High Suppression Ratio Research Articles

Electroencephalographic and Cardiovascular Assessments of Isoflurane-Anesthetized Dogs.

This study investigated the use of frontal electroencephalography (EEG) to monitor varying levels of isoflurane anesthesia in dogs. The patient state index (PSI), burst suppression ratio (SR), and waveforms, were continuously recorded while mean arterial blood pressure (MBP), heart rate, responses to electric stimuli, and subjective anesthetic "depth" were assessed every 3 min. At deep anesthesia (2.5× MAC - 3.2%), the PSI (6.5 ± 10.8) and MBP (45.6 ± 16.4 mmHg) were the lowest, and SR was the highest (78.3 ± 24.0%). At 1× MAC (1.3%), the PSI and MBP increased significantly to 47.8 ± 12.6 and 99.8 ± 13.2, respectively, and SR decreased to 0.5 ± 2.5%. The EEG was predominantly isoelectric at 2×-2.5× MAC, indicating unconsciousness and unresponsiveness. As anesthesia lightened, waveforms transitioned to flatter and faster activity patterns with a response to noxious stimuli, suggesting regained consciousness. The PSI and MBP exhibited a stronger correlation (ρ = 0.8098, p = 0.001) than the relationship of PSI with heart rate (ρ = -0.2089, p = 0.249). Five of the six dogs experienced rough recovery, possibly due to high SR and low MBP. These findings suggest that EEG monitoring in dogs can be a valuable tool for the real-time tracking of brain states and can be used to guide the management of isoflurane anesthesia.

A microwave photonic radio frequency memory with tunable delay resolution and Doppler frequency shift

Radar target simulation is essential for radar development. In this paper, a microwave photonic radio frequency memory (RFM) is proposed and experimentally verified. The input radio frequency (RF) signals are delayed and stored in a recirculating loop with a 4-bit binary optical true time delay line (OTTDL), which enables the achievement of the tunable delay resolution and multiple replications. The Doppler frequency shift (DFS) of the delayed signals is achieved by a Mach-Zehnder modulator (MZM) and two cascaded acousto-optic modulators (AOMs), which facilitate a wide tuning range, high precision, and a high spurious suppression ratio (SSR). The experimental results demonstrate that the system has 16 distinct delay resolutions ranging from 0.045 us to 7.576 us. Furthermore, 30 circulations are achieved in the test, indicating that the theoretical maximum storage time is approximately 225 us. Additionally, the frequency shift for 1 GHz–18 GHz RF pulse signals can be tuned over a range of 10 Hz to 10 MHz, with a SSR exceeding 40 dB.

Microwave Photonics Broadband Doppler Velocity Simulator with High Spurious Suppression Ratio by Using Serrodyne Modulation

A Doppler velocity simulation method based on serrodyne modulation is proposed to achieve the frequency shift from hundred hertz to megahertz. One sub-phase modulation (PM) in a dual-parallel dual-drive Mach–Zehnder modulator loads a sawtooth signal to achieve a small frequency shift of the optical carrier. The other three sub-PMs implement carrier-suppressed double-band modulation of the RF signal. The RF signal is directly coupled from the receiving antenna to the modulator’s RF port without any electrical devices like a 90° hybrid, which ensures a broad operational bandwidth of the system. After filtering out one of the RF modulation sidebands by an optical filter, Doppler frequency shifting (DFS) is realized through frequency beating. The half-wave voltage of modulators rapidly decreases at low frequency shifts, leading to an increase in spurious signals. In order to improve the spurious suppression ratio (SSR) of DFS, a digital pre-distortion compensation based on the measured half-wave voltage is implemented in the frequency domain. Experimental results show that SSRs are larger than 35 dB when frequency shifts range from 0.1 kHz to 1 MHz. The RF operation bandwidth covers 2–40 GHz. The effectiveness of a Doppler velocity simulator is evaluated, and the simulation velocity error is less than 0.06 km/h. The proposed method has potential applications in both broadband electronic warfare and traffic metering applications.

Twelve-channel LAN wavelength-division multiplexer on lithium niobate

Abstract A twelve-channel local-area-network (LAN) wavelength-division multiplexing (LWDM) filter is proposed and demonstrated with a uniform channel spacing of 4.5 nm (800 GHz) in the O-band of 1270–1330 nm by using x-cut lithium-niobate-on-insulator (LNOI) photonic waveguides for the first time. The present LWDM filter consists of twelve single-channel bandpass filters based on multimode waveguide gratings (MWGs) assisted with a TE0/TE1 mode (de)multiplexer. In particular, two stages of MWGs in cascade are introduced for each single-channel bandpass filter, in order to achieve high sidelobe suppression ratios, thus reducing interchannel crosstalk. For the fabricated twelve-channel LWDM filter, all the channels have very excellent box-like spectral responses with low excess losses of ∼0.6 dB, broad 1-dB bandwidths of ∼2.9–3.4 nm (which is close to 75 % of the channel spacing), and ultra-low interchannel crosstalk of <−40 dB in experiments. In addition, the present device is highly tolerant to the random variations of the etching depth (±20 nm) and the grating waveguide width (±20 nm) of the LNOI photonic waveguides, showing great potential for high-capacity WDM systems.

Wideband image-reject RF channelization based on soliton microcombs (invited paper)

Wideband radio frequency (RF) channelization is essential for the reception and detection of cross-band RF signals in various applications, including communications, radar, and spectrum sensing. However, digital channelizers are inefficient at performing RF channelization over a working bandwidth above 10 GHz. Meanwhile, current photonic RF channelizers face challenges in simultaneously considering a wideband, multi-channel, and a high crosstalk suppression ratio. In this work, we proposed and demonstrated a wideband image-reject RF channelization scheme based on integrated dual-soliton microcombs. The dual-soliton microcombs are used for RF spectral copies and heterodyne detection, respectively. Supported by image-reject mixers, the RF channelization is verified with an 8–37 GHz working bandwidth, a 1.2 GHz channel bandwidth, and 25 channels. The image suppression ratio is higher than 34 dB for single-tone signals and 20 dB for wideband signals. Our approach provides an innovative architecture of integrated photonic RF channelizers with high performance, which can benefit a wide range of RF applications by miniaturizing the systems.

Watt-level 1.6 μm dissipative soliton ultrafast laser and external generation of ∼70 fs noise-like pulses for supercontinuum generation

Here, we propose a high power dissipative soliton (DS) laser with a central wavelength of ∼1612 nm. The whole laser system includes the mode-locking oscillator and the corresponding master oscillator power amplifier (MOPA). The mode-locking oscillator is a nonlinear amplifier loop mirror (NALM) cavity, which has a net normal dispersion enabling the generation of nJ-level DS pulses. To further enhance the output power of the 1.6 μm DS pulses, the specially-designed MOPA system consisting of multiple-stage single-pass amplifier is constructed, which can amplify the output power to watt level and meanwhile keeps a high suppression ratio to C-band amplified spontaneous emission (ASE). This high power 1.6 μm DS laser will have further applications in biomedical research and material processing. In the amplifier, we observe the automatic evolution of the DS pulses into the noise-like (NL) pulses under high pumping strength. At the maximum pump power, the MOPA system delivers the NL pulses with an output power of over 2 W. The narrowest spike duration is ∼70 fs (fs). This 1.6 μm fs-scale NL laser is a good pump source for generating the mid-infrared supercontinuum without short wavelength region loss. To demonstrate the superiority of this NL laser, a broad supercontinuum from ∼0.87 μm to ∼3.75 μm waveband is achieved with a piece of highly germanium-doped (Ge-doped) fiber.

Towards a tapered Yb-doped fiber-based narrow linewidth single-mode fiber laser with a high signal to Raman ratio.

We demonstrate an all-fiber high-power narrow-linewidth fiber laser based on a homemade tapered Yb-doped fiber (T-YDF). The laser performance is investigated and systematically compared with different seed powers and pump manners. The experimental results reveal that the injected seed power requires a trade-off designed to take into account the impact of spectral broadening, nonlinear effects, and transverse mode instability (TMI). Compared with the co-pump manner, the counter-pump manner performs well in inhibiting nonlinearities, spectral broadening, and improving the TMI threshold. Under the counter-pump manner, this narrow-linewidth T-YDF amplifier realized a 2.09 kW output power with a 3 dB spectral linewidth of ∼0.34 nm, a beam quality of M2∼1.28 and a high Raman suppression ratio over 53.5 dB, the highest reported power for such a T-YDF-based narrow-linewidth single-mode laser, to the best of our knowledge. This work provides a promising pathway towards implementing monolithic high-power narrow-linewidth single-mode fiber lasers.

Evaluating Injury Severity in Neonatal Encephalopathy Using Automated Quantitative Electroencephalography Analysis: A Pilot Study

Quantitative analysis of electroencephalography (qEEG) is a potential source of biomarkers for neonatal encephalopathy (NE). However, prior studies using qEEG in NE were limited in their generalizability due to individualized techniques for calculating qEEG features or labor-intensive pre-selection of EEG data. We piloted a fully automated method using commercially available software to calculate the suppression ratio (SR), absolute delta power, and relative delta, theta, alpha, and beta power from EEG of neonates undergoing 72 h of therapeutic hypothermia (TH) for NE between April 20, 2018, and November 4, 2019. We investigated the association of qEEG with degree of encephalopathy (modified Sarnat score), severity of neuroimaging abnormalities following TH (National Institutes of Child Health and Development Neonatal Research Network [NICHD-NRN] score), and presence of seizures. Thirty out of 38 patients met inclusion criteria. A more severe modified Sarnat score was associated with higher SR during all phases of TH, lower absolute delta power during all phases except rewarming, and lower relative delta power during the last 24 h of TH. In 21 patients with neuroimaging data, a worse NICHD-NRN score was associated with higher SR, lower absolute delta power, and higher relative beta power during all phases. QEEG features were not significantly associated with the presence of seizures after correction for multiple comparisons. Our results are consistent with those of prior studies using qEEG in NE and support automated qEEG analysis as an accessible, generalizable method for generating biomarkers of NE and response to TH. Additionally, we found evidence of an immature relative frequency composition in neonates with more severe brain injury, suggesting that automated qEEG analysis may have a use in the assessment of brain maturity.

A multiple sensitive attributes data publishing method with guaranteed information utility

AbstractData publishing methods can provide available information for analysis while preserving privacy. The multiple sensitive attributes data publishing, which preserves the relationship between sensitive attributes, may keep many records from being grouped and bring in a high record suppression ratio. Another category of multiple sensitive attributes data publishing, which reduces the possibility of record suppression by breaking the relationship between sensitive attributes, cannot provide the sensitive attributes association for analysis. Hence, the existing multiple sensitive attributes data publishing fails to fully account for the comprehensive information utility. To acquire a guaranteed information utility, this article defines comprehensive information loss that considers both the suppression of records and the relationship between sensitive attributes. A heuristic method is leveraged to discover the optimal anonymity scheme that has the lowest comprehensive information loss. The experimental results verify the practice of the proposed data publishing method with multiple sensitive attributes. The proposed method can guarantee information utility when compared with previous ones.

Breaking the resolution-bandwidth limit of chip-scale spectrometry by harnessing a dispersion-engineered photonic molecule

The chip-scale integration of optical spectrometers may offer new opportunities for in situ bio-chemical analysis, remote sensing, and intelligent health care. The miniaturization of integrated spectrometers faces the challenge of an inherent trade-off between spectral resolutions and working bandwidths. Typically, a high resolution requires long optical paths, which in turn reduces the free-spectral range (FSR). In this paper, we propose and demonstrate a ground-breaking spectrometer design beyond the resolution-bandwidth limit. We tailor the dispersion of mode splitting in a photonic molecule to identify the spectral information at different FSRs. When tuning over a single FSR, each wavelength channel is encoded with a unique scanning trace, which enables the decorrelation over the whole bandwidth spanning multiple FSRs. Fourier analysis reveals that each left singular vector of the transmission matrix is mapped to a unique frequency component of the recorded output signal with a high sideband suppression ratio. Thus, unknown input spectra can be retrieved by solving a linear inverse problem with iterative optimizations. Experimental results demonstrate that this approach can resolve any arbitrary spectra with discrete, continuous, or hybrid features. An ultrahigh resolution of <40 pm is achieved throughout an ultrabroad bandwidth of >100 nm far exceeding the narrow FSR. An ultralarge wavelength-channel capacity of 2501 is supported by a single spatial channel within an ultrasmall footprint (≈60 × 60 μm2), which represents, to the best of our knowledge, the highest channel-to-footprint ratio (≈0.69 μm−2) and spectral-to-spatial ratio (>2501) ever demonstrated to date.

3.3 kW narrow linewidth FBG-based MOPA configuration fiber laser with near-diffraction-limited beam quality

This paper demonstrates a narrow-linewidth fiber laser with near-diffraction-limited beam quality and high Raman suppression ratio by utilizing Master Oscillator Power-Amplifier structure based on narrow-bandwidth fiber Bragg gratings. The output power reaches 3.31 kW with a slope efficiency of 85.0 %. At the maximum output power, the 3 dB, 10 dB, and 20 dB linewidths are 0.40 nm, 1.20 nm, and 3.09 nm, respectively. The beam quality M2 factor is 1.32 and the Raman suppression ratio reaches 26.3 dB. A pair of narrow-bandwidth fiber gratings were used in the oscillator to compress the linewidth of the seed laser. We used backward-pumping configuration and plum-coiled gain fiber in the amplification stage to suppress the Raman effect and select transverse mode by fiber-bending. Finally, a compact all-fiber laser was obtained with narrow-linewidth, high beam quality, and effective suppression of the Raman effect. To the best of our knowledge, this is the highest output power for a sub-nanometer-linewidth laser using narrow-bandwidth fiber gratings and none-wavelength-locked laser diodes, which achieves near-diffraction-limit beam quality. This provides a solution for high-power narrow-linewidth laser sources with high beam quality.

GaSb surface grating distributed feedback interband cascade laser emitting at 3.25 µm.

A second-order distributed feedback interband cascade laser emitting at 3.25 µm was designed, grown, and fabricated. By coherent epitaxy of a GaSb cap layer instead of the conventional thin InAs cap on top of the laser structure, a high-quality surface grating was made of GaSb and gold. Enough coupling strength and a significant inter-modal loss difference were predicted according to the simulation within the framework of couple-wave theory. Lasers having 2-mm-long cavities and 4.5-µm-wide ridges with high-/anti-reflection coatings were fabricated. The continuous-wave threshold current and maximum single-mode output power were 60 mA and 24 mW at 20°C, respectively. The output power of 5 mW was still kept at 55°C. Continuous tuning free from mode hopping and high single-mode suppression ratios (>20 dB) were realized at all injection currents and heat-sink temperatures, covering a spectral range of over 20 cm-1.

Design of Ultracompact High‐Speed‐Integrated Lithium–Niobate Periodic Dielectric Waveguide Modulator

Modern communications and microwave photonics require compact electro‐optic modulators with ultrahigh bandwidth and low power consumption. These requirements can be satisfied by integrated lithium–niobate electro‐optic modulators with high bandwidth and low power consumption. However, most integrated lithium–niobate modulators cannot achieve a good balance between an ultracompact size and a high modulation bandwidth. These challenges are overcome by designing an integrated lithium–niobate periodic dielectric waveguide modulator, featuring a compact modulation length of 87.4 μm, a theoretical modulation bandwidth over 600 GHz, a voltage‐length product of 0.0874 V cm, and a high sideband suppression ratio up to 36.1 dB. These performances are achieved by taking advantage of a capacitor configuration consisting of a nonresonant periodic dielectric waveguides sandwiched between two indium tin oxide (ITO) electrodes. This design provides an ultrabroadband and compact solution to next‐generation communications and microwave photonics.

10 GHz regeneratively mode-locked thulium fiber laser with a stabilized repetition rate.

GHz pulsed thulium-doped fiber laser with stabilized repetition rate can enable a wide range of applications. By employing regenerative mode-locking and cavity stabilization technique, we have for the first time demonstrated a 10 GHz polarization-maintaining thulium-doped fiber laser, which has a long-term repetition-rate stabilization and picosecond timing-jitter. In our experiment, a RF circuitry is designed to extract the 10 GHz longitudinal clock signal so that stable regenerative mode-locking is achieved. A piezo actuator-based phase-lock-loop is used to lock the regeneratively mode-locked pulses to a local reference synthesizer. The regeneratively mode-locked pulses with picosecond pulse width exhibit a high super-mode suppression ratio of 60 dB. In addition, the repetition rate of the laser shows good long-term stability with a variation of 8 Hz in 8 hours, corresponding to a cavity free spectral range fluctuation of less than 16 mHz. Meanwhile, the Allan deviation of the stabilized 10 GHz regeneratively mode-locked pulses is measured to be as low as 2 × 10-12 over 1000 s average time, which is only limited by the stability of the reference synthesizer. Such an ultra-stable 10 GHz pulsed thulium fiber laser may find potential application in 2 µm optical communication, material processing and spectroscopy.

Channel-multiplexing for quasi-distributed acoustic sensing with orthogonal codes.

With the increasing demands for large-scale acoustic sensing in many important fields such as hydrophone, vehicle tracking and pipeline monitoring, optical fiber-based distributed acoustic sensing (DAS) has experienced a rapid development. In recent years, quasi-distributed acoustic sensing (QDAS) based on single mode fiber with enhanced point array has emerged, which is a good approach to improve signal-to-noise ratio and deal with the interference-fading problem in DAS. However, similar to DAS, the performance of QDAS is also limited by the finite frequency domain resources. To break the trade-off between sensing bandwidth and distance, additional frequency domain resources are always needed to multiplex the sensing channel. Multiple-input multiple-output coding technology is an approach to realize QDAS channel-multiplexing with the orthogonal probe waves in the same frequency band. In this paper, the iteration constrain condition of the orthogonal codes is modified, and the generation method of more orthogonal codes with high and consistent suppression ratio for QDAS is provided. In the demonstration experiment, the QDAS has successfully achieved 5 times the sensing bandwidth expansion on a 5.19 km fiber based on 5 new orthogonal codes on the same frequency, with 5 m spatial resolution and 10 p ε/H z strain noise level.

An improved vibration control method of a flexible non-uniform shaped manipulator

This paper presents an improved vibration control method that controls the amplitudes of residual vibrations of a flexible non-uniform shaped manipulator with higher suppression ratio. The proposed new method suppresses the residual vibrations that occur after motion by shaping the velocity input. By considering the parameters of the experimental system, an analytical model is established according to the natural frequency of the system which is effective in the vibrations that occur in the direction of motion. To demonstrate the accuracy of the established model, transient analysis is performed by the Fast Fourier Transform (FFT) method and the resulting dynamic response is compared with the response of the experimental system. The motivation of this study is to add the shaped exponential-harmonic velocity input to the end of the trapezoidal or triangular velocity input to suppress the velocity response that is in the region of the residual vibrations. The effects of changes in the amplitude, frequency, exponential decay factor, phase angle and application time parameters of the exponential-harmonic input on the control of the residual vibration amplitudes are examined. The obtained results are compared with the experimental results and it is observed that the proposed vibration control method has succeeded in suppressing the residual vibrations by up to 99%. Thanks to the proposed method, the time needed for the manipulator to reach the steady-state time at the end of the motion was reduced from 18 s to the motion time.

Performance analysis of reconfigurable multifunctional photonic filters using triple coupled microring resonators

In this paper, we have introduced a new device architecture based on triple coupled microring resonators structure. The analytical model of the device is developed and performance analysis is carried out. The novelty of this device is that it performs as a multifunctional reconfigurable photonic filter in which multiple filtering functions such as notch, bandpass and bandstop responses are achieved by programming the coupling coefficients associated with it using thermal or electro optic tuning. Moreover, it can be used as a tuneable photonic true time delay line. As a bandpass reconfigurable filter, the maximally flat-top rectangular shape like bandpass response of 42 dB suppression ratio, and maximally flat-top bandwidth tunability of 1 GHz to 45 GHz are achieved. The notch filter response has an ultra-high rejection ratio of 148 dB. The flat bottom bandstop response has high suppression ratio of 81.5 dB within 7 GHz bandwidth. The device exhibits minimum group delay distortion over 18 GHz bandwidth, and a minimum of 8 ps and a maximum of 58 ps time delay tunability.

Abstract 376: Confounders of Early Processed EEG to Stratify Neurological Injury After Cardiac Arrest

Introduction: Electroencephalographic suppression ratio (SR) measured six hours after resuscitation from cardiac arrest (SR6) can stratify risk of neurological-etiology death (NED) after cardiac arrest. Confounders of this tool for risk stratification have not been described. Hypothesis: Misclassification of risk of NED by SR6 is explained by characteristics of the patient, arrest, or treatment. Methods: Comatose patients prospectively enrolled in an IRB-approved cardiac arrest database were treated by protocol. Patients with brain death or death after withdrawal of life support measures (WLST) due to poor neurological prognosis were considered NED; neuroprognostication follows European Resuscitation Council guidelines. We analyzed patients misclassified by the SR6; high SR that did not suffer NED, or low SR6 that had NED. We reviewed factors associated with misclassification in bivariate analysis, and performed chart review for potential confounders of SR6. Results: Among 364 patients resuscitated from cardiac arrest and with complete data, SR6 predicted NED with AUC 0.89, and an optimal cutoff value of 55.5%. Forty (11%) patients with high SR6 and 17 (5%) with low SR6 were misclassified. In bivariate analysis, factors associated with high SR misclassification were older age 62.6(±14.9) vs. 56.4 (±16) p=0.02, prior neuropathology [20% vs 9.1%, p=0.049], and longer no-flow time (7 [4-9] vs 5 [2-7] minutes, p=0.01). Those associated with low SR misclassification were heart failure [29.4% vs 11.4%, p=0.045] hypertension [82.4% vs 44.6%, P=0.003], obesity [29.4% vs 10.7%, p=0.04], seizures [47.1% vs 21.5%, p=0.03], and higher BMI 33.9 [26.5-36.1] vs 27.8 [23.7-31.3], p=0.04. In chart review, misclassification was associated with early WLST due to family preference, drug or alcohol overdose, seizures, death due to non-neurological cause, preexisting neurological disease, and “favorable” SR6 trajectory. Conclusion: Age, seizures, drug overdose, and non-neurological causes of death may confound accurate neurological risk stratification using processed EEG very early after cardiac arrest. In addition to these “fixed” confounders, a few patients have dynamic SR that improves after 6 hours, and deserve further study.

Curvature Sensing Setup Based on a Fiber Laser and a Long-Period Fiber Grating

In this letter, a curvature sensing setup based on a fiber ring laser containing a long-period fiber grating (LPFG) is presented. The LPFG operates as a wavelength selective filter and as a curvature sensing head. The LPFG consists of a periodically tapered fiber section written by a CO2-laser glass processing system. The experimental results show that by increasing the curvature values from 0 to 0.266 $\text{m}^{-1}$ , the laser wavelength emission shifts linearly from 1572 to 1560 nm, and a curvature sensitivity of −42.488 nm/ $\text{m}^{-1}$ is achieved. In addition, the laser emission has a linewidth of 0.05 nm, a slope laser efficiency of 0.43%, and a high single-mode suppression ratio (SMSR) of 60 dB. Finally, this fiber laser offers output power stability at room temperature, compactness, and robustness.

Filterless frequency octupling circuit using dual stage cascaded polarization modulators

ABSTRACTThis paper demonstrates the photonic generation of millimetre-wave carriers by frequency octupling of a radio frequency (RF) carrier using a circuit with two parallel arms each containing two polarization modulators in series. The low RF drive power required and the absence of optical filters make this architecture suitable for generating highly stable and tunable optical millimetre-waves. A transfer function representation is used to analyse the operation and a simulation using Virtual Photonic Inc. software package is presented as a proof of concept. The simulation results show very high unwanted optical and electrical side harmonic suppression ratio for a wide range of modulation index compared to the prior art. Further, considering the practical scenario, operating tolerance against the imbalances in the key parameters is established. The unwanted RF sidebands are more than 19 dB and 30 dB below the desired signal power even when a deviation of ±3° is considered in individual RF phase and polarizer angle respectively.