Biomedical subjects
Publications and source records attributed to Paul S Westbrook.
We demonstrate a fourth-order polarimeter that employs two-photon detection to measure the fourth-order polarization coherency matrix (FOCM) of an optical signal. We measure the FOCM of picosecond pulses subjected to polarization mode dispersion (PMD). The fourth-order polarimeter distinguishes different PMD states even when the state of polarization, including the degree of polarization, is constant.
We show that the addition of a polarization controller and bias differential group delay to a spectral polarimeter increases the amount of polarization information that can be extracted from a Stokes spectrum measurement. We use this biased spectral polarimetry on 40-Gbit/s signals to measure the polarization mode dispersion of the optical fiber through which they propagate. Our measurements do not require any control of the polarization at the fiber input. Averaging measurements from several settings of the polarization controller yields improved accuracy, and, after data rejection is applied, both the accuracy and the number of valid data points is increased when using several measurements.
Using volume current analysis, we describe the scattering from intracore fiber gratings with various nonuniformities and find that effects of cross-sectional and longitudinal variations can be roughly decoupled. We show that cross-sectional asymmetry affects the azimuthal pattern of scattering around the fiber and find good agreement with real gratings exhibiting UV-induced grating asymmetry across the core. We also show that longitudinal variations affect the spread of scatter angles with respect to the fiber axis, and this angular spread depends on the Fourier transform of the profiles of the grating period, the average index, and the index modulation of the grating.
We measured the polarization dependence of light scattered from a tilted fiber grating and found disagreement with previous volume-current perturbation analysis. However, by including the longitudinal E field of the guided wave we were able to obtain good agreement, demonstrating that, although it is small, this component cannot be neglected when scattering of weakly guided waves is considered. A first-order approximation formula for the polarization dependence was also obtained and is shown to be accurate within most of the resonance band of scattering.
We demonstrate a novel interferometric technique for highly accurate characterization of phase masks used in optical fiber grating fabrication. The principle of the measurement scheme is based on the analysis of the interference pattern formed between the first- and zero-order beams transmitted through or reflected from the grating under test. For spatial resolution of a few millimeters, our methods allow the determination of local variations of the order of 1-microm grating period with an accuracy of a few picometers. These methods are applicable to a broad class of diffractive grating structures.