Optical phase conjugation assisted scattering lens: variable focusing and 3D patterning

Abstract

Variable light focusing is the ability to flexibly select the focal distance of a lens. This feature presents technical challenges, but is significant for optical interrogation of three-dimensional objects. Numerous lens designs have been proposed to provide flexible light focusing, including zoom, fluid, and liquid-crystal lenses. Although these lenses are useful for macroscale applications, they have limited utility in micron-scale applications due to restricted modulation range and exacting requirements for fabrication and control. Here, we present a holographic focusing method that enables variable light focusing without any physical modification to the lens element. In this method, a scattering layer couples low-angle (transverse wave vector) components into a full angular spectrum, and a digital optical phase conjugation (DOPC) system characterizes and plays back the wavefront that focuses through the scattering layer. We demonstrate micron-scale light focusing and patterning over a wide range of focal distances of 22–51 mm. The interferometric nature of the focusing scheme also enables an aberration-free scattering lens. The proposed method provides a unique variable focusing capability for imaging thick specimens or selective photoactivation of neuronal networks.

Broadband transparent and CMOS-compatible flat optics with silicon nitride metasurfaces [Invited]

“…Prominent examples include imaging through biological tissue or other highly scattering media such as fog, which distort incident wavefronts and hinder image formation. Some disordered media, however, can be used to enhance wavefront shaping capability, leveraging multiple scattering to expand both the spatial extent and range of wavevectors in an optical system [66][67][68][69][70][71][72]. In this case, the employed disordered medium must be fully characterized to understand its effect on an incident wavefront.…”

“…In this case, the employed disordered medium must be fully characterized to understand its effect on an incident wavefront. In knowing the effect of the disordered medium, the distortion it introduces can be removed via post-processing or exploited in conjunction with a source to achieve more sophisticated functionalities [70][71][72][73]. Fig.…”

Three-dimensional focusing through scattering media using conjugate adaptive optics with remote focusing (CAORF)

“…An advantage of using the SLM as a wavefront corrector is the ability to generate an arbitrary pattern through the scattering layer [17,29]. To generate a 3d pattern, the phase often needs to be measured at different Z planes because of the limited axial FOV.…”

“…The first demonstration of focusing through scattering media by Vellekoop et al [17] showed its potential for applications in fluorescent laser scanning microscopy. Several groups [23][24][25][26][27][28][29] further demonstrated the lateral or axial scanning of the focus behind the scattering layer utilizing the memory effect. Lateral scanning is realized by either rotating the beam around the scanning layers or by adding tip/tilt to the compensation phase.…”

“…This paper also gives thorough simulations and experimental analysis of both CAORF and the conventional CAO without RF, which shows the benefits of maintaining conjugation during axial scanning. In additional, the proposed system rotates the beam at the objective pupil plane instead of at the conjugate plane at the scattering layers [29,31]. It can be easily integrated into a conventional laser scanning fluorescent microscope.…”