Toward optimal performance of systems for digital optical phase conjugation

Digital optical phase conjugation (DOPC) emerges as a promising technique for controllable optical delivery in strongly scattering media. Notably, due to the long-standing challenges in accurate alignment of the wave-front sensor and spatial light modulator (SLM), conventional DOPC systems heavily rely on digital calibration for misalignments between these two devices, which will significantly increase the pixel crosstalk of the SLM and thus degrade the performance of DOPC systems. To circumvent this digital calibration for mitigation of the pixel crosstalk, here we propose and demonstrate a real-space alignment scheme for DOPC systems based on single-pixel imaging, which enables precise alignment of the SLM and wave-front sensor: (i) with off-plane alignment precision of submillimeter and milliradian for axial and angular positions, respectively, and (ii) with in-plane pixel match at subpixel resolution. With additional efforts on fidelity optimization of optical phase-conjugation, deformations on the phase-conjugated wave front can almost be removed and the DOPC system would exhibit ultrahigh performance, with peak-to-background ratio (PBR) approaching the theoretical limit (more than 90%) in the time-reversed optical refocusing test. It can be anticipated that all DOPC-based applications will tremendously benefit from this near-theoretical-limit performance of optical phase conjugation for improved capacity and practical utility.