Humidity insensitive TOPAS polymer fiber Bragg grating sensor

We report the first experimental demonstration of a humidity insensitive polymer optical fiber Bragg grating (FBG), as well as the first FBG recorded in a TOPAS polymer optical fiber in the important low loss 850nm spectral region. For the demonstration we have fabricated FBGs with resonance wavelength around 850 nm and 1550 nm in single-mode microstructured polymer optical fibers made of TOPAS and the conventional poly (methyl methacrylate) (PMMA). Characterization of the FBGs shows that the TOPAS FBG is more than 50 times less sensitive to humidity than the conventional PMMA FBG in both wavelength regimes. This makes the TOPAS FBG very appealing for sensing applications as it appears to solve the humidity sensitivity problem suffered by the PMMA FBG. © 2011 Optical Society of America.

Nonlinear soliton propagation in a few mode optical fibre

We experimentally demonstrate adiabatic soliton propagation in the fundamental mode of a few mode optical fibre and more complex behaviour in a higher order mode, indicating that the impact of nonlinearities differs for each mode.

Strain and temperature sensitivity of a single-mode polymer optical fiber

We have measured the optical phase sensitivity of fiber based on poly(methyl methacrylate) under near-single-mode conditions at 632.8 nm wavelength. The elongation sensitivity is 131±3 × 105 rad m-1 and the temperature sensitivity is -212±26 rad m -1 K-1. These values are somewhat larger than those for silica fiber and are consistent with the values expected on the basis of the bulk polymer properties. © 2005 Optical Society of America.

Highly sensitive liquid level sensor using a polymer optical Bragg grating for industrial applications

A novel and highly sensitive liquid level sensor based on a polymer optical fiber Bragg grating (POFBG) is reported for the first time. The sensitivity of the sensor is found to be 57 pm/cm of liquid, enhanced by more than a factor of 5 when compared to an equivalent sensor based on silica fiber. © 2015 OSA.

Gratings in polymer fibres

We report on recent progress in polymer optical fibre grating sensors, covering developments in our understanding of the fundamental behaviour of the devices, improvements to the usability of the technology and the opening up of new applications. © 2014 OSA.

Inverse four-wave mixing and self-parametric amplification in optical fibre

An important group of nonlinear processes in optical fibre involve the mixing of four waves due to the intensity dependence of the refractive index. It is customary to distinguish between nonlinear effects that require external/pumping waves (cross-phase modulation and parametric processes such as four-wave mixing) and those arising from self-action of the propagating optical field (self-phase modulation and modulation instability). Here, we present a new nonlinear self-action effect—self-parametric amplification—which manifests itself as optical spectrum narrowing in normal dispersion fibre, leading to very stable propagation with a distinctive spectral distribution. The narrowing results from inverse four-wave mixing, resembling an effective parametric amplification of the central part of the spectrum by energy transfer from the spectral tails. Self-parametric amplification and the observed stable nonlinear spectral propagation with a random temporal waveform can find applications in optical communications and high-power fibre lasers with nonlinear intracavity dynamics.

Controlling the properties of microstructured plastic optical fiber Bragg gratings using acousto-optic excitation

A fine control of the mPOF Bragg grating spectrum properties, such as maximum reflected power and 3dB bandwidth, through acousto-optic modulation (AOM) using flexural regime is presented. A numerical comparison of the strain field along mPOFBG - AOM and the similar structure with SMFBG-AOM was presented, showing that the strain field amplitude is higher along the mPOFBG due to its smaller mechanical stiffness. The obtained results can be used in the development of fine-tuned optical filters using low voltage sources and low frequency regimes, to obtain tunable optical filters and to control the shape of the spectrum. Studies of the behavior in different gratings (such as phase shifted and long period gratings) for photonic applications, such as tunable notch filters or tunable cavities, are in progress. It can potentially be applied on tunable optical filters for POF transmission. © 2012 IEEE.

Optical fibre gratings with response to 2μm and their sensing capabilities

Recently, we have extended fibre grating devices in to mid-IR range. Fibre Bragg gratings (FBGs) and long-period gratings (LPGs) with spectral responses from near-IR (800nm) to mid-IR ( ∼ 2μm) have been demonstrated with transmission loss as strong as 10-20dB. 2μm FBG and LPG showed temperature and refractive index (RI) sensitivities of ∼ 91pm/°C and 357nm/RIU respectively. Finally, we have performed a bio sensing experiment by monitoring the degradation of foetal bovine serum at room temperature. The results encouragingly show that the mid-IR LPGs can be an ideal biosensor platform as they have high RI sensitivity and can be used to detect concentration change of bio-samples. © 2012 SPIE.

A lower bound on the per soliton capacity of the nonlinear optical fibre channel

A closed-form expression for a lower bound on the per soliton capacity of the nonlinear optical fibre channel in the presence of (optical) amplifier spontaneous emission (ASE) noise is derived. This bound is based on a non-Gaussian conditional probability density function for the soliton amplitude jitter induced by the ASE noise and is proven to grow logarithmically as the signal-to-noise ratio increases.

Optical fibre limits:an approach using ASE channel estimation

In this talk we investigate the usage of spectrally shaped amplified spontaneous emission (ASE) in order to emulate highly dispersed wavelength division multiplexed (WDM) signals in an optical transmission system. Such a technique offers various simplifications to large scale WDM experiments. Not only does it offer a reduction in transmitter complexity, removing the need for multiple source lasers, it potentially reduces the test and measurement complexity by requiring only the centre channel of a WDM system to be measured in order to estimate WDM worst case performance. The use of ASE as a test and measurement tool is well established in optical communication systems and several measurement techniques will be discussed [1, 2]. One of the most prevalent uses of ASE is in the measurement of receiver sensitivity where ASE is introduced in order to degrade the optical signal to noise ratio (OSNR) and measure the resulting bit error rate (BER) at the receiver. From an analytical point of view noise has been used to emulate system performance, the Gaussian Noise model is used as an estimate of highly dispersed signals and has had consider- able interest [3]. The work to be presented here extends the use of ASE by using it as a metric to emulate highly dispersed WDM signals and in the process reduce WDM transmitter complexity and receiver measurement time in a lab environment. Results thus far have indicated [2] that such a transmitter configuration is consistent with an AWGN model for transmission, with modulation format complexity and nonlinearities playing a key role in estimating the performance of systems utilising the ASE channel emulation technique. We conclude this work by investigating techniques capable of characterising the nonlinear and damage limits of optical fibres and the resultant information capacity limits. REFERENCES McCarthy, M. E., N. Mac Suibhne, S. T. Le, P. Harper, and A. D. Ellis, “High spectral efficiency transmission emulation for non-linear transmission performance estimation for high order modulation formats," 2014 European Conference on IEEE Optical Communication (ECOC), 2014. 2. Ellis, A., N. Mac Suibhne, F. Gunning, and S. Sygletos, “Expressions for the nonlinear trans- mission performance of multi-mode optical fiber," Opt. Express, Vol. 21, 22834{22846, 2013. Vacondio, F., O. Rival, C. Simonneau, E. Grellier, A. Bononi, L. Lorcy, J. Antona, and S. Bigo, “On nonlinear distortions of highly dispersive optical coherent systems," Opt. Express, Vol. 20, 1022-1032, 2012.

Molecular alignment relaxation in polymer optical fibers for sensing applications

A systematic study of annealing behavior of drawn PMMA fibers was performed. Annealing dynamics were investigated under different environmental conditions by fiber longitudinal shrinkage monitoring. The shrinkage process was found to follow a stretched exponential decay function revealing the heterogeneous nature of the underlying molecular dynamics. The complex dependence of the fiber shrinkage on initial degree of molecular alignment in the fiber, annealing time and temperature was investigated and interpreted. Moreover, humidity was shown to have a profound effect on the annealing process, which was not recognized previously. Annealing was also shown to have considerable effect on the fiber mechanical properties associated with the relaxation of molecular alignment in the fiber. The consequences of fiber annealing for the climatic stability of certain polymer optical fiber-based sensors are discussed, emphasizing the importance of fiber controlled pre-annealing with respect to the foreseeable operating conditions.

Thermal effects on the photoelastic coefficient of polymer optical fibers

We measure the radial profile of the photoelastic coefficient C(r) in single-mode polymer optical fibers (POFs), and we determine the evolution of C(r) after annealing the fibers at temperatures from 40°C to 80°C. We demonstrate that C(r) in the fibers drawn from a preform without specific thermal pre-treatment changes and converges to values between 1.2 and 1.6×10-12 Pa-1 following annealing at 80°C. The annealed fibers display a smoothened radial profile of C(r) and a lowered residual birefringence. In contrast, the mean value of C(r) of the fiber drawn from a preform that has been pre-annealed remains constant after our annealing process and is significantly higher, i.e., 4×10-12 Pa-1. The annealing process decreases the residual birefringence to a lower extent as well. These measurements indicate the impact of annealing on the thermal stability of the photoelastic coefficient of POFs, which is an essential characteristic in view of developing POF-based thermomechanical sensors.

Aviation fuel gauging sensor utilizing multiple diaphragm sensors incorporating polymer optical fiber Bragg gratings

A high-performance fuel gauging sensor is described that uses five diaphragm-based pressure sensors, which are monitored using a linear array of polymer optical fiber Bragg gratings. The sensors were initially characterized using water, revealing a sensitivity of 98 pm/cm for four of the sensors and 86 pm/cm for the fifth. The discrepancy in the sensitivity of the fifth sensor has been explained as being a result of the annealing of the other four sensors. Initial testing in JET A-1 aviation fuel revealed the unsuitability of silicone rubber diaphragms for prolonged usage in fuel. A second set of sensors manufactured with a polyurethane-based diaphragm showed no measurable deterioration over a three month period immersed in fuel. These sensors exhibited a sensitivity of 39 pm/cm, which is less than the silicone rubber devices due to the stiffer nature of the polyurethane material used.

Fabrication, Optical Analysis and Photonic Applications of Certain Metallic Nanostructure-Integrated Dye Doped Polymer Optical Fibers” submitted by Ms. Suneetha Sebastian

Polymer Optical Fibers have occupied historically a place for large core flexible fibers operating in short distances. In addition to their practical passive application in short-haul communication they constitute a potential research field as active devices with organic dopants. Organic dyes are preferred as dopants over organic semiconductors due to their higher optical cross section. Thus organic dyes as gain media in a polymer fiber is used to develop efficient and narrow laser sources with a tunability throughout the visible region or optical amplifier with high gain. Dyes incorporated in fiber form has added advantage over other solid state forms such as films since the pump power required to excite the molecules in the core of the fiber is less thereby utilising the pump power effectively. In 1987, Muto et.al investigated a dye doped step index polymer fiber laser. Afterwards, numerous researches have been carried out in this area demonstrating laser emission from step index, graded index and hollow optical fibers incorporating various dyes. Among various dyes, Rhodamine6G is the most widely and commonly used laser dye for the last four decades. Rhodamine6G has many desirable optical properties which make it preferable over other organic dyes such as Coumarin, Nile Blue, Curcumin etc. The research focus on the implementation of efficient fiber lasers and amplifiers for short fiber distances. Developing efficient plastic lasers with electrical pumping can be a new proposal in this field which demands lowest possible threshold pump energy of the gain medium in the cavity as an important parameter. One way of improving the efficiency of the lasers, through low threshold pump energy, is by modifying the gain of the amplifiers in the resonator/cavity. Success in the field of Radiative Decay Engineering can pave way to this problem. Laser gain media consisting of dye-nanoparticle composites can improve the efficiency by lowering the lasing threshold and enhancing the photostability. The electric field confined near the surface of metal nanoparticles due to Localized Surface Plasmon Resonance can be very effective for the excitation of active centers to impart high optical gain for lasing. Since the Surface Plasmon Resonance of nanoparticles of gold and silver lies in the visible range, it can affect the spectral emission characteristics of organic dyes such as Rhodamine6G through plasmon field generated by the particles. The change in emission of the dye placed near metal nanoparticles depend on plasmon field strength which in turn depends on the type of metal, size of nanoparticle, surface modification of the particle and the wavelength of incident light. Progress in fabrication of different types of nanostructures lead to the advent of nanospheres, nanoalloys, core-shell and nanowires to name a few. The thesis deals with the fabrication and characterisation of polymer optical fibers with various metallic and bimetallic nanostructures incorporated in the gain media for efficient fiber lasers with low threshold and improved photostability.