Optical sensing system

Claim 2

An optical sensing system comprising: means (2, 4, 2-1...2-n, 102, 104, 102-1, 102-2) for generating an input optical signal whose intensity is modulated by an oscillating input signal with a fixed frequency f; first means (16, 106, 130) for transferring the input optical signal; sensing means (21, 21-1...21-n) for splitting the input optical signal into two light components (23, 25), the intensity of at least one component thereof being modulated by a physical quantity to be sensed; optical power subtracting means (29, 29-1...29-n) for providing a time delay τ = (2m+1)/2f (m=1, 2, ...n) between the two light components transferred from said sensing means (21, etc) and composing the two light components to substantially substract the optical intensity of one light component from that of the other light component and'supply the optical power subtracted light beam as an output optical signal; second means (32, 32-1...32-n, 136) for transferring the output optical signal; and means (34, 36, 38, 36-1...36-n, 38-1...38-n) for detecting the output optical signal supplied from the second means (32, 32-1...32-n, 136) and phase-comparing the output optical signal with the input signal supplied from said input optical signal generating means (2, 4, 2-1...2-n, 102, 104, 102-1, 102-2) to generate an in-phase signal or an out-of-phase signal.

Claim 3

An optical sensing system according to claim 1, wherein said means (2, 4) for generating the input optical signal produces an incoherent light beam.

Claim 4

An optical sensing system according to claim 2, wherein said sensing means (21, 21-1...21-n) is comprised of a polarizer (10) for linearly polarizing the light beam of the input optical signal launched, a sensor (20, 20-1...20-n) for elliptically polarizing the linearly polarized light beam depending on the physical quantity, and an analyzer (22) for splitting the light beam elliptically polarized by said sensor (20, 20-1...20-n) into two light components linearly polarized.

Claim 5

An optical sensing system according to claim 1, wherein said optical sensing system includes means (2, 4, 102, 104, 102-1, .102-2) for transferring the input optical signal as a reference optical signal from said means for generating the light beam to said phase composing means.

Claim 6

An optical sensing system according to claim 1, wherein said sensing means (21, 21-1...21-n) includes a number of sensors (21-1...21-n) with a number of different modulation characteristics to which substantially the same physical quantities to be measured are applied, said optical power subtracting means (29, 29-1...29-n) includes a number of optical subtracters (29-1...29-n) optically coupled with said corresponding sensors, said detecting means (34, 36, 38, 36-1...36-n, 38-1...38-n) includes a number of detectors (34, 36-1...36-n) for detecting the light beams of the output signal supplied from said optical subtracters, and a number of comparators (38-1...38-n) for comparing the detected signals with the input signals, and said first means (16, 106, 130) for transferring said light beam include a star coupler (40) for splitting the light beam of the input optical signal into a number of input light beams and for transferring them to said sensors (21-1...21-n).

Claim 7

An optical sensing system according to claim 1, wherein said light beam generating means (2, 4, 2-1 ...2-n, 102, 104, 102-1, 102-2) includes a number of light sources (2-1...2-n) for producing light beams with different wavelengths whose intensity are modulated, said first means (16, 106, 130) for transferring the light beam includes a multiplexer (42) for multiplexing the light beams with different wavelengths, an optical waveguide (6) for transferring the light beam multiplexed, and a demultiplexer (44) for demultiplexing the light beam transferred, said sensing means (21, 21-1...21-n) includes a number of sensors (21-1...21-n) for modulating the light beams with different wavelengths supplied from said demultiplexer (44), said optical power subtracting means (29, 29-1:..29-n) includes a number of optical subtracters (29-1...29-n) optically coupled with said sensors (21-1...21-n), said second means (32, 32-1...32-n, 136) for transferring said light beams includes a multiplexer (46) for multiplexing the output light beams with different wavelengths supplied from said optical subtracter, a waveguide (32) for transferring the light beam multiplexed, and a demultiplexer (48) for demultiplexing the light beam transferred, and said detecting means (34, 36, 38, 36-1...36-n, 38-1...38-n) includes a number of detectors (34, 36-1...36-n) for detecting the output light beams with different wavelengths supplied from said demultiplexer (48) and a comparator (38-1... 38-n) for comparing the detected signal with the input signal.

Claim 8

An optical sensing system according to claim 1, wherein said optical power subtracting means (29, 29-1...29-n) includes a reflecting optical path (26, 28) which elongates one of the light component (25) optical paths relative to the other (23) by a predetermined length.

Claim 9

An optical sensing system according to claim 1, wherein said sensing means (21, 21-1...21-n) is a 3 dB optical directional coupler (60).

Claim 10

An optical sensing system according to claim 1, wherein said optical power subtracting means (29, 29-1...29-n) includes an optical fiber (72) which elongates one of the light component (25) optical paths relative to the other (23) by a predetermined length.

Claim 11

An optical sensing system according to claim 9, wherein said optical power subtracting means (29, 29-1...29-n) includes a 3 dB optical directional coupler (62) for composing both the light beam components.

Claim 12

An optical sensing system according to claim 8 or 9, wherein said 3 dB optical directional coupler (62) is integrated onto an optical substrate (50).

Claim 13

An optical sensing system according to claim 1, wherein said sensing means (21, 21-1...21-n) includes a couple of single modes optical fibers (114, 116) through which two light components are transferred, and at least one of said fibers (114, 116) is supplied with a physical quantity to be measured.

Claim 14

An optical sensing system according to claim 12, wherein said optical fibers (114, 116) are different in the lengths, being supplied with the physical quantity.

Claim 15

An optical sensing system according to claim 1, wherein said input optical signal generating means (102, 102-1; 102-2, 4) produces a coherent light beam, said mixing means (29) includes multi-mode optical fibers (114, 116) with different lengths for transmitting both the light components.

Claim 16

An optical sensing system according to claim 1, wherein said input optical signal generating means (102, 102-1, 102-2, 4) produces a coherent light beam and said optical power subtracting means (29) includes single mode optical fibers (114, 116) with different lengths for transmitting both the light components, which are each longer than the coherent length of the coherent light source.

Claim 17

An optical sensing system according to claim 14 or 15, wherein said optical power subtracting means (29) includes a light attenuator (126) optically coupled with either of said optical fibers (114, 116) for adjusting the light intensities of the two light components.

Claim 18

An optical sensing system according to claim 1, wherein said input optical signal generating means (102, 102-1, 102-2, 4) is comprised of two light sources (102-1, 102-2) for producing two light beams with different wavelengths, said first means (16, 106, 130) is comprised of a multiplexer (128) for multiplexing the light beams with different wavelengths, an optical fiber (130) for transmitting the multiplexed light beam, and a demultiplexer (132) for demultiplexing the light beam transmitted and for supplying the light beam with one of the wavelengths to said sensing means (21), said second means (32, 136) for transferring said light beam is comprised of a multiplexer (134) for multiplexing an output light beam with one of the wavelengths modulated by said sensing means (21) and an input light beam with the other light beam transmitted from said multiplexer (134), an optical fiber (136) for transmitting the light beam multiplexed and a demultiplexer (138) for demultiplexing the light beam supplied through said fiber (136), and said detecting means (34, 36, 38) includes photo-detectors (34, 36) for detecting the light intensities with different wavelengths supplied from said multiplexer (134), and a comparator (38) for phase-comparing two signals supplied from said photo-detectors (34, 36).