Free space optical communication system

• US 5,748,813 A
• Filed: 03/28/1995
• Issued: 05/05/1998
• Est. Priority Date: 07/28/1992
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications Public Limited Company
• Inventors: Smyth, Peter Paul, Williams, Douglas Lawrence, White, Trevor Keith, Cassidy, Stephen Anthony
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US08/379,449
• Time in Patent Office: 1,134 Days
• Field of Search: 359/172, 359/173, 385/24, 385/147
• US Class Current: 385/24
• CPC Class Codes: H04B 10/1149 Arrangements for indoor wireless networking of information

Abstract

An optical communication system for free space communication includes an optical source including a modulator to modulate the optical output to provide an optical signal. The optical source is connected to an optical fiber to pass the signal therealong. The optical fiber includes an antenna having an optical fiber transmit portion with a core, and a cladding, the cladding including at least one substantially flat surface extending along its length and arranged to couple light out of the optical fiber through the substantially flat surface(s). A scattering structure scatters into free space light thus coupled out of the fiber.

Claims

1. An optical communication system for free space communication comprising:

an optical source including means to modulate the optical output to provide an optical signal, said optical source being connected to an optical fibre to pass said signal therealong, the optical fibre including antenna means including an optical fibre transmit portion having a core and a cladding;

said cladding of said optical fibre transmit portion including a flat surface extending along its length and means to couple light out of the optical fibre through said flat surface, and scattering means to incoherently scatter into free space light thus coupled out of the fibre; and

a plurality of said antenna means being provided at spaced intervals along the optical fibre.

2. An optical communication system as in claim 1 wherein each said optical fibre transmit portion includes a coating surrounding said cladding.

3. An optical communication system as in claim 2 wherein the distance between said core and said flat surface and the relative refractive indices of the cladding and the coating is such that said optical signal from each optical fibre transmit portion is scattered into free space to provide incoherent scattered light outside the fibre.

4. An optical communication system as in claim 1 wherein at each antenna means light from within the optical fibre is scattered through an angle of more than 90°

to the direction of passage of light along the fibre.

5. An optical communication system as in claim 1 wherein each antenna means includes means to further incoherently scatter the light into free space.

6. An optical communication system as in claim 5 wherein each said further scattering means includes a diffuser in the form of a diffuse screen or scattering lens elements.

7. An optical communication system as in claim 6 wherein said scattering lens elements are lenticular elements include sprayed transparent material on at least one of said at least one flat surface with individual droplets of the sprayed material being set thereonto.

10. An optical communication system as in claim 2 wherein the coating is transparent to said light and said glass beads are provided within the coating or on the outer surface or the coating of both.

11. An optical communication system as in claim 5 wherein each said further scattering means comprises irregularities in the core of the fibre.

12. An optical communication system as in claim 11 wherein the irregularities comprise crystals within the fibre core which provide Rayleigh scattering.

13. An optical communication system as in claim 5 wherein each said further scattering means comprises a holographic element.

14. An optical communication system as in claim 13 wherein said holographic element is formed on at least one of said flat surfaces of said fibre.

15. An optical communication system as in claim 1 wherein successive spaced optical fibre transmit portions are arranged so as to transmit an increasing proportion of the available light in the fibre.

16. An optical communication system as in claim 1 wherein each optical fibre transmit portion is between 1 to 100 m in length.

17. An optical communication system as in claim 1 wherein each optical fibre transmit portion is between 1 and 10 m in length.

18. An optical communication system as in claim 16 wherein the optical source is arranged to transmit an optical signal of 10 mW to 1 W along the optical fibre.

19. An optical communication system as in claim 1 wherein the optical fibre includes a dopant capable when stimulated of amplifying the signal from the source as the signal travels along the fibre.

20. An optical communication system as in claim 19 wherein the optical source and a pump source are connected to the fibre through a wavelength multiplexer, the pump source providing a signal at a shorter wavelength than the signal from the optical source to stimulate the dopant in the fibre.

21. An optical communication system as in claim 1 wherein the source is a laser having a power output up to 200 mW and the light transmitted from the optical communication system is arranged so that it is not possible, with a lens of up to 50 mm diameter, to focus the light to provide an energy density sufficient to damage a human as defined.

22. An optical communication system as in claim 1 wherein the distance (d) between the periphery of said core and said flat surface of the cladding is between 1 and 10 μ

m.

24. An optical communication system as in claim 1 wherein said cladding is surrounded by a coating of diameter in the range 250 to 400 μ

m.

25. An optical communication system as in claim 24 wherein said cladding is surrounded by a coating of diameter in the range approximately 350 μ

m.

8. An optical communication system as in clam 5 wherein each said further scattering means comprises glass beads.

9. An optical communication system as in claim 8 wherein the glass beads have diameters in the range of 3 to 18 μ

m.

23. An optical communication system as in clam 22 wherein the distance (d) between the periphery of said core and said flat surface of the cladding is approximately 5 μ

m.

26. An optical communication system for free space communication comprising:

an optical source, including means to modulate the optical output to provide an optical signal,

said optical source being connected to an optical fibre to pass said signal thereto, the optical fibre including signal transmit means having an optical fibre transmit portion with a core and cladding,

the core including optically effective irregularities whereby some of said optical signal from the optical fibre transmit portion is scattered through the cladding to provide incoherent scattering into free space outside the fibre; and

a plurality of optically effective irregularities at spaced intervals along the optical fibre.

27. An optical communication system as in claim 26 wherein said irregularities comprise small crystals within the fibre core which provide Rayleigh scattering.

28. An optical communication system comprising:

an optical fibre adapted to be coupled to a source of optical signals;

said optical fibre including at least one portion having a D-shaped cross section disposed to progressively radiate a portion of said optical signal therefrom; and

a light diffusing structure disposed to incoherently scatter said radiated optical signal into free space.

29. An optical communication system as in claim 28 comprising a plurality of said optical fibre portions having D-shaped cross section at spaced intervals along the optical fiber.

30. An optical communication system as in claim 28 wherein said light diffusing structure includes a fibre coating.

32. An optical communication system as in claim 28 wherein said light diffusing structure comprises glass beads embedded within a cladding layer of the fibre.

33. An optical communication system as in claim 28 wherein said light diffusing structure comprises transparent material sprayed onto said fibre so that droplets of the material adhere to said fibre.

34. An optical communication system as in claim 28 wherein said light diffusing structure comprises irregularities within the fibre core.

35. An optical communication system as in claim 29 further including means for causing approximately equal amounts of optical power to be radiated by each successive radiation portion of the fibre.

31. An optical communication system as in clam 30 wherein said fibre coating further comprises glass beads embedded therein.