Polarization diversity detection for fiber interferometers using active feedback control of output polarization-mode selection.

The application of an adaptive polarization diversity detection technique in an interferometric fiber sensor system is described. The approach utilizes feedback control of the polarization modes selected at the sensor output and produces the optimum level of total interference signal while allowing the states of polarization of the light in the signal and reference arms of the interferometer to vary randomly.

Observation of input-polarization-induced phase noise in interferometric fiber-optic sensors.

It is shown that polarization fluctuations in the input fiber to an interferometric sensor can result in the generation of excess phase noise in the output. Experimental observations of this phenomenon are compared with theoretical models, and the impact of this noise source in interferometric sensors is briefly discussed.

Internal rotation of the birefringence axes in polarization-holding fibers.

An internal rotation of the birefringence axes has been measured in a variety of polarization-holding fibers. The rotation of the axes causes coupling of the major-field components of the fundamental modes, which limits the polarization-extinction ratio in short lengths of birefringent fibers to -45 dB in some cases. A practical consequence of the rotation of the axes is a reduction of the polarization-holding ability of devices such as fiber couplers that are made with these 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 material's properties. The fiber's birefrin-gence can be predicted from a linear extrapolation of the low-temperature data.

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.

Repetitively pulsed mode-locked Nd:phosphate glass laser oscillator-amplifier system.

Performance of a repetitively pulsed mode-locked Nd:glass laser system employing athermal phosphate glass in the oscillator and amplifier stages is described. Improved passive mode-locking characteristics of the oscillator are achieved through use of a l00-microm thick intracavity etalon, enabling reliable generation of transform-limited pulses typically of 5-psec duration. The system produces 1054-nm pulses of high beam quality and ~25-mJ energy at a pulse repetition rate of ~0.2 Hz. Subsequent frequency-doubling steps give conversion efficiencies of ~50% and 25%, respectively.