Organic Photo detector Directly Deposited onto the Cut End of a Plastic Optical Fiber

Organic Photodetector Directly Deposited onto the Cut End of a Plastic Optical Fiber

Cristina Rottondi
DEI PhD Student

DEI - Aula 3B
26 Ottobre 2011
Ore 10.30


Plastic Optical Fibers (POF) have recently experienced a great development and diffusion for optical data transmission over short distances in many different application fields (i.e automotive industry, home networking…). Optical data transmission systems are made of a light-emitting device, such as a laser or light-emitting diode (LED), a light guiding medium, i.e. the optical fiber, and a receiver, i.e. a photodetector.
Given the good optoelectronic properties of organic materials and aiming to benefit from the advantages they offer in terms of manufacturing cost, it could be a premium choice to exploit organic devices as both the light transmitter and receiver for the optical system. Nevertheless, the optical coupling between the organic devices and the optical fiber both at the transmitter and at the receiver side could represent a limiting factor to the maximum achievable efficiency of the system. While Fresnel losses at the POF/glass interface are quite easy to reduce, e.g. by use of optical grease, geometrical coupling is a far more complex issue, which becomes even more critical as the fiber’s diameter is decreased to improve the data transmission rate. Indeed, this problem would not subsist at all if the organic devices, i.e. OLED and OPD, could be realized by direct deposition onto the cut end of the fiber, exploiting the unique properties of solution-processibility that are typical of organic materials: in this case, auto-alignment would be intrinsically guaranteed and the geometrical efficiency of light collection both OLED-to-POF and POF-to-OPD would be maximized with no dependence on the diameter of the fiber. Focusing on the photodetector’s side, the aim of the project is to realize an organic photodetector directly deposited onto the cut end of a plastic optical fiber and to evaluate its performance in terms of electro-optical characterizations: the direct deposition of the active material onto the cut end of the POF (with the only interposition of a few hundreds of nm thick layer to serve as the metal contact) would minimize the losses due to the divergence of the output beam, which typically require the active area of the detector to be bigger than the core of the fiber thus negatively affecting the performance of the device in terms of dark currents and intrinsic capacitance.

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