Speckle-scale focusing in the diffusive regime with time reversal of variance-encoded light (TROVE)

Abstract

Focusing of light in the diffusive regime inside scattering media has long been considered impossible. Recently, this limitation has been overcome with time reversal of ultrasound-encoded light (TRUE), but the resolution of this approach is fundamentally limited by the large number of optical modes within the ultrasound focus. Here, we introduce a new approach, time reversal of variance-encoded light (TROVE), which demixes these spatial modes by variance-encoding to break the resolution barrier imposed by the ultrasound. By encoding individual spatial modes inside the scattering sample with unique variances, we effectively uncouple the system resolution from the size of the ultrasound focus. This enables us to demonstrate optical focusing and imaging with diffuse light at unprecedented, speckle-scale lateral resolution of ~ 5 μm.

Super-resolution photoacoustic imaging through a scattering wall

“…Several recent techniques have overcome this limitation using acoustic waves, either with an ultrasound guide-star 15 or a photoacoustic feedback [16][17][18] . Two modifications of the ultrasound guide-star method have allowed for the creation of an optical focus smaller than the acoustic spot size 19,20 . Si et al 19 frequency modulated diffuse light with a focused ultrasound transducer and then time reversed the encoded light using optical phase conjugation.…”

Optics: Super vision

“…In 2013, for instance, Yang's team achieved this feat with unprecedented resolution by picking out a fluorescent bead just one micrometre across sandwiched between two artificial opaque layers 5 . Yang, together with biologist Benjamin Judkewitz and the rest of his team did this by illuminating the medium and letting the light bounce its way through to the other side, then reflecting it back with a 'timereversing' mirror, which effectively forces every light ray to exactly retrace its steps.…”

Effects of digital phase-conjugate light intensity on time-reversal imaging through animal tissue

“…Therefore, some technique to suppress scattering effects is necessary for practical applications of light in these fields. In recent years, a principle of scattering suppression using the time-reverse capability of phaseconjugate light has been proposed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Various attempts based on this principle have been undertaken, such as the time-reversed ultrasonically encoded (TRUE) method [1,[4][5][6][7][8].…”