Multimode microfiber interferometer for dual-parameters sensing assisted by Fresnel reflection

A compact and low cost fiber sensor based on single multimode microfiber with Fresnel reflection is proposed and demonstrated for simultaneous measurement of refractive index and temperature. The sensor is fabricated with two simple steps including fiber tapering and then fiber endface cleaving. The reflection spectrum is an intensity modulated interference spectrum, as the tapered fiber generates interference pattern and the cleaved endface provides intensity modulation. By demodulating the fringe power and free spectrum range (FSR) of the spectrum, RI sensitivities of -72.247dB/RIU and 68.122nm/RIU, as well as temperature sensitivities of 0.0283dB/degrees C and -17pm/degrees C are obtained. Further, the sensing scheme could also provide the feasibility to construct a more compact sensing probe for dual-paramters measurement, which has great potential in bio/chemical detection.

Fast and widely tunable Bragg grating reflection filter

A fiber Bragg grating filter device linearly tunable over 45 nm is presented. The device has a maximum tuning speed of 19 nm/ms with a wavelength setting time below 1.5 ms.

Simple design of nonuniform fiber Bragg grating with sharp reflection

In this paper we consider the possibility of using intermediate solutions, in which ideal apodisation profile for a dispersion-free, sharp-reflection profile fibre Bragg grating approximated in different degrees. The ideal apodisation profile for a flat dispersion, 50 GHz bandwidth grating was obtained using the layer-peeling algorithm. To verify the modelled results a version of the 5-section grating has been manufactured with excellent agreement between the model and the experimental results. The performance penalty due to multiple reflections from the FBGs in different situations was studied. The results showed that in the approximated gratings some post-compensation must be included to account for the local deviations from zero dispersion. © 2003 IEEE.

Direct femtosecond laser inscription in transparent dielectrics

Since 1996 direct femtosecond inscription in transparent dielectrics has become the subject of intensive research. This enabling technology significantly expands the technological boundaries for direct fabrication of 3D structures in a wide variety of materials. It allows modification of non-photosensitive materials, which opens the door to numerous practical applications. In this work we explored the direct femtosecond inscription of waveguides and demonstrated at least one order of magnitude enhancement in the most critical parameter - the induced contrast of the refractive index in a standard borosilicate optical glass. A record high induced refractive contrast of 2.5×10-2 is demonstrated. The waveguides fabricated possess one of the lowest losses, approaching level of Fresnel reflection losses at the glassair interface. High refractive index contrast allows the fabrication of curvilinear waveguides with low bend losses. We also demonstrated the optimisation of the inscription regimes in BK7 glass over a broad range of experimental parameters and observed a counter-intuitive increase of the induced refractive index contrast with increasing translation speed of a sample. Examples of inscription in a number of transparent dielectrics hosts using high repetition rate fs laser system (both glasses and crystals) are also presented. Sub-wavelength scale periodic inscription inside any material often demands supercritical propagation regimes, when pulse peak power is more than the critical power for selffocusing, sometimes several times higher than the critical power. For a sub-critical regime, when the pulse peak power is less than the critical power for self-focusing, we derive analytic expressions for Gaussian beam focusing in the presence of Kerr non-linearity as well as for a number of other beam shapes commonly used in experiments, including astigmatic and ring-shaped ones. In the part devoted to the fabrication of periodic structures, we report on recent development of our point-by-point method, demonstrating the shortest periodic perturbation created in the bulk of a pure fused silica sample, by using third harmonics (? =267 nm) of fundamental laser frequency (? =800 nm) and 1 kHz femtosecond laser system. To overcome the fundamental limitations of the point-by-point method we suggested and experimentally demonstrated the micro-holographic inscription method, which is based on using the combination of a diffractive optical element and standard micro-objectives. Sub-500 nm periodic structures with a much higher aspect ratio were demonstrated. From the applications point of view, we demonstrate examples of photonics devices by direct femtosecond fabrication method, including various vectorial bend-sensors fabricated in standard optical fibres, as well as a highly birefringent long-period gratings by direct modulation method. To address the intrinsic limitations of femtosecond inscription at very shallow depths we suggested the hybrid mask-less lithography method. The method is based on precision ablation of a thin metal layer deposited on the surface of the sample to create a mask. After that an ion-exchange process in the melt of Ag-containing salts allows quick and low-cost fabrication of shallow waveguides and other components of integrated optics. This approach covers the gap in direct fs inscription of shallow waveguide. Perspectives and future developments of direct femtosecond micro-fabrication are also discussed.

Attenuated total reflection-FT-IR spectroscopic imaging of protein crystallization

Protein crystallization is of strategic and commercial relevance in the post-genomic era because of its pivotal role in structural proteomics projects. Although protein structures are crucial for understanding the function of proteins and to the success of rational drug design and other biotechnology applications, obtaining high quality crystals is a major bottleneck to progress. The major means of obtaining crystals is by massive-scale screening of a target protein solution with numerous crystallizing agents. However, when crystals appear in these screens, one cannot easily know if they are crystals of protein, salt, or any other molecule that happens to be present in the trials. We present here a method based on Attenuated Total Reflection (ATR)-FT-IR imaging that reliably identifies protein crystals through a combination of chemical specificity and the visualizing capability of this approach, thus solving a major hurdle in protein crystallization. ATR-FT-IR imaging was successfully applied to study the crystallization of thaumatin and lysozyme in a high-throughput manner, simultaneously from six different solutions. This approach is fast as it studies protein crystallization in situ and provides an opportunity to examine many different samples under a range of conditions.

Continuous-wave ultraviolet light induced fiber Bragg gratings in few- and single-mode microstructured polymer optical fibers

Reported are observations and measurements of the inscription of fibre Bragg gratings in two different types of microstructured polymer optical fibre: few-moded and endlessly single mode. Contrary to FBG inscription in silica microstructured fibre, where high energy laser pulses are a prerequisite, we have successfully used a low power CW laser source operating at 325nm to produce 1-cm long gratings with a reflection peak at 1570 nm. Peak reflectivities of more than 10% have been observed.

Broadband fiber Bragg grating with channelized dispersion

We present here a new class of multi-channel Fiber Bragg grating (FBG), which provides the characteristics of channelized dispersion but does so with only a single reflection band. An FBG of this type can provide pure phase control of the spectral waveform of optical pulses without introducing any deleterious insertion-loss-variation. We anticipate that this new class of FBG will find some applications in wavelength-division- multiplexing systems.

Ultra-long raman laser with a feedback based on the Rayleigh scattering

This paper reports the Rayleigh scattering effects in ultra-long Raman fibre laser. It has been found that in a long fibre cavity (-100 km) the distributed feedback due to Rayleigh back scattering at propagation of light between fibre Bragg grating reflectors may be comparable with the lumped feedback provided by the FBG itself. As a result, Raman lasing in the fibre span limited by lumped (FBG) reflector at one side only appears possible due to significant reflection from the RS-based "random" distributed mirror at the other side. Thus, it concludes that a distributed Rayleigh scattering "random" mirror can form a cavity together with a single FBG spliced to the opposite cavity end.

Professionalisation and ophthalmic optics

This thesis is a sociological study of the ophthalmic optical profession in Britain. It includes a survey of the development of ophthalmic optics as an occupation and three questionnaire, surveys, one each of first and final year ophthalmic optics students, and one of practising opticians. The developmental survey showed that four themes have been important in the occupation's process of professionalisation - the actions of the opticians' leaders, the gradual unification of the bodies, representing segments of the profession, the struggle with medicine and the involvement of ophthalmic opticians in state-organised optical welfare schemes. The student surveys showed that the profession is now recruiting largely from middle class, state educated groups, and increasingly from women, who hold significantly different attitudes to income, independence and career commitment. In general, both first and final year students considered service to be rather more important than furthering knowledge. Practising opticians have been recruited increasingly, from middle class backgrounds, mostly from state selective secondary schools, but with a large minority from non-state schools. The self-recruitment rate of the profession (18.9%) is very similar to that for British medical students. Significant differences in concepts of professionalism were found among ophthalmic opticians of different ages, sexes and types of practice but few among those in different areas of practice. In general, ophthalmic opticians seemed to stress service more·than furthering knowledge. It is suggested that the leaders of the profession have 'negotiated' considerable autonomy for its members and that the possibilities for commercialism within the ophthalmic optician's professional role are intrinsically no greater than those in more 'established' professions.

Characterisation and performance of a Terfenol-D coated femtosecond laser inscribed optical fibre Bragg sensor with a laser ablated microslot for the detection of static magnetic fields

We present a novel device for the characterisation of static magnetic fields through monitoring wavelength shifts of femtosecond inscribed fibre Bragg grating and micromachined slot, coated with Terfenol-D. The device was sensitive to static magnetic fields and can be used as a vectoral sensor for the detection of magnetic fields as low as 0.046 mT with a resolution of ± 0.3mT in transmission and ± 0.7mT in reflection. The use of a femtosecond laser to both inscribe the FBGs and micromachine the slot in a single stage prior to coating the device significantly simplifies the fabrication.

Dissipative nonlinear structures in fiber optics

Optical fiber materials exhibit a nonlinear response to strong electric fields, such as those of optical signals confined within the small fiber core. Fiber nonlinearity is an essential component in the design of the next generation of advanced optical communication systems, but its use is often avoided by engineers because of its intractability. The application of nonlinear technologies in fiber optics offers new opportunities for the design of photonic systems and devices. In this chapter, we make an overview of recent progress in mathematical theory and practical applications of temporal dissipative solitons and self-similar nonlinear structures in optical fiber systems. The design of all-optical high-speed signal processing devices, based on nonlinear dissipative structures, is discussed.