency comb, and polarization sensitivity is observed.