Transmission Notch Research Articles

Design of slot radiating RF planar sensor for homogeneity check of dielectric discontinuity

AbstractIn this paper, a 2.8‐GHz RF planar sensor with radiating slots is proposed for effective checking of discontinuity in homogeneous dielectric samples. The slots etched in the ground plane reduce the effective area for sample placement, which increases in the case of a conventional ring at the desired frequency. Several forms of discontinuity are analyzed and measured with the help of varying geometrical configurations of Teflon, wood, and polyethylene samples with varying permittivity. It is observed that due to the uniform distribution of fields among all the radiating slots any sort of configurational discontinuity is detected by the sensor in terms of the shift in resonant frequency and S21 transmission notch. The simulations are carried out using CST‐MWS and the equivalent model is developed using ADS. The numerical analysis is carried out using Origin software and the measurement is carried out using Taconic TLY‐5 substrate by photolithographic etching.

Highly Sensitive Differential Microwave Sensor for Soil Moisture Measurement

This paper presents a highly sensitive differential soil moisture sensor (DSMS) using a microstrip line loaded with triangular two-turn resonator (T2-SR) and complementary of the rectangular two-turn spiral resonator (CR2-SR), simultaneously. Volumetric Water Content (VWC) or permittivity sensing is conducted by loading the T2-SR side with dielectric samples. Two transmission notches are observed for identical loads relating to T2-SR and CR2-SR. The CR2-SR notch at 4.39 GHz is used as a reference for differential permittivity measurement method. Further, the resonance frequency of T2-SR is measured relative to the reference value. Based on this frequency difference, the permittivity of soil is calculated which is related to the soil VWC. Triangular two-turn resonator (T2-SR) resonance frequency changes from 4 to 2.38 GHz when VWC varies 0% to 30%. The sensor’s operation principle is described through circuit model analysis and simulations. To validate the differential sensing concept, prototype of the designed 3-cell DSMS is fabricated and measured. The proposed sensor exhibits frequency shift of 110 MHz for 1% change at the highest soil moisture content (30%) for sandy-type soil. This work proves the differential microwave sensing concept for precision agriculture.

Nested nonconcentric microring resonators with high-Q and large fabrication tolerance

Microring resonators are one of the most sought-after optical components for realizing several on-chip functionalities that include sensing, data routing, new frequency generation, and quantum photonic applications. Many of these applications demand a high quality factor and large notch depth (high extinction ratio), which can be achieved by critical coupling. However, the critical coupling is very sensitive to fabrication accuracies and thermal drift. Geometrical parameters of the resonators are generally swept to attain critical coupling, where a few designs can pass the critical coupling condition criteria. In this work, we propose a methodology to circumvent this vital issue. The proposed technique is based on coupled-resonator systems where two different microrings are embedded into a larger microring, referred to as a nonconcentric nested microring resonator (NN-MRR). The NN-MRR configuration relaxes the requirement of the critical coupling condition by 20% when the strip optical waveguide has either smooth or rough sidewalls. Numerical simulations reveal that, unlike standard MRR, a high Q -factor ( > --> 1 0 5 ) and a large transmission notch depth > --> 10 d B can be maintained irrespective of the rings’ coupling conditions for the nested MRRs. Besides the extra degree of freedom of design provided by the inner rings, the other significant advantage of the proposed NN-MRR is its compactness. We believe that the nested MRR arrangement could be highly efficient for biosensing, nonlinear, and quantum applications within a broad ambient temperature range. We have fabricated the NN-MRRs in a silicon-on-insulator platform through electron beam lithography and experimentally demonstrated the theoretical and numerical findings.

Compact Size, and Highly Sensitive, Microwave Sensor for Non-Invasive Measurement of Blood Glucose Level

None-invasive blood glucose measurement enables effective diagnosis and treatment of diabetic patients. The existing microwave sensors suffer from low sensitivity and large size. This article presents a highly sensitive and compact size non-invasive microwave sensor for real-time blood glucose measurements. We have developed a new sensing technique using directly connected Branch Line Coupler and Split Ring Resonators. This technique significantly improves the sensitivity by mitigating the limited coupling between transmission lines and resonators. In addition, using Split Ring Resonators reduces the sensor size due to capacitive and inductive effects, which are loaded to the Branch Line Coupler. The proposed sensing function is based on shifting the transmission notch frequency in coupled arm of the Branch Line Coupler, which is caused by loading the Split Ring Resonators with varying glucose concentration. A prototype sensor is fabricated and successfully tested using several glucose concentrations in deionized water. Experimental results demonstrate 0.72 MHz/mgdL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> measurement sensitivity, which is higher in comparison with available sensors in PCB technology. The prototype sensor size is 3.5×3.5×0.16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Experimental investigation and simulation of phase-shifted fiber Bragg gratings

This work reports the inscription and investigation of phase-shifted fiber Bragg gratings. A method for the inscription of such structures that makes it possible to vary the full width at half-maximum of the transmission notch in the reflection band within the range of 8–76 pm is proposed. The influence of the amplitude of the induced refractive index modulation and length of the formed structure on the studied parameter is investigated and analyzed. The results are presented as curves for data collected experimentally and theoretically. The investigation conducted in this study makes it possible to manufacture structures with known widths of the transmission notches, opening up a wide spectrum of possibilities to design optical elements based on such specific Bragg grating structures (e.g., fiber-optic sensors, tunable transmission filters, and demultiplexers).

An Effective Analysis Method for Millimeter-Wave Broadband Mixers

To realize the broadband characteristic of GaAs Schottky-diode-based mixers, an effective analysis method based on the proposed simplified formulas combined with full-wave simulation is given in this letter. The complex nonlinear analysis is simplified, and the dimension of key circuit has been estimated based on simplified formulas. A 3-D electromagnetic simulation software has been used for accurate circuit dimension from the perspective of signal transmission notches. This optimization method simplifies the calculation process and saves the design time. To verify the above-mentioned technique, an E-band broadband fundamental mixer and a W-band broadband sub-harmonic mixer are fabricated and measured. The mixers have broadband characteristics and the measured results are in good agreement with the simulation results. The proposed method can be used to intuitively and quickly remove intermediate frequency (IF) output power nulls in broadband mixers' working frequency band.

Low Power All-Digital Radio-Over-Fiber Transmission for 28-GHz Band Using Parallel Electro-Absorption Modulators

We present a low-power all-digital radio-over-fiber (RoF) transmitter for the 28 GHz band using sigma-delta modulation. Using a parallel electro-absorption modulator (EAM) structure, the radio signal upconversion is split between the electrical and the optical domains. This halves the maximum bandwidth requirement of the driver circuit with respect to conventional implementations. Furthermore, the effect of chromatic dispersion can be mitigated by tuning the optical phase and amplitude applied to the individual modulators, such that transmission notches are partially removed. The modulator structure is described using simplified models and verified in VPI TransmissionMaker. Experimental results using a 140 mW non-return-to-zero (NRZ) driver and parallel EAMs are provided and yield an error vector magnitude (EVM) of 7.6% (5.2%) when transporting a radio signal modulated at 28 GHz with 5.25 Gb/s (2.625 Gb/s) 64-QAM over 10 km standard single mode fiber (SSMF) at 1560 nm.

Filtering Quasi-Yagi Strip-Loaded DRR Antenna With Enhanced Gain and Selectivity by Metamaterial

This paper presents a design approach of broadband filtering quasi-Yagi DRR Antenna using a strip-loaded dielectric ring resonator (DRR) and near-zero-index (NZI) metamaterial (NZIM). The ring strip is loaded to the inside wall of the DRR so that the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01δ</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21δ</sub> modes of the DRR can be close. Meanwhile, they function as a dual-mode magnetic dipole (M-dipole) driver and can be differentially excited at the same time for designing a wideband quasi-Yagi antenna. Benefiting from the dual-mode operation of the strip-loaded DRR, the end-fire gain across the operating band of the antenna is stable with preliminary bandpass filtering characteristics. To improve the in-band gain and enhance the filtering capability, a new coplanar NZIM with wideband NZI characteristic and dual transmission notches in the lower and upper stopbands of the preliminary gain passband, is introduced and put in the front of the DRR driver. To verify the proposed design concept, an X-band filtering quasi-Yagi antenna with the NZIM is fabricated and measured. Good agreement between the simulated and measured results can be observed. The wideband antenna has a measured -10 dB impedance bandwidth of about 16% (8.5 - 10 GHz). Within it, the peak gain of antenna reaches 8.3 dBi and 1-dB gain fractional bandwidth is about 10.8%. Meanwhile, it exhibits good gain bandpass response due to the transmission notches of the NZIM.

An Effective Analysis Method for Removing Output Power Nulls in Millimeter-Wave Broadband Frequency Multipliers

An effective analysis method is proposed for broadband GaAs Schottky diode-based frequency multipliers. Frequency multipliers output power nulls in the working frequency band have been estimated and removed from the perspective of multiplier transmission notches. Transmission characteristics of the input signal from radio frequency RF input port to Schottky lumpports and the desired harmonic from Schottky lumpports to RF output port are analyzed. Key circuit parts and their dimensions that result in transmission notches are intuitively calculated and analyzed based on 3-D electromagnetic simulation. To verify the above-mentioned technique, three multiplier prototypes based on single, dual, and reverse Schottky junction diodes are fabricated and measured. The measured output power nulls coincides with simulated transmission notches. The proposed method can be utilized to intuitively and quickly remove output power nulls in broadband frequency multipliers working frequency band.

Direct laser writing of a phase-shifted Bragg grating waveguide for ultrasound detection.

We demonstrate a phase-shifted Bragg grating waveguide (PS-BGW) fabricated by a direct laser writing technique via two-photon polymerization as a high-frequency ultrasonic sensor. The PS-BGW device has a cross-sectional area of 1.5 μm×2 μm, and the grating length is about 100μm. The optical resonant spectrum is investigated numerically and experimentally. The result shows that the fabricated device with a grating depth of 250nm and a quarter wave phase lead to a 20-nm stopband and a 0.085-nm full-linewidth of the transmission notch, making it suitable for photonic sensing applications. Here, the PS-BGW device is demonstrated for the detection of acoustic waves, which can cause strain or deformation of the device and lead to a shift in the resonance wavelength. The sensitivity and the limitations of the device for ultrasound detection are also investigated.

Simultaneous measurement of refractive index and temperature with high sensitivity based on a multipath fiber Mach-Zehnder interferometer.

We present and experimentally demonstrate a highly sensitive sensor for simultaneously measuring the refractive index (RI) and temperature based on a multipath fiber Mach-Zehnder interferometer. The sensor is fabricated by sandwiching a segment of weak-coupling seven-core fiber (SCF) with two short multimode fibers, and then splicing it with lead-in and lead-out single-mode fibers, respectively. Six outer cores of the SCF are half-etched chemically for enhancing the interaction between light and matter. A high-quality transmission spectrum with 23dB fringe visibility is obtained. Due to the strong interaction between the outer core modes and cladding modes with the surrounding medium, the proposed fiber structure exhibits not only an extremely high RI sensitivity of -1802.26 nm/RI unit from 1.427 to 1.442, but also a superior temperature sensitivity of 82pm/°C from 10°C to 90°C. Moreover, RI and temperature can be discriminated simultaneously by measuring the central wavelength shifts of two transmission notches. This sensor has outstanding advantages of high sensitivity, easy fabrication, simple structure, and low cost, and may find applications in multiparameter highly sensitive sensing.

A Novel Method for PIT Effects Based on Plasmonic Decoupling**Supported by the Key Disciplines of Physics of Guizhou Province under Grant No QXWB[2013]18, the Major Research Projects for Innovation Groups of Guizhou Province under Grant No KY[2018]028, the National Natural Science Foundation of China under Grant No 11464052, the Science and Technology Foundation of Guizhou Province under Grant No J[2015]2149,

A tunable dual-band stop-band THz spectrum can be realized in a hybrid structure, which consists of metal nanoribbon arrays clad by graphene nanoribbons. Dual-band spectra can be controlled separately by the nanoribbon width w and graphene chemical potential μc. We explain that two local plasmonic modes excited at graphene ribbons belong to different gratings, which uncouple with each other by electro-magnetic shielding of the metal ribbons. Furthermore, plasmonic induced transparent (PIT) effects can also be realized by making the two transmission notches close to each other, with better performance than the PIT system based on plasmonic coupling, such as with a larger extinction radio and a tunable transparency window.

Sub-wavenumber linewidth mid-infrared notch filter enabled by a dual-period plasmonic structure

Abstract A transmission notch filter based on surface-plasmon resonance is proposed and numerically studied in the mid-infrared region. The metal structure is a dual-period grating constructed by using smaller-period gold arrays as the duty portions of a larger-period grating. The plasmonic filter shows high transmission of >85% over broad mid-infrared range, and a single notch at ∼ 4. 073 μ m with 24 dB extinction ratio. The stop bandwidth of the filter is ∼ 0.75 nm ( ∼ 0.45 cm−1), corresponding to the quality factor as high as 5400, which is improved by at least one order of magnitude. The rejection wavelength and bandwidth of the filter can be designed by adjusting the structure parameters. Additionally, the angle and polarization of the incidence and refractive index of the surrounding medium affect the performance of the filter.

Differential Sensors Using Microstrip Lines Loaded With Two Split-Ring Resonators

This paper presents a microwave sensor using a pair of split-ring resonators (SRRs). The sensor is designed by loading a microstrip transmission line by two identical SRRs on its sides. Differential permittivity sensing is performed by loading the SRRs with dielectric samples. One transmission notch is observed for the identical loads, whereas the non-identical samples produce two split notches. The sensor’s operating principle is described through a circuit model analysis. A prototype of the designed sensor is fabricated and experimentally validated for verifying the differential sensing concept. The developed device can be used to compare or differentially characterize solid dielectric samples improving the robustness to environmental factors producing cross-sensitivity or miscalibration.

Phase-Shifted Bragg Grating Inscription in PMMA Microstructured POF Using 248-nm UV Radiation

In this work, we experimentally validate and characterize the first phase-shifted polymer optical fiber Bragg gratings (PS-POFBGs) produced using a single pulse from a 248-nm krypton fluoride laser. A single-mode poly (methyl methacrylate) optical fiber with a core doped with benzyl dimethyl ketal for photosensitivity improvement was used. A uniform phase mask customized for 850-nm grating inscription was used to inscribe these Bragg structures. The phase shift defect was created directly during the grating inscription process by placing a narrow blocking aperture in the center of the UV beam. The produced high-quality Bragg grating structures, presenting a double dips, reject 16.3 dB (97.6% reflectivity) and 13.2 dB (95.2% reflectivity) of the transmitted power, being therefore appropriate for sensing or other photonic applications. Its transmission spectrum possesses two sharp transmission notches, allowing a significant increase in measurement resolution compared to direct interrogation of a single grating. The reflection and transmission spectra when multiple phase shifts are introduced in the fiber Bragg grating structure are also shown. The PS-POFBG's strain, temperature, pressure, and humidity characteristics have been experimentally analyzed in detail to assess their potential usage as sensors.

Interferometric interrogation of [formula omitted]-phase shifted fiber Bragg grating sensors

Interferometric interrogation technique realized for conventional fiber Bragg grating (FBG) sensors is historically known to offer the highest sensitivity measurements, however, it has not been yet explored for π-phase-shifted FBG (πFBG) sensors. This, we believe, is due to the complex nature of the reflection/transmission spectrum of a πFBG, which cannot be directly used for interferometric interrogation purpose. Therefore, we propose here an innovative as well as simple concept towards this direction, wherein, the transmission spectrum of a πFBG sensor is optically filtered using a specially designed fiber grating. The resulting filtered spectrum retains the entire characteristics of a πFBG sensor and hence the filtered spectrum can be interrogated with interferometric principles. Furthermore, due to the extremely narrow transmission notch of a πFBG sensor, a fiber interferometer can be realized with significantly longer path difference. This leads to substantially enhanced detection limit as compared to sensors based on a regular FBG of similar length. Theoretical analysis demonstrates that high resolution weak dynamic strain measurement down to 4 pε∕Hz is easily achievable. Preliminary experimental results are also presented as proof-of-concept of the proposed interrogation principle.

Fabrication of long period fiber gratings of subnanometric bandwidth.

This Letter reports on the fabrication of long period fiber gratings having subnanometric bandwidths in the 1500nm spectral region. Large gratings have been photo inscribed in a high NA fiber; the grating pitch and the order of the HE cladding mode are optimized to produce gratings with a large number of periods and prevent the coupling to TE, TM, or EH modes. Resonances with a FWHM of 0.83 and 0.68nm have been achieved for gratings 15 and 20cm long, respectively; the free spectral range between the transmission notches is 125nm. The polarization effects and the sensitivity of the gratings to temperature and to strain variations are presented as well.

Design of an On-Chip Highly Sensitive Misalignment Sensor in Silicon Technology

Advanced micromachining technology has made magnificent progress for fabrication of non-planar circuits. Using this technology, circuits and systems can be implemented in a more cost-effective way. Unlike the conventional planar circuit, low-cost and highly sensitive misalignment sensor is required to detect imperfect placement of different micro-devices, which may be of the order of sub-micrometers. Currently, this is hardly to be achieved by using the existing approaches. In this letter, we present a novel sensor design approach utilizing the parasitic capacitance of an integrated coupled-line resonator for misalignment sensing. Due to vertical misalignment between two metal strips, the parasitic capacitance of the sensor varies, which results in a resonance shift from 53 to 68 GHz, while a reasonably strong transmission notch is still maintained. Taking advantage of this principle, misalignment can be effectively detected. To prove the concept, several devices are fabricated in a standard silicon technology. Three samples with the same structure are used to evaluate the reliability, while eight different structures are used to verify the concept. All results are extensively validated through both simulation and measurements.

Mid-wave infrared narrow bandwidth guided mode resonance notch filter.

We have designed, fabricated, and characterized a guided mode resonance notch filter operating in the technologically vital mid-wave infrared (MWIR) region of the electromagnetic spectrum. The filter provides a bandstop at λ≈4.1 μm, with a 12 dB extinction on resonance. In addition, we demonstrate a high transmission background (>80%), less than 6% transmission on resonance, and an ultra-narrow bandwidth transmission notch (10 cm-1). Our filter is optically characterized using angle- and polarization-dependent Fourier transform infrared spectroscopy, and simulated using rigorous coupled-wave analysis (RCWA) with excellent agreement between simulations and our experimental results. Using our RCWA simulations, we are able to identify the optical modes associated with the transmission dips of our filter. The presented structure offers a potential route toward narrow-band laser filters in the MWIR.

Modeling human echolocation of near-range targets with an audible sonar.

Blind humans echolocate nearby targets by emitting palatal clicks and perceiving echoes that the auditory system is not able to resolve temporally. The mechanism for perceiving near-range echoes is not known. This paper models the direct mouth-to-ear signal (MES) and the echo to show that the echo enhances the high-frequency components in the composite MES/echo signal with features that allow echolocation. The mouth emission beam narrows with increasing frequency and exhibits frequency-dependent transmission notches in the backward direction toward the ears as predicted by the piston-in-sphere model. The ears positioned behind the mouth detect a MES that contains predominantly the low frequencies contained in the emission. Hence the high-frequency components in the emission that are perceived by the ears are enhanced by the echoes. A pulse/echo audible sonar verifies this model by echolocating targets from 5 cm range, where the MES and echo overlap significantly, to 55 cm. The model predicts that unambiguous ranging occurs over a limited range and that there is an optimal range that produces the highest range resolution.