Laser metrology systems are a key component of stellar interferometers, used to monitor path lengths and dimensions internal to the instrument. Most interferometers use 'relative' metrology, in which the integer number of wavelengths along the path is unknown, and the measurement of length is ambiguous. Changes in the path length can be measured relative to an initial calibration point, but interruption of the metrology beam at any time requires a re-calibration of the system.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard interferometers, and making it possible to measure distance with sub-nanometer accuracy. We describe the design of the system, show results for target distances up to 1 meter, and demonstrate how the system can be scaled to kilometer-scale distances. In recent experiments, we have used white light interferometry to augment the 'truth' measurements and validate the zero-point of the system.
MSTAR is a general-purpose tool for conveniently measuring length with much greater accuracy than was previously possible, and has a wide range of possible applications.
Recent use of quantum mechanics to guide the improvement of molecular hyperpolarizability and the use of statistical mechanical analysis of the effects of intermolecular electrostatic interactions to improve the acentric ordering of organic chromophores has led to the realization of electro-optic coefficients, r33, greater than 100 pm/V (at telecommunication wavelengths). This material design and development paradigm is likely to lead to further improvement in electro-optic activity, which will in turn facilitate the development of a variety of electro-optic devices with drive (Vπ) voltage requirements of less than one volt. The utility of organic electro-optic materials for development of high bandwidth devices is now well documented. What is less obvious is the utility of organic electro-optic materials for the fabrication of complex (including conformal, flexible, and three-dimensional) device structures. In this communication, we review recent improvements in electro-optic activity; thermal and photochemical stability; and processability of organic electro-optic materials and the use of these materials to fabricate conformal and flexible electro-optic devices and devices based upon single and multiple coupled ring microresonators.
The MSTAR sensor (Modulation Sideband Technology for Absolute Ranging) is a new system for measuring absolute distance, capable of resolving the integer cycle ambiguity of standard intrferometers, and making it possible to measure distance with sub-nanometer accuracy. The sensor uses a single laser in conjugation with fast phase modulators and low-frequency detectors. We describe the design of the system - the principle of operation, the metrology source, beam-launching optics, and signal processing - and show results for target distance up to 1 meter. We then demonstrate how the system can be scaled to kilometer-scale distances.