Attenuation in photonic bandgap guiding hollow-core photonic crystal fiber (HC-PCF) has not beaten the fundamental silica Rayleigh scattering limit (SRSL) of conventional step-index fibers due to strong core-cladding optical overlap, surface roughness at the silica cladding struts, and the presence of interface modes. Hope has been revived recently by the introduction of hypocycloid core contour (i.e., negative curvature) in inhibited-coupling guiding HCPCF. We report on several fibers with a hypocycloid core contour and a cladding structure made of a single ring from a tubular amorphous lattice, including one with a record transmission loss of 7.7 dB/km at ~750 nm (only a factor ~2 above the SRSL) and a second with an ultrabroad fundamental band with loss in the range of 10-20 dB/km, spanning from 600 to 1200 nm. The reduction in confinement loss makes these fibers serious contenders for light transmission below the SRSL in the UV-VIS-NIR spectral range and could find application in high-energy pulse laser beam delivery or gas-based coherent and nonlinear optics
In this Letter, we present the first, to the best of our knowledge, experimental demonstration of high-order harmonic mode-locking of an all-fiber Mamyshev oscillator. The laser is entirely realized using standard step-index fiber. It delivers time-stable pulse trains with average powers reaching more than 100 mW at the fundamental mode-locked repetition rate (7.7 MHz) and 1.3 W at the 14th harmonic (107.8 MHz).
We present the experimental investigation of timing jitter and relative intensity noise of a Mamyshev ring oscillator operating in the fundamental mode-lock regime. We find that both timing jitter and intensity noise spectra are correlated to the output optical power with noise increase close to the loss of the mode-locking. In addition, we have investigated the dependence of the spectral filters wavelength separation on both timing jitter and intensity noise showing a severe degradation with filters overlapping.
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