US 6,522,797 B1Granted

Seismic optical acoustic recursive sensor system

AssigneeInput/Output, Inc.

InventorsLee E. Siems, Grevson Knapp, John Maida

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Abstract

A marine seismic fiber optic acoustic sensor system having internal mirrors with a low reflectivity written into the fiber to form a series of continuous, linear sensors incorporated in a single fiber, each sensor bounded by a pair of internal mirrors. A pulsed laser provides optical signals to the fiber at a pulse width less than twice the travel time to assure that there will be no phase or frequency modulation of signals returned from the sensors and reflected optical energy is returned through the same fiber to an optical coupler where it is input to a compensating interferometer to produce interference signals which are then time division multiplexed to produce signals corresponding to acoustic signals received by each mirror bound sensor. Calibration to remove local temperature effects is provided by using a desensitized reference fiber with internal mirrors identical to the sensitized fiber, by a piezoelectric stretcher built into the fiber or any other conventional calibration technique.

Claims30

Dependent claims

An optical sensor system for seismic exploration comprising:

at least one single mode optical fiber, mounted within a linear casing, the fiber having an input end and an opposite terminal end;
a plurality of partially reflective intrinsic fiber mirrors incorporated into the fiber at predetermined, spaced intervals within the fiber, each pair of adjacent mirrors defining a long gauge, linear, acoustic sensor;
a first optical coupler coupled to the input end of the fiber, the optical coupler having a first and a second output port;
a pulsed laser optically coupled to the first output port of the optical coupler wherein the laser is adapted to provide an optical pulse width equal to or less than twice the one way time of travel of optical energy between the predetermined mirror intervals;
a compensating interferometer optically coupled to the second output port of the first optical coupler for receiving optical energy reflected from the internal mirrors, the interferometer including a first path and a second path wherein the second path includes a time delay to the two way time of travel of optical energy between the predetermined mirror intervals;
and
a calibration system for calibrating the sensor system to substantially remove the effects of temperature and acceleration on the optical signal being received by the interferometer, the calibration system including a piezoelectric stretcher incorporated in the fiber, the stretcher having an input terminal for connection to a signal generator and an output terminal for connection to a signal receiver.

4 more elements

An optical sensor system for seismic exploration comprising:

at least one single mode optical fiber, mounted within a linear, pressure sensitive casing, to form a continuous, linear acoustic sensor, the fiber including an input end and an opposite terminal end and at least two, spaced apart, two-by-two, ratio optical couplers between the fiber's input end and the fiber's terminal end, each ratio coupler having an input fiber having a non-reflective terminal end and an output fiber having an intrinsic fiber reflective terminal end;
a first additional optical coupler coupled to the input end of the single mode fiber, the optical coupler having first and a second output port;
a pulsed laser optically coupled to the first output port of the additional optical coupler wherein the laser is adapted to provide an optical pulse width equal to or less than twice the time of travel of optical energy between the intervals between reflective terminal ends of the ratio optical couplers;
and
a compensating interferometer optically coupled to the second output port of the first additional optical coupler for receiving optical energy reflected from the reflective terminal ends of the ratio optical couplers, the interferometer including a first path and a second path wherein the second path includes a time delay equal to the two way time of travel of optical energy between the reflective terminal ends of the at least two ratio optical couplers;
and a calibration system for calibrating the sensor system to remove the effects of temperature on the optical signal being received by the interferometer, wherein the calibration system includes a piezoelectric stretcher incorporated in the cable, the stretcher having an input lead for connection to a signal generator and an output end for connection to a signal receiver.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/144,953Filed 1 Sep 1998
Granted: 18 Feb 2003
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G01V 1/201
Arrangements of receiving elements, e.g. geophone pattern: constructional details of seismic cables, e.g. streamers
G01H 3/005
Measuring characteristics of vibrations by using a detector in a fluid: testing or calibrating of detectors covered by the subgroups of G01H3/00
G01H 9/004
Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means: using fibre optic…
G01V
Geophysics