Propagation and Control of Broadband Optical and Radio Frequency Signals in Complex Environments
thesisposted on 15.05.2019, 14:46 by Bohao Liu
A complex environment causes strong distortion of the field, inhibiting tasks such as imaging and communications in both the optical and radio-frequency (RF) region. In the optical regime, strong modal dispersion in highly multimode fiber (MMF) results in a scrambled output field in both space (intensity speckles) and time (spectral and temporal speckles). Taking advantage of the pulse shaping technique, spatial and temporal focusing has been achieved in this thesis, offering potential opportunities for nonlinear microscopy and imaging or space-division multiplexed optical communication through MMF. In the RF regime, multipath effect in wireless RF channel gives multiple echoes with random delay and amplitude attenuation at the receiver end. Static channel sounding and compensation with ultra-broadband spread spectrum technique resolves the issue by generating a peaking signal at the receiver, significantly improving the signal-to-noise/interference performance. However, the limited communication speed in the static approach makes it challenging for sounding and compensation in a dynamic channel. Here, we achieve real-time channel sounding and compensation for dynamic wireless multipath channel with 40 micro-seconds refresh rate by using a fast processing field programmable gate array (FPGA) unit, providing potential opportunities for mobile communications in indoor, urban, and other complex environments. Furthermore, by combining broadband photonics and RF radar technologies, a high depth and transverse resolution wide bandwidth (15 GHz) W-band (75 - 110 GHz) photonic monopulse-like radar system for remote target sensing is demonstrated, offering prospects for millimeter wave 3-D sensing and imaging.