Optical transmission system

Claim 1

An optical transmission system comprising a light source, a first interferometer wherein lightfrom the source can be modulated, the optical output of the first interferometer being propagated along an optical path to a second interferometer wherein the optical input can be demodulated, the output of the second interferometer being applied to photodetec tor means.

Claim 6

A system according to any preceding claim wherein the optical path is an optical fibre.

Claim 7

A system acording to any preceding claim including a third interferometer which also receives the optical output from the optical path, the second and third interferometers having internal path lengths which differ by V4 (where k is the wavelength of the main centre frequency of the source), and a second photodetector means to which the output of the third interferometer is applied.

Claim 8

A system according to anyone of claims 1-5 wherein one of the mirrors of the second interferometer is misaligned with respect to the internal path axis, there being two photodetectors arranged spaced apart in a direction which is normal to the axis and in the direction of the misalignment.

Claim 9

A system according to any preceding claim wherein the light source is incoherent.

Claim 10

A system according to any preceding claim including a plurality of first interferometers each with a different coloured optical filter in series therewith, the outputs of all the first interferometers being propagated simultaneously along the same optical path to the second interferometer.

Claim 11

A system according to anyone of claims 1-8 including means for acoustically modulating the first interferometer.

Claim 12

A system according to any preceding claim wherein the output of the second interferometer is compared with a fixed reference value and an error signal derived therefrom provides a feedback signal to adjust the second interferometer to maintain it in a constant phase relationship with the first interferometer.

Claim 13

A system according to any preceding claim wherein the light source is located adjacent the second interferometer and light therefrom is applied to the first interferometer via an optical fibre.

Claim 14

A system according to any preceding claim including beam splitter means for extracting a portion of the received light from the optical path, said extracted portion being applied to a photodetector the output of which is applied to an automatic gain control means for the photodetector output.

Claim 17

A method of transmitting information by optical signals comprising illuminating a first inter- ferometer with light, modulating the first interferometerwith an information signal whereby the output of the interferometer is modulated, receiving the modulated output at a second interferometer, and detecting the output of the second interferometer to provide an electrical output signal corresponding to the information signal. 4 GB 2 106 736 A 4

Claim 18

A method of transmitting information by optical signals comprising illuminating a first inter- ferometer with light, modulating the first interferometerwith an information signal whereby the output of the interferometer is modulated, receiving the modulated output at a second interferometer, and detecting the output of the second interferometer to provide an electrical output signal corresponding to the information signal. 4 GB 2 106 736 A 4

Claim 19

A method of transmitting information substantially as described with reference to any one of Figures 1, 7, 8, 9, 1 Oa, 1 Ob, 11, 12, 13a, or 13b. Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1983. Published byThe Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained. 4

Claim 20

A method of transmitting information substantially as described with reference to any one of Figures 1, 7, 8, 9, 1 Oa, 1 Ob, 11, 12, 13a, or 13b. Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1983. Published byThe Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained. 4