High-precision measurement of pixel positions in a charge-coupled device.

The high level of spatial uniformity in modern CCD's makes them excellent devices for astrometric instruments. However, at the level of accuracy envisioned by the more ambitious projects such as the Astrometric Imaging Telescope, current technology produces CCD's with significant pixel registration errors. We describe a technique for making high-precision measurements of relative pixel positions. We measured CCD's manufactured for the Wide Field Planetary Camera II installed in the Hubble Space Telescope. These CCD's are shown to have significant step-and-repeat errors of 0.033 pixel along every 34th row, as well as a 0.003-pixel curvature along 34-pixel stripes. The source of these errors is described. Our experiments achieved a per-pixel accuracy of 0.011 pixel. The ultimate shot-noise limited precision of the method is less than 0.001 pixel.

Multimode fiber-optic broad spectral band interferometer.

We have developed techniques that permit broad spectral band interference fringes to be observed on a mode-by-mode basis, using long lengths of few-mode fiber without the detrimental effects of incoherent modal superimposition. Modes are spatially by a cladding etching technique. Mode orientation and polarization are preserved by using elliptical core fibers.

Picosecond streak camera display of an intermodal coupling matrix at a multimode fiber splice.

We have developed a technique that permits direct visualization of the coupling matrix for all guided modes of a moderately multimode fiber optic at a splice or mode coupler. The matrix is formed by an array of spots at the output of a picosecond streak camera. The technique also permits unambiguous determination of the phase velocity and group velocity of the modes.

Selective mode injection and observation for few-mode fiber optics.

By etching the cladding along several millimeters of circular- or elliptical-core few-mode fiber optics, we gain access to the core and can inject extremely pure modes. The same etching technique allows one to measure the modal purity at the far end of the fiber. Modal purities of -26 dB have been obtained. We also demonstrate a holographic technique that allows all the light of each mode to be focused to an independent spot.

Coupling starlight into single-mode fiber optics.

We have calculated the efficiency with which starlight can be coupled into a single-mode fiber optic that is placed in the focal plane of a telescope. The calculations are performed for a wide range of seeing conditions, with and without rapid image stabilization, and for a wide range of wavelengths. The dependence of coupling efficiency on the f-ratio of the incident beam is explored. Also, we calculate the coupling efficiency as a function of displacement for a perfect Airy pattern. We have also used a computer program which simulates atmospheric wavefronts to determine the variance of instantaneous coupling efficiency as a function of seeing. In perfect conditions, the maximum efficiency at the LP(11) mode cutoff is 78% due to the mismatch of the Airy pattern and the nearly Gaussian mode of the fiber. Maximum total coupled power is attained at d/r(0) = 4 with rapid image stabilization.

Single-mode fiber optics in a long-baseline interferometer.

We have investigated the potential for using single-mode fiber optics to link two or more telescopes in a large optical to near-IR astronomical interferometer. On an optical bench, we observed the effects of dispersion, temperature, and birefringence on wide-bandwidth interference fringes using up to 30 m of single-mode fiber in each arm of a Twyman-Green interferometer.