Abstract: Ultrafast lasers are in great demand for digital communication, ultrafast spectroscopy, material processing and medicine[1-2].Saturable absorbers, which become transparent under intense light, are the key devices to enable such ultrafast pulse generation[1].Carbon nanotubes (CNTs) are excellent saturable absorbers, and have great potential for applications in photonics[3].By tuning the nanotube diameter it is easy to cover a broad optical range of interest for applications. CNT saturable absorbers can be produced by wet chemistry and can be easily integrated into polymer photonic systems[3-4].Here, we review the fabrication and characterization of saturable absorbers based on CNT-polymer composites[3-13].These are successfully used to mode-lock lasers in a broad spectral range from 1µm to 2µm[3-13].We report a fiber laser generating 2.4ps pulses continuously tunable between 1518 and 1558nm[10].We also present a stretched-pulse fiber laser system generating sub-20fs pulses[11-12].This allows us achieve high power outputs, exceeding 1.6W[13].We will then extend our investigation to grapheme[3].Graphene is also a promising wide band saturable absorber[3,14].We report the linear and nonlinear optical characterization of graphene-polymer composites prepared using wet chemistry[14]. These are then integrated in a fiber laser cavity, to generate ultrafast pulses. We obtain sub-200fs pulses at 1560nm with a 15.6nm spectral bandwidth[15].Tunable mode-locked[16] and Q-switched[17] pulses using grapheme based saturable absorbers are demonstrated. An average output power of ~1W is also achieved by mode-locking a solid-state laser[18].Graphene is expected to mode-lock lasers from visible to IR due to its broad absorption range[3,14-19].

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