D. Amarasinghe

Abstract: Interest in semiconducting polymers as gain media has grown over recent years, due to their high gain over a broad bandwidth, simple processing techniques,low manufacturing costs, and their potential to being electrically pumped. [1,2] These polymers have been shown to be suitable for photonic devices such as lasers [1,3–7] and amplifiers, [8–13] and can be used in conjunction with polymer optical fibers (POF) for short-haul telecommunication networks, which are to replace twisted pair cables. [14,15] In particular, amplifying devices are needed to compensate for the loss of signal during transmission and splitting. Semiconducting polymers have potential for excellent compatibility with POF, including broad-bandwidth amplification matching the POF transmission window. Gains of up 21 and 18dB/mm using the polymers poly(2- methoxy-5-(2 0 -ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) [8,9] at high repetition rates of 5kHz have been demonstrated. Along with high gain, key material parameters for these devices are large ampli-fication bandwidth and long gain lifetimes [8] . Gain-saturation mechanisms, which limit the amplifier performance, are not well understood. In the present work, we have explored the scope of improving the perfomance of polymer optical amplifiers by diluting the chromophores responsible for the gain with higher-energy conjugated segments, in a co-polymer. We find that optical amplification of 1000 times can be obtained with 100 fs pulses in fluorene benzothiadiazole copolymer waveguides. A gain cross-section of 3 (cid:1) 10 (cid:2) 17 cm