Search

The study shows that, in waveguide (WG) configuration, the coupling of a 2D plasmonic metamaterial grating (MMG) having a conventional Bragg period along the guide but a distinct period along the transverse axis can lead to Electromagnetically‐Induced‐Transparency (EIT) behavior. This epitomizes that metamaterials, as functional photonic building blocks, can lead to low losses in many standard devices if properly designed. The study reported the observation in passive WGs of a marked Fano‐type EIT resonance with record high‐quality factor: Q = 5000 and contrast >20 dB. Unlike any standard metal grating, MMG‐assisted waveguides exhibit strong grating coupling strength and low‐loss properties simultaneously. This concept is further applied to demonstrate single‐frequency‐emission electrically‐injected Distributed Feedback (DFB) lasers in the near‐infrared telecom domain. The key point is that laser emission occurs at the peak of EIT, i.e., the maximum in transmission. It therefore addresses one of the main critical issues of DFB lasers related to the single frequency yield. The laser performances are state‐of‐the‐art (Ith < 20 mA, Pmax > 20 mW at I = 200 mA, SMSR > 50 dB, optical feedback tolerance >−21 dB compliant with IEEE 802.3 standard). The presented approach, compatible with existing industrial technologies, is promising for real‐life telecom applications. [ABSTRACT FROM AUTHOR]

The Radixact system (Accuray Inc., Sunnyvale, CA) is the latest platform release based on the TomoTherapy technology. The most recent system does not apply a leaf latency model correction after plan optimization to ensure the correct MLC leaf‐open time (LOT) agreement between the TPS and machine delivery. The MLC uses optical sensors to measure the delivered LOTs in real‐time and individual leaf‐specific latency corrections are made to ensure agreement. The aim of this study was to assess the performance of the Radixact MLC with leaf‐specific latency correction using the optical sensor's real‐time feedback. Specifically, the study statistically evaluated the MLC LOT errors observed from 290 plan‐specific quality assurance (PSQA) measurements. Repeatability testing was performed to quantify the uncertainty in the MLC feedback system delivery by analyzing > 1300 delivered treatment fractions throughout the course of radiotherapy. The clinical impact was evaluated by estimating the resulting dose difference in the patient targets due to the measured plan latencies. Our study measured an average plan latency equal to 2.0 ± 0.4 ms (0.6% ± 0.2%) for 290 PSQAs. Repeatability tests showed a mean standard deviation in plan latencies measuring 0.05 ms (0.02%). The deviation from the TPS in the mean target dose due to the plan latencies was estimated to be 0.0% ± 0.2% (range: ‐0.7%–1.1%). The current MLC system with real‐time optical sensor feedback is capable of accurately delivering the TPS‐generated sinograms. Repeatability test results showed that the system allows for high reliability in daily sinogram delivery. The MLC latency deviations were shown to have minimal clinical impact on the overall target dosimetry. [ABSTRACT FROM AUTHOR]

In simulations of radiative‐convective equilibrium (RCE), and with sufficiently large domains, organized convection enhances top of atmosphere outgoing longwave radiation due to the reduced cloud coverage and drying of the mean climate state. As a consequence, estimates of climate sensitivity and cloud feedbacks may be affected. Here, we use a multi‐model ensemble configured in RCE to study the dependence of explicitly calculated cloud feedbacks on the existence of organized convection, the degree to which convection within a domain organizes, and the change in organized convection with warming sea surface temperature. We find that, when RCE simulations with organized convection are compared to RCE simulations without organized convection, the propensity for convection to organize in RCE causes cloud feedbacks to have larger magnitudes due to the inclusion of low clouds, accompanied by a much larger inter‐model spread. While we find no dependence of the cloud feedback on changes in organization with warming, models that are, on average, more organized have less positive, or even negative, cloud feedbacks. This is primarily due to changes in cloud optical depth in the shortwave, specifically high clouds thickening with warming in strongly organized domains. The shortwave cloud optical depth feedback also plays an important role in causing the tropical anvil cloud area feedback to be positive which is directly opposed to the expected negative or near zero cloud feedback found in prior work. Plain Language Summary: Tropical clouds play an important role in the uncertainty associated with understanding how the Earth's climate responds to an imposed warming. Here, we look at how organized cloud systems associated with the tropics affect the processes that govern the climate response to warming. We find that strongly organized cloud systems reduce how strongly the Earth responds to warming. This is primarily associated with the changes in the optical properties of high clouds. These cloud properties impact the overall understanding of the role tropical clouds play in modulating the Earth's temperature and calls into question prior assumptions of its behavior. Key Points: Domains with organized convection have cloud feedbacks with the same sign but larger inter‐model spread than domains without organizationThe cloud feedback parameter is less positive, or even negative, for more strongly organized domainsIn radiative‐convective equilibrium, the tropical anvil cloud area feedback is positive due to the shortwave cloud optical depth feedback [ABSTRACT FROM AUTHOR]

Background and purpose: By employing three surface‐guided radiotherapy (SGRT)‐assisted positioning methods, we conducted a prospective study of patients undergoing SGRT‐based deep inspiration breath‐hold (DIBH) radiotherapy using a Sentine/Catalys system. The aim of this study was to optimize the initial positioning workflow of SGRT‐DIBH radiotherapy for breast cancer. Materials and methods: A total of 124 patients were divided into three groups to conduct a prospective comparative study of the setup accuracy and efficiency for the daily initial setup of SGRT‐DIBH breast radiotherapy. Group A was subjected to skin marker plus SGRT verification, Group B underwent SGRT optical feedback plus auto‐positioning, and Group C was subjected to skin marker plus SGRT auto‐positioning. We evaluated setup accuracy and efficiency using cone‐beam computed tomography (CBCT) verification data and the total setup time. Results: In groups A, B, and C, the mean and standard deviation of the translational setup‐error vectors were small, with the highest values of the three directions observed in group A (2.4 ± 1.6, 2.9 ± 1.8, and 2.8 ± 2.1 mm). The rotational vectors in group B (1.8 ± 0.7°, 2.1 ± 0.8°, and 1.8 ± 0.7°) were significantly larger than those in groups A and C, and the Group C setup required the shortest amount of time, at 1.5 ± 0.3 min, while that of Group B took the longest time, at 2.6 ± 0.9 min. Conclusion: SGRT one‐key calibration was found to be more suitable when followed by skin marker/tattoo and in‐room laser positioning, establishing it as an optimal daily initial set‐up protocol for breast DIBH radiotherapy. This modality also proved to be suitable for free‐breathing breast cancer radiotherapy, and its widespread clinical use is recommended. [ABSTRACT FROM AUTHOR]

The cloud feedback may result in amplification or damping of Arctic warming. Two common techniques used to diagnose the top‐of‐the‐atmosphere cloud feedback are the Adjusted Cloud Radiative Effect (AdjCRE) method and the Cloud Radiative Kernel (CRK) method. We apply both to CMIP5 and CMIP6 model data, finding that the AdjCRE calculated Arctic shortwave cloud feedback is twice as correlated with sea ice loss in CMIP5, and four times in CMIP6, as the CRK method. We find that the CRK method produces Arctic all‐sky residual percentages exceeding 20% in 15 of 18 models. We use the CRK method to decompose the feedback in CMIP5 and CMIP6 finding that its median value changed from negative to positive driven by a less‐negative cloud optical depth feedback. Despite its lack of closure, we conclude that the CRK method is better suited for Arctic SW feedbacks as it is less impacted by surface albedo changes. Plain Language Summary: The cloud feedback is the process by which cloud property changes in a warming climate can either further enhance warming or damp it. The Arctic is warming faster than the rest of the globe, and one of the largest sources of uncertainty in its climate projections is the cloud feedback. There are two popular methods to calculate the cloud feedback: the Adjusted Cloud Radiative Effect technique, and the Cloud Radiative Kernel technique. In this paper we compare the two methods in a suite of climate models by considering the extent to which changes in Arctic sea ice impact the cloud feedbacks. From this analysis we conclude that the Cloud Radiative Kernel method is less affected by sea ice loss. We then apply the Cloud Radiative Kernel technique to data from the two most recent generations of global climate models to investigate how polar day Arctic cloud feedbacks have changed between these generations. We find that the median value of these Arctic feedbacks is slightly positive in the newest generation of models, a change from slightly negative in the previous generation that is largely fueled by a weakening of the feedback associated with changes in cloud optical depth. Key Points: The Cloud Radiative Kernel method is less sensitive to surface albedo changes than the Adjusted Cloud Radiative Effect techniqueThe Cloud Radiative Kernel method provides poor radiative closure in a suite of global climate modelsThe median shortwave Arctic cloud feedback in recent climate models is slightly positive due to a weakened cloud optical depth feedback [ABSTRACT FROM AUTHOR]

The surface temperature‐mediated change in cloud properties, referred to as the cloud feedback, continues to dominate the uncertainty in climate projections. A larger number of contemporary global climate models (GCMs) project a higher degree of warming than the previous generation of GCMs. This greater projected warming has been attributed to a less negative cloud feedback in the Southern Ocean. Here, we apply a novel "double decomposition method" that employs the "cloud radiative kernel" and "cloud regime" concepts, to two data sets of satellite observations to decompose the interannual cloud feedback into contributions arising from changes within and shifts between cloud morphologies. Our results show that contributions from the latter to the cloud feedback are large for certain regimes. We then focus on interpreting how both changes within and between cloud morphologies impact the shortwave cloud optical depth feedback over the Southern Ocean in light of additional observations. Results from the former cloud morphological changes reveal the importance of the wind response to warming increases low‐ and mid‐level cloud optical thickness in the same region. Results from the latter cloud morphological changes reveal that a general shift from thick storm‐track clouds to thinner oceanic low‐level clouds contributes to a positive feedback over the Southern Ocean that is offset by shifts from thinner broken clouds to thicker mid‐ and low‐level clouds. Our novel analysis can be applied to evaluate GCMs and potentially diagnose shortcomings pertaining to their physical parameterizations of particular cloud morphologies. Plain Language Summary: Climate models project that rising levels of greenhouse gas emissions will raise Earth's global mean surface air temperature. However, the amount of warming to be expected remains highly uncertain. A main underlying cause for this uncertainty is the representation of atmospheric clouds in these models. In particular, the response of clouds to global warming, known as the "cloud feedback" over the Southern Ocean has been linked to higher levels of projected warming. To address the uncertainty, we apply a novel method to two satellite data sets. This method teases apart contributions from changing cloud properties such as their horizontal spatial coverage and their ability to reflect sunlight, to the cloud feedback, and then further dissects each of these contributions into those arising from changes occurring both within groups of cloud types and changes occurring between these groups. Results suggest that a general shift from thick storm‐track clouds to thinner oceanic low‐level clouds exacerbates warming in the Southern Ocean but are partially counterbalanced by cloud thickening in part due to stronger near‐surface winds in the same region. Our novel methods and results can potentially be used to evaluate climate models and aid in tracing their shortcomings to poorly represented physical processes. Key Points: MODIS satellite observations indicate that in the Southern Ocean the interannual cloud optical depth feedback is slightly positiveMore frequently occurring thin low‐level clouds and fewer storm‐track clouds contribute to a positive feedback in the Southern OceanStrengthened near‐surface winds contribute to a negative low‐level cloud feedback in the Southern Ocean [ABSTRACT FROM AUTHOR]

The response of tropical high clouds to surface warming and their radiative feedbacks are uncertain. For example, it is uncertain whether their coverage will contract or expand in response to surface warming and whether such changes entail a stabilizing radiative feedback (iris feedback) or a neutral feedback. Global satellite observations with passive and active remote sensing capabilities over the last two decades can now be used to address such effects that were previously observationally limited. Using these observations, we show that the vertically averaged coverage exhibits no significant contraction or expansion. However, we find a reduction in coverage at the altitude where high clouds peak and are particularly radiatively‐relevant. This results in a negative longwave (LW) feedback and a positive shortwave (SW) feedback which cancel to yield a near‐zero high‐cloud amount feedback, providing observational evidence against an iris feedback. Next, we find that tropical high clouds have risen but have also warmed, leading to a positive, but small, high‐cloud altitude feedback dominated by the LW feedback. Finally, we find that high clouds have been thinning, leading to a near‐zero high‐cloud optical depth feedback from a cancellation between negative LW and positive SW feedbacks. Overall, high clouds lead the total tropical cloud feedback to be small due to the negative LW‐positive SW feedback cancellations. Plain Language Summary: Tropical high clouds can have both cooling and heating effects: by reflecting sunlight, they cool the planet and by preventing terrestrial radiation from escaping to space, they also heat the planet. Despite their influence on how much heat gets stored in the Earth system, there is a surprisingly poor understanding of how these clouds will respond to global warming. This uncertainty is largely due to the paucity of observational data. Now, however, instruments aboard satellites orbiting Earth have provided unprecedented data on the changes in the vertical structure of clouds as well as their heat impacts. Our work shows that the dominant signal in the satellite cloud record is the rise of high clouds in response to warming, not any net contraction of coverage. The high clouds are also found to be warming and thinning. Overall, these high cloud changes induce less reflection of sunlight and allow more terrestrial radiation to escape to space. However, these radiative effects cancel and altogether cause no significant heating impact in the tropics. Key Points: Tropical high clouds are rising, warming, thinning, and when vertically averaged, are not contractingTropical high clouds show a positive altitude radiative feedback and near‐zero optical depth and amount radiative feedbacks [ABSTRACT FROM AUTHOR]

The immune regulation of the lymphatic system, especially the lymph node (LN), is of great significance for the treatment of diseases and the inhibition of pathogenic organisms spreading in the body. However, achieving precise spatiotemporal control of immune cell activation in LN in vivo remains a challenge due to tissue depth and off‐target effects. Furthermore, minimally invasive and real‐time feedback methods to monitor the regulation of the immune system in LN are lacking. Here, focused ultrasound responsive immunomodulator loaded nanoplatform (FURIN) with near‐infrared II (NIR‐II) luminescence is designed to achieve spatiotemporally controllable immune activation in LN in vivo. The NIR‐II persistent luminescence of FURIN can track its delivery in LN through bioimaging. Under focused ultrasound (FUS) stimulation, the immunomodulator encapsulated in FURIN can be released locally in the LN to activate immune cells such as dendritic cells and the NIR‐II mechanoluminescence of FURIN provides real‐time optical feedback signals for immune activation. This work points to a FUS mediated, spatiotemporal selective immune activation strategy in vivo with the feedback control of luminescence signals via ultrasound responsive nanocomposite, which is of great significance in improving the efficacy and reducing the side effect of immune regulation for the development of potential immunotherapeutic methods in the future. [ABSTRACT FROM AUTHOR]

This study quantifies the contribution of individual cloud feedbacks to the total short‐term cloud feedback in satellite observations over the period 2002–2014 and evaluates how they are represented in climate models. The observed positive total cloud feedback is primarily due to positive high‐cloud altitude, extratropical high‐ and low‐cloud optical depth, and land cloud amount feedbacks partially offset by negative tropical marine low‐cloud feedback. Seventeen models from the Atmosphere Model Intercomparison Project of the sixth Coupled Model Intercomparison Project are analyzed. The models generally reproduce the observed moderate positive short‐term cloud feedback. However, compared to satellite estimates, the models are systematically high‐biased in tropical marine low‐cloud and land cloud amount feedbacks and systematically low‐biased in high‐cloud altitude and extratropical high‐ and low‐cloud optical depth feedbacks. Errors in modeled short‐term cloud feedback components identified in this analysis highlight the need for improvements in model simulations of the response of high clouds and tropical marine low clouds. Our results suggest that skill in simulating interannual cloud feedback components may not indicate skill in simulating long‐term cloud feedback components. Plain Language Summary: Cloud feedback—the radiative response of clouds to changes in temperature—is determined by the contributions from various cloud types and exhibits large uncertainty. Here, we use satellite observations to evaluate how the individual cloud feedback components in response to interannual variability are represented in the latest generation of climate models. The total cloud feedback is positive in the observations, mainly driven by changes in the altitude of high clouds, changes in the cloud cover over land, and changes in the reflectivity of high and low clouds over extratropical regions. The climate models were driven by observed sea‐surface temperature, sea‐ice conditions, and radiative forcing, so they can be directly compared to the observations. We found the models simulate a total cloud feedback that agrees with the observed positive total cloud feedback in general. However, the models consistently overestimate the decrease of cloud amount over land and in oceanic regions of tropical descent and consistently underestimate the increase of high‐cloud altitude and the decrease of extratropical high‐ and low‐cloud optical depth. Models that better simulate cloud feedback in response to short‐term fluctuations do not perform better in simulating long‐term cloud feedback under global warming. Key Points: Individual short‐term cloud feedback components in climate models are assessed by comparing against satellite observationsModel biases are mainly driven by tropical marine low‐cloud, high‐cloud altitude, and extratropical high‐cloud optical depth feedbacksSkill in simulating short‐term cloud feedbacks is not correlated with skill in simulating long‐term cloud feedbacks [ABSTRACT FROM AUTHOR]

Spectroscopic detection of radiocarbon dioxide (14CO2) offers several advantages, including real‐time detection, on‐site measurement capability, and ease of operation. Here, we propose a novel 14CO2 detection technique that utilizes optical feedback linear cavity enhanced absorption spectroscopy. The feedback phase is actively compensated by adjusting the light path length. The combination of cavity‐based technique and optical feedback enables the recording of stable and enhanced 14CO2 spectra. Through Allan deviation analysis, a minimal detectable 14CO2 concentration of 3.5 parts‐per‐trillion is achieved. This technique has the potential to contribute to the monitoring of the radiocarbon emissions in the air of nuclear power plants. [ABSTRACT FROM AUTHOR]

Multiwavelength plasmonic nanolasers are central to the quest for ultradense and versatile photonic integrations. However, the insufficient optical feedback and mode selection strategies result in a high lasing threshold and multi‐mode operation with limited spectral purity and stability. Here, a multiwavelength near‐infrared plasmonic nanolaser with high mode purity by leveraging a nontrivial "H"‐shape plasmonic cavity is demonstrated. The nanolaser is constructed by inserting InGaAs/GaAs multi‐quantum‐disk (MQD) nanowires into a metallic Fabry‐Perot cavity consisting of a pair of Ag nanowires positioned on an ultrasmooth Au film. The design is endowed with strong optical feedback to enhance the energy transfer between the exciton and plasmon, rendering a significant reduction of the lasing threshold. More importantly, the "H"‐shape cavity is featured with a large flexibility in tuning the resonance wavelength, where multiwavelength lasing with the virtues of single‐mode is realized at room temperature. The results make a crucial step toward near‐infrared multiwavelength plasmonic nanolasers and open up exciting opportunities for applications such as ultracompact photonic integrated circuits and high‐throughput biochemical sensing. [ABSTRACT FROM AUTHOR]

Single‐frequency semiconductor lasers represent a critical role in optical communications, light detection and ranging systems, photonics integrated circuits, etc. Here, combining atom‐like quantum dot (QD) materials and advanced lateral gratings, a high‐power, ultra‐low‐noise 1.3 µm InAs/GaAs QD distributed feedback laser is demonstrated. Stable single‐longitudinal‐mode output power of 100 mW from 25 ℃ to 85 ℃ is achieved with a maximum side mode suppression ratio of 62.6 dB, and the variations of threshold current and slope efficiency over the temperature range are slight, indicting a high temperature stability. A record‐narrow intrinsic linewidth of 1.62 kHz is achieved at 55 ℃ with a white noise level of merely 515 Hz2 Hz–1, and a minimum averaged relative intensity noise of only –166 dB/Hz between 0.1 GHz and 20 GHz is obtained at 25 ℃. Furthermore, a strong tolerance to external optical feedback (〉 –14 dB) is demonstrated in the range from 25 ℃ to 85 ℃, with a maximum value of –8 dB at 85 ℃. This high‐quality single‐frequency laser fabricated with simplified processes and compact size paves the way for its future large‐scale applications such as high‐capacity optical communication, high‐precision optical detection, high‐speed optical interconnections, etc. [ABSTRACT FROM AUTHOR]

Colloidal quantum wells (CQWs) have emerged as a promising class of gain material in various optical feedback configurations. This is due to their unique excitonic features arising from their 1D quantum confinement. However, existing methods for integrating CQW onto microresonators will cause low laser quality due to uneven CQW coating. To overcome this, the use of liquid‐interface kinetically driven self‐assembly is proposed to coat ultrathin, close‐packed layers of colloidal CdSe/Cd1−xZnxS core/shell CQWs between 7 and 14 nm onto the surface of silica microsphere cavities. The fabricated CQW‐whispering‐gallery‐mode microlasers possess a commendable high quality (Q) factor of 13 000 at room temperature. Stable single‐mode lasing output is demonstrated through evanescent field coupling between a CQW‐coated microsphere and a thin uncoated microfiber in a 2D‐3D microcavity configuration. These promising results highlight the suitability of the liquid‐interface kinetically driven self‐assembly method for realizing ultrathin CQW‐coated microlasers and its high compatibility for integrating colloidal nanocrystals onto complex 3D microstructures for future miniaturized colloidal optoelectronic and photonic applications. [ABSTRACT FROM AUTHOR]

Random fiber laser (RFL) utilizing stimulated Raman scattering and distributed random Rayleigh backscattering in fiber as optical gain and feedback mechanisms, respectively, has been developed rapidly in the past decade. Here, it is found, for the first time, that the combination of a high‐order pump and new transmission fiberthat has lower transmission loss, Rayleigh backscattering coefficient, and Raman gain coefficient than standard single‐mode fibercan break the length limits of both random fiber lasing and sensing. With a higher‐order pump and ultralow loss fiber (ULLF), the position of maximum intracavity lasing power can be shifted toward the far end of the fiber span resulting in more remote pump power for the erbium‐doped fiber (EDF) inserted in the fiber span, which plays a dominant role of cavity length extension in RFL. A 200 km ultralong single‐ended RFL and sensor are experimentally demonstrated, which are the longest single‐ended RFL and sensor with functional remote reflectors reported to date. It is believed that the proposed combination of high‐order random lasing and ULLF with EDF can become a general method to extend the working distance of various fiber sensing systems for safety monitoring of ultralong infrastructures, such as power transmission lines and oil/gas pipelines. [ABSTRACT FROM AUTHOR]

Quasi-2D lead halide perovskites have garnered increasing interest as lasing gain media. Relatively simple fabrication, high refractive index, and unique quantum well structure encourage their use in traditional cavity lasers and cavity-free systems called random lasers (RLs). Despite tremendous advances reported thus far, coherent random lasing in quasi-2D perovskite subwavelength films has not been reported. Consequently, coherent optical feedback mechanisms in quasi-2D perovskite systems are still unexplored. Here, this work reports the observation of coherent random lasing in subwavelength quasi-2D perovskite films. Statistical analysis of spectral measurements reveals Lévy-like intensity fluctuations, replica symmetry breaking confirms random lasing, and the coherent modes are studied with spectral and spatial correlation techniques. The observed coherent lasing modes are found to be extended states that arise from the random crystal grain structure during fabrication and span the entire pump volume. These modes out-compete diffusive lasing due to their coherence. [ABSTRACT FROM AUTHOR]

Control over multiple optical elements that can be dynamically rearranged to yield substantial three‐dimensional structural transformations is of great importance to realize reconfigurable plasmonic nanoarchitectures with sensitive and distinct optical feedback. In this work, we demonstrate a transformable plasmonic helix system, in which multiple gold nanoparticles (AuNPs) can be directly transported by DNA swingarms to target positions without undergoing consecutive stepwise movements. The swingarms allow for programmable AuNP translocations in large leaps within plasmonic nanoarchitectures, giving rise to tailored circular dichroism spectra. Our work provides an instructive bottom‐up solution to building complex dynamic plasmonic systems, which can exhibit prominent optical responses through cooperative rearrangements of the constituent optical elements with high fidelity and programmability. [ABSTRACT FROM AUTHOR]

Chip‐scale, electrically‐pumped terahertz (THz) frequency‐combs (FCs) rely on nonlinear four‐wave‐mixing processes, and have a nontrivial phase relationship between the evenly spaced set of emitted modes. Simultaneous monitoring and manipulation of the intermode phase coherence, without any external seeding or active modulation, is a very demanding task for which there has hitherto been no technological solution. Here, a self‐mixing intermode‐beatnote spectroscopy system is demonstrated, based on THz quantum cascade laser FCs, in which light is back‐scattered from the tip of a scanning near‐field optical‐microscope (SNOM) and the intracavity reinjection monitored. This enables to exploit the sensitivity of FC phase‐coherence to optical feedback and, for the first time, manipulate the amplitude, linewidth and frequency of the intermode THz FC beatnote using the feedback itself. Stable phase‐locked regimes are used to construct a FC‐based hyperspectral, THz s‐SNOM nanoscope. This nanoscope provides 160 nm spatial resolution, coherent detection of multiple phase‐locked modes, and mapping of the THz optical response of nanoscale materials up to 3.5 THz, with noise‐equivalent‐power (NEP) ≈400 pW √Hz−1. This technique can be applied to the entire infrared range, opening up a new approach to hyper‐spectral near‐field imaging with wide‐scale applications in the study of plasmonics and quantum science, inter alia. [ABSTRACT FROM AUTHOR]

An active feedback network‐based bandwidth extension technique for CMOS differential transimpedance amplifier (TIA) is proposed in 0.18 µm CMOS process technology. The design consists of three stages in differential mode. The first stage is a common‐source amplifier that minimizes noise. A common collector stage is used for level shifting and buffering in the second stage. The third stage is a differential amplifier that provides additional gain. In addition to these three stages, an active CMOS negative feedback circuit is used for extending the bandwidth. The proposed design achieves a gain of 45.2 dBΩ with a 3 dB bandwidth of 21.23 GHz. The active feedback circuit provides an additional bandwidth of 7.3 GHz. The TIA achieves a data rate of 30 Gb/s with input‐referred noise current density of 63.1 pA/Hz $\sqrt{\mathrm{Hz}}$ and jitter of 9.07 ps. The TIA consumes a power of 10.3 mW with a supply voltage of 1.8 V. [ABSTRACT FROM AUTHOR]

Optical feedback for either the excitation or the signal is an effective approach to enhance the detection sensitivity of Raman scattering spectroscopy. A combination of plasmonic and optical feedback schemes may supply multifold enhancement mechanisms with further improved efficiency. Herein, a plasmonic Bragg grating (PBG) consisting of periodically distributed silver nanoslabs coated onto the sidewalls of the grating lines is reported. Localized surface plasmons excited in the silver nanoslabs with a large width/thickness ratio facilitate enhanced local field and Raman interaction. Asymmetric Bragg diffraction not only supplies optical feedback along the grating plane to extend largely the laser–molecule interaction distance but also enables efficient collection of the Raman signal through back‐diffraction into the detection system. Such a design accomplishes "volume" surface‐enhanced Raman scattering with a modulation depth of more than 500 nm and strong optical feedback, extending largely the limited interaction distance of surface plasmons. With respect to the scheme using Ag films for enhancement, a further enhancement factor larger than 2.8 × 103 has been achieved by the PBG device in the direct detection of the low‐concentration water solution of R6G molecules. The discovered photophysics is potentially important for practical applications in in situ water pollutant detection. [ABSTRACT FROM AUTHOR]

Pure organic room‐temperature phosphorescence (RTP) materials can be used in optoelectronics, biochemical equipment, sensors and biological imaging. In the past few years, dynamic covalent chemistry has attracted significant attention because it provides a new way to produce intelligent optical materials with feedback functions. Two polymers are synthesized through supramolecular‐mediated [4+4] photocyclodimerization of anthracene, which can be reversibly transformed by photoreversible dynamic covalent bonds. The polymers show decent phosphorescence emission with different colors at room temperature, achieving the conversion between blue phosphorescence and cyan phosphorescence. This study provides a novel method for designing and synthesizing pure organic RTP materials with tunable emissions through dynamic covalent bonds. [ABSTRACT FROM AUTHOR]

Herein, recent progress in fiber optofluidic lasers and their applications in biochemical detection are reviewed. The unique properties of optical fibers are introduced for the development of optofluidic microlasers, including high quality factor, small mode volume, high aspect ratio, high reproducibility, and low cost. Optical fiber microresonators based on Fabry–Pérot cavity, microring resonator or photonic bandgap cavity are highlighted to provide optical feedback for optofluidic lasing. For applications, the capability of fiber optofluidic lasers is emphasized to perform biochemical analysis with ultrahigh sensitivity, fast response, high throughput, and disposable optical biodetection. The challenges and prospects for fiber optofluidic lasers are also discussed. [ABSTRACT FROM AUTHOR]

The dynamical properties of an optical neuron formed by a quantum dot semiconductor laser model subjected to optical injection and optical feedback are analyzed. The parameter space spanned by the injection strength and frequency detuning of the optical injection is systematically scanned and modulations of the bifurcation boundaries that induce complex scenarios are found, which enable new opportunities to introduce the optical setup as an optical neuron. The counterintuitive behavior of coherence resonance for different setups of a single‐driven optical neuron under optical feedback is also found. Following the results, the microscopically motivated quantum dot laser rate equation model is reduced to the normal form of a saddle‐node infinite period (SNIPER) bifurcation for low injection strengths and a network of four such SNIPER systems in a globally coupled setup is studied. A new phenomenon is observed, which is called collective coherence resonance. This novel dynamical behavior is connected to the coexistence of a network‐wide SNIPER bifurcation and a change in stability for the synchronized manifold, analyzed via the master stability function. [ABSTRACT FROM AUTHOR]

Perovskite quantum dots (QDs) are of interest for solution‐processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self‐assembly strategy that relies on sodiumd—an assembly director that passivates the surface of the QDs and induces self‐assembly to form ordered three‐dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self‐assembly and superlattice formation. Compared to conventional organic‐ligand‐passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron‐length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter‐dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red‐shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond‐sustained lasing with a threshold of 25 µJ cm–2. [ABSTRACT FROM AUTHOR]

The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of colored DOM to these lakes is an extensively researched topic, but little is known about potential reciprocal feedbacks between the optical properties of DOM and internal microbial processes in the water. We performed 28‐day dark laboratory incubation trials on water from 101 subarctic tundra lakes in northern Sweden, measuring the microbial decay of DOM and the resulting dynamics in colored (CDOM) and fluorescent (FDOM) DOM components. While losses in dissolved oxygen during the incubations corresponded to a 20% decrease in mean DOM, conversely the mean CDOM and total FDOM increased by 22% and 30%, respectively. However, the patterns in microbial transformation of the DOM were not the same in all lakes. Notably, along the gradient of increasing ambient CDOM (water brownness), the lakes showed decreased microbial production of protein‐like fluorescence, lowered DOM turnover rates and decreasing bacterial growth per unit of DOM. These trends indicate that browning of subarctic lakes systematically change the way that bacteria interact with the ambient DOM pool. Our study underscores that there is no unidirectional causal link between microbial processes and DOM optical properties, but rather reciprocal dependence between the two. [ABSTRACT FROM AUTHOR]

Lasing from cells has recently been subject of thorough investigation because of the potential for sensitive and fast biosensing. Yet, lasing from individual cells has been studied in high‐quality resonators, resulting in limited dependence of the lasing properties on the cellular microenvironment. Here, lasing is triggered by cells floating in a low quality factor resonator composed of a disposable poly(methyl methacrylate) (PMMA) cell counting‐slide, hence in absence of conventional high‐reflectivity optical cavities. The exceptional spectral narrowing and the steep slope increase in the input–output energy diagram prove occurrence of laser action in presence of cells. The observed biolasing is an intrinsically dynamic signal, with large fluctuations in intensity and spectrum determined by the optical properties of the individual cell passing through the pump beam. Numerical simulations of the scattering efficiency rule out the possibility of optical feedback from either WGM (whispering gallery mode) or multiple scattering within the cell, and point to the enhanced directional scattering field as the crucial contribution of cells to the laser action. Finally, principal component analysis of lasing spectra measured from freely diffusing cells yields spectral fingerprints of cell populations, which allows discriminating cancer from healthy Rattus glial cells with high degree of confidence. [ABSTRACT FROM AUTHOR]

The concept of lumped optical nanoelements (or metactronics), wherein nanometer‐scale structures act as nanoinductors, nanocapacitors, and nanoresistors, has attracted a great deal of attention as a simple toolbox for engineering different nanophotonic devices in analogy with microelectronics. While recent studies of the topic have been predominantly focused on linear functionalities, nonlinear dynamics in microelectronic devices plays a crucial role and provides a majority of functions, employed in modern applications. Here, the metactronics paradigm is extended and nonlinear dynamical modalities are added to those nanophotonic devices that have never been associated with optical nanoantennas. Specifically, it is shown that nonlinear dimer nanoantennae can operate in the regimes of tristable and astable multivibrators as well as chaos generators. The physical mechanism behind these modalities relies on the Kerr‐type nonlinearity of nanoparticles in the dimer enhanced by a dipolar localized surface plasmon resonance. This allows one to provide a positive nonlinear feedback at moderate optical intensities, leading to the desired dynamical behavior via tuning the driving field parameters. The findings shed light on a novel class of nonlinear nanophotonic devices with a tunable nonlinear dynamical response. [ABSTRACT FROM AUTHOR]

This article studies the feasibility of applying negative feedback structure in continuous Class‐F power amplifiers to improve the gain and efficiency flatness. The operation principle of the negative feedback structure under small and large signal input states is presented. The gain and efficiency are increased at high frequency part and decreased at low frequency by introducing the negative feedback structure, and the flatness is improved. Multiharmonic bilateral pull is used to obtain the optimum impedances, to reduce the interaction between source and load side, and the influence of parasitic parameters. A highly flatness amplifier with the negative feedback structure is designed operating at 1.6‐2.6 GHz by using a Cree GaN HEMT CGH40010H device. The measurement results show a gain flatness of 1.1 dB, and a power‐added efficiency flatness of 9%. [ABSTRACT FROM AUTHOR]

We have demonstrated that the bifurcation patterns can generate by the double Panda‐ring resonator system, where the first system is configured as the input source, while the second system is the feedback control systems. The key concept of the proposal is the two nonlinear side ring resonators that can induce the nonlinear Kerr effect into the center ring. The feedback signals generated from the second ring will induce into the first Panda‐ring, from which the required bifurcation behaviors are obtained. By adjusting the suitable parameters, the simulation results obtained have shown that there are the various exciting bifurcation behaviors in both systems that can be used for the applications such as textile pattern design, information security, and biosensors. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a novel technique for generating ultrashort pulses using a semiconductor laser subject to strong optical feedback from short external cavities. The influence of three system parameters, viz. the external cavity length, the injection current and the feedback strength on the characteristics of the ultrashort pulses is numerically investigated. The results show that the pulse width decreases and the pulse peak increases with increase of any of these three parameters. The repetition frequency of the ultrashort pulses decreases with increase of the feedback strength but increases with increase of the injection current. Based on these results, ultrashort pulses with a pulse width of 3.6 ps and a repetition frequency of 2.3 GHz have been achieved when the injection current is four times the threshold current. The pulse width can be further decreased and the repetition frequency can be further increased by appropriately adjusting the external cavity length and feedback strength. The results presented in this study open up a new route for designing ultrashort pulse generators for incorporation in future photonic integrated optical circuits. [ABSTRACT FROM AUTHOR]

A novel coupled electro‐optic delayed feedback chaotic system is proposed and studied here. Both electrical coupling and optical coupling are used in this model, where electrical coupling is mainly used to suppress the time‐delay signature, and optical coupling is mainly used to improve its complexity. The dynamical performances and complexity are demonstrated, and the simulation results show that the complexity of this model has been greatly improved. Moreover, the time‐delay signature cannot be recognised with a low gain, and the suppress effect will be enhanced by increasing the gain coefficient. Comparing with other recently proposed models, the authors model is competitive in security, and has potential applications in secure communication and random number generation. [ABSTRACT FROM AUTHOR]

ABSTRACT We propose a linear class-D amplifier for the driver stages of RF CMOS linear power amplifiers. To minimize the chip areas for the driver stages of the linear power amplifiers, we propose a technique for the class-D amplifier to be operated as a linear amplifier. The linear gain and proper bias point for the linear operation are obtained with additional load capacitance and a feedback resistor, respectively. To verify the feasibility of the proposed linear class-D amplifier, we designed a 1.8-GHz CMOS linear power amplifier with a differential structure using 180-nm RF CMOS technology. From the measured linearity and maximum average output power with a WCDMA modulated input signal, we successfully verify the linear operation of the proposed linear class-D amplifier. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:565-569, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, 40-Gb/s all-optical 3R regeneration with a monolithic amplified feedback laser (AFL) as the all-optical clock recovery and a semiconductor optical amplifier delayed interferometer (SOA-DI) as the optical decision gate has been experimentally demonstrated. A 40-GHz optical clock with low timing jitter and uniform amplitude was successfully recovered from the polarization mode dispersion (PMD) and noise degraded signal by the AFL. The PMD degraded signal was restored by the 3R regenerator with the Q-factor and the amplitude uniformity improved. Bit-error rate improvement of the noise degraded signal has also been achieved using the 3R regenerator. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:433-436, 2016 [ABSTRACT FROM AUTHOR]

The spaser offers an opportunity to achieve coherent optical sources at nanometer scales due to the extreme confinement of optical fields. However, achievement of spasers with directional propagation in the visible wavelength region remains a challenge thus far, owing to the unique optical feedback mechanism and large dissipative losses of the metal cavity. Here, we experimentally demonstrate for the first time a spaser showing highly directional emission in the visible by using a periodic subwavelength hole array perforated in a metal film, which function as plasmonic nanocavities, along with an organic laser dye to supply gain. The lasing occurs in the red wavelength region and shows a single mode. It is suggested that the optical feedback for spasing is provided by the SPP-Bloch wave, which is supported by the fact that no spasing was attained in aperiodic holes as well as in periodic holes that do not support the SPP-Bloch wave at the spasing wavelength. [ABSTRACT FROM AUTHOR]

A chaotic ultra-wideband (UWB) over fiber link based on optical feedback laser diode which generates the chaotic laser signals is proposed and demonstrated. Flexible generation of up to 1.44 Gb/s on-off keying chaotic-UWB signals is successfully achieved. Without utilizing any dispersion compensation module, the signals with bit rate of 1.44 Gb/s were detected using a digital signal processing receiver after 20-km optical fiber and 0.6-m wireless channel transmission. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1504-1507, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27615 [ABSTRACT FROM AUTHOR]

This paper investigates numerically influence of the external-cavity length on the type of the route-to-chaos of semiconductor lasers under external optical feedback. The study is based on numerical solution of a time-delay model of rate equations, and the solutions are employed to construct bifurcation diagrams and to examine the Fourier frequency spectrum of the laser output. The ratio of the relaxation frequency to the external-cavity resonance frequency is employed to measure the influence of the length of the external cavity. The route-to-chaos is period doubling when this frequency ratio is less than unity. The route is sub-harmonic when the frequency ratio increases up to 2.25. When the frequency ratio increases further, the transition to chaos becomes quasi-periodic characterized by the compound-cavity frequency and the relaxation frequency as well as their difference. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The principles of microwave and feedback theory are independently applied to the analysis of both optical and terahertz-regime multilayer systems. An analogy between the two approaches is drawn, and useful recursion relations, along with a signal-flow approach, are presented for both reflection and transmission cases. These relations, in terms of S-parameters, allow an exact analytical solution for even arbitrary, active, stratified structures, not only for any wavelength in the radio-frequency spectrum, but also for optical wavelengths. This approach also provides a bridge between the microwave and optical bands and leads to beneficial design solutions for intermediate bands such as the THz regime. Comparisons with conventional methodologies are provided using practical multilayer simulations. In addition, graphical design techniques from microwave theory are used along with examples for efficient design and understanding. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1308–1312, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24301 [ABSTRACT FROM AUTHOR]

This paper demonstrates numerical analysis of the dynamics and intensity noise of fibre-grating semiconductor lasers (FGSLs). The induced phenomenon of strong optical feedback (OFB) is analysed. The simulations are based on an improved time-delay rate equations model of a single-mode laser that takes into account the multiple round-trips of the lasing field in the fibre cavity. The analyses are performed in terms of the temporal trajectory of the laser intensity, bifurcation diagram and relative intensity noise (RIN). We explore influence of the fibre-cavity length on the dynamics and RIN. The results show that when the fibre cavity is short, the regime of strong OFB is characterized by either continuous-wave (CW) operation or periodic pulsation. The pulsation frequency is locked at the frequency separation of either the compound-cavity modes or the external fibre-cavity modes. The corresponding RIN level is close to or higher than the level of the solitary laser depending on pulse symmetry. When the fibre cavity is long, the laser exhibits unstable dynamics over wider range of OFB. Moreover, the strong-OFB pulsation becomes beating quasi-periodic at the relaxation oscillation frequency and the fibre-cavity mode-separation frequency. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Traffic load conditions can excite relaxation oscillations in a chain of gain-clamped erbium-doped fiber amplifiers (EDFA) in packet switched WDM optical networks. Crosstalk interaction depends on the delay between packets and cumulates along the amplifier chain, resulting in great power variations between packets, impairing system performance. © 2006 Wiley Periodicals,Inc.Microwave Opt Technol Lett 48:1894–1897, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21781 [ABSTRACT FROM AUTHOR]

A new and novel type of gain-clamped erbium-doped fiber amplifier (EDFA) is characterized the using conventional amplified spontaneous emission interpolation (ASE-I) method and the relatively new time-domain extinction (TDE) technique. The performance difference resulting from the measurement technique gives a gain deviation of 1.3 and 1.8 dB and noise-figure deviation of 0.8 and 1.3 dB for 1550.9-nm and 1553.3-nm input-signal wavelengths, respectively. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 261–264, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20605 [ABSTRACT FROM AUTHOR]

Dynamic gain fluctuations in a ring-laser gain-clamped EDFA submitted to WDM traffic fluctuations are experimentally investigated. We measured the effect of relaxation oscillations that build up with laser action upon the BER on a 10-Gb/s optical transmission. Power penalties up to 1 dB are observed for resonant-traffic fluctuations. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 77–80, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20552 [ABSTRACT FROM AUTHOR]

This paper is an attempt to apply injection locking taking into consideration the effects of antiphase optical feedback. A theoretical and experimental investigation of injection locking on a Fabry-Perot type semiconductor laser is presented, and the effects of the optical feedback (optical self-injection) an explained. In the analysis, the formulation similar to that of Lang is adopted considering the optical self-injection to the injected mode, which corresponds to the free-running mode. The effects of mode jumping arc included preparing the side mode, which is expressed by the rate equation for the photon density with varying modal gain. The calculated results and the experimental results agree well qualitatively. It is shown that with proper self-injection the locking range is nearly four times wider than an ordinary one. [ABSTRACT FROM AUTHOR]

A fundamental and analytical model on optoelectronic integrated functional devices is discussed. In this model, the optoelectronic device with the positive feedback consists of the light emitter and the photodetector, which are electrically connected in series. The positive optical feedback is considered from the light emitter to the photodetector. A steady-state solution is discussed for the optical functions of the device for various parameters. The light emitter is treated as the current-light transducer, and the photodetector is modeled as the resistance which varies with the input-light intensity. The parameters of voltage V, load resistance RL, light feedback ratio β, and conversion efficiency A are introduced. For those parameters, the condition for each optical function of the device is solved. The two cases for the detector characteristics are discussed and the distribution map of functions is obtained. Also, the parameter fitting is made to compare with the experimental results obtained for the hybrid structure and a reasonable agreement is achieved. [ABSTRACT FROM AUTHOR]

Modification of the spectral response of a periodically coupled metallic nanostructure is reported. A thin SU‐8 dielectric cavity was fabricated on a nanopatterned gold film. Additional resonance peaks are observed in the transmitted spectrum due to the interaction between excited surface plasmon polaritons (SPPs) and optical feedback provided by the dielectric cavity. A comparison with transmitted spectra from a planar gold/dielectric cavity configuration confirms the hybridisation of extraordinary optical transmission through interaction between SPPs and optical Fabry‐Pérot modes in the cavity. [ABSTRACT FROM AUTHOR]

A new continuously tunable optoelectronic oscillator based on shifted dispersion‐induced RF‐fading is proposed and experimentally demonstrated. The design provides wideband continuously all‐optical tunability by incorporating the shifted RF‐fading based on a Mach‐Zehnder structure in an optoelectronic feedback loop. By simply varying the path difference between the two arms of the Mach‐Zehnder configuration via an adjustable variable delay line, the fundamental frequency of the oscillator can achieve extremely high and continuous tuning with a frequency upper bound dependent on the delay properties of the variable optical delay line. [ABSTRACT FROM AUTHOR]

The article informs about a new technique for overcoming the ranging limitation of frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) devices using a differential detection scheme between the frequency-fixed carrier and frequency modulated subcarrier. It also mentions how using FMCW-LiDAR devices as three dimensional (3D) imaging sensors could be used in cutting-edge technology such as robotics and autonomous vehicles.

It is shown that although inadvertent weak coherent optical feedback can adversely affect the small-signal response of a directly modulated semi-conductor laser, its effect on large-signal modulation response can be small. The result is of significance to the response of directly modulated lasers in subcarrier multiplexed systems. [ABSTRACT FROM AUTHOR]

The stability of vertical cavity surface emitting lasers with distant external optical feedback is analyzed numerically by using the rate equation model. Results for the different cavity designs are compared. The effects of the nonlinear gain coefficient on RIN and spectral linewidth is investigated. The results can be considered as a guideline to the laser design. [ABSTRACT FROM AUTHOR]

The characterisation of surface roughness is important in process control and metrology. A simple, low cost sensor which can be used for this measurement is one based on laser optical feedback interferometry. A target containing samples of similar abrasive paper with different levels of roughness was characterised using a sensor based on this technique, and the resulting measurements show that the standard deviation of the optical feedback signal was proportional to the roughness of the surface. [ABSTRACT FROM AUTHOR]

This paper describes a symmetry‐breaking plasmonic lattice structure that can support narrow resonances as optical feedback for nanolasing. A scalable technique is developed to fabricate nanocrescent arrays with low‐structural symmetry unit cells to achieve in‐plane quadrupolar lattice plasmon modes. These lattice plasmons with extremely narrow linewidths preserve nonzero net dipole moments under normal excitation. Ultrafast band‐edge lasing can be switched on and off by changing the polarization of the incident pump light. The quadrupolar lattice plasmon lasing process is simulated with a semi‐quantum model and the sharp tips on the nanocrescents accelerate the lasing buildup process and enhance stimulated emission. [ABSTRACT FROM AUTHOR]