a-SiC:H Based Devices as Optical Demultiplexers
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1246-B07-07
a-SiC:H Based Devices as Optical Demultiplexers P. Louro1,2, M. Vieira1,2,3, J. Costa1,2, M. A Vieira1,2, M. Fernandes1,2, A. Fantoni1,2, M. Barata1,2 1
Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal CTS-UNINOVA, Lisbon, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal 2
ABSTRACT In this paper we present results on the use of a multilayered a-SiC:H heterostructure as a wavelength-division demultiplexing device (WDM) for the visible light spectrum. The WDM device is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO heterostructure in which the generated photocurrent at different values of the applied bias can be assigned to the different optical signals. The device was characterized through spectral response measurements, under different electrical bias. Demonstration of the device functionality for WDM applications was done with three different input channels covering wavelengths within the visible range. The recovery of the input channels is explained using the photocurrent spectral dependence on the applied voltage. The influence of the optical power density was also analysed. An electrical model, supported by a numerical simulation explains the device operation. Short range optical communications constitute the major application field, however other applications are also foreseen. INTRODUCTION In optical communications one of the major issues of data transmission is the bandwidth of the channel, i.e. the capacity and speed of the transmission [1]. Wavelength division demultiplexing (WDM) is a common technique used to increase the bandwidth of the system. It consists on injecting different optical signals associated to different wavelengths into the same physical transmission medium, the optical fiber. The multiplexed signals travel along the fiber and are recovered at the reception end using a demultiplexer device. Several devices such as diffraction gratings, dielectric films, array waveguide gratings, fiber Bragg gratings, are used for the implementation of the WDM technique. In this paper we discuss the use of a multilayered a-SiC:H structure as a WDM device in the visible light spectrum [2], which is the transmission window used in many short range optical communication systems [3]. These multilayered structures work as wavelength separation devices [4] with a spectral sensitivity tuned by the external applied voltage. EXPERIMENTAL DETAILS Device Architecture In Figure 1 a) it is shown the configuration of the WDM device, which is composed by two stacked p-i-n photodiodes: pin1 and pin2. The front photodiode (pin1) based on a-SiC:H has a thin absorber layer (200 nm) which holds the collection of short wavelengths.
pin 1 (a-SiC:H)
pin 2 (a-Si:H)
200 nm
1000 nm
a)
TCO
Light
TCO
λ1 λ2 λ3
GLASS
Applied voltage 1x10
27
pin 2
650 nm 550 nm 470 nm
-3
-1
s )
pin 1
Generation rate (m
The back one (pin2) is based on aSi:H and its absorber is thicker (1000 nm) which enhances the collection of long wavel
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