  Imaging techniques based on single-pixel detection, such as ghost imaging,
can reconstruct or recognize a target scene from multiple measurements using a
sequence of random mask patterns. However, the processing speed is limited by
the low rate of the pattern generation. In this study, we propose an ultrafast
method for random speckle pattern generation, which has the potential to
overcome the limited processing speed. The proposed approach is based on
multimode fiber speckles induced by fast optical phase modulation. We
experimentally demonstrate dynamic speckle projection with phase modulation at
10 GHz rates, which is five to six orders of magnitude higher than conventional
modulation approaches using spatial light modulators. Moreover, we combine the
proposed generation approach with a wavelength-division multiplexing technique
and apply it for image classification. As a proof-of-concept demonstration, we
show that 28x28-pixel images of digits acquired at GHz rates can be accurately
classified using a simple neural network. The proposed approach opens a novel
pathway for an all-optical image processor.
