Search

Terahertz sparse deconvolution based on an iterative shrinkage algorithm is presented in this study to characterize multilayered structures. With an upsampling approach, sparse deconvolution with superresolution is developed to overcome the time resolution limited by the sampling period in the measurement and increase the precision of the estimation of echo arrival times. A simple but effective time-domain model for describing the temporal pulse spreading due to the frequency-dependent loss is also designed and introduced into the algorithm, which greatly improves the performance of sparse deconvolution in processing time-varying pulses during the propagation of terahertz waves in materials. Numerical simulations and experimental measurements verify the algorithms and show that sparse deconvolution can be considered as an effective tool for terahertz nondestructive characterization of multilayered structures.

We propose a coupling-induced intensity-sensing mechanism based on a microring resonator. Different from the conventional intensity sensor, the resonator is working under the analyte-induced variable coupling. The coupling coefficients are highly sensitive to changes of the analyte, thus leading to significant analyte-dependent output intensity. This advanced sensing mechanism is proved with a detection limit of 1.23×10^−7, predicted based on the coupled-mode theory. By introducing a phase bias in the Mach–Zehnder interferometer, the detection limit may be enhanced further to 4×10^−8, which is demonstrated to be up to 1 order of magnitude more sensitive than that provided by comparable conventional sensors.

The photonic crystal structure with parallelogram lattice, capable of bending a self-collimated wave with free angles and partial bandgap reflection, is presented. The equifrequency contours show that the direction of the collimation wave can be turned by tuning the angle between the two basic vectors of the lattice. Acute, right, and obtuse angles of collimating waveguide bends have been realized by arc lattices of parallelogram photonic crystals. Moreover, partial bandgap reflection of the parallelogram lattice photonic crystals is validated from the equifrequency contours and the projected band structures. A waveguide taper based on this partial bandgap reflection is also designed and proved to have above 85% transmittance over a very wide operating bandwidth of 180 nm.

A theoretical study of the interaction of intense terahertz transients and broadband optical pulses in quantum wells is presented. The approach is based on a numerical solution of the anisotropic semiconductor Bloch equations and includes, self-consistently, both continuum and excitonic effects. In the optical regime we recover the dynamic Franz–Keldysh effect showing THz sidebands in the optical absorption spectrum. In the THz regime we discern a series of harmonically generated upshifted THz transients. It is demonstrated pictorially that the upshifted transients are formed by the creation of highly anisotropic interfering, relative-motion electron–hole wave packets. We also investigate the influence of ellipticity of the driving field and chirped optical pulses. The field interaction with the quantum well is shown to be highly nonperturbative for typical free-electron laser fields. A series of propagating charge-carrier wave packets are analyzed, and a connection is made to analogies in the high-field physics of atomic ensembles.