dB Cutoff Research Articles

Electronic Detection of Photonic Band Gaps in Nanolithographic Metallic Gratings

In nanolithographic metallic gratings we investigate the dependence of photonic band gaps on geometrical parameters. Finite element modeling was used to develop a model for an optoelectronic device with periodicity of 470 nm and concomitantly the electronic response of a nanofabricated metal-semiconductor-metal photodetector grating was experimentally studied under a sweeping monochromatic light source. The grating spectral response increased in the region between 470 nm and 520 nm, corroborating the computational results. This increase is understood to occur because photons with wavelength shorter than approximately 520 nm are energetic enough to excite interband transitions in the Au, but the period of the structure acts as a cutoff where incident photons with wavelength shorter than the period are less likely to form surface plasmon polaritons. This cutoff originates from a photonic band gap. Magnetic field intensity profiles at the 3 dB cutoff indicate that a surface plasmon wave exists where each finger interacts with the next through overlapping magnetic fields, suggesting that the cutoff is a surface plasmon wave effect. Localized surface plasmon effects were observed at longer wavelengths in the modeled absorbance. The effects of three geometrical parameters on the spectral dependence of modeled absorbance were investigated.

Interpreting MAIA Microperimetry Using Age- and Retinal Loci-Specific Reference Thresholds.

PurposeMacular Integrity Assessment (MAIA) microperimetry is used widely in clinical trials and routine practice to assess paracentral scotoma. Current interpretation of MAIA is based on an assumed uniform 25 decibel (dB) cutoff for normal function irrespective of subject age and retinal location. We examined this convention by establishing an age- and loci-specific reference in healthy eyes and comparing this to the <25 dB cutoff.MethodsRetrospective MAIA results from healthy eyes were analyzed for prevalence of loci with <25 dB. At each locus, a new reference cutoff was derived from quantile regression of sensitivity against age at the 2.5th percentile. Two clinical cases of serial MAIA testing were analyzed using the new approach and compared to the <25 dB cutoff.ResultsFifty-four and 56 age-matched (range: 16–75 years) healthy eyes underwent small (37 loci) and large (68 loci) grid testing, respectively. Retinal sensitivity <25 dB was found in 5% of the small grid (1998 data points) and 10% of the large grid (3808 data points). These were found predominantly in older subjects and at the central point or in the perifoveal region. Quantile regression at each individual locus showed age-related decline with a median gradient of 0.6 dB/decade.ConclusionsWe caution against using <25 dB cutoff in MAIA interpretation and advocate an age- and loci-specific cutoff criterion.Translational RelevanceOur study suggests that MAIA interpretation is influenced by the criterion used for defining abnormal pointwise measurement.

Design and analysis of a modified rectangular-shaped lowpass filter based on LC equivalent circuit

In this paper, a new compact microstrip lowpass filter (LPF) with a sharp roll off and wide stopband is presented. The structure is composed of a defected rectangular-shaped resonator and a rectangular shape resonator as a suppressing cell. All resonators and their additional components are analyzed based on their LC equivalent circuits, and the role of each section and its equivalent circuit are described. The LPF with 3 dB cutoff frequency at 1.44 GHz has advantages such as low insertion loss and high return loss. Based on the measurement results, the proposed LPF has a sharp transition band that is 0.22 GHz from −3 to −20 dB. On the other hand, the measured value of the group delay in the whole passband is only 47 ns, which is one of the essential advantages of this filter. The designed LPF has been simulated, fabricated and, measured. There is a proper agreement between simulation and measured results.

An ultrasensitive self-driven broadband photodetector based on a 2D-WS2/GaAs type-II Zener heterojunction.

High-performance broadband photodetectors have attracted extensive research interest because of their significance in optoelectronic applications. In this study, a highly sensitive room-temperature (RT) broadband photodetector composed of a WS2/GaAs type-II van der Waals heterojunction was demonstrated, which exhibited obvious photoresponse to broadband light illumination from 200 to 1550 nm beyond the limitation of the bandgaps. Impressive device performances were achieved in terms of a low noise current of ∼59.7 pA, a high responsivity up to 527 mA W-1, an ultrahigh Ilight/Idark ratio of 107, a large specific detectivity of 1.03 × 1014 Jones, a minimum detection light intensity of 17 nW cm-2 and an external quantum efficiency (EQE) up to 80%. Transient photoresponse measurements revealed that the present detector is capable of working at a high frequency with a 3 dB cutoff frequency up to 10 kHz and a corresponding rise/fall time of 21.8/49.6 μs. Notably, this heterojunction device demonstrated Zener tunneling behaviors with a threshold voltage of -4 V. The capacitance-voltage (C-V) properties of the heterojunction were investigated to understand the device performances. In addition, the as-fabricated device can function as an image sensor with an outstanding imaging capability. Considering the above superior features, the proposed WS2/GaAs type-II van der Waals heterojunction may find great potential in high-performance broadband photodetection applications.

Compact microstrip lowpass filter with high harmonics suppression using defected structures

A compact microstrip lowpass filter with sharp selectivity and wide stopband designed on the basis of dual-plane, is presented. Initially, a basic one pole defected ground structure (DGS) filter is modified so as to achieve sharp selectivity as well as compact size. The modified DGS reduces the circuit size of the filter by 68.8%. To suppress the higher order harmonics, mirrored symmetrical uniform impedance stubs are designed in the top surface of the substrate, thereby wide stopband up to 20 GHz is achieved. The stopband suppression level of the filter is improved by incorporating a spurline resonator which acts as a defected microstrip structure (DMS) in the top microstrip line. The designed filter has 3 dB cutoff frequency of 2.11 GHz with high relative stopband bandwidth of 159.2% within the rejection level of 18 dB. The wide passband frequency range of the proposed filter covers the GSM, GPS, Wi-Fi communications and various L-band applications such as aircraft surveillance etc.

High-Speed Mid-Infrared Interband Cascade Photodetector Based on InAs/GaAsSb Type-II Superlattice

High speed mid-wave infrared (MWIR) photodetectors have applications in the areas such as free space optical communication and frequency comb spectroscopy. However, most of the research on the MWIR photodetectors is focused on how to increase the quantum efficiency and reduce the dark current, in order to improve the detectivity (D*), and the 3dB bandwidth performance of the corresponding MWIR photodetectors is still not fully studied. In this work, we report and characterize a MWIR interband cascade photodetector based on InAs/GaSb type-II superlattice with a 50% cutoff wavelength at ~5.3 um at 300 K. The 3 dB cutoff frequency is 2.4 GHz at 300 K, for a 40 {\mu}m circular diameter device under -5 V applied bias. Limitations on the detector high speed performance are also discussed.High speed mid-wave infrared (MWIR) photodetectors have applications in the areas such as free space optical communication and frequency comb spectroscopy. However, most of the research on the MWIR photodetectors is focused on how to increase the quantum efficiency and reduce the dark current, in order to improve the detectivity (D*), and the 3dB bandwidth performance of the corresponding MWIR photodetectors is still not fully studied. In this work, we report and characterize a MWIR interband cascade photodetector based on InAs/GaSb type-II superlattice with a 50% cutoff wavelength at ~5.3 um at 300 K. The 3 dB cutoff frequency is 2.4 GHz at 300 K, for a 40 um circular diameter device under -5 V applied bias. Limitations on the detector high speed performance are also discussed.

Can the Orexin Antagonist Suvorexant Preserve the Ability to Awaken to Auditory Stimuli While Improving Sleep?

The safety profile of the dual orexin receptor antagonists (DORAs) are currently unknown with regard to nocturnal responsivity among people with insomnia. We compared the auditory awakening thresholds (AATs) of the DORA suvorexant (10 and 20 mg) versus placebo in 12 individuals with DSM-5 insomnia. The study used a double-blind, placebo-controlled, three-way crossover design. Participants were randomly assigned to a treatment sequence that included placebo, suvorexant 10 mg, and suvorexant 20 mg. At the time of maximum drug concentration, auditory tones were played during stable stage N2 sleep. Tones increased by 5-decibel (db) increments until the participant awakened. The db at awakening was recorded as the AAT and compared between conditions. The proportion of awakenings higher than 85 db was also compared between conditions. Finally, sensitivity analyses were also conducted using surrounding thresholds (80 db and 90 db). The mean AAT did not differ significantly between either dose of suvorexant compared to placebo. Moreover, the proportions of individuals who remained asleep at the AAT 85 db cutoff did not differ across conditions. In addition, wake after sleep onset decreased and total sleep time increased in the suvorexant 20 mg condition compared to placebo. Suvorexant (10 and 20 mg) preserved the ability to respond to nocturnal stimuli, whereas the 20-mg dose improved the sleep of people with insomnia. This suggests that DORAs such as suvorexant can effectively treat insomnia while allowing patients to awaken to nocturnal stimuli in the environment. Registry: ClinicalTrials.gov; Title: A Phase IV 3-Way Double-blind, Randomized, Crossover Study to Compare the Awakening Threshold Effects (Responsivity) of Belsomra 10 mg and 20 mg to Placebo in Non-elderly Insomniacs; Identifier NCT03312517; URL: https://clinicaltrials.gov/ct2/show/NCT03312517. Drake CL, Kalmbach DA, Cheng P, Roth T, Tran KM, Cuamatzi-Castelan A, Atkinson R, SinghM, Tonnu CV, Fellman-Couture C. Can the orexin antagonist suvorexant preserve the ability to awaken to auditory stimuli while improving sleep? J Clin Sleep Med. 2019;15(9):1285-1291.

Compact low‐pass/band‐pass filters based on quarter‐mode substrate integrated waveguide and a connected network of CSRRs

In this study, a compact low-pass filter (LPF) and two compact dual-wideband band-pass filters (BPFs) are proposed based on a connected network of complementary split-ring resonators (CSRRs) and open CSRRs (OCSRRs). The LPF is designed based on microstrip structure, and then the structure is changed to quarter-mode substrate integrated waveguide for designing the dual-band BPFs. The 3 dB cutoff frequency of the LPF is 1.84 GHz and its size is 0.094λ g × 0.094λ g , where λ is the guide wavelength at 3 dB cutoff frequency. The LPF has a wide stop-band, up to 16 GHz. The first proposed dual-wideband BPF has the centre frequencies of 3.85 and 8.03 GHz, with 3 dB fractional bandwidths of 31.69 and 13.7%, respectively. Finally, a sharper dual-band BPF is obtained by cascading two proposed dual-wideband BPFs and optimising them for the desirable response. The measured centre frequencies of the second dual-band BPF are 3.65 and 7.15 GHz with 3 dB fractional bandwidths of 28.21 and 12.52%, respectively. The measurement results of the fabricated filters are in good agreement with the simulation ones. The filters are compared with similar reported filters in the literature, which confirm the compactness of the proposed filters..

Implementation of lateral Ge–on–Si heterojunction photodetectors via rapid melt growth and self-aligned microbonding for Si photonics

Heterogeneous integration of Ge on a Si lateral p–i–n junction by rapid melt-growth method and self-aligned microbonding is presented. A very thin Ge (100 nm) strip butt-coupled to a Si waveguide for implementing a waveguide photodetector is reported with a low dark current of 1 nA at −3 V bias. The measured 3 dB cut off frequency for the photodetectors is 30 GHz. The internal device responsivity is estimated to be 0.72 A W−1 at the reverse bias of 3 V.

All-fiber MZI-Interleaver with self-feedback fiber resonator

In order to improve the transmission performance of all-fiber Mach-Zehnder interferometer (MZI), a novel all-fiber MZI interleaver is proposed and discussed in this paper. All-fiber interleaver consists of one 2×2 fiber coupler and one coupler with self-feedback fiber ring resonator. According to its structure, the output expression of the device is deduced by using optical fiber transmission theory and matrix theory, and numerical simulation analysis is performed. The results show that the device adopts the phase adjustment effect introduced by the self-feedback optical fiber resonator with reasonable parameters, and its 25 dB cutoff bandwidth is 46.7 GHz which accounts for 93.4% of the 50 GHz frequency interval. The output spectrum is similar to the square wave output. This device requires 2 fiber couplers, which is less than the number of couplers needed for the conventional all-fiber MZI-interleaver. When considering the existence of transmission loss, there is no difference in the amplitude of the two interference optical signals, which reduces the influence of transmission loss on the extinction characteristics of the filter. Compared with the conventional unbalanced MZI type interleaver with an optical fiber resonant ring, the structure is simple and compact, and has a certain anti-deviation ability. It also reduces the difficulty of making the device, which makes it play an important role in the future of dense wavelength division multiplexing systems.

Design and fabrication of microstrip lowpass filter using asymmetric hairpin resonator

In this letter, a compact microstrip lowpass filter (LPF) is designed using serial connecting of two modified asymmetric hairpin resonators. The proposed design is consists of four open-circuited stubs that are used to suppress spurious harmonics in the stopband. The proposed filter has wide-stop band with attenuation level better than −28 dB from 2.16 up to 26.1 GHz and sharp roll-off. The proposed LPF has −3 dB cutoff frequency equal to 2.11 GHz, wide stopband width around 12th harmonic suppression and insertion loss less than 0.1 dB at about 85% of the passband. The excellent agreement is observed between the simulated results and measured values of the fabricated LPF.

A compact lowpass filter with ultra-high figure-of-merit for integrating with Class-F/F−1 power amplifiers

This Paper presents a microstrip lowpass filter (LPF) with compact size, and ultra-wide stopband. The structure consists of a semi-circular shaped resonator (SCSR) and circular patches as the suppressing cell. The proposed LPF has a − 3 dB cutoff frequency at 1.53 GHz. It also has suitable performances such as an extended stopband width from 1.62 to 19.1 GHz (with the attenuation level of more than − 20 dB), ultra-sharp transition-band of 0.09 GHz (from − 3 to − 20 dB). Low insertion loss, high return loss and flat group delay in the region of the passband are very significant properties of this LPF. A proper agreement between the simulation and measurement results has been achieved after the fabrication and testing. Proposed LPF has an ultra-high figure-of-merit (FOM) of 126168, showing its strong efficiency. Forasmuch as harmonic control circuits (HCCs) play a key role in designing Class-F/F−1 power amplifiers (PAs); the asymmetric high performance LPFs can be used at the input and output of these PAs in the HCC section. Therefore, the proposed LPF can be suggested for this application.

Lowpass Filter with Wide Stopband Based on T-Shaped Resonator Loaded Step-Impedance Hairpin Resonator

A lowpass filter with wide stopband based on stepped impedance hairpin resonator is proposed. Multiple transmission zeros are created in the stopband region by different size T-shaped resonator to achieve wide stopband. A lowpass filter with 3dB cutoff frequency (fc) at 3.2GHz is designed, simulated and fabricated. Experimental results indicate that stopband can be extended to more than 7fc with a rejection level of 20dB after loading T-shaped resonator. The insertion loss is lower than 0.4dB and return loss is better than 16dB in the passband. Excluding the feed lines, the size of the filter is less than 0.26λg X 0.06λg. The modified filter is of good value in engineering application for its small size, sharp cutoff frequency response and wide stopband.

Panchromatic All‐Polymer Photodetector with Tunable Polarization Sensitivity

AbstractIn this report, a high‐performance all‐polymer organic photodetector that is sensitive to linearly polarized light throughout the visible spectrum is demonstrated. The active layer is a bulk heterojunction composed of an electron donor polymer PBnDT‐FTAZ and acceptor polymer P(NDI2OD‐T2) that have complementary spectral absorption resulting in efficient detection from 350 to 800 nm. The blend film exhibits good ductility with the ability to accommodate large strains of over 60% without fracture. This allows the film to undergo large uniaxial strain resulting in in‐plane alignment of both polymers making the film optically anisotropic and intrinsically polarization sensitive. The films are characterized by UV–vis spectroscopy and grazing incidence wide‐angle X‐ray scattering showing that both polymers have similar in‐plane backbone alignment and maintain packing order after being strained. The films are integrated into devices and characterized under linear polarized light. The strain‐oriented detectors have maximum photocurrent anisotropies of 1.4 under transverse polarized light while maintaining peak responsivities of 0.21 A W−1 and a 3 dB cutoff frequency of ≈1 kHz. The demonstrated performance is comparable to the current state of the art all‐polymer photodetectors with the added capability of polarization sensitivity enabling new application opportunities.

Performance Analysis of Modulation Response of a Designed 1550 nm Oxide Confined Vertical Cavity Surface Emitting Laser

This paper aims to present the impact of using oxidized layer and the effect of oxide aperture size on VCSEL’s modulation performance. After the introduction of oxidized layer, the characteristics of VCSEL have improved immensely, especially in modulation performance. The peak material gain of Al0.06Ga0.24In0.70As/InP MQW VCSEL found from the MATLAB simulation tools has been utilized for investigating the modulation characteristics of the laser model. The optical output power of 27.23 dBm is found at 2.5 mA of current injection. Later, by varying the injection current up to 2.5 mA a maximum frequency of resonance of 10.75 GHz and the equivalent -3dB cut off frequency of 11.85 GHz are achieved. It is seen that with the reduction of oxide aperture size and increase of injection current, the frequency of resonance in addition to the -3dB cut off frequency of the laser increases. The use of oxidized layer and impact of aperture size effect on VCSEL’s -3dB cut off frequency.

High-frequency very long wave infrared quantum cascade detectors

High speed quantum cascade detectors (QCDs) in a very long wave infrared range have been fabricated and characterized. Based on the resonant longitudinal optical-phonon scattering extraction relaxation mechanism, the QCD material behaves at an intrinsically high speed. In order to achieve high speed operation, we integrated microwave technology into the device process to reduce the parasitic parameters and ensure a low time constant of the effective resistance, iInductance, capacitance (RLC) circuit. The peak response is located at 14.2 μm at 77 K. The electrical response characteristics of these QCDs was tested using a microwave rectification technique. The −3 dB cutoff frequency of a 100 × 100 μm2 QCD is 3.2 GHz. The cutoff behavior of our devices were modeled with a second order filter RLC circuit model and showed good agreement with the experimental data.

Design of a Unipolar Barrier for a Nanocrystal-Based Short-Wave Infrared Photodiode

Nanocrystals are promising materials for the design of low-cost, infrared (IR) detectors. Here we focus on HgTe colloidal quantum dots (CQDs) as an active material for detection in the extended short-wave infrared (2.5 μm as cutoff wavelength). In this paper, we propose a strategy to enhance the performances of previously reported photodiodes. In particular, we integrate in this diode a unipolar barrier, whose role is to reduce the dark current injection and subsequently enhance the signal-to-noise ratio. We demonstrate that such unipolar barrier can be designed from another layer of HgTe CQDs with a wider band gap. Using a combination of IR spectroscopy and photoemission, we show that the barrier is resonant with the absorbing layer valence band, while presenting a clear offset with the conduction band. The combination of contacts with improved design and use of a unipolar barrier allows us to reach a detectivity as high as 3 × 108 Jones at room temperature with 3 dB cut off frequency above 10 kHz.

Novel spoof surface plasmon polaritons on a planar metallic strip with periodic semi-elliptical grooves at microwave frequency

ABSTRACTIt is well known that traditional microstrip (MS) transmission lines suffer from high transmission losses at microwave and millimeter wave frequencies. To solve the issue, a novel periodic subwavelength structure is proposed in this work with semi-elliptical grooves (SEGs) on a lateral edge of MS line, for the propagation of spoof surface plasmon polaritons (SSPPs) in the microwave regime. Dispersion relations are analyzed by a numerical method using ANSYS’s HFSS (High-Frequency Structure Simulator), and ability to operate efficiently in primary mode is demonstrated. A comparison with other structures is also accomplished and found that more strong resonant modes are created by the coupling between upper metal strip with textured SEGs and the lower ground layer which are confined near the surface of this grating structure. It has been observed that the cutoff frequency (fc) and the level of field confinement depend on the geometric parameters, and SEG-based SSPPs efficiently minimize the asymptotic frequency by 65% and 12% as compared to MS and Vee-groove structures, respectively. We further investigate a planar and highly efficient, low-pass plasmonic filter with 3 dB cutoff frequency of 11.4 GHz and significantly reduced insertion loss (>−1.9 dB) in the passband. A prototype is fabricated for validation by standard PCB manufacturing process; good agreement between experimental and simulation results confirms the excellent performance of this compact filter in the entire passband with smaller transmission losses. Such a plasmonic metamaterial structure presents a unique and highly unexplored geometry which strongly supports confined SSPPs, therefore, can play a significant role in advanced integrated plasmonics circuitry and applications.

High-Performance Organic Photodetectors from a High-Bandgap Indacenodithiophene-Based π-Conjugated Donor–Acceptor Polymer

A conjugated donor-acceptor polymer, poly[4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-2,7-diyl- alt-5-(2-ethylhexyl)-4 H-thieno[3,4- c]pyrrole-4,6(5 H)-dione-1,3-diyl] (PIDT-TPD), is blended with the fullerene derivative [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) for the fabrication of thin and solution-processed organic photodetectors (OPDs). Systematic screening of the concentration ratio of the blend and the molecular weight of the polymer is performed to optimize the active layer morphology and the OPD performance. The device comprising a medium molecular weight polymer (27.0 kg/mol) in a PIDT-TPD:PC61BM 1:1 ratio exhibits an external quantum efficiency of 52% at 610 nm, a dark current density of 1 nA/cm2, a detectivity of 1.44 × 1013 Jones, and a maximum 3 dB cutoff frequency of 100 kHz at -5 V bias. These results are remarkable among the state-of-the-art red photodetectors based on conjugated polymers. As such, this work presents a functional organic active material for high-speed OPDs with a linear photoresponse at different light intensities.

A miniaturized lowpass bandpass diplexer with high isolation

A new compact and wide band lowpass-bandpass diplexer with simple structure is designed and fabricated in this paper. T shaped and Z shaped resonators are used in the lowpass channel and two coupled open stubs are used in the bandpass channel. The designed diplexer has 3 dB cutoff frequency of 1 GHz in the lowpass channel and operating frequency of 2.4 GHz in the bandpass channel. The obtained insertion losses in the lowpass and bandpass channels are 0.25 dB and 0.58 dB, respectively. The obtained isolation between the two output ports is better than 35 dB. The overall size of the fabricated lowpass bandpass diplexer is obtained 45.6 mm × 28.6 mm, which shows good miniaturization, compared with other similar diplexers.