2,877 research outputs found
Sub-diffraction thin-film sensing with planar terahertz metamaterials
Planar metamaterials have been recently proposed for thin dielectric film
sensing in the terahertz frequency range. Although the thickness of the
dielectric film can be very small compared with the wavelength, the required
area of sensed material is still determined by the diffraction-limited spot
size of the terahertz beam excitation. In this article, terahertz near-field
sensing is utilized to reduce the spot size. By positioning the metamaterial
sensing platform close to the sub-diffraction terahertz source, the number of
excited resonators, and hence minimal film area, are significantly reduced. As
an additional advantage, a reduction in the number of excited resonators
decreases the inter-cell coupling strength, and consequently the resonance Q
factor is remarkably increased. The experimental results show that the
resonance Q factor is improved by 113%. Moreover, for a film with a thickness
of \lambda/375 the minimal area can be as small as 0.2\lambda by 0.2\lambda.
The success of this work provides a platform for future metamaterial-based
sensors for biomolecular detection.Comment: 8 pages, 6 figure
Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators
Recent advances in nonlinear optics have revolutionized integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si₃N₄ and SiO₂. While semiconductor materials feature much higher nonlinear coefficients and convenience in active integration, they have suffered from high waveguide losses that prevent the realization of efficient nonlinear processes on-chip. Here, we challenge this status quo and demonstrate a low loss AlGaAs-on-insulator platform with anomalous dispersion and quality (Q) factors beyond 1.5 × 10⁶. Such a high quality factor, combined with high nonlinear coefficient and small mode volume, enabled us to demonstrate a Kerr frequency comb threshold of only ∼36 µW in a resonator with a 1 THz free spectral range, ∼100 times lower compared to that in previous semiconductor platforms. Moreover, combs with broad spans (>250 nm) have been generated with a pump power of ∼300 µW, which is lower than the threshold power of state-of the-art dielectric micro combs. A soliton-step transition has also been observed for the first time in an AlGaAs resonator
Nonlinear Optics of Split-Ring Resonators and their Application as a Thermal Detector
The experiments presented in this thesis aim to provide a contribution to the progress in the field of linear and nonlinear optics of metamaterials and their applications. The nonlinear optical experiments are focussed on second-harmonic generation of gold split-ring resonator arrays as a paradigmatic building block of metamaterials. In addition, this thesis presents a thermal detector based on a modified split- ring resonator structure
- …