Effects of high temperature and pressure on silica optical fibre sensors

We report on the 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. Amorphous carbon hermetic coating has shown a reduction of these effects by an order of magnitude at 300°C. These results have strong implications for the deployment of fibre sensors in oil wells

Expanded-beam connector design study

A theoretical analysis of an expanded-beam connector is presented, and it is shown that considerable scope exists for optimization of the design. A ray-tracing technique is used to quantify the importance of various parameters in determining the insertion loss. The design guidelines are presented in graphical form, and their usefulness is demonstrated in several examples of practical interest

Noise characteristics of erbium-doped fibre amplifier pumped at 980nm

We show that quantum-limited noise operation of an erbium-doped fibre amplifier is possible when pumped at 980nm. A noise figure of 2.9±0.4dB was measured for pump powers of only 5.8mW, consistent with a population inversion factor close to unity

An optical fibre switch employing a Sagnac interferometer

Local area networks and high-bit-rate telecommunications demand fast switches for modulators, re-routing and demultiplexing. Optically-driven nonlinear optical switches based on intensity-dependent phase shifts in an optical fibre have been demonstrated at femtosecond switching speeds. An all optical switch has the benefit of compatibility with the rest of the optical network and its availability would considerably enhance the capabilities of optical transmission systems. An optical fibre switch which exploits the non-linearity in silica fibre may be polarimetric or interferometric. However, most configurations are very environmentally unstable and suffer large phase shifts due to temperature and vibration. The exception is the Sagnac interferometer, which uses the same path for both interfering beams and is therefore only sensitive to perturbations that occur in a time less than the loop transit time. We describe here the basic theory of operation of the Sagnac fibre switch, followed by an experimental demonstration of a stable switch operating on a picosecond time scale

Novel fabrication technique for planar glass waveguides

A novel technique has been developed for the deposition of low-loss planar glass waveguides by directly spin coating from the liquid, thus overcoming the problems of reproducing glass stoichiometry when depositing from the vapour

Compact high-power tunable three-level operation of double cladding Nd-doped fiber laser

We present a compact high-power continuous-wave tunable neodymium-doped double cladding fiber laser operating on three-level 4F3/2 - 4I9/2 transition with a maximum output power up to 810 mW. At 926.7 nm, it has a maximum slope efficiency of 49.3% against absorbed 808-nm pump. By compressing the fiber Bragg grating, 15-nm tuning range is achieved

Frequency doubling in Ga:La:S optical glass with microcrystals

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

Twin core non-linear couplers with gain and loss

Twin core nonlinear couplers that include gain and loss are examined. Of various structures (ranging from couplers composed of two active cores and two lossy cores to those composed of one active or lossy core and one conventional core) considered, the most interesting case is the coupler composed of' one core with a certain amount of gain and the other core with an equal amount of loss where ideal low power switching is possible in a comparatively short coupler. The presence of gain in one core is found to be responsible for reduction in switching power and/or shortening in the device length, while the introduction of the loss in the other core plays a role of idealizing switching. A physical model is also presented to explain the demonstrated merits based on the operation of linear couplers with gain and loss

Second-generation erbium-doped fibre amplifiers for advanced optical communications

The erbium doped fibre amplifier (EDFA) [1] has seen rapid development and is now established as a key component in future optical networks. To date, EDFA development has been driven by specific requirements, primarily the single-channel, point-to-point fibre links. There are, however, many more applications which may require, for example, either broadband or narrowband amplifiers and signal-processing functions. In addition, non-telecommunication applications can benefit enormously by the use of EDFAs

Development of low and high birefringence optical fibres

The polarization properties of single-mode optical fibers are easily modified by environmental factors, While this can be exploited in a number of fiber sensor devices. it can be troublesome in applications where a stable output polarization-state is required. Fibers with both low and high birefringence have been developed to enhance or diminish their environmental sensitivity, and recent progress in each area is reviewed. Low-birefringence fibers are described which are made by spinning the preform during the draw. In addition. developments in high-birefringence fibers which maintain a polarization state over long lengths are summarized. The effect on performance of external factors such as bends, transverse pressure, and twists is analyzed. Consideration is also given to polarization mode-dispersion as a potential limiting factor in ultrahigh bandwidth systems