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

Polarization-maintaining fibers and their applications are reviewed. The classification of high-birefringent fibers and low-birefringent fibers and their fabrication methods and characteristics are discussed in Section II. Analytical methods and numerical methods for fiber design on the birefringence are presented in Section III. Degradation factors of polarization maintenance expressed as crosstalk or mode-coupling parameters caused by internal origins such as structural imperfections, wavelength, and nonlinear effects, and by external origins such as temperature fluctuations, mechanical perturbations, and electromagnetic effects, are discussed in Section IV. Characterization methods on beat length, mode coupling, stress distribution, and mechanical strength are presented in Section V. Applications to the fiber devices and nonlinear effects, and splicing methods for the polarization-maintaining fibers are described in Sections VI and VII.

Polarization-maintaining fibers and their applications

Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.

Polarization in optical fibers

A theoretical and experimental analysis of the polarization properties of twisted single-mode fibers is presented. It is shown that whereas a conventionally twisted fiber possesses considerable optical rotation, a fiber which has a permanent twist imparted by spinning the preform during fiber drawing exhibits almost no polarization anisotropy. It is thus possible to virtually eliminate the commonly observed fiber linear birefringence. As a consequence, fibers made in this way are ideally suited for use in the Faraday-effect current transducer. It is further shown that a permanent twist of a few turns/meter effectively eliminates polarization mode-dispersion. The technique therefore appears attractive for enhancing the bandwidth of very long unrepeatered telecommunication links.

/pdf/birefringence-and-polarization-mode-dispersion-in-spun-5d672pzofv.pdf

Birefringence and polarization mode-dispersion in spun single-mode fibers.

The theory of highly elliptically birefringent fibers fabricated by spinning a linearly birefringent fiber during the draw is described. These fibers are particularly interesting for application as Faraday-effect fiber current monitors, since, in contrast to conventional fibers, they can be wound in small multiturn coils while retaining their sensitivity. The fiber and its application in three optical schemes are modeled using Jone calculus and are also experimentally investigated. A simple optical configuration is proposed, combining the elliptically birefringent fiber and a broad-spectrum light source. An accurate, compact, and robust current monitor is obtained. The sensor is characterized by a measurement repeatability of +or-0.5%, a temperature drift of 0.05%/ degrees C and a sensitivity of 1 mA RMS/Hz/sup 1/2/. Further, the performance of this sensor with optimized fiber length for a given measurement bandwidth is predicted. >

/pdf/electric-current-sensors-employing-spun-highly-birefringent-6ap8owhv7r.pdf

Electric current sensors employing spun highly birefringent optical fibers

The polarization and magnetooptic properties of a sample of single-mode optical fiber have been investigated. The fiber acts as a linear retarder, and the degree of retardation is dependent on the external pressure applied to the fiber. The stress optic coefficient is found to be 8.72 x 10(-10) N(-1) m(2). The direction of linear polarization is rotated when a longitudinal magnetic field is applied to the fiber (Faraday effect). The Verdet constant is 1.56 x 10(-2) min A(-1). The intrinsic specific linear retardation of the fiber is found to be less than 0.44 rad m(-1) from the magnetooptic measurements. The fiber has been used in an experimental current measurement device.

Smith Am

Papers

Polarization and magnetooptic properties of single-mode optical fiber