Periodic fibre devices for advanced applications in all-optical systems

The main objective of this work is to investigate advanced applications of fibre gratings with the combination of nonlinear fibre optical effects, including the stimulated Raman scattering (SRS), Kerr effects, four-wave mixing (FWM) and second-harmonic generation. A Raman distributed-feedback (R-DFB) fibre laser formed in a passive optical fibre by using Raman gain is considered as the most promising route to generate a single-frequency and narrow-linewidth laser source at any wavelength given a proper pump source.In this thesis, the R-DFB fibre laser has been intensively studied both numerically and experimentally. Simulation results of centre pi phase-shifted R-DFB fibre lasers show that the longer length of the DFB grating, the higher Raman gain coefficient and the lower background loss of the host fibre are always beneficial for achieving low threshold R-DFB fibre lasers. 30 cm long centre pi phase-shifted R-DFB fibre lasers have been respectively demonstrated in two types of commercially available Ge/Si fibres of PS980 and UHNA4. Both un-polarised and linearly polarised CW Yb-doped fibre lasers at ~1.06 µm were used as the pump sources. The R-DFB fibre lasers are single-frequency operation at around 1.11 µm and have 3 dB linewidth less than 2.5 kHz; lasing thresholds down to sub-watt power levels; total output powers up to ~2 W; and total conversion efficiencies against incident pump power around 13%. Ultra-wide range (>110 nm) wavelength conversion by using FWM in these 30 cm-long R-DFB fibre lasers have been observed and up to ~-25 dB FWM conversion efficiency has been obtained.The nonlinearities and photosensitivity of several high-index non-silica glasses and fibres are also studied in order to incorporate fibre Bragg gratings (FBGs) with the highly nonlinear fibres to form R-DFB fibre lasers with lower thresholds. In particular, the Raman gain coefficient of a house-made tellurite glass fibre has been found to be ~35 times higher than the silica fibre and a SRS-assisted supercontinuum from ~1.1-1.7 µm has been observed in the fibre with a length of ~1.35 m by pumping at ~1.06 µm in the normal dispersion region of the fibre.Preliminary investigations into concatenating periodic poled silica fibres (PPSFs) to improve the frequency-doubling conversion efficiency are also presented

Effects of phase and amplitude noise on pi phase-shifted DFB Raman fibre lasers

We show that p phase-shifted Distributed Feedback (DFB) Raman fibre lasers of 30cm length are resilient against phase and amplitude errors up to ~5%, with negligible deterioration of the threshold and slope-efficiency of the lasers

Differences in structural connectivity between diabetic and psychological erectile dysfunction revealed by network-based statistic: A diffusion tensor imaging study

IntroductionType 2 diabetes mellitus (T2DM) has been found to be associated with abnormalities of the central and peripheral vascular nervous system, which were considered to be involved in the development of cognitive impairments and erectile dysfunction (ED). In addition, altered brain function and structure were identified in patients with ED, especially psychological ED (pED). However, the similarities and the differences of the central neural mechanisms underlying pED and T2DM with ED (DM-ED) remained unclear.MethodsDiffusion tensor imaging data were acquired from 30 T2DM, 32 ED, and 31 DM-ED patients and 47 healthy controls (HCs). Then, whole-brain structural networks were constructed, which were mapped by connectivity matrices (90 × 90) representing the white matter between 90 brain regions parcellated by the anatomical automatic labeling template. Finally, the method of network-based statistic (NBS) was applied to assess the group differences of the structural connectivity.ResultsOur NBS analysis demonstrated three subnetworks with reduced structural connectivity in DM, pED, and DM-ED patients when compared to HCs, which were predominantly located in the prefrontal and subcortical areas. Compared with DM patients, DM-ED patients had an impaired subnetwork with increased structural connectivity, which were primarily located in the parietal regions. Compared with pED patients, an altered subnetwork with increased structural connectivity was identified in DM-ED patients, which were mainly located in the prefrontal and cingulate areas.ConclusionThese findings highlighted that the reduced structural connections in the prefrontal and subcortical areas were similar mechanisms to those associated with pED and DM-ED. However, different connectivity patterns were found between pED and DM-ED, and the increased connectivity in the frontal–parietal network might be due to the compensation mechanisms that were devoted to improving erectile function

Hsa-miRNA-765 as a key mediator for inhibiting growth, migration and invasion in fulvestrant-treated prostate cancer

Fulvestrant (ICI-182,780) has recently been shown to effectively suppress prostate cancer cell growth in vitro and in vivo. But it is unclear whether microRNAs play a role in regulating oncogene expression in fulvestrant-treated prostate cancer. Here, this study reports hsa-miR-765 as the first fulvestrant-driven, ERβ-regulated miRNA exhibiting significant tumor suppressor activities like fulvestrant, against prostate cancer cell growth via blockage of cell-cycle progression at the G2/M transition, and cell migration and invasion possibly via reduction of filopodia/intense stress-fiber formation. Fulvestrant was shown to upregulate hsa-miR-765 expression through recruitment of ERβ to the 5′-regulatory-region of hsa-miR-765. HMGA1, an oncogenic protein in prostate cancer, was identified as a downstream target of hsa-miR-765 and fulvestrant in cell-based experiments and a clinical study. Both the antiestrogen and the hsa-miR-765 mimic suppressed HMGA1 protein expression. In a neo-adjuvant study, levels of hsa-miR-765 were increased and HMGA1 expression was almost completely lost in prostate cancer specimens from patients treated with a single dose (250 mg) of fulvestrant 28 days before prostatectomy. These findings reveal a novel fulvestrant signaling cascade involving ERβ-mediated transcriptional upregulation of hsa-miR-765 that suppresses HMGA1 protein expression as part of the mechanism underlying the tumor suppressor action of fulvestrant in prostate cancer. © 2014 Leung et al

Fiberized novel wavelength-scale planar waveguides

The modern glass optical fiber, starting from the simplest circularly symmetric waveguide geometry, has been widely inspired by the geometrical structure and functionalities of glass or non-glass based planar channel waveguides. For instance, the currently well-developed microstructured optical fiber [1] has been inspired by works on planar photonic crystal waveguides [2]. On the other hand, planar channel waveguides, such as slab waveguides, ridge waveguides and slot waveguides, are typically fabricated by various processing approaches, e.g., deposition, sputtering, etching, lithography and so on, at relatively low temperatures. Compact microstructured planar waveguide devices play important roles in various technical areas including telecoms application, sensing, and biomedical diagnostics and imaging. In comparison with planar waveguides, optical fibers have numerous advantages, e.g., long length, low cost per unit length due to the high yield, and low propagation loss. Fiberization of planar waveguides is a simple and neat idea to combine the advantages of both planar and fiber waveguides for realizing economic and compact photonic devices

Fabrication of multiple parallel suspended-core optical fibers by sheet-stacking

We demonstrate the fabrication of a novel type of optical fibers with multiple parallel air-suspended cores by the sheet-stacking method. Using this technique we have constructed optical fibers with up to 10 parallel micron-size suspended cores. No extra scattering loss from the fabrication process was observed in a fabricated dual air-suspended core fiber. The sheet-stacking method opens the way towards using a wide range of optical glasses for manufacturing multiple parallel suspended-core specialty optical fibers with novel optical functionalities such as dispersion tunability. Fusion splicing has also been successfully used to connect such a multiple core fiber with a conventional silica fiber

Detailed study of four-wave mixing in Raman DFB fiber lasers

We both experimentally and numerically studied the ultra-compact wavelength conversion by using the four-wave mixing (FWM) process in Raman distributed-feedback (R-DFB) fiber lasers. The R-DFB fiber laser is formed in a 30 cm-long commercially available Ge/Si standard optical fiber. The internal generated R-DFB signal acts as the pump wave for the FWM process and is in the normal dispersion range of the fiber. Utilizing a tunable laser source as a probe wave, FWM frequency conversion up to ~40 THz has been demonstrated with conversion efficiency > -40 dB. The principle of such a wide bandwidth and high conversion efficiency in such a short R-DFB cavity has been theoretically analyzed. The simulation results match well with the experimental data

Sub-watt threshold, kilohertz-linewidth Raman distributed-feedback fiber laser

We report a low-threshold, narrow linewidth Raman distributed-feedback (R-DFB) fiber laser at 1109.54 nm based on a 30 cm long center pi phase-shifted Bragg grating written directly in a commercially available germano-silica (Ge/Si) fiber. The R-DFB was pumped by a continuous-wave (CW) linearly polarized fiber source at 1064 nm, and the threshold power, full width at half-maximum (FWHM) linewidth and slope efficiency with respect to the incident pump power are measured to be 440 mW, <2.5 kHz (measured with a 29.75 km fiber delay line) and 13.5%, respectively. An rf spectrum analyzer confirms that the R-DFB fiber laser exhibits single-frequency performance

Ultrawide-range four-wave mixing in Raman distributed-feedback fiber lasers

We report ultrawide-range and highly efficient wavelength conversion by exploiting four-wave mixing (FWM) in Raman distributed-feedback (R-DFB) fiber lasers. The lasers are 30 cm long center pi phase-shifted DFB gratings UV written in commercially available germano-silica (Ge/Si) single-mode fibers (PS980 from Fibercore Ltd., and UHNA4 from Nufern). The R-DFB lasing signal acts as a pump wave for the FWM process within the DFB cavity, and the obtained FWM conversion efficiency is around -25 dB with a maximum wavelength conversion range of 112 nm