Resistance thermometry provides a time-tested method for taking temperature measurements. However, fundamental limits to resistance-based approaches has produced considerable interest in developing photonic temperature sensors to leverage advances in frequency metrology and to achieve greater mechanical and environmental stability. Here we show that silicon-based optical ring resonator devices can resolve temperature differences of 1 mK using the traditional wavelength scanning methodology.An even lower noise floor of 80 μK for measuring temperature difference is achieved in the side-of-fringe, constant power mode measurement.Temperature measurements play a central role in modern life ranging from process control in manufacturing 1 , physiological monitoring 2 and tissue ablation 3 in 2 medicine, and environmental control and monitoring in buildings 4 and automobiles 5 .Despite the ubiquity of thermometers, the underlying technology has been slow to advance over the last century. 6 The standard bearer for accurate temperature measurement, the standard platinum resistance thermometer (SPRT) was initially developed over a century ago. 6,7 Furthermore, many modern temperature sensors still rely on resistance measurements of a thin metal film or wire whose resistance varies with temperature. 6 Though resistance thermometers can routinely measure temperature with uncertainties of 10 mK, they are sensitive to mechanical shock which causes the resistance to drift over time requiring frequent off-line, expensive, and time consuming calibrations. 7In recent years there has been considerable interest in developing photonic devices as an alternative to resistance thermometers 8-10 as they have the potential to provide greater temperature sensitivity while being robust against mechanical shock and electromagnetic interference. Furthermore, the low weight, small form factor photonic devices might be multiplexed to provide a low-cost sensing solutions.Photonic temperature sensors exploit temperature dependent changes in a material's properties -typically, a combination of thermo-optic effect and thermal expansion. The temperature dependence of the ring resonator arises from temperatureinduced changes in refractive index (n) and in the physical dimensions of the ring. A qualitative analysis of a ring resonator yields a resonance wavelength for a single ring resonator of:where m is the vacuum wavelength, n eff is the effective refractive index, m is the mode number, L is the ring perimeter, and T is the temperature. Thus, the temperature-induced shift in wavelength is given by:Where the group index is n g = [ ( ) . The variation in the refractive index due to the thermal expansion coefficient for silicon (3.57 x 10 -6 /K) is a factor of 100 smaller 4 than that of the estimated thermo-optic effect (2 x 10 -4 /K) of the silicon waveguide and thus not included in our analysis of the performance of ring resonator devices. wafer with a 220 nm thick layer of silicon on top of a 2 μm thick buried oxide layer that isolates the ...
Bound states in the continuum (BICs) have exhibited extraordinary properties in photonics for enhanced light-matter interactions that enable appealing applications in nonlinear optics, biosensors, and ultrafast optical switches. The most common strategy to apply BICs in a metasurface is by breaking symmetry of resonators in the uniform array that leaks the otherwise uncoupled mode to free space and exhibits an inverse quadratic relationship between quality factor (Q) and asymmetry. Here, we propose a scheme to further reduce scattering losses and improve the robustness of symmetry-protected BICs by decreasing the radiation density with a hybrid BIC lattice. We observe a significant increase of radiative Q in the hybrid lattice compared to the uniform lattice with a factor larger than 14.6. In the hybrid BIC lattice, modes are transferred to Г point inherited from high symmetric X, Y, and M points in the Brillouin zone that reveal as multiple Fano resonances in the far field and would find applications in hyperspectral sensing. This work initiates a novel and generalized path toward reducing scattering losses and improving the robustness of BICs in terms of lattice engineering that would release the rigid requirements of fabrication accuracy and benefit applications of photonics and optoelectronic devices.
Terahertz (THz) waves have exhibited promising applications in imaging, sensing, and communications, especially for the next-generation wireless communications due to the large bandwidth and abundant spectral resources. Modulators and waveguides to manipulate THz waves are becoming key components to develop the relevant technologies where metamaterials have exhibited extraordinary performance to control free-space and on-chip propagation, respectively. In this review, we will give a brief overview of the current progress in active metadevices and topological photonic crystals, for applications of terahertz free-space modulators and on-chip waveguides. In the first part, the most recent research progress of active terahertz metadevices will be discussed by combining metamaterials with various active media. In the second part, fundamentals of photonic topological insulations will be introduced where the topological photonic crystals are an emerging research area that would boost the development of on-chip terahertz communications. It is envisioned that the combination of them would find great potential in more advanced terahertz applications, such as reconfigurable topological waveguides and topologically-protected metadevices.
The ability to spin-selectively absorb circularly polarized light (CPL) plays a critical role in various photonic devices. Here we propose and investigate a broadband chiral metamaterial composed of asymmetric split-ring resonators (SRRs), showing a wide spin-selective absorption band from 950 nm to 1200 nm with pronounced circular dichroism (CD) up to 20°. We demonstrate that the broadband absorption spectra originate from induced dual chiral resonance modes. Meanwhile, the two different resonances can be adjusted independently, suggesting great flexibility to the designed chiral absorption band for different purposes. Also, the chiralselective absorption performance is highly dependent on the oblique incident angle due to the extrinsic chirality. The chiral resonance modes can either be enhanced or destructed under oblique incidence. Such angle-dependent broadband chiral metamaterials may find potential applications for spin-orbit communications, chiral detection, polarimetric imaging, and biosensors.
In this paper, a wide-angle broadband perfect absorber is composed of a periodical metamaterial heterostructure. The structure is designed according to the concept that the metamaterial absorber's resonant frequency range can be manipulated by adjusting the filling factor of a bi-insulator heterostructure. The calculated results reveal that the four-layer herostructure has four perfect absorption peaks at the range of the terahertz frequency band. The related absorption bandwidth is 300 GHz and the average absorptivity is 98.6%. At the same time, the structure is insensitive to the incident angle.
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