Continuous amplified digital optical phase conjugator for focusing through thick, heavy scattering medium

Digital optical phase conjugation (DOPC) is a well-known technique for generating a counter-propagating wavefront and reversing multiple scattering effects. Until now, implementations of DOPC are mostly based on a switching geometry. For some applications such as optical tweezers in turbid media, however, switching-based DOPC could fail to grab fast-moving particles. Besides, a DOPC modality with temporally-continuous gain is required. In this paper, a continuous amplified digital optical phase conjugator (CA-DOPC) is introduced to form a focusing point after passing through a heavily scattering medium. To achieve high-precision alignment between the CMOS image sensor and the spatial light modulator (SLM) in the CA-DOPC, an optical phase conjugator along with a specially designed alignment pattern was used. In this research, the CA-DOPC showed its ability to form a focus point in 2-mm-thick chicken muscle tissue. In addition, a continuous gain of 166 and peak-to-background ratio (PBR) of 3×10⁵ were observed in the case of 0.5-mm chicken muscle tissue.