M. Chafer

Ultralow transmission loss in inhibited-coupling guiding hollow fibers

Attenuation in photonic bandgap guiding hollow-core photonic crystal fiber (HC-PCF) has not beaten the fundamental silica Rayleigh scattering limit (SRSL) of conventional step-index fibers due to strong core-cladding optical overlap, surface roughness at the silica cladding struts, and the presence of interface modes. Hope has been revived recently by the introduction of hypocycloid core contour (i.e., negative curvature) in inhibited-coupling guiding HC-PCF. We report on several fibers with a hypocycloid core contour and a cladding structure made of a single ring from a tubular amorphous lattice, including one with a record transmission loss of 7.7 dB/km at ∼750  nm (only a factor ∼2 above the SRSL) and a second with an ultrabroad fundamental band with loss in the range of 10–20 dB/km, spanning from 600 to 1200 nm. The reduction in confinement loss makes these fibers serious contenders for light transmission below the SRSL in the UV–VIS–NIR spectral range and could find application in high-energy pulse laser beam delivery or gas-based coherent and nonlinear optics.

Near diffraction-limited performance of an OPA pumped acetylene-filled hollow-core fiber laser in the mid-IR

We investigate the mid-IR laser beam characteristics from an acetylene-filled hollow-core optical fiber gas laser (HOFGLAS) system. The laser exhibits near-diffraction limited beam quality in the 3 μm region with M2 = 1.15 ± 0.02 measured at high pulse energy, and the highest mid-IR pulse energy from a HOFGLAS system of 1.4 μJ is reported. Furthermore, the effects of output saturation with pump pulse energy are reduced through the use of longer fibers with low loss. Finally, the slope efficiency is shown to be nearly independent of gas pressure over a wide range, which is encouraging for further output power increase.

Raman gas self-organizing into deep nano-trap lattice

Trapping or cooling molecules has rallied a long-standing effort for its impact in exploring new frontiers in physics and in finding new phase of matter for quantum technologies. Here we demonstrate a system for light-trapping molecules and stimulated Raman scattering based on optically self-nanostructured molecular hydrogen in hollow-core photonic crystal fibre. A lattice is formed by a periodic and ultra-deep potential caused by a spatially modulated Raman saturation, where Raman-active molecules are strongly localized in a one-dimensional array of nanometre-wide sections. Only these trapped molecules participate in stimulated Raman scattering, generating high-power forward and backward Stokes continuous-wave laser radiation in the Lamb–Dicke regime with sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth as low as ∼14 kHz, more than five orders of magnitude narrower than conventional-Raman pressure-broadened linewidth, and sidebands comprising Mollow triplet, motional sidebands and four-wave mixing.

Shaping photon-pairs time-frequency correlations in inhibited-coupling hollow-core fibers

We experimentally show how multiband dispersion properties of inhibited-coupling hollow-core fibers allow to control the spectral correlations of photon pairs generated through four-wave-mixing in a fiber filled with non-linear gas.

Toward power scaling in an acetylene mid-infrared hollow-core optical fiber gas laser: effects of pressure, fiber length, and pump power

The effect of gas pressure, fiber length, and optical pump power on an acetylene mid-infrared hollow-core optical fiber gas laser (HOFGLAS) is experimentally determined in order to scale the laser to higher powers. The absorbed optical power and threshold power are measured for different pressures providing an optimum pressure for a given fiber length. We observe a linear dependence of both absorbed pump energy and lasing threshold for the acetylene HOFGLAS, while maintaining a good mode quality with an M-squared of 1.15. The threshold and mode behavior are encouraging for scaling to higher pressures and pump powers.

2-µm wavelength-range low-loss inhibited-coupling hollow core-PCF

We report on the design and fabrication of inhibited-coupling guiding hollow-core photonic crystal fiber with a transmission band optimized for low loss guidance around 2 μm. Two fibers design based on a Kagome-lattice cladding have been studied to demonstrate a minimum loss figure of 25 dB/km at 2 μm associated to an ultra-broad transmission band spanning from the visible to our detection limit of 3.4 μm. Such fibers could be an excellent tool to deliver and compress ultra-short pulse laser systems, especially for the emerging 2-3 μm spectral region.

Inhibited-coupling HC-PCF based beam-delivery-system for high power green industrial lasers

We report on an ultra-low loss Hollow-Core Photonic Crystal Fiber (HC-PCF) beam delivery system (GLO-GreenBDS) for high power ultra-short pulse lasers operating in the green spectral range (including 515 nm and 532 nm). The GLOBDS- Green combines ease-of-use, high laser-coupling efficiency, robustness and industrial compatible cabling. It comprises a pre-aligned laser-injection head, a sheath-cable protected HC-PCF and a modular fiber-output head. It enables fiber-core gas loading and evacuation in a hermetic fashion. A 5 m long GLO-BDS were demonstrated for a green short pulse laser with a transmission coefficient larger than 80%, and a laser output profile close to single-mode (M2 <1.3).

Macroscopic motion of the self-nanostructured Raman gas

The recent findings of line narrowing in Raman-active continuous-wave-pumped gas [1] showed that the Stokes scattering occurs in a Lamb-Dicke regime and is associated to formation of array of deep subwavelength nanotraps, which resulted in a sub-recoil linewidth Stokes radiation [1]. The results also showed that this nanotrap lattice exhibits a macroscopic motion. Here we present theoretical and numerical analysis of this phenomenon, addressing the peculiarities of field distribution and fascinating effect of nanotrap lattice in motion.

Parametric four-wave mixing sidebands in strongly driven Raman molecular D2-filled HC-PCF

The development of the Raman gas-filled hollow core photonic crystal fibers allow to exacerbate the light-matter interaction with extremely high efficiency. Among the nonlinear optical effect that were extensively explored we count stimulated Raman scattering, with demonstrations like over 5-octaves wide Raman comb using H2-filled inhibited coupling guiding HC-PCF pumped with a picosecond pulsed laser [1]. Furthermore, Raman-active gases are known to exhibit very weak susceptibility outside the Raman frequencies, and thus are considered to be poor media for the generation of new frequencies through parametric four-wave mixing (FWM).

Lamb-Dicke sub-recoil narrowing of high-power CW stokes Raman source

A new way to reach the Lamb-Dicke regime in molecular gases has been reported in [1]. This is achieved by trapping H2 molecule during Stimulated Raman Scattering (SRS) in a photonic band gap hollow-core fiber (PBG HC-PCF) pumped with a high power CW laser [1]. The molecular trapping process occurs in a self-assembled manner, whereby the Raman active molecules are confined in nanometer-wide sections by a periodic and ultra-deep potential thanks to a spatially modulated Raman saturation. It has permitted to obtain sub-recoil linewidths as low as 14 kHz which is 5 orders of magnitude lower than the expected H2 Doppler-broadened linewidth for a product of the input power and the pressure below 1000 W.bar. Above this threshold the linewidth broadens due to the generation of the second-order Stokes.