Transmission medium | EPFL Graph Search

A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modulate sound, and a transmission medium for sounds may be air, but solids and liquids may also act as the transmission medium. Vacuum or air constitutes a good transmission medium for electromagnetic waves such as light and radio waves. While a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by absorption or reflection or refraction at the interfaces between media. Technical devices can therefore be employed to transmit or guide waves. Thus, an optical fiber or a copper cable is used as transmission media. Electromagnetic radiation can be transmitted through an optical medium, such as optical fiber, or through twisted pair wires, co

Analysis of Optical and Morphological Properties of Aluminium Induced Texture Glass Superstrates

Corsin Battaglia, Juan Wang

Texturing the glass surface is a promising method for improving the light trapping properties of superstrate thin-film silicon solar cells, as it enables thinner absorber layers and, possibly, higher cell efficiencies. In this paper we present the optical and morphological properties of borosilicate glass superstrates textured with the aluminium induced texture (AIT) method. High haze values are achieved without any reduction in the total optical transmission of the glass sheets after the AIT process. Scanning electron microscope and atomic force microscope (AFM) measurements reveal a laterally uniform surface morphology of the AIT texture. We demonstrate that the surface roughness and thus the transmission haze can be controlled by adjusting the AIT process parameters. From the AFM images, we extract histograms of the local height and angle distributions of the texture. Samples with a wide angle distribution are shown to produce the highest optical haze. The results of this analysis provide a better understanding of the correlation between the AIT process parameters and the resulting surface morphology. This analysis is further extended to an amorphous silicon pin solar cell deposited onto the textured glass substrate. (C) 2012 The Japan Society of Applied Physics

Japan Society of Applied Physics2012

Control of pulsed light propagation through multimode optical fibers

Edgar Emilio Morales Delgado

Visualization of organs and cells in the interior of living beings is a challenging task due to the light absorption and multiple light scattering occurring in biological tissue that prevents the di-rect transmission of images. A standard visualization approach is based on the use of endo-scopes which is accomplished through apertures in the body. Since their invention, the light transmission capability of optical fibers has enabled fiber optic based endoscopy with devices based on bundles of optical fibers that can directly relay images. Due to their small diameter, fiber optic endoscopes are standard in minimally invasive applications either with a white light illumination or as a fluorescent imaging device. The principle behind fluorescent endoscopy consists on the scanning of light intensity over a fluorescent sample, which is achieved by se-quential illumination of each one of the fiber bundles or by mechanical scanning of a single-mode double-cladding fiber. Collecting the fluorescent signal through the light guiding medium, an image can be reconstructed. The main drawback of fiber bundle endoscopes is the pixelated limited resolution given by the presence of thousands of cores that conform the bundle. In the double cladding fiber endoscopes, there is a limit to the miniaturization of the endoscope due to the requirement of mechanical elements at the tip of the fiber to scan the illumination over the sample. In this thesis, methods for focusing and digital scanning of optical light pulses through multimode optical fibers without any distal mechanical element are developed. Such techniques are based on spatial light modulation. Spatial phase modulation allows the control of light propagation in scrambling media, as in a multimode fiber, enabling the generation of intensity light foci or arbitrary intensity profiles. The high intensity of the transmitted pulses permits multi-photon imaging through multimode optical fibers, resulting in imaging probes of higher resolution than in the case of fiber bundles. We demonstrate in a working prototype that this approach provides all the advantages of multi-photon microscopy at the tip of an ultra-thin probe, such as a reduced photo bleaching of the sample, optical sectioning and enhanced image contrast. The developed methods can also be employed for material processing that requires high in-tensity light pulses. In specific, we demonstrate additive manufacturing, also known as 3D printing, at the tip of an ultra-thin needle. The working principle is based on two-photon polymerization, which is accomplished by scanning intense light pulses on a photosensitive material that hardens when exposed to light. All other additive manufacturing methods require very large nozzles or components in close proximity to the structure that they build, up to now. With an ultra-thin 3D printing probe we enable micro-fabrication through very small apertures, in places of difficult access or in the interior of living beings. We call it, endofabrication.

EPFL2017

Multifunctional Hyperelastic Structured Surface for Tunable and Switchable Transparency

Romain Christophe Rémy Fleury, Taha Goudarzi, Rayehe Karimi Mahabadi

We leverage the crucial hyperelastic properties of a multifunctional structured surface to optimize the reconfigurability of the electromagnetic transmission under large nonlinear mechanical deformations. This multiphysics, multifunctional, hyperelastic structured surface (HSS) offers two simultaneous intriguing functionalities; tunability and switchability. It is made of copper resonators and a Polydimethylsiloxane (PDMS) substrate, which is one of the most favorable deformable substrates due to its hyperelastic behavior. The proposed HSS is fabricated via an original cost-effective technique and the multiphysics functionalities are captured in both experimental tests and numerical simulations. Leveraging the hyperelastic behavior, we demonstrate up to 8% percent shift in the resonance frequency in the GHz range, for average applied mechanical strains of around 17%. The hyperelastic deformations can continuously increase/decrease the magnitude of the scattering parameter S21 in the frequency range of 10.9 GHz to 11.8 GHz by more than 40 dB, changing from being largely transparent to opaque and vice versa. The potential of hyperelastic behavior to account for the multifunctionality of the HSS is validated experimentally.

2021

Control of pulsed light propagation through multimode optical fibers

Edgar Emilio Morales Delgado

EPFL2017