Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

A scheme for instantaneous frequency measurement(IFM)using two parallel I/Q modulators based on optical power monitoring is proposed.The amplitude comparison function(ACF)can be constructed to establish the relationship between the frequency of radio frequency(RF)signal and the power ratio of two optical signals output by two I/Q modulators.The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators.The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line.The feasibility of the scheme is verified,and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given.Compared with previous IFM schemes,the structure of this scheme is simple.Polarization devices,a photodetector and an electrical power meter are not used,which reduces the impact of the environmental disturbance on the system and the cost of the system.In simulation,the measurement range can reach 0 GHz-24.5 GHz by adjusting the delay amount of the electrical delay lineτ=20 ps.The measurement error of the scheme is better at low frequency,and the measurement error of low frequency 0 GHz-9.6 GHz can reach-0.1 GHz to+0.05 GHz.

Amplification characteristics in active tapered segmented cladding fiber with large mode area

A kind of tapered segmented cladding fiber(T-SCF)with large mode area(LMA)is proposed,and the mode and amplification characteristics of T-SCFs with concave,linear,and convex tapered structures are investigated based on finite-element method(FEM)and few-mode steady-state rate equation.Simulation results indicate that the concave tapered structure can introduce high loss for high-order modes(HOMs)that is advantageous to achieve single-mode operation,whereas the convex tapered structure provides large effective mode area that can help to mitigate nonlinear effects.Meanwhile,the small-to-large amplification scheme shows further advantages on stripping off HOMs,and the large-to-small amplification scheme decreases the heat load density induced by the high-power pump.Moreover,singlemode propagation performance,effective mode area,and heat load density of the T-SCF are superior to those of tapered step index fiber(T-SIF).These theoretical model and numerical results can provide instructive suggestions for designing high-power fiber lasers and amplifiers.

Sacrificial template synthesis of(V_(0.8)Ti_(0.1)Cr_(0.1))_(2)AlC and carbon fiber@(V_(0.8)Ti_(0.1)Cr_(0.1))_(2)AlC microrods for efficient microwave absorption

The morphology of MAX phase powders significantly influences their microwave absorption properties.However,the traditional synthesis via solid-state reactions produces irregular powders,and the preparation of MAX phase powders with specific morphology remains a challenge.Herein,(VTiCr)Al C MAX phase microrods were fabricated for the first time in NaCl/KCl molten salts using vanadium,titanium,chromium,aluminum,and short carbon fibers as precursors.It was found that despite acting as a carbon source,carbon fibers also acted as sacrificial templates.By adjusting the molar ratio of metal powders and short carbon fibers,a series of carbon fiber@(V_(0.8)Ti_(0.1)Cr_(0.1))_(2)AlC microrods with core-sheath structure were also obtained.Carbon fiber@(V_(0.8)Ti_(0.1)Cr_(0.1))_(2)AlC microrods with a molar ratio of 8:2 showed the optimum microwave absorption performance.The reflection loss(RL)value reached up to–63.26 d B at 2.40 mm,and the effective absorption bandwidth(EAB)was about 5.28 GHz with a thickness of2.02 mm.Based on the electromagnetic parameter analysis and theoretical simulation,the enhanced microwave absorption performance was attributed to the synergistic effect of different factors like dielectric loss,magnetic loss,multiple reflection,and scattering.This work offers a facile route to modulate the morphology of MAX phase powders and may accelerate its application as microwave absorbers.

Facile synthesis of hollow Ti_(3)AlC_(2)microrods in molten salts via Kirkendall effect

The microstructure and morphology of Ti_(3)AlC_(2)powders not only affect the preparation of Ti_(3)C_(2) MXene but also have a great influence on their potential applications,such as microwave absorbers,alloy additives,or catalytic supports.However,the synthesis of Ti_(3)AlC_(2)powders with desired microstructure and morphology remains a challenge.Herein,hollow Ti_(3)AlC_(2)microrods were prepared for the first time in NaCl/KCl molten salts by using titanium,aluminum,and short carbon fibers as starting materials.It was found that the short carbon fibers not only performed as carbon source but also acted as sacrificial template.Furthermore,it was revealed that TiC and Ti2AlC were initially formed on the surface of carbon fibers.The subsequent reactions between the outer Ti,Al and the inner carbon were dominated by the Kirkendall effect which gave rise to the formation of a hollow structure.Based on this mechanism,hollow Ti_(3)AlC_(2)microspheres and a series of hollow TiC,Ti_(2)AlC,and V_(2)AlC powders were also successfully fabricated.This work provides a facile route to synthesize hollow MAX phases and may give enlightenment on preparing other hollow carbide powders via the Kirkendall effect in the molten salts.