A photonic circuit is generally described as a structure in which light propagates by unitary exchange and transfers reversibly between channels. In contrast, the term 'diffusive' is more akin to a ...chaotic propagation in scattering media, where light is driven out of coherence towards a thermal mixture. Based on the dynamics of open quantum systems, the combination of these two opposites can result in novel techniques for coherent light control. The crucial feature of these photonic structures is dissipative coupling between modes, via an interaction with a common reservoir. Here, we demonstrate experimentally that such systems can perform optical equalisation to smooth multimode light, or act as a distributor, guiding it into selected channels. Quantum thermodynamically, these systems can act as catalytic coherent reservoirs by performing perfect non-Landauer erasure. For lattice structures, localised stationary states can be supported in the continuum, similar to compacton-like states in conventional flat-band lattices.
Abstract
The thin and flexible nature of optical fibres often makes them the ideal technology to view biological processes in-vivo, but current microendoscopic approaches are limited in spatial ...resolution. Here, we demonstrate a route to high resolution microendoscopy using a multicore fibre (MCF) with an adiabatic multimode-to-single-mode “photonic lantern” transition formed at the distal end by tapering. We show that distinct multimode patterns of light can be projected from the output of the lantern by individually exciting the single-mode MCF cores, and that these patterns are highly stable to fibre movement. This capability is then exploited to demonstrate a form of single-pixel imaging, where a single pixel detector is used to detect the fraction of light transmitted through the object for each multimode pattern. A custom computational imaging algorithm we call SARA-COIL is used to reconstruct the object using only the pre-measured multimode patterns themselves and the detector signals.
Solitary pulmonary nodules (SPNs) are a clinical challenge, given there is no single clinical sign or radiological feature that definitively identifies a benign from a malignant SPN. The early ...detection of lung cancer has a huge impact on survival outcome. Consequently, there is great interest in the prompt diagnosis, and treatment of malignant SPNs. Current diagnostic pathways involve endobronchial/transthoracic tissue biopsies or radiological surveillance, which can be associated with suboptimal diagnostic yield, healthcare costs and patient anxiety. Cutting-edge technologies are needed to disrupt and improve, existing care pathways. Optical fibre-based techniques, which can be delivered
the working channel of a bronchoscope or
transthoracic needle, may deliver advanced diagnostic capabilities in patients with SPNs. Optical endomicroscopy, an autofluorescence-based imaging technique, demonstrates abnormal alveolar structure in SPNs
Alternative optical fingerprinting approaches, such as time-resolved fluorescence spectroscopy and fluorescence-lifetime imaging microscopy, have shown promise in discriminating lung cancer from surrounding healthy tissue. Whilst fibre-based Raman spectroscopy has enabled real-time characterisation of SPNs
Fibre-based technologies have the potential to enable
characterisation and real-time microscopic imaging of SPNs, which could aid immediate treatment decisions in patients with SPNs. This review discusses advances in current imaging modalities for evaluating SPNs, including computed tomography (CT) and positron emission tomography-CT. It explores the emergence of optical fibre-based technologies, and discusses their potential role in patients with SPNs and suspected lung cancer.
We present a method with potential for fabricating freeform air-silica optical fibre preforms which is free from the stacking constraints associated with conventional stack-and-draw. The method, ...termed Axi-Stack, is enabled by the precision machining of short cross-sectional preform discs by ultrafast laser assisted etching; a laser-based microfabrication technique which facilitates near arbitrary shaping of the preform structure. Several preform discs are stacked axially and fused together via ultrafast laser welding to construct the preform, which can be drawn to fibre using conventional methods. To illustrate the Axi-Stack process, we detail the fabrication of a 30 cm long solid-core photonic crystal fibre preform with a square lattice of cladding holes and characterise fibre drawn from it.
ABSTRACT
We present a new way to mitigate focal-ratio degradation (FRD) when using optical fibres to transport multimode light. Our approach exploits a custom multicore fibre (MCF) with six ...dissimilar cores that are single-mode at ∼1550 nm wavelength and minimally coupled over 7 m. We fabricated adiabatic mode-selective photonic lanterns (PLs) at each end of the MCF to create a fibre link with multimode ports, the PLs coupling each spatial mode of the multimode ports to a specific core of the MCF and vice versa. The PL-MCF-PL link exhibits superior FRD behaviour compared to a conventional multimode fibre that also supports six modes, because it inhibits the transfer of light from lower order modes to higher order modes. These results open up a potential powerful new approach to mitigate FRD in multimode fibre links, with particular applications in astronomical instruments.
We observe Wannier-Stark (W-S) localization in curved photonic lattices, realized using arrays of evanescently coupled optical waveguides. By correctly tuning the strength of inter-site coupling in ...the lattice, we observe that W-S states become increasingly localized, and eventually fully localized to one site, as the curvature of the lattice is increased. We then demonstrate that tunneling can be successfully restored in the lattice by applying a resonant sinusoidal modulation to the lattice position, an effect that is a direct analogue of photon-assisted tunneling. This precise tuning of the tunneling matrix elements, through resonant modulation-assisted tunneling, opens a novel route for the creation of gauge fields in laser-fabricated photonic lattices.
We demonstrate the use of ultrafast laser pulses to precisely ablate the side of polymer multicore optical fibres (MCF) in such a way that light is efficiently coupled out of a set of MCF cores to ...free space. By individually exciting sets of MCF cores, this flexible "micro-window" technology allows the controllable generation of light sources at multiple independently selectable locations along the MCF. We found that the maximum fraction of light that could be side coupled from the MCF varied between 55% and 73%.
Hollow core negative curvature fibres (NCFs) are a relatively new class of microstructured optical fibre with potential applications in areas such as the delivery of high power laser light and gas ...sensing. For sensing, it is necessary for the measurand to interact with the guided mode. To facilitate this, a novel femtosecond laser-based machining protocol has been developed that allows the precision sculpting of access slots into the NCF core along the length of the fibre. The process is a direct-write process using a digitally defined scanning strategy with no need for physical masks or additional processing such as wet etchants and/or focussed ion beam machining. Due to the inherent flexibility of the machining strategy and the high level of control over the depth of material removal, it is likely that this new technique will be transferable to a wide range of microstructured fibres.
Previous reports of ultrafast laser welding of glass-to-glass have indicated that a pre-existing optical contact (or very close to) between the parts to be joined is essential. In this paper, the ...capability of picosecond laser welding to bridge micron-scale gaps is investigated, and successful welding, without cracking, of two glasses with a pre-existing gap of 3 µm is demonstrated. It is shown that the maximum gap that can be welded is not significantly affected by welding speeds, but is strongly dependent on the laser power and focal position relative to the interface between the materials. Five distinct types of material modification were observed over a range of different powers and surface separations, and a mechanism is proposed to explain the observations.
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