The ground-based lidar is an active remote sensing instrument to profile the lower atmosphere effectively. In general, a lidar receives an analog signal from a lower altitude, a photon count from a higher altitude, and glues them in order to profile the atmosphere effectively. We propose the Levinson recursion algorithm-based Wiener filter over an original lidar signal to convert an analog signal to virtual count. This count is further glued with photon counting through mean square error method, and the results are compared with the linear regression algorithm. It is found that the proposed algorithm enhances the scaled analog from 152 to 8780 MHz in 355 nm, 131 to 3591 MHz in 387 nm, and 79 to 2956 MHz in 408 nm wavelengths. Furthermore, the improvement in correlation coefficients is found to be 0.9899, 0.9942, and 0.9807 for 355, 387, and 408 nm wavelengths, respectively. The proposed algorithm can be applied to any ground-based lidar system for an accurate profiling of the lower atmospheric compositions.
We demonstrate the generation of dissipative soliton in an all-normal dispersion passively mode-locked ytterbium-doped fiber laser using few-layer molybdenum diselenide (MoSe2) as a saturable absorber. By adopting the cost-effective liquid phase exfoliation approach, few-layer MoSe2 nanosheets are exfoliated and mixed with polyvinyl alcohol (PVA) to prepare a free-standing MoSe2-PVA film. The developed film is attached between two fiber ferrules to make a fiber compatible saturable absorber device. By incorporating this saturable absorber in an all-normal dispersion laser cavity, a stable dissipative soliton with a pulse width of 471 ps and 3-dB bandwidth of 4.26 nm centered at 1040 nm is generated. The fundamental repetition rate and the average power are measured as 15.44 MHz and 2 mW, respectively. To the best of our knowledge, this is the first demonstration of a dissipative soliton generation in 1 μm wavelength region using few-layer MoSe2 saturable absorber. These results exhibit the significant potential of MoSe2-based saturable absorber in the near-IR region for all-fiber mode-locked lasers.
We design various silicon nanowire embedded photonic crystal fibers (SN-PCFs) with different core geometries, namely, circular, rectangular and elliptical using finite element method. Further, we study the optical properties such as group velocity dispersion (GVD), third order dispersion (TOD) of x and y-polarized modes and effective nonlinearity for a wavelength range from 0.8 to 1.6 μm. The proposed structure exhibits almost flat GVD (0.8 to 1.2 μm wavelength), zero GVD (≈ 1.31 μm) and small TOD (0.00069 ps3/m) at 1.1 μm wavelength and high nonlinearity (2916 W-1m-1) at 0.8 μm wavelength for a 300 nm core diameter of circular core SN-PCF. Besides, we have been able to demonstrate the supercontinuum for the different core geometries at 1.3 μm wavelength with a less input power of 25 W for the input pulse of 20 fs. The numerical simulation results reveal that the proposed circular core SN-PCF could generate the supercontinuum of wider bandwidth (900 nm) compared to that from rest of the geometries. This enhanced bandwidth turns out to be a boon for optical coherence tomography (OCT) system.
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