Multilayered a-SiC:H device for Wavelength-Division (de)Multiplexing applications in the visible spectrum
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Multilayered a-SiC:H device for Wavelength-Division (de)Multiplexing applications in the visible spectrum Manuela Vieira1,2, Miguel Fernandes1, Paula Louro1,2, Manuel Augusto Vieira1,3, Manuel Barata1,2, and Alessandro Fantoni1 1 Electronics Telecommunication and Computer Dept., ISEL, Rua Conselheiro EmÃdio Navarro, Lisbon, 1959-007, Portugal 2 CTS, UNINOVA, Monte da Caparica, Caparica, 2829-516, Portugal 3 Traffic Dept., CML, Lisbon, 1049-001, Portugal ABSTRACT A multiplexer is a device that combines two or more signals onto a single output without losing their specificity. In this paper we present results on the use of multilayered a-SiC:H heterostructures either as wavelength-division multiplexing or demultiplexing device (WDM). The WDM is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO heterostructure which faces the modulated light incoming together from different beams, each one with a specific wavelength and transmission rate. By reading out, at different applied bias, the photocurrent generated by all the incoming optical carriers, the information is multiplexed or demultiplexed and can be transmitted and recovered again. The devices were characterized through spectral response measurements, under different electrical bias and frequencies. Results show that in the multiplexing mode the output signal is balanced by the wavelength of each incoming optical carrier and modulated by their frequencies. In the demultiplexing mode the photocurrent is controlled by the applied voltage allowing to regain the transmitted information. An electrical model is presented to explain the device operation. INTRODUCTION Recent advances on the production of polymer optical fibers (POF) [1] have opened possibilities for short distance communication systems at low cost. POF (Polymer Optical Fibers) present acceptable attenuation in light transmission within the visible spectrum and are presently used as a single channel transmission line [2]. To improve the data transmission rate, Wavelength Division Multiplexing (WDM) [3] can be employed for signal multiplexing and demultiplexing in the visible spectrum, which demands the conception of new devices. For WDM two key elements are crucial, a multiplexer and a demultiplexer. Although these two components are well known for infrared telecommunication systems, they must be completely renewed for the different transmission windows in the POF fibers, that work within the visible spectrum. Digital home appliance interfaces, home and car network and traffic control applications are foreseen due to the low cost associated to the a-SiC:H and POF technologies. In this paper we present results on the optimization of multilayered a-SiC:H heterostructures either for wavelength-division multiplexing or demultiplexing applications in the visible spectrum.
DEVICE OPERATION The element sensor is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO double heterostructure produced by PECVD. Deposition conditions are described elsewhere [4]. The thickness an
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