We review the recent progress on the enhanced inhibited coupling in kagome hollow-core photonic crystal fiber by
introducing negative curvature in the fiber-core shape. We show that increasing the hypocycloid contour curvature leads
to a dramatic decrease in transmission loss and optical overlap with the silica surround and to a single modedness.
Fabricated hypocycloid-core hollow-core photonic crystal fibers with a transmission loss in the range of 20-40 dB/km
and for a spectral range of 700 nm-2000 nm have now become typical.
We report a study on de-phasing mechanisms in Rb-filled hypocycloidal core shape Kagome hollowcore photonic crystal fibers. We experimentally measure the atomic polarization relaxation rates in Rb loaded bare silica Kagome hollow-core photonic crystal fibers at six different geometries. The measurements show a polarization relaxation time ranging from from ~ 16 μs for a 30 μm core inner-diameter HC-PCF to ~34 μs for a 96 μm core inner-diameter HC-PCF. The measured polarization lifetimes are much longer than the typical transit time for the atomic vapor at room temperature. We perform the theoretical analysis of the mechanisms of atomic de-coherence taking to account the fiber geometries and further experimental parameters. The analysis demonstrates that at given experimental conditions the main contribution to the polarization rotation signal comes from the transversally slow atoms. The effective temperature of the polarized atoms is than lower than the room temperature. We perform the Monte-Carlo simulations to calculate the atomic polarization relaxation rate in fibers with different inner core radius and negative curvature parameters. The calculated values are in a good agreement with the experimental results.
We report a comparative study on dephasing mechanisms between inner core coated and uncoated sections
of the same Kagome hypocycloid-shaped core hollow core photonic crystal fibers (HC-PCF) filled with rubidium
vapor. The comparison is performed by measuring the atomic polarization relaxation and electromagnetically
induced transparency (EIT) linewidth in Rb loaded polydimethylsiloxane (PDMS) inner wall coated and bare
silica core Kagome HC-PCF. The measurements show a polarization relaxation time of 32μs in a PDMS coated
Kagome HC-PCF and 24μs in uncoated Kagome HC-PCF. A minimum EIT linewidth of 6.2±0.8MHz is achieved in
PDMS coated Kagome HC-PCF, and 8.3±0.9 MHz for the uncoated Kagome HC-PCF.
We report on recent design and fabrication of Kagome type hollow-core photonic crystal fiber (HC-PCF) for the
purpose of high power fast laser beam transportation. The fabricated seven-cell three-ring hypocycloid-shaped large
core fiber exhibits an up-to-date lowest attenuation (among all Kagome fibers) of 40dB/km over a broadband
transmission centered at 1500nm. We show that the large core size, low attenuation, broadband transmission, single
modedness, low dispersion and relatively low banding loss makes it an ideal host for high power laser beam
transportation. By filling the fiber with helium gas, a 74μJ, 850fs and 40kHz repetition rate ultra-short pulse at
1550nm has been faithfully delivered with little propagation pulse distortion. Compression of a 105μJ laser pulse
from 850fs to 300fs has been achieved by operating the fiber in ambient air.
We report on progress in different hollow core photonic crystal fiber (HC-PCF) design and fabrication for atomic
vapor based applications. We have fabricated a Photonic bandgap (PBG) guiding HC-PCF with a record loss of
107dB/km at 785nm in this class of fiber. A double photonic bandgap (DPBG) guiding HC-PCF with guidance bands
centred at 780nm and 1064nm is reported. A 7-cell 3-ring Kagome HC-PCF with hypocycloid core is reported, the
optical loss at 780nm has been reduced to 70dB/km which to the best of our knowledge is the lowest optical loss
reported at this wavelength using HC-PCF. Details on experimental loading of alkali metal vapours using a far off
red detuned laser are reported. This optical loading has been shown to decrease the necessary loading time for Rb
into the hollow core of a fiber. The quantity of Rb within the fiber core has been enhanced by a maximum of 14%
through this loading procedure.
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