Focusing light deep inside and through thick biological tissue is critical to many applications. However, optical scattering prevents light from being focused through thick biological tissue, which restricts biophotonics to a limited depth of about 1 mm. To break this optical diffusion limit, digital optical phase conjugation (DOPC) based wavefront shaping techniques are being actively developed. Previous DOPC systems employed spatial light modulators that modulated either the phase or the amplitude of the conjugate light field. Here, we achieve optical focusing through scattering media by using polarization modulation based generalized DOPC. First, we describe an algorithm to extract the polarization map from the measured scattered field. Then, we validate the algorithm through numerical simulations, and find the focusing contrast achieved by polarization modulation is similar to that achieved by phase modulation, and is higher than those achieved by binary-phase and binary-amplitude modulations. Finally, we build a system using an inexpensive twisted nematic liquid crystal based spatial light modulator, and experimentally demonstrate light focusing through 3-mm thick chicken breast tissue. Since the polarization modulation based SLMs are widely used in displays and are having more and more pixel counts with the prevalence of 4K displays, these SLMs are inexpensive and valuable devices for wavefront shaping. Thus, we anticipate that polarization modulation based SLMs will gain their prevalence in the field of wavefront shaping.
Jiamiao Yang, Yuecheng Shen, Yan Liu, Ashton Hemphill, and Lihong Wang, "Focusing light through scattering media by polarization modulation based generalized digital optical phase conjugation (Conference Presentation)," Proc. SPIE 10502, Adaptive Optics and Wavefront Control for Biological Systems IV, 105020L (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2287467.5751643371001.
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