Ultrafast Surface Imaging With an Increased Spatial Resolution Based on Polarization-Division Multiplexing

Optical time stretch has been employed for ultrafast optical imaging based on space-to-wavelength-to-time mapping. However, temporal overlap between two adjacent time-stretched pulses is a disadvantageous factor that limits the spatial resolution, or the frame rate has to be reduced by reducing the pulse repetition rate to avoid the temporal overlap. To increase the spatial resolution without reducing the frame rate, we propose a novel technique based on polarization-division multiplexing, using a polarization modulator to generate two polarization interleaved pulse trains. Since two adjacent optical pulses are orthogonally polarized, the spacing between two adjacent pulses for one polarization direction is doubled, and the spatial resolution is doubled by using a dispersive element with two times the dispersion. The proposed approach is experimentally evaluated. An imaging system with an increased spatial resolution is demonstrated.