We experimentally demonstrate the observation of a frequency-shift dynamics at a temporal boundary in the terahertz (THz) region relying on a scheme that controls the structural dispersion of a metalsemiconductor waveguide. Ultrafast structural-dispersion switching is achieved within a subpicosecond timescale by illuminating a waveguide surface with an optical pump pulse during the propagation of a THz pulse in the waveguide. Owing to the relatively high conversion efficiency, up to 23%, under the condition that the frequency shift is sufficiently larger than the bandwidth of the incident pulse, the rapid variation of the THz frequency around the temporal boundary is directly observed in the time domain.
Arrays of patch antennas have impacted
modern telecommunications
in the RF range significantly, owing to their versatility in tailoring
the properties of the emitted radiation such as beam width and polarization,
along with their ease of fabrication. At higher frequencies, in the
terahertz (THz) range, there is a pressing need for a similar monolithic
platform to realize and enable the advanced functionalities available
in the RF technology. This platform would benefit a wide variety of
fields such as astronomy, spectroscopy, wireless communications, and
imaging. Here, we demonstrate THz lasers made of arrays of 10 ×
10 patch antenna microcavities that provide up to 25 mW output power
with robust single mode frequency and spatial mode. This device architecture
leads to an unprecedented beam divergence, better than 2° ×
2°, which depends only on the number of resonators. This allows
to functionalize the device while preserving a high quality far-field
pattern. By interconnecting the symmetric square microcavities with
narrow plasmonic wires along one direction, we introduce an asymmetry
into the originally degenerate and cross-polarized TM01 and TM10 modes, leading to a precise control of the resonant
frequency detuning between the TM modes. This feature allows devices
to be designed that radiate with any coherent polarization states
from linear to circular. Large-scale full-wave simulations of the
emission from entire arrays support our experimental results. Our
platform provides a solution to finally achieve monolithic terahertz
emitters with advanced integrated functionalities such as active beam
steering and polarization control.
We perform a comprehensive study on the emission from finite arrays of patch antenna microcavities designed for the terahertz range by using a finite element method. The emission properties including quality factors, far-field pattern and photon extraction efficiency are investigated for etched and non-etched structures as a function of the number of resonators, the dielectric layer thickness and period of the array. In addition, the simulations are achieved for lossy and perfect metals and dielectric layers, allowing to extract the radiative and nonradiative contributions to the total quality factors of the arrays. Our study show that this structure can be optimized to obtain low beam divergence (FWHM <10°) and photon extraction efficiencies >50% while keeping a strongly localized mode. These results show that the use of these microcavities would lead to efficient terahertz emitters with a low divergence vertical emission and engineered losses.
We study the emission of THz quantum cascade lasers (QCLs) designed in arrays of Patch Antenna Microcavities (PAM). The array geometry is an effective strategy to control the losses and to achieve phase locking, allowing for beam shaping and high photon outcoupling efficiency. We demonstrate a 40-fold enhanced emission compared to standard ridge waveguides and a gaussian beam divergence as low as 2° x 2°.
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