Fig. 1. (a) Forward propagation of scattered light; (b) Back propagation of phase-conjugated light ^[33]

Fig. 2. (a) Light field measurement process; (b) Light field modulation process, SLM: Spatial light modulator

Fig. 3. (a) Speckle background; (b) Optical focus achieved with rough system alignment (PBR~61); (c) Optical focus achieved with fine system alignment (PBR~52000)^[38]

Fig. 4. Operational principle for TRUE; (a) The ultrasonic guide star tags a portion of scattered light that passes through the ultrasonic focus, causing a small amount of frequency shift; (b) The phase conjugate mirror selectively reflects the frequency-shifted light, realizing optical focusing inside the scattering medium

Fig. 5. Operational procedures for TRUE; (a) Light field measurement process; (b) Light field modulation process. φ(r), phase map of scattered light, which is captured by the camera

Fig. 6. Results for high-speed TRUE system optical focusing ^[64]

Fig. 7. Schematics of employing TRUE and optogenetics ^[66]

Fig. 8. Schematics of employing TRUE focusing for the treatment of congenital cataracts. (a) A cataract harvested from a human; (b) Projecting stripes through the cataractous lens with TRUE focusing and direct focusing^[68]