Noise management for optical time delay interferometry

Abstract

An integrated fiber interferometry interrogator for generating superimposed waves is disclosed. The system is optimized for efficiency and vibration attenuation. The system comprises an optical light source for generating a first signal, a first signal splitter which splits the first signal into a reference signal and an interrogation signal, optical modulators for modulating the signals, a fiber coupler connected to a fiber under test, an isolator, a circulator with a plurality of connections for directing the signals, a signal mixer for mixing the signals into superimposed waves, and photo diodes for receiving the superimposed waves.

What is claimed is: 
     
         1 . An integrated fiber optic interferometry interrogator system to generate superimposed waves, the system comprising:
 an optical light source, wherein the optical light source generates a first signal;   a first signal splitter coupled to an output of the optical light source, wherein the first signal splitter splits the first signal into a reference signal and an interrogation signal;   a first optical modulator to modulate the reference signal;   a second optical modulator to modulate the interrogation signal;   a fiber coupler connected to a fiber under test;   a circulator comprising a plurality of connections, wherein
 a first connection of the plurality of connections receives the modulated interrogation signal, 
 a second connection of the plurality of connections transmits the modulated interrogation signal through the optical coupler and receives from the optical coupler a modulated signal backscattered from the fiber under test, and 
 a third connection of the plurality of connections that transmits through an isolator the modulated signal backscattered from the fiber under test; 
   a signal mixer comprising a plurality of signal couplers configured to receive the modulated signal backscattered from the isolator connected to the fiber under test,
 receive the reference signal modulated by the first optical modulator, 
 mix the two received signals into the superimposed waves, and 
 transmit the superimposed waves into a plurality of photo diodes, wherein one or more of the photo diodes output an RF signal comprising the superimposed waves. 
   
     
     
         2 . The system of  claim 1 , wherein the light source is a laser. 
     
     
         3 . The system of  claim 2 , wherein the laser is one of continuous wave (CW) and pulse modulated CW. 
     
     
         4 . The system of  claim 1 , wherein the first optical modulator is at least one of acousto-optical modulator and electro-optical modulator and wherein the second optical modulator is at least one of acousto-optical modulator and electro-optical modulator. 
     
     
         5 . The system of  claim 1 , wherein the fiber under test comprises at least one of a single-mode type, multimode type, and polarization preserving type fiber optic cable. 
     
     
         6 . The system of  claim 1 , wherein the signal couplers are at least one of signal splitter and signal combiner. 
     
     
         7 . The system of  claim 1 , wherein the fiber under test has a length L and the light source is a laser having the capability to generate a signal with sufficient stability to retain coherency in propagation along the fiber under test for a distance at least equal to two times the length L. 
     
     
         8 . The system of  claim 1 , wherein the fiber under test has a coating thereon made of a thermoplastic material having the combined characteristics of a low Young's modulus and a Poisson's ratio below that of natural rubber, wherein the coating enhances the longitudinal component of strain variation derived from an acoustic wave signal. 
     
     
         9 . The system of  claim 1 , wherein the plurality of photo diodes are connected to a plurality of amplifiers and wherein the amplifiers generate radio frequency signals. 
     
     
         10 . The system of  claim 1 , further comprising a power supply. 
     
     
         11 . The system of  claim 1 , wherein the system elements are at least one of optimally coupled, connected, and linked for at least one of maximum efficiency and lowest loss, wherein maximum efficiency includes at least one of cable length and number of splices. 
     
     
         12 . The system of  claim 1 , wherein all signal splitters and signal couplers use signal attenuators on all unused ports. 
     
     
         13 . The system of  claim 12 , wherein the signal attenuator is a mandrel. 
     
     
         14 . The system of  claim 1 , wherein the system is enclosed by a material conducive for vibration attenuation. 
     
     
         15 . The system of  claim 1 , wherein the modulated backscattered signals are generated from at least one of acoustic pressure waves, electromagnetic fields, mechanical strain or pressure, and thermal strain or pressure. 
     
     
         16 . A method for generating superimposed waves with an integrated fiber optic interferometry interrogator system, the method comprising:
 generating a first signal;   splitting the first signal into a reference signal and an interrogation signal;   modulating the reference signal using a first optical modulator;   modulating the interrogation signal using a second optical modulator;   using a circulator comprising a plurality of connections operative to
 receive at a first connection the modulated interrogation signal, 
 transmit from a second connection the modulated interrogation signal into a fiber under test, 
 receive a modulated signal backscattered from the fiber under test, and 
 transmit from a third connection the modulated signal backscattered from the fiber under test; 
   using a signal mixer comprising a plurality of signal couplers to:
 receive the modulated signal backscattered from the fiber under test, 
 receive the modulated reference signal from the first optical modulator, 
 mix the two received signals into the superimposed waves. 
   
     
     
         17 . The method of  claim 16 , wherein the fiber under test has a length L and the light source is a laser having the capability to generate a signal with sufficient stability to retain coherency in propagation along the fiber under test for a distance at least equal to two times the length L. 
     
     
         18 . The method of  claim 16 , wherein the fiber under test has a coating thereon made of a thermoplastic material having the combined characteristics of a low Young's modulus and a Poisson's ratio below that of natural rubber, wherein the coating enhances the longitudinal component of strain variation derived from an acoustic wave signal. 
     
     
         19 . The method of  claim 16 , wherein the system is enclosed by a material conducive for vibration attenuation. 
     
     
         20 . The method of  claim 16 , wherein the modulated backscattered signals are generated from at least one of acoustic pressure waves, electromagnetic fields, mechanical strain or pressure, and thermal strain or pressure.