Finite cladding effects in highly birefringent fibre taper-polarisers

Experimental results show that the refractive index of the outside medium affects the performance of fibre polarisers made by tapering high-birefringent bow-tie fibres. Both narrowband and wideband polarisers have been constructed having extinction ratios of 35 and 26 dB, respectively.     

Bandwidth-limiting effects in coherent optical communications systems based on polarisation-preserving fibres

Interference effects caused by small polarisation misalignments are shown to produce a significant nonlinear distortion of a coherent analogue FM signal transmitted via polarisation-preserving fibres. High-quality transmission of a 100 MHz sinusoidal signal over 10 km of fibre requires alignment accuracies of output and input polarisers better than 2.5 degrees.     

Bidirectional optical transmission using polarised light waves

Bidirectional optical transmission using polarised light waves is demonstrated for the first time. Transmission of 100 Mbit/s signals over 13.6 km of polarisation-maintaining fibre occurs simultaneously in both directions at 1.55/?m. LD transmitters with polarisation-maintaining fibre pigtails, polarisation-maintaining fibre couplers, fibre polarisers and Ge-APD receivers are used.     

Polarisation insensitive operation of ferroelectric liquid crystaldevices

The accepted mode of operation of ferroelectric liquid crystal devices is to place them between crossed polarisers. The authors demonstrate that such devices may be used as diffractive modulators without polarisers. A one-to-many polarisation independent switch is presented for singlemode optical fibre networks, based on dynamic liquid crystal holograms     

High performance metal-clad fibre-optic polarisers

The principle of polarisation-selective resonant coupling between a guided optical mode and a metal surface plasmon wave through the evanescent field of the fibre was used to develop fibre-optic polarisers with extinction ratios in excess of 70 dB and losses less than 0.5 dB at 850 nm wavelength. The influence of fibre and thin-film parameters on the polariser performance was investigated both theoretically and experimentally. An improved measurement method for the polariser extinction ratio is demonstrated.<>     

Fibre-embedded optical isolator

A fibre-embedded optical isolator without a lens element is proposed and fabricated. The isolator consists of beam-expanding fibres, laminated polarisers and a Faraday rotation garnet. Backward and forward losses at 1.3 mu m wavelength are 36.9 and 1.6 dB, respectively.<>     

Spacing-tunable multiwavelength fibre laser

A novel spacing-tunable multiwavelength fibre laser is proposed and demonstrated. A spacing-tunable comb filter consisting of polarisers and a polarisation maintaining fibre (PMF) was used. By changing the pressure position on the PMF, the wavelength spacing can be controlled. 1.46 nm-spaced nine wavelengths and 0.73 nm-spaced 14 wavelengths, when the pressure point was 4 and 8 m, respectively, has been demonstrated     

Measurement of group birefringence and dispersion of polarisation maintaining erbium-doped silica fibre

The group birefringence and chromatic dispersion of a polarisation maintaining bow-tie erbium-doped silica fibre have been measured in the wavelength range 1.2-1.68 mu m by an interferometric measurement technique without any polarisers. The group birefringence is lower than that of a conventional bow-tie fibre and the zero dispersion wavelengths of the two polarisation modes are shifted to 1.613 and 1.630 mu m.<>     

New configuration of polarisation-independent isolator using a polarisation-dependent one

In optical communication systems using fibre amplifiers, polarisation-independent isolators with high isolation are desirable. A simple effective method to realise polarisation-independent optical isolators is proposed. The isolator consists of spatial walk-off polarisers, half-wave plates, and a conventional polarisation-dependent isolator. The measured forward loss of the assembled isolator is 0.38 dB and 0.32 dB at 1.3 and 1.55 mu m wavelengths, respectively. The backward loss is 55.5 dB and 63.5 dB at 1.3 and 1.55 mu m wavelengths, respectively.<>     

TE-pass and TM-pass waveguide polarisers with buried birefringentpolymer

TE-pass and TM-pass waveguide polarisers in polymer waveguides using a buried layer of highly birefringent polyimide are presented. The two polarisers are fabricated based on a consistent process to insert polyimide for the buried ribs in TE-pass polarisers and for lateral cladding in TM-pass polarisers: respectively. Polarisation extinction ratios of 35 and 40 dB are obtained for the TE-pass and TM-pass polarisers, respectively     

Chalcogenide holey fibres

The fabrication of the first non-silica holey or microstructured optical fibre is reported. The chalcogenide glass gallium lanthanum sulphide was used. Applications of such fibres include optical switching, high power-delivery, acousto-optic devices, air-guiding fibres, fibre sensors, mid-IR devices, amongst others. In addition, holey fibre technology provides an improved route towards fabricating singlemode compound glass fibres     

Optical fibres coated with a UV-curable material at a speed of 12 m/s

The letter reports the successful achievement of coating silica fibre at a rate of greater than 10 m/s. We draw 125 ?m-diameter fibres from silica rods and preforms, and coated in-line with UV-curable material. All fibres were proof-tested at two different stress levels of 0.7 and 1.4 GN/m2 We also checked the transmission properties of the fibre. It is found that the optical properties of the fibre remain the same while the mechanical properties are comparable to those of the fibres coated at a low speed.     

Nitrogen doped silica core fibres: a new type ofradiation-resistant fibre

γ-radiation-induced loss spectra were measured in a radically new optical fibre with a refractive index profile shaped by nitrogen-doped silica. The fibre showed unique radiation resistance comparable only to the best results for pure silica core fibres and much better than the radiation resistance of germanosilicate fibres     

Higher-density single-mode optical fibre cables than 1 fibre/mm2, containing hundreds of fibres

A slotted-rod structure was investigated to obtain the maximum fibre density of high-fibre-count cables. A 500-fibre cable with a fibre density of 1.5 fibres/mm2 was designed and manufactured. The manufactured cable was composed of 10-fibre ribbons inserted into the designed slots. The optical losses of the cabled single-mode fibres were confirmed to be stable at 1.3 and 1.55 ?m. This cable has the highest fibre density of existing optical cables.     

Optical fibre cable with ultra-high density of more than 3 fibres/mm/sup 2/

Proposed is an ultra-high-density 100-fibre cable that uses 0.25 mm diameter mono-coated optical fibres with a low bending loss. This cable has great advantages in terms of cable weight and diameter and will be easy to install in a small space in underground ducts and/or on residential and business premises. The optical fibre with the optimum low bending loss is selected experimentally to obtain optical fibre cable with the maximum fibre density. A 100-fibre cable with a fibre density of more than 3 fibres/mm² and a cable diameter of 6.3 mm was obtained     

Photosensitivity measurement in optical fibre with Bragg grating interferometers

A new technique based on two low-finesse fibre Bragg grating Fabry-Perot interferometers to study photosensitivity in optical fibre is presented. Phase evaluation using the Fourier spectra allows precise determination of the evolution of the refractive index with accumulated fluence. Results are given for different germanium/boron codoped fibres and for hydrogen-loaded fibres.     

Sub-stoichiometric functionally graded titania fibres for water-splitting applications

The photo-electro-chemical (PEC) splitting of water requires semiconductor materials with a minimum energy gap of 1.23 eV along with conduction and valence bands overlapping the oxidation of H₂O and reduction of H⁺ respectively. The aim of this work is to overcome the limitations of stoichiometric titania by manufacturing fine scale fibres that exhibit a compositional gradient of oxygen vacancies across the fibre length. In such a fibre configuration the fibre end that is chemically reduced to a relatively small extent performs as the photoanode and the oxygen vacancies enhance the absorption of light. The fibre end that is reduced the most consists of Magnéli phases and exhibits metallic electrical conductivity that enhances the electron-hole separation. The structure and composition of the functionally graded fibres, which were manufactured through extrusion, pressureless sintering and carbo-thermal reduction, are studied using XRD and electron microscopy. Electrochemical impedance spectroscopy measurements were performed in a three-electrode electrochemical system and showed that the oxygen vacancies in the functionally graded fibres affect the flat band potential and have increased carrier density. The efficiency of the system was evaluated with PEC measurements that shows higher efficiency for the functionally graded fibres compared to homogeneous TiO₂ or Magnéli phase fibres. The functionally graded and fine scale fibres have the potential to be used as an array of active fibres for water splitting applications.     

Bandwidth and loss measurements of graded-index microstructured polymer optical fibre

The first bandwidth measurements of graded-index microstructured optical fibres are presented, demonstrating that this novel fibre geometry can provide high-bandwidth multimode polymer fibres without the need for complex doping techniques as with conventional polymer fibres.     

Superfluorescence from Yb- and Yb–Er-doped phosphotellurite glass fibres

Short length, air-clad, multimode fibres were fabricated using high concentration Yb- and Yb–Er-doped phosphotellurite glass. Superfluorescent light sources are obtained by optically pumping the fibres using a 980 nm laser diode. Ytterbium-doped fibre showed amplified spontaneous emission (ASE) in the 1000–1100 nm wavelength region, whereas Yb–Er-codoped fibre in both 1000–1100 nm (due to Yb³⁺ ions) and 1450–1650 nm (due to Er³⁺ ions) wavelength regions. The ASE spectra from the fibres are compared for different fibre lengths and pump powers. The observed change in the ASE spectral shape and the shift in peak wavelength with the length of the optical fibre is discussed.     

Thin-film polariser for Ti:LiNbO3 waveguides at ?=1.3?m

Thin-film polarisers using a dielectric buffer layer and a metallic overlay on Ti:LiNbO3 channel waveguides for ? = 1.3 ?m have been designed and fabricated. The TM mode extinction ratio better than 35 dB and negligible TE mode excess losses have been measured with Si3N4/Al polarisers 2 mm long.