Optical sensor

1. An optical sensor comprising:

an optical cavity defined by a dielectric body and responsive to one or more physical environmental conditions; and

a waveguide having a terminal end attached to a lens and spaced apart from the optical cavity such that light is optically coupled from the terminal end of the waveguide to the optical cavity through the lens,

wherein the distance between the terminal end of the waveguide and the optical cavity is sufficient such that, in use, the waveguide is maintained at a first temperature that would not damage the optical or mechanical properties of the waveguide and the dielectric body is maintained at a second temperature higher than the first temperature and that would be sufficient to damage the optical or mechanical properties of the waveguide;

the optical sensor further comprising an optical alignment mechanism for providing alignment between the waveguide and the optical cavity, the optical alignment mechanism comprising a ball joint having a ball arranged to support the lens and a socket arranged to adjustably support the ball.

2. The optical sensor of claim 1 , wherein the distance is greater than 10 mm.

3. The optical sensor of claim 1 , wherein the ball is fixed in position relative to the socket by a fixture.

4. The optical sensor of claim 3 , wherein the fixture is a weld.

5. The optical sensor of claim 1 further comprising a housing having a proximal end and a distal end and arranged to support the dielectric body at the proximal end and to support the waveguide at the distal end.

6. The optical sensor of claim 5 , wherein the ball joint is arranged within the housing.

7. The optical sensor according to claim 1 further comprising a collimator for collimating the light emitted from the waveguide.

8. The optical sensor of claim 7 , wherein the collimator is a beam expander.

9. The optical sensor of claim 7 , wherein the collimator comprises the lens.

10. The optical sensor of claim 9 , wherein the attachment between the terminal end of the waveguide and the lens is a fusion bond.

11. The optical sensor of claim 9 , wherein the lens comprises a first surface including a curved portion surrounded by a planar portion.

12. The optical sensor of claim 11 , wherein the lens further comprises a planar second surface parallel with the planar portion of the first surface.

13. The optical sensor of claim 11 , wherein the curved portion is formed by micro-machining.

14. The optical sensor of claim 11 , wherein the curved portion is formed by etching.

15. The optical sensor according to claim 9 , further comprising a lens mount.

16. The optical sensor of claim 15 , wherein the lens mount comprises a plurality of spring fingers for supporting the lens.

17. The optical sensor of claim 16 , wherein the plurality of spring fingers apply axial force to the lens.

18. The optical sensor according to claim 9 , wherein the lens is formed from sapphire or silica.

19. The optical sensor according to claim 9 , wherein the lens is moulded.

20. The optical sensor according to claim 1 , wherein the optical cavity in the dielectric body is defined at one end by a membrane deflectable in response to changes in external pressure.

21. The optical sensor of claim 20 , wherein the optical cavity is defined between the membrane and a dielectric slab and wherein a second optical cavity is defined by the two parallel faces of the dielectric slab such that light is optically coupled from the terminal end of the waveguide to the optical cavity; and said second optical cavity is responsive to changes in temperature due to thermal expansion or contraction of the dielectric slab causing a variation in the separation of the two parallel faces.