Tunable multiresonance using complementary circular metamaterial

Larger-Than-Unity External Optical Field Confinement Enabled by Metamaterial-Assisted Comb Waveguide for Ultrasensitive Long-Wave Infrared Gas Spectroscopy

Nanophotonic waveguides that implement long optical pathlengths on chips are promising to enable chip-scale gas sensors. Nevertheless, current absorption-based waveguide sensors suffer from weak interactions with analytes, limiting their adoptions in most demanding applications such as exhaled breath analysis and trace-gas monitoring. Here, we propose an all-dielectric metamaterial-assisted comb (ADMAC) waveguide to greatly boost the sensing capability. By leveraging large longitudinal electric field discontinuity at periodic high-index-contrast interfaces in the subwavelength grating metamaterial and its unique features in refractive index engineering, the ADMAC waveguide features strong field delocalization into the air, pushing the external optical field confinement factor up to 113% with low propagation loss. Our sensor operates in the important but underdeveloped long-wave infrared spectral region, where absorption fingerprints of plentiful chemical bonds are located. Acetone absorption spectroscopy is demonstrated using our sensor around 7.33 μm, showing a detection limit of 2.5 ppm with a waveguide length of only 10 mm.

A voltage-controllable VO2 based metamaterial perfect absorber for CO2 gas sensing application

Vanadium dioxide (VO₂) based metamaterial perfect absorbers (MPAs) have high potential application values in sensing gas molecules. However, a tuning mechanism via temperature manipulation lacks the compatibility with electronic devices. In this study, a voltage-controllable device is proposed by integrating an MPA and micro-electro-mechanical system (MEMS) based microheater for CO₂ gas sensing application. The MPA is composed of a metal-dielectric-metal (MDM) structure and tailored to form an H-shaped metamaterial. The central bar of the H-shaped metamaterial is composed of a VO₂ material, which exhibits perfect absorption in the CO₂ gas absorption spectrum, i.e., at a wavelength of 2.70 μm. The intergated microheater is patterned by using fractal theory to provide high heating temperature and high uniformity of surface temperature. By precisely driving a DC bias voltage on the microheater, the MPA is heated and it can exhibit switchable optical properties with high efficiency. These results provide a strategy to open an avenue for sensors, absorbers, switches, and programmable devices in infrared wavelength range applications.

Design of Tunable Terahertz Metamaterial Sensor with Single- and Dual-Resonance Characteristic

We present two types of refractive index sensors by using tunable terahertz (THz) metamaterial (TTM) based on two concentric split-ring resonators (SRRs) with different splits. By modifying the distance between SRRs and substrate, TTM shows tunable single- and dual-resonance characteristic. The maximum tuning range of resonance is 0.432 THz from 0.958 THz to 1.390 THz. To demonstrate a great flexibility of TTM in real application, TTM device is exposed on the surrounding ambient with different refractive index (n). The sensitivity of TTM can be enhanced by increasing SRR height, which is increased from 0.18 THz/RIU to 1.12 THz/RIU under the condition of n = 1.1. These results provide a strategy to improve the sensing performance of the metamaterial-based sensing device by properly arranging the geometric position of meta-atoms. The proposed TTM device can be used for tunable filters, frequency-selective detectors, and tunable high-efficiency sensors in the THz frequency range.

Tunable Terahertz Metamaterial with Electromagnetically Induced Transparency Characteristic for Sensing Application

We present and demonstrate a MEMS-based tunable terahertz metamaterial (TTM) composed of inner triadius and outer electric split-ring resonator (eSRR) structures. With the aim to explore the electromagnetic responses of TTM device, different geometrical parameters are compared and discussed to optimize the suitable TTM design, including the length, radius, and height of TTM device. The height of triadius structure could be changed by using MEMS technique to perform active tunability. TTM shows the polarization-dependent and electromagnetic induced transparency (EIT) characteristics owing to the eSRR configuration. The electromagnetic responses of TTM exhibit tunable characteristics in resonance, polarization-dependent, and electromagnetically induced transparency (EIT). By properly tailoring the length and height of the inner triadius structure and the radius of the outer eSRR structure, the corresponding resonance tuning range reaches 0.32 THz. In addition to the above optical characteristics of TTM, we further investigate its potential application in a refraction index sensor. TTM is exposed on the surrounding ambient with different refraction indexes. The corresponding key sensing performances, such as figure of merit (FOM), sensitivity (S), and quality factor (Q-factor) values, are calculated and discussed, respectively. The calculated sensitivity of TTM is 0.379 THz/RIU, while the average values of Q-factor and FOM are 66.01 and 63.83, respectively. These characteristics indicate that the presented MEMS-based TTM device could be widely used in tunable filters, perfect absorbers, high-efficient environmental sensors, and optical switches applications for THz-wave optoelectronics.

Flexible and Controllable Metadevice Using Self-Assembly MEMS Actuator

In this work, an actively tunable optical metadevice is proposed to realize multifunctional application by integrating self-assembly electrothermal actuator (ETA) and magnetic metamaterial. The released frame of ETA can control the deformed height of the metamaterial plate and then provide high robustness. By driving the external electromagnetic field, the metamaterial plate is actuated and rotated by a magnetic force to manipulate the incident electromagnetic response. The transmission intensities of the metadevice can be gradually increased to characterize "on" and "off" states. Along with the inputs of light source and magnetic field, the transmission results of the metadevice could provide the output of time-difference optical signal and then carry with digital information in the further optical logic operation. Such an actuation method provides an ideal platform for actively tunable metamaterial with a large tilt angle and displacement. MEMS-based metamaterial is a strategy to open an avenue for optical communication, 3D imaging, and optical logic switching applications.

Tunable infrared metamaterial-based biosensor for detection of hemoglobin and urine using phase change material

This paper reports about the outcomes from an investigation carried out on tunable biosensor for detection using infrared in the range of 1.5 µm and 1.65 µm. The biosensor is made of phase change material formed by different alloy combinations, Ge₂Sb₂Te₅ (GST). The nature of GST allows for the material to change phase with changes in temperature, giving the tunable sensing property for biosensing application. Sensor built with amorphous GST (aGST) and crystalline GST (cGST) in different design structures were tested on different concentrations of biomolecules: hemoglobin (10 g/l, 20 g/l, 30 g/l and 40 g/l); and urine (0-1.5 mg/dL, 2.5 mg/dL, 5 mg/dL and 10 mg/dL). The tunable response observed from the tests demonstrates the potential application of the materials in the design of switching and sensing systems.

Tunable Split-Disk Metamaterial Absorber for Sensing Application

We present four designs of tunable split-disk metamaterial (SDM) absorbers. They consist of a bottom gold (Au) mirror layer anchored on Si substrate and a suspended-top SDM nanostructure with one, two, three, and four splits named SDM-1, SDM-2, SDM-3, and SDM-4, respectively. By tailoring the geometrical configurations, the four SDMs exhibit different tunable absorption resonances spanning from 1.5 µm to 5.0 µm wavelength range. The resonances of absorption spectra can be tuned in the range of 320 nm, and the absorption intensities become lower by increasing the gaps of the air insulator layer. To increase the sensitivity of the proposed devices, SDMs exhibit high sensitivities of 3312 nm/RIU (refractive index unit, RIU), 3362 nm/RIU, 3342 nm/RIU, and 3567 nm/RIU for SDM-1, SDM-2, SDM-3, and SDM-4, respectively. The highest correlation coefficient is 0.99999. This study paves the way to the possibility of optical gas sensors and biosensors with high sensitivity.

Tunable metamaterial-based silicon waveguide

A tunable metamaterial (MM)-based silicon (Si) waveguide is presented that is composed of an MM nanodisk array on a Si-on insulator substrate. A significant modulation efficiency of transmission intensity could be realized by elevating individually or simultaneously the column number of MM nanodisks. For a convenient description, an MM-based Si waveguide with one, two, three, four, and five columns of MM nanodisks are denoted as MM-1, MM-2, MM-3, MM-4, and MM-5, respectively. Transmission intensity of MM-based Si waveguides could be switched between on and off states by driving different columns of MM nanodisks on the Si waveguide surface. Transmission intensities could be attenuated from 100% to 56%, 24%, 6%, 1%, and 0% for MM-1, MM-2, MM-3, MM-4, and MM-5, respectively, at the wavelength of 1.525 µm. Furthermore, the MM-5 device is exposed to an ambient environment with different refraction indices. It exhibits a linear relationship of resonance dips and refraction indexes. The proposed design of the MM-based Si waveguide provides potential possibilities in an optical switch, variable optical attenuator, and sensor applications.

Tunable multiresonance using complementary circular metamaterial: publisher's note

This publisher's note contains corrections to Opt. Lett.45, 3633 (2020)OPLEDP0146-959210.1364/OL.394137.

Reconfigurable Terahertz Metamaterial Using Split-Ring Meta-Atoms with Multifunctional Electromagnetic Characteristics

We propose a reconfigurable terahertz (THz) metamaterial (RTM) to investigate its multifunctional electromagnetic characteristics by moving the meta-atoms of split-ring resonator (SRR) array. It shows the preferable and capable adjustability in the THz frequency range. The electromagnetic characteristics of the proposed RTM device are compared and analyzed by moving the meta-atoms in different polarized transverse magnetic (TM) and transverse electric (TE) modes. The symmetrical meta-atoms of RTM device exhibit a resonant tuning range of several tens of GHz and the asymmetrical meta-atoms of RTM device exhibit the better tunability. Therefore, an RTM device with reconfigurable meta-atoms possesses the resonance shifting, polarization switching, electromagnetically induced transparency (EIT) switching and multiband to single-band switching characteristics. This proposed RTM device provides the potential possibilities for the use of THz-wave optoelectronics with tunable resonance, EIT analog and tunable multiresonance characteristics.

Tunable Infrared Metamaterial Emitter for Gas Sensing Application

We present an on-chip tunable infrared (IR) metamaterial emitter for gas sensing applications. The proposed emitter exhibits high electrical-thermal-optical efficiency, which can be realized by the integration of microelectromechanical system (MEMS) microheaters and IR metamaterials. According to the blackbody radiation law, high-efficiency IR radiation can be generated by driving a Direct Current (DC) bias voltage on a microheater. The MEMS microheater has a Peano-shaped microstructure, which exhibits great heating uniformity and high energy conversion efficiency. The implantation of a top metamaterial layer can narrow the bandwidth of the radiation spectrum from the microheater to perform wavelength-selective and narrow-band IR emission. A linear relationship between emission wavelengths and deformation ratios provides an effective approach to meet the requirement at different IR wavelengths by tailoring the suitable metamaterial pattern. The maximum radiated power of the proposed IR emitter is 85.0 µW. Furthermore, a tunable emission is achieved at a wavelength around 2.44 µm with a full-width at half-maximum of 0.38 µm, which is suitable for high-sensitivity gas sensing applications. This work provides a strategy for electro-thermal-optical devices to be used as sensors, emitters, and switches in the IR wavelength range.

Polarization-Sensitive Metamaterials with Tunable Multi-Resonance in the Terahertz Frequency Range

We propose two designs of polarization-sensitive metamaterials (PSMs), which are composed of face-to-face spilt-ring resonators (SRRs) and a cut-wire resonator (CWR) sandwiched by two face-to-face SRRs. For convenient description, they are denoted as PSM_1 and PSM_2, respectively. PSM_1 and PSM_2 are fabricated by tailoring Au layers with periodic configurations on silicon-on-insulator (SOI) substrates. By changing the incident polarization light, the electromagnetic responses of PSM_1 can be manipulated between single-resonance and dual-resonance, while those of PSM_2 exhibit switching behavior between single-resonance and triple-resonance. By enlarging the distance between the gap centers of the two face-to-face SRRs along the y-axis direction, the electromagnetic responses of PSM_1 show switching characteristics from single-resonance to triple-resonance at the transverse electric (TE) mode and from dual-resonance to triple-resonance at the transverse magnetic (TM) mode. PSM_2 exhibits switching characteristics from single-resonance to triple-resonance at the TE mode and from dual-resonance to quad-resonance at the TM mode. Furthermore, by changing the width of the CWR under the condition of two face-to-face SRRs with a constant gap distance, PSM_2 exhibits stable electromagnetic responses at the TE mode and tunable resonances at the TM mode, respectively. This work paves the way to the possibility of metamaterial devices with great tunability, switchable bandwidth, and polarization-dependence characteristics.

Tunable Terahertz Metamaterial Using an Electric Split-Ring Resonator with Polarization-Sensitive Characteristic

We present a tunable terahertz (THz) metamaterial using an electric split-ring resonator (eSRR), which exhibits polarization-sensitive characteristics. The proposed eSRR is composed of double symmetrical semicircles and two central metal bars. By changing the lengths of two metal bars, the electromagnetic responses can be tuned and switched between dual-band and triple-band resonances in transverse magnetic (TM) mode. Furthermore, by moving the bottom metal bar to change the gap between the two metal bars, the first resonance is stable at 0.39 THz, and the second resonance is gradually blue-shifted from 0.83 to 1.33 THz. The tuning range is 0.50 THz. This means that the free spectrum ranges (FSR) could be broadened by 0.50 THz. This proposed device exhibits a dual-/triple-band switch, tunable filter, tunable FSR and polarization-dependent characteristics. It provides an effective approach to perform tunable polarizer, sensor, switch, filter and other optoelectronics in THz-wave applications.