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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Parity-Time Symmetry in Scattering Problems
摘要： The realization that non-Hermitian parity-time (PT) symmetric Hamiltonians can exhibit entirely real spectra has raised considerable interest in the physics and engineering communities. In the context of optics and photonics, in particular, mathematical analogies with quantum mechanical problem have enabled several breakthrough in terms of observing and utilizing PT-symmetry in closed guided-wave systems. On the other hand, less attention has been paid to the scattering behavior of open PT-symmetric systems. In this chapter, we consider canonical PT-symmetric open systems and explore some of the scattering characteristics of coupled waveguide cavity arrangements. In this regard, we show how an open PT-symmetric configuration can be compared to a closed system, and how the scattering properties are related to the spectral properties of the PT-symmetric system and the associated phase transitions. Afterwards, different scattering geometries are explored in one, two and three dimensions. In addition, we review recent investigations on this topic and highlight opportunities for future research.
关键词： Non-Hermitian Hamiltonians,Parity-Time Symmetry,Optics,Photonics,Scattering Problems
更新于2025-09-10 09:29:36
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Nonlinear manipulation of surface plasmons on graphene-TMDC Bragg reflectors
摘要： In this study, we benefit from the nonlinear optical tunability of the graphene-transition metal dichalcogenide (G-TMDC) heterostructure and the strong confinement of the electromagnetic fields of surface plasmon polaritons (SPPs) on graphene in order to propose a highly tunable nonlinear optical Bragg reflector. Recently, two-dimensional (2D) TMDCs are the subject of intense researches because of their nonlinear optical properties at near infrared wavelengths which are very intriguing for various optical applications. We choose two kinds of 2D-TMDCs, MoSe2 and WSe2, with the strongest second order optical nonlinearity at near infrared range to properly design the periodic variation of the propagating SPP waves on the graphene layer. We utilize theoretical method of quantum electrostatic heterostructure to compute the dielectric function of graphene-TMDCs. Different nonlinearities of two TMDCs lead to noticeable tuning of the full width at half maximum (FWHM) and the central Bragg wavelength of the reflector which let design various optical devices. We design an add/drop filter, a nonlinear switch, and an AND/OR optical logic gate based on our proposed Bragg reflector. Our finite difference time domain numerical and transfer matrix analytical results reveal that by increment of the optical intensity up to 6 MW/cm2 which is below the pulse damage threshold of graphene, due to the second order nonlinearity, a 10-nm red-shift in central Bragg wavelength is observed and the 20-nm FWHM at linear regime decreases to 1.5 nm. The SPP intensities of 0.8 MW/cm2 and 1.53 MW/cm2 fulfill the requirements for AND and OR logical operations with 57 and 66.51 dB extinction ratios, respectively.
关键词： Nonlinear optical materials and devices,Surface plasmons,Nonlinear optics,Optical switches,Bragg grating
更新于2025-09-10 09:29:36
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On-chip programmable pulse processor employing cascaded MZI-MRR structure
摘要： Optical pulse processor meets the urgent demand for high-speed, ultra wideband devices, which can avoid electrical con?nements in various ?elds, e.g., all-optical communication, optical computing technology, coherent control and microwave ?elds. To date, great efforts have been made particularly in on-chip programmable pulse processing. Here, we experimentally demonstrate a programmable pulse processor employing 16-cascaded Mach-Zehnder interferometer coupled microring resonator (MZI-MRR) structure based on silicon-on-insulator wafer. With micro-heaters loaded to the device, both amplitude and frequency tunings can be realized in each MZI-MRR unit. Thanks to its recon?gurability and the pulse processor has exhibited integration ability, versatile functions. First, it can serve as a fractional differentiator whose tuning range is 0.51 – 2.23 with deviation no more than 7%. Second, the device can be tuned into a programmable optical ?lter whose bandwidth varies from 0.15 to 0.97 nm. The optical ?lter is also shape tunable. Especially, 15-channel wavelength selective switches are generated.
关键词： all-optical devices,integrated optics devices,optical processing,pulse shaping
更新于2025-09-10 09:29:36
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High-resolution speckle imaging
摘要： One of the most exciting and challenging pursuits of 21st-century astrophysics is to identify an exoplanet—that is, a planet orbiting an alien sun—on which life may exist. Such a planet is likely to reside in the habitable zone of its sun, meaning that it can harbor liquid water on its surface. Many astrobiologists posit that a life-harboring planet must also be small, rocky, and similar in density to our own. One critical input to any future discovery will be a precise determination of the planet radius, a value that will probably be obtained with the help of high-resolution speckle imaging.
关键词： speckle imaging,exoplanet,adaptive optics,atmospheric turbulence,high-resolution imaging
更新于2025-09-10 09:29:36
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All-optical mode conversion and temperature sensing via transient-grating in step-index fiber
摘要： We demonstrate the formation of Kerr-induced transient long period grating in a standard single-mode ?ber (SMF28) using sub-nanosecond laser pulses and it’s application as an ef?cient all-optical mode conversion and temperature sensing. The ?ber supports LP01 and LP11 spatial modes at 1064 nm wavelength. The beating between two guided modes induces refractive index grating exploiting the Kerr effect. The probe beam co-propagating with the pump at the same wavelength but with different polarization, exhibits ef?cient mode conversion ef?ciency from LP01 to LP11 mode. Temperature sensitivity is measured owing to the change in mode conversion ef?ciency due to the shift in resonant peak wavelength with the increase in temperature. The change in temperature is manifested by the change in spectral power of probe beam at the output. Experimental result demonstrates an average temperature sensitivity of 0.15 Watt/oC. The transient nature of the grating with high sensitivity makes our approach unique from the existing results and can open a route for potential applications.
关键词： Fiber nonlinear optics,optical sensing,Fiber mode coupling
更新于2025-09-10 09:29:36
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An Arbitrated Proxy Blind Signature Based on Hyper Entanglement Analysis
摘要： Motivated by the hyperentangled Bell states analysis, an arbitrated quantum proxy blind signature (QPBS) scheme is developed. Four participants accomplish the task of signing and verifying via exchanging the entanglement of polarization and spatial-mode degrees of freedom. Alice blinds message and sends it to a proxy signatory David who is delegated by the original signatory Charlie. David generates a signature using the delegating code while Bob verifies the signing with the help of an arbitrator Trent. Unlike previous schemes, the verifying phase is no longer executed only by a recipient. Analysis shows that when the even numbers of blinding string always equal 1, the scheme protects the proxy blind signature against forgery and disavow while maintaining the properties of verifiability and identifiability.
关键词： Blind signature,Quantum optics,Proxy signature,Hyper entanglement
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Semi-Physical Integration of Scattering Models for Microwaves and Optical Wavelengths
摘要： Various approaches exist to model scattering of a vegetation canopy above ground in terms of optical and radar wavelengths. Due to the different scattering properties these two spectral regions are modelled separately for visible/ infrared bands and for microwave regions. The newly developed RadOptics model (RO-M) integrates these two spectral regions semi-physically into one radiative transfer (RT)-based model framework, resting on the law of Beer-Bougert-Lambert. Due to the integrative nature of RO-M, it can calculate/simulate the canopy and soil reflectances for the optical and radar spectrum using a single unified model architecture. By Applying RO-M in radar domain (ROR-M) it is shown that the observed dependence of Backscattering coefficient on Leaf Area Index (LAI), soil moisture content and frequency can be simulated consistently with results in literature. The results of the RO-M within the optical domain (ROO-M) present an equivalent trend of reflectance and band ratio values with LAI compared to studies in literature.
关键词： physics,optics,vegetation,modeling,microwaves,soil
更新于2025-09-10 09:29:36
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Hybrid Integration of RF Photonic Systems
摘要： Radio-frequency (RF) photonics is demonstrating superior performance in communication systems using discrete components. As systems establish an upgrade path balancing challenging bandwidth requirements with size, weight, and power constraints, the time is ripe for transition to a more efficient and cost-effective hybrid manufacturing technology. This technology has been applied to the construction of an optical coherent receiver for the down conversion of RF signals from 10–18 to 2 GHz. Light from a distributed feedback semiconductor laser is split between two lithium niobate Mach-Zehnder modulators, driven either by a tunable local oscillator tone or an RF signal coming, for example, from a receiving antenna. The modulated light signals are combined with an optical coupler and filtered by two fiber Bragg gratings that select one optical sideband from each signal. Detection of the filtered light by a balanced photo-detector produces an electrical signal at an intermediate frequency equal to the beat difference between the frequencies of the RF signal and the local oscillator. Packaging of optical and opto-electronic components within a common enclosure where light routing is performed by micro-optics has allowed a significant decrease in the size, weight, and power consumption of the receiver.
关键词： photonic down conversion,optical coherent receiver,tunable receiver,RF photonics,micro-optics,photonic mixer,frequency down conversion,Avionics
更新于2025-09-10 09:29:36
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Generation of Nearly Flattop Ultra-Broadband Response in a QPM Device Using a Phase Shifter
摘要： We have theoretically demonstrated the efficient generation of nearly flattop ultra-broadband response in a periodic quasi-phase matching (QPM) device using a single phase shifter (PS) domain. The flat broadband response is generated using optical parametric generation (OPG) with a QPM device of grating period Λ = 27 μm. The choice of grating period and pump source depends on the group velocities of signal and idler wavelengths to match close to the degeneracy point. We have identified the location of phase shifter domain, which generates a nearly flattop OPG gain bandwidth of ?λ = 1.41 μm. The variations in broadband response are studied when the location and width of phase shifter domains are altered. When compared to a periodic device, the phase shifter domain included QPM structure exhibits higher tolerance to temperature in retaining the smoothness of the broadband response. Furthermore, we have generated the same ultra-broadband response by introducing multiple phase shifter domains at suitable locations in a periodic QPM device.
关键词： optical superlattices,optical mixing,Nonlinear optics,optical harmonic generation
更新于2025-09-10 09:29:36
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Fast Restoration of Aberration-Degraded Extended Object Based on Local Region Abstraction
摘要： The compensating capability of wavefront sensorless adaptive optics (WFSless AO) system for extended object images degraded by aberration is severely limited to correction speed due to largely sized images and low frame rate of camera. To improve the correction capability of WFSless AO system, a method based on local region abstraction (LRA) is presented according to the sparse characteristics of extended object imaging. The experiment results of image restoration with WFSless AO system based on LRA show that the correction speed of this method is 8–20 times faster than that of the previous method for the static aberration, the image restoration speed is improved by about 3.5 times under the dynamic aberration.
关键词： image restoration,correction speed,Adaptive optics system,LRA,aberration
更新于2025-09-10 09:29:36