J. M. Dziedzic

Observation of optical resonances of dielectric spheres by light scattering

Use of the wavelength and size dependence of light scattering from optically levitated liquid drops is demonstrated as a sensitive means of detecting optical resonances of dielectric spheres. High resolution spectra are presented of the radiation pressure, far- and near-field backscatter, and 90 degrees scatter. Excellent agreement is found between experimental spectra and high resolution Mie calculations of Chylek et al. Strong evidence supporting the van de Hulst dielectric surface-wave model for these resonances is presented. Use of resonances for high precision measurement of sphere size and sphere distortion, index of refraction, temperature, and vapor pressure is discussed.

Simultaneous determination of refractive index and size of spherical dielectric particles from light scattering data

The diameter and refractive index of micrometer sized spherical dielectric particles are simultaneously deduced using the wavelength dependence of backscattering data from optically levitated particles. The accuracy of the results is set by experimental errors in the determination of the wavelength of backscatter resonance peaks and the ratio of slopes of specified peaks. At present the refractive index and diameter can be deduced with relative errors of 5 x 10(-5). This represents the most accurate determination of absolute size and refractive index yet made by light scattering. A reduction of these errors by an order of magnitude is possible. We assume a priori knowledge of diameter and refractive index with accuracy of 10(-1) and 5 x 10(-3), respectively.

Optical Kerr effect in long fibers

Optical Kerr modulation of >100% is demonstrated in long birefringent optical fibers using low laser powers of ~1 W. We have experimentally investigated the effects of group-velocity dispersion, thermal stability of polarization, and fiber birefringence. Use of fiber Kerr modulation as a fast optical shutter is studied, and it is concluded that resolution times shorter than 1 psec are possible in principle.

In-line fiber-polarization-rocking rotator and filter

An in-line polarization rotator has been built into a single-mode birefringent fiber. The rotator utilizes periodic twists of the fibers principal axes, which were formed by rocking the preform as the fiber was drawn. The polarization conversion between the principal axes is wavelength dependent, with a bandwidth inversely proportional to the number of twist periods. The bandwidth of the present rotator was 4.8 nm for 100% conversion in a fiber length of 170 cm.

Controlled micromanipulation of human sperm in three dimensions with an infrared laser optical trap: effect on sperm velocity*†

Individual human sperm can be micromanipulated in three dimensions using a 1.06 microns Nd:YAG laser trap. Single sperm swimming with velocities in the range of 65 to 85 microns/sec can be trapped with 40 mW of power through 120 seconds without a deleterious effect on velocity. Even though it will be necessary to further evaluate the effects of laser light on specific functions of sperm, our data suggest that decreasing the time of manipulation to a minimum will increase the safety of the micromanipulation procedures. Laser traps may play a role in assisted reproductive technology by facilitating the selective transport of individual sperm.

Outer diameter measurement of low birefringence optical fibers by a new resonant backscatter technique.

A new, highly precise, optical fiber outer diameter measuring technique based on near-field resonant backscattered light is described. Relative accuracies of +/-10(-2) microm were achieved in diameter measurements using Fabry-Perot resonances and +/-10(-3) microm in average diameter measurements using dielectric surface-wave resonances for ~100-microm fibers. The shape of a new type of low birefringence spun fiber, made by rapidly spinning a near circular preform in the pulling oven, was measured. We observed a small ellipticity which rotated helically along the fiber. The possibility of making absolute and real-time outer diameter measurements is discussed.

Laser induced refractive index inhomogeneities and absorption saturation effects in CdS

We have studied an optically-induced index inhomoganeity in CdS. Using ∼10 mW of focused laser radiation whose frequency is near the band gap, a reduction in index as large as one part in 103was observed which resulted in induced lenses with focal lengths as short as 1 mm. We also find large absorption saturation and highly efficient recombination radiation (green edge emission) accompanying the index effects. Changes in optical transmission of two orders of magnitude and quantum conversion efficiencies of ∼50 percent were measured. The effects occur in selected samples near liquid nitrogen and liquid hydrogen temperature. Various mechanisms for the inhomogeneities are discussed. The effect is ultimately attributed to the presence of compensated Cd acceptor vacancies which act, directly or indirectly, as absorbing centers. The relevance of these effects to laser-induced index inhomogeneities occurring in LiNbO 3 and LiTaO 3 is discussed.

Tension-adjusted in-line optical-fiber attenuator

We describe an in-line, single-mode fiber attenuator using a combination of polarization-preserving and single-polarization fibers. The attenuation is adjustable over a 30-dB range by varying the birefringence of a short lengthof fiber with tension. The insertion loss is 1.3 dB. The tension birefringence arises from the difference in Poissons ratio between the noncircular stress cladding and the silica substrate glass.

Polarization-selective 3-dB fiber directional coupler

Measurements on a 3-dB polarization-selective fiber directional coupler demonstrate that the polarization selectivity arises from different mismatches for the propagation constants of the two polarizations.