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.<>     

Optical-fibre flowmeter

A technique is described for the measurement of fluid flow using an optical-fibre transducer. The flowmeter has no mechanical moving parts and causes no pressure drop in the liquid stream. The optical system and the detection electronics are intrinsically very simple. Results from a prototype meter are given, and improvements in this design, particularly in the turbulence characteristics of the meter tube, should improve measurement accuracy to an estimated ±5%.     

Reflection circular polarisers

Conducting surfaces corrugated with rectangular grooves which convert linearly polarised incident waves to circular polarisation are described. Design data for normal incidence and for incidence at 45° to the normal are given.     

Optical-fibre connector

A connector for joining plastics-coated, multimode fibres has low insertion loss and good environmental stability. The connector is suitable for field installation by a portable installation fixture and using simple tools.     

Optical-fibre phase modulator

A clip-on piezoelectric transducer is described which may be easily attached to a plastics-coated optical fibre and used to phase modulate signals within the glass fibre. The technique is applicable to a 1-way optical telemetry highway.     

Optical-fibre waveguide with a single-crystal core

Some properties of a new single-crystal optical fibre are described. The fibre is constructed with the nonlinear optical crystal meta-nitroaniline as its core. In its present configuration, the fibre acts as an effective polariser. Alternative configurations may yield a number of electro-optic fibre devices.     

Optical-fibre tap with low insertion loss

We report a fibre-tapping element which uses part of the insertion loss of a fibre connector or splice as useful optical signal power. A tapping fraction of up to 70% has been measured with a total insertion loss of 0.22 dB.     

Short W-tunnelling fibre polarisers

Measurements of a 4·8 cm W-tunnelling fibre polariser show a 39 dB polarisation extinction ratio over a useful bandwidth of 4% centred at 633 nm     

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     

Optical-fibre excitation by finite beams

Simple formulas are given for trapped-mode power excited by a spot of light illuminating an optical fibre. The results are used to discuss features of Gaussian-beam excitation.     

Optical-fibre loss for high-speed drawing

The influence of high-speed drawing on optical-fibre losses is investigated. Transmission losses near the 0.85 ?m wavelength remain about 3 dB/km for drawing speeds in the range 20?300 m/min. Lower OH-ion content and increased colouration are observed at higher speeds.     

Optical-fibre unit for optical submarine cable

An optical-fibre unit with a strain-relaxing effect is proposed for realising a highly reliable optical-fibre submarine cable. The basic design of the new type of optical-fibre unit means that optical fibres are not subjected to the same strain as the fibre unit directly when the unit is elongated. The test result of the strain-relaxing effect of an experimental optical-fibre unit was about 0.2%, and optical fibres returned to the original position in the fibre unit after the tension was released.     

Optical-fibre coupling to high-silica channel waveguides with fibre-guiding grooves

A practical coupling technique between high-silica multimode channel waveguides and optical fibres has been demonstrated using guiding grooves formed simultaneously with waveguides on a substrate. The fibre-waveguide (15 mm long)-fibre insertion loss was 1.23 dB.     

Optical-fibre end preparation by spark erosion

Before splicing two optical-fibre waveguides, endfaces have to be prepared which are plane and perpendicular to the fibre axis A new method for preparing endfaces is proposed which is simple and reliable. The fibre surface is eroded by sparks and the fibre is then broken by hand.     

Single-mode transmission selective integrated-optical polarisers in LiNbO3

Novel low-loss integrated-optical polarisers and analysers are reported for single-mode operation in LiNbO3 waveguides. The operation is based on the polarisation-selective transmission of short proton-exchanged waveguide channels filling discontinuities in Ti-diffused channel waveguides. Extinction ratios exceeding 32 dB are experimentally demonstrated with 0.8 dB excess loss.     

Small periodicity FSS screens with enhanced bandwidth performance

A novel approach for obtaining small periodicity frequency selective surface (FSS) screens with enhanced bandwidth performance is proposed. The issue of miniaturising FSS unit cells has gained extreme importance in recent metamaterials applications. To this end several procedures have been suggested in the literature. However, such procedures usually result in a bandwidth degradation as long as miniaturisation is improved. On the contrary, the bandwidth performance of the structures here presented is enhanced as the FSS periodicity gets smaller. Application of such structures to the synthesis of artificial magnetic conductors are also presented.     

Annular ring coupled circular patch with enhanced performance

An annular ring loaded circular microstrip patch antenna is presented which reduces the excitation of surface waves. This configuration, as compared to a conventional circular patch, is no more difficult to fabricate, has a greater impedance bandwidth, much higher surface wave efficiency and higher gain. Both impedance behaviour and radiation characteristics of the modified patch are considered. Very good agreement between experiment and theory is achieved     

Optical polarisers of high extinction ratio integrated on oxidised silicon substrate

Theoretical performances of integrated polarisers realised by metallic coating of planar waveguides on oxidised silicon substrate are discussed. Measurements are reported for aluminium and chromium-gold coatings, giving extinction ratios in excess of 40 dB, with attenuations (TE polarisation) lower than 1 dB, and interaction lengths of about 2 mm.     

Optical-fibre Fabry?Perot frequency discriminator for communications applications

We demonstrate the use of a fibre Fabry?Perot interferometer as an optical frequency discriminator for communications applications. The operation of this device has been characterised for sinusoidally phase-modulated signals. Distortion results are presented for several modulation frequencies and modulation depths. It is observed that distortion is acceptably low for modulation frequencies up to nearly the spectral width of the Fabry?Perot bandpass.     

Vertical-cavity surface-emitting laser active regions for enhanced performance with optical pumping

We have developed an improved active region design for optically pumped vertical-cavity surface-emitting lasers. The design makes use of carrier-blocking layers to segment the absorber and promote uniform carrier populations in the quantum wells with pump efficiencies near 75%. A model to calculate the carrier distribution in the active region and a design methodology are presented along with a metric to describe the carrier uniformity in the quantum wells. Experimental verification of the performance improvements shows an over 50% reduction in device thresholds and an increase of 20/spl deg/C in maximum operating temperatures.