We present findings on High Harmonic Generation (HHG) in solids utilizing a high-energy fiber laser system operating at 1550 nm. The driving laser source comprises an Erbium-Doped Fiber chirped pulse Amplifier (EDFA) combined with a post-compression stage employing a hollow-core photonic crystal fiber (HC-PCF) filled with noble gases. Nonlinear self-compression in the HC-PCF enables the generation of ultrashort pulses with a duration of 50 fs and energy of 0.91 μJ at a repetition rate of 660 kHz. In a first step, harmonics up to H7 were observed when focusing the laser into small bandgap materials such as Zinc Oxide (ZnO). Subsequently, the system was enhanced to measure high harmonics in the extreme ultraviolet (XUV) range, with harmonics up to H25 observed using a large bandgap material, magnesium oxide (MgO). To the best of our knowledge, this represents the first solid-state HHG source driven by a high-energy few-cycle fiber laser in the telecom region.
We report on the development of FastLas, a scalable and versatile Ultra-Short Pulse (USP) laser compression technology. This system compresses down to a 50-20 fs range, USP lasers with pulse widths from 900 fs to 200 fs, energies from a few μJ to 1 mJ, average power from 100 mW to 100 W, and wavelengths from 343 nm in UV to 1.8μm in IR. It utilizes a gas-filled hollow-core photonic crystal fiber to broaden and compress any USP laser spectrum. As a result, FastLas presents an adaptable pulse compression solution, offering potential for applications in various industrial and scientific fields.
Hollow-Core Photonic Crystal Fiber (HCPCF) technology has revolutionized Ultra-Short Pulse (USP) laser beam delivery. Industry-grade USP laser beam delivery system (BDS) modules, developed by GLOphotonics, however, display polarization fluctuations during movement. To overcome this, we've developed a BDS module maintaining constant polarization irrespective of motion. This BDS uses an inhibited-coupling HCPCF with an injected beam from a 1030 nm wavelength USP laser. Demonstrating a 97% transmission rate and stable linear polarization (34dB of polarization extinction ratio (PER)), it showed less than 3% power fluctuation and less than 1% polarization fluctuation during movement. This marks a significant advancement in BDS applications.
We report on the development of inhibited-coupling hollow-core photonic crystal fiber with record-low transmission loss of ⪅50 dB/km at 266 nm, and solarization-free. 2 meter-long patchcords with SMA terminations were made and their UV handling and lifespan were tested. A laser beam from a 266 nm wavelength laser-source emitting 1 ns wide and 30 μJ energy pulses was injected into the hollow-core fiber patchcord, achieving a total transmission rate of 93%. The laser beam was kept continuously coupled to the patchcord for over 100 hrs. The results show excellent stability in transmitted power (fluctuations of less than 2.6%) and in mode quality. To our knowledge this the first fiber guidance of DUV laser that combines high energy handling and long lifespan. The results mark a major milestone in the adoption of fiber UV laser beam delivery by the industrial community.
We report on a Raman laser emitting in the yellow spectral range using a CO2-filled hollow-core photonic crystal fiber. Taking advantage of a state-of-art inhibited-coupling hollow-core photonic crystal fibre, exhibiting minimum transmission loss of approximately 1 dB/km in the 500-600 nm region, we were able to develop an extremely compact and simple yellow-Raman laser scheme, allowing to emit as much as 60 mW of average power at the 574.5 nm wavelength while using a compact, microchip laser as a pump source. This solution provides an innovative and scalable alternative for the other yellow laser schemes, which are of high demand in the field of biophotonics due to their effective interaction with hemoglobin and melanin.
We report the first, to our knowledge, linear HCPCF-bundle for USP laser beam-delivery, power-modulation, and spatial-shaping. This bundle comprises four identical inhibited coupling HCPCFs arranged in a linear array with a relative pitch-variation of less than 2% relative variation in array pitch. Each HCPCF is equipped with an acousto-optic modulator (AOM) for independent power modulation. A laser beam, from 1030 nm wavelength, 100μJ energy USP laser, is split into four beams and coupled to each of the HCPCFs in the bundle using a diffractive optic element. The system's insertion loss (from input to output through the AOM) is measured to be over 70%. The bundle system emits an array of four Gaussian beams, each with equal energy and beam size (both having less than 1% variation beam to beam). Each beam's power can be modulated independently. This development marks a significant advancement in harnessing HCPCF technology in applications requiring high-power light with spatial and temporal structuring.
Many applications such as nonlinear microscopy and strong field optoelectonics require high-energy (> 100 nJ) ultrashort (< 100 fs) pulses above 1.55 µm out of a singlemode fiber. Here, we report on high-energy amplification in tapered Er-doped fiber fabricated by the powder technique. The system based on direct amplification is free from stretcher and compressor units. We generate 90 fs MW-class pulses at 1600 nm by amplification and management of nonlinear effects in the tapered fiber. Despite the output 100 µm core diameter, the emitted beam is near-diffraction limited.
We report on an optical fiber based iodine vapor spectroscopy cell. The formed photonic microcell (PMC) is a standalone FC/APC connectorized Iodine filled hollow core photonic crystal fiber (HCPCF) demonstrating transmission efficiency as high as 75% (1.2 dB insertion loss) and an absorption contrast reaching 70% on the P(33) 6-3 transition (i.e. ~633 nm wavelength) at room temperature. Iodine exhibits an astounding amount of transitions on the green-red spectral range. Hence, as a demonstration of its application as a frequency reference, we have generated many sub-Doppler spectral transparencies over the 631-635 range using saturated absorption spectroscopy for laser frequency stabilization.
Micro processing applications using femtosecond lasers have developed thanks to the quality of the process. A challenge still to be addressed is the capability to deliver the beam through a fibre. One solution is the use of hollow-core inhibited coupling fibres, nevertheless its use requires a beam stabilization to insure a stable operation.
This study attempts to qualify two beam stabilisation systems: two piezo motors coupled with four quadrant detectors and Cailabs’ all-optical mode-cleaner system based Multi-Plane Light Conversion (MPLC) technology. To do such output fibre transmission efficiency and beam quality are investigated under controlled fluctuation of beam pointing.
We report on the pulse compression performance using FastLas module for different industrial ultra-short pulse lasers. The compression module enables compression down to pulse-duration below 50 fs in most of the representative ultra-short pulse lasers with pulse-duration in the range of 700-250 fs and average power in the range of 10-100W. The overall optical transmission of the module ranges between 70% and 90%, and the output beam quality corresponds M2 of less than 1.2.
We report on a 100-fs GHz burst laser with up to 100-W average output power. This laser is based on a Tangor femtosecond laser with GHz burst option followed by nonlinear pulse compression in a gas-filled hollow core Kagomé fiber. Combining pulse compression with hollow core fiber transport is an attractive extension for industrial femtosecond lasers. Laser ablation of metals, silicon, and sapphire have been performed with this new laser source in order to study the impact of the ultrashort pulse duration on the laser matter interaction with GHz bursts.
A beam delivery system (BDS) fibered with hollow core photonic crystal fibre (HC-PCF) has been identified as very promising for ultra-short pulse (USP) laser micromachining for it allows flexible, secured and robust laser beam delivery to the work piece. These features are of paramount importance for vertical markets such as automotive or consumer electronics. We report on a system that integrates a BDS, a laser beam pointing stabilization module and a 50 W power, 250 fs pulsewidth Yb-based USP laser. The BDS comprises a low loss, low dispersion and high damage threshold Inhibited-Coupling (IC) HC-PCF. The latter is ruggedized with a semi-rigid industrial cable with ends attached respectively to an injection head for ease of laser beam coupling, and to an output connector for beam delivery to the work piece. The injection head is aligned with a special module for laser beam jitter stabilization and beam-shape control and monitoring. Also, it exhibits the necessary gas and thermal handling to minimize parasitic optical nonlinear effect or photoionization and power induced heating. To test the endurance of this fibered-USP laser system, it was continuously run over 17 hours. The results show exceptional integrity in the power transmission (86 ±1%), spectral and temporal structure and beam quality (M2~1.1). The BDS output beam shows a pointing stability of only 0.7±0.1 μrad. These results represent an important milestone towards the industrialization of fiber delivered USP laser-based machines.
We report on several ultra-short pulse compression schemes based on hollow-core photonic crystal fiber filled with a chosen gas-phase medium and undertaken in a versatile module coined “FastLas”. The scheme relies on dispersion management by both fiber design and gas pressure management to offer a highly versatile pulse compressor. Furthermore, the gas is also used to set the required optical nonlinearity. This type of hollow fiber based compressor is scalable with the laser wavelength, pulse energy and initial pulse-width. Among the achieved pulse compression, we list a self-compression of 500-600 fs ultra-short pulse Yb-laser and with energy range of 10-500 μJ. By simply scaling the fiber length we demonstrated pulses as short as ~20 fs for the whole energy range. Here, the self-compression is achieved through solitonic dynamic. Conversely, we demonstrated pulse compression based on self-phase modulation by adjusting the fiber and gas dispersion. Among the pulse compressors we have developed, based on self-phase modulation, we cite the compression of a frequency-tripled micro-Joule pulse-energy Yb-laser with a pulse width of 250 fs. The results show compressed UVpulses with temporal width in the range of 50-60 fs.
Photonic Crystal Fibers represent a good platform for the development of sensitive and cheap sensors for the detection of protein and DNA sequence. The holes running along the fiber allows the infiltration of biological substances and for biological layers to attach on the air-dielectric interfaces. In addition, the presence of a hollow core can further increase the infiltration feasibility and the sensor sensitivity.
Recently, the possibility in using hollow core tube lattice fibers (HC-TLFs) for label-free DNA detection have been numerically investigated. The sensing is based on the waveguiding mechanism, that is inhibited-coupling which makes the HC-TLF transmission properties particularly sensitive to the thickness of the glass struts composing the microstructured cladding of those fibers. The molecular interactions between the surface of the glass and the target to be detected results in a generation of a biological layer which modifies the strut thickness and thus the fiber transmission properties.
The aim of the present work is to experimentally demonstrate that HC-TLF can be successfully used as bio sensor for proteins. After a functionalization of the silica surface through a solution of aptes, a layer of biotin was deposited on inner surfaces of the fiber. The fiber was than infiltrated with a solution containing streptavidin and an additional bio-layer is deposited on the surfaces. The experimental results demonstrated a red shift of the entire fiber transmission spectrum of about 7 nm corresponding to an additional bio-layer with thickness of 6.45 nm which is fully compatible with the size of streptavidin molecules of about 6nm.
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.
KEYWORDS: Pulsed laser operation, Beam delivery, Fiber lasers, Head, Cladding, Near field, High power lasers, Near field optics, Photonic crystal fibers, Laser systems engineering
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).
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.
Over the last few years, there has been an increasing demand for medium-grade gyroscopes to fill the gap (in terms of cost and performance) between MEMS and current optical devices. There has also been a longstanding quest for a compact high-grade gyroscope to reduce the size of current inertial navigation units and make them available for most carriers (extending their time of GPS-free autonomous navigation). In this paper, we will describe two approaches we are following towards these goals, with support from the European Space Agency: the solid-state ring laser gyroscope and the resonant hollow-core fiber optic gyroscope.
Raman-gas filled HC-PCF has proved to be an outstanding Raman-convertor, as illustrated by the generation of more than 5 octaves wide Raman comb using a hydrogen-filled Kagome HC-PCF pumped with high power picosecond-laser, or the generation of multiline Raman-source in the UV-Vis using a very compact system pumped with micro-chip laser. Whilst these demonstrations are promising, a principal challenge for the industrialization of such a Raman source is its lifetime as the H2 diffusion through silica is high enough to leak out from the fiber within only a few months. Here, we report on a HC-PCF based Raman multiline source with a very long life-span. The system consists of hydrogen filled ultra-low loss HC-PCF contained in highly sealed box, coined CombBox, and pumped with a 532 nm micro-chip laser. This combination is a turnkey multiline Raman-source with a "shoe box" size. The CombBox is a robust and compact component that can be integrated and pumped with any common pulsed laser. When pumped with a 32 mW average power and 1 ns frequency-doubled Nd:Yag microchip laser, this Raman-source generates 24 lines spanning from 355 to 745 nm, and a peak power density per line of 260 mW/nm for the strongest lines. Both the output power and the spectrum remained constant over its monitoring duration of more than six months. The spectrum of this multiline laser superimposes with no less than 17 absorption peaks of fluorescent dyes from the Alexa Fluor family used as biological markers.
We report on high power Raman-converter frequency stage based on hydrogen-filled inhibited-coupling hollow-core photonic crystal fibers pumped by an Yb-fiber picosecond laser. This fiber Raman-convertor can operate in two SRS emission regimes by simply controlling the fiber length or the gas pressure. It can set to either generate favorably single laser line or to generate an extremely wide Raman comb. Based on this we demonstrate a pico-second pulse Raman source of 9.3 W average-power at 1.8 μm, and an ultra-wide Raman comb spanning over more than five octaves from UV to mid-infrared, containing around 70 laser lines.
We report on a Hollow Core-Photonic Crystal Fiber (HC-PCF) based high power ultra-short pulse laser beam delivery system (GLO-BDS) that combines ease-of-use, high laser-coupling efficiency, robustness and industrial compatible cabling. The GLO-BDS 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. 5 m long GLO-BDS were demonstrated for Yb USP laser, Ti:Sapphire laser and frequency-doubled Yb USP laser. They all exhibit a transmission coefficient larger than 80%, and a laser output profile close to single mode (M2 <1.3).
The dramatic progress in power-scaling of ultra-short pulse (USP) lasers and their growing use in industrial applications call for flexible and robust beam delivery systems (BDS) over several meters with no temporal or modal distortions. Inhibited coupling (IC) hypocycloid Kagome hollow-core photonic crystal fiber (HC-PCF) has recently proved to be an excellent solution for guiding these USP. In order to reduce further the attenuation of such fiber and then to increase the BDS capabilities, we report on an optimized IC Kagome HC-PCF exhibiting record loss level (8.5dB/km at 1030nm) associated with a 225nm wide 3-dB bandwidth and low bend sensitivity.
The duration of energetic ultrashort pulses is usually limited by the available gain bandwidth of ultrashort amplifiers used to amplify nJ or pJ level seed to hundreds of μμJ or even several mJ. In the case of Ytterbium-doped fiber amplifiers, the available bandwidth is of the order of 40 nm, typically limiting the pulse duration of high-energy fiber chirped-pulse amplifiers to durations above 300 fs. In the case of solid-state amplifier based on Yb:YAG crystals, the host matrix order restricts the amplification bandwidth even more leading to pulses in the low picosecond range. Both architecture would greatly benefit from pulse durations well-below what is allowed by their respective gain bandwidth e.g. sub-100 fs for fiber amplifier and sub-300 fs for solid-state Yb:YAG amplifier. In this contribution, we report on the post-compression of two high energy industrial ultrashort fiber and thin-disk amplifiers using an innovative and efficient hollow core fiber structure, namely the hypocycloid-core Kagome fiber. This fiber exhibits remarkably low propagation losses due to the unique inhibited guidance mechanism that minimize that amount of light propagating in the silica cladding surrounding the hollow core. Spectral broadening is realized in a short piece of Kagome fiber filled with air at 1 atmosphere pressure. For both amplifiers, we were able to demonstrate more than 200 μJ of energy per pulse with duration <100 fs in the case of the fiber amplifier and <300 fs in the case of the thin disk amplifier. Limitations and further energy scaling will also be discussed.
We report on the fiber-based transmission of sub-ps single-mode pulses with an average power of 50 W at a wavelength of 1030 nm generated by a TruMicro Series 5000 Femto Edition thin disk amplifier. The air-filled hollow-core Kagométype delivery fiber exhibits a hypocycloid core wall and is tailored to offer very low dispersion and nonlinearity at 1030 nm. It minimizes the mode overlap with the glass components to obtain a sufficiently high damage threshold. With propagation losses of only 20 dB/km and an optimized mode matching and coupling by means of a telescope and a 5- axes table we achieve an overall transmission efficiency of more than 80% with a resulting M2 of 1.15. Our laser source offers the selection of repetition rates from 200 to 800 kHz which translates to pulse energies between 60 and 250 μJ. The pulse duration of 900 fs is maintained at the fiber exit, while the spectral width broadens to 20 nm due to self phase modulation in the air core, which could be used to further compress the pulses temporally. Using a fiber-based beam transport allows for mechanical decoupling of the processing head from the laser source, increasing flexibility for applications in the field of material processing with ultra-short pulsed lasers.
Tremendous progress has been achieved in the last years in the field of ultrafast high-power sources. Among the
different laser technologies driving this progress, thin-disk lasers (TDLs) have gained significant ground, both from
amplifiers and modelocked oscillators. Modelocked TDLs are particularly attractive, as they allow for unprecedented
high energy and average powers directly from an oscillator. The exponential progress in the performance of these
sources drives growing needs for efficient means of beam delivery and pulse compression at high average power (<
100 W) and high peak power (> 10 MW). This remains a challenging regime for standard fiber solutions:
microstructured large-mode-area silica photonic-crystal fibers (PCFs) are good candidates, but peak powers are limited
to ≈4-6 MW by self-focusing. Hollow-core (HC) capillaries are adapted for higher peak powers, but exhibit high losses
and are not suitable for compact beam delivery. In parallel to the progress achieved in the performance of ultrafast laser
systems, recent progress in novel hollow-core PCF designs are currently emerging as an excellent solution for these
challenges. In particular, Inhibited-coupling Kagome-type HC-PCFs are particularly promising: their intrinsic guiding
properties allow for extremely high damage thresholds, low losses over wide transmission windows and ultra-low
dispersion.
In our most recent results, we achieve pulse compression in the hundred-watt average power regime using
Kagome-type HC-PCFs. We launch 127-W, 18-μJ, 740-fs pulses from our modelocked TDL into an Ar-filled fiber (13
bar), reaching 93% transmission. The resulting spectral broadening allows us to compress the pulses to 88 fs at 112 W of
average power, reaching 105 MW of peak power, at 88% compression efficiency. These results demonstrate the
outstanding suitability of Kagome HC-PCFs for compression and beam delivery of state-of-the-art kilowatt-class
ultrafast systems.
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 have now demonstrated and characterized gas-filled hollow-core fiber lasers based on population inversion from
acetylene (12C2H2) and HCN gas contained within the core of a kagome-structured hollow-core photonic crystal fiber.
The gases are optically pumped via first order rotational-vibrational overtones near 1.5 μm using 1-ns pulses from an
optical parametric amplifier. Transitions from the pumped overtone modes to fundamental C-H stretching modes in both
molecules create narrow-band laser emissions near 3 μm. High gain resulting from tight confinement of the pump and
laser light together with the active gas permits us to operate these lasers in a single pass configuration, without the use of
any external resonator structure. A delay between the emitted laser pulse and the incident pump pulse has been observed
and is shown to vary with pump pulse energy and gas pressure. Furthermore, we have demonstrated lasing beyond 4 μm
from CO and CO2 using silver-coated glass capillaries, since fused silica based fibers do not transmit in this spectral
region and chalcogenide fibers are not yet readily available. Studies of the laser pulse energy as functions of the pump
pulse energy and gas pressure were performed. Efficiencies reaching ~ 20% are observed for both acetylene and CO2.
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.
We report on recent developments on fabrication and optical guidance of Kagome-lattice hollow-core photonic crystal
fiber (HC-PCF). These include the design and fabrication of a hypocycloid-shaped core Kagome HC-PCF that combines
a record optical attenuation with a baseline exhibiting ~180 dB/km over a transmission bandwidth larger than 200 THz.
These results are corroborated with theoretical simulations which show that both the core-shape and the cladding ring
number play role in inhibited coupling, inducing core-mode confinement for the fundamental transmission band. We also
show that the inhibited coupling is weaker for the first higher-order transmission band by theoretically and
experimentally comparing Kagome HC-PCF with a single anti-resonant ring hollow-core fiber.
A photonic microcell (PMC) is a length of gas-filled hollow core-photonic crystal fiber (HC-PCF) which is hermetically
sealed at both ends by splicing to standard single mode fiber. We describe advances in the fabrication technique of PMCs
which enable large core Kagome-lattice HC-PCFs to be integrated into PMC form. The modified fabrication technique
uses fiber-tapering to accommodate the large dimensions of the fiber and enables low loss splices with single mode fiber
by reducing mode field mismatch. Splice losses as low as 0.6 dB are achieved between 1-cell defect Kagome HC-PCF
and single mode fiber. Relative to the previously reported PMCs, which were based on photonic bandgap HC-PCF, the
present Kagome HC-PCF based PMC provides broad optical transmission, surface mode-free guidance and larger core at
the cost of slightly increased fiber attenuation (~0.2 dB/m). Therefore, the integration of this fiber into PMC form opens
up new applications for PMC-based devices. The advantage of the large core dimensions and surface mode free guidance
for quantum optics in gas-filled HC-PCF are demonstrated by generation of narrow sub-Doppler features in an acetylenefilled
large core PMC.
Drawing on recent advances in understanding the origin of the photonic band gap observed in hollow core photonic
crystal fibers, we apply the photonic tight binding model to a high air filling fraction fiber. By studying the interdependent
effect of the apex, strut and air-hole resonators present in the photonic crystal cladding, we demonstrate that it
is possible for a second photonic band gap windows to extend significantly below the air-line, whilst the general
properties of the fundamental band gap remains relatively unaffected. We fabricate several hollow core fibers with
extremely thin struts relative to the apex size. All fibers exhibit two strong transmission windows that bridge the
benchmark laser wavelengths of 1064nm and 1550nm. These results pave the way to extend the guidance capability of
low-loss hollow core fibers.
We have developed an all-fiber system which we use to demonstrate slow and fast light based on electromagnetically
induced transparency in a 20 meter acetylene-filled photonic microcell. Using this system, 30 ns pulses of probe light
were delayed and advanced by up to 5 ns and 1 ns respectively. The delay/advance is tunable through the probe detuning
and the coupling Rabi frequency. Through optimization of experimental parameters such as acetylene pressure, coupling
laser power and decoherence rates it is shown that a pulse delay of 30 ns/m is possible. Limitations imposed on the fiber
length by resonance group velocity dispersion and spectral reshaping are also discussed. In addition to optical buffering,
we suggest a slow-light based fiber optical gyroscope with an enhanced signal-to-noise ratio of ~ 92.
Optical fiber sources have experienced a massive growth over the past ten years principally due to the compactness,
robustness and good spatial quality of such systems. Fiber sources now cover a large spectrum from visible to near
infrared helped on this point by the development of microstructured fibers (MOFs). A particular class of MOFs also
called hollow-core photonic crystal fibers (HC-PCFs) offers to get rid of silica's absorption thanks to band gap guidance
and therefore to extend transmission range of silica fibers. We propose here two all-fiber architectures based on HCPCFs
in view to generate mid infrared wavelengths by amplification of spontaneous Raman scattering (SRS) in gaseous
medium. We report on design, fabrication and characterization of two kinds of HC-PCF matching the architecture needs.
We review recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibers.
Two classes of hollow-core photonic crystal fiber are identified, one guides via a photonic bandgap and the other guides
by virtue of an inhibited coupling between core and cladding mode constituents. For the former fiber type, we explore
how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the antiresonant
reflection optical wave-guidance. For the second type of fiber, which can guide over a broad wavelength range,
we examine the nature of the inhibited coupling.
The good optical transmission of hollow-core photonic crystal fiber and their relative low insertion loss in
conventional fiber network gave rise to a new type of all-fiber
gas-phase devices. These range from Raman converters
as laser sources, compact frequency standard devices for laser frequency control to electromagnetically-induced
transparency and saturable absorption for quantum optical devices. Here I report on the performance of these devices
and their prospects.
We review the progress made on the fabrication and applications of hollow-core photonic crystal fibres. The mechanism of the light guidance in these fibers is described along with their dispersion properties. We review the HC-PCF fabrication, the different results achieved in the fields of laser-induced particle guidance, low-threshold stimulated Raman scattering in hydrogen (vibrational and rotational) and in laser frequency metrology. Finally, we show the different new prospects opened up by these fibres.
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