Technical field

This invention relates to fibreoptic connector systems and in particular fibreoptlc connectors and associated electronics useful mainly in fibreoptic sensor applications.

Background art

Efficient fibreoptic sensors have been developed or are under development, capable of measuring a wide variety of parameters. A number of these sensors comprise an optical fibre length and an appropriate system at one of its ends that converts chances in the quantity to be measured into light changes. The same single fibre is often used to both transmit light to the measuring system at its end and to transmit it back to a suitable photodetector. In several fields of sensor applications it Is generally desirable for the fibreoptic sensor to be disposable after a single use or to be capable of disconnection and reconnection. A problem arising in using these disposable or reconnectable sensors is that of connecting the disposable length of the optical fibre bearing the sensing system at its other end to an appropriate electro-optical apparatus that launches

light into the disposable length of the fibre and detects the light coming back from the sensing end, modulated by the quantity under measurement. Usually these systems utilise a fibre-optic coupler or a beam-splitter in the form of a semitransparent mirror. Accurate alignment is required in order to achieve this connection and this calls for carefully machined connectors that inevitably raise the cost of the system. Small misalignments of the connector system during a measuring session require adjustments to the signal offset level.

Disclosure of invention

According to the present invention there is provided a fibreoptic connector system, which in association with appropriate electronic circuitry, renders unnecessary accurate optical alignment at the point of contact between the disposable or reconnected length of optical fibre and the electro-optical apparatus comprising:

A light emitting and receiving structure either in the form of a fibreoptic bundle consisting of a number of optical fibres of a small diameter Kith one or more of them connected to a light source serving as light emitters, the rest of them connected to a photodetector, serving as light sensing fibres or in

the form of a tubular light waveguide or hollow optical fibre surrounding one or more optical fibres of small diameter said tubular waveguide or hollow optical fibre connected to a photodetector and said optical fibres surrounded by said tubular waveguide or hollow optical fibre connected to a light source; a length of optical fibre of a diameter larger than the diameter of fibres comprising the fibreoptic bundle, mounted in an appropriate connector and facing said fibreoptic bundle and facing at least one optical fibre of said bundle; means to bring said fibreoptic bundle and said length of larger diameter optical fibre in close proximity facing each other; appropriate electronic circuitry to compensate for misalignments of said fibreoptic bundle and said larger diameter optical fibre, and light losses resulting from factors such as surface imperfections of the two structures, accumulation of dust particles and tolerances in the manufacture of the said length of larger diameter optical fibre and surrounding and supporting structures. Said electronic circuit automatically compensates for offset shifts of signal by averaging light received back by the receiving fibres of said bundle and using this average as the signal reference. One method of achieving thiε averaging is by low-pass filtering of the received

signal, the filter characteristics determining the speed by which automatic offsetting is achieved. Once said automatic offset adjustment has been fulfilled, said electronic circuitry can be disconnected by the user to restore signal low frequency performance if so desired.

Brief description of drawings

For the purposes of promoting a better understanding of the principles of the invention, particular features of the invention will be highlighted by way of examples with reference to the accompanying drawings in which;

Fig 1 shows a cross section view of said fibreoptic bundle comprising seven similar fibres of small diameter, the central fibre 11 used to launch light and the rest of the fibres used to sense light coming back from said larger diameter fibre the bundle being surrounded by supporting structure 12.

Fig 2 shows a longitudinal section view of said connector assembly comprising a fibreoptic bundle 21 with a central light launching fibre 22 facing a larger diameter optical fibre 23 with sensor system 2U at its other end. Eccentricity of said larger diameter fibre due to tolerances of surrounding and supporting structures 25 do not signi icantly affect

the quantity of light received provided that fibre 23 faces the entire surface of the smaller diameter fibre 22.

Fig 3 shows said tubular light waveguide or hollow optical -fibre 31 surrounding optical fibre 32. This structure can be used instead of said fibreoptic bundle.

Fig U shows a block diagram of automatic offsetting electronic circuit whereby a feed-back loop with a low-pass filter Ul is used to compensate for connector imper ections and tolerances. Filter Ul output is used as a reference of the full-wave rectifier circuitry 42. The signal is subsequently filtered by means of low-pass filter -13.