Bend behaviour of polarising optical fibres

Experimental results are presented which show how both bend radius and the orientation of the fibre in the bend considerably affect the single-polarisation operation of bow-tie fibres.     

Polarisation preservation in multimode fibres

Birefringent multimode fibres have been found to preserve polarisation except for one mode near cutoff. Experimental observations and theoretical considerations show that polarisation ratios better than 20 dB are possible, offering the potential for building polarisation-sensitive multimode fibre components.     

Polarisation conservation in single-mode fibres

There exist proper orthogonal elliptical polarisation states, which are maintained over long fibre length without converting. When one of the proper polarisation states is excited, orthogonal polarisation less than ?40 dB is confirmed after 5 km single-mode fibre transmission. It is also proposed that twisted single-mode fibres show a high degree of polarisation for any incident polarisation state. The polarisation characteristics are hardly affected by external perturbations.     

Polarisation maintenance in circularly birefringent fibres

The feasibility of twisted circularly birefringent polarisation maintaining fibres is investigated. It is shown that the twist rate required to provide immunity from external effects is excessively large.     

Fabrication of long-length high-strength single-mode silica fibres

The letter reports an alternative approach to the realisation of long, low-attenuation, high-strength single-mode optical fibres suitable for high bit-rate transmission over long distances in adverse environments. We show that low attenuation (less than 0.45 dB km) can be achieved in combination with high proof-test levels (1% ? 2% strain) in fibre lengths greater than 5 km, using natural fused-quartz tubing, and report a 15 km fibre having an attenuation of 0.44 dB km which survived a proof test at 1% strain.     

Polarisation state stabilisation in optically nonlinear birefringent fibres

It is shown that a stable polarisation state can be achieved in linearly birefringent fibres by introducing an initial twist. When the twist is properly terminated, the random coupling of power can balance the linear and ronlinear couplings along the straight section of the fibre.     

Polarisation characteristics of graded-core stress-applied polarisation-maintaining fibres

Polarisation characteristics of stress-applied polarisation maintaining fibres having graded-index cores with ?-power profile are investigated. It is found that when the stress-applying parts approach the core, the dependence of modal birefringence B on the normalised frequency v for the triangular profile is considerably different from that for the step-index profile, and the absolutely single-mode operation can be easily realised compared with the conventional step-index profile.     

Polarisation mode dispersion measurements in long single mode fibres

A frequency domain determination of polarisation mode dispersion in single mode fibres is described, which allows one to obtain directly the group delay difference for long fibres. The results of such measurements are shown on a birefringent fibre with elliptical cross-section which maintains an extinction ratio between linearly polarised eigenstates greater than 10 dB over 1 km.     

Polarisation mode dispersion measurements in long single mode fibres

A new method to measure polarisation mode dispersion is described, in which the accuracy is more than 0.1 ps. 0.17 ps polarisation mode dispersion was obtained for about 1 km length of fibre. The result is compared with the retardation obtained for a short length of the fibre.     

Polarisation fluctuation of submarine-cabled single-mode optical fibres in ocean installation

Polarisation fluctuations of the power spectrum with time in an optical fibre submarine cable installation are reported for the first time. It was found that the power spectrum of polarisation fluctuation was less than 60 Hz, and the maximum power spectrum was between 5Hz and 10Hz during the cable installation within a maximum cable tension of 18 kN (?1.8 tons) and a cable laying speed of 3.5 n mile/h, respectively.     

Polarisation characteristics in long length v.a.d. single-mode fibres

Polarisation characteristics in long single-mode fibres are investigated. Single-mode fibres used in the experiment have been fabricated by the v.a.d. (vapour-phase axial deposition) method. It was shown from the measurements on a 21 km single-span v.a.d. fibre that the state of polarisation of the incident light beam can be maintained over a long length when the incident plane of polarisation coincides with the major or minor axis of the single-mode optical fibre.     

Polarisation selective all-fibre Fabry-Perot filters with superimposed chirped Bragg gratings in high-birefringence fibres

Periodic highly birefringent filters with 50 and 100 GHz free spectral range and finesse of up to 20 are demonstrated. With a polarisation peak separation of 25 GHz, the polarisation crosstalk was measured to be less than -16 dB.     

Comment: Polarisation characteristics in long length v.a.d. single-mode fibres

An assumption stated in a previous letter, concerning states of polarisation of a single-mode fibre, is criticised. Experimental proof is required to support the assumption.     

A dispersive polarising MM-wave interferometer

The layout and operation of a polarising double beam interferometer is described which is suitable for measurements of the complex refractive index in the frequency range from 1 to 15 wavenumbers using coherent sources. Phase shakers are applied to average over the standing wave patterns.     

Fibre-optic polarising beam splitter employing birefringent-fibre coupler

An in-line fibre-optic polarising beam splitter, consisting of a fused birefringent-fibre coupler, is reported. Splitting of the orthogonally polarised lights was accomplished by increasing the difference of coupling ratios for the two polarisation modes. When a light at 1.402 ?m wavelength was coupled to the input lead, each polarisation was split on to different output leads, showing extinction ratios of more than 17 dB in both leads.     

关于空气间隔棱镜空气隙厚度的再研究

空气间隔偏振棱镜的气隙厚度可无穷减小,以获得大的半视场角,但其消光比将受到严重影响。本文给出获得高消光比的条件。     

Polarisation modulation in long couplers

A simple mathematical model of long tapered couplers shows that the modulation of the output power due to polarisation has a period which varies inversely with the square of wavelength. This prediction is in agreement with experimental measurements.     

Design of a corrugated polarising main reflector

The realisation of a polarising main reflector for use in a W-band Cassegrain antenna system is described. The main reflector has rectangular grooves cut in its entire surface to change the polarisation from linear to circular. In addition, the use of the FD-TD (finite difference time domain) method for predicting the performance of an axisymmetric dielectric cone subreflector is shown.<>     

Polarisation independent bandpass FSS

The spectral transmittance of a frequency selective surface (FSS), which consists of two free-standing arrays of short-circuited nested annular slots, is presented. The FSS was designed to provide a minimum of 20 dB isolation between the frequency bands 316.5-325.5 and 349.5-358.5 GHz when the filter operates in the TE and TM planes at 45deg incidence. Experimental results, which are in close agreement with the computed transmission coefficients, show that the maximum insertion loss is 0.9 dB, and the minimum cross-polar discrimination is at least 21 dB in the passbands. The FSS yields virtually identical spectral responses in the two polarisation planes over the frequency range 315-359 GHz.