Cavity Configuration Research Articles

Generation of multi-wavelength square pulses in the dissipative soliton resonance regime by a Yb-doped fiber laser* *Project supported by the National Natural Science Foundation of China (Grant No. 41875040), the Natural Science Foundation of Anhui Province, China (Grant No. 2008085MF211), the Foundation for Young Talents in College of Anhui Province (Grant No. gxyqZD2019034), and the Key Natural Science Research Project

Multi-wavelength square pulses are generated in the dissipative soliton resonance (DSR) regime by a Yb-doped fiber laser (YDFL) with a long cavity configuration. The spectral filter effect provided by a passive fiber with low-stress birefringence facilitates the establishment of multi-wavelength operation. Through appropriate control of the cavity parameters, a multi-wavelength DSR pulse can be generated in single- and dual-waveband regions. When the multi-wavelength DSR works in the 1038 nm waveband, the pulse duration can broaden from 2 ns to 37.7 ns. The maximum intra-cavity pulse energy is 152.7 nJ. When the DSR works in the 1038 nm and 1080 nm wavebands, the pulse duration can be tuned from 2.3 ns to 10.5 ns with rising pump power. The emergence of the 1080 nm waveband is attributed to the stimulated Raman scattering (SRS) effect. Our work might help a deeper insight to be gained into DSR pulses in all-normal-dispersion YDFLs.

Single-Port Superluminescent-Diode Gain-Chip for Tunable Single-Wavelength and Dual-Wavelength Blue-Laser

Reconfigurable photonic technology combining multiple functionalities in a single gain-chip is a crucial light-based platform for enabling hybrid applications. Here, we report on achieving a widely tunable and reconfigurable blue laser source using a single-port gain medium based on an InGaN/GaN superluminescent diode (SLD). As compared to tunable laser-diode emitters based solely on stimulated emission from a laser diode used as the gain medium, our amplified spontaneous emission system is capable of fast switching between the stimulated and amplified spontaneous emission regimes for on-demand use of time-incoherent, or time-coherent light with single- or dual-wavelengths. The single- and dual-wavelength laser tunability is designed using various external cavity (EC) configurations for a continuous selection and smooth transition of the emission wavelength from 436 nm to 443 nm. Moreover, the InGaN SLD can amplify the optical power within the EC configuration by 6.5 dB. Thus, the prototype system opens up a viable route for designing reconfigurable light sources based on a single gain chip, and promises disruptive innovation for medical instrumentation, optical sensing technology, and optical communication.

Comparative evaluation of compressive strength of different packable composites with different cavity configurations – An in Vitro Study

Comparative evaluation of compressive strength of different packable composites with different cavity configurations – An in Vitro Study

Tunable Multi-Wavelength Bright-Dark and Dark-Bright Pulse Pairs Fiber Lasers

We have experimentally demonstrated tunable multi-wavelength bright-dark and dark-bright pulse pairs in an all normal dispersion Yb-doped fiber laser (YDFL) with a long cavity configuration. By carefully adjusting the pump power and the polarization state, bright-dark pulse pairs could be converted into dark-bright pulse pairs at the same wavelength. The comb filter provided by the tapered fiber facilitated the formation of the multi-wavelength pulses. And the wavelength-tunable for both bright-dark pulse pairs and dark-bright pulse pairs could be achieved by using a tapered fiber and rotatable polarization controller in the cavity to control the cavity losses. The tunable ranges were 14 nm and 4 nm with wavelength spacings of ~3.5 nm and ~3.7 nm for dual-wavelength pulse pairs and triple-wavelength pulse pairs, respectively.

Spatially resolved fibre cavity ring down spectroscopy

This paper presents a fibre cavity ring down spectroscopy probed by Rayleigh scattering optical frequency domain reflectometry (OFDR), which provides spatial location of stimuli and improved signal to noise ratio for distributed sensing measurements. A section of optical fibre was integrated into an active fibre ring cavity with optical gain and interrogated by the OFDR system for 11 cycles with a single laser scan. Through the cavity ring down configuration, root-mean-squared (RMS) noise of distributed temperature and strain measurements was reduced to 6.9 mK and less than 0.1 με, respectively for 1-cm spatially resolved measurements. Our work shows that the active fibre cavity configuration can be combined with distributed fibre sensing schemes to achieve both high spatial resolution and high sensitivity measurements.

Effect of back cavity configuration on performance of elastic panel acoustic liner with grazing flow

This paper reports a comprehensive numerical study of noise mitigation performance of elastic panel liner comprising an elastic panel and a cavity beneath exposed to low Mach number grazing flow. A time-domain direct aeroacoustic simulation (DAS) seamlessly coupled with panel dynamics is adopted for its least assumptions taken on duct flow unsteadiness and acoustical behaviors so that both linear and nonlinear aeroacoustic-structural interactions of the problem can be fully explored. The numerical method is well validated with theoretical and experimental works on a liner with thick cavity reported in literature. The noise mitigation of liner with various combinations of cavity depth, panel length and cavity shape, are explored and the present numerical results show that back cavity configuration plays an important role in the liner problem. A decomposition method is applied to DAS acoustic solutions for uncovering the role of aeroacoustically induced panel vibration. The nonlinear effect due to aeroacoustic-structural interaction is found to be of secondary importance. Extensive cross spectral analyses between duct aeroacoustics and panel vibration reveal that the overall liner performance is largely determined by the liner elastic panel whose aeroacoustic and vibration responses are greatly modified by the variations of back cavity acoustics of the back cavity with different shapes. Based on these understandings a new configuration with acoustic absorption materials placed on a cavity wall is proposed. Detailed analysis of its numerical results shows that the introduction of acoustic absorption effectively relieves the cavity acoustics and modifies the panel responses in such a way that an enhanced liner mitigation performance over a broadband can be achieved.

All Polarization-maintaining Passively Mode-locked Ytterbium-doped Fiber Lasers, Behavior under Two Different Cavity Configurations

ABSTRACT In this work, we review our recent investigations on the behavior of a polarization-maintaining passively mode-locked ytterbium-doped laser in two different cavity configurations, namely: fiber-ring (FR) and Fabry-Perot (FP). Opposed to standard configurations that rely on the use of strong filtering within the cavity by including an ad hoc component with this purpose, here the filtering action is solely performed by the spectral overlapping of the different components within the fiber lasers. We found that the lack of a specific filter within the cavity does not deteriorate the performance as compared with previous works. We also report the changes in the output light pulses when the net dispersion of the cavity was varied. Additionally, different lengths of an ad hoc anomalous polarization-maintaining (PM) photonic crystal fiber (PCF) were used as intracavity dispersion compensator, to shift the operation of the laser from net-normal to the net-anomalous regime. The shortest output light pulses [6 ps (FR) and 8 ps (FP)] were obtained when the net-cavity dispersion approached zero. Since the obtained light pulses were far to be transform-limited, we also discuss the possibility of out-of-cavity recompression by using the same PM-PCF mentioned above. After recompression, pulse widths of 3 ps were obtained, limited by the available length of PM PCF.

Flow dynamics and azimuthal behavior of the self-excited acoustic modes in axisymmetric shallow cavities

Self-excitation of acoustic resonance in axisymmetric cavities can lead to a complex flow–acoustic coupling, which may result in severe noise generation. In this work, a large eddy simulation is performed to model the different flow–sound coupling mechanisms during the self-excitation of various excitable acoustic modes in an axisymmetric shallow cavity configuration with an aspect ratio of L/d = 1 over the lock-in region. The compressible Navier–Stokes equations are solved at a resolution sufficient to capture the flow and the acoustic dynamics. The excitation of three acoustic modes of different aerodynamic characteristics over the range of the tested flow velocities was observed. These modes are a stationary diametral mode, a spinning diametral mode, and a longitudinal mode. The initiation and separation of vortices over the cavity mouth accompanying the self-excitation of each mode involve different dynamics. If two antisymmetric series of vortical crescents separate successively at the leading edge, a stationary acoustic mode is excited. The formation of a continuously rotating helical vortex, connecting the leading edge and the trailing edge, leads to the excitation of the diametral spinning mode. The excitation of the longitudinal mode is associated with symmetric rings of vortices. Complex patterns of flow velocities and Reynolds stresses in the circumferential direction are observed for the diametral modes but not for the longitudinal mode. In all cases, the excitation of acoustic resonance requires a synchronization of the vortex separation and impingement processes, which is necessary for efficient feedback to sustain the flow–sound coupling mechanism.

Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures

Second harmonic generation and sum frequency generation (SHG and SFG) provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable. They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths. Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics. Here we explore lithographically defined AlGaInP nano(micro)structures/Al2O3/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow- and broadband infrared (IR) wavelength regimes (1300–1600 nm). The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm × 250 nm, with a mode area on the deep subwavelength scale (λ2/135) at fundamental wavelengths. Remarkably, we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides. This together with mode analysis highlights the origin of the improved SHG/SFG efficiency. We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1 µm diameter AlGaInP disks/Al2O3/Ag with a conversion efficiency of 14.8% MW−1 which is five times the SHG value using the narrowband IR source. In both configurations, the hybrid plasmonic structures exhibit >1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts. Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.

Terahertz radiation processes in critically coupled graphene plasmonic nanostructures

Plasmonic excitations in graphene nanostructures provide a particularly effective means to enhance light–matter interactions at THz frequencies. Here, we investigate the use of graphene nanoribbons for narrowband THz light emission based on the excitation of plasmonic oscillations under current injection and their resonant decay into free-space radiation. A detailed theoretical model of the underlying plasmon-enhanced thermal emission mechanism is presented, whose predictions are in good agreement with the recent experimental demonstration of this phenomenon. This model highlights the key role played by the nanostructure absorption efficiency to maximize the output radiation at the plasmonic resonance frequency. Based on this idea, we explore the integration of graphene nanoribbons with nearby metallic antennas in an open cavity configuration in order to promote critical coupling to free-space radiation and correspondingly enhance the absorption (and, therefore, radiation) efficiency by up to two orders of magnitude. The simulation results indicate that this approach is promising for the development of novel THz sources with technologically relevant emission characteristics.

Numerical Investigation of Open Cavities with Parallel Insulated Baffles

This research reports the outcome of a numerical investigation of convection in ventilation square cavities contains parallel insulated baffles. The left and right walls of the cavity are kept at the high temperature. Whereas the top, bottom cavity walls, parallel baffles are adiabatic. The opening slots are positioned at the top, bottom corners of the hot vertical walls. The governing Navier-Stokes equations are formulated in the form of vorticity- stream functions. The finite difference method is used to find the values of the primitive variables. The effects of baffles size (Sb − 0.25, 0.50, 0.75), 3 various positions of the parallel baffle, Rayleigh number (103 − 106), Reynolds number (30, 300, 600) are discussed with the flow fields, isotherms, and Nusselt number. It is found that the behavior of ventilation cavities does not only depend on the size of the baffles and its positions. It highly depends on the configuration of the ventilation cavity too. Further, the flow fields are restricted by the largest baffles size of Sb = 0.75.

High sensitive label-free optical sensor based on Goos\u2013H\xe4nchen effect by the single chirped laser pulse

We consider a four-level molecular system with two ground-state vibrational levels and two excited-state vibrational levels inside a constant cavity configuration. We discuss the reflected and transmitted Goos–Hänchen (GH) shifts of a positive and negative single-chirped laser pulse. The impacts of the laser field detuning, intensity of applied laser field, and appropriately tuning the chirp rate on GH shifts are then analyzed. It is also found that this sensor is very sensitive to the refractive index of the intracavity medium, which can coherently be controlled by the medium parameters. The results show that such a sensor can be most effective for detecting biological molecules with low concentration than the large number density, where a bit variation in the concentration of sample will lead to a great variation on the GH shifts.

Evaluation of Tongue Functions After Free Flap Reconstruction.

Squamous cell carcinoma of the tongue is the most common malignancy of the oral cavity, the lateral border being the commonest site. The treatment strategies mandate surgery followed by appropriate reconstruction as the first line of management. There are many suitable methods of reconstruction of tongue defects after surgery, but the principle of an ideal reconstruction method should provide not only satisfactory structural cosmesis, but also good restoration of function. We present our experience with the skin lined free flaps reconstruction for defects of the tongue and floor of mouth, and present analyses of the functional outcomes of reconstruction. This prospective longitudinal study included 93 patients and was conducted in a tertiary care center in Punjab. All patients underwent free flap reconstruction after tumor removal. The functional outcome of the tongue following reconstruction was evaluated 9months after the completion of treatment. Functions were assessed and matched with sexes and age-matched normal individuals. The data obtained were analyzed by the student 't' test and the p values < 0.05 were considered statistically significant. The duration of swallowing in patients with FRF flap and ALT flap when compared to the normative was significant (< 0.05). There were changes in configuration and volume of the oral cavity after surgery which generates resonant and articulatory alterations, thus the intelligibility of the patient's speech is lowered. There is also a restriction in the tongue movements and reduction in the sensations of the reconstructed part of the tongue. Both the free ALT flap and the FRF flap can provide acceptable functional restoration of the tongue after radical tumor resection.

Implication of geometrical configuration of cavity on combustion performance in a strut-based scramjet combustor

The present work describes the numerical investigation on the implication of the geometrical configuration of a cavity with a strut-based scramjet combustor. Firstly, the combustion characteristics of a combustor with a cavity and the combustor without a cavity are compared and evaluated to portray the effect of a cavity. On the other hand, a separate study is performed to investigate the interplay of cavity parameters namely, length to depth (L/D) ratio of a cavity and angle of a cavity (α) on the performance of a strut-based scramjet combustor. Our study reveals the formation of a strong recirculation zone in the cavity region which improves the mixing and combustion efficiency in the case of a cavity-based combustor. It is observed that the combustion commences relatively earlier in the case of a cavity-based combustor and reaches to its peak value of around 80%. Further, the size of a recirculation region depends on the distance between the strut injector and the length of a cavity. Moreover, the shear layer is observed in the cavity region inducing a weak shock at the trailing edge of a cavity which deteriorates the performance of a scramjet combustor particularly for a higher angle of a cavity(α) and lowers L/D ratio of a cavity. Also, the combustion efficiency is found to be optimal with moderate pressure losses at L/D = 4 and α = 300.

A RARE PRESENTATION OF APICAL HYPERTROPHIC CARDIOMYOPATHY

SESSION TITLE: Fellows Cardiovascular Disease Posters SESSION TYPE: Fellow Case Report Posters PRESENTED ON: October 18-21, 2020 INTRODUCTION: Apical Hypertrophic Cardiomyopathy (AHCM) is an uncommon morphological variant of HCM in which the hypertrophy of the myocardium predominantly involves the apex of the left ventricle. These patients do not have Left ventricular outflow tract (LVOT) obstruction but may have midventricular obstruction. Most patients with AHCM present with no or mild symptoms, although presentation with angina, HF, myocardial infarction, atrial fibrillation (AF), or ventricular fibrillation has been reported. CASE PRESENTATION: A 49yr old male with PMHx of HTN who presented to ED with VFib arrest, shock x1. Patient was sleeping in bed when his wife noticed him snoring and suddenly stopped breathing, gasped for breath. CPR for ∼10 min. EMS arrived and the patient was found to be Vfib and he was shocked . ROCS was achieved and the patient was communicative enroute, never intubated and was hemodynamically stable. Family history was significant for CAD in mother. One sibling with CABG. and another with "Arrhythmia and thick heart muscle". Initial EKG with giant/ deep T inversions in V3-V6 and early repolarization changes in V1,V2 (Figure1). Patient underwent emergent cardiac cath which showed clean coronaries and normal ejection fraction. Spade sign was observed on ventriculogram which is characteristic of Apical Hypertrophic Cardiomyopathy (AHCM)(Figure2). AICD was placed on hospital day (HD) 2 for secondary prevention of cardiac arrest. Patient was discharged on HD 4. DISCUSSION: Typical features of apical HCM include•Audible and palpable fourth heart sound, reflecting impaired LV relaxation•"Giant” negative T waves on electrocardiogram (ECG), particularly in the left precordial leads•"Spade-like” configuration of the LV cavity at end-diastole on imaging•Associated apical wall motion abnormalities which may include hypokinesis and aneurysm formation CONCLUSIONS: APCM is an uncommon and underappreciated. High index of suspicion and early recognition on EKG,echocardiography, left ventriculography, most accurately with CMR will aid in early diagnosis, appropriate close follow-up and management. The long-term prognosis for some morphologic subgroups of AHCM might be better than for other HCM phenotypes. However, up to one fourth of individuals can develop significant morbidity with heart failure, apical fibrosis, apical aneurysm formation, ventricular tachycardia and cardiac arrest. Periodic lifelong follow-up is recommended for asymptomatic patients with AHCM. Family screening should be considered. Symptomatic patients are initially treated with medical therapy; however, since nearly all patients with apical HCM do not have evidence of LVOT or mid cavity obstruction, septal reduction therapy is almost never an option in those patients. Risk stratification for ventricular tachyarrhythmias and SCD is the same as for other patients with HCM and should be considered for prophylactic AICD placement(Figure 3). Reference #1: Maron BJ. Clinical course and management of hypertrophic cardiomyopathy. N Engl J Med. 2018; 379:655–668. Reference #2: Stainback RF. Apical hypertrophic cardiomyopathy. Tex Heart Inst J. 2012;39(5):747-749. Reference #3: Rowin EJ, Maron MS, Chan RH, et al. Interaction of adverse disease-related pathways in hypertrophic cardiomyopathy. Am J Cardiol 2017;120:2256-2264. DISCLOSURES: no disclosure on file for Byoungchul Kim; No relevant relationships by Ratnam Santoshi, source=Web Response No relevant relationships by Rajendra Shetty, source=Web Response

High-Q, directional and self-assembled random laser emission using spatially localized feedback via cracks

Lasers based on Fabry–Pérot or whispering gallery resonators generally require complex fabrication stages and sensitive alignment of cavity configurations. The structural defects on reflective surfaces result in scattering and induce optical losses that can be detrimental to laser performance. On the other hand, random lasers can be simply obtained by forming disordered gain media and scatterers, but they generally show omnidirectional emission with a low Q-factor. Here, we demonstrate directional random lasers with a high Q-factor emission (∼1.5 × 104) via self-assembled microstructural cracks that are spontaneously formed upon radial strain-release of colloidal nanoparticles from the wet to dry phase. The rough sidewalls of cracks facilitate light oscillation via diffuse reflection that forms a spatially localized feedback, and they also serve as the laser out-coupler. These self-assembled cracks exhibit random lasing at optical pump powers as low as tens of μJ/mm2. We demonstrate a wide variety of random lasers from nano- and biomaterials including silica nanoparticles, fluorescent proteins, and biopolymers. These findings pave the way toward self-assembled, configurable, and scalable random lasers for sensing, displays, and communication applications.

High power mode-locked fiber laser with cylindrical vector beam generation

We demonstrate a high power passively mode-locked fiber laser with a linear cavity configuration, which generates cylindrical vector beam (CVB) using few-mode fiber Bragg grating (FM-FBG) as transverse mode separator and nonlinear optical loop mirror as longitudinal mode locker. The laser operating at 1066.9 nm outputs mode-locked CVB pulses with spectral bandwidth of 1.7 nm and repetition rate of 5.026 MHz. The output power reaches 320 mW under pump power of 6.82 W. The CVB purity is over 94 %. The mode-locked CVB fiber laser with simple all-fiber configuration and high output power has important application prospects in material processing, microscopic imaging and so on.

Full-Open Cavity Multi-Wavelength Random Fiber Laser With Double Brillouin Frequency Spacing

A multi-wavelength Brillouin-Raman random fiber laser (BRRFL) with wavelength spacing of double Brillouin frequency shift (BFS) has been proposed for the first time, to the best of our knowledge. This BRRFL has an extremely simple full-open cavity configuration made up of only one roll of fiber, where bidirectional stimulated Raman/Brillouin scattering (SRS/SBS) and Rayleigh scattering based random distributed feedback coexist. In order to further enhance the performance of the BRRFL, a combination of erbium-doped fiber amplifier and single-mode fiber is incorporated into one side for random lasing regeneration. Both the side-mode suppression ratio (SSR) and order number of generated Brillouin Stokes lines (BSLs) show some improvements. A total of 66 BSLs with double BFS spacing has been obtained. Furthermore, the demonstrated laser system offers a wide tunable range with excellent flatness of spectral envelope. The proposed laser featuring simple structure and double BFS spacing would enable promising potentials in optical communication and sensing systems.

Experimental and numerical study on crack development characteristics between two cavities in rock-like material under uniaxial compression

The understanding of failure mechanisms of rocks containing multiple cavities is important for stability assessment of rock excavations in rock engineering applications. However, published research is still limited on the failure mechanism between cavities and quantitative assessment of the crack development characteristics for different cavity configurations. In this research, specimens containing two cavities were investigated for their displacement characteristics and failure mechanisms under uniaxial compression. Digital image correlation (DIC) was used to measure the displacements of the specimens in experiments, while the failure process was modelled using the Particle Flow Code (PFC) software. A density-based clustering method was used to detect micro-crack clusters and the well-known statistical tool of Principal Component Analysis (PCA) was applied innovatively in this work to define the macro-cracks. The clustering method was further developed in this work for vector analysis so that the displacement vectors around macro-cracks could be classified into different types based on the failure mechanism to understand the crack development characteristics. The crack development between two cavities and failure mechanism for different geometrical configurations were subsequently studied in detail using experimental and numerical results.

Exploring entanglement in open cavity parametric oscillators: From triply to doubly resonant cavities

We use a versatile model to evaluate the multipartite entanglement and the nonclassical light generation in optical parametric oscillators, exploring the differences between doubly and triply resonant cavity configurations. We demonstrate the entanglement of the pump mode with converted fields in both situations, and the fundamental differences of oscillators using parametric down conversion and four wave mixing processes as the intracavity amplification technique. The strong correlations involving the sidebands of the pump and converted fields give the signatures of a rich dynamic of multipartite entanglement.