Electrically Reconfigurable Phase-Change Transmissive Metasurface.

Programmable and reconfigurable optics hold significant potential for transforming a broad spectrum of applications, spanning space explorations to biomedical imaging, gas sensing, and optical cloaking. The ability to adjust the optical properties of components like filters, lenses, and beam steering devices could result in dramatic reductions in size, weight, and power consumption in future optoelectronic devices. Among the potential candidates for reconfigurable optics, chalcogenide-based phase change materials (PCMs) offer great promise due to their non-volatile and analogue switching characteristics. Although PCM have found widespread use in electronic data storage, these memory devices are deeply sub-micron-sized. To incorporate phase change materials into free-space optical components, it is essential to scale them up to beyond several hundreds of microns while maintaining reliable switching characteristics. This study demonstrated a non-mechanical, non-volatile transmissive filter based on low-loss PCMs with a 200 µm×200 µm switching area. The device/metafilter can be consistently switched between low- and high-transmission states using electrical pulses with a switching contrast ratio of 5.5 dB. The device was reversibly switched for 1250 cycles before accelerated degradation took place. The work represents an important step toward realizing free-space reconfigurable optics based on PCMs. This article is protected by copyright. All rights reserved.

Erratum: Roadmap for phase change materials in photonics and beyond.

[This corrects the article DOI: 10.1016/j.isci.2023.107946.].

Roadmap for phase change materials in photonics and beyond.

Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their diverse applications in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum. It discusses various device configurations and optimization techniques, including deep learning-based metasurface design. The integration of PCMs with Photonic Integrated Circuits and advanced electric-driven PCMs are explored. PCMs hold great promise for multifunctional device development, including applications in non-volatile memory, optical data storage, photonics, energy harvesting, biomedical technology, neuromorphic computing, thermal management, and flexible electronics.

Electrical programmable multilevel nonvolatile photonic random-access memory.

Photonic Random-Access Memories (P-RAM) are an essential component for the on-chip non-von Neumann photonic computing by eliminating optoelectronic conversion losses in data links. Emerging Phase-Change Materials (PCMs) have been showed multilevel memory capability, but demonstrations still yield relatively high optical loss and require cumbersome WRITE-ERASE approaches increasing power consumption and system package challenges. Here we demonstrate a multistate electrically programmed low-loss nonvolatile photonic memory based on a broadband transparent phase-change material (Ge2Sb2Se5, GSSe) with ultralow absorption in the amorphous state. A zero-static-power and electrically programmed multi-bit P-RAM is demonstrated on a silicon-on-insulator platform, featuring efficient amplitude modulation up to 0.2 dB/µm and an ultralow insertion loss of total 0.12 dB for a 4-bit memory showing a 100× improved signal to loss ratio compared to other phase-change-materials based photonic memories. We further optimize the positioning of dual microheaters validating performance tradeoffs. Experimentally we demonstrate a half-a-million cyclability test showcasing the robust approach of this material and device. Low-loss photonic retention-of-state adds a key feature for photonic functional and programmable circuits impacting many applications including neural networks, LiDAR, and sensors for example.

Electrically reconfigurable non-volatile metasurface using low-loss optical phase-change material.

Active metasurfaces promise reconfigurable optics with drastically improved compactness, ruggedness, manufacturability and functionality compared to their traditional bulk counterparts. Optical phase-change materials (PCMs) offer an appealing material solution for active metasurface devices with their large index contrast and non-volatile switching characteristics. Here we report a large-scale, electrically reconfigurable non-volatile metasurface platform based on optical PCMs. The optical PCM alloy used in the devices, Ge2Sb2Se4Te (GSST), uniquely combines giant non-volatile index modulation capability, broadband low optical loss and a large reversible switching volume, enabling notably enhanced light-matter interactions within the active optical PCM medium. Capitalizing on these favourable attributes, we demonstrated quasi-continuously tuneable active metasurfaces with record half-octave spectral tuning range and large optical contrast of over 400%. We further prototyped a polarization-insensitive phase-gradient metasurface to realize dynamic optical beam steering.

Reconfigurable all-dielectric metalens with diffraction-limited performance.

Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency, especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning in the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles and propose a new figure-of-merit (FOM) tailored for reconfigurable meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 µm wavelength. The reconfigurable metalens features a record large switching contrast ratio of 29.5 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents a key experimental demonstration of a non-mechanical tunable metalens with diffraction-limited performance.

Deep learning modeling approach for metasurfaces with high degrees of freedom.

Metasurfaces have shown promising potentials in shaping optical wavefronts while remaining compact compared to bulky geometric optics devices. The design of meta-atoms, the fundamental building blocks of metasurfaces, typically relies on trial and error to achieve target electromagnetic responses. This process includes the characterization of an enormous amount of meta-atom designs with varying physical and geometric parameters, which demands huge computational resources. In this paper, a deep learning-based metasurface/meta-atom modeling approach is introduced to significantly reduce the characterization time while maintaining accuracy. Based on a convolutional neural network (CNN) structure, the proposed deep learning network is able to model meta-atoms with nearly freeform 2D patterns and different lattice sizes, material refractive indices and thicknesses. Moreover, the presented approach features the capability of predicting a meta-atom's wide spectrum response in the timescale of milliseconds, attractive for applications necessitating fast on-demand design and optimization of a meta-atom/metasurface.

Broadband transparent optical phase change materials for high-performance nonvolatile photonics.

Optical phase change materials (O-PCMs), a unique group of materials featuring exceptional optical property contrast upon a solid-state phase transition, have found widespread adoption in photonic applications such as switches, routers and reconfigurable meta-optics. Current O-PCMs, such as Ge-Sb-Te (GST), exhibit large contrast of both refractive index (Δn) and optical loss (Δk), simultaneously. The coupling of both optical properties fundamentally limits the performance of many applications. Here we introduce a new class of O-PCMs based on Ge-Sb-Se-Te (GSST) which breaks this traditional coupling. The optimized alloy, Ge2Sb2Se4Te1, combines broadband transparency (1-18.5 µm), large optical contrast (Δn = 2.0), and significantly improved glass forming ability, enabling an entirely new range of infrared and thermal photonic devices. We further demonstrate nonvolatile integrated optical switches with record low loss and large contrast ratio and an electrically-addressed spatial light modulator pixel, thereby validating its promise as a material for scalable nonvolatile photonics.

Ultralow Dispersion Multicomponent Thin-Film Chalcogenide Glass for Broadband Gradient-Index Optics.

A novel photothermal process to spatially modulate the concentration of sub-wavelength, high-index nanocrystals in a multicomponent Ge-As-Pb-Se chalcogenide glass thin film resulting in an optically functional infrared grating is demonstrated. The process results in the formation of an optical nanocomposite possessing ultralow dispersion over unprecedented bandwidth. The spatially tailored index and dispersion modification enables creation of arbitrary refractive index gradients. Sub-bandgap laser exposure generates a Pb-rich amorphous phase transforming on heat treatment to high-index crystal phases. Spatially varying nanocrystal density is controlled by laser dose and is correlated to index change, yielding local index modification to ≈+0.1 in the mid-infrared.

Maximum diameter versus volumetric assessment for the response evaluation of vestibular schwannomas receiving stereotactic radiotherapy.

PURPOSE: To explore the feasibility of maximum diameter as a response assessment method for vestibular schwannomas (VS) after stereotactic radiosurgery or fractionated stereotactic radiotherapy (RT), we analyzed the concordance of RT responses between maximum diameters and volumetric measurements. Materials and. METHODS: Forty-two patients receiving curative stereotactic radiosurgery or fractionated stereotactic RT for VS were analyzed retrospectively. Twelve patients were excluded: 4 did not receive follow-up magnetic resonance imaging (MRI) scans and 8 had initial MRI scans with a slice thickness >3 mm. The maximum diameter, tumor volume (TV), and enhanced tumor volume (ETV) were measured in each MRI study. The percent change after RT was evaluated according to the measurement methods and their concordances were calculated with the Pearson correlation. The response classifications were determined by the assessment modalities, and their agreement was analyzed with Cohen kappa statistics. RESULTS: Median follow-up was 31.0 months (range, 3.5 to 86.5 months), and 90 follow-up MRI studies were analyzed. The percent change of maximum diameter correlated strongly with TV and ETV (r(p) = 0.85, 0.63, p = 0.000, respectively). Concordance of responses between the Response Evaluation Criteria in Solid Tumors (RECIST) using the maximum diameters and either TV or ETV were moderate (kappa = 0.58; 95% confidence interval, 0.32-0.85) or fair (kappa = 0.32; 95% confidence interval, 0.05-0.59), respectively. Conclusions: The percent changes in maximum diameter and the responses in RECIST were significantly concordant with those in the volumetric measurements. Therefore, the maximum diameters can be used for the response evaluation of VS following stereotactic RT.

Long-lived monolithic micro-optics for multispectral GRIN applications.

The potential for realizing robust, monolithic, near-surface refractive micro-optic elements with long-lived stability is demonstrated in visible and infrared transmitting glasses capable of use in dual band applications. Employing an enhanced understanding of glass chemistry and geometric control of mobile ion migration made possible with electrode patterning, flat, permanent, thermally-poled micro-optic structures have been produced and characterized. Sub-surface (t~5-10 µm) compositional and structural modification during the poling process results in formation of spatially-varying refractive index profiles, exhibiting induced Δn changes up to 5 × 10-2 which remain stable for >15 months. The universality of this approach applied to monolithic vis-near infrared [NIR] oxide and NIR-midwave infrared [MIR] chalcogenide glass materials is demonstrated for the first time. Element size, shape and gradient profile variation possible through pattern design and fabrication is shown to enable a variety of design options not possible using other GRIN process methodologies.

Self-Organized Freestanding One-Dimensional Au Nanoparticle Arrays.

One-dimensional Au nanoparticle arrays encapsulated within freestanding SiO2 nanowires are fabricated by thermal oxidation of Au-coated Si nanowires with controlled diameter and surface modulation. The nanoparticle diameter is determined by the Si nanowire diameter and Au film thickness, while the interparticle spacing is independently controlled by the Si nanowire modulation. The optical absorption of randomly oriented Au nanoparticle arrays exhibits a strong plasmonic response at 550 nm. Scanning transmission electron microscopy (STEM)-electron energy loss spectrum (EELS) of nanoparticle arrays confirmed the same plasmonic response and demonstrated uniform optical properties of the Au nanoparticles. The plasmonic response in the STEM-EELS maps is primarily confined around the vicinity of the nanoparticles. On the other hand, examination of the same nanowires by energy-filtered transmission electron microscopy also revealed significant enhancement in the plasmonic excitation in the regions in between the nanoparticles. This versatile route to synthesize one-dimensional Au nanoparticle arrays with independently tailorable nanoparticle diameter and interparticle spacing opens up opportunities to exploit enhanced design flexibility and cost-effectiveness for future plasmonic devices.

Titanium dioxide nanowire sensor array integration on CMOS platform using deterministic assembly.

Nanosensor arrays have recently received significant attention due to their utility in a wide range of applications, including gas sensing, fuel cells, internet of things, and portable health monitoring systems. Less attention has been given to the production of sensor platforms in the µW range for ultra-low power applications. Here, we discuss how to scale the nanosensor energy demand by developing a process for integration of nanowire sensing arrays on a monolithic CMOS chip. This work demonstrates an off-chip nanowire fabrication method; subsequently nanowires link to a fused SiO2 substrate using electric-field assisted directed assembly. The nanowire resistances shown in this work have the highest resistance uniformity reported to date of 18%, which enables a practical roadmap towards the coupling of nanosensors to CMOS circuits and signal processing systems. The article also presents the utility of optimizing annealing conditions of the off-chip metal-oxides prior to CMOS integration to avoid limitations of thermal budget and process incompatibility. In the context of the platform demonstrated here, directed assembly is a powerful tool that can realize highly uniform, cross-reactive arrays of different types of metal-oxide nanosensors suited for gas discrimination and signal processing systems.

Fabrication of high performance thin-film transistors via pressure-induced nucleation.

We report a method to improve the performance of polycrystalline Si (poly-Si) thin-film transistors (TFTs) via pressure-induced nucleation (PIN). During the PIN process, spatial variation in the local solidification temperature occurs because of a non-uniform pressure distribution during laser irradiation of the amorphous Si layer, which is capped with an SiO2 layer. This leads to a four-fold increase in the grain size of the poly-Si thin-films formed using the PIN process, compared with those formed using conventional excimer laser annealing. We find that thin films with optimal electrical properties can be achieved with a reduction in the number of laser irradiations from 20 to 6, as well as the preservation of the interface between the poly-Si and the SiO2 gate insulator. This interface preservation becomes possible to remove the cleaning process prior to gate insulator deposition, and we report devices with a field-effect mobility greater than 160 cm(2)/Vs.

Dexamethasone Induces Apoptosis of Nasal Polyp-Derived Tissue Cultures Through JNK and p38 MAPK Activation.

OBJECTIVES: Glucocorticoids, such as dexamethasone (DEX), increase apoptosis in a variety of white cells in nasal polyps and apoptosis is an important factor in the resolution of inflammation. However, the mechanism of glucocorticoids induced apoptosis in nasal polyp remains unclear. In this study the authors evaluated which pathways were engaged in apoptosis induced by DEX in an ex vivo model of nasal polyps. METHODS: Nasal polyp tissues were cultured using an air-liquid interface method. Cultures were maintained in the absence or presence of DEX (10 or 100 µM) for 24 hours. To investigate the involvement of the apoptotic signaling pathways in nasal polyp, such as caspase cascades, Fas-FasL signaling pathway, mitochondrial pathway and p38 mitogen-activated protein kinase (MAPK)/JNK pathway, the authors performed reverse transcription-polymerase chain reaction and Western blotting. RESULTS: The expression ratios of FasL, activated form of caspase-8, caspase-9, and caspase-3 were significantly higher in DEX-treated polyps (P<0.01). In the Bcl-2 family expression, the anti-apoptotic molecules, Bcl-2 and Bcl-XL decreased, but pro-apoptotic molecules, Bax increased, and Bid and Bad were activated. In the conventional MAPKs, JNK, and the phospho-p38 MAPK were significantly higher, but phospho-extracellular signal-regulated kinase (ERK)1/2 was significantly lower in DEX-treated polyps (P<0.01). CONCLUSION: DEX induces apoptosis of nasal polyp via caspase cascades, Fas-FasL signaling pathway, mitochondrial pathway and p38 MAPK/JNK pathway.

Recombinant human BMP-2 enhances osteogenesis of demineralized bone matrix in experimental mastoid obliteration.

CONCLUSIONS: From the results, recombinant human bone morphogenic protein 2 (rhBMP-2) activated demineralized bone matrix (DBM) for the enhancement of bone regeneration. These results might provide a basis for the clinical application of BMP-2 in mastoid obliteration. OBJECTIVE: The purpose of this study was to evaluate the enhanced osteogenesis of rhBMP-2-loaded DBM using a gelatin sponge in the mastoid obliteration model. METHODS: The bulla obliteration was done using rhBMP-2 (0.075 mg/ml)/DBM in experimental group I (n = 7) and rhBMP-2 (0.375 mg/ml)/DBM in experimental group II (n = 7). In the control group (n = 7), the bullae were obliterated using PBS/DBM. To assess the active mineralization of new bone formation, each group received intravenous calcein blue at 4 weeks, oxytetracycline hydrochloride at 8 weeks, and alizarin red at 10 weeks. The animals in each group were sacrificed 12 weeks post-surgery. Osteogenesis was evaluated by in vivo CT and histological observation. RESULTS: The largest amount of bone had formed in experimental group II compared with other groups according to CT and histopathological findings. Histomorphometric analysis showed that there were significant differences between each group. Confocal microscopic findings revealed that three distinct colors that corresponded to sequential osteogenesis were observed in group II. However, poor sequential osteogenesis was observed in the control group.

Formation of silicon nanoparticles by a pressure induced nucleation mechanism.

Formation of silicon nanoparticles (SiNPs) was achieved using excimer laser crystallization of an amorphous Si (a-Si) thin film using a SiO2 capping layer (C/L) with improved thin-film transistor (TFT) performance due to the enlarged grain size of polycrystalline Si (poly-Si). After laser irradiation of an a-Si thin film covered with C/L, fluctuation in the surface morphology of the C/L was observed above the critical laser energy density (Ecr) with the formation of SiNPs. The grain size of the poly-Si layer after crystallization increased abruptly at the same time. A non-uniform pressure distribution beneath the SiO2 C/L was proposed for the initiation of nucleation, which is named pressure induced nucleation (PIN) mechanism. Following nucleation, the release of latent heat made it difficult for the remnant liquid Si to solidify and the volume increased due to the density difference between the liquid and solid Si. Consequently, the pressure on the liquid Si caused SiNPs to sprout through the SiO2 C/L as grains grew from the low temperature to high temperature point. This study offers not only a simple method to fabricate SiNPs with controllable size/density but also larger grain size with lower laser energy density, which leads to higher TFT performance.

Clinical efficacy of initial intratympanic steroid treatment on sudden sensorineural hearing loss with diabetes.

OBJECTIVE: The purpose of this study is to compare the efficacy of intratympanic steroid injection (ITSI) with that of systemic steroids as an initial treatment of sudden sensorineural hearing loss (SNHL) with diabetes. STUDY DESIGN: Prospective, nonrandomized multicenter clinical trial. SETTING: Multicenter study in Busan and Masan, South Korea. SUBJECTS AND METHODS: A total of 114 sudden SNHL patients who were diagnosed with diabetes were divided into peroral (PO) group (n = 48), intravenous (IV) group (n = 32), and intratympanic (IT) group (n = 34). In the PO group, prednisolone was used orally for 10 days, per schedule. In the IV group, prednisolone was administered intravenously for seven days, followed by oral administration of tapered doses for another several days. In the IT group, dexamethasone was injected into the tympanic cavity four times within a two-week period. Hearing outcome was assessed before and after the treatment. RESULTS: All groups showed significant improvement with criteria of 15 dB (P < 0.05). However, there was no significant difference in hearing gain and recovery rate among groups (P > 0.05). Systemic steroid treatment was stopped for two patients in the IV group and for one in the PO group due to uncontrolled hyperglycemia. However, in the IT group, there were no patients who failed to control their blood sugar level. CONCLUSION: ITSI is as effective as systemic steroid treatment for sudden SNHL patients with diabetes and it can avoid undesirable side effects. Therefore, we consider ITSI to be a more reasonable alternative as an initial treatment for sudden SNHL patients with diabetes.

Epitympanoplasty with mastoid obliteration technique: a long-term study of results.

OBJECTIVE: To report the long-term results of epitympanoplasty with mastoid obliteration technique. SUBJECTS AND METHODS: Two hundred adult cases had undergone epitympanoplasty with mastoid obliteration from December 1994 to May 2003. The mean postoperative observation period was 91 months, with a minimum of five years. Epitympanoplasty with mastoid obliteration technique has four major procedures: the widening of the external auditory canal and removal of the scutum; preservation of the posterior canal wall; epitympanoplasty; and mastoid obliteration. We examined postoperative complications and hearing outcomes. RESULTS: There was no retraction pocket formation and recurrence of cholesteatoma. Residual cholesteatoma in the tympanic cavity was seen in 10 cases (5%) and three cases were seen in the mastoid cavity (1.5%). Other complications were otorrhea (15 cases), perforation (8 cases), material extrusion (6 cases), and posterior auricular infection (4 cases). The average preoperative pure tone air-bone gap, postoperative pure tone air-bone gap, and air-bone gap closure were 31.5 +/- 12.4 dB, 25.3 +/- 12.2 dB, and 6.2 +/- 12.6 dB, respectively. There were significant differences between the preoperative and postoperative values (P < 0.01). CONCLUSIONS: The authors believe that epitympanoplasty with mastoid obliteration technique can combine the advantages of canal wall down and canal wall up techniques while improving their shortcomings.

Relationship between bone mineral density and clinical features in women with idiopathic benign paroxysmal positional vertigo.

OBJECTIVE: To evaluate the relationship between bone mineral density (BMD) and clinical features in women with idiopathic benign paroxysmal positional vertigo (IBPPV). STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Patients with BMD measurements made after a diagnosis of IBPPV were included. The IBPPV (n = 78) and control groups (n = 177) were divided into ordinal age categories of similar size. Group A (n = 20) patients were aged 20 to 39 years, Group B (n = 21) patients were aged 40 to 49 years, Group C (n = 18) patients were aged 50 to 59 years, and Group D (n = 19) patients were aged 60 to 69 years. INTERVENTIONS: In each age range, the BMD values were compared according to the number of canalith repositioning maneuvers (CRMs) or the presence of recurrence. We divided all patients into 2 groups with the normal and abnormal BMD values and compared both groups based on the number of CRMs or the frequency of recurrence. MAIN OUTCOME MEASURES: The BMD value, the number of CRMs, and the presence of recurrence. RESULTS: In Groups A, B, and C, there was a significant difference in the BMD values between the control, 1-visit, and 2-or-more-visits subgroups. In Group D, the 2-or-more-visits subgroup had a lower BMD value than other subgroups. The difference in the number of CRMs between the normal and abnormal BMD groups was significant. In Groups A and B, there was a significant difference in the BMD values between the control, first-attack, and recurrent-attacks subgroups. In Groups C and D, the recurrent-attacks subgroup had lower BMD values than other subgroups. The difference in the frequency of recurrence between the normal and abnormal BMD groups was significant. CONCLUSION: Patients with IBPPV had lower BMD values compared with control subjects, and patients with low BMD values showed a significant increase in the number of CRMs required and the recurrence rate.