We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5 mW at 974 nm and a wide range of pulse-repetition rate from 3.3 to 65.9 kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.

The transverse load and temperature sensitivities of fibre Bragg gratings (FBG) fabricated in a range of commercially available stress and geometrically induced high birefringent (HiBi) fibres have been experimentally investigated. The wavelength reflected by the FBG in each polarisation eigenmode was measured independently and simultaneously using a custom designed interrogation system. The highest transverse load sensitivity, of 0.23 ±0.02 nm/(N/mm), was obtained with HiBi FBGs fabricated in elliptically clad fibre. This was ~25% higher than for any other HiBi fibre, which, coupled with the small diameter of the fibre, makes it a good candidate for an embedded or surface mounted strain sensor. The highest temperature sensitivity of 16.5 ± 0.1 pm/ 0 C, approximately 27% greater than any other fibre type, was obtained with the HiBi FBG fabricated in Panda fibre. HiBi FBG sensors fabricated in D-clad fibre were the only ones to exhibit identical temperature sensitivities for the slow and fast axes (11.5 ± 0.1 pm/ 0 C).

We have demonstrated a high-energy Q-switched double-clad thulium-doped fiber laser (TDFL) using a graphene-oxide-deposited tapered fiber (GODTF) device as a saturable absorber operating at a wavelength of 2 μm for the first time. Because of the side-interaction of the graphene-oxide with the evanescent field on the taper waist, the GODTF devices have potential for offering high laser damage threshold. Using a 788 nm laser diode as the pump source, the TDFL generated stable single transverse mode Q-switched pulses with a single pulse energy of 6.71 μJ (corresponding to an average power of 302 mW) at a wavelength of 2032 nm. This is significantly higher than the highest pulse energy/average power from any rare-earth-doped fiber lasers employing a graphene or graphene-oxide based Q-switch so far. The demonstrated TDFL in this paper represents an encouraging step towards the practical applications of graphene or graphene-oxide based Q-switched 2 μm TDFLs.

We report the development of a fibre Bragg grating (FBG) interrogation system that is capable of detecting independently and simultaneously the two orthogonally polarized signals reflected from a polarization-maintaining (PM) FBG. This relaxes the constraints on the bandwidth of the FBG spectrum, allowing the use of a shorter PM FBG (larger bandwidth) for sensing applications where a higher spatial resolution is required. It imposes no limitation on the measurable strain range and strain profile. The interrogation system is capable of decoding the complex spectral responses of a PM FBG subjected to a transverse load.

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