Tunable Mirror Research Articles

Electrically Tunable Chiral Ferroelectric Nematic Liquid Crystal Reflectors

AbstractManipulating light is an important area of optical research and development. To that end, tunable dichroic devices in which the reflectivity at differing wavelengths can be adjusted, are particularly valuable. This work is motivated by recent studies of the optical properties of chiral ferroelectric nematic liquid crystals (FNLCs). Here electro‐optical studies are presented on two room temperature, FNLC materials that demonstrate electrically tunable reflectivity when subject to a field below 0.2 V µm−1. Moreover, under appropriate conditions, the reflectivity can also be electrically (and reversibly) tuned (without change of color) from 0% to 40%. Reversible, low voltage tunable mirrors, having miniscule power consumption and operable around ambient temperature are expected to be useful in diverse applications ranging from energy‐saving, smart windows to virtual reality interfaces.

Programming quadric metasurfaces via infinitesimal origami maps of monohedral hexagonal tessellations: Part I

The control of the shape of complex metasurfaces is a challenging task often addressed in the literature. This work presents a class of tessellated plates able to deform into surfaces of preprogrammed shape upon activation by any flexural load and that can be controlled by a single actuator. Quadric metasurfaces are obtained from infinitesimal origami maps of monohedral hexagonal tessellations of the plane, that is pavings in which all tiles are congruent to each other. Monohedral tessellated portions can be joined together to obtain more complex shapes, which can be locally synclastic or anticlastic and can have a certain roughness. We broaden previous work by providing a complete characterization of all the three known types of monohedral tessellations composed by irregular hexagons. The proposed two-dimensional structures may have applications in prosthetics, tissue engineering, wearable devices, energy harvesting devices, tunable focus mirrors and adaptive facades. The study is divided in two parts. In Part I, after introducing the discrete kinematics of tessellated plates, it is proved analytically that essentially each type of monohedral hexagonal tessellation possesses only one deformation mode. Afterwards, several numerical examples are provided to demonstrate the variety of achievable surface shapes. In Part II, first the metasurfaces corresponding to assigned tile geometries are given a continuum description, which establishes that the continuous interpolant is always a quadric. Then, experimental results on fabrication, assembly and surface accuracy are reported.

Non-Hermitian Waveguide Cavity QED with Tunable Atomic Mirrors.

Optical mirrors determine cavity properties by means of light reflection. Imperfect reflection gives rise to open cavities with photon loss. We study an open cavity made of atom-dimer mirrors with a tunable reflection spectrum. We find that the atomic cavity shows anti-PT symmetry. The anti-PT phase transition controlled by atomic couplings in mirrors indicates the emergence of two degenerate cavity supermodes. Interestingly, a threshold of mirror reflection is identified for realizing strong coherent cavity-atom coupling. This reflection threshold reveals the criterion of atomic mirrors to produce a good cavity. Moreover, cavity quantum electrodynamics with a probe atom shows mirror-tuned properties, including reflection-dependent polaritons formed by the cavity and probe atom. Our Letter presents a non-Hermitian theory of an anti-PT atomic cavity, which may have applications in quantum optics and quantum computation.

Compact silicon nitride interferometers.

We demonstrate a compact silicon nitride interferometer which uses waveguides with the same length and different effective indices instead of similar effective indices and different lengths. In such structures there is no need to have waveguide bends. This not only reduces losses but also results in an order of magnitude smaller footprint and thus enables much higher integration densities. We also study the tunability of this interferometer using thermo-optical effects induced by a simple aluminum heater and show that thermal tuning can compensate for the effects of fabrication variations on the spectral response. The application of the proposed design in a tunable mirror is also briefly discussed.

Long-wavelength infrared zoom system using tunable concave and convex mirrors

We propose and demonstrate a long-wavelength infrared (LWIR) zoom system with focus tunable mirrors. The designed system consists of two focus tunable mirrors, four static lenses, and a detector. The zoom magnification can be changed by altering the focal length of the two mirrors through a control of the radius of the surface curvature of the mirrors. The shape of the mirrors can be concave or convex, which means that the focal length can vary from negative to positive. The fixed-focus lenses are designed to correct the aberrations of the tunable mirrors and are made of a material with good transparency at LWIR. Following the above design, an LWIR zoom system with the characteristic of being concave or convex is realized for the first time, and its results demonstrate 2x magnification and speeds up to 5 Hz. The proposed zoom system is free from mechanical moving parts and has potential as a low-cost LWIR system with high-speed zoom.

Temperature-Dependent Anisotropic Refractive Index in β-Ga2O3: Application in Interferometric Thermometers

An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red-infrared Fabry-Perot optical resonances when excited with different laser powers. The origin of this shift is mainly related to the variation in the temperature of the refractive index. A comparison of these two experimental results was performed by finite-difference time-domain (FDTD) simulations, considering the exact morphology of the wires and the temperature-dependent, anisotropic refractive index. The shifts caused by temperature variations observed by μ-PL are similar, though slightly larger than those obtained with FDTD when implementing the n(λ,T) obtained with ellipsometry. The thermo-optic coefficient was calculated.

Widely tunable 2 µm hybrid laser using GaSb semiconductor optical amplifiers and a Si3N4 photonics integrated reflector

Tunable lasers emitting in the 2-3 µm wavelength range that are compatible with photonic integration platforms are of great interest for sensing applications. To this end, combining GaSb-based semiconductor gain chips with Si3N4 photonic integrated circuits offers an attractive platform. Herein, we utilize the low-loss features of Si3N4 waveguides and demonstrate a hybrid laser comprising a GaSb gain chip with an integrated tunable Si3N4 Vernier mirror. At room temperature, the laser exhibited a maximum output power of 15 mW and a tuning range of ∼90 nm (1937-2026 nm). The low-loss performance of several fundamental Si3N4 building blocks for photonic integrated circuits is also validated. More specifically, the single-mode waveguide exhibits a transmission loss as low as 0.15 dB/cm, the 90° bend has 0.008 dB loss, and the 50/50 Y-branch has an insertion loss of 0.075 dB.

Wave Propagation Properties of a One‐Dimensional Photonic Crystal with Double Negative Metamaterial

AbstractIn this simulation work, the wave vector and reflectance properties of a 1DPC made of dielectric/metamaterial multilayer structure employing TMM, for TE and TM modes are studied. For TE mode, it is observed that the obtained wide bandgap increases with increase in the angle of incidence, whereas the narrow bandgap also shows a minor increase with increase in the incident angle. It is noted that bandgap increases with increase in the incident angle in TE mode, while bears opposite behavior in TM mode and decreases with increase in the incident angle. If the DPS thickness is increased, the number of bands increases in both TE and TM modes, while the wide bandgaps for TE and TM decreases in width. In both cases of the increased DPS width, it is found that the narrow bandgap obtained in TM mode is showing enhancement with an increase in incident angle, and exhibits ultra‐tunable behavior. Some other researchers have reported earlier that a complementary split‐ring resonator based metamaterial with effective medium ratio has influence on the extraction of effective permittivity, permeability, and refractive index, where DNG regions exist in the ranges 6.34–7.39 and 8.20–9.98 GHz. Comparing with the proposed DNG, the study finds that the aforesaid values correspond to frequency regime taken in our case, 1–10 GHz, particularly the middle of the range 1–10 GHz, where broadband is obtained, which is satisfactory. The insights included in the article can be employed in designing microwave broadband reflectors, tunable mirrors, and can be proved to be useful in photovoltaic cells. Such PC can also be employed in designing super lenses as well as optical cloaking, and the miniaturization of antennas.

Surface-emitting THz quantum cascade laser frequency comb with tunable external mirror dispersion compensation

We present a surface emitting THz quantum cascade laser frequency comb with an adjustable chromatic dispersion compensation via a mechanically tunable GTI cavity. Surface emission and high optical feedback into the laser cavity are achieved by a planarized ridge waveguide design with low reflectivity facets and two broadband patch array antennas for coupling to an external mirror (back side) and for power extraction (front side). We demonstrate direct and reproducible manipulation of the frequency comb state, specifically the comb stability and beatnote frequency tuning, by controlling the position of an external movable mirror.

Miniature Deformable MEMS Mirrors for Ultrafast Optical Focusing.

Here, we introduce ultrafast tunable MEMS mirrors consisting of a miniature circular mirrored membrane, which can be electrostatically actuated to change the mirror curvature at unprecedented speeds. The central deflection zone is a close approximation to a parabolic mirror. The device is fabricated with a minimal membrane diameter, but at least double the size of a focused optical spot. The theory and simulations are used to predict maximum relative focal shifts as a function of membrane size and deflection, beam waist, and incident focal position. These devices are demonstrated to enable fast tuning of the focal wavefront of laser beams at ≈MHz tuning rates, two to three orders of magnitude faster than current optical focusing technologies. The fabricated devices have a silicon membrane with a 30-100 μm radius and a 350 nm gap spacing between the top and bottom electrodes. These devices can change the focal position of a tightly focused beam by ≈1 mm at rates up to 4.9 MHz and with response times smaller than 5 μs.

Effects of electric quadrupole interactions with tunable atomic mirrors

Recent studies have involved electric quadrupole effects in atoms interacting with the evanescent mode. This type of surface mode is usually produced by the total internal reflection in a dielectric-vacuum atz=0, and its intensity distribution is very close to the outer surface z>0 half-space. Coating the planar surface of a dielectric substrate with multilayer dielectric thin film of different thicknesses provides an enhanced in such evanescent modes. This type of mode can be used purely as an atomic mirror. We show that the use of such elements for atomic optics gives significant enhancement of the evanescent mode magnitude without degrading the quality of the atomic reflection process. In addition, the decay depth of the evanescent mode can be conveniently controlled by design parameters. This property keeps the atom-light interaction timeτ, and thus the probability of decay emission, very low, which means a high degree of coherence property.

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

Design and characteristics of reflectivity tunable mirror with MZI and loop waveguide on SOI

To achieve a reconfigurable photonic integrated circuit with active elements, we proposed a reflectivity tunable mirror constructed using a Mach–Zehnder interferometer (MZI) with a micro heater and loop waveguide on a silicon photonics platform. In this paper, the principle of the operation, design, fabrication, and measurement results of the mirror are presented. In theory, the phase shift dependence of the mirror relies on the coupling coefficient of the directional couplers of the MZI. When the coupling coefficient was 0.5 and 0.15, the reflection could be turned on and off with a phase shift of and respectively. The reflection power of the fabricated mirror on the silicon on insulator substrate was changed by more than 20 dB by a phase shift. In addition, it was demonstrated that the phase shift dependence of the mirror changes with the coupling coefficient of the fabricated devices.

Optical Microfluidic Waveguides and Solution Lasers of Colloidal Semiconductor Quantum Wells.

The realization of high-quality lasers in microfluidic devices is crucial for numerous applications, including biological and chemical sensors and flow cytometry, and the development of advanced lab-on-chip (LOC) devices. Herein, an ultralow-threshold microfluidic single-mode laser is proposed and demonstrated using an on-chip cavity. CdSe/CdS@Cdx Zn1- x S core/crown@gradient-alloyed shell colloidal semiconductor quantum wells (CQWs) dispersed in toluene are employed in the cavity created inside a poly(dimethylsiloxane) (PDMS) microfluidic device using SiO2 -protected Ag mirrors to achieve in-solution lasing. Lasing from such a microfluidic device having CQWs solution as a microfluidic gain medium is shown for the first time with a record-low optical gain threshold of 17.1 µJ cm- ² and lasing threshold of 68.4 µJ cm- ² among all solution-based lasing demonstrations. In addition, air-stable SiO2 protected Ag films are used and designed to form highly tunable and reflective mirrors required to attain a high-quality Fabry-Pérot cavity. These realized record-low thresholds emanate from the high-quality on-chip cavity together with the core/crown@gradient-alloyed shell CQWs having giant gain cross-section and slow Auger rates. This microfabricated CQW laser provides a compact and inexpensive coherent light source for microfluidics and integrated optics covering the visible spectral region.

Simulation on tunable graphene metasurface focusing mirror based on flexible substrate

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Thermally tunable terahertz omnidirectional photonic bandgap and defect mode in 1D photonic crystals containing moderately doped semiconductor

A new one-dimensional photonic crystal (1DPC) containing moderately doped silicon (m-Si) semiconductor is proposed and its tunable properties are theoretically investigated. The tunable complex permittivity of m-Si with temperature is the central idea that makes the 1DPC thermally tunable. The 1DPC systems such as (m-Si/SiO2)12 and defective (m-Si/SiO2)6D(m-Si/SiO2)6 are examined in the spectral range of 0.4–0.8 THz with varying temperature from 40 to 100 K. Air and m-Si are considered as defect layer (D) in two different 1DPC systems. Our simulation shows that the photonic band gap (PBG) shifts to higher frequency and the omnidirectional PBG gets narrower with increasing temperature. The defect mode in both defective 1DPCs shifts to higher frequency with increasing temperature. The temperature sensitivity of peak transmission is found better in the air defective 1DPC, while that of defect frequency is better in the m-Si defective 1DPC. The angle of incidence and polarization dependency of the defect modes are studied in detail. The present work can be utilized for the development of tunable omnidirectional mirrors and narrow bandpass filters in the terahertz region as well as THz light based thermal sensors.

Synthesis of nickel nanoparticles by a green and convenient method as a magnetic mirror with antibacterial activities

In this work, a simple protocol was described for the synthesis of nickel magnetic mirror nanoparticles (NMMNPs) including antibacterial activities. The identification of NMNPs was carried out by field-emission scanning electron microscopy (FESEM) images, energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) pattern, transmission electron microscopy (TEM) images and vibrating sample magnetometer (VSM) curve. The antibacterial activities are investigated against S. aureus and E. coli as the Gram-positive and Gram-negative bacteria, respectively. The UV–Vis absorption was also studied in the present of NMMNPs at different time intervals that disclosed decreasing of the bacterial concentration. More than 80% of the bacteria were disappeared after treating in the presence of NMMNPs for 18 h. The Ni-NPs revealed an excellent mirror attribute with a well-controlled transmission (7%). A better light-reflectivity over conventional glass or a mercury mirror proved their utility for domestic uses in comparison with conventional mirrors as rather toxic materials like mercury. Owing to its magnetic properties, this kind of mirror can be easily made onto glass by using an external magnet. An ordered crystalline structure, admissible magnetic properties, substantial antibacterial activities, tunable mirror properties, mild reaction conditions, and overall, the facile synthesis are the specific features of the present protocol for the possible uses of NMMNPs in diverse applications.

Band gap characteristics of 1D static and moving photonic crystal

We have studied theoretically the realistic factors for the formation of PBGs in 1D PCs for all incident angles and polarizations, using the transfer matrix method. The results show that these factors significantly influence the behaviour of photonic band characteristics and transmission coefficient, which can be enhanced or suppressed by adjusting the frequency, angle of incidence, optical path length or manipulating the geometry of the 1D PCs. This method can be used conveniently to study the band gap characteristics when the 1D PC moves with uniform velocity. The dielectric constants of the layers are transformed due to motion of the PC. The frequency range of the crystal band gap is shifted towards low frequency with increasing velocity. The moving crystal concept enables novel photonic devices such as optically tunable mirrors, all optical diodes and cavities.

A type of arrangement for photonic crystal structures interacting with a Terahertz wave with omnidirectional and thermal effects

Omnidirectional photonic bandgaps are a new special type of one-dimensional quasi-photonic crystals that contains semiconductor and dielectric material layers and are investigated here in the Terahertz wave range. The proposed medium is constructed with a special type of layer arrangement, which uses both the Fibonacci sequence as a quasi-periodic sequence and the absolute periodic sequence in a period. As the Terahertz bandgaps of the transmittance spectrum are essential in some devices, the tuning and manipulation of these bandgaps has been of great interest in recent years. One of the best methods of manipulating these bandgaps to reach the desired outcome is by changing their arrangement using different types of quasi-periodic sequences in the structure. The beneficial results of applying these sequences have been clearly observed. So, we propose another new type of arrangement here in order to completely satisfy the changing methods of the photonic crystal structures. According to the results of the current investigation, it has been demonstrated that the proposed arrangement could be used to achieve a wide variety of desirable states. The semiconductor could make the bandgaps tunable via temperature changes through its thermally tunable permittivity. These types of media, which can operate as tunable Terahertz filters and mirrors, offer many promising omnidirectional Terahertz components and devices.

Switchable All-Dielectric Magnetic-Electric Mirror Based on Higher-Order Dipoles

Both magnetic and electric mirrors have great applied values in military, medical, and signal-transmission technology because of their electromagnetic properties. Although many kinds of artificial magnetic conductors, such as arrays of Mie resonance--based dielectric cubes or disks, have been demonstrated to be able to approximate a magnetic mirror, most of them, however, work within a narrow and invariable frequency band, and most attention is paid to magnetic dipole resonance of first order. Here, we investigate the resonant mechanism of dielectric cuboids and employ the dipole resonance of higher order to obtain a bifunctional and reconfigurable all-dielectric electric and magnetic mirror controlled by temperature. A prototype device is designed and fabricated with $\mathrm{Ca}$-${\mathrm{La}}_{2}{\mathrm{O}}_{3}$-${\mathrm{Ti}\mathrm{O}}_{2}$ ferroelectric cuboids as building blocks, and its reflecting effects are successfully demonstrated, as well as the tunability of working frequency by varying temperature. Moreover, electric and magnetic dipole resonances of higher order are proved to have superior resonant characteristics to the primary ones, which can effectively suppress the spectral overlapping between the adjacent magnetic and electric resonances and thus makes such all-dielectric reflector possible to switch between magnetic mirror and electric mirror. Furthermore, the proposed cuboids have the potential to expand to active phase-control metasurface devices and Huygens' sources with better impedance matching. Our work reveals the specific optical properties of higher-order dipolar resonances and opens the door towards the realization of tunable and reconfigurable magnetic-electric mirrors.