Light filtering devices using background wavelength processing techniques
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Light filtering devices using background wavelength processing techniques M. A. Vieira1,3, M. Vieira1,2, P. Louro1,2, V. Silva1,2, A. S. Garção2,3 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]. 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. 2
ABSTRACT This paper reports on light filtering devices based on a-SiC:H tandem pi´n/pin heterostructures. The spectral sensitivity is analyzed. Steady state optical bias with different wavelengths, are applied from each front and back sides and the photocurrent is measured. Results show that it is possible to control the sensitivity of the device and to tune a specific wavelength range by combining radiations with complementary light penetration depths. The transfer characteristics effects due to changes in the front and back optical bias wavelength are discussed. Input red, green and blue pulsed communication channels are transmitted together, each one in a specific bit sequence and the multiplex signal is analyzed. By superimposing appropriate background and depending on the channel/background wavelength combinations, the device behaves as a long- or a short- pass filter, producing signal attenuation, or as an amplifier, producing signal gain. A physical model is presented to support the filter properties of the device. INTRODUCTION Multilayered Si/C structures based on amorphous silicon technology are expected to become reconfigurable to perform wavelength division multiplexing (WDM) optoelectronic logic functions [1, 2]. Filters are used to emphasize signals in a certain wavelength range and to reject signals in other ranges. They have a nonlinear magnitude-dependent response to each incident light wave. This nonlinearity provides the possibility for selectively removing and adding wavelength and can be used to boost signal after multiplexing or before demultiplexing. Double pi’n/pin a-SiC:H heterostructures, through an adequate engineering design of the multiple layers’ thickness, absorption coefficient and dark conductivities can accomplish those functions [3, 4]. Here, we propose a photodetector with integrated optical thin film filters. By means of optical control signals applied to the device, the photonic function may be modified, giving reconfiguration. A new method is presented for optical routing using wavelength background processing techniques DEVICE CONFIGURATION AND OPERATION The sensor element is a multilayered heterostructure based on a-Si:H and a-SiC:H. The configuration shown in Fig. 1, includes two stacked p-i-n structures sandwiched between two transparent contacts. The thicknesses and optical gap of the front í'- (200nm; 2.1 eV) and back i(1000nm; 1.8eV) layers are optimized for light absorption in the blue and red ranges, respectively. The device operates within the visible range using as input color channels (data)
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