Tunable Resonant Cavity Research Articles

Temperature Tunable 4D Polymeric Photonic Crystals

AbstractPhotonic crystals owe their multitude of optical properties to the way their structure creates interference effects. It is therefore possible to influence the photonic response by acting on their physical structure. In this article, tunable photonic crystals made by elastic polymers that respond to their environment are explored, in particular with a physical deformation under temperature variation. This creates a feedback process in which the photonic response depends on its physical structure, which itself is influenced by the environmental changes. By using a multi‐photon polymerization process specifically optimized for soft responsive polymers such as Liquid Crystalline Networks, highly resolved, reproducible, and mechanically self‐standing photonic crystals are fabricated. The physical structure of the 3D woodpile can be tuned by an external temperature variation creating a reversible spectral tuning of 50 nm in the telecom wavelength range. By comparing these results with finite element calculations and temperature induced shape‐change, it is confirmed that the observed tuning is due to an elastic deformation of the structure. The achieved nanometric patterning of tunable anisotropic photonic materials will further foster the development of reconfigurable photonic crystals with point defects acting as tunable resonant cavities and, more in general, of 4D nanostructures.

Determining a Perturbation Factor to Design Tunable Resonant Cavities in SIW Technology

This paper presents an effective and novel design procedure employing a novelty named as Perturbation Factor to predict the resonance frequency of resonant cavities in SIW technology perturbed by a shape perturbation. The design procedure can be applied in tunable cavities and bandpass filters with shunt reactance of symmetrical inductive window, and regarding the application technologies, rectangular waveguide resonators and resonant cavities in SIW can be employed due to the equivalence of operation between both technologies. Its straightforward application allows a frequency variation of up to 20% using only one metal post which allows the reduction of the fabrication cost and the preservation of the frequency response across the considered bandwidth. To validate the design procedure, two resonant cavities were fabricated, a rectangular resonant cavity designed to operate at 5.0 GHz and 6.0 GHz and a square resonant cavity designed to operate at 6.0 GHz and 7.2 GHz, and frequency variations of 17.74% and 21.81% were obtained for the rectangular and square cavities, respectively. Still regarding the reached results, was verified a mean error of 1.75% for the predicted resonance frequency, which validates the design procedure. The experimental results are in good agreement with the full-wave computational results and electromagnetic theory.

Low-Loss Mechanically Tunable Resonator and Phase Shifters in Groove Gap Waveguide Technology

This research is focused on the design and realization of high-performance high-power variable phase shifters in groove gap waveguide technology. Specifically, it is shown that the unique characteristic of groove gap waveguides, which is its proper operation without the need for electrical connection between the top and bottom sections of the waveguide, can be used to design mechanically tunable devices. Using the proposed method, a mechanically tunable cavity resonator and phase shifters with a wide range of achievable phase shifts are presented. To validate the concept, a phase shifter with 540 degrees relative phase shift at 15 GHz is designed, fabricated, and measured. Moreover, a multi-layer version of the proposed phase shifter with stationary feed ports and improved performance is presented.

Tunable microwave amplitude equalizer based on spurline and tunable resonant cavities

A tunable microwave amplitude equalizer is proposed to realize arbitrarily prescribed transmission responses, which is mainly composed of a spurline and some tunable resonant cavities. Compared with traditional resonant-cavity equalizers, the introduction of the spurline can significantly reduce the total number of the tunable cavities, and can improve the attenuation level. The operation mechanism of the equalizer is detailed analyzed, and the experimental results demonstrate that the amplitude equalizer can realize an attenuation control of about 25 dB at the frequency band of 5.0–6.0 GHz, and the return loss is better than 17 dB.

3.4/4.0 GHz Tunable Resonant Cavity in SIW Technology Using Metal Post and PIN Diode on a Low-Cost Biasing Network for 5G Applications

This paper presents a dual-band resonant cavity in Substrate Integrated Waveguide (SIW) technology to operate in the range from 3.3 GHz to 4.2 GHz, spectrum considered for the Fifth Generation (5G) network. The cavity was designed to operate at 3.4 GHz and 4.0 GHz. To achieve different states, a jumper and a PIN diode switch are considered as switching elements, connecting and disconnecting the bottom and the upper walls of the SIW resonant cavity through a metal post inserted inside its internal volume. A fitting equation is proposed to predict the maximum resonance frequency caused by the insertion of a single metal post inside the internal volume of the SIW resonant cavity and a new low-cost biasing network is designed on a thin dielectric substrate allocated on the upper wall of the SIW resonant cavity, using transmissions lines and a single capacitor, reducing the final cost and the insertion losses. Good agreement was observed among the fitting equation, computational electromagnetic simulations, and experimental results, validating the proposed methods.

Thermal and electrical tuning of whispering gallery modes in liquid crystal-filled hollow glass microsphere

This paper demonstrates a thermally and electrically tunable hollow glass microsphere resonant cavity filled with dye-doped nematic liquid crystal. We controlled the orientation of in-sphere liquid crystal and encapsulated it with polydimethylsiloxane film. The typical whispering gallery modes (WGMs) lasing spectra were obtained under a pulsed laser pump and the effects of the temperature and electric field on the peaks wavelengths were studied. The WGM spectra present a blueshift significantly with increasing temperature and electric field due to the decrease in the effective refractive index.

Continuously Tuned Ku-Band Cavity Filter Based on Dielectric Perturbers Made by Ceramic Additive Manufacturing for Space Applications

This paper presents a concept of a tunable cavity resonator composed of a resonating cavity and a dielectric perturber. This tunable resonator is designed and measured to prove the tuning mechanism obtained by varying the angle of rotation of the perturber. A rotation from 0 to 90 produces a tuning ratio of 1:1.25, i.e., a tuning range of 22.2% around 11.5 GHz while maintaining an unloaded Q factor between 1500 and 2300. After this first experimental validation, a third-order bandpass filter is then designed and measured using the same base principle. Using a single mechanical movement, all three resonators’ perturbers are synchronously rotated to create a third-order Chebyshev bandpass filter maintaining a 516±38-MHz bandwidth (for a return loss better than 10 dB) from 9.915 to 12.189 GHz. A 20.6% tuning range is then obtained at approximately 11 GHz with an estimated Q factor from 1400 to 2150. These performances have been obtained by using specifically shaped dielectric perturbers, which have been made by a ceramic additive manufacturing (AM) process (stereolithography). This technology has enabled the perturbers’ specific geometries and embedded supporting elements to be feasible. A sixth-order Chebyshev bandpass filter has also been theoretically proposed using full wave simulations.

PXIe-Based LLRF Architecture and Versatile Test Bench for Heavy Ion Linear Acceleration

This paper describes the architecture of a digital LLRF system for heavy-ion acceleration developed under the specification of the projected future heavy-ion accelerator facility in Huelva, Spain. A prototype LLRF test bench operating at 80 MHz in CW mode has been designed and built. The core LLRF control has been digitally implemented on a PXIe chassis, including an FPGA for digital signal processing and a real time controller. The test bench is completed with a low phase and amplitude noise signal generator used as master frequency reference, an analog front end for reference modulation and signal conditioning, some RF components completing the circuit, as well as a tunable resonant cavity at 80 MHz, whose RF amplitude, phase and frequency are real-time controlled and monitored. The presented LLRF system is mainly digitally implemented using a PXIe platform provided by National Instruments , and is based on IQ modulation and demodulation. The system can be configured to use both direct sampling and undersampling techniques, resulting thus in a high performance and versatile RF control system without the need of excessive computational resources or very high speed acquisition hardware. All the system is programmed using the LabVIEW environment, which makes the prototyping process and its reconfigurability much easier.

One-process fabrication of metal hierarchical nanostructures with rich nanogaps for highly-sensitive surface-enhanced Raman scattering

One-process fabrication of highly active and reproducible surface-enhanced Raman scattering (SERS) substrates via ion beam deposition is reported. The fabricated metal–dielectric–metal (MDM) hierarchical nanostructure possesses rich nanogaps and a tunable resonant cavity. Raman scattering signals of analytes are dramatically strengthened due to the strong near-field coupling of localized surface plasmon resonances (LSPRs) and the strong interaction of LSPRs of metal NPs with surface plasmon polaritons (SPPs) on the underlying metal film by crossing over the dielectric spacer. The maximum Raman enhancement for the highest Raman peak at 1650 cm−1 is 13.5 times greater than that of a single metal nanoparticle (NP) array. Moreover, the SERS activity can be efficiently tailored by varying the size and number of voids between adjacent metal NPs and the thickness of the dielectric spacer. These findings may broaden the scope of SERS applications of MDM hierarchical nanostructures in biomedical and analytical chemistry.

Are conduits superconductor-like and supported by tetrahedra structure of hyaluronic matrix in living systems? New perspectives

All biological-medical treatments need a ground regulation in the intermeshed control loop system in animate matter. The focus of our contribution is to suggest a possible mechanism in this interconnected system that will work in order to supply/assist a higher ordered servo loop. Bonghan ducts indicate similarities to so-called meridians or conduits that are the central part in Chinese Medicine for the energy Qi. It is assumed that the nervous system demands a highly redundant and rapid communication system (RCS) probably established via the extracellular matrix (ECM) and triggered by a threshold value for the entire body. Metabolic processes could work in the picosecond's range while the nervous system is on the time scale at least one order of magnitude lower; probably most of them in the millisecond range. Long-range coherent electromagnetic phenomena and recent experiments indicate a structured superconducting-like system with the Josephson-effect behavior in biological systems. In the ECM are the components proteoglycans and glycosaminoglycans (PG/GAGs) and among them the ubiquitarian hyaluronic acid plays probably an important role and can behave as liquid crystals while the charge transport is performed via proton "jumping" in the proton-chains. Therefore, the water molecules have to be confident on a nanometer scale, lowering their energy states, and set up a phase transition with a rapid jumping of the protons through the water-carbon-chains. These partial chains could probably be modeled by tiny pyramids of the atoms. We propose that in order to set up those long-range coherent effects, a vortex is created. By doing Qi Gong, an energetic vortex through the body is established and the entire body can be modeled by two-base plane-faced pyramids acting as a tunable cavity resonator obeying electrodynamics laws. Therefore, the phenomenon's of pyramids should be considered in animate and inanimate matter in order to achieve long-range coherent effects, which by now controversially discussed and to go new ways to come over the clutter.

Efficiency evaluation of ground-penetrating radar by the results of measurement of dielectric properties of soils

The work considers the depth evaluation of ground penetrating radar (GPR) surveys using the attenuation factor of electromagnetic radiation in a medium. A method of determining the attenuation factor of low-conductive non-magnetic soils is developed based on the results of direct measurements of permittivity and conductivity of soils in the range of typical frequencies of GPR. The method relies on measuring the shift and width of the resonance line after a soil sample is being placed into a tunable cavity resonator. The advantage of this method is the preservation of soil structure during the measurement.

Optical nano-imaging of gate-tunable graphene plasmons

The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes. However, because photons do not possess charge, a way of controlling them efficiently by electrical means has so far proved elusive. A promising way to achieve electric control of light could be through plasmon polaritons—coupled excitations of photons and charge carriers—in graphene. In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can readily be tuned electrically by varying the graphene carrier density. Although evidence of optical graphene plasmon resonances has recently been obtained spectroscopically, no experiments so far have directly resolved propagating plasmons in real space. Here we launch and detect propagating optical plasmons in tapered graphene nanostructures using near-field scattering microscopy with infrared excitation light. We provide real-space images of plasmon fields, and find that the extracted plasmon wavelength is very short—more than 40 times smaller than the wavelength of illumination. We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume. The cavity resonance is controlled in situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors. This successful alliance between nanoelectronics and nano-optics enables the development of active subwavelength-scale optics and a plethora of nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing, and strongly enhanced light–matter interactions for quantum devices and biosensing applications.

High stability and linear tuning wavelength tunable resonant cavity enhanced photo-detector grown on GaAs

A wavelength tunable resonant cavity enhanced photo-detector grown on GaAs is fabricated. The quantum wells of In0.25Ga0.75As/GaAs in the active region are grown by molecular beam epitaxy. The peak of the response spectrum at 0 work bias is located at 1071 nm. When the tuning voltage rises from 0 V to 21 V, the peak shows a blue shift of 23 nm, reaching 1048 nm. Statistical results show that there is a stable accurate corresponding relation between the tuning voltage and the response peak. The relation is approximately linear when the tuning voltage is greater than 5 V. Some theoretical analysis is performed on the test results.

Plasmon Resonant Cavities in Vertical Nanowire Arrays

We investigate tunable plasmon resonant cavity arrays in paired parallel nanowire waveguides. Resonances are observed when the waveguide length is an odd multiple of quarter plasmon wavelengths, consistent with boundary conditions of node and antinode at the ends. Two nanowire waveguides satisfy the dispersion relation of a planar metal-dielectric-metal waveguide of equivalent width equal to the square field average weighted gap. Confinement factors over 10(3) are possible due to plasmon focusing in the interwire space.

An Automatically Tunable Cavity Resonator System

A tunable cavity resonator is described that uses a feedback control system to alter its resonant characteristics in response to changes in its environment, without changing the physical dimensions of the resonator. Tuning wires inserted into the cavity are connected or disconnected to the cavity wall under the control of a binary algorithm that searches for desirable operating states from among a very large number of possible switch configurations. The ability of the cavity to be tuned in response to changes in either cavity loading or resonator size is investigated using simulations, and the feasibility of the system is thereby demonstrated. Measurements made using a laboratory prototype show that the cavity may be automatically tuned in response to changes in the properties of the materials within the cavity.

Lead salt resonant cavity enhanced detector with MEMS mirror

We describe a tunable resonant cavity enhanced detector (RCED) for the mid-infrared employing narrow gap lead-chalcogenide (IV–VI) layers on a Si substrate. The device consists of an epitaxial Bragg reflector layer, a thin p–n+ heterojunction with PbSrTe as detecting layer and a micro-electro-mechanical system (MEMS) micromirror as second mirror. Despite the thin absorber layer the sensitivity is even higher than for a conventional detector. Tunability is achieved by changing the cavity length with a vertically movable MEMS mirror. The device may be used as miniature infrared spectrometer to cover the spectral range from <3 μm up to >30 μm.

A $Ku$-Band High-$Q$ Tunable Filter With Stable Tuning Response

A Ku-band tunable filter with a very stable notch level and in-band RF performance is presented in this paper. A new coupling iris configuration for stable RF performance over the tuning range is realized. The filter employs two dual-mode TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> tunable cavity resonators with a set of flexible bellows. A tuning range of more than 500 MHz at 12 GHz while maintaining a high Q is demonstrated using the introduced resonator. Design techniques, including an RF-mechanical tradeoff analysis, are detailed and addressed.

A comb drive actuated vertically moving micromirror for tunable mid-infrared Resonant Cavity Enhanced Detectors

The realization of a vertically moving micromirror using electrostatic actuation in a comb drive configuration is presented. The micromirror is designed for the use in tunable mid-infrared Resonant Cavity Enhanced Detectors (RCEDs). It can be displaced more than 2.5 μm with less than 30 V actuation voltage. In addition to the pure out-of-plane movement, the mirror can be tilted by applying different voltages at the different comb drive actuators. A voltage difference of 30 V on opposite comb drive actuators induces a mirror tilt of 0.23°. Measured spectra of a tunable RCED employing the presented micromirror are included.

Epitaxial Lead Chalcogenides on Si for Mid-IR Detectors and Emitters Including Cavities

Lead chalcogenide (IV–VI narrow-gap semiconductor) layers on Si or BaF2(111) substrates are employed to realize two mid-infrared optoelectronic devices for the first time. A tunable resonant cavity enhanced detector is realized by employing a movable mirror. Tuning is across the 4 μm to 5.5 μm wavelength range, and linewidth is <0.1 μm. Due to the thin (0.3 μm) PbTe photodiode inside the cavity, a higher sensitivity at higher operating temperatures was achieved as compared to conventional thick photodiodes. The second device is an optically pumped vertical external-cavity surface-emitting laser with PbTe-based gain layers. It emits at ∼5 μm wavelength and with output power up to 50 mW pulsed, or 3 mW continuous wave at 100 K.

Tunable resonant cavity enhanced detectors using vertically actuated MEMS mirrors

Highly sensitive photodetectors for the mid-infrared have recently been obtained by placing a photodiode inside a Fabry-€“Perot cavity (Arnold et al 2005 Appl. Phys. Lett. 87 141103). These resonant cavity enhanced detectors (RCED) are sensitive at the resonances which depend on the distance between the two mirrors of the cavity (Unlu and Strite 1995 J. Appl. Phys. 78 608). Displacing one of these mirrors then makes it possible to change the cavity length and thus select the detection wavelength. The design, simulation and fabrication of a MEMS mirror is discussed in detail and its integration with the counter mirror and the photodiode, both grown by molecular beam epitaxy, are presented. Results obtained with external mirrors moved by piezoactuation as well as first measurements of a complete tunable RCED using electrostatically driven vertically moving MEMS mirrors are presented. Such tunable detectors are of interest in thermographic and spectroscopic applications.