Improvements relating to optical devices

Claim 2

An optical device comprising a length of optical fibre of predetermined convex configuration supported by fibre mounting and/or attachment means, the convex outer part of the optical fibre having a portion thereof removed therefrom closely adjacent to or even just entering the core of the optical fibre to produce a substantially flat surface therealong on which a reflective diffraction grating of predetermined form is provided according to the function requirements of the device.

Claim 3

An optical device as claimed in claim 1, in which the optical lines or corrugations of the diffraction grating are disposed orthogonally relative to the direction of light propogation along the optical fibre so that a beam of light having a wavelength λ g = 2V where V equals the grating period will undergo Bragg diffraction as it impinges on the grating and the diffracted beam will be guided by the optical fibre back along the incident path.

Claim 4

An optical device as claimed in claim 1 or claim 2, in which the diffraction grating is produced by applying photoresist material to the aforesaid substantially flat surface of the optical fibre and then exposing the material to a suitable interference pattern derived from laser means after which the photoresist is developed.

Claim 5

An optical device as claimed in claim 3, in which following the development of the photoresist material the grating is formed as a depth modulation of the photoresist.

Claim 6

An optical device as claimed in claim 4, in which the depth modulation of the photoresist is transferred into the optical fibre itself by the use of an ion-beam milling technique.

Claim 7

An optical device as claimed in claim 1 or claim 2, in which the diffraction grating is produced by exposing photochromic material dissolved in a suitable matrix and applied to the aforesaid flat surface of the optical fibre to interfering laser beams which accordingly produce a modulation of the photochromic material along the grating surface.

Claim 8

An optical hydrophone or other optical system for sensing strain or deformation of optical fibre means according to our Patent No. 2136113B in which optical fibre means is arranged to be subjected to fibre deforming forces during use of the system and means is provided for producing a coherent signal for transmission along the optical fibre means, in which the optical fibre means comprises at points along its length respective discontinuities from which a light signal being transmitted along the optical fibre means will be partially reflected both along the fibre means and combined with the light signal being transmitted down the firbe means so that heterodyning occurs between the interfering signals and in which the combined light signals are applied to demodulation means which provides an output indicative of the acoustic or other deforming force acting on the optical fibre means, said discontinuities provided along the length of the optical fibre means being constituted by a plurality of optical devices according to any of claims 1 to 6 introduced at predetermined points along the length of an optical fibre defining said optical fibre means and common to all the optical devices.

Claim 9

An optical sensing system as claimed in claim 7, comprising an optical fibre mounting and/or attachment means having formed in a surface thereof a plurality of curved grooves for receiving spaced apart relatively short lengths or portions of a common optical fibre, the short lengths of the optical fibre then being secured, as by adhesive, within the curved grooves so that the short lengths of optical fibre have a convex configuration after which the grooved surface of the mounting and/or attachment means is polished or paved away to remove part of the outer convex surface of the lengths of optical fibre within the curved grooves closely adjacent to or just entering the core of the optical fibre to produce substantially flat surfaces therealong and diffraction gratings are then provided on the plurality of flat surfaces to define reflective points along the optical fibre and the fibre mounting and/or attachment means is finally divided up into separate parts so that a plurality of optical devices are effectively distributed along the length of the common optical fibre.

Claim 10

An optical sensing system as claimed in claim 8, in which the optical fibre mounting and/or attachment means comprises a plurality of grooved blocks of glass or silicon bonded together prior to winding the optical fibre around the bonded structure so that portions of the fibre engage the curved grooves in which they are cemented.