A.D. Kersey

A simple fibre Fabry-Perot sensor

Abstract A simple fibry Fabry-Perot sensor is described in which the uncoated cleaved ends of a length of single mode fibre are employed as the mirror surfaces to produce high visibility cosine squared fringes in the back reflected light. In an accelerometer configuration the device displayed a below resonance sensitivity of ⩾200 rads/g.

Non-contact surface vibration analysis using a monomode fibre optic interferometer incorporating an open air path

A very high sensitivity non-contacting vibration analysis system based upon a monomode fibre optic Mach Zehnder interferometer incorporating an open air path is described. The system was operated in both a closed loop limited tracking range (>105) homodyne mode and an effective infinite tracking range novel pseudo-heterodyne mode. For periodic signals, amplitude detection sensitivities of approximately 2*10-10 m at 10 Hz to 5*10-11 m at 10 kHz have been demonstrated for both modes of operation.

Single-mode fibre-optic holography

A fibre-optic holographic system is described in which the functions of all the optical components conventionally used to produce holograms-such as beam splitters, mirrors and beam expanding spatial filters-are performed with single-mode optical fibres. Design considerations are discussed, and an electronic servo system which provides compensation for thermally induced phase shifts is described.

All single-mode fibre optic holographic system with active fringe stabilisation

The recording of reflection holograms through single-mode optical fibres has been demonstrated. An all fibre Michelson interferometer formed by the cleaved ends of the object and reference fibres was utilised to provide phase compensation in the fibre arms via an electronic servo in conjunction with a piezoelectric phase modulator.

Solid state and fibre optic laser Doppler velocimeters

Abstract Laser Doppler velocimetry (LDV) has become established as an important technique for the measurement of velocities of macroscopic objects and fluids: the dynamic range is large (∼10 -6 -10 5 ms -1 ) and the measurement is absolute and non-invasive. However, the size and cost of LDV has restricted its use in some areas. This paper presents two separate approaches to reduce these problems: we describe a compact LDV system incorporating a solid state laser diode and also an investigation of the feasibility of a fibre optic LDV system in which the conventional optical components are replaced by fibre optics. The experimental arrangement used for the solid state LDV system was of the Doppler difference type; i.e. a system of parallel interference fringes is focused in the measurement volume, so that a particle passing through this volume produces a scattered light signal which is intensity modulated. In its simplest form, the technique cannot determine the direction of motion of the particle, but this difficulty may be overcome by causing the fringes to ‘move’ within the measurement volume with known velocity. In the present experiments, the laser output frequency was modulated by modulating its drive current; since the path lengths of the two beams interfering in the measurement volume were unequal, fringe motion was achieved. The fibre optic LDV experiment was also of the Doppler difference type, and it was demonstrated that the necessary stabilised interference fringe system could be projected using a fibre optic system. An electronic servo was devised to compensate for the random differential thermal drifts in the fibres which would otherwise have produced unacceptable drifts in the fringe pattern.

High frequency non-mechanical optical linear polarisation state rotator

A high frequency non-mechanical optical linear polarisation state rotation generator is described which may be directly applied to measurement systems requiring switched or continuously modulated linear polarisation states. Rotation rates in excess of 100 kHz have been demonstrated.

Temperature sensing with single-mode optical fibres

Temperature measurements using two different types of fibre optic interferometer are described. Details are given of an all single-mode fibre Michelson temperature sensor utilising two different signal processing techniques. With the emission frequency of the diode laser stabilised and the interferometer held in quadrature a temperature resolution of approximately 1 mK is achieved. A remote polarimetric temperature sensor is described in which the modal birefringence of a short length of polarisation preserving fibre is monitored through a 90 m length of input fibre.

A simple fibre Fabry-Pérot sensor

Abstract A simple fibre Fabry-Perot sensor is described in which the uncoated cleaved ends of a lenght of single mode fibre are employed as the mirror surfaces to produce high visibility near perfect cosine-squared fringes in the back-reflected light. The experimentally observed signal-to-noise performance of the interferometer illuminated by a HeNe gas laser and a semiconductor diode laser is reported. In an accelerometer configuration the device displayed a below resonance sensitivity of ≥200 rad g-1.

Fibre Optic Laser Doppler Velocimetry

The use of fibre optics in laser Doppler velocimetry (LDV) promises increased versatility of the technique and novel optical designs. This paper discusses the properties of optical fibres and related components relevant to LDV design, and the likely limitations on system performance. The discussion is illustrated by descriptions of prototype systems constructed in these laboratories: a high power (~ 0.5 W) argon ion laser based system; a compact system incorporating a piezo-electric phase shifter to provide directional information; and a diode laser based system.

Linearised Remote Sensing Using A Monomode Fibre Polarimetric Sensor

A remote polarimetric sensor configuration is described, and two signal detection schemes which can be utilised in conjunction with the sensor to provide a linearised output are demonstrated.