Showing papers on "Phase conjugation published in 2023"

Compensation of emulated atmospheric disturbance and tracking of a moving object by a real-time digital phase conjugate mirror using a liquid crystal spatial light modulator

Abstract: We developed a fast-response digital phase conjugate mirror using a 700 Hz high-speed liquid crystal spatial light modulator and a high-speed camera. The total delay from signal light acquisition to phase conjugate light generation was 9.7 ms at 1246 × 1024 and 5.9 ms at 640 × 512. The tracking experiment performed on a target moving at a constant distance perpendicular to the optical axis, produced an error of 2%. Furthermore, a heated soldering iron, used to compensate for artificially generated air disturbance, showed that beam wandering and intensity fluctuations were reduced by 86% and 55%, respectively, compared to a phase conjugate mirror with added delay. Phase conjugate light irradiation of a continuously moving target at a maximum speed of 0.9 mm s−1 was also performed. This study shows that real-time digital phase conjugate mirrors can correct wavefront distortion caused by air fluctuation, which is a major challenge in long-distance wireless optical transmission in the turbulent atmosphere, without complicated control, and prevent beam quality degradation in the presence of atmospheric disturbance.

Phase conjugation with spatially incoherent light in complex media

Abstract: Shaping light deep inside complex media, such as biological tissue, is critical to many research fields. Although the coherent control of scattered light via wavefront shaping has made significant advances in addressing this challenge, controlling light over extended or multiple targets without physical access inside a medium remains elusive. Here we present a phase conjugation method for spatially incoherent light, which enables the non-invasive light control based on incoherent emission from multiple target positions. Our method characterizes the scattering responses of hidden sources by retrieving mutually incoherent scattered fields from speckle patterns. By time-reversing scattered fluorescence with digital phase conjugation, we experimentally demonstrate focusing of light on individual and multiple targets. We also demonstrate maximum energy delivery to an extended target through a scattering medium by exploiting transmission eigenchannels. This paves the way to control light propagation in complex media using incoherent contrasts mechanisms.

Single-shot Digital Optical Fluorescence Phase Conjugation Through Forward Multiply Scattering Samples

Abstract: Aberrations and multiple scattering in biological tissues critically distort light beams into highly complex speckle patterns. In this regard, digital optical phase conjugation (DOPC) is a promising technique enabling in-depth focusing. However, DOPC becomes challenging when using fluorescent guide-stars for four main reasons: The low photon budget available, the large spectral bandwidth of the fluorescent signal, the Stokes shift between the emission and the excitation wavelength, and the absence of reference beam preventing holographic measurement. Here, we demonstrate the possibility to focus a laser beam through multiple-scattering samples by measuring speckle fields in a single acquisition step with a reference-free and high-resolution wavefront sensor. By taking advantage of the large spectral bandwidth of forward multiply scattering samples, Digital Fluorescence Phase Conjugation (DFPC) is achieved to focus a laser beam at the excitation wavelength while measuring the broadband speckle field arising from a micron-sized fluorescent bead.

Phase-preserving amplitude regeneration in a Mamyshev regenerator with mid-stage optical phase conjugation

Abstract: We experimentally demonstrate phase-preserving amplitude regeneration of an RZ-QPSK signal by placing an optical phase conjugator between two Mamyshev regenerators, improving intensity noise 2.8 times, Q-factor by 2.4 dB and EVM by 4.0%.