Integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre for DNA probe immobilization

In this paper, we demonstrate the integration of a 3D hydrogel matrix within a hollow core photonic crystal fibre (HC-PCF). In addition, we also show the fluorescence of Cy5-labelled DNA molecules immobilized within the hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino groups of biomolecules using an appropriate cross-linker, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of probe molecules to be available per unit area. The HC-PCFs, on the other hand, can be designed to maximize the capture of fluorescence to improve sensitivity and provide longer interaction lengths. This could enable the development of fibre-based point-of-care and remote systems, where the enhanced sensitivity would relax the constraints placed on sources and detectors. In this paper, we will discuss the formation of such polyethylene glycol diacrylate (PEGDA) hydrogels within a HC-PCF, including their optical properties such as light propagation and auto-fluorescence.

All-optical phase and amplitude regenerator for next-generation telecommunications systems

Fibre-optic communications systems have traditionally carried data using binary (on-off) encoding of the light amplitude. However, next-generation systems will use both the amplitude and phase of the optical carrier to achieve higher spectral efficiencies and thus higher overall data capacities(1,2). Although this approach requires highly complex transmitters and receivers, the increased capacity and many further practical benefits that accrue from a full knowledge of the amplitude and phase of the optical field(3) more than outweigh this additional hardware complexity and can greatly simplify optical network design. However, use of the complex optical field gives rise to a new dominant limitation to system performance-nonlinear phase noise(4,5). Developing a device to remove this noise is therefore of great technical importance. Here, we report the development of the first practical ('black-box') all-optical regenerator capable of removing both phase and amplitude noise from binary phase-encoded optical communications signals.

All-optical OFDM and distributed Raman amplification : challenges to enable high capacities and extend reach

We review recent advances in all-optical OFDM technologies and discuss the performance of a field trial of a 2 Tbit/s Coherent WDM over 124 km with distributed Raman amplification. The results indicate that careful optimisation of the Raman pumps is essential. We also consider how all-optical OFDM systems perform favourably against energy consumption when compared with alternative coherent detection schemes. We argue that, in an energy constrained high-capacity transmission system, direct detected all-optical OFDM with `ideal' Raman amplification is an attractive candidate for metro area datacentre interconnects with ~100 km fibre spans, with an overall energy requirement at least three times lower than coherent detection techniques.

Polymer fiber Bragg gratings

This chapter deals with gratings recorded in polymeric optical fibers (POFs); predominantly those based on poly (methyl methacrylate) (PMMA). We summarise the different mechanical and optical properties of POFs which are relevant to the application of POF Bragg gratings and discuss the existing literature on the subject of the UV photosensitivity of PMMA. The current state of the art in POF grating inscription is presented and we survey some of the emerging applications for these devices.

Nanotube-polymer composites for ultrafast photonics

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Discriminating contact in lumen with a moving flexible digit using fibre Bragg grating sensing elements

Minimal access procedures in surgery offer benefits of reduced patient recovery time and less pain, yet for the surgeon the task is more complex, as both tactile and visual perception of the working site is reduced. In this paper, experimental evidence of the performance of a novel sensing system embedded in an actuated flexible digit element is presented. The digit represents a steerable tip element of devices such as endoscopes and laparoscopes. This solution is able to discriminate types of contact and tissue interaction, and to feed back this information with the shape of the flexible digit. As an alternative to this information, force level, force distribution, and other quantifiable descriptors can also be evaluated. These can be used to aid perception in processes such as navigation and investigation of tissues through palpation. The solution is pragmatic, and by virtue of its efficient mechanical construction and a polymer construction, it offers opportunities for a disposable element with suitability for magnetic resonance imaging (MRI) and other scanning environments. By using only four photonics sensing elements, full perception of tissue contact and the shape of the actuated digit can be described in the feedback of this information. The distributive sensory method applied to the sensory signals relies on the coupled values of the sensory data transients of the four deployed sensing elements to discriminate tissue interaction directly in near real time.

Strain response of POF sensors

With regard to polymer fibre Bragg gratings, we investigate one of the consequences of the visco-elastic nature of the constituent polymer: hysteresis in the response of wavelength shift vs sensor elongation. We show that when a grating sensor is directly bonded to a substrate, the hysteresis is reduced by a factor of 10 from the case where the sensor is freely suspended between two supports.

All-optical passive 2R regeneration for N×40 Gbit/s WDM transmission using NOLM and novel filtering technique

We propose an all-optical passive 2R regeneration method for WDM (N×40 Gbit/s) dispersion-managed RZ transmission based on specially designed WDM guiding filters and in-line nonlinear optical loop mirrors. By system optimisation, the feasibility of 150 GHz-spaced × l6 channel transmission over 25,000 km of standard fibre is numerically demonstrated.

All-optical passive regeneration of 40 Gbit/s soliton data stream using dispersion management and in-line NOLMs

It is numerically demonstrated, for the first time, that dispersion management and in-line nonlinear optical loop mirrors can achieve all-optical passive regeneration and distance-unlimited transmission of a soliton data stream at 40 Gbit/s over standard fibre.

Optical data transmission using periodic in-line all-optical format conversion

We introduce a novel transmission technique of periodic in-line all-optical format conversion between return-to-zero and non-return-to-zero-like aimed at delaying the accumulation of format-specific impairments. A particular realization of this approach using in-line normal dispersion fibre-enhanced nonlinear optical loop mirrors at 40Gbit/s data rate is presented.

All-optical passive regeneration of 40 Gbit/s soliton data stream using dispersion-management and in-line nonlinear optical loop mirrors

We numerically demonstrate for the first time that dispersion management and in-line nonlinear optical loop mirrors can achieve all-optical passive regeneration and distance-unlimited transmission of a soliton data stream at 40 Gbit/s over standard fibre.

All-optical passive 2R regeneration for N × 40 Gbit/s WDM transmission using NOLM and novel filtering technique

We propose a passive all-optical 2R regeneration method for WDM (N×40 Gbit/s) dispersion-managed RZ transmission based on specially designed WDM guiding filters and in-line nonlinear optical loop mirrors. By system optimisation, the feasibility of 150 GHz-spaced × 16 channel 25000 km transmission over standard fibre is numerically demonstrated.

Characterization of ultra-long Raman fibre lasers

We present results on characterization of lasers with ultra-long cavity lengths up to 84km, the longest cavity ever reported. We have analyzed the mode structure, shape and width of the generated spectra, intensity fluctuations depending on length and intra-cavity power. The RF spectra exhibit an ultra-dense cavity mode structure (mode spacing is 1.2kHz for 84km), in which the width of the mode beating is proportional to the intra-cavity power while the optical spectra broaden with power according to the square-root law acquiring a specific shape with exponential wings. A model based on wave turbulence formalism has been developed to describe the observed effects.

Investigation of EDFA power transients in circuit-switched and packet-switched optical networks

Erbium-doped fibre amplifiers (EDFA’s) are a key technology for the design of all optical communication systems and networks. The superiority of EDFAs lies in their negligible intermodulation distortion across high speed multichannel signals, low intrinsic losses, slow gain dynamics, and gain in a wide range of optical wavelengths. Due to long lifetime in excited states, EDFAs do not oppose the effect of cross-gain saturation. The time characteristics of the gain saturation and recovery effects are between a few hundred microseconds and 10 milliseconds. However, in wavelength division multiplexed (WDM) optical networks with EDFAs, the number of channels traversing an EDFA can change due to the faulty link of the network or the system reconfiguration. It has been found that, due to the variation in channel number in the EDFAs chain, the output system powers of surviving channels can change in a very short time. Thus, the power transient is one of the problems deteriorating system performance. In this thesis, the transient phenomenon in wavelength routed WDM optical networks with EDFA chains was investigated. The task was performed using different input signal powers for circuit switched networks. A simulator for the EDFA gain dynamicmodel was developed to compute the magnitude and speed of the power transients in the non-self-saturated EDFA both single and chained. The dynamic model of the self-saturated EDFAs chain and its simulator were also developed to compute the magnitude and speed of the power transients and the Optical signal-to-noise ratio (OSNR). We found that the OSNR transient magnitude and speed are a function of both the output power transient and the number of EDFAs in the chain. The OSNR value predicts the level of the quality of service in the related network. It was found that the power transients for both self-saturated and non-self-saturated EDFAs are close in magnitude in the case of gain saturated EDFAs networks. Moreover, the cross-gain saturation also degrades the performance of the packet switching networks due to varying traffic characteristics. The magnitude and the speed of output power transients increase along the EDFAs chain. An investigation was done on the asynchronous transfer mode (ATM) or the WDM Internet protocol (WDM-IP) traffic networks using different traffic patterns based on the Pareto and Poisson distribution. The simulator is used to examine the amount and speed of the power transients in Pareto and Poisson distributed traffic at different bit rates, with specific focus on 2.5 Gb/s. It was found from numerical and statistical analysis that the power swing increases if the time interval of theburst-ON/burst-OFF is long in the packet bursts. This is because the gain dynamics is fast during strong signal pulse or with long duration pulses, which is due to the stimulatedemission avalanche depletion of the excited ions. Thus, an increase in output power levelcould lead to error burst which affects the system performance.

Enhanced spectral sensitivity of fibre long period gratings to refractive index of aqueous solutions utilising copper patterned coatings

A set of long period grating devices have been fabricated in photosensitive single mode fibre coated with a series of copper rings (period of 380μm, 50% duty cycle and length of 4cm). The long period gratings were inscribed with a uniform UV-laser exposure across the entire length of the copper ring patterned coating. The devices ranged in copper thickness from 0.5μm to 1.5μm. In addition, a control long period grating was fabricated in the same type of fibre with the same period for comparison. The refractive index and temperature spectral sensitivity of these devices were investigated and it was found that the index and temperature sensitivity is a function of the thickness of the copper rings, as supported by theoretical modelling. Furthermore, the index sensitivity of these devices in the 1.333 index region is greater than the control long period grating. The patterned 0.5μm coated long period grating gave a sensitivity of Δλ/Δn = -74 nm leading to a resolution of 1.4×10-3 compared to the control which had a sensitivity of Δλ/Δn = -32 nm with a resolution of 3.2×10-3 in the index region of 1.320 to 1.380 (aqueous solution regime). This demonstrates a two fold increase in the sensitivity. This novel fibre long period grating device shows potential for increasing the resolution of measurements of the index of aqueous solutions.