Flexible dielectric optical fibers guiding light in a hollow core were conceptually imagined at the end of the 19th century, but first demonstrated in practice about 2 decades ago. Since then, many geometric variants have been described and implemented, and theoretical models developed and finessed. Despite this, for a fairly long time the key metric by which their performance was judged – attenuation – has remained quite considerably higher than standard all-glass fibers. In this paper, we describe the recent breakthroughs in hollow core fiber technology. We trace the story of this breakthrough from the theoretical exploration of a new design of hollow core fiber, through early implementations, up to the staggering results achieved over the last 18 months. The progress reported concerns not only a reduction in the fiber attenuation level, but also a considerable improvement in modal quality of the fibers, which have led to excellent data transmission performance. These fabricated fibers tell a story of improvements in all aspects of the technology, including preform preparation, performance modelling, fiber draw dynamics and coatings.
Supercontinuum generation (SCG) is the production of continuous spectral broadening. Efficient SCG is affected by the group velocity dispersion (GVD), nonlinear characteristics, waveguide geometrical parameters, and pump wavelength. Photonic crystal fibers (PCFs) offer promising advantages over standard fibers such as desirable dispersion properties and controllable mode area. Silicon (Si) is known for its large refractive index which enhances the nonlinear effect in silicon waveguides. The promising properties of silicon is combined with the strong characteristics of photonic crystals in a silicon-core PCF to broaden the spectrum. The effect of varying the pump power, and input pulse wavelength on the broadening bandwidth is studied. The modal characteristics of the reported PCF are calculated using full vectorial finite element method (FV-FEM) with perfectly matching layers (PML) boundary conditions. In this investigation, the effective mode index, dispersion profile of the fundamental quasi TM-mode of the silicon-based PCF are simulated to quantify the performance of the suggested design. The simulation results show that the proposed PCF produces spectral broadening spanning the wavelength range 1000 – 3000 nm with bandwidths ranging from 892 ± 50 to 1659 ± 50 nm at both telecommunications’ wavelengths 1.3 μm and 1.55 μm as well as at the zero dispersion wavelength (ZDW) of 2.0 μm through a device length of 10 mm. It is also found that increasing the pump wavelength from 1.3 μm to 2.0 μm widens the SC spectra by 715 ± 50 nm.
We perform a numerical analysis of mid-infrared photoluminescence emitted by praseodymium (III) doped chalcogenide selenide glass pumped at near-infrared wavelengths. The results obtained show that an effective inversion of level populations can be achieved using both 1480 nm and 1595 nm laser diodes. The rate of the spontaneous emission achieved when pumping at 1480 nm and 1595 nm is comparable to this achieved using the standard pumping wavelength of 2040 nm.
In the UK, it is now recognised that 1 in 2 people born after 1960 will develop some form of cancer during their lifetime. Diagnosing patients whilst in the early stages drastically improves their chances of survival but up until now the gold standard for cancer detection is via a lengthy excision biopsy procedure, which relies on the skill of a histopathologist. Evidently, the need for a faster solution is paramount. The mid-infrared (MIR) spectral region covers the wavelengths 3-25 μm and characteristic vibrational spectra unique to each molecular type. Subtle changes in the specific spectral response within this region are indicative of changes within the cells relative to normal cells, signifying the presence or absence of a disease. Our goal is to carry out disease diagnosis in vivo. Reaching these wavelengths has previously presented difficulties as conventional MIR blackbody light sources are weak and optical fibers for transmitting MIR light to/from tissue in vivo can be limited by strong material absorption such as silica glass >2.4 μm and tellurite, and heavy metal fluoride, >4.75 μm. However, chalcogenide glasses have been shown to transmit MIR light out to 25 μm. This paper reports on a glass composition in the Ge-Sb-Se system and its suitability as an optical fiber for the transmission of MIR to and from tissue samples, enabling in vivo mapping for an immediate diagnostic response- a technique termed ‘optical biopsy’.
Chalcogenide glasses are promising materials for mid-infrared (IR) fiber lasers (i.e. 3 - 25 μm wavelength range). These
glasses exhibit low phonon energies, together with large refractive indices, rare earth (RE-) ion solubility and sufficient
mechanical and chemical robustness. Optical quality of the fiber is key. Gallium is known to promote RE-ion solubility
in chalcogenide glasses, probably forming a [Pr(III)] - Se - [Ga(III)] associated type complex. Here, indium is investigated as an alternative additive to gallium in Pr3+-doped Ge-As-Se chalcogenide glasses. Indium has the same outer electronic structure as gallium. Moreover, indium has the advantage of being heavier than gallium, potentially promoting a lower phonon-energy, local environment of the RE-dopant. Zero to ~2000 ppmw (nominal parts per million by weight) Pr3+-
doped Ge-As-In-Se bulk glasses are prepared using the melt-quench method. ~500 ppmw Pr3+- doped Ge-As-In-Se,
optically-clad fiber is realized via fiber-drawing of extruded fiberoptic preforms. Fiber absorption and emission spectra
are collected and compared with those of the bulk glasses.