We experimentally demonstrated a fiber laser with tunable linewidth based on self-injection locking (SIL) and the stimulated Brillouin scattering (SBS) effect. The linewidth-tuning operation is achieved by limiting injection power within the third regime of the feedback effect. SBS can realize single longitudinal mode (SLM) by the ultra-narrow gain range, and generate ultra-narrow laser linewidth because of the high Q value. Additionally, we use Brillouin erbium fiber laser (BEFL) to replace the ordinary Brillouin ring cavity to obtain better SLM property. The lasing with ultra-narrow linewidth is steadily emitted after eliminating the mod-hopping caused by SIL and confirming the stable occurrence of SBS. In addition, The Lorentzian linewidth of DFB (1.7 kHz) and SIL with different injection power are measured by the delayed self-heterodyne interferometry (50 km delay fiber). The Lorentzian linewidth of the BEFL (60 Hz) is accurately measured by the Voigt fitting.
We investigate the chiral spectral singularities, i.e., laser threshold modes, in PT-symmetric dielectric metasurfaces originating from quasi-bound states in the continuum. The poles, referred to as the quasi-bound states in the continuum, of scattering matrix can move to the upper complex frequency plane from the lower half-plane by increasing the balanced gain and loss. The maximal intrinsic optical chirality of laser threshold mode has been theoretically demonstrated via the large transmission circular dichroism spectra. Our work paves the way for studying the enhanced optical chirality in non-Hermitian nanophotonics empowered by quasi-bound states in the continuum, together with various intriguing applications, such as chiral coherent perfect absorber and laser.
The ultra-wideband supercontinuum generation (SCG) in a Te-based chalcogenide (ChG) photonic crystal fiber (PCF) is simulated in the mid-infrared (MIR) waveband. The PCF core and cladding materials are G e 20 A s 20 S e 15 T e 45 and G e 20 A s 20 S e 17 T e 43 , respectively. The supercontinuum (SC) broadening affected by the core diameter and fiber absorption is considered. The selected PCFs at different pumping wavelengths can demonstrate the generation of ultra-wideband MIR supercontinuum according to the simulated results. We consider SC broadening with and without fiber absorption. A SC range from 3 to 25 µm is demonstrated by simulation in a PCF with a core diameter of 8 µm and a pump wavelength of 6 µm considering the fiber absorption. With the increase of the peak power and the pulse width and the decrease of the core diameter, the degree of coherence gradually degraded. To the best of our knowledge, this is the first demonstration of the possibility of SCG up to the waveband of 25 µm in fiber. Our results highlight the potential of a novel Te-based chalcogenide multi-material PCF for SCG. We also provide a way to generate the SCs to longer wavebands than 20 µm in fiber, especially up to the far-infrared waveband.
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