Femtosecond pulse generation and amplification in Yb-doped fibre oscillator-amplifier system

Abstract

In recent times ytterbium (Yb) doped fibre-based mode-locked master oscillator and power amplifier have attracted a great deal of interest because of their inherent advantages like flexibility, reliability, compactness, high power handling capability and diffraction limited output beam quality as compared to the solid-state counterpart. But, to successfully develope of high-power femtosecond oscillator-amplifier system based on Ybdoped fibre, an appropriate choice of the mode-locking regime and the amplifier geometry are required. Development of an all-fibre integrated high-power Yb-doped fibre oscillatoramplifier system in which the advantages of a fibre-based system can be fully exploited remained a challenge as it requires the careful optimization of dispersion, nonlinearity, gain and ASE contribution.In this article, femto-second pulse generation in Yb-doped fibre oscillator in different mode-locking regimes are reviewed and the details of development and characterization of an all-fibre, high-power, low-noise amplifier system seeded by an all-normal-dispersion mode-locked Yb-doped fibre laser oscillator is described. More than 10 W of average power is obtained from the fibre oscillator-amplifier system at a repetition rate of 43 MHz with diffraction-limited beam quality. Amplified pulses are de-chirped to sub-160 fs duration in a grating compressor. This is the first 10 W-level source of femtosecond pulses with completely fibre-integrated amplification comprised of commercially available components.

Mode-Locked Fiber Lasers for Optical Time-Domain Reflectometry and Sensing

“…Finally, if the transformed light is again linearly polarized by an analyzer, the throughput in the cavity becomes intensity-dependent. With proper polarization control on the fiber ring cavity, the architecture with aid of an analyzer plays a role like an artificial fast saturable absorber [11,12,81], which provides smaller loss for higher intensities and larger loss for smaller intensities to suppress the low-level radiation so as to achieve passive mode-locking in the laser cavity . From equation 2.17, the light is decomposed into orthogonal components:…”

“…In contrast, B = 2 for a circularly birefringent fiber (θ = π/2). Figure 2.17 Works in the literature have reported the use of nonlinear polarization rotation (NPR) to generate a passive mode-locked laser [11,12,[80][81][82]. Figure 2.18 shows an experimental schematic using an SOA as an NPR device.…”

“…Such laser configuration has been shown to produce subpicosecond pulses [11]. The physical mechanisms that guarantee mode-locked in PML fiber lasers are the nonlinear polarization rotation [11,[79][80][81][82]. This is accomplished in a ring topology, where an SOA and an erbium doped fibre amplifier (EDFA) act as gain media while the NPR effect is enforced by the SOA.…”

“…When a highpower optical pulse impinges on the SOA, the pulse's leading edge can deplete the SOA gain and saturate the device, so that a much lower gain is provided for the trailing edge of the pulse. Hence, as the SOA provides polarisation dependent gain, the refractive index saturation will also be polarisation dependent so that SOA will act as a nonlinear polarization rotation device [11,12,[79][80][81][82]. This feature can be used as a pulse compression mechanism by properly adjusting light polarisation along the cavity.…”