Fiber optical time-division-multiplexed unbalanced pulsed interferometer with polarization fading compensation
First Claim
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1. A fiber optics pulsed interferometer comprising:
- a source of pulsed optical signals periodically delivering periodic polarized optical pulses; and
,an unbalanced fiber optic compensating interferometer for producing timed two-pulse sequences in which a predetermined one of said two pulses alternates its polarization orientation from sequence to sequence, said unbalanced fiber optics compensating interferometer including;
a long arm and a short arm;
means responsive to said periodic polarized optical pulses for splitting each periodic polarized optical pulse to provide optical signals to said long and short arm, and for switching the polarization of said optical signals in at least one of said arms, the optical signals passing through said arms and being combined in a coupler to deliver a separated two-pulse sequence, the polarizations of a predetermined one of the individual pulses in each two-pulse sequence alternating from sequence to sequence.
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Abstract
Apparatus and methods for reducing and preventing polarization fading in unbalanced measuring interferometers. An extended interferometer having a plurality of sensors and a compensating interferometer are used. They are driven from a pulsed optical signal source wherein the optical signal comprises sequences of two pulses each. To prevent polarization fading the polarization of a predetermined one of each two-pulse sequence is switched, preferably orthogonally, from sequence to sequence. Interference pulse output groups are produced for each two-pulse driving sequence. Each output group has the same number of usable pulses as the number of sensors in the interferometer.
65 Citations
27 Claims
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1. A fiber optics pulsed interferometer comprising:
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a source of pulsed optical signals periodically delivering periodic polarized optical pulses; and
,an unbalanced fiber optic compensating interferometer for producing timed two-pulse sequences in which a predetermined one of said two pulses alternates its polarization orientation from sequence to sequence, said unbalanced fiber optics compensating interferometer including; a long arm and a short arm; means responsive to said periodic polarized optical pulses for splitting each periodic polarized optical pulse to provide optical signals to said long and short arm, and for switching the polarization of said optical signals in at least one of said arms, the optical signals passing through said arms and being combined in a coupler to deliver a separated two-pulse sequence, the polarizations of a predetermined one of the individual pulses in each two-pulse sequence alternating from sequence to sequence. - View Dependent Claims (5, 6)
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- 2. A pulsed interferometer as recited in which said predetermined one of said two pulses alternates its polarization from being the same polarization and being orthogonal thereto.
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7. In combination:
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a first measuring unbalanced fiber optic interferometer having a plurality of fiber optics sensors in a ladder network said sensors having a predetermined time delay for optical signals; said sensors being in at least one of the serial input and output fibers of said ladder network, and a plurality of shunt fibers optically connecting said input and output fibers of said measuring interferometer; a source of pulsed optical signals; a compensating second unbalanced fiber optic interferometer having two arms of different optical lengths, the difference in optical length between such arms being substantially equal to the time delay in one of said sensors, to cause said interferometer to produce sequences of two optical signal pulses for each optical signal pulse it receives, a detector for converting optical signals into electrical signals, coupled to receive output signals from said first interferometer; a polarization switching means, coupled into a predetermined one of the arms of said second interferometer to switch the polarization orientation of a predetermined one of the pulses of said two-pulse sequences produced by said predetermined arm; and a timer, connected to said optical signal source to synchronize pulses delivered from said optical source to said second interferometer, and connected to said polarization switching means to continually toggle the polarization orientation of said predetermined pulses between two polarization orientations consecutively from sequence to sequence. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. An apparatus for remotely sensing environmental effects without polarization signal fading, comprising:
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a source of pulsed optical signals periodically delivering polarized optical pulses; an unbalanced fiber optics compensating interferometer, including means for switching the polarization of optical signals in one of its arms, coupled to receive said periodic pulses and to deliver separated two-pulse sequences, the polarizations of a predetermined one of the individual pulses of each pair of pulses alternating from sequence to sequence; an unbalanced measuring second fiber optics interferometer including environmentally sensitive elements, coupled to receive on its input fiber said alternating sequences of pulses from said first interferometer, producing output groups of optical interference pulses on its output fiber, one group for each of its said input sequences, the interference visibilities of the pulses of said output groups alternating between two sets of values from group to group; and signal processing means, including means for converting said output groups of optical interference pulses into electrical signals, and including means for processing interference pulse signals of consecutive ones of said output groups to produce signals that are measures of the environmental parameters sensed by said sensors. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
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Specification