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1. P4

Super-continuum generation using noise-like pulses from a large normal dispersion passively mode locking fiber laser Liang Dou (Student)(1), Yan Gao (Student)(1), Anshi Xu (1), Ming Tang (2), Ping Shum (2) 1: State Key Laboratory of Advanced Optical Communication Systems & Networks, Electronics Department, Peking University, Beijing, 100871, China ([email protected]) 2: Network Technology Research Centre, Nanyang Technological University, 637553, Singapore Abstract High energy Noise-like pulses has been generated from a passively mode locking fiber laser with large normal dispersion. Super-continuum more than 600nm can be generated directly by launching the pulses into high nonlinear fiber. Introduction Super-continuum (SC) generation in optical fiber has been the subject of intensive research in recent years [1]. These ultra broadband light sources are potentially useful for several applications, including optical coherence tomography and sensing [2]. Pulses from passively mode locking fiber laser are a promising way to generate SC thanks to its high pulse energy and short pulse width. These days, pulse energy from fiber laser cavity has been improved by using self-similarity fiber laser [3]. Also, it has been known that additive pulse mode locked lasers could support another operation mode called noise-like pulse mode, whose energy is always larger than the conventional mode locking pulses. Recently it has been demonstrated that this noise-like pulses can still generate SC by passing through highly nonlinear fiber (HNLF) [4]. In this paper, we first report high energy noise-like pulses generated from large normal dispersion laser cavity. In addition, we demonstrate the SC generation by using the noise-like pulse as a seed pulse into HNLFs.

Experimental configuration The configuration of the laser is shown in Fig. 1. Inside the laser cavity, 6m long erbium doped fiber (EDF) is backward pumped by 1480 nm laser diode. The large normal dispersion is provided by 14 m dispersion compensation fiber (DCF) and its disperion at 1550nm is 120 ps 2/km. Total cavity length is 22 m and the total dispersion of the cavity is more than 1.68 ps2. We utilise additive-pulse modelocking mechanism by using wave plates and a polarisation sensitive isolator which are all mounted on a 76 mm fiber bench. Another WDM coupler was used to couple the residual pump light out of the laser cavity, and a 50/50 coupler was used as the laser output. The pulse properties are examined by optical spectrum analyzer (OSA), autocorrelator and optical oscilloscope.

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Results and discussion Self-started mode-locking can be achieved by carefully adjusting the wave plates on the fiber bench. The average output power of noise-like pulses is 19.6dBm and its period is lOns, hence the pulse energy is about 10nJ. The optical spectrum and autocorrelation trace are shown in Fig 2 (a) and Fig 2 (b), respectively. From the autocorrelation trace, there is a narrow peak riding on the broad pedestal, which indicates that there are a number of short pulses inside each large pulse. By shortening the scan range of the autocorrelator we could infer that the pulse width of the narrow peak inside the pulse is about 300fs. From the optical oscilloscope, the large noise-like pulse width is about 1 ns.

1-4244-1591-8/07/$25.00 C2007 IEEE

92

Poster Speaker: Liang Dou

Poster Session

1. P4

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After achieving this high energy pulses directly from laser cavity, we examine the SC generation from the noise-like pulses. The output pulses are launched into a 50Cm-long highly nonlinear fiber (HNLF), the dispersion and the nonlinear coefficient are -1 ps2/km and 10NV/km at 1550 nm, respectively. As shown in Fig 3(a), the super-continuum spectrum is generated from 1150nm to 1750nm and the measurement is actually limited by the scan range of optical spectrum analyzer (650nm-1 750nm). The output power after the HNLF is 6dBm, which is more than 13dB lower than the input signal. |VPK Ive0

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(b) Fig. 3 Optical spectrum and autocorrelation trace of super-continuum generated by the noise state pulse Conclusions In this paper, about 10 nJ noise-like pulses has been generated from a passively mode locking fiber laser with large normal dispersion. By launching the pulses into 500m HNLF, SC more than 600nm can be generated directly. References 1 John M. Dudley et al, Reviews of Modern Physics, Vol. 78 (2006), page 1135-1184 2 Goery Gentry et al, Optical Fiber Sensors (OFS), paper TuA2, 2006 3 F. 0. llday et al, Phys. Rev. Lett, Vol. 92 (2004), page 213902. 4 Y. Takushima et al, IEE/ELECTRONICS LETTERS, Vol. (2005), page 399-400.

Liang, Dou (student) received his BS degree from Electronics Department of Peking University, in 2003. Now he is a PH.D student in State Key Laboratory of Advanced Optical Communication Systems & Networks, Electronics Department, Peking University. His research interest has been in the area of fiber lasers and fiber amplifiers. Yan Gao, Anshi Xu, Ming Tang, Ping Shum, information not available at the time of submission.

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