Multimode Fiber Speckle Imaging Using Integrated Optical Phased Array and Wavelength Scanning
Gaolei Hu, Yue Qin, Hon Ki Tsang
Abstract
The silicon optical phased array has emerged as a promising approach for speckle imaging through multimode fibers. High spatial resolution typically requires a large number of phase channels. In this paper, we propose and demonstrate a high-resolution wavelength-scanning multimode fiber imaging system, enabled by an integrated optical phased array with only 8 phase shifters. By scanning 50 different wavelengths within a 10-nm span, the number of linearly independent speckle patterns is significantly increased from 57 to 3000, ensuring high spatial resolution imaging. The speckle imaging model is modified for use with the wavelength-scanning system, and an algorithm based on particle swarm optimization is proposed for the automatic multiwavelength compensation. Two algorithms are used for image reconstruction. The pseudo-inverse method is computationally efficient and suitable for real-time imaging, while the iterative algorithm based on total-variation regularization can provide better image quality. An equivalent spatial resolution of 1.75 μm is experimentally achieved with a field of view diameter of 105 μm. The number of resolvable points is estimated to be ∼3000, which is two orders of magnitude greater than the number of phase shifters.