Serge Dubovitsky

MSTAR: a submicrometer absolute metrology system

The Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor permits absolute distance measurement with subnanometer accuracy, an improvement of 4 orders of magnitude over current techniques. The system uses fast phase modulators to resolve the integer cycle ambiguity of standard interferometers. The concept is described and demonstrated over target distances up to 1 m. The design can be extended to kilometer-scale separations.

Coherent range-gated laser displacement metrology with compact optical head

We describe a new architecture for laser displacement metrology with a drastic reduction in the size and complexity of the optical head. Connected by a single optical fiber, the compact heads are easy to integrate and readily multiplexed to support applications requiring large numbers of sensors. The approach is made possible by modulating the outgoing laser light with a binary random noise code, allowing the detected signals to be discriminated based on their propagation delay. We demonstrate a displacement resolution of 1.1 nm rms.

Polarization compensation: a passive approach to a reducing heterodyne interferometer nonlinearity

Cyclic errors that are due to optical leakage limit the precision of displacement measurements made with optical interferometers. A method for real-time estimation of leakage components is introduced and is used to implement a novel passive technique for suppression of cyclic nonlinearities that uses only adjustments of existing polarizers and quarter-wave plates. This approach is used to reduce the cyclic error from 3 nm to 300 pm for an interferometer operating at a wavelength of 1320 nm.

The StarLight metrology subsystem

We describe a metrology subsystem for NASAs StarLight mission, a space-based separated-spacecraft stellar interferometer. It consists of dual-target linear metrology, based on a heterodyne interferometer with carrier phase modulation, and angular metrology designed to sense the pointing of the laser beam. The dual-target operation enables one metrology beam to sense displacement of two targets independently. We present the current design, breadboard implementation of the metrology subsystem in a stellar interferometer testbed and the present state of development of flight qualifiable subsystem components.

Radiation effects on fused biconical taper wavelength division multiplexers

The effects of radiation on fused biconical taper wavelength division multiplexers are presented. A theoretical model indicates that index changes in the fiber are primarily responsible for the degradation of these devices. >

3D Metrology Camera

We describe a concept for a metrology system that can simultaneously determine the Cartesian coordinates of thousands of targets and has no moving parts. The system is called the MSTAR3D system and is based on two color interferometry where the conventional photodiode has been replaced with an extremely fast focal plane array. It permits the measurement of the three-dimensional position of multiple targets with a fraction of a millimeter accuracy. In this paper, the concept will be described in detail. Proof of concept measurements have been performed on a candidate camera. The measured parameters have been used in error budgets for performance validation of the concept. It will be shown that a metrology system like MSTAR3D can determine the xyz position with sub-millimeter accuracy. This is sufficient accuracy for most large structure metrology systems and wave front corrections for large radar antennas.

Absolute Optical Metrology: Nanometers to Kilometers

We provide an overview of developments in high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.