1,720,972 research outputs found
Fabrication and characterisation of circularly birefringent helical fibres
No full textA technique for fabricating helical-core circularly birefringent fibres is reported. Extremely high levels of circular birefringence are achieved (B = 2.1 x 10-4 at 633nm). Because of its unique structure, this fibre remains single-mode up to V values of 25
High-performance composite metal/glass fibre polarisers
No full textContinuous composite metal/glass single-mode fibre polarisers have been fabricated. The devices exhibit an extinction ratio greater than 48dB with an insertion loss of less than 1dB at 830nm. Moreover, an extinction ratio of more than 40dB can be obtained over a 250nm spectral window ~1300nm
Helical-core circularly-birefringent fibres
No full textA new type of circularly-birefringent fibre is demonstrated based on the optical rotation which occurs in a helical core fibre. The birefringence is an order of magnitude higher than that obtained with previous fibres
Fabrication of polarisation-maintaining fibres using gas-phase etching
No full textA new fabrication technique for the production of high-birefringence fibres is described. The process is shown to produce fibres with a cross-sectional geometry which is close to the optimum predicted by stress analysis. As a result, fibres with extremely short beat lengths (0.55 mm at a wavelength of 633 nm) have been produced
Polarisation characteristics of fibres for coherent detection systems
No full textCoherent transmission systems utilising the optical heterodyning principle require a stable polarisation state for both the local oscillator and incoming signal waves. For a fixed input state the output polarisation of a single-mode fibre in general varies according to the prevailing environmental conditions. Efficient heterodyning can be obtained only by stabilising the output state. This may be accomplished by either (i) designing the fibre polarisation properties to be intrinsically immune to the environment, or (ii) by actively controlling the output to maintain the required state of polarisation at the detector. In this paper the design, manufacture and properties of fibres suited to both these approaches will be considered
Circularly birefringent single-mode optical fibres
No full textThe rotation of polarised light which occurs in a twisted anisotropic medium is exploited to produce very high circular birefringence in single-mode optical fibres. Beat lengths of less than 5 mm have already been achieved in some preliminary experiments
Thermal properties of highly birefringent optical fibres and preforms
No full textTemperature cycling of highly birefringent optical fibers and preforms has been used to investigate the thermal properties of bow-tie and elliptically clad structures. The thermal hysteresis of the birefringence is shown to be a direct consequence of the thermal history of the fiber or preform and has been related to volume changes in the stress-producing borosilicate sections. Annealing increases the axial stress as well as the stress anisotropy and hence the birefringence. Increases of up to a factor of 2 in the birefringence on suitable thermal treatment indicate a new method for further improvement of high birefringence fibers. The implications of the results in the design, fabrication, and use of such fibers are discussed
Broadband metal/glass single-mode fibre polarisers
No full textContinuous metal/glass fibre polarisers incorporating Ga or In/Sn alloy have been fabricated. An extinction ratio of greater than 37dB with an insertion loss of less than 1 dB can be obtained over a 250nm spectral window around 1300nm. Extinction ratios as high as 52dB have been measured at 830 nm
Analytic solution for the birefringence produced by thermal stress in polarization-maintaining optical fibers
No full textPolarization-maintaining optical fibers are usually made by inducing a large anisotropic thermal stress in the core so that it appears highly birefringent. A simple analytic solution has been found for the birefringence in terms of the cross-sectional distribution of the high-expansion material used to create the thermal stress. The analysis is able to predict optimal structures which efficiently utilize the available stress and thus maximize the birefringence. It is shown that the optimum structure has a cross-sectional geometry resembling a bow-tie. Design rules are given whereby the dimensions may be chosen and these are verified in a simple experiment
Single-polarisation operation of highly birefringent bow-tie fibres
No full textExperimental results show that bow-tie fibres with high levels of stress-induced birefringence can be operated such that they support only a single linearly polarised mode. Under these conditions the loss of the fibre is 5 dB/km for the guided mode and 55 dB/km for the suppressed mode. For short-length operation as a polariser, extinction ratios as high as 50 dB/m have been obtained
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