Search

Silicon nitride (SiN) optical phased arrays (OPAs) have emerged as a potential alternative to their silicon counterparts, owing to their low nonlinearity, easy scalability, and low propagation loss. However, the development of SiN OPAs for light detection and ranging (LiDAR) applications has attracted less attention due to the low thermo–optic (TO) effect of SiN. Moreover, SiN OPAs are considered to be undesirable for transmitters in LiDAR systems because of the limited longitudinal tuning efficiency of SiN grating antenna. We present a hybrid integrated SiN–polymer OPA for realizing an efficient LiDAR. Owing to the large TO effect of polymer, the proposed OPA with polymeric phase modulators resolves the power dissipation drawback of the SiN devices. The polymeric modulators are integrated with a SiN power splitter and grating antenna, and the coupling loss is alleviated via a spot-size converter. Additionally, a steering angle magnifying lens is used to enhance the tuning efficiency of the antenna, expanding the longitudinal beam steering range. The prepared OPA transmitter equipped with the lens exhibits decent two-dimensional beam steering, featuring stable emission characteristics over a 12° × 30° field of view. With the transmitter, efficient time-of-flight based LiDAR is demonstrated to provide a detection range of 10 m under a peak optical power of 55 dBm. The proposed SiN–polymer OPA is highly anticipated to circumvent the challenges of conventional SiN counterparts and potentially spearhead the development of a prominent OPA platform for advanced LiDAR schemes.

Silicon nitride (SiN) optical phased arrays (OPAs) have emerged as a potential alternative to their silicon counterparts, due to their potential use in enhanced solid-state light detection and ranging. Grating antennas based on a SiN waveguide suffer from a limited beam steering efficiency, owing to the relatively lower effective refractive index of the waveguide. To mitigate this limitation, we propose and demonstrate a backward-emitting SiN OPA incorporating a reinforced grating vector, which provides efficient wavelength-tuned beam steering along the longitudinal direction. Two backward-emitting OPAs were primarily characterized by their steering efficiency and the spectral emission for the main lobe, and they were compared with a forward-emitting device using a weakened grating vector. The results indicated that strengthening the grating vector for the antenna improved the beam steering efficiency but adversely affected the dependence of its directionality on the wavelength. The directionality was particularly inspected, with respect to major design parameters for the grating antennas, including the pitch and etch depth of a SiN grating, as well as the thickness of a buried oxide and SiN core layer. The proposed backward-emitting OPA scheme is expected to significantly promote its feasibility as an advanced beam scanning device.

An optical phased array (OPA) in silicon nitride (SiN) is conspicuously highlighted as a vital alternative to its counterpart in silicon. However, a limited number of studies have been conducted on this array in terms of wavelength-tuned beam steering. A SiN OPA has been proposed and implemented with a grating antenna that incorporated an array of shallow-etched waveguides, rendering wavelength-tuned beam steering along the longitudinal direction. To accomplish a superior directionality on a wavelength-tuned beam steering, the spectral beam emission characteristics of the antenna have been explored from the viewpoint of a planar structure that entails a buried oxide (BOX), a SiN waveguide core, and an upper cladding. Two OPA devices having substantially different thicknesses of the resonant cavities, established by combining the BOX and SiN core, were considered theoretically and experimentally to scrutinize the spectral emission characteristics of the antenna on beam steering. Both of the fabricated OPA devices steered light by an angle of 7.4° along the longitudinal direction for a wavelength ranging from 1530 to 1630 nm, while they maintained a divergence angle of 0.2°×0.6° in the longitudinal and lateral directions. Meanwhile, the OPA fabricated on a substantially thick BOX layer featured a limited steering performance to attain a stabilized response over a broad spectral region. We examined the influence of the cavity thickness on the spectral response of the antenna in terms of optical thickness. Based on the two antenna characteristics, it was confirmed that the grating antenna emitted the beam with a higher efficiency when the optical thickness of the cavity corresponded to odd integer multiples of the quarter wavelength. This work is a considerable strategy for designing a stabilized SiN OPA over a desired spectral region.

Background Although hypertension (HTN) is a well-established major risk factor for renal progression in patients with chronic kidney disease (CKD), few studies investigating its role in renal deterioration in the general population with normal renal function (NRF) have been published. Here, we analyzed the correlation between blood pressure (BP) and impaired renal function (IRF) in Korean adults with NRF. Methods Data for the study were collected from the national health screening database of the Korean National Health Insurance Service. Patients whose baseline estimated glomerular filtration rate (eGFR) was less than 60 mL/min/1.73 m2 or whose baseline urinalysis showed evidence of proteinuria were excluded. IRF was defined as an eGFR below 60 mL/min/1.73 m2. We performed follow up for eGFR for 6 years from 2009 to 2015 and investigated IRF incidence according to baseline BP status. We categorized our study population into two groups of IRF and NRF according to eGFR level in 2015. Results During 6 years of follow-up examinations, IRF developed in 161,044 (2.86%) of 5,638,320 subjects. The IRF group was largely older, and the incidence was higher in females and patients with low income, HTN, diabetes mellitus, dyslipidemia, and obesity compared with the NRF group. Subjects whose systolic BP was more than 120 mmHg or whose diastolic BP was more than 70 mmHg had an increased risk of developing IRF compared with subjects with lower BP (odds ratio [OR], 1.037; 95% confidence interval [CI], 1.014–1.061 vs. OR, 1.021; 95% CI, 1.004–1.038). Conclusion BP played a major role in renal progression in the general population with NRF. Strict BP control may help prevent CKD in the general population., Graphical Abstract

Convex combination of two adaptive filters is an efficient method to improve adaptive filter performances. In this paper, a subband convex combination method of two adaptive filters for fast convergence rate in the transient state and low steady state error is presented. The cost function of mixing parameter for a subband convex combination is defined, and from this, the coefficient update equation is derived. Steady state analysis is used to prove the stability of the subband convex combination. Some simulation examples in system identification scenario show the validity of the subband convex combination schemes.

Voltage fluctuations are one of the power quality problems, which cause light flickers. Generally, voltage fluctuations are described as an amplitude modulation (AM). To determine the flicker severity, the flickermeter concept was developed in an IEC 61000-4-15 standard. Flickermeter of IEC 61000-4-15 as an international standard for flicker measurement recommends square demodulation method to detect flicker signals. This paper suggests a new effective method using filter bank to detect and estimate flicker signals, which is effective in comparison with square demodulation method. For the accurate detection of flicker signals, the filter bank is designed with a full consideration of the spectrum characteristics of AM signals. The frequency and magnitude of the detected signals by the filter bank are estimated using recursive method. Computer simulations were performed on synthesized signals to prove validity of the proposed method.

It is well known, combination scheme is suitable for improving the performance of adaptive algorithms. In this paper, we propose a subband combination scheme for sparse impulse response systems. The combination is carried out in subband domain. In this convex combination, SIPNLMS and SNLMS are derived for fast convergence and small steady state error respectively. And mixing parameters are described by minimum mean square error and stochastic gradient algorithm. In adaptive system identification scenario, the advantages of this proposed method are illustrated.

It is very important to detect power quality disturbances effectively in power quality monitoring. In industrial and commercial power systems, voltage sags, voltage swells, transients, and interruptions are main disturbances which affect sensitive equipments. This paper presents a signal processing technique which combines filter bank system and adaptive filter for power quality disturbances detection and localization. In this method, the filter bank system which has binary tree structure is designed for decomposing input power signal to subband signal components. In each subband, adaptive filters are operated as predictor, and the residual values of each adaptive predictor are used to detect power quality disturbances. The usefulness of the proposed method is demonstrated by synthesized signals harmonically.

Tumor lysis syndrome (TLS) is an oncologic emergency that is caused by massive tumor cell lysis. It is commonly associated with hematological cancers like leukemia and lymphoma and uncommonly with solid nonhematologic tumors as well. However, spontaneous tumor lysis syndrome (STLS) without any cytotoxic chemotherapy rarely occurs in solid tumors. We describe a case of STLS in a metastatic adenocarcinoma of unknown primary and review the literature of STLS in solid non-hematologic tumors to identify various risk factors for pathogenesis of this entity.