This work aims at illuminating an UTC-PD array with a multicore fiber towards multiple THz carrier generation. This photonics-based transmitter is expected to increase either the data rate via spatial multiplexing on different carriers or the emitted THz-power and therefore the transmission reach of THz systems operating in 300 GHz band. Preliminary results of the characterization of the sub-systems of the transmitter that is under development are presented here.
Impedance matching in negative index 2D air hole array was addressed by the retrieval of the effective parameters. By
solving the eigenvalues problem, we first stress the major difference between an electromagnetic confinement in air for
the ground right handed branch and in the host matrix for the left handed one. We then calculate the complex
transmission and reflection coefficients for a finite slab from which the effective refractive index and impedance are
deduced by using a Fresnel inversion technique. The criterion n = -1 was found incompatible with the impedance
matching condition z = 1. Also, the relevance of the dispersion characteristics was assessed by a technique based on
spatial Fourier transform.
An original all-dielectric design that performs cloaking at terahertz frequencies is demonstrated. The cloak consists of
radially positioned discretized micrometer-sized cylindrical elements. Based on Mie theory and under adequate
excitation conditions (H along the rod axis), high-κ cylinders exhibit a strong magnetic resonance dependent on the
cylinder radii and material properties. Full-wave simulations coupled with a field-summation retrieval technique were
employed to adjust the electromagnetic response of individual ferroelectrics rods (Ba0.5Sr0.5TiO3; ε = 200 - tan δ = 2.10-2).
The rods magnetic plasma frequency was engineered such that the full cloak displays a progressive variation in its
permeability radial component; hence satisfying, for this polarization, the reduced equations derived from the conformal
transformation theory. The cloaking performance was assessed by modelling the complete micro-structured device.
Results unambiguously show that cloaking of any wavelength scaled objects located inside the cloak is achieved above
the Mie resonance frequency at 0.58 THz for the present device. In particular, the phase fronts of the electric field behind
the device are well reconstructed with a high value in transmission of the incident plane wave. This also means that the
absorption losses are small within the cloak in comparison with the metallic systems originally proposed. Although
cloaking is observed in a narrow band, this all-dielectric configuration provides an attractive route for designing cloaking
devices at microwave and terahertz frequencies.
A review is given of recent theoretical and experimental studies on the liquid crystal (LC) infiltration of 3D photonic crystal (PC) structures so as to obtain tunable Bragg reflection and transmission characteristics. It is shown that large-pore and non-close-packed inverse opals formed by sintering, or by a multiple-layer conformal deposition technique, provide a simple and effective dielectric scaffold for liquid crystal infiltration. The dynamic optical properties are strongly dependent on the scaffold structure and the dielectric contrast between the scaffold and the LC. Experimental structures were fabricated using precise, conformal, low temperature atomic layer depositions of Al2O3 and TiO2 to create inverse opals and non-close-packed inverse opals, which were subsequently infiltrated with the nematic liquid crystals 5CB and MLC2048. The dependence of the visible/infrared reflectance and transmittance were investigated as functions of applied electric field amplitude and frequency for applications in optical modulation and switching.
We present experimental and theoretical investigations of tunable large-pore inverse opals fabricated by combining conformal films in patterned template structures with infiltrated liquid crystals. Ultra-conformal films allow opal templates to be inverted and used as scaffolding for fabricating a large-pore dielectric backbone that serves as a patterned template for electro-optic/non-linear or conventional materials. Additionally, theoretical results of tunable non-close-packed inverse opals fabricated by a multi-layer atomic layer deposition process and infiltrated with lead lanthanum zirconium titanate are presented. The structural properties of the device are defined by the template, while the dynamic properties are controlled independently by the choice of electro-optic/non-linear material. A variety of dielectric templates were modeled by choosing conformal coatings to define structures that exhibit either large Bragg peak tunability or width. The dynamic optical properties of the tuned large-pore and non-close-packed inverse opals are discussed and a model is presented for characterizing the controlled fabrication of optimized photonic crystal structures using multi-component conformal film deposition. Experimental measurements and modeling both indicate enhanced static and dynamic tunability to the photonic properties of infiltrated inverse templates compared to typical tunable opal-based inverse structures.
We report the controllable and tunable fabrication of structurally modified non-close-packed inverse shell opals using multi-layer atomic layer deposition and present a model and simulation algorithm to calculate the structural parameters critical to fabrication. This powerful, flexible and unique technique enables opal inversion, structural modification and backfilling and was applied to the fabrication of TiO2 non-close-packed inverse opals. Using successive conformal backfilling it was possible to tune the Bragg peak over 600 nm and enhance the Bragg peak width by >50%. Additionally, band structure calculations, using dielectric functions approximating the true network topology, were used to predict the optical properties during the fabrication process. 3D finite-difference-time-domain results predict experimentally achievable structures with a complete band gap as large as 7.2%. Additionally, the refractive index requirement was predicted to decrease from 3.3 in an 86% infiltrated inverse shell opal to 3.0 in an optimized non-close-packed inverse shell opal. It was also shown for these structures that the complete photonic band gap peak can be statically tuned by over 70% by increasing the backfilled thickness.
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