Highlights of 2013

In this paper a tunable multi-wavelength erbium doped fiber laser, based on a Mach–Zehnder interferometer, is presented. Here the interferometer is achieved by splicing a piece of photonic crystal fiber (PCF) between two segments of a single-mode fiber. The laser can emit a single, double, triple or quadruple line, which can be tuned from 1530 to 1556 nm by controlling the polarization state. Finally it is shown, by experimental results, that the laser has high stability at room temperature.

In this paper a novel highly birefringent neodymium-doped microstructured optical fiber is presented. The modal properties of the structure are analyzed numerically using a fully vectorial finite difference method. Results obtained are compared with experimental near-field measurements. The emission properties of the structure have also been investigated. The emission cross-sections at 900, 1064 and 1334 nm have been measured. Laser action has been achieved at a wavelength of 1064 nm in the simplest configuration, based on Fresnel light reflection at both ends of the fiber. The optical conversion efficiency was 9% and the slope efficiency reached 16%. A laser configuration with an external fiber Bragg grating has also been studied; promising results obtained for this configuration suggest that such a laser can find applications in sensing.

We propose and demonstrate the most compact low threshold multiwavelength Brillouin–erbium fiber laser (MBEFL) incorporating a 100-m long photonic crystal fiber (PCF) as a Brillouin gain medium. This optimized configuration with a simple ring cavity makes it possible for the first time to achieve more than 22 Brillouin Stokes waves with a line spacing of 0.08 nm (∼10 GHz) and more than −20 dBm power in conjunction with a 100-m long PCF. Using a pre-amplified Brillouin power approach in a ring cavity realizes a low threshold multiwavelength laser with a Brillouin pump power of around 8 dBm at an injected 980 nm pump power of 125 mW. Anti-Stokes lines are also obtained due to four-wave mixing and bidirectional operation.

A fiber-based supercontinuum source, comprising a graphene mode-locked erbium fiber laser and a highly nonlinear photonic crystal fiber (PCF), is reported. The nonlinear fiber has zero-dispersion wavelength shifted towards 1500 nm specifically for pumping with compact femtosecond and sub-picosecond fiber lasers operating in this spectral area. A chirped pulse amplification system seeded by a graphene mode-locked laser, generating linearly polarized 850 fs pulses and a pulse energy of 20 nJ at a repetition rate of 50 MHz, was used as the pump source. A 6 cm long, soft-glass PCF sample enabled generation of a supercontinuum spanning over an octave from 1000 to over 2300 nm in a 20 dB dynamic range. The measured results are interpreted numerically, based on a solution to the nonlinear Schrödinger equation using the split-step Fourier method; assignment of the nonlinear processes taking part in the observed broadening is proposed. The developed model is then used to estimate supercontinuum performance in the presented fiber with improved experimental conditions.

The passive mode-locking of an erbium-doped fiber laser (EDFL) with a medium gain is demonstrated and compared by using three different types of carbon nanotubes (CNTs) doped in polyvinyl alcohol (PVA) films. Nano-scale clay is used to disperse the CNTs doped in the PVA polymer aqueous solution to serve as a fast saturable absorber to initiate passive mode-locking. The three types of CNT based saturable absorbers, namely single-walled (SW), double-walled (DW) and multi-walled (MW), are characterized by Raman scattering and optical absorption spectroscopy. The SW-CNTs with a diameter of 1.26 nm have two absorption peaks located around 1550 ± 70 and 860 ± 50 nm. In contrast, the DW-CNTs with a diameter of 1.33 nm reveal two absorption peaks located at 1580 ± 40 and 920 ± 50 nm. By using the SW-CNT based saturable absorber, the passively mode-locked EDFL exhibits a pulsewidth of 1.28 ps and a spectral linewidth of 1.99 nm. Due to the increased linear absorption of the DW-CNT based saturable absorber, the intra-cavity net gain of the EDFL is significantly attenuated to deliver an incompletely mode-locked pulsewidth of 6.8 ps and a spectral linewidth of 0.62 nm. No distinct pulse-train is produced by using the MW-CNT film as the saturable absorber, which is attributed to the significant insertion loss of the EDFL induced by the large linear absorption of the MW-CNT film.