Abstract
A traditional ultrafast fibre laser has a constant cavity length that is independent of the pulse wavelength. The investigation of distributed ultrafast (DUF) lasers is conceptually and technically challenging and of great interest because the laser cavity length and fundamental cavity frequency are changeable based on the wavelength. Here, we propose and demonstrate a DUF fibre laser based on a linearly chirped fibre Bragg grating, where the total cavity length is linearly changeable as a function of the pulse wavelength. The spectral sidebands in DUF lasers are enhanced greatly, including the continuous-wave (CW) and pulse components. We observe that all sidebands of the pulse experience the same round-trip time although they have different round-trip distances and refractive indices. The pulse-shaping of the DUF laser is dominated by the dissipative processes in addition to the phase modulations, which makes our ultrafast laser simple and stable. This laser provides a simple, stable, low-cost, ultrafast-pulsed source with controllable and changeable cavity frequency.
Highlights
A traditional ultrafast fibre laser has a constant cavity length that is independent of the pulse wavelength
When the Passively mode-locked (PML) fibre laser operates at the fundamental cavity frequency, it delivers a pulse train whose individual pulses are spaced by the round-trip time inside the laser cavity
The pulse-shaping mechanism for distributed ultrafast (DUF) fibre lasers is absent because the nonlinear effects in this type of laser are difficult to balance the very large anomalous dispersion induced by the linearly chirped fibre Bragg gratings (LCFBGs)
Summary
A traditional ultrafast fibre laser has a constant cavity length that is independent of the pulse wavelength. The investigation of distributed ultrafast (DUF) lasers is conceptually and technically challenging and of great interest because the laser cavity length and fundamental cavity frequency are changeable based on the wavelength. We propose and demonstrate a DUF fibre laser based on a linearly chirped fibre Bragg grating, where the total cavity length is linearly changeable as a function of the pulse wavelength. The PML fibre laser with chirped FBG design was first reported in 199534,35 This type of linear-cavity laser is widely utilised in modern research and industrial applications because of the all-fibre structure, easy fabrication, and reliability. A DUF fibre laser using an LCFBG is proposed and demonstrated experimentally It differs from the conventionally concentrated ultrafast fibre lasers because the total cavity length of the DUF laser is linearly changeable as a function of the pulse wavelength. Our unique experimental observations are confirmed by our numerical simulations
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