The current state of the art of optical fiber sensors is reviewed. The principles of operation are detailed and the various types of fiber sensors are outlined. Achievable performance and limitations are discussed and a description of technology used to fabricate the sensor is presented. The characteristics of acoustic, magnetic, gyro, laser diode, and other sensors are described. Trends in the development of this sensor technology and expected application areas are briefly outlined.

Optical fiber sensor technology

A beam of light is split and introduced into different ends of a light path whose rotation is to be sensed. At least one frequency shifter is placed in the light path to affect the frequency difference of the two beams so as to introduce or adjust a nonreciprocal phase shift. The beams are then mixed back together and the resultant beam is detected and analyzed by suitable circuitry to provide an output indicative of rotation of the light path.

Phase nulling optical gyro

The frequency of an optical signal output from an optical source is controlled by dividing a signal output from the source into two signal portions each of which is guided along its own optical path. The signal portions are combined to form two optical beams each including components of the two signal portions and having intensities dependent on an adjusted frequency of the two beams.

Apparatus and method for optical signal source stabilization

This paper reviews the basics of the interferometric fiber-optic gyroscope: fundamental principle based on Sagnac effect, importance of reciprocity and single-mode propagation, analysis of coherence and polarization problems, signal processing techniques. It also describes the technological progresses of guided-wave components (single-mode optical fiber, semi-conductor diode source, integrated optics, in-line fiber components). Finally, recent trends like multi-axis configurations and rare-earth doped fiber source are presented.

Fundamentals of the interferometric fiber-optic gyroscope

A fiber optic rotation sensor, employing the Sagnac effect comprising all fiber optic components positioned along a continuous, uninterrupted strand of fiber optic material. The rotation sensor includes a detection system utilizing a modulator or modulators for phase modulating at first and second harmonic frequencies light waves which counter-propagate through a loop formed in the fiber optic strand. Each modulator is operated at a specific frequency to eliminate amplitude modulation in the detected optical output signal. A phase sensitive detector generates a feedback error signal proportional to the magnitude of the first harmonic in the output optical signal. The feedback error signal controls a modulator which controls the amplitude of the second harmonic driving signal for the second harmonic phase modulator such that the first harmonic component in the output signal from the rotation sensor is cancelled or held within a small range of amplitudes.

Gated fiber optic rotation sensor with extended dynamic range

Two methods are presented for sensitive measurement of nonreciprocal phase shift (NRPS) in a multi -turn fiber Sagnac interferometer for application in inertial rotation sensing. Both techniques are capableof producing an NRPS modulation of amplitude ± r radians at a rate sufficiently high for shot -noise - limitedperformance. The first method produces an NRPS by generating a nonreciprocal refractive index using theelectro -optic effect, and requires orthogonal polarization in the cw and ccw beams. The second method produces an NRPS by generating a nonreciprocal propagation frequency using two acousto -optic shifters;there is no requirement on light polarization. When either method is used in conjunction with phase- sensi-tive detection, feedback compensation, and adequate laser intensity, shot -noise -limited measurement be- comes possible. Preliminary performance data is included. Introduction Currently there is considerable interest in using a multiturn fiber Sagnac interferometer for the mea-surement of inertial rotation.l Such a measurement is difficult to perform because the nonreciprocal phaseshift (NRPS) induced in the fiber by inertial rotation is very small. For a rotation rate SZ, the NRPS 04) is

S. Ezekiel

Papers

Techniques for Shot-Noise-Limited Inertial Rotation Measurement Using a Multiturn Fiber Sagnac Interferometer