Research Associate Zhipei Sun

Department of Engineering, Universityof Cambridge

Time: 3:00 pm, October 26, 2011

Place: Meeting Rm.，3rd floor，LLP

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].

[1] M. E. Fermann et.al. Ultrafast Lasers Technology and Applications (Marcel Dekker,2003).

[2] Z. Sun, A.C. Ferrari, NaturePhotoics,5,446(2011).

[3] T. Hasan et.al. Adv. Mater. 21, 3874 (2009).

[4] V. Scardaci et. al. Physica E 37, 115-118(2007).

[5] V. Scardaci et. al. Adv. Mater. 20, 4040(2008).

[6] E. J. R. Kelleher et al., Laser. Phys. Lett., 7,790 (2010).

[7] Z. Sun, et al., Appl. Phys. Lett. 93, 061114 (2008).

[8] E. J. R. Kelleher et al. Opt. Lett. 34, 3526(2009

[9] S.J. Beecher et. al. Appl. Phys. Lett. 97, 111114(2010).

[10] F.Wang et al. Nature Nano. 3, 738(2008).

[11] Z.Sun et al. Nano Res. 3, 404 (2010). [12] D.Popa et. al. Submitted (2011).

[13] Z.Sun et al.,Appl. Phys. Lett.95, 253102 (2009).

[14] Z.Sun et. al. ACS Nano 4,803 (2010).

[15] D. Popa et.al. Appl. Phys. Lett. 97, 203106 (2010).

[16] Z. Sun et al. Nano Res. 3,653 (2010).

[17] D. Popa et.al. Appl. Phys. Lett. 98, 073106 (2011).

[18] F. Bonaccorso et al., Nat. Photonics, 4,611 (2010).

[19] A. K. Geim and K. S. Novoselov, Nat. Mater. 6,183(2007).