Home VLC using pinpin a-SiC:H multilayer devices
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Home VLC using pinpin a-SiC:H multilayer devices 1
P. Louro ,2, V. Silva1,2, I. Rodrigues1, M. A. Vieira1,2, M. Vieira1,2,3 1 Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro Emídio Navarro, 1949-014 Lisboa, Portugal Tel: +351 21 8317290, Fax: +351 21 8317114, [email protected] ; 2 CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal
ABSTRACT In this paper an integrated wavelength optical filter and photodetector for Visible Light Communication (VLC) is used. The proposed application uses indoor warm light lamps lighting accomplished by ultra-bright light-emitting diodes (LEDs) pulsed at frequencies higher than the ones perceived by the human eye. The system was analyzed at two different wavelengths in the visible spectrum, one in the blue (430 nm) and the other in the red (626 nm) regions, driven at different currents in order to change their optical intensities. The signals were transmitted into free space and measured using a pin-pin photodetector based on a-SiC:H/a-Si:H. This detector behaves as an optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light. The output photocurrent was measured for different optical intensities of the transmitted optical signal and the extent of each signal was tested. An electrical model was used to support the physical operation of the device. INTRODUCTION Visible Light Communication (VLC) makes use of modulated light in the visible spectrum to encode, transmit and broadcast information. This type of wireless optical communication system is based on the fast switching property of Light Emitting Diodes (LEDs) that can be modulated for free space communications [1, 2]. Therefore, in addition to the usual function of indicator or illumination device, LEDs can also be a communication vehicle for the transmission of information. In this paper we propose the use of a multilayered pinpin device based on a-SiC:H [3, 4] to work as a photodetector operating in the pertinent range of operation for VLC (375 nm – 780 nm). Here we demonstrate the possibility of decoding two transmission optical channels supplied by two different wavelength LEDs. Optoelectronic characterization of the device is presented and shows the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. An optoelectronic model supports the experimental results and a numerical simulation is presented to support the physical operation of the device. SYSTEM The proposed system uses indoor lighting of warm light lamps accomplished by ultra-bright LEDs pulsed at 1 kHz. The system was analyzed using two different visible wavelengths in the blue (430 nm) and in the red (626 nm) regions of the visible spectrum that were driven at different currents in order to change their optical intensity, to simulate the operating range for each LED.
Figure 1 Design of the proposed VLC system in a domestic lighting
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