Synchronously mode-locked ®ber laser based on parametric gain modulation and soliton shaping Lijun Wang, Yikai Su, Anjali Agarwal, Prem Kumar * Center for photonic Communication and Computing, Department of Electrical and Computer Engineering, Northwestern University, Evanston, IL 60208-3118, USA Received 12 March 2001; received in revised form 14 May 2001; accepted 14 May 2001 Abstract A novel synchronously mode-locked ®ber laser is demonstrated by combining the parametric gain modulation in a pulse-pumped nonlinear optical loop mirror NOLM) with the soliton shaping property of a nonlinear amplifying loop mirror NALM). Parametric gain modulation induced by the synchronous pump pulses within the NOLM starts and de®nes the timing of the mode-locked signal pulses, while the nonlinear intensity discrimination in the NALM stabilizes the mode-locked pulses and optimizes their shapes. A stream of 1.3 ps transform-limited soliton pulses is generated when the NOLM is pumped by a mode-locked ®ber laser. Moreover, we ®nd that the timing jitter of the synchronously mode-locked pulse train is suppressed by more than 10 dB when compared to the pumping laser. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Fiber lasers; Mode locking; Parametric ampli®cation; Nonlinear optical loop mirrors; Nonlinear amplifying loop mirrors; Soliton shaping and control; Timing jitter suppression The parametric nonlinearity of optical ®ber is being exploited for functions such as broadband wavelength conversion, dispersion compensation, and cross-connect interchanging in ®ber-optic communication systems and networks [1±3]. In contrast to the gain in an EDFA, the parametric gain is dynamic, depending on the intensity rather than the average power of the pump light. This characteristic is attractive for applications such as nonlinear amplitude limitation and equaliza- tion in all-optical signal processing [4]. Previously, we have reported a broadly tunable 70 nm) picosecond-pulse ®ber-optic parametric oscillator FOPO) by synchronously pumping a nonlinear optical loop mirror NOLM) made out of disper- sion-shifted ®ber DSF) [5,6]. Recently, we have also demonstrated a scheme for all-optical clock recovery by utilizing the dynamic parametric gain to synchronize and equalize the clock pulses [7]. In this paper, we report a novel synchronously mode-locked ®ber laser in which the parametric gain modulation in a pulse-pumped NOLM is combined with the soliton shaping property of a nonlinear amplifying loop mirror NALM) [8,9]. Previously, synchronous FM mode locking of a ®ber laser has been demonstrated by sharing a ®ber span with the incident pulse stream, which acts as a phase modulator because of the induced 15 July 2001 Optics Communications 194 2001) 313±317 www.elsevier.com/locate/optcom * Corresponding author. Tel.: +1-847-491-4128; fax: +1-847- 491-4455. E-mail address: kumarp@northwestern.edu P. Kumar). 0030-4018/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0030-401801)01301-3