Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers.

S. Turitsyn,B. C. Yao,W. L. Zhang,X. L. Cao,H. Wu,Z. N. Wang,Y. J. Rao,J. H. Zhou,D. Churkin,M. Q. Fan,C. W. Wong,Y. Wu,Y. R. Li,Y. F. Chen

doi:10.1038/srep18526

Abstract

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses.

Highlights

High nonlinearity with ultrafast response[35,36]; (2) high-power sustainability[14,20,21,22], (3) high mechanical strength and durability[37], and (4) compatibility with silicon waveguide and fiber hybrids[36,38,39]
When light transmits along the graphene-coated D-shaped fiber (GDF), as shown schematically in the inset, it can be regarded as a x-polarization transmission filter
With the x-polarization periodically modulated by the polarization rotator (PR), the transmission is a sinusoidal-like temporal wave after passing the GDF

Summary

Introduction

High nonlinearity with ultrafast response[35,36]; (2) high-power sustainability[14,20,21,22], (3) high mechanical strength and durability[37], and (4) compatibility with silicon waveguide and fiber hybrids[36,38,39]. With graphene-based hybrids as a static absorber, mode-locking and Q-switching have been examined[31,32], albeit still requiring a conventional resonant cavity lasing structure. We report graphene-based pulse generation with cavity-free random fiber lasers, for the first time. By dynamically modulating the polarization via a polarization rotator (PR) and transmitting through a designed graphene-coated D-shaped fiber (GDF), the continuous wave (CW) from the arbitrarily-polarized random fiber laser is transformed into coherent sub-nanosecond pulses even in the non-resonant single-pass configuration. The PR and the GDF hybrid waveguide serves simultaneously as the linearly polarized pulse generator (polarization modulation) and the pulse reshaper (saturable absorption). The pulses generated from the GDF inherit merits of the CW random fiber laser such as a high pump-power Stokes conversion efficiency, and offer unique advantages such as a power-dependent singly-polarized output with polarization extinction ratios up to 41 dB, and wide tunability in both pulsewidths and repetition rates, across two and three orders of magnitude respectively

Methods

Results

Conclusion