Fibre pulsed lasers are increasingly being adopted as the laser of choice in a number of industrial applications, such as micromachining, drilling and marking. In peak-power-driven applications, such as marking, it is essential to retain high peak powers (in excess of 2.5 to 5 kW) at high repetition rates in order to achieve faster character marking and increased throughput.
Distributed feedback (DFB) fibre-laser sensors have been shown to exhibit many characteristics useful in a range of sensing applications. Uniquely, fibre laser sensors enable the wavelength division multiplexing of a number of devices while maintaining the individual sensor characteristics of extremely high strain sensitivity, high dynamic range and very wide measurement bandwidth in small diameter sensors. These factors have led us to investigate a range of applications including hydrophone arrays, accelerometer designs, embedded acoustic emission sensors and acoustic pickups for musical instruments. This paper provides an overview of the optimised DFB sensor performance, interrogation and sensor configurations along with results and a discussion of the future developments of this technology.
We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass
single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M<sup>2</sup> = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a
thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.
We report high pulse energy actively Q-Switched fibre laser systems in MOPA and single stage configurations. The system was comprised of a Q-Switched master oscillator and power amplifier in either GTwave or end pumped fibres. A number of different fibre lengths and core diameters were used to explore the laser capabilities. A Q-Switched master oscillator operating at 10 kHz repetition rate with typical pulse durations of 40-50 ns at ~ 1070 nm is demonstrated. The laser operation was investigated for pulse repetition rate from 10 to 100 kHz for higher average output powers. After the power amplifier pulse energies as high as 1.1 mJ were obtained.
We report for the first time, more than 400 mW of output power at 1056.1nm from a distributed feedback (DFB) fiber laser. The DFB fiber laser comprises a simple π-phase-shifted Bragg grating written into a photosensitive ytterbium-doped fiber. The laser operates with a single longitudinal mode at a wavelength defined by the phase shift and the grating period. Without any internal polarisation selection mechanism, the cavity supports orthogonal polarisation modes, which operate simultaneously. The DFB fiber laser was pumped by a 976nm amplified spontaneous emission (ASE) source based on a ytterbium doped jacketed air clad (JAC) fiber pumped by a 915nm multimode laser diode source. An output of 400mW at 1056.1nm was obtained from the output port while 70mW was obtained from the other port, when pumped with 1.5W of 976nm radiation. The total output from the DFB fiber laser was approximately linear with increasing pump power and the overall performance was limited by the available pump power. The spectral characteristics and signal to noise ratio remained similar over the pump power range. The output of the DFB was in single-mode fiber (ie. M<sup>2</sup>~1).