3 research outputs found
Turn-Key Stabilization and Digital Control of Scalable, N GTI Resonator Based Coherent Pulse Stacking Systems
Coherent Pulse Stacking Amplification (CPSA) is a new time-domain coherent addition
technique that overcomes the limitations on pulse energies achievable from optical amplifiers. It
uses reflecting resonators to transform a sequence of phase- and amplitude-modulated optical
pulses into a single output pulse enabling high pulse energy for fiber lasers.
This thesis focuses on utilizing efficient algorithms for stabilization and optimization
aspects of CPSA and developing a robust, scalable, and distributed digital control system with
firmware and software integration for algorithms, to support the CPS (Coherent Pulse Stacking)
application. We have presented the theoretical foundation of the stochastic parallel gradient
descent (SPGD) for phase stabilization, discussed its performance criteria, its convergence, and its
stability. We have presented our software and hardware development for time-domain coherent
combing stabilization (specifically, an FPGA (Field Programmable Gate Array)-based Control
system with software/firmware development to support stabilization and optimization algorithms).
Analytical formulations of output stacked pulse profile as a function of input pulse train amplitudes
and phase and stacker cavity parameters have been derived so as to build up a foundation for a
GTI (Gires-Tournois-Interferometer) Cavity-based noise measurement technique. Time-domain
and frequency domain characterization techniques have been presented to analyze phase and
amplitude noise in the stacking system. Stacking sensitivity to errors in different control
parameters (stacker cavity phase, pulse amplitude, and phases) for different stacker configurations
have been analyzed. Noise measurement results using GTI cavities with different round-trip time
has have been presented and we have shown how effectively the stacking phase noise in the system
can be reduced by improving the noise performance of the mode-locked oscillator. Simulation and
Experimental results for stabilizing different stacker configurations have been presented. Finally
an algorithmic control system along with software/hardware development for optimizing
amplitudes and phases of the input burst has been implemented to increase stacking fidelity. A
complete detailed description, and simulation of the Genetic Algorithm as an alternative algorithm
for optimizing the stacked pulse fidelity has been presented. Comparison between SPGD and
Genetic Algorithm results has been done to evaluate their performance.
To summarize, this thesis provides theoretical, experimental, and implementation aspects
of controlling CPSA system by introducing efficient control algorithms and developing a turn-key
digital control system which is scalable to large number of stacker cavities.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147664/1/msheikhs_1.pd
Performance assessment of lower VHF band for short‐range communication and geolocation applications
The focus of this paper is to characterize near‐ground wave propagation in the lower very high frequency (VHF) band and to assess advantages that this frequency band offers for reliable short‐range low‐data rate communications and geolocation applications in highly cluttered environments as compared to conventional systems in the microwave range. With the advent of palm‐sized miniaturized VHF antennas, interest in low‐power and low‐frequency communication links is increasing because (1) channel complexity is far less in this frequency band compared to higher frequencies and (2) significant signal penetration through/over obstacles is possible at this frequency. In this paper, we quantify the excess path loss and small‐scale fading at the lower VHF and the 2.4 GHz bands based on short‐range measurements in various environments. We consider indoor‐to‐indoor, outdoor‐to‐indoor, and non‐line‐of‐sight outdoor measurements and compare the results with measurements at higher frequencies which are used in conventional systems (i.e., 2.4 GHz). Propagation measurements at the lower VHF band are carried out by using an electrically small antenna to assess the possibility of achieving a miniaturized, mobile system for near‐ground communication. For each measurement scenario considered, path loss and small‐scale fading are characterized after calibrating the differences in the systems used for measurements at different frequencies, including variations in antenna performance.Key PointsLow VHF has favorable short‐range characteristics and low signal distortionPenetration through many layers of building walls is possible at low VHFNovel miniaturized VHF antennas with reasonable performance have been designedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111943/1/rds20240.pd