We have developed an all-solid, step-index multimode fibre based on compound "soft-glasses" yielding a very-high NA reaching 0.96 at 1064nm. By further extending the methods of holographic control of light propagation in multimode fibres, we were able to mitigate the adverse effect of mode-dependent loss affecting the new fibre type. This enabled harnessing the full available NA almost completely, and demonstrating high-resolution focussing with output NAs up to 0.91 through lensless fibres. Further, we show that the NA and pureness of such foci allow stable three-dimensional optical confinement of micrometre-sized dielectric objects. Being inherently holographic, this technique is capable of generating an arbitrary number of optical tweezers, as well as precisely repositioning them independently in all directions. The versatility of the new instrument is demonstrated by simultaneous and dynamic 3D manipulation of large assemblies of dielectric microparticles, as well as manipulation of micro-objects inside optically inaccessible environments such a turbid cavity through an opening as small as 0.1mm.
Moreover, the possibility of generating aberration-free foci with NA approaching 0.9 across the fibre core opens new perspectives for high-resolution holographic micro-endoscopy, paving the way for the delivery of advanced microscopy techniques through hair-thin fibre-optic probes.
Over the last two decades the interest in photonic crystal fiber (PCF) has grown considerably, particularly in nonlinear optics where it allows enhanced control over the dispersion landscape. Although silica is the material most commonly used to fabricate PCF, its limited window of transmission and its susceptibility to optical damage at wavelengths below ~350nm is driving the development of fibers made from glasses with transmission windows extending into the deep ultraviolet and the mid-infrared. An alternative is offered by gas-filled hollow-core fiber, in which the light propagates predominantly in the gas.
In kagomé-style hollow-core PCF filled with noble gas, the weak anomalous dispersion of the empty fiber is balanced by the normal dispersion of the filling gas, resulting in a versatile system whose dispersion landscape can be adjusted in real time [Travers et al., JOSAB 28, A11 (2011)]. Under appropriate conditions the launched pulse undergoes soliton self-compression followed by emission of a band of dispersive radiation in the UV. UV light tunable down to 113 nm has been generated with this technique [Russell et al., Nat. Photon. 8, 278 (2014)].
Solid-core ZBLAN (fluorozirconate) glass PCF is transparent from 0.2 to ~7.8µm. Launching ~1nJ 140fs pulses at 1µm wavelength into a ~1µm diameter core resulted, after 4cm of propagation, in generation of a supercontinuum spectrum extending from ~210nm to beyond 2µm. In strong contrast to silica PCF, the ZBLAN PCF showed no signs of any solarization-related damage, even when operating over many hours [Jiang et al., Nat. Photon. 9, 133 (2015)].
Hollow-core photonic crystal fibre (HC-PCF) offers strong light confinement and long interaction lengths in an optofluidic channel. These unique advantages have motivated its recent use as a highly efficient and versatile microreactor for liquid-phase photochemistry and catalysis. In this work, we use a soft-glass HC-PCF to carry out photochemical experiments in a high-index solvent such as toluene. The high-intensity and strong confinement in the fibre is demonstrated to enhance the performance of a proof-of-principle photolysis reaction.
We present an overview of rare-earth doped heavy metal oxide and oxy-fluoride glasses which show promise as host
materials for lasers operating in the 2-5 μm spectral region for medical, military and sensing applications. By
engineering glass composition and purity, tellurite and germanate glasses can support transmission up to and beyond 5
μm and can have favourable thermal, mechanical and environmental stability compared to fluoride glasses. We discuss
techniques for glass purification and water removal for enhanced infrared transmission. By comparing the material
properties of the glass, and spectroscopic performance of selected rare-earth dopant ions we can identify promising
compositions for fibre and bulk lasers in the mid-infrared. Tellurite glass has recently been demonstrated to be a suitable
host material for efficient and compact lasers in the ~2 μm spectral region in fibre and bulk form and the next challenge
is to extend the operating range further into the infrared region where silica fibre is not sufficiently transparent, and
provide an alternative to fluoride glass and fibre.
In this study, we report the fabrication and engineering of an infrared fibre evanescent wave spectroscopic (FEWS)
sensor using GeTeSe chalcogenide fibres, which manifests high temperature durability (glass transformation temperature
at 260°C) and extended infrared transmission from 1.5 to 18 μm. We also report the methodologies adopted for the
fabrication of fibres, including the purification of starting chemicals for high spectral purity, glass melting, quenching
and annealing, fabrication of fibre performs. The designed FEWS sensor consists of a 40 cm unstructured GeTeSe fibre
coupled with a Fourier transform infrared (FTIR) spectrometer and a Mercury-Cadmium-Tellurium (MCT) infrared
detector, and the active sensing length of the fibre is 3 cm. In this paper, we demonstrate the sensing results with various
analytes and investigate the sensitivity of this sensor.
Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP)
interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were
5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is
consistent with the value of 1.22pm/με obtained for a germanate fibre FBG. The Young's modulus for germanate and
tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as
24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG.
The invited paper explains the transmission properties of a range of near-, mid-, and far-IR optical fibres for their
applications in chemical and biological sensing. Methods for the fabrication of single and multiple-core mid-IR fibres are
discussed in view of controlling the thermal and viscosity properties for fibre drawing. In particular, the need for
removing impurity bands in the 5000 to 1000 cm-1 range is explained. The importance of engineering multi-core fibres
is also discussed for simultaneous measurements of Raman, IR and surface plasmon enhanced modes together with say,
temperature using a mid-IR transmitting tellurite fibre e.g. in a chemical process. The paper explains the principles and
advantages of evanescent wave coupling of light at the resonant frequency bands for chemical sensing using a fibre
evanescent wave spectroscopic sensor having a GeTeSe chalcogenide fibre. Using fibre based techniques, measurements
for Cr6+ ions in solution and As3+ and As5+ in solids have been characterized at visible and mid-IR regions, respectively.
In this paper we also explain the importance of using mid-IR fibres for engineering novel laser and broadband sources
for chemical sensing.
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