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The great success of optical fibres in telecommunications has generated numerous applications in a number of related fields, such as sensing, biophotonics and high-power lasers. The topic remains extraordinarily buoyant and new materials, structures and applications emerge unabated. The talk will review recent developments and explore future possibilities.

Powering the optical fibre internet with its huge global reach, photonics has changed our lives. Optical fibres snake across continents and oceans carrying terabits per second of data in a vast information network that brings untold human connectivity. But capacity demand continues to grow at a startling rate, doubling every two years, while the internet is estimated as burning several percent of world energy usage. The optical internet is reaching its capacity limits. The solution to these consequences of unbridled demand is more photonics, reaching further into the network with optics to overcome the existing bottlenecks and employing next-generation optical components - Internet 2.0.The great success of optical fibres and planar circuits in telecommunications has generated numerous tantalising applications in a number of related fields, such as sensing, bio- and nano-photonics and high-power lasers. Incredibly, the same fibres that carry tiny internet signals can also generate kilowatts of power, sufficient to cut through inch-thick steel and perhaps drive the next generation of high energy physics.The talk will celebrate optical fibre technology and asks what next?

This paper reviews the progress in rare-earth doped fibre technology towards power scaling of high-brightness fibre sources.

Biosensors now play a vital and essential role in medicine, industry and the environment, providing routine analysis, crucial monitoring, and early detection of problems and crisis points. Biosensors are increasingly finding applications in homeland security, as well as in bio/pharmaceutical research. The market for biosensors is forecast to swell to £5.7 billion in 2007, with an annual growth rate of around 10 per cent [1], as new techniques address the issues of accuracy, response time, ease of use and cost, which currently determine specific implementation in different sectors.

Born out of the telecom revolution, the supreme attributes of rare-earth doped fibers has allowed Yb-doped fiber lasers to be power-scaled from 0.1 to several kW’s in only a few years. Remarkably, we still see fiber lasers being limited by the diodes rather than the fibers themselves, even as output powers have continued to rise well into the multi-kW regime. Despite these impressive results, high-power fiber laser development is still in its infancy with a high rate of progress. Limited investment rather than the fundamentals of the technology is the biggest hurdle to the 10 kW-level from a single-emitter diffraction-limited fiber source. Looking to the future, fiber sources are also extremely attractive for beam combining for power-scaling to perhaps 100’s of kW. Of particular interest here is the astounding single-frequency powers that have been obtained, also now approaching 1 kW. This presentation will discuss progress and prospects for high-power fiber sources, treating "simple" power-scaling as well as more sophisticated single-frequency and pulsed sources at different wavelengths. Adding the attributes of small size, maintenance-free operation, and high thermal and electrical efficiency, we see that fiber lasers have the potential to change every industry and discipline they encounter and challenge currently held views on how to make things, how to repair things, and how to destroy things.

First demonstration of planar Bragg gratings UV written into collapsed fibre planar samples with >200µm cladding thickness is presented. Multiple gratings were written across the sample profile to accurately determine core layer flatness and uniformity.

Fiber lasers have caught the imagination for applications requiring beam combination up to a 100kW or more. Their near-perfect beam quality, stability and versatility, coupled with the low cost of the gain medium, make them ideal candidates for coherently combining perhaps up to a 100 individual fiber amplifier beams. Using optical fibre circuitry derived from telecommunications, we can envisage all-fibre laser systems which are robust and transportable, with straight-forward management of heat load. The latter attribute comes from the large surface to volume ratio, the efficiency of fiber laser and the thermal stability of silica. For coherent beam combination, we require single-frequency output in a stable, polarised beam. Progress towards high-power single-frequency lasers will be reviewed, together with the expected limitations to the technology. Recent work on pulsed fiber lasers will also be reviewed, together with prospects for beam combination to overcome the pulse energy limitations that result from the small active volume of the fiber core.

In recent years there have been dramatic advances in fibre lasers. Currently, conventional single-strand cladding-pumped fibre lasers can generate output powers beyond 1 kW with high beam quality. Indeed, this fibre circuitry combined with pump-diode technology provides a unique high-gain environment for robust designs, which is also all-solid state, compact, stable, reliable, and reproducible. Here we review the recent progress in high-power MOPAs based on rare-earth-doped fibres and discuss fundamental aspects and prospects. We present our up-to-date experimental results with particular attention to a multitude of cladding-pumped, refined power amplifier regimes, including continuous-wave and pulsed fibre MOPA sources based on ytterbium-doped fibres operating at 1.1 µm and erbium:ytterbium co-doped fibres at 1.5 µm.

When Ted Maiman invented the laser in 1960, his breakthrough accomplishment changed the world. We are all familiar with the "lasers" used by fictional heroes such as James Bond, Luke Skywalker and Captain James T. Kirk. What is less well known is the level of complex science and engineering that has been mastered and refined over the last 40 years to produce the laser systems of today. Whether they are simple semiconductor lasers for DVD players or giant systems for laser fusion, they are now essential tools for medics, scientists, engineers, construction workers, and disc jockeys alike. This year's Mountbatten Lecture will present the story of the fibre laser, from lab conception to industrial and military applications with a tantalising glimpse into the manufacturing industries of the future.

Cladding-pumped fiber lasers and amplifiers offer a number of unique properties. These enabled the very rapid power-scaling seen in the last few years. However, there are many additional advantages, that enable the power to be combined with exceptional control of the output characteristics. Such sources promise to make a drastic difference in a range of new applications. The figure shows the progress in reported output powers from single mode or nearly diffraction-limited fiber lasers at wavelengths around 1.1µm, which now exceeds 1 kW (see, e.g., [1]). Advances in high-power multimode diode and fiber technology, combined with the inherent power-scalability of cladding-pumped fibers, lie behind this rapid progress. Compared to the telecom technology and especially erbium-doped fiber amplifiers that these high-power fiber lasers have evolved from, the most important differences in the fiber design are the use of double-clad fibers, the much larger core and inner cladding sizes that allow for the launch of high-power, large, pump beams and increases the damage threshold, as well as the use of ytterbium-doping. The high efficiency of low-loss Yb-doped fiber lasers (YDFLs) – over 80% is possible with high-quality, high-purity fabrication – means that even a 1 kW fiber laser generates no more than ~200 W of heat. This exceptionally low heat load simplifies heat-sinking. The overall efficiency is further enhanced by improvements in diode efficiency, which is currently at ~70%.

We discuss fundamental aspects of high-power fiber lasers and describe their recent dramatic advances and prospects including our up-to-date experimental results with particular attention to kilowatt-class, refined power amplifier regimes.

We review the rapid recent progress in the development of high-power fibre laser and amplifier devices. Use of cladding pump technology now provides a route to compact and efficient laser and amplifier systems with high beam quality and output powers up to the kilowatt level. The technology can also be used to obtain high quality pulsed performance in the ns to fs regime.

Photosensitivity of different concentrations of antimony (Sb) codoped alumino-silicate optical fibres are analysed. Bragg gratings with index modulations of ~3 x 10-4 are reported. The temperature stability of the gratings is tested and those in higher concentration fibres are found to be more temperature-resistant.

A single-frequency, single-mode, plane-polarized ytterbium-doped all-fiber master-oscillator – power amplifier source at 1060nm generated 264W of cw output power (pump-power limited) The final-stage amplifier operated with a high gain of 19dB and a high conversion efficiency of 68%.

Bragg gratings with index modulations of ~3 x 104 is reported in antimony (Sb) codoped fibres. Gratings in germanium-free fibres of different Sb concentration are analysed and those in higher concentration fibres are found the more temperature-resistant.

An L-band (1618nm) fibre-DFB laser pumped at 1534nm is demonstrated for the first time. It has a threshold of

A single-polarized fiber DFB laser with keyed axis output is demonstrated from a D-shaped fiber configuration. The laser shows an output power of 3.8dBm and strong axis alignment when spliced to a polarization maintaining fiber.

Bragg gratings in optical fibre waveguides have now been around for nearly 25 years and they were soon after being realised identified as one of the most significant fibre-optic inventions with potentials in a wide variety of areas among telecommunications equivalent to that of the erbium doped fibre amplifier. Following their creation a plurality of infibre functions were thought possible with low or no insertion-loss. Although fabrication and control of vital grating parameters was limited in the early stages of their life, initially a number of filtering functions were identified for obvious demonstrations. It soon became apparent though that not just standard filtering manipulation was possible. Identifying the true potential of the devices has let to considerable effort being concentrated on their full exploitation implying building an infrastructure supported by theoretical design [2] and manufacturing techniques [3,4] around them. These techniques combined have let to a scenario where currently it is the imagination more than the actual design and manufacturing capabilities that imposes a limitation to what is being demonstrated. We will in this presentation discuss and highlight some of the most recent advances in Bragg grating devices and applications in advanced components. In particular we will show examples of the latest in Bragg gratings for dispersion-control, short pulse manipulation and advanced filtering applications and speculate into what the future holds for these unique devices.

The gain efficiency of a fully optimized erbium-doped fiber amplifier (EDFA) is calculated as a function of the fiber numerical aperture and dopant confinement in the core and is shown to agree well with experimental data. A gain efficiency of 8.9 dB/mW is demonstrated. This is the best reported value to date for modified chemical vapor deposition (MCVD) fibers. In addition, the detrimental effect of pump and signal background losses on the optimal gain efficiency is considered in detail. >

Laser emission at 1317nm has been observed for the first time in a neodymium doped fluoroaluminate glass waveguide fabricated by a combination of hot dip spin coating and direct UV writing.

Enhanced UV photosensitivity and increase in defects' concentration have been observed in GeO2-doped optical fibres thermally treated using CO2 laser.

Aluminium fluoride based glass [AlF3-M(II)F2-xPO3 M=Mg, Ca, Ba, Sr] fibres have potential for use as 1.3µm amplifiers, but successful application depends on improving their poor mechanical strength. Surface contamination of the preform is a major factor contributing to the lack of strength; it can be improved by chemical etching. As the glass components are highly unreactive, few etching studies have been reported in the literature. In this work, two multicomponent etches have been identified for the purpose and characterised. Optimum working compositions are 0.4M AlCl3 - 6 H2O / 1M HCl and 50% HF (48%) / 30% HNO3 (68%) / 20% H2O plus 3M H3BO3. Both yield fibres of significantly improved strength and quality, although the former etch tends to perform slightly better. Furthermore, an etch procedure has been developed for the aluminium chloride mixture which enables good strength fibre to be pulled in a controlled and reproducible manner.

Chalcogenide glasses are usually known for their good infrared and poor visible transparency which limit their applications to passive and active devices in the infrared wavelength region. Gallium lanthanum sulphide glasses, however, show visible transparency down to 500nm. The low phonon energy of the glass increases the radiative quantum efficiency of rare-earth energy levels compared to commonly used fluorozirconate glasses and provides long-lived intermediate levels for efficient two-step excitation to visible energy levels. Green and red upconversion emission has been observed in Pr3+, Nd3+, Ho3+, and Er3+ doped glasses under Ti:sapphire pumping in wavelengths regions where diode laser sources are easily available. Lifetime measurements reveal the excitation process is either excited-state absorption or upconversion caused by ion-ion interactions. Modification of the glass with lanthanum oxide or caesium chloride improves the visible transparency and shifts the UV absorption edge to 450nm and 400nm, respectively, and also improves the fibre drawing of these glasses.

Progress in the development of the elusive pump-efficient 1.3µm optical fibre amplifier is reviewed. Four possibilities exist, all in non-silica glass. At present, there is no clear winning technology, but the availability of high-power pump diodes could favour the more conventional approaches. The telecommunications industry is currently undergoing a rapid transformation towards all-optical systems and networks. The upgrade to all-optical operation is well advanced in the long-haul 1.5µm networks which take advantage of the highly successful Er3+-doped optical fibre amplifier (EDFA) introduced in 1987 [1]. The result is a global optical amplifier market expected to be worth nearly £1 billion pa by 2004, despite the fact that EDFAs are not appropriate for operation at the 1.3µm zero-dispersion window that dominates existing terrestrial fibre systems. An optical amplifier at 1.3µm is required to upgrade presently installed optical links and to promote a balanced evolution of the optical network and to support the expected traffic requirements needed for interactive video and multimedia services. It is worth noting that with development in optical fibre manufacturing, there is now a need for amplifiers spanning the full transmission window from 1.2µm to 1.7µm. The research in fibre amplifiers at 1.3µm encompasses study of active ions with suitable transitions like rare-earth ions Pr3+, Dy3+ and Nd3+ in different host glasses such as in fluorides, chlorides and chalcogenides. The first generation of 1.3µm praseodymium-doped fluoride fibre amplifiers (PDFFAs) based on Pr3+-doped ZBLAN is already available on the market. It is characterised by a gain peak at 1300nm and 3dB bandwidth of 25-40nm depending on input power.[2] The ground state absorption (GSA) to the metastable state is broad, 950-1060nm with line centre at 1010nm, allowing use of different pump wavelengths. However, the absorption is weak and a PDFFA fibre is normally at least 10 metres long. The PDFFA's biggest limitation is in pump efficiency owing to a high nonradiative decay rate from the metastable to an intermediate level which dominates the 1.3µm emission. A 30dB gain amplifier requires 300mW pump power around 1017nm. This cannot be easily achieved with a single semiconductor pump laser. For this reason, PDFFA devices have been pumped by expensive Nd:YLF lasers at 1047nm, away from the peak absorption wavelength, and the pump requirement is further increased to 600mW levels.[3] The development of sufficiently intense semiconductor lasers for peak absorption LD pumping of PDFFAs will encourage the realisation of the second generation of such amplifiers based on lower phonon energy glasses than ZBLAN, such as Pb-Ga-In (PGI) fluoride glass, with thermal stability against crystallisation and a fibre loss similar to stable ZrF4-based glasses. The amplifier pump efficiency improves dramatically when the quantum efficiency is increased by placing Pr3+ in very-low phonon-energy glass to reduce multiphonon quenching. Sulphide-based chalcogenide glasses have phonon energies of ~400cm in ZBLAN, the radiative quantum efficiency can be greater than 50% (c.f. ~4% in ZBLAN, ~7% in PGI). Gain measurement results using Ga-Na-S fibre report a peak net gain at 1.34µm and a gain coefficient (bi-directional pumping configuration) of 0.81dB/mW, compared to the best PGI fluoride fibre of 0.36dB/mW. The amplifier is thus able to deliver 30dB net gain with less than 100mW of 1017nm pump power.[5] However, the biggest drawback is that the gain peak is red-shifted in a sulphide host to about 1.34µm, so that the gain is well down at 1310nm, the preferred operating wavelength. Dysprosium in low phonon energy glasses such as sulphides and chlorides has a suitable transition at 1.3µm.[6,7] The emission is centered at 1310nm with FWHM of 40nm and the quantum efficiency is expected to be around 70%. However, Dy3+ exhibits a significant GSA, which must be bleached in order to achieve net gain, i.e., it behaves like a 3-level amplifier. To date, no fibre gain measurements have been reported. Nd3+ is another active dopant. Novel glass design has resulted in a glass composition based on AlF3 such that the gain peak is inside the second telecom window at 1310nm (near the zero-dispersion region of silica at 1317nm). It is a four-level system and the transition from the metastable level is purely radiative. In order to achieve a high gain amplifier, the competing 1050nm amplified-stimulated-emission must be filtered out. The use of gratings is one possible means of achieving the desired filter characteristics. In Nd3+-doped AlF3-glass fibre, there is the potential for an efficient and inexpensive optical amplifier able to deliver 30dB gain using 3+ at 800nm and the high solubility of the ion in the glass gives a short device. Conclusion: Although there are four candidate fibres for 1.3µm doped fibre amplifiers (Pr3+ in ZBLAN, PGI or sulphide, Nd3+ in AlF) each has disadvantages compared to the EDFA operating at 1.53µm. Many of these disadvantages are fundamental and lead to an amplifier which is expensive, or has compromised performance. The commercial development which can change this is the availability of high-power pump sources which would ease the current preoccupation with pump efficiency.

A family of fluoroaluminate glasses has been identified as the ideal host for doping with Nd3+ for use in the development of lasers and amplifiers in the second telecom window. For optimum performance, a fibre with high numerical aperture (NA), fibre length of 5cm and loss of 10dB/m is required. The high NA implies a core diameter of 3µm is needed and thus the core-to-clad interface represents greater than 50% of the core area. Crystallisation in the interface introduces large scattering losses. The critical step in the fabrication process is preform fabrication. We will present results comparing the different techniques employed and thermal and mechanical fabrication process modelling consistent with our experimental observations and detail the advantages and limiting parameters for the different processes. Rod-in-tube is the simplest technique of preform fabrication and works exceptionally well for oxide glasses. Fluorides are highly prone to surface crystallisation. We have looked at the fibre losses as functions of polishing material, polishing time, and etching. It is a good first step to test the optical properties and performance in a fibre. Rotational casting is usually employed in fluoride glasses. The high Tg(450°C) and large expansion coefficient ( >150x10-7/°K. We will compare the results of rotational casting with built-in-casting and the influence of processing time, thermal history and mould material (thermal conductivity). Extrusion as a procedure for preform fabrication is specially suitable for fluoraluminates. Extrusion allows one to operate at temperatures nearer Tg than Tx. Preforms can be prepared with small cores and thus avoid the thermal cycling involved in sleeving to get the singlemode fibre. To date our losses for fibres with 5-8µm cores vary from 100dB/m using rod-in-tube to 20dB/m using extrusion.

We report on the observed effects of liquids at high temperature and pressure on silica optical fibres, sensors and gratings. We propose that the diffusion of molecules into the silica and the resultant expansion of the network are responsible for observed fibre expansions of up to 0.2% and Bragg wavelength increases of 2nm at 1525nm. A developmental solution in the form of amorphous carbon hermetic coatings has shown a reduction of these effects by an order of magnitude at 300°C.

Diode-pumped rare-earth doped fibre lasers in the mid-infrared wavelengths region would offer a compact and efficient alternative to the either relatively weak or very complex existing mid-infrared sources such as thermal emitters, gas lasers and OPOs. A prerequisite for the rare-earth host material is a low phonon energy leading to mid-infrared transparency and to low nonradiative decay rates and therefore higher quantum efficiencies of mid-infrared transitions. Conventional silica glass fibres cannot fulfill these requirements leading to a need for new glass materials with lower phonon energies which must also be suitable for fibre pulling. Our approach towards mid-infrared laser sources is based on the stable, non-toxic and non-hygroscopic chalcogenide glass gallium lanthanum sulphide (GLS) with the molar composition 70Ga2S3:30La2S3 which has been pulled into fibre form successfully [1]. It has a low phonon energy (425 cm) and a wide infrared transmission extending beyond 8µm. The characterization of undoped GLS glasses and fibres such as loss measurements and theoretical loss calculations will be presented in another paper at this conference [2]. In this paper we present the spectroscopy of rare-earth doped GLS glasses and fibres which show fluorescence at wavelengths which are interesting for gas sensing and remote sensing. Examples are the 3.4µm emission from praseodymium and the 4.3µm emission from dysprosium which overlap with the strong fundamental absorption bands of methane and carbon dioxide, respectively, and could therefore find application as gas sensors for these two important greenhouse gases. The emission of thulium at 3.8µm and holmium at 3.9µm fall into the atmospheric window with the highest transmission and could therefore be suitable for remote sensing applications. Laser action an the above transitions has not been achieved to date but the first laser action in a rare-earth doped chalcogenide glass fibre which has been demonstrated in a neodymium doped GLS fibre shows the potential for mid-infrared fibre lasers in this chalcogenide glass system [3].

A new method for suppression of coupling from guided optical modes into cladding modes in an optical fiber Bragg grating using a fiber with a strongly depressed cladding is proposed. Strong suppression of the coupling has been demonstrated both theoretically and experimentally.

Optical fibres drawn from sulphide-based glasses have been studied now for almost two decades. Initial work began in the 1970s where fibres from glasses based on arsenic sulphide or germanium sulphide rapidly found application as infrared waveguides, providing transmission to beyond 5 microns. A flurry of activity began when the possibility of an ultra-low loss, less than 10dB/km, waveguide was postulated in infrared materials operating at their intrinsic loss minimum. Unfortunately, this low loss was never realized and with the invention of the optical fibre amplifier operating at 1550 nm, an ultra-low loss waveguide became in some ways redundant. However, use of these fibres as passive infrared waveguides continued, for applications as diverse as remote sensing, laser surgery and power delivery for laser machining. In the early 1990s, the demonstration of an optical fibre amplifier for the 1300 nm telecommunications window, motivated again the application of non-silica optical fibres. First, a fluoride fibre device showed amplification with pump efficiencies of only a few percent. In 1993, Becker demonstrated what was probably the first active application of a sulphide glass. Measurements on bulk samples of rare-earth doped gallium lanthanum glass showed the possibility of pump efficiencies of over 60%. This lead to a widespread activity to demonstrate a low-loss sulphide glass optical fibre and an 1300 nm optical fibre amplifier. As research into gallium lanthanum sulphide and other sulphide-based glasses accelerated, it was gradually realized that the very properties which silica glass fibres lack for active applications can be found with the sulphides. Sulphide glasses, by virtue of their high refractive index provide high radiative rates for rare-earth transitions, boosting the efficiency of fibre lasers and amplifiers and the low energies of the atoms which from the glass ensure low non-radiative rates, minimizes the loss of pump energy via vibrations or heating of the glass. The high linear refractive index indicates high non-linear indices, with gallium lanthanum sulphide glass now identified as having the largest non-resonant nonlinearity reported to date. Already, this non-linearity has been exploited through a low-power all optical high speed switch in relatively high loss arsenic sulphide based fibres. Like silica, sulphide glasses are photosensitive, but with enhanced photosensitivity which can be exploited, not with high power excimer lasers operating in the ultraviolet, but with a simple low power He-Ne laser at 633 nm. In the past year, Bragg gratings have been achieved with reflectivities > 90% at wavelengths around 1550 nm. While silica glass may now be the ultimate passive waveguide, an active application such as the erbium-doped fibre amplifier is the exception rather than the rule. In this paper, applications of sulphide fibres for active applications will be reviewed. Recent progress in several applications, including the 1.3 micron amplifier, photonic switching and work extending into the infrared will be reported and the prospects for a future generation of sulphide-fibre based devices examined.

We report on laser action in a Neodymium doped Gallium Lanthanum Sulphide glass fibre. Laser action at 1080nm was obtained in a 22mm long multimode glass fibre with a neodymium doped core, fabricated by the rod-in-tube technique. The laser was pumped continuous wave with a Ti:sapphire laser at 815nm and showed a self-pulsing behaviour.

We report laser action in a neodymium doped gallium lanthanum sulphide glass fibre at 1.08µm. To our knowledge, this is the first demonstration of laser action in a rare-earth doped chalcogenide glass fibre.

Second harmonic generation in gallium-lanthanum-sulphide (Ga:La:S) and GeS2+Ga:La:S glasses is investigated. It is shown that microcrystals of Ga:La:S and of alpha-phase of gallium-sulphide (alpha-Ga2S3), whose presence in the glass matrix is revealed by x-ray diffraction analysis, are responsible for the frequency doubling process.

We have demonstrated both theoretically and experimentally strong suppression of coupling of the guided fundamental mode into cladding modes in a Bragg grating by introducing a depressed cladding around the core region. We have also studied the effect for different depression depths.

To further improve the workability of Ga2S3-La2S3 (GLS) glass suitable for 1.3µm fibre amplifiers, we have studied the addition of a series of third components (both sulphides, i.e. Na2S, CaS and In2S3, and halides, LaR3, R = F, Cl, Br and I) into the binary GLS system. This paper describes the effect of various third components on the thermal, rheological and optical properties of the GLS. The structural role of each individual addition to the GLS glass was analysed upon its chemical bonding characteristics. Some modified GLS glasses show much enhanced UV transmission and greater workability for fibre fabrication.

The effect on structure and property of adding fluoride into Tm3+ doped lead-germanate glass was established and verified experimentally. It was found that up to 10 mol% of fluoride could be introduced into our original lead-germanate composition while retaining the high thermal stability ideal for fibre fabrication. Much improved spectroscopic features, namely increased fluorescent lifetimes from 3H4 and 3F4 levels in Tm3+ with increasing fluorine content, were observed. At the same time it was found that the radiative properties of Tm3+ were left unchanged by fluoride addition, indicating that reduced multiphonon relaxation was responsible for the increased fluorescent lifetimes. This was well explained and foreseen by our established structure-property relation in terms of adding fluorine to the glass. In conclusion, fluoro-germanate glass shows advantages over germanate glass in optical properties and over fluoride glass in chemical and mechanical properties for practical fiber device applications. [Presentation slides]

Refractive index changes as high as ~5 x 10-4 in a phosphorus-doped germanosilicate fibre were observed for the first time without hydrogen loading during grating formation with a 193 nm laser. Dynamics was studied and it was found that Type IIa gratings was easily formed in this fibre.

Optical fibre amplifiers have seen widespread adoption in terrestrial and undersea applications and various projections suggest a billion dollar market within the next five years. Their ready availability from a number of suppliers has spurred major developments in soliton communications, WDM systems, CATV and, in the near future, the distribution network. By effectively removing the problem of fibre-loss, the fibre amplifier has been instrumental in the demise of major projects on coherent transmission and on fluoride fibre. By removing the loss barrier, the amplifier in turn has spurred world-wide research on dispersion compensation, both for newly-installed fibre links and for uprating the installed fibre base. Now that optical fibre amplifiers are virtually a commodity, it is timely to take stock of present amplifier performance and ask what could be improved, as well as to predict what might be expected in the near future. The talk poses a number of possible scenarios, for example, the ready-availability of a low-cost 1.3µm amplifier. What role might be played by semiconductor amplifiers, following impressive recent reports of their performance? Is there a need for amplifiers at other wavelengths in the near infra-red, both for telecoms and LIDAR applications? The talk will review the possibilities in all these areas and attempts some predictions for future developments.

We report on the demonstration of optical fibres based on the Ga:La:S system. Core-clad structures have now been fabricated by the rod and tube method and pulled into lengths over 200 metres. Transmission over the wavelength range 1.0 to 6.5 microns, with fibre loss approaching the absorption and scattering level of the bulk glass is obtained, opening the possibility of new fibre device applications of this promising glass host. Progress towards low-loss single-mode fibre will be outlined along with applications a optical fibre amplifiers operating at 1.3 microns and fibre lasers at wavelengths in the 3-5 micron region.

Index change (~1.4 x 10-3) of 3 times larger than in germanosilicate fibres is demonstrated. Both fibre loss at 1.55µm and high temperature stability of the gratings are much improved comparing to those in B-codoped germanosilicate fibres.

We report on the performance of a low timing-jitter, diode-driven, Nd:YLF pumped 5ps, 30-40 GHz soliton source based on beat signal conversion in a dispersion decreasing fibre. We demonstrate for the first time data encoding at 40 Gbit/s and transmission of the pulse trains over 205 km.

Strong photosensitive gratings of both type I and II have been demonstrated in germanium-free tin-doped phosphosilicate fibre. An index change of ~1.2 x 10-3 has been achieved in 40 seconds of exposure. This is the first time that such strong gratings were written in a phosphorous-containing silica fibre and that type II gratings were written in a germanium-free fibre.

The idea of varying the axial distribution of dispersion along a length of optical fibre as a means of manipulating and controlling the soliton supporting nature of the fibre and thereby the characteristics of soliton pulses propagating through the medium has been around for some while. A number of specific applications have been suggested in particular techniques for bright and dark soliton generation, pulse compression and most notably techniques for high frequency soliton transmission. The experimental realisation of most of these techniques however has been hindered by difficulties in the reliable fabrication of dispersion varying fibres. A technique for the fabrication of such fibres was first developed by workers at General Physics Institute, Moscow. Control of the waveguide dispersion was achieved by active control of fibre diameter during the pull. Fibre lengths of up to 2km were fabricated and successfully used in the first experimental demonstrations of high frequency (>60 GHz) bright soliton generation and pulse compression. Subsequent to these first experimental results a number of other groups have commenced fabrication programs on such fibres, extending the techniques to fibre lengths of 40km. In this presentation we describe our latest achievements in Dispersion Decreasing Fibre (DDF) fabrication and report on two applications of the technology. Firstly, we describe a robust, diode-pumped, 40GHz bright soliton transmitter, and secondly we demonstrate loss compensation in a 38km loss-matched dispersion varying fibre.