Search

In this research, we introduce a novel approach to create a tunable multi-channel plasmonic mid-infrared filter. This innovative filter comprises a single layer of graphene deposited on an improved Fibonacci quasiperiodic structure. What makes this filter particularly intriguing is its capacity to adjust its filtering characteristics by manipulating the chemical potential of graphene and other relevant structural parameters. We delve into a comprehensive analysis of the results through dispersion relations, shedding light on the mechanisms underlying its tunability. The proposed structure holds potential for applications in sensors, tunable devices, and next-generation integrated photonic circuits. Ultimately, our investigation deepens our understanding of how nonperiodic structures can effectively achieve a multi-channel plasmonic filter, potentially leading to more efficient photonic components and devices across industries. [ABSTRACT FROM AUTHOR]

This article presents a new class of ring-resonator-loaded waveguide notch filters with a broad tuning range, low cost, and improved performance. The proposed approach employs a complementary asymmetric split-ring resonator coupled to a microstrip transmission line and excited in a rectangular waveguide. An equivalent circuit model is proposed to explain the working principle of the proposed notch filter. The adjustment of the operating frequency is based on the additive manufacturing of a metallic copper patch allocated on the microstrip transmission line, which enables extensive tuning capabilities and consistent performance with minimum variations across the tuning window. For demonstration purposes, a filter employing a WR-28 waveguide and photolithography-manufactured resonator is prototyped and experimentally validated. The measured results indicate a broad 8 GHz tuning range with a consistent insertion loss, ranging from 23.4 to 31.4 GHz. An inverse regression model is constructed using measurement data obtained for tuning patches of various sizes, which allows for determining the relationships between the operating frequency and the copper patch size. The resulting calibration curve enables rapid filter tuning to the required frequency by inserting metallic patches of the model-predicted size. [ABSTRACT FROM AUTHOR]

Periodic arrays of sub‐wavelength‐scale holes in plasmonic metal films are known to provide resonant transmission peaks via the extraordinary optical transmission (EOT) effect. Active control of the spectral position of such transmission peaks can be obtained by adding a layer of phase‐change material (PCM) to the EOT device. Switching the PCM layer between its amorphous and crystalline states can shift the spectral position of the resonance, enabling potential applications in the fields of active filtering and sensing (e.g., multispectral sensing), and for signal modulation. Here, the design, fabrication, and characterization of active EOT devices are targeted at various important regions of the optical spectrum. [ABSTRACT FROM AUTHOR]

This article describes the use of dielectric rods to reconfigure combline filters both with respect to center frequency and bandwidth. In this context, a new filter topology is developed in order to maximize the achievable reconfiguration range. The design of a prototype is discussed in detail, clearly demonstrating the feasibility of center frequency and bandwidth reconfiguration, with the same filter structure, while maintaining an equiripple return loss. In addition to theory, a combline filter prototype is also fabricated, tuned and measured in several configurations showing excellent agreement with simulations, thereby fully validating both the basic concept and the design procedure.

This article reports a novel inset resonator configuration for coaxial filter applications with quasi-elliptic responses. The design and analysis of the inset resonator are discussed in detail and accurately modeled as a capacitively-loaded stepped-impedance half-wavelength resonator featuring more compactness, high quality factor, and enhanced spurious responses in comparison with conventional half-wavelength and combline resonators. Additionally, the operating frequency can be tuned intrinsically through the displacement of the coaxial resonator, eliminating the need for any additional tuning elements and maintaining a stable quality factor. Two quasi-elliptic inset resonator type filters are implemented in planar and longitudinal coupling configurations, respectively. The first takes the form of a folded four-pole 2.93 GHz filter with two symmetrical transmission zeros. The fabricated filter has a compact structure of 29.76 cm 3, an insertion loss better than 0.73 dB, a return loss better than 18 dB, and a wide spurious-free band up to $3.5\cdot f _{0}$ . The second inset-type quasi-elliptic filter is realized in a longitudinal inline arrangement. An example of a 2.53 GHz three-pole filter is presented with a closely-positioned transmission zero, wide spurious-free band ( $\approx 3\cdot f _{0}$ ), and a very compact structure of $55.7\times 33\times 33$ mm 3.

Abstract Free-spectral-range (FSR)-free optical filters have always been a critical challenge for photonic integrated circuits. A high-performance FSR-free filter is highly desired for communication, spectroscopy, and sensing applications. Despite significant progress in integrated optical filters, the FSR-free filter with a tunable narrow-band, high out-of-band rejection, and large fabrication tolerance has rarely been demonstrated. In this paper, we propose an exact and robust design method for add-drop filters (ADFs) with an FSR-free operation capability, a sub-nanometer optical bandwidth, and a high out-of-band rejection (OBR) ratio. The achieved filter has a 3-dB bandwidth of

In this paper, we present a microwave photonic filter bandpass filter with narrow bandwidth and high quality (Q) factor is presented which with a bandwidth of 7.8 MHz, a gain response of 24 dB, and Q factor is 2412. This performance is achieved through tailoring one Brillouin gain spectrum by two Brillouin loss spectrums. By precise control of the individual pump power and frequency, a narrowed bandpass filter is generated. We achieve this performance through the mathematical formulation of the Stimulated Brillouin scattering (SBS) spectrum relative frequency shift and SBS pumps power ratio, resulting in precise parameters resolution of the narrowest filter bandwidth leading to experimentally demonstration. We further show the variation trend of the filter bandwidth and gain response, leading to exploit the general discipline of this technology.

In this paper, we studied the transmission properties, including photonic band gap (PBG) and defect mode properties, of one-dimensional photonic crystals (1D PCs) consisting of gradient materials. When keeping the average refractive index of the gradient materials in the 1D gradient-material PCs (1D GPCs) the same as the index of the corresponding normal materials in the 1D normal-material PCs (1D NPCs), by transfer matrix method, we found that the complete 1D GPCs with high-index gradient materials benefit to achieve larger omni-PBG than that in 1D NPCs. In our high-index gradient material case, for TE(TM) wave, the optimal omni-PBGs in 1D GPCs with first- and second-order gradient materials are 38.6% (50.2%) and 15.9% (22.3%) larger than that in 1D NPCs; while for the optimal relative bandwidths of omni-PBG, the corresponding promotions are 41.1% (52.3%) and 16.1% (22.6%), respectively. In addition, when defective 1D GPCs have gradient-material defect, the position of defect modes can be adjusted by selecting proper parameters of the gradient materials. These types of research are useful for designing wide PBG devices and tunable narrow-band filters which have potential application in optical communication. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical study of transmittance characteristics in a 1D superconducting photonic Pell quasi-crystal. The results indicate the shift in the defect mode induced by superconductor materials through thermo-optical effect. The lower the working temperature, the larger the Q-factor, which makes the filtering effects stronger. We believe that our findings may open opportunities for designing near-infrared tunable filters. [ABSTRACT FROM AUTHOR]

Recently, electro-optic integrated photonic elements have attracted considerable interest owing to their widespread application in optical communication and signal processing. The strong electro-optical properties and the complementary metal–oxide semiconductor (CMOS) technology compatibility of silicon–organic hybrid structures makes them promising photonic platforms. This study investigated a novel implementation of a high-speed electrically tuned bandpass optical filter using finite-difference time-domain and eigenmode expansion numerical methods. The proposed device was based on a Fabry–Perot cavity and was realized via an electro-optic organic molecular glass filled slot waveguide with Bragg gratings. Furthermore, the calculation considered the plasma dispersion effect, free-carrier absorption in the silicon component of the slot waveguide for different applied voltages, and doping profiles corresponding to ion implantation. It is shown that the spatial distribution of charge carrier density formed by the surface states accumulation/depletion layers has a significant effect on the optical properties of the slot waveguide. Lithographic distortions in the geometry of the proposed structures during fabrication were also considered. Therefore, this paper presents an optical filter designed for fabrication using CMOS-compatible processes on silicon-on-insulator wafers. The filter produced a 3 nm tunable range for a 10 V bias voltage swing, a 0.3 nm full width at half maximum (FWHM) passband with a center at 1550 nm at zero bias voltage, and a 12.5 nm free spectral range with a 27 dB extinction ratio. The proposed device outperforms many narrow passband analogs in terms of sensitivity (tunability: 0.3 nm/V) and can be applied extensively in the fields of optical communications and photonic spectral signal processing. [ABSTRACT FROM AUTHOR]

This paper presents the design and characterization of a miniaturized tunable bandpass filter utilizing high-Q ceramic coaxial resonators and commercially available RF-MEMS tunable digital capacitors. A proof-of-concept 2-pole tunable filter occupying only 10 × 10 mm2 is demonstrated with a frequency tuning range of 800-1100 MHz and bandwidth tuning range of 6-13%.

This letter presents a 31-tap analog finite impulse response (FIR) filter capable of synthesizing bandpass, bandstop, and multinull filter responses with continuous center frequency and bandwidth tuning from less than 1 to 20 GHz. The FIR filter delay-lines are realized using Polystrata 3-D air-metal-dielectric technology and are heterogeneously integrated directly on top of a CMOS die using 100- $\mu \text{m}$ -diameter Sn63Pb37 solder bumps. The CMOS chip contains 7-bit programmable weighting circuits at each delay-line tap to allow synthesis of arbitrary frequency responses limited only by the $Q$ -factor of a 31-tap FIR filter and dynamic range of the weighting elements. The final assembly is 5.04 $\times $ 3.85 $\times $ 3.64 mm3, consumes 200–350 mA from a 1.8-V supply, and shows good repeatability between measured samples. [ABSTRACT FROM AUTHOR]

A continuously tunable Ku-band waveguide diplexer is proposed in this paper. This diplexer is based on a hybrid coupler topology and is composed of an input filter centered at 11.9 GHz with a 200 MHz bandwidth, a pair of ladder-type hybrid couplers, and a pair of tunable filters. This diplexer can provide two bandpass channels (channels 1 and 2) that can continuously go from a state where the bandwidths of channels 1 and 2 are maximum (up to 140 MHz) and minimum (down to 40 MHz), respectively, to another configuration where the bandwidth of channel 1 is the largest and the bandwidth of channel 2 is the narrowest. We propose a tunable filter based on TE012 mode circular cavities that are perturbed by low-loss dielectric inserts to obtain such performance. The resonant frequency of these cavities can be continuously tuned between 11.8 and 12 GHz due to the linear movement of the dielectric perturber. The design process for these components is presented and a breadboard device has been manufactured and measured to prove the concept. Different measured configurations of the diplexer are demonstrated, showing that the 200 MHz operating bandpass between 11.8 and 12 GHz can be efficiently separated into two tunable channels. The measured bandwidth of channels 1 and 2 in the manufactured diplexer can be tuned from 135 to 40 MHz (and vice versa) while maintaining an average guard band between the channels of approximately 26 ± 7 MHz. The obtained bandwidth tuning ratios are 3.2 for the highest channel and 3.1 for the lowest channel. [ABSTRACT FROM AUTHOR]

This paper aims to present some outcomes from a European Space Agency (ESA) Technology Research Programme (TRP) project on R&D of new design techniques, concepts, and filtering configurations for tunable IF (intermediate frequency) filters with a compact footprint, wide bandwidth tuning range (covering from 49 to 478 MHz at f0 = 1 GHz) as well as equivalent high-Q performance (i.e. low insertion loss variation and high selectivity by using low-Q resonators). In order to obtain a wide tuning range, the proposed filtering configuration utilizes a new tuning technique that only necessitates control of coupling values with simple DC control circuits, without the need of tuning the electrical length of resonators to avoid deviating the center frequency. Furthermore, in order to achieve the equivalent high-Q performance, a novel lossy technique by using a centrally resistor-loaded half-wavelength resonator is adopted. For the proof of concept, a six-pole prototype filter is designed, fabricated, and tested. [ABSTRACT FROM AUTHOR]

The applicability of resonant waveguide grating (RWG)-based structures as filters to control the spectral response in an optical communication system is investigated. A new physical model for the structure is established on the basis of the Fabry–Pérot (FP) etalon model and coupled leaky mode theory (CLMT). It is found that the flat-top spectral response of the filter is achieved by the combined effect of the guided-mode resonance of an RWG and its Fabry–Pérot resonance (FPR). The bandwidth-tunable spectral response of the filter can be varied according to the change in the eigenvalues of the RWG by changing the structural parameters such as strip width of the grating and incident angle. The flat-top and bandwidth-tunable RWG-based resonant filter is a promising application for high-performance optical communication systems.

This paper presents a systematic study of a compact and reconfigurable periodic structure in GaAs MMIC technology. Compactness is achieved by the introduction of spiral inductors in a conventional unit cell without disturbing the reactive loading mechanism. The proposed architecture exhibits a 28.3% wider stopband with 62.6% smaller footprint compared to a conventional structure. The compactness and bandwidth improvement in the proposed structure is explained with the help of dispersion and circuit analysis. The reconfigurability built into the design using PIN diodes allows stopband switching, dual-band operation and tuning capabilities with the mere use of a single reactive load in its unit cell. To the best of the authors knowledge, it is the first time a reconfigurable MMIC implementation is realized using the proposed structure or even the conventional design. As a guide to design, sensitivity analysis to filter performance is presented for important structure parameters. Switching element parasitics are discussed in two ways: firstly, with the design and measurement of structures with idealized switching conditions and in second, with the circuit and full-wave EM modelling of the finite periodic structure with the actual PIN diodes. The on-chip measurements of the fully reconfigurable filter show excellent agreement with simulations.

We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with the method of zero-pole theory. As a proof of concept, the proposed structure is fabricated on the Si3 N4 waveguide platform. In the experiment, the 3-dB bandwidth of the proposed filter can be continuously tuned from 14.1 GHz to 4.1 GHz, maintaining a rectangular transmission response, and the wavelength can also be continuously tuned. This reconfigurable rectangular optical lattice filter shows the potential in many practical applications for reconfigurable optical signal processing due to flexibility and reconfigurability.

In this paper, a wideband bandpass filter (BPF) with simultaneous bandwidth and notch tuning is proposed, by using a dual cross-shaped resonator (DCSR) with parallel-coupled three-line (PCTL) feeding. It is found that three intrinsic transmission zeros can be generated by the proposed DCSR, while two of the zeros are used for the implementation of passband edge zeros and the other one is for a notch. Three varactors are used to implement the bandwidth and notch tuning independently. These innovative integrated functions of both tunable bandwidth and notch in a single architecture are proposed for the first time. On the other hand, the PCTL can provide sufficiently strong coupling in the desired passband. The proposed BPF can achieve the bandwidth tuning with a fixed notch inside/outside the passband, and the bandwidth can also be kept unchanged when tuning a notch within the passband. The prototyped BPF centered at 6 GHz reports that the absolute bandwidth (ABW) can be varied from 2.5 to 5.8 GHz, while the fractional bandwidth (FBW) is tuned from 41.7% to 96.7% together with notch frequency tuning of 5.0 to 8.2 GHz. The experimental measurements are in good agreement with the theoretical analysis.

In this paper, a trisection filter with reconfigurable transmission zeros based on the evanescent‐mode cavity (EVA) resonators is proposed. The design incorporates three EVA resonators. The varactors are set between two EVA resonators. By controlling the varactor capacitance value, couplings can be switched between electrical coupling and magnetic coupling. Based on this technique, the resulting two zeros can be designed to the desired position. Furthermore, a novel method by analyzing the magnitude and phase of trisection filters is proposed. Using this method, the transmission zeros position can be determined quickly. Measurement shows that the filter covers a frequency range of 2.11–2.83 GHz. Two transmission zeros can be arbitrarily designed to the left or right sides of the passband. Good agreement is obtained between simulated and measured results. [ABSTRACT FROM AUTHOR]

A silicon metasurface with a symmetry-protected quasi-dark resonant mode is designed and demonstrated as a refractometric sensor and tunable notch filter in the near-infrared spectrum. The resonant mode is excited by perturbing a periodic array of Si cuboids patterned on a glass substrate. Thanks to the delocalized nature of the resonant mode, intense light-matter interaction with the overlayer material is manifested. Such interaction leads to strong dependence of the resonant wavelength on the overlayer refractive index and high achievable quality factors, including the case of lossy materials. High sensitivity and figure of merit is calculated for operation of the metasurface as a refractometric sensor. In a complementary approach, three types of tunable notch filters are demonstrated, based on the use of thermo-optic, electro-optic polymers, and nematic liquid crystals. [ABSTRACT FROM AUTHOR]

This article presents a compact, low loss, wide tuning range, high temperature superconducting (HTS) bandpass filter at very high frequency (VHF) band. The filter consists of four zigzag open-loop resonators loaded with gallium arsenide (GaAs) varactors as tuning elements. Each resonator is biased independently. The filter circuit is fabricated on a 3-inch HTS thin film deposited on a LaAlO3 substrate. The filter demonstrates a frequency tuning range of 73.2−118 MHz, which is a tunability of 48%, an insertion loss of 0.6−2.2 dB, and a 3-dB fractional bandwidth of 3.2–4.3%. Besides, the return loss of the filter is better than 16.6 dB in the whole tuning range, with slight adjustment of bias voltages for different resonators. [ABSTRACT FROM AUTHOR]

This paper presents a novel output filter approach for continuously frequency-tunable digital power amplifiers, suitable for future seamless and band-less applications in 5G, e.g. for cognitive radios (CR). The presented tunable output filter is based on a multi-bandstop lowpass response to regenerate the original microwave signal at the output of the digital amplifier stage by suppressing unwanted frequency components. Compared to conventional tunable bandpass solutions, it offers higher tunability, higher linearity, good power handling capability and moderate losses especially around the carrier frequency. A tunable power amplifier (PA) demonstrator consisting of a 4-stage digital GaN PA MMIC and the novel tunable filter, is designed and fabricated for a carrier frequency range from 1 GHz to 3 GHz. Tunability is achieved by using commercial barium strontium titanate (BST) varactors. Small signal measurements were performed to evaluate tunability and suppression capabilities of the novel filter structure, which reveal a frequency tunability of 67% with a suppression level of at least 13 dB for the undesired frequency components. The proposed filter structure exhibits a linearity over the tuning range with an OIP3 between 66 dBm to 70 dBm and high power handling capability. Finally, the performance analysis of the tunable PA demonstrator shows an peak efficiency of 70%. Due to frequency limitations of the used PA stage, the efficiency slowly degrades to 20% at the upper frequency band edge. Simultaneously, the output power varies between 27 dBm to 31 dBm.

This paper presents the design of a highly‐tunable single‐ended and balanced filter with improved upper stopband performance. The proposed filters are designed using a spurline and a U‐shaped stepped impedance resonator (SIR) with a varactor diode connected to the open‐circuited end. A spurline is introduced in both designs to achieve wide stopband performance by suppressing the higher‐order modes. The proposed filters have high tunable ranges (single‐ended: 2.35‐3.99 GHz; balanced: 2.39‐4 GHz), low insertion losses (IL) (single‐ended: 0.07‐0.2 dB; balanced: 0.21 to 1.1 dB) and wide upper stopband performance (single‐ended: 3.79f1 with a rejection level higher than 20 dB; balanced: 3.79f1 with a rejection level higher than 20 dB). Performance of both filters are experimentally validated by comparing the experimental results with the simulated ones. Both filters can cover most of the fifth‐generation (5G) wireless communication bands with different biasing voltages (capacitance). When both filters are compared with state‐of‐the‐art filters, the proposed filters are found to achieve high tunable ranges with low IL and wide upper stopband performance. [ABSTRACT FROM AUTHOR]

The applicability of resonant waveguide grating (RWG)-based structures as filters to control the spectral response in an optical communication system is investigated. A new physical model for the structure is established on the basis of the Fabry–Pérot (FP) etalon model and coupled leaky mode theory (CLMT). It is found that the flat-top spectral response of the filter is achieved by the combined effect of the guided-mode resonance of an RWG and its Fabry–Pérot resonance (FPR). The bandwidth-tunable spectral response of the filter can be varied according to the change in the eigenvalues of the RWG by changing the structural parameters such as strip width of the grating and incident angle. The flat-top and bandwidth-tunable RWG-based resonant filter is a promising application for high-performance optical communication systems. [ABSTRACT FROM AUTHOR]

This paper presents octave-tunable resonators and filters with surface mounted lumped tuning elements. Detailed theoretical analysis and modeling in terms of tuning range and unloaded quality factor Qu are presented in agreement with simulated and measured results. Based on the models, a systematic design method to maximize tuning ratio and optimize Qu of the resonator is suggested. A resonator tuning from 0.5 to 1.1 GHz with Qu ranging from 90 to 214 is demonstrated using solid-state varactors. A two-pole filter with a tuning range of 0.5-1.1 GHz with a constant 3-dB fractional bandwidth (FBW) of 4 ± 0.1% and insertion loss of 1.67 dB at 1.1 GHz is demonstrated along with a three-pole filter with a tuning range of 0.58-1.22 GHz with a constant 3-dB FBW of 4 ± 0.2% and insertion loss of 2.05 dB at 1.22 GHz. The measured input third-order intermodulation is better than 17 dBm over the frequency range for the two-pole filter. © 2013 IEEE.

This article presents a novel toroidal metasurface that is able to support a toroidal response at almost all incident angles for a transverse magnetic (TM) wave at the microwave range. A flat band is observed from the calculated band structure where the radiation power of the toroidal response is highest around 7.51 GHz. A high transmission at a resonant frequency is observed from the simulated and measured transmission coefficients with different incident angles, whereas the transmission is lower at the rest frequency range. The resonance frequency at a high sensitivity of 0.78 GHz/refraction index unit (RIU) is experimentally demonstrated, which is very sensitive to the thickness and the refraction index of the surrounding materials such that the proposed toroidal metasurface could be used for a tunable highly efficient filters. [ABSTRACT FROM AUTHOR]

5G and its evolution towards 6G is unlocking new use cases that will require the reconsideration of the existing network architectures and its operation. As the network will be required to support new service types and radio protocol splits, the traditional physical point to point connections will need to be replaced with a transport network up to the antenna site to guarantee low latency services and high bandwidth. Optical based transport is a key enabler to realize such a convergent network, where the traditional fixed infrastructure in use for mobile services and mobile infrastructure should also support enterprises services. The Software Defined Network (SDN) and Network Function Virtualization (NFV) technology plays a key role to evolve towards digitalization. It allows to simplify the creation of new services and to implement a real decoupling between the infrastructure and the network functions that run virtually, on generic processing units located everywhere in the network. Supporting automation is a key requirement that traditional optical technology is not able to meet. In this paper the reference scenarios for the access network are presented with the analysis of their requirements and the enabling optical solutions based on integrated silicon photonics. [ABSTRACT FROM AUTHOR]

A generalized structure that is capable of implementing power-law filters derived from 1st and 2nd-order mother filter functions is presented in this work. This is achieved thanks to the employment of Operational Transconductance Amplifiers (OTAs) as active elements, because of the electronic tuning capability of their transconductance parameter. Appropriate design examples are provided and the performance of the introduced structure is evaluated through simulation results using the Cadence Integrated Circuits (IC) design suite and Metal Oxide Semiconductor (MOS) transistors models available from the Austria Mikro Systeme (AMS) 0.35 μm Complementary Metal Oxide Semiconductor (CMOS) process.

A metal-dielectric-metal (MDM) waveguide coupled with fixed height to length (bi/ai = 0.8) stubs is proposed in our work. Then, an obvious band-stop filtering phenomenon can be observed in MDM waveguide coupled with single fixed height to length stub. Interestingly, the MDM waveguide coupled with two fixed height to length stubs exhibits better band-stop filtering performance than that in a single fixed height to length stub coupled waveguide structures. The phase difference analysis and transmission line theory are established to discuss the transmission spectrum and the wide band-stop filtering phenomenon of our proposed structure. Inconceivably, the bandwidth of band-stop filtering can reach to 1750 nm through tuning structure parameters and the number of the fixed height to length stub. These results may provide great potential applications for plasmonic filtering devices.

A mechanically tunable, constant-absolute-bandwidth (ABW) bandstop filter is realized using the metamaterial-based electromagnetic bandgap structure (MTM-EBG). The MTM-EBG is embedded within a microstrip (MS) line and used to produce a bandstop filtering response, with a topology that is compact, uniplanar, and fully printable. A three-cell MTM-EBG-based MS bandstop filter is designed and experimentally verified for operation centered at 4.18 GHz with a 10-dB rejection bandwidth of 247 MHz. This filter is then made tunable by placing a dielectric plate directly on the surface of the MTM-EBGs. Moving this plate across the surface of the MTM-EBGs changes their reactive loading and, consequently, shifts their response. To ensure a constant ABW, the dielectric plate is perforated to produce an effective plate permittivity that varies for each unit cell. The tunable filter is then fabricated, with the dielectric plate applied to the MTM-EBG-based bandstop filter using a 3-D printed superstructure. A tuning range of 3.80 GHz ± 6.2% and a 10-dB bandstop ABW of 244 MHz ± 1.3% are demonstrated, showing good agreement with the simulated data. The MTM-EBG-based tunable bandstop filter has a variation in ABW comparable to 3-D filters (which typically have substantially lower variation in ABW than fully planar filters) while occupying substantially less area than alternate planar realizations. [ABSTRACT FROM AUTHOR]

Compact, tunable and wide band stop filter (BSF) for wireless application is presented. The proposed filter is composed of compact rectangular microstrip open loop resonator with stub loaded resonator as building blocks of the filter. First, two vertical lumped capacitors are inserted in the open loop resonator from top to bottom of the substrate at the place which has maximum electric field to decrease the resonance frequency which in turn miniaturize the filter size. The resonance frequency of the fundamental mode is shifted from 5.5 to 4.2 GHz when lumped capacitors of 0.2 pF are added. Second, the capacitance of the open-ended stub can be changed to control the second resonance mode of the filter. Also, by inserting another vertical capacitor at the end of the open-ended stub, the second resonance mode can be controlled and reduced. Finally, by properly selecting the capacitance of the third lumped capacitor, the second resonance mode can be designed to be close to the fundamental mode and hence wide band stop filter can be achieved. The proposed BSF has some appropriate features such as compact size (its size has more than 40% size reduction), wide stopband and most importantly tunability of stopband. The band stop filter has a center frequency of 6.2 GHz, a stop band from 3.5 to 9 GHz, insertion loss lower than − 30 dB, and a return loss higher than 0.4 dB is accomplished inside the stop band. The measured results have good matching with the simulated results. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a rectangular optical lattice filter with reconfigurable bandwidth and wavelength. The proposed reconfigurable rectangular lattice filter consists of three-stage cascaded ring-assisted Mach-Zehnder interferometers (RAMZIs), and each RAMZI unit serves as an approximate optical elliptical filter with optimized shape factor. The scheme and design principle are presented with the method of zero-pole theory. As a proof of concept, the proposed structure is fabricated on the Si $_3$ N $_4$ waveguide platform. In the experiment, the 3-dB bandwidth of the proposed filter can be continuously tuned from 14.1 GHz to 4.1 GHz, maintaining a rectangular transmission response, and the wavelength can also be continuously tuned. This reconfigurable rectangular optical lattice filter shows the potential in many practical applications for reconfigurable optical signal processing due to flexibility and reconfigurability. [ABSTRACT FROM AUTHOR]

Semiconductor quantum dots in photonic integrated circuits enable scaling quantum‐information processing to many single photons and quantum‐optical gates. Obtaining high‐purity and coherent single photons from quantum dots requires spectral filtering to select individual excitonic transitions. Here, an on‐chip wavelength‐tunable filter integrated with a single‐photon source, which preserves the optical properties of the emitter, is demonstrated. Nanomechanical motion is used for tuning the resonant wavelength over 10 nm, enabling operation at cryogenic temperatures, and single‐photon emission from a quantum dot under non‐resonant excitation is demonstrated without resorting to free‐space optical filters. These results are key for the development of fully integrated de‐multiplexing, multi‐path photon encoding schemes, and multi‐emitter circuits. [ABSTRACT FROM AUTHOR]

Agile optical systems and elastic optical networks demand for flexible, high-performance laser sources. We demonstrate a hybrid silicon-fiber laser that can be largely tuned in wavelength, switched in frequency spacing and easily switched between multi- and single-wavelength operations. Single-mode laser with a fiber-coupled output power of 6 to 8 dBm was measured across the spectral range of 1545 to 1560 nm. No significant sign of power limitation from nonlinear absorption or free carrier generation in silicon was found. It is thus expected that a higher output can be obtained by improving the gain saturation performances as well as the fiber-to-chip coupling efficiency. For multiwavelength operation, we have achieved a frequency spacing switchable between 56 GHz, 75 GHz, and 225 GHz. For both the multi- and single-wavelength operations, a linewidth of less than 20 kHz was measured. All the tuning mechanisms have been realized on the silicon chip, providing a scalable solution for tunable fiber lasers with minimized cost and integration complexity. [ABSTRACT FROM AUTHOR]

Electric field-based frequency tuning of acoustic resonators at the material level may provide an enabling technology for building complex tunable filters. Tunable acoustic resonators were fabricated in thin plates (h/ $\lambda ~\sim ~0.05$) of X-cut lithium niobate (LiNbO3) (90°, 90°, $\psi = 170^{\circ }$). LiNbO3 is known for its large electromechanical coupling (${K} ^{2}$) for the shear and symmetric Lamb modes (SH0: ${K} ^{2} =40$ %, S0: ${K} ^{2} =30$ %) in thin plates and, thus, applicability for low-insertion loss and wideband filter applications. We demonstrate the effect of a dc bias in X-cut LiNbO3 to shift the resonant frequency by ~0.4% through direct tuning of the resonator material. A nonlinear acoustic computation predicted 0.36% tuning, which was in excellent agreement with the tuning measurement. For X-cut, we predicted electrical tuning of the S0 mode up to 1.6% and for Y-cut the electrical tuning of the SH0 and S0 modes was up to 7.0% with ${K} ^{2} =27.1$ %. The mechanism is based on the nonlinearities that exist in the piezoelectric properties of LiNbO3. The X-cut SH0 mode resonators were centered near 335 MHz and achieved a frequency tuning of 6 kHz/V through the application of a dc bias. [ABSTRACT FROM AUTHOR]

A compact, tunable linear optofluidic Bragg filter is simulated, designed, fabricated, and characterized. The device consists of a nanocavity sandwiched by two symmetrical film stacks made of high- and low-refractive-index dielectric materials. The fabrication parameters are simulated by using the commercial software Essentical Macleod. The resonant wavelength can be linearly shifted by up to 34.8 nm when the refractive index of the liquid injected into the Bragg nanocavity varies from 1.333 to 1.51. Meanwhile, the filter has a narrow bandwidth of 1.1 nm and a very high extinction ratio of -20.2 dB with the sensitivity (Δλ/Δn ) of 374 nm/RIU.

By combining advanced fluid control technology with surface plasmonic resonance phenomenon, we could take advantage of various unique characteristics of plasmonics without changing the original structure to realize a tunable color filtering system. By modifying the wetting properties of solid surface with an electric field, electro-fluid control technology could tune the curvature of two-phase fluid interface continuously and, therefore, change the distributions of silver nanoparticles on the interface accordingly. Based on this fluidic optical design, we investigated the influencing factors of color filtering performance by modeling, finally got an optimized design to achieve broad spectrum filtering system. As the color filtering function is realized simply and rapidly by charging, and therefore, this design could improve the efficiency of the electro-optical systems and is a promising idea for many applications, such as the dynamic display devices.

A first-of-its-kind design methodology to realize thermally actuated origami-inspired multilayer Miura frequency selective surfaces (MLM-FSSs) using a polyester-based substrate is presented in this article that can change its frequency response according to the variation in its ambient temperature. In order to maintain the optimum interlayer distance between the two-layer Miura-FSS structures, a specialized low-loss origami-inspired spacer layer is introduced that preserves its desired overall frequency response during different folding configurations. It also features an unprecedented high mechanical strength, making it suitable for a wide range of terrestrial, outer-space, and biomedical applications. The frequency response and its relationship to kinematics of the proposed structure are also presented in detail, which gives a unique insight into the operation principles of such structures. The proposed structure features twice the bandwidth as compared to single-layer Miura-FSS, an excellent angle of incidence rejection, and is the first demonstration of a fully inkjet-printed MLM-FSS that is realized completely by a rigid heat-sensitive substrate as opposed to traditional cellulose-based Miura-FSSs that lack self-actuation mechanism as well as rigidity, which is a key attribute of most practical thick origami structures. [ABSTRACT FROM AUTHOR]

This article reports the design of high-selectivity tunable bandpass filters with constant absolute bandwidth (CABW) using dual-mode (DM) substrate-integrated-waveguide (SIW) resonators. The even and odd modes are coupled to the source and load using an L-shaped coupling scheme instead of the conventional doublet scheme, and thus, each mode produces either one reflection zero or one transmission zero (TZ). Each resonator has one contactless tuner to change the frequencies of both modes simultaneously, and a controllable separation between the two modes can be obtained over the whole tuning range (TR). The proposed resonator is utilized as the building block in four prototype filters with different TZ locations. The first filter is in a principle back-to-back topology, and it distributes TZs on both sides of the passband and has a CABW across the entire TR. The rest three further explore techniques to improve the out-of-band selectivity, i.e., introducing source/load coupling to increase the reject level and relocating the TZs on one side of the passband to build a spectrum with high rejection. All filters are based on two DM SIW resonators with only two tuners. Compared to state-of-the-art works, the proposed filters offer a wide constant-BW TR, low insertion loss, high selectivity, and good nonlinear performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to widely tune high-quality factor evanescent-mode cavity resonators and filters using contactless tuners. The proposed method resolves multiple challenges facing reliable manufacturing and operation of these filters by avoiding the attachment of the flexible tuner to the cavity and replacing it with capacitive contactless tuners. This paper discusses the design consideration and tradeoffs as well as demonstrates the performance of the proposed concept using the substrate-integrated-waveguide technology. The resonators demonstrate more than octave tuning range (TR), quality factor up to 650, and power handling exceeding 100 W. In addition, the second-order bandpass filters are demonstrated, along with the long-term measurements, showing better than 1.17% frequency error after a 15-h stability test, and less than 1.47% frequency error after a 450 cycles repeatability test over an octave TR from 1.8 to 3.6 GHz. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a tunable planar layered thin film (PLTF) structure operating at the short-wavelength infrared spectrum by employing the phase transition of vanadium dioxide through thermal stimulus. We obtain 400-nm spectral wavelength shift of scattering resonances by heating up or cooling down the structure. This temperature change leads to a contrast in the scattering intensities so that the contrast of transmission at Fabry–Perot resonance wavelength of 1.75 μm is obtained by the numerical simulations and verified by the measurements. We add a metasurface layer on the tunable PLTF structure, and we theoretically investigate and numerically demonstrate the scattering effects of this modified design. In this case, the contrast of transmission is enhanced compared to the only PLTF design due to Mie-type scattering. We also indicate that the normally incoming infrared light passes through the proposed design with a bending angle at room temperature whereas the intensity of the bending light is not appreciable at high temperature. Thus, we have achieved the so-called thermally adjustable infrared light bending/steering. The dynamic devices based on these kinds of pure planar layered and metasurface incorporated structures can be employed in numerous active photonic applications in the infrared spectrum. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the design of a tunable RF filter dedicated for multistandard operation in Software Defined Radio (SDR) receivers. This filter is based on the Dual-Behaviour Resonators (DBR) topology realized in microstrip technology with PTFE substrate and using SMV1405 varactors as tuning elements. It provides the independent control of its center frequency and bandwidth relative to the radio standards UMTS, Wi-Fi and LTE (Band N°7). The center frequency ranges from 2.142 to 2.65 GHz and the required bandwidth varies from 86 to 108 MHz. S-parameters simulations and measurements with non-linearity study are provided to evaluate the performance of the designed filter. A very good agreement between simulations and measurements is obtained and the designed filter shows acceptable performances in terms of insertion and return losses which are less than 6 dB and more than 14 dB, respectively for all bands. Moreover, linear properties regarding receiver requirements with a minimum 1-dB compression point (P1dB) of 11.4 dBm and a minimum third order intercept point (IP3) of 21.2 dBm are satisfying. [ABSTRACT FROM AUTHOR]

An electrostatically actuated MEMS cantilever beam-based waveguide Bragg grating tunable optical filter has been designed and simulated. The tunable filter is obtained by shifting the reflected wavelength of the waveguide Bragg grating located on the electrostatically actuated cantilever beam. An approach to increasing the electrostatic actuation of the beam by having an electrode underneath the beam is used and a large wavelength tuning range for the optical filter is achieved. Dimensions of the device are chosen such that full-width-halfmaximum is 0.75 nm, thus capable of filtering adjacent channels of the dense wavelength division multiplexing (DWDM) network. The filter has a tuning range of 10.65 nm (1552.52 to 1563.17 nm) providing add/drop functionality for 14 adjacent DWDM channels. [ABSTRACT FROM AUTHOR]