Reviewing Photo-sensing Devices Using a-SiC Based Materials
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Reviewing photo-sensing devices using a-SiC based materials M. Vieira1,2,3, M. Fernandes1,2, P. Louro1,2, A. Fantoni1,2, M. A Vieira1,2, J. Costa1,2, M. Barata1,2 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, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, 2829-516, Caparica, Portugal. 1
ABSTRACT In this paper a double pi’n/pin a-SiC:H voltage and optical bias controlled device is presented and it behavior as image and color sensor, optical amplifier and multiplex/demultiplex device discussed. The sensing element structure (single or tandem) and the light source properties (wavelength, intensity and frequency) are correlated with the sensor output characteristics (lightto-dark sensitivity, resolution, linearity, bit rate and S/N ratio). Depending on the application, different readout techniques are used. When a low power monochromatic scanner readout the generated carriers the transducer recognize a color pattern projected on it acting as a color and image sensor. Scan speeds up to 104 lines per second are achieved without degradation in the resolution. If the photocurrent generated by different monochromatic pulsed channels is readout directly, the information is multiplexed or demultiplexed. It is possible to decode the information from three simultaneous color channels without bit errors at bit rates per channel higher than 4000bps. Finally, when triggered by appropriated light, it can amplify or suppress the generated photocurrent working as an optical amplifier. An electrical model is presented to support the sensing methodologies. Experimental and simulated results show that the tandem devices act as charge transfer systems. They filter, store, amplify and transport the photogenerated carriers, keeping its memory (color, intensity and frequency) without adding any optical pre-amplifier or optical filter as in the standard p-i-n cells. INTRODUCTION Whether we hope to view images or count photons, we use devices that work by absorbing photons and turning them into information. Traditional optics has relied heavily on the human eye for the evaluation of light distributions, using photographic films as an intermediate storage medium, when necessary. With the advent of computers and digital image processing, imaging electronic sensors have become indispensable tools. The current need for communication also demands the transmission of huge amounts of information. To increase the capacity of transmission and allow bidirectional communication over one strand fiber, wavelength-division multipexing (WDM) is used [1]. WDM systems have to accomplish the transient color recognition of two or more input channels in addition to their capacity of combining them onto one output signal without losing any specificity (wavelength and bit rate). Only the visible spectrum can be applied when using polymer optical fiber for communication. So, the deman
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