Dual-wavelength Fourier Ptychography Using a Single LED

We propose dual-wavelength Fourier ptychography for topographic measurement. To extend the axial measurement range, a single light-emitting diode (LED) and two appropriate bandpass filters are employed. This provides a speckle-free phase image, and reduces the possibility of a systematic error, which yields a high-quality topographic image. The proposed system can measure the surface topography in the range of nano- to micro-structures. The performance of the system is experimentally verified.