| Fringe modulation waveform optimization has been a goal at the Navy Precision Optical Interferometer (NPOI) for a number of years. The development of a new fast delay line (FDL) control system has presented an opportunity to study this issue in detail. A frequency sweep analysis of the FDL system was performed to determine an approximate transfer function for the system. An algorithm was developed to use this transfer function using a gradient decent approach in the complex domain, optimizing the odd harmonics of the triangle wave to produce a linear modulation waveform.;The algorithm was implemented on the actual FDL hardware used by the NPOI. A mean filter was introduced at the modulation mirror, allowing the algorithm to converge to a solution, and give information that can be used as diagnostic tools for the NPOI FDL carts. The resulting implementation on NPOI hardware showed excellent results with a root mean square deviation (RMSD) residual of less than 1nm of the modulation waveform at the modulation mirror, from a modeled 7-odd harmonic triangle wave. |
