Imaging system

1. A fiber coupler, comprising:

a first optical fiber and a second optical fiber, each of said fibers comprising a single-mode core and a multi-mode layer surrounding said core, said respective multi-mode layers having a numerical aperture greater than a numerical aperture of said respective cores and a compensator for compensating for signal dispersion resulting from group-velocity dispersion and comprising a grating structure;

wherein said multi-mode layer of said first fiber is fused to said multi-mode layer of said second optical fiber, and said cores of said first and second fibers are configured not to couple light from said core of said first fiber into said core of said second fiber.

2. A coupler as claimed in claim 1 , wherein said first optical fiber and said second optical fiber comprise photonic crystal fibers.

3. An imaging system, comprising: a fiber coupler comprising a first optical fiber and a second optical fiber, each of said fibers comprising a single-mode core and a multi-mode layer surrounding said core, said respective multi-mode layers having a numerical aperture greater than a numerical aperture of said respective cores, wherein said multi-mode layer of said first fiber is fused to said multi-mode layer of said second optical fiber, and said cores of said first and second fibers are configured not to couple light from said core of said first fiber into said core of said second fiber; and a compensator for compensating for signal dispersion resulting from group-velocity dispersion and comprising a grating structure.

4. An imaging system as claimed in claim 3 , wherein said system forms part of an endoscope.

5. An imaging system as claimed in claim 3 , including a gradient index (GRIN) lens.

6. An imaging system as claimed in claim 5 , including a multi-mode fiber.

7. An imaging system as claimed in claim 6 , wherein the GRIN lens is positioned in spaced relation relative to an end of said fiber.

8. An imaging system as claimed in claim 6 , wherein the lens has a pitch of between 0.2 and 0.29 and is spaced from the fiber by a distance of between 0.5 and 10 mm.

9. An imaging system as claimed in claim 3 , including a scanning mechanism comprising a microelectromechanical system (MEMS) mirror, for reflecting an excitation signal in varying directions in order to scan a sample.

10. An imaging system as claimed in claim 3 , wherein said compensator comprises a grating pair or Bragg grating.

11. An imaging system as claimed in claim 3 , wherein said compensator is configured to provide prechirping.

12. An imaging system as claimed in claim 3 , wherein said coupler has a splitting ratio optimised to enhance detection efficiency of said system.

13. A method of splitting an optical signal, comprising:

transmitting said signal into a first optical fiber of a fiber coupler comprising said first optical fiber and a second optical fiber, each of said fibers comprising a single-mode core and a multi-mode layer surrounding said core, said respective multi-mode layer having a numerical aperture greater than a numerical aperture of said respective core, wherein said first multi-mode layer is fused to said second multi-mode layer, and said first cores is not fused to said second core;

coupling a first component of said signal transmitted in said multi-mode layer of said first optical fiber into said multi-mode layer of said second optical fiber; and

minimizing coupling of a second component of said signal transmitted in said core of said first optical fiber into said core of said second optical fiber; and compensating for signal dispersion resulting from group-velocity dispersion with a compensator comprising a grating structure.

14. A method as claimed in claim 13 , wherein said first optical fiber and said second optical fiber comprise photonic crystal fibers.

15. A fiber coupler, comprising:

a first optical fiber and a second optical fiber, each of said fibers comprising a single-mode core and a multi-mode layer surrounding said core, said respective multi-mode layers having a numerical aperture greater than a numerical aperture of said respective cores; and

a compensator for compensating for signal dispersion resulting from group-velocity dispersion;

wherein said multi-mode layer of said first fiber is fused to said multi-mode layer of said second optical fiber, and said cores of said first and second fibers are configured not to couple light from said core of said first fiber into said core of said second fiber.

16. An imaging system as claimed in claim 15 , wherein said compensator is configured to provide prechirping.

17. A method of splitting an optical signal, comprising:

transmitting said signal into a first optical fiber of a fiber coupler comprising said first optical fiber and a second optical fiber, each of said fibers comprising a single-mode core and a multi-mode layer surrounding said core, said respective multi-mode layer having a numerical aperture greater than a numerical aperture of said respective core, wherein said first multi-mode layer is fused to said second multi-mode layer, and said first cores is not fused to said second core;

coupling a first component of said signal transmitted in said multi-mode layer of said first optical fiber into said multi-mode layer of said second optical fiber;

minimizing coupling of a second component of said signal transmitted in said core of said first optical fiber into said core of said second optical fiber; and

compensating for signal dispersion resulting from group-velocity dispersion.