Precision interferometry for measuring wavefronts of multi-wavelength optical pickups

A novel wavefront measurement interferometer is developed that enables the user to evaluate the wavefronts of multi-wavelength optical pickups. In this interferometer, instead of transparent pinholes used in Mach-Zehnder interferometers, reflection dot pinhole mirrors are used to generate reference wavefronts for different wavelengths which make the optical system very flexible and simple compared with those using transparent pinholes. The interferometer is designed to operate at wavelengths of 405nm, 650nm and 780nm over an NA range of up to 0.95, which is very difficult to realize when transparent pinholes are used for generating reference wavefronts. The three-beam problem is solved and the optics of the interferometer is simplified by employing a software filter instead of using spatial filters in the optics of the interferometer. The instrument has an equal optical path length that enables the user to measure pickups with a very short coherence length. A new method by which asymmetric aberration components, such as astigmatic and coma aberrations, can be calibrated by rotating the measured lens with 90 and 180 degrees is proposed and the calibration results are verified by using a high precision reference point source. System accuracy is also evaluated by comparing with the measurement results obtained by commercial Fizeau type interferometer and a good agreement is achieved. (c) 2008 Optical Society of America.