Observation of ultraslow and stored light pulses in a solid.

We report ultraslow group velocities of light in an optically dense crystal of Pr doped Y2SiO5. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 micros. Deceleration and "stopping" or trapping of the light pulse was also observed. These reductions of the group velocity are accomplished by using a sharp spectral feature in absorption and dispersion that is produced by resonance Raman excitation of a ground-state spin coherence.

Turbulence-aberration correction with high-speed high-gain optical phase conjugation in sodium vapor.

Optical aberrations that are due to high-speed turbulence in the aero-optical regime are corrected with optical phase conjugation based on coherent population trapping in sodium vapor. Experimental measurements of an unheated, forced helium jet in air have demonstrated aberration correction by a factor of 7.8 at a forcing frequency of 18kHz with an optical power gain of 32.

Distortion-free gain and noise correlation in sodium vapor with four-wave mixing and coherent population trapping.

We observed optical gain as great as 30 with nearly distortion-free beam propagation in optically dense sodium vapor, using four-wave mixing. Moreover, 15-dB classical noise correlations were seen in the amplified probe and conjugate beams. To achieve this performance in such a strongly absorbing medium, one must suppress unwanted absorption and self-focusing effects. This is accomplished with coherent population trapping.

Fiber-optic polarization and phase modulator utilizing transparent piezofilm with indium tin oxide electrodes.

A highly efficient optical polarization and phase modulator formed by the placement of a thin transparent piezofilm with indium tin oxide electrodes directly in the path of the output from an optical fiber is presented. Various configurations that differ in the clamping conditions, utilization of epoxy, and optical arrangement are presented. For a film thickness of 63.9 µm, a linear phase-shifting coefficient of 0.131 rad/voltage peak (Vp) at 2 kHz and of 0.508 rad/Vp at 7.4 kHz is demonstrated. An intrinsic birefringence of 0.0328 between the directions along the stretch and its perpendicular in the plane of the film has been measured. The polarization modulation coefficient was determined to be 0.323 rad/Vp at 8.423 kHz, corresponding to a half-wave voltage of 8.353 Vp. Applications of the device involving concurrent spatiotemporal polarization and phase modulation are indicated.

Split-cavity cross-coupled extrinsic fiber-optic interferometric sensor.

A new configuration of the fiber-optic extrinsic Fabry-Perot interferometer is demonstrated. This configuration utilizes two sensor heads on a single directional coupler in a split-cavity cross-coupled extrinsic fiber interferometric (SCEFI) arrangement to provide a four-beam interference. The need for quadrature phase biasing is eliminated, with a new spectrum analysis detection scheme devised for the SCEFI in a no-feedback condition. Good agreement between the model for interference and the experimental results is demonstrated. Wide applications for fiber sensor multiplexing and split-cavity étalons for filters in wavelength-division-multiplexing systems are indicated.

Linear measurement of static phase change in optical homodyne interferometers: an analysis.

A new highly accurate linear method of dc phase-shift measurement based on spectrum analysis in a general optical homodyne interferometer is presented. The dc phase is superimposed onto a controllable ac phase modulation. The dc phase error is theoretically analyzed based on the excellently matching predicted and experimental reports of ac phase error. Significantly, for low values of dc phase, a constant correction factor can be utilized that leads to an ultralow minimum detectable dc phase shift.

Minimum detectable phase shift in spectrum-analysis techniques of optical interferometric vibration detection.

The minimum detectable phase shift indicated in recent experimental reports of new linear spectrumanalysis techniques of optical interferometric vibration detection is established as the direct consequence of the 1/f noise voltage in the system components. The dynamic range and inaccuracy predicted by the simple theoretical model presented is in good agreement with experimental measurements. The conclusions of the analysis are compared with experimental reports of heterodyne shot-noise-limited optical systems. With this effective tool the generic class of spectrum-analysis techniques can be analyzed and relatively weighed to assess the effect of noise. This analysis is applicable to optical interferometry in general, although the experiments specifically involved fiber-optic modulators.

Interferometric measurement of fiber strain hysteresis and nonlinearity for sensitivity optimization.

A simple and reliable fringe-counting method is used to determine the fiber static elastic response in fiber-optic sensors and modulators. Large strain hysteresis and nonlinearity have been observed in the commonly employed configuration of bonding a bare fiber onto a strain element. Jacketed fibers show reduced hysteresis and nonlinearity in their elastic response. Reductions in hysteresis from 23% to 1% of the maximum strain and in the nonlinearity by a factor of 3 have been measured.

Static phase change in a fiber optic coil hydrophone.

For low acoustic frequencies, the acoustooptic interaction in a fiber optic interferometric coil hydrophone has been modeled on assumptions of hydrostatic and radial stress. However, an inherent ambiguity exists in the way by which the correct model has been chosen. It is established through unambiguous experimental determination of the sign of the induced static phase change that the hydrostatic model alone is valid. The method involves the use of a phase modulator constructed by bonding an optical fiber onto a piezoelectric PVF(2) film. Theoretical considerations which also favor the hydrostatic model are presented.

Linear readout of dynamic phase change in a fiber-optic homodyne interferometer.

A new technique that provides linear measurement of dynamic phase change in a no-feedback, no-phase-bias fiber-optic interferometer is described. The phase measurement is unaffected by random changes in phase, source intensity, and fringe visibility. A minimum detectable phase shift of 0.1 rad has been measured for the configuration reported.

Universal dynamic phase-calibration technique for fiber-optic interferometric sensors and phase modulators.

A new technique for dynamic phase calibration that utilizes only visual observation of the fringe pattern is demonstrated for use in fiber-optic interferometric sensors and phase modulators. The need for a photodetector and its associated electronic circuitry is completely eliminated. Observations show that random changes in phase, source intensity, and fringe visibility do not affect the phase calibration. Since no phase bias or feedback is necessary, the new method is simple and fast. This technique is of universal applicability to any two-beam interferometer incorporating dynamic sinusoidal displacements.