S. C. Rashleigh

High birefringence in tension-coiled single-mode fibers.

Coiling a single-mode fiber of radius r under tension onto a cylinder of radius R produces a linear birefringence of βtc ≃ 28 × 107∊2r/R deg/m in the fiber at λ = 0.63 μm, where ∊z is the relative fiber elongation. Polarization beat lengths down to 2.5 cm have been realized this way, providing excellent polarization holding.

Polarization holding in birefringent single-mode fibers

Perturbations in highly birefringent single-mode fibers couple the two polarization modes and degrade the polarization-holding ability. With a broadband source we demonstrate wavelength averaging of the power in either mode, permitting a simple measurement of the power transfer to the cross-polarized mode as a function of fiber length. Using this technique, we confirm experimentally the theory of random mode coupling between the polarization modes.

Magnetic-field sensing with a single-mode fiber

A fiber-optic magnetic-field sensor is constructed by bonding a single-mode fiber to a nickel cylinder. The magnetic field, by means of the magnetostrictive effect, alters the state of polarization of light in the fiber. A sensitivity of 1.76 x 10(-2) rad/m Oe is demonstrated, permitting detection of fields as small as 4.4 x 10(-6) Oe/m of fiber.

Acoustic sensing with a single coiled monomode fiber

A single monomode fiber-optic acoustic sensor is proposed. The acoustic wave differentially changes the phase velocities of the polarization eigenmodes in a tension-coiled fiber, leading to a polarization rotation of the transmitted light. Sensitivities exceeding those of multimode fiber-optic hydrophones and ~40 times less than those of the two-fiber interferometric sensor should be realizable while environmental instability problems and the sensor complexity are significantly reduced.

Wavelength dependence of birefringence in highly birefringent fibers.

A simple technique is used to measure the wavelength dependence of the birefringence in highly birefringent fibers. In stress-induced fibers, the stress and shape birefringences reinforce each other, whereas in elliptical-core fibers the stress and shape birefringences can either reinforce each other or partially cancel, depending on the wavelength.

Measurement of fiber birefringence by wavelength scanning: effect of dispersion.

Scanning the wavelength in high-birefringence fibers inherently measures the group delay difference, and not the phase delay difference, between the two polarization modes. Dispersion of the birefringence will result in a 10-20% error in fiber beat lengths interpolated from such measurements, even if only stress birefringence is present. Geometrical dispersion can introduce even larger errors in some fibers.

Temperature dependence of stress birefringence in an elliptically clad fiber

The stress birefringence in a fiber with a three-component silica-glass elliptical cladding is found to be a strongly nonlinear function of temperature. The observed birefringence is a factor of 1.6 greater than that predicted from linear approximations of this dependence and estimates of the fiber materials properties. The fibers birefrin-gence can be predicted from a linear extrapolation of the low-temperature data.

Optical Kerr effect in fiber gyroscopes: effects of nonmonochromatic sources

The effects of source bandwidth on the optical Kerr effect are calculated. We show that the nonreciprocal Kerr bias error in fiber gyroscopes may be substantially reduced by using broadband sources.

Dual-input fiber-optic gyroscope

A fiber-optic gyroscope is operated at maximum sensitivity by supplying two equal-intensity inputs with a specific phase difference to the gyroscope beam splitter. When the beam-splitter outputs have equal intensity, reciprocity requires the Sagnac interferometer to be at quadrature. A sensitivity of approximately 0.93 rad(-1) is demonstrated with a minimum-detectable rotation rate of 0.4 deg/sec.

Influence of the fiber diameter on the stress birefringence in high-birefringence fibers

The influence of the outer diameter of the constraining region on the stress-induced birefringence in high-birefringence fibers is investigated for three fiber structures. Generally, the outer diameter should be three times larger than the mean diameter of the stress-producing regions to ensure that the birefringence is close to maximum.