J. Nold

Ultrafast nonlinear optics in gas-filled hollow-core photonic crystal fibers [Invited]

We review the use of hollow-core photonic crystal fibers (PCFs) in the field of ultrafast gas-based nonlinear optics, including recent experiments, numerical modeling, and a discussion of future prospects. Concentrating on broadband guiding kagome-style hollow-core PCF, we describe its potential for moving conventional nonlinear fiber optics both into extreme regimes—such as few-cycle pulse compression and efficient deep ultraviolet wavelength generation—and into regimes hitherto inaccessible, such as single-mode guidance in a photoionized plasma and high-harmonic generation in fiber.

Pressure-controlled phase matching to third harmonic in Ar-filled hollow-core photonic crystal fiber

We report tunable third-harmonic generation (THG) in an Ar-filled hollow-core photonic crystal fiber, pumped by broadband <2 microJ, 30 fs pulses from an amplified Ti:sapphire laser system. The overall dispersion is precisely controlled by balancing the negative dielectric susceptibility of the waveguide against the positive susceptibility of the gas. We demonstrate THG to a higher-order guided mode and show that the phase-matched UV wavelength is tunable by adjusting the gas pressure.

Influence of ionization on ultrafast gas-based nonlinear fiber optics

We numerically investigate the effect of ionization on ultrashort high-energy pulses propagating in gas-filled kagomé-lattice hollow-core photonic crystal fibers by solving an established uni-directional field equation. We consider the dynamics of two distinct regimes: ionization induced blue-shift and resonant dispersive wave emission in the deep-UV. We illustrate how the system evolves between these regimes and the changing influence of ionization. Finally, we consider the effect of higher ionization stages.

Five-ring hollow-core photonic crystal fiber with 1.8 dB/km loss

A 19-cell hollow-core photonic crystal fiber reaching 1.8±0.5 dB/km loss at 1530 nm is reported. Despite expanded corner holes in the first ring adjacent to the core, and only five cladding rings, the minimum loss is close to the previously published record of 1.7 dB/km at a comparable wavelength, achieved in a fiber with seven cladding rings. Since each additional cladding ring requires a significant increase in fabrication time and complexity, it is highly desirable to use as few as possible while still achieving low loss. Modeling results confirm that further reducing cladding deformations would yield only a small decrease in loss. This demonstrates that loss comparable to the previously demonstrated lowest-loss bandgap fibers can be achieved with fiber structures that are significantly simpler and faster to fabricate.

Manipulation of coherent Stokes light by transient stimulated Raman scattering in gas filled hollow-core PCF

Transient stimulated Raman scattering is investigated in methane-filled hollow-core photonic crystal fiber. Using frequency-chirped ps-pulses at 1.06 microm as pump and tunable CW-radiation as Stokes seed, the vibrational excitation of the CH(4) molecules can be controlled on the sub T(2) time-scale. In this way the generated Stokes pulse can be phase-locked to the pump pulse and its spectrum manipulated.

4% conversion of sub-µJ near-IR pulses to deep UV in fundamental mode of Ar-filled PCF

We report extreme self-compression of sub-µJ 30 fs pulses at 800 nm in Ar-filled hollow-core PCF, resulting in 4% conversion to deep UV light in the fundamental guided mode, pressure-tunable from 220–270 nm.

Phase-matching and Gain of deep-UV dispersive-wave generation

Gas-filled hollow-core photonic crystal fibres enable nonlinear fibre optics in parameter regimes hitherto impossible with glass-core fibres, such as: ultra-violet transmission, pressure tuneable zero dispersion wavelengths down to 200 nm, and ultra-short duration soliton energies at the microjoule level. Two techniques for ultra-violet light generation in such fibres have utilised these properties: third harmonic generation [1], and dispersive wave generation [2]. In this work we study the phase-matching and gain landscapes of the latter case.

Nonlinear optics in gas-filled HC-PCF in the plasma regime

Laser-driven ionization in Ar-filled HC-PCF is accessed through self-compression of few-microjoule pulses. Modeling confirms that the observed blue-shifted spectral bands are caused by light-plasma interactions over an extended length in the fiber.

UV continuum generation in Ar-filled hollow-core PCF

We numerically model the generation, by continuous emission of dispersive waves in an Ar-filled hollow-core PCF with an axially increasing gas pressure distribution, of a UV continuum spanning 175-250 nm.

Five-ring hollow-core photonic bandgap fiber with 1.8 dB/km loss

A 19-cell hollow-core photonic bandgap fiber reaching 1.8±0.5 dB/km loss is reported. Despite expanded corner-holes in the first ring adjacent to the core, and only five cladding rings, the minimum loss is close to the previous record of 1.2 dB/km.