Improved spectral characteristics of a single-mode semiconductor laser using a fibre grating and a reduced laser diode length

Use of a reduced laser diode length with a fibre Bragg reflector leads to decreased mode-hopping and a factor of 3 improvement in temperature stability of the lasing wavelength over Δ T=22°C. Single frequency output power of 1.7 mW in the fibre with 45 dB side mode suppression was obtained

Dispersion measurements of chirped fibre gratings

A wavelength scanning interferometric technique has been used to provide phase dispersion and time delay measurements of photorefractive fibre gratings with sub-picosecond time-delay and 3µm wavelength resolutions for the first time. Chirped fibre grating filters for dispersion compensation in long fibre telecommunications links have been fully characterised

Tunable dispersion compensating grating in a 10Gbit/s 100-220km step index fibre link

Chirped fibre gratings are of particular interest for compensating the dispersion (~17ps/nm.km @ 1.55µm) of installed step index (SI) fibre links since they are compact, low-loss, polarisation-insensitive and offer high negative-dispersion. In this paper we present a detailed investigation of the bandwidth-dispersion trade-off for a fixed (40mm) length tunable linearly-chirped fibre grating. In addition we demonstrate that such a grating can precisely compensate the dispersion in a 10Gbit/s transmission experiment for SI fibre lengths in the range 103-216km

Strong photosensitive gratings in tin-doped phosphosilicate optical fibres

Strong photosensitive gratings of both type I and II have been demonstrated in germanium-free tin-doped phosphosilicate fibers. The fibers have strong absorption (~0.8 dB/µm) at the writing wavelength of ~248 nm because of tin doping. This is the first time to our knowledge that such strong gratings have been written in a phosphorous-containing silica fiber without low-temperature hydrogenation and that type II gratings have been written in a germanium-free fiber. The tin-doping technique can be used to write gratings in rare-earth-doped phosphosilicate fibers and to produce low-N.A. fibers for mass production of strong single-pulse type II gratings during fiber pulling

Chirped fibre gratings for temperature-independent strain sensing

A temperature-independent strain sensor using a chirped fibre grating is demonstrated with a strain resolution of 0.1 % over the total measurement range

Chirped fibre Bragg gratings fabricated using etched tapers

We have demonstrated a technique capable of controllably producing fibre Bragg gratings with any arbitrary chirp profiles. The technique involves making a taper on the outer cladding of a section of fibre by differential etching along the length of the fibre. A grating is then written over the taper in the usual manner. A strain gradient develops over the taper when a tension is applied to the fibre and this strain gradient is used to introduce a chirp in the gratings. The chirp can be introduced either during or after grating writing. Tension can be used to tune the central wavelength and chirp the gratings if desired. Linearly chirped gratings with bandwidth up to 4.8nm have been produced to demonstrate the controllability of the technique. These gratings are ideal for use in dispersion compensation and optical pulse shaping

Fabrication of chirped fibre gratings using etched tapers

A technique for fabricating fibre gratings with an accurately controlled chirp profile is demonstrated. It involves writing a grating over a section of fibre, the cladding of which has been tapered by etching in HF acid. A strain gradient along the taper is used to produce the chirp either during or after writing. Linearly chirped gratings with bandwidth up to 4.8nm have been demonstrated. Transmission filters have also been demonstrated when a step is made in the taper

Fabrication of high numerical aperture fluoroaluminate fibres

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

Spectral characteristics of a reduced cavity single-mode semiconductor fibre grating laser for applications in dense WDM systems

Use of a reduced laser diode length (150µm) with a short fibre Bragg reflector leads to decreased mode-hopping and a factor of 3 improvement in temperature stability of the lasing wavelength over Δ T=22°C. CW single-frequency output power of 1.7mW in the fibre with 45 dB side mode suppression was obtained

A dispersion tunable grating in a 10Gbit/s 100-220km step index fibre link

A dispersion tunable 40mm fibre grating has been employed in a 10Gbit/s, step-index fibre link. Dispersion is effectively compensated for span lengths in the range 103-216km. However, at the longer spans the increased dispersion of the grating results in a reduced bandwidth and therefore its centre wavelength is found to be critical (± 0.005nm)