Created by sebastien.popoff on 27/10/2014
Modes of step-index multimode fibers
Scattering media were the first type of "complex media" for which wavefront shaping techniques were applied. Quickly, applications were developed for multimode fibers as well. One can consider multimode fiber as a complex media; because of its inherent modal dispersion (different modes travel at different speeds) and also because of the possible coupling between modes, the output field of the fiber does not resemble its input one. Wavefront shaping in multimode fibers has had a fast development because of its applications in biomedical endoscopic imaging and for telecommunications, where the exploitation of the spatial modes in multimode fibers offers a promising way to increase data rates compared to single-mode fibers.
I present here quickly the expression of the modes of a step-index multimode fiber and the so-called linearly polarized modes, that are convenient for manipulation using shaping techniques.
Created by sebastien.popoff on 24/10/2014
How to use a binary amplitude Deformable Miror Device (DMD) as a phase modulator: The "superpixel" method
I previously presented a technique based on the Lee hologram that allows to use a binary amplitude modulator (like a DLP chip you find in standard projectors) to perform a phase modulation (or amplitude and phase modulation). Recently, a new technique was introduced in [S.A. Goorden et al., Opt. Express (2014)] that allows an accurate complex modulation with less loss in term of spatial resolution. This post is more a highlight on this paper than a proper tutorial. In a nutshell, while the Lee hologram only takes advantage of one dimension to encode the amplitude and phase in fringes, this technique exploits both dimensions of the pixel array using superpixels.
Created by sebastien.popoff on 01/07/2014
From diffusive to ballistic-like transport in absorbing media
Intuitively, absorption of light is detrimental for imaging as it reduces the intensity of the image we see. On the other hand, scattering is also a known obstacle for imaging as it mixes light sending it in all the directions. In the present paper, S.F. Liew and his collaborators from Yale University (CT, USA) and the University of Twente (The Netherlands) show that, contrary to appearances, absorption can in fact help light to follow a direct path through disordered media.
Created by sebastien.popoff on 23/06/2014
Maximally efficient imaging through multimode fiber
Joel A. Carpenter
CLEO 2014, San Jose, CA, USA