Wavefront shaping techniques in complex media
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- Category: Highlights
- Published on Tuesday, 04 November 2014 09:41
[highligth] A microwave spatial modulator to improve in-home WiFi
[N. Kaina et al., Sci. Rep. (2014)]
Wavefront shaping is not limited to optical waves. Similar techniques can be used for any kind of wave for which one can control dynamically the phase over a large number of independent elements. In [N. Kaina et al., Sci. Rep. (2014)], the authors demonstrate the use of their Spatial Microwave Modulator (SMM) to control the propagation of radio frequency waves inside a room to improve the WiFi signal at any chosen position. The system is passive as there is no energy transfer from the modulator to the WiFi signal, it only controls the local phase of the waves reflected of the modulator. The device is thin and has the typical size of small poster, it can be conveniently placed on the wall of a typical room without any loss of space.
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- Category: Multimode fibers
- Published on Monday, 27 October 2014 00:08
[tutorial] 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 a quick tutorial on the calculation of the modes of a step index multimode fiber and how to find the so called linearly polarized modes, that are convenient for manipulation using shaping techniques.
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- Category: Spatial Lights Modulators (SLMs)
- Published on Friday, 24 October 2014 10:43
[tutorial] 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 take advantage of one dimension to encode the amplitude and phase in fringes, this technique exploits both dimensions of the pixel array using "superpixels".
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- Category: Highlights
- Published on Tuesday, 01 July 2014 11:45
[highlight] 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 an known obstacle for imaging as it mixes light sending it in all the dirrections. 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.
Without absorption, spatial information of an object transmitted through an opaque material is totally mixed and difficult to recover. The reason is that the photons are multiply scattered, hence their propagation directions are randomized at every scattering event. In their recent numerical calculation study, the authors noticed that when absorption becomes strong, the transport of light occurs via much straighter paths.
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- Category: Wavefront shaping talks
- Published on Monday, 23 June 2014 09:03
Maximally efficient imaging through multimode fiber
Joel A. Carpenter
CLEO 2014, San Jose, CA, USA
Thursday, 12 June, 2014
Abstract:
Polarization diverse images are generated at the end of a multimode fiber using spatial light modulators to completely characterize propagation through the fiber in terms of the eigenmodes.
http://dx.doi.org/10.1364/CLEO_SI.2014.STh1H.3
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- Category: Postdoc offers
- Published on Friday, 20 June 2014 11:51
PostDoctoral position in the Bioimaging and Neurophotonics lab
Berlin, Germany
Postdoctoral and doctoral positions are available in the Bioimaging and Neurophotonics lab under supervision of Prof. Benjamin Judkewitz. Supported by the German Excellence Initiative, the lab is based at the Charité and Humboldt University campus in the heart of Berlin.
