Chong Pei Ho

Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics

We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integrating microactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunable metamaterial design for application such as filters, absorbers, sensors, and spectral imagers.

Micro-electro-mechanically switchable near infrared complementary metamaterial absorber

We experimentally demonstrate a micro-electro-mechanically switchable near infrared complementary metamaterial absorber by integrating the metamaterial layer to be the out of plane movable microactuator. The metamaterial layer is electrostatically actuated by applying voltage across the suspended complementary metamaterial layer and the stationary bottom metallic reflector. Thus, the effective spacing between the metamaterial layer and bottom metal reflector is varied as a function of applied voltage. With the reduction of effective spacing between the metamaterial and reflector layers, a strong spectral blue shift in the peak absorption wavelength can be achieved. With spacing change of 300 nm, the spectral shift of 0.7 μm in peak absorption wavelength was obtained for near infrared spectral region. The electro-optic switching performance of the device was characterized, and a striking switching contrast of 1500% was achieved at 2.1 μm. The reported micro-electro-mechanically tunable complementary metamaterial absorber device can potentially enable a wide range of high performance electro-optical devices, such as continuously tunable filters, modulators, and electro-optic switches that form the key components to facilitate future photonic circuit applications.

Dual band complementary metamaterial absorber in near infrared region

In this paper, we present the dual band absorption characteristics of complementary metamaterial absorber in near infrared (1.3–2.5 μm) region. The dual band absorption is caused by two distinct resonance mechanisms—electrical resonance and cavity resonance. Electrical resonance occurs in the metal layer—top complementary metamaterial and the cavity resonance occurs in the spacer cavity formed between the top complementary metamaterial and bottom metal reflector layers. In order to elucidate the resonant mechanisms and study the effects of geometrical variations on both the resonant absorption behaviours, two sets of experiment were performed. It was seen that with increasing complementary metamaterial pattern dimension, the electrical resonance absorption peak showed a blue shift, while the cavity resonance showed a slight red shift. However, on the other hand, for the increase in spacer thickness, the cavity resonance peak showed a strong red shift, while the electrical resonance peak remained uninfluen...

Active control of near-field coupling in conductively coupled microelectromechanical system metamaterial devices

We experimentally report a structurally reconfigurable metamaterial for active switching of near-field coupling in conductively coupled, orthogonally twisted split ring resonators (SRRs) operating in the terahertz spectral region. Out-of-plane reconfigurable microcantilevers integrated into the dark SRR geometry are used to provide active frequency tuning of dark SRR resonance. The geometrical parameters of individual SRRs are designed to have identical inductive-capacitive resonant frequency. This allows for the excitation of classical analogue of electromagnetically induced transparency (EIT) due to the strong conductive coupling between the SRRs. When the microcantilevers are curved up, the resonant frequency of dark SRR blue-shifts and the EIT peak is completely modulated while the SRRs are still conductively connected. EIT modulation contrast of ∼50% is experimentally achieved with actively switchable group delay of ∼2.5 ps. Electrical control, miniaturized size, and readily integrable fabrication process of the proposed structurally reconfigurable metamaterial make it an ideal candidate for the realization of various terahertz communication devices such as electrically controllable terahertz delay lines, buffers, and tunable data-rate channels.

Microelectromechanically tunable multiband metamaterial with preserved isotropy

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

Micro-electro-mechanically tunable metamaterial with enhanced electro-optic performance

We experimentally demonstrate a micro-electro-mechanically tunable metamaterial with enhanced electro-optical performance by increasing the number of movable cantilevers in the symmetrical split ring resonator metamaterial unit cell. Simulations were carried out to understand the interaction of the incident terahertz radiation with out-of-plane deforming metamaterial resonator. In order to improve the overall device performance, the number of released cantilever in a unit cell was increased from one to two, and it was seen that the tunable range was doubled and the switching contrast improved by a factor of around five at 0.7 THz. This simple design approach can be adopted for a wide range of high performance electro-optical devices such as continuously tunable filters, modulators, and electro-optic switches to enable future photonic circuit applications.

Periodic Array of Subwavelength MEMS Cantilevers for Dynamic Manipulation of Terahertz Waves

We experimentally demonstrate the active manipulation of terahertz (THz) waves using a periodic array of electrostatically actuated subwavelength microelectromechanical system cantilevers, which effectively behave like a metamaterial. The design methodology for achieving desired ON- and OFF-state resonance frequencies through electromechanical optimization is presented. The microcantilever metamaterial has a switching range of 0.29 THz and a modulation depth of 60% at 0.59 THz. Utilizing metal layer thickness to optimize the devices, an improvement of 40% is achieved in switching range. The microcantilever metamaterials are highly miniaturized, extremely scalable, and electrically controlled with attractive electro-optic performance. Multiple cantilevers can be placed in a desired fashion to form complex unit cell geometry to realize advanced THz manipulation, such as polarization switching, bandwidth tunable filters, multicolor imagers, and so on.

Development of Polycrystalline Silicon Based Photonic Crystal Membrane for Mid-Infrared Applications

Free-standing polycrystalline silicon (Si) based photonic crystal (PhC) membranes with etched circular and square holes are developed to display high reflectivity in the mid-infrared (MIR) region. Greater than 90% reflection was measured in the MIR wavelengths around 3.58 μm. By using square air holes in the PhC membrane, the mechanical strength of the polycrystalline Si membrane can be enhanced as square air holes have a lower filling factor of 36% of air holes, compared to 49% in circular air holes while keeping the reflectance around 3.45 μm more than 90%. Such Si PhC membranes offer opportunities for specific applications like filters. To illustrate the feasibility of such devices, simulation works are done by configuring two Si PhC membranes to create a Fabry-Perot interferometer operating in MIR region. The filtered peak shows a full width half maximum of 0.08 nm which corresponds to a quality factor of around 43800, thus demonstrating the possibility of high-resolution applications such as gas sensing and hyperspectral imaging.

Microfluidic metamaterial sensor: Selective trapping and remote sensing of microparticles

We experimentally demonstrate the integration of a microfluidic trap array on top of metamaterial resonators for size selective trapping and remote sensing of microparticles. A split-ring resonator (SRR) design supports strongly confined electric field in the capacitive split gap at the fundamental inductive-capacitive resonance mode. The tightly confined electric field in the SRR gap forms a hot-spot that has become an enabling platform for sensing applications. Here, we extend the concept of metamaterial sensing to “trapping and sensing” by fabricating trapezoidal shaped structures near the split gap that enables trapping of microparticles in the split-gap region of each SRR. The proposed microfluidic metamaterial sensor enables sensing of different refractive index microparticles in terms of change in the transmitted amplitude and resonance frequency of the fundamental resonance mode operating in the terahertz spectral region. The proposed approach exploits the advantages offered by microfluidics, meta...

Polarization controllable multispectral symmetry-breaking absorberin mid-infrared

This work presents the polarization control of interchangeable multispectral absorption based on the dual-band metamaterial absorber in split mode. Large modulation depth of absorption is obtained during multi-band transition through polarization control.