Showing papers in "Progress in Electromagnetics Research-pier in 2020"
TL;DR: Several state-of-the-art methods of solving ISPs with DL are reviewed, and some insights are offered on how to combine neural networks with the knowledge of the underlying physics as well as traditional non-learning techniques.
Abstract: In recent years, deep learning (DL) is becoming an increasingly important tool for solving inverse scattering problems (ISPs). This paper reviews methods, promises, and pitfalls of deep learning as applied to ISPs. More specifically, we review several state-of-the-art methods of solving ISPs with DL, and we also offer some insights on how to combine neural networks with the knowledge of the underlying physics as well as traditional non-learning techniques. Despite the successes, DL also has its own challenges and limitations in solving ISPs. These fundamental questions are discussed, and possible suitable future research directions and countermeasures will be suggested.
153 citations
TL;DR: In this paper, the superscattering from subwavelength structures in the isotropic environment with near-zero index is theoretically investigated, and it is shown that a smaller n can give rise to a larger single-channel limit.
Abstract: Enhancing the scattering of light from subwavelength structures is of both fundamental and practical significance. While the scattering cross section from each channel cannot exceed the single-channel limit, it is recently reported that the total cross section can far exceed this limit if one overlaps the contribution from many channels. Such a phenomenon about enhancing the scattering from subwavelength structures in free space is denoted as the superscattering in some literature. However, the scatterer in practical scenarios is not always in free space but may be embedded in environments with non-unity refractive index n. The influence of environments on the superscattering remains elusive. Here the superscattering from subwavelength structures in the isotropic environment with near-zero index are theoretically investigated. Importantly, a smaller n can lead to a larger total cross section for superscattering. The underlying mechanism is that a smaller n can give rise to a larger singlechannel limit. Our work thus indicates that the scattering from subwavelength structures can be further enhanced if one simultaneously maximizes the single-channel limit and the contribution from many channels.
39 citations
TL;DR: In this paper, a high gain Fabry-Perot antenna with radar cross section (RCS) reduction property is presented, where a receiver-transmitter metasurface is designed and used as the partially reflective surface (PRS).
Abstract: This paper presents a high gain Fabry-Perot antenna with radar cross section (RCS) reduction property. A receiver-transmitter metasurface is designed and used as the partially reflective surface (PRS) of the antenna to realize high gain and wideband RCS reduction. Firstly, the working principle of the unit cell is similar to the reception and radiation of two patch antennas. The unit cell is designed to present high reflectivity through tuning the impedance matching between two patches. This can ensure that the antenna obtains high gain. Then, the ground plane in the middle makes the reflection phase from different sides of the unit cell be tuned independently. Two unit cells with same reflection phase from the bottom side and 180◦ reflection phase difference from the top side are obtained through tuning the size of the transmitter patch. With the improved chessboard arrangement of these two unit cells, the incident wave can be scattered into many directions. So the metasurface presents a good RCS reduction property. More importantly, thanks to the high reflectivity of the metasurface, almost all the electromagnetic waves from the outside are reflected and rarely enter the cavity. Therefore, the antenna achieves good in band RCS reduction. The measured results of the fabricated antenna agree well with the simulated ones, which verify the correctness of the design. The antennas reaches the maximum gain of 18.2 dBi at 10 GHz. Wideband RCS reduction and good in band RCS reduction are also obtained by the antenna.
37 citations
28 citations
TL;DR: The fundamental implicit FDTD schemes are unconditionally stable and feature the most concise update procedures with matrix-operator-free right-hand sides (RHS), which constitute the basis of unification for many implicit schemes including classical ones.
Abstract: This paper presents an overview and review of the fundamental implicit finite-difference time-domain (FDTD) schemes for computational electromagnetics (CEM) and educational mobile apps. The fundamental implicit FDTD schemes are unconditionally stable and feature the most concise update procedures with matrix-operator-free right-hand sides (RHS). We review the developments of fundamental implicit schemes, which are simpler and more efficient than all previous implicit schemes having RHS matrix operators. They constitute the basis of unification for many implicit schemes including classical ones, providing insights into their inter-relations along with simplifications, concise updates and efficient implementations. Based on the fundamental implicit schemes, further developments can be carried out more conveniently. Being the core CEM on mobile apps, the multiple one-dimensional (M1-D) FDTD methods are also reviewed. To simulate multiple transmission lines, stubs and coupled transmission lines efficiently, the M1-D explicit FDTD method as well as the unconditionally stable M1-D fundamental alternating direction implicit (FADI) FDTD and coupled line (CL) FDTD methods are discussed. With the unconditional stability of FADI methods, the simulations are fast-forwardable with enhanced efficiency. This is very useful for quick concept illustrations or phenomena demonstrations during interactive teaching and learning. Besides time domain, many frequency-domain methods are well-suited for further developments of useful mobile apps as well.
27 citations
TL;DR: This work develops an ultra-wideband frequency selective metasurface (FSmS) that completely encompasses the Ku-band from 12–18 GHz with steep band edges and is optimized by a multi-objective genetic algorithm mimicking evolutionary processes.
Abstract: Metasurfaces enable a new avenue to create electrically thin multi-layer structures, on the order of one-tenth the central wavelength (λc), with engineered responses. Altering the subwavelength spatial features, e.g., λc/80, on the surface leads to highly tunable electromagnetic scattering characteristics. In this work, we develop an ultra-wideband frequency selective metasurface (FSmS) that completely encompasses the Ku-band from 12–18 GHz with steep band edges. The geometrical structure of the metasurfaces is optimized by a multi-objective genetic algorithm mimicking evolutionary processes. Analysis is performed from oneto four-layer metasurface structures with various thicknesses. Computational electromagnetic simulations for these frequency selective metasurfaces are presented, discussed, and experimentally validated. The concepts presented in this work can be applied to design metasurfaces and metamaterials from the microwave to the optical regimes.
27 citations
TL;DR: The purpose of this paper is to review state-ofthe-art methods including both algorithms and hardware implementations in EIT, and offers some insights on classification and comparison for the advanced reconstruction algorithms in mainstream.
Abstract: In recent years, electrical impedance tomography (EIT) has attracted intensive interests due to its noninvasive, ionizing radiation-free, and low-cost advantages, which is promising for both biomedical imaging and industry nondestructive tests. The purpose of this paper is to review state-ofthe-art methods including both algorithms and hardware implementations in EIT. More specifically, for the advanced reconstruction algorithms in mainstream, we offer some insights on classification and comparison. As for the measurement equipment, the structure, configuration modes, and typical systems are reviewed. Furthermore, we discuss the limitations and challenges in EIT technique, such as low-spatial resolution and nonlinear-inversion problems, where future directions, such as solving EIT problems with deep learning, have also been addressed.
23 citations
TL;DR: In this paper, the fundamental theory of orbital angular momentum (OAM) was introduced, and the latest development of OAM in wireless communication was presented, where the controversial topic of whether OAM provides a new degree of freedom was discussed.
Abstract: It becomes more and more challenging to satisfy the long-term demand of transmission capacity in wireless networks if we limit our research within the frame of traditional electromagnetic wave characteristics (e.g., frequency, amplitude, phase and polarization). The potential of orbital angular momentum (OAM) for unleashing new capacity in the severely congested spectrum of commercial communication systems is generating great interest in wireless communication field. The OAM vortex wave/beam has different topological charges, which are orthogonal to each other. It provides a new way for multiplexing in wireless communications. Electromagnetic wave or synthetic beam carrying OAM has a spiral wavefront phase structure, which may provide a new degree of freedom or better orthogonality in spatial domain. In this paper, we introduce the fundamental theory of OAM. Then, OAM generation and reception methods are equally demonstrated. Furthermore, we present the latest development of OAM in wireless communication. We further discuss the controversial topic “whether OAM provides a new degree of freedom” and illustrate our views on the relationship between OAM and MIMO. Finally, we suggest some open research directions of OAM.
19 citations
TL;DR: In this article, the impact of group velocity dispersion (GVD) on topological photonics in a one-dimensional ring resonator array has been investigated, and it is shown that the GVD brings a natural vague boundary in the frequency dimension, so the topological edge state still propagates at several frequency modes unidirectionally along the spatial axis.
Abstract: We recently proposed a two-dimensional synthetic space including one spatial axis and one synthetic frequency dimension in a one-dimensional ring resonator array [Opt. Lett., Vol. 41, No. 4, 741–744, 2016]. Nevertheless, the group velocity dispersion (GVD) of the waveguides that compose rings was ignored for simplicity. In this paper, we extend the previous work and study the topological one-way edge states in such a synthetic space involving GVD. We show that the GVD brings a natural vague boundary in the frequency dimension, so the topological edge state still propagates at several frequency modes unidirectionally along the spatial axis. Positions of such vague boundary can be controlled by changing the magnitude of the GVD. In particular, a relatively strong GVD can degrade this two-dimensional synthetic space to one-dimensional spatial lattice, but yet the one-way state is still preserved in simulations. Our work therefore exhibits the impact of the GVD on topological photonics in the synthetic space, which will be important for future practical experimental implementations.
19 citations
TL;DR: In this article, a 3D metallic structure using the 3D printing technique has been designed and fabricated for the consideration of the required bands, and the volume size of the antenna element is 163 × 61.9 × 10 mm3.
Abstract: This paper presents a design study of a shark-fin antenna for future railway communications. Three specific bands are considered here as LTE-R (700 MHz), LTE (2100 MHz), and Lower 5G band (3500 MHz). A 3-D metallic structure using the 3D printing technique has been designed and fabricated for the consideration of the required bands. The volume size of the antenna element is 163 × 61.9 × 10 mm3. The multi-physical simulations in terms of the smooth air flow and lower drag coefficient are performed for analyzing the need of shark-fin radome cover. More than 70 MHz bandwidth was observed for the LTE-R band and also a wide band response from 1.4 GHz to 4.2 GHz was observed that cover the required bands well, i.e., the LTE, and Lower 5G band. The proposed shark-fin antenna results in the expected omnidirectional radiation pattern in the horizontal plane, with the radiation efficiency of 71.7%, 92.6%, and 96.4% in the railway environment for the LTE-R, LTE, and Lower 5G band frequency, respectively.
16 citations
TL;DR: Good agreement between simulated and measured results is obtained in all the three operating states of the design, which makes it suitable for compact reconfigurable systems.
Abstract: In this work, a Tri-Band frequency reconfigurable antenna for LTE (Long Term Evolution)/WiFi (Wireless Fidelity)/ITS (Intelligent Transportation Systems) applications is presented. The proposed design consists of a wine glass shaped slotted radiating patch along with a switchable rectangular ring type slot on the ground plane. This structure operates in three different states viz. state1, state-2, and state-3 at 4.5 GHz (LTE band), 5.9 GHz (ITS band), and 3.8 GHz (LTE band)/5GHz (Wi-Fi band), respectively, with an overall compact size of 30×30×0.762 mm3. Multi-band resonances are obtained by incorporating slots in the main radiating element and ground plane. Moreover, switching among these bands is achieved by placing two PIN diodes at optimized positions on the rectangular ring slot in the ground plane. For the proposed design, good agreement between simulated and measured results is obtained in all the three operating states of the design, which makes it suitable for compact reconfigurable systems.
TL;DR: In this paper, the problem of evaluating the shielding effectiveness of a thin metallic circular disk with finite conductivity against an axially symmetric vertical magnetic dipole is addressed, and a low-frequency solution is finally extracted in a closed form.
Abstract: The problem of evaluating the shielding effectiveness of a thin metallic circular disk with finite conductivity against an axially symmetric vertical magnetic dipole is addressed. First, the thin metallic disk is modeled through an appropriate boundary condition, and then, as for the perfectly conducting counterpart, the problem is reduced to a set of dual integral equations which are solved in an exact form through the application of the Galerkin method in the Hankel transform domain. A second-kind Fredholm infinite matrix-operator equation is obtained by selecting a suitable set of basis functions. A low-frequency solution is finally extracted in a closed form. Through a comparison with results obtained from a full-wave commercial software, it is shown that such a simple approximate solution is accurate up to the frequency where the surface-impedance model of the thin disk is valid.
TL;DR: The algorithm can distinguish the two types of patients effectively: the average accuracy of classification on the test set can reach 96.2% stably and this algorithm may be critical for the early detection and precise treatment for the patients with mood disorders.
Abstract: A variety of psychological scales are utilized at present as the most important basis for clinical diagnosis of mood disorders. An experienced psychiatrist assesses and diagnoses mood disorders based on clinical symptoms and relevant assessment scores. This symptom based clinical criterion is limited by the psychiatrist’s experience. In practice, it is difficult to distinguish the patients with bipolar disorder with depression episode (bipolar depression, BD) from those with major depressive disorder (MDD). The functional near-infrared spectroscopy (fNIRS) technology is commonly used to perceive the emotions of a human. It measures the hemodynamic parameters of the brain, which correlate with cerebral activation. Here, we propose a machine learning classification method based on deep neural network for the brain activations of mood disorders. Large time scale connectivity is determined using an attention long short term memory neural network and short-time feature information are considered using the InceptionTime neural network in this method. Our combined method is referred to as AttentionLSTM-InceptionTime (ALSTMIT). We collected fNIRS data of 36 MDD patients and 48 BD patients who were in the depressed state. All the patients were monitored by fNIRS during conducting the verbal fluency task (VFT). We trained the model with the ALSTMIT network. The algorithm can distinguish the two types of patients effectively: the average accuracy of classification on the test set can reach 96.2% stably. The classification can provide an objective diagnosis tool for clinicians, and this algorithm may be critical for the early detection and precise treatment for the patients with mood disorders.
TL;DR: A comprehensive review of the state of the art of electromagnetic-circuital-thermal multiphysics simulation method is presented in this paper, where a brief introduction of related theories like governing equations, numerical methods, and coupling mechanisms is also included.
Abstract: Electromagnetic-circuital-thermal multiphysics simulation is a very important topic in the field of integrated circuits (ICs), microwave circuits, antennas, etc. This paper presents a comprehensive review of the state of the art of electromagnetic-circuital-thermal multiphysics simulation method. Most efforts were focused on electromagnetic-circuital co-simulation and electromagnetic-thermal cosimulation. A brief introduction of related theories like governing equations, numerical methods, and coupling mechanisms is also included.
TL;DR: In this article, a coherent reflectivity model for both ice sheet thermal emission and backscattering was developed to calculate coherent reflections from the cap layers, and the WKB approximation was used to calculate the transmission for the slowly varying profile below the cap layer.
Abstract: The Ultra-Wideband Software defined microwave radiometer (UWBRAD) was developed to probe internal ice sheet temperatures using 0.5–2 GHz microwave radiometry. The airborne brightness temperature data of UWBRAD show a significant reduction due to reflections of surface layering of density fluctuations making difficult the retrieval of subsurface temperature in the kilometer range of depth. Such reflections can be measured by the ultra-wideband radar in the same frequency range suggesting a combined active and passive remote sensing of polar ice sheets. In this paper, we develop a coherent reflectivity model for both ice sheet thermal emission and backscattering. Maxwell equations are used to calculate the coherent reflections from the cap layers, and the WKB approximation is used to calculate the transmission for the slowly varying profile below the cap layers. Results are then shown to demonstrate the use of radar measurements to compensate reflection effects on brightness temperatures. It is shown that the reflections corrected brightness temperature is directly related to the physical temperature and absorption profile making possible the retrieval of subsurface temperature profile with multi-frequency measurements.
TL;DR: This paper presents the design of flexible parasitic element patch (FPEP) antenna with defects on ground plane at ISM band for biomedical application and the measurement data with respect to reflection coefficient, and radiation pattern are presented.
Abstract: This paper presents the design of flexible parasitic element patch (FPEP) antenna with defects on ground plane at ISM band for biomedical application. The antenna resonates at 2.46 GHz frequency with reflection coefficient of −16.8 GHz in free space and at 2.45 GHz frequency when being placed on cotton and the single layer skin tissue of human body. The proposed parasitic element patch antenna is used to measure the body temperature, and the specific absorption rate (SAR) of the proposed antennas is 1.0 W/kg. The measurement data with respect to reflection coefficient, and radiation pattern are presented.
TL;DR: In this paper, a reconfigurable bandwidth based on a concentric ring slot antenna using graphene is proposed for medical imaging applications in Terahertz (THz) applications.
Abstract: In this article, we design a reconfigurable bandwidth based on a concentric ring slot antenna using graphene. The developed antenna has good agreement between simulated and experimental results. The use of graphene in Terahertz (THz) has shown better performance than metal, and the variation in the chemical potential of graphene provides excellent performance properties, good return loss reaching −33.288 dB, bandwidth reconfiguration from 255 GHz to 406 GHz, and a good gain. These results are promising for THz applications and particularly for the application of medical imaging. The modeling and validation are performed using the CST Simulator.
TL;DR: The whole system was applied to the study of spectral characteristics of blood oxygen in human hands and the microscopic identification of algae, showing a great potential of clinical and marine applications of this dual-mode hyperspectral imager.
Abstract: A dual-mode hyperspectral imager using field of view scanning needs no moving macro parts. It could work in dual-mode (macro imaging and micro imaging) and is equipped with a conjugated camera for quick object-selection and focusing. By adjusting the imaging lens and achieving the image clarity on the conjugated camera, we could find the correct location and focusing of the ROIs simultaneously instead of inefficiently checking the hyperspectral image after the whole scanning process. The whole system was applied to the study of spectral characteristics of blood oxygen in human hands and the microscopic identification of algae, showing a great potential of clinical and marine applications of our system.
TL;DR: In this paper, the authors developed numerical methods for using vector spherical and spheroidal waves in the hybrid method to calculate the multiple scattering of objects of complex shapes, based on the rigorous solutions of Maxwell equations in the form of Foldy-Lax multiple scattering equations (FL).
Abstract: In this paper, we develop numerical methods for using vector spherical and spheroidal waves in the hybrid method to calculate the multiple scattering of objects of complex shapes, based on the rigorous solutions of Maxwell equations in the form of Foldy-Lax multiple scattering equations (FL). The steps in the hybrid method are: (1) calculating the T -matrix of each single object using vector spherical/spheroidal waves and (2) vector spherical/spheroidal waves addition theorem. We utilize the commercial software HFSS to calculate the scattered fields of a complex object on the circumscribing sphere or spheroid for multiple incidences and polarizations. The T -matrix of spherical waves or spheroidal waves are then obtained from these scattered fields. To perform wave transformations (i.e., addition theorem) for vector spherical/spheroidal waves, we develop robust numerical methods. Numerical results are illustrated for T-matrices and numerical vector addition theorems.
TL;DR: In this paper, a periodic millimeter wave leaky-wave antenna (LWA), which has two different types of radiator elements that enable backward-to-forward radiation, is proposed.
Abstract: A periodic millimeter wave leaky-wave antenna (LWA), which has two different types of radiator elements that enable backward to forward radiation, is proposed. The unit-cell of the LWA consists of two quarter-wavelength microstrip lines and two corrugated substrate integrated waveguide (CSIW) cells with S-shaped quarter-wavelength open-circuit stubs. In addition to two parallel edge radiators, a single etched transverse slot with a tilt angle acts as an ancillary radiator, which ensures impedance matching in a large frequency range and achieves the backward to forward scanning. We analyze the proposed design through simulations, characterize a fabricated prototype, and find it to have good radiation properties including broad impedance bandwidth. The measurement results show a high peak gain from 11 to 15.8 dBi with a large scanning angle range from −34◦ to +22◦ in the K-band operating frequency range.
TL;DR: In this paper, the authors reconstruct a series of formulas to demonstrate the Scheimpflug principles, with reference at the hinge point, based on directly measurable parameters, without measuring the instrument parameters.
Abstract: Scheimpflug LIDAR has attracted considerable attention in the recent years, and has been widely applied in many fields due to its infinite depth of field. In this study, we reconstruct a series of formulas to demonstrate the Scheimpflug principles, with reference at the hinge point. These formulas based on directly measurable parameters are simple in form. Base on this, we report a new calibration for the Scheimpflug system, without measuring the instrument parameters. We also confirm that the result of calibration is accordance with the actual setting of the system. To take full advantage of the infinite depth of field of the Scheimpflug system, we have designed and carried out the system, combining with a rotary stage, to obtain the entire volumetric profile for a target of interest in a cycle rotation. To the best of our knowledge, this is the first time Scheimpflug system is utilized to perform a three-dimensional volumetric profile measurement.
TL;DR: A novel compact patch antenna with Defected Ground structure (DGS) operating for Wireless applications is proposed and investigated, and excellent agreement is obtained between measured and simulated results.
Abstract: A novel compact patch antenna with Defected Ground structure (DGS) operating for Wireless applications is proposed and investigated. This proposed antenna generates four separate resonances to cover 3.271 GHz (WiMax), 4.92 GHz (WiFi), 6.35 GHz (Space applications), and 11.04 GHz (Fixed Satellite applications) while maintaining overall compact size of 32 × 32 × 1.6 mm3 using an FR-4 substrate commonly available with a permittivity of εr = 4.4. The proposed microstrip patch antenna (MSPA) consists of a square radiator in which a periodic slot is etched out along with square defects on ground surface and a microstrip feed line. The periodic slot with DGS modifies the total current path thereby making the antenna operate at five useful bands. Structure displays the impedance bandwidth of 8.34% (3.10–3.37 GHz), 2.00% (4.88–4.98 GHz), 14.68% (6.27–7.194 GHz), and 5.41% (10.79–11.39 GHz) with gains 3.25 dB, 2.45 dB, 5.65 dB, and 4.47 dB, respectively. The antenna performance is analyzed using numerous parametric optimization studies, field distributions, and currents. Excellent agreement is obtained between measured and simulated results.
TL;DR: In this article, a cylindrical dielectric resonator antenna (DRA) with the capability of switching between circular, linear horizontal and linear vertical polarizations is introduced, operating at the center frequency of 3.25 GHz.
Abstract: A new design for a cylindrical dielectric resonator antenna (DRA) with a capability of switching between circular, linear horizontal and linear vertical polarizations is introduced. The DRA, operating at the center frequency of 3.25 GHz, is fed by a microstrip line through two dog-bone slots. In this design, only two PIN diodes are employed as switching elements which significantly decreases the complexity of DC biasing circuits compared to existing designs. The PIN diodes are embedded in transformers connected to the feeding microstrip lines. This technique conveniently allows to make compensations for parasitic effects of the PIN diodes junction capacitors on the antenna matching bandwidth. The circular, linear horizontal and linear vertical polarizations have a bandwidth of 22%, 17% and 18%, respectively. The 3-dB axial ratio bandwidth for the circular polarization is 12%. The measured results obtained from prototyped antenna agree well with simulated results of the designed antenna system, which confirms the validity of the design process.
TL;DR: In this article, a multilevel fast physical optics (MLFPO) method is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers.
Abstract: The multilevel fast physical optics (MLFPO) is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers. This method is based on the quadratic patch subdivision and the multilevel technology. First, the quadratic patches are employed rather than the planar patches to discretize the considered scatterer. Hence, the number of the contributing patches is cut dramatically, thus making the workload of the MLFPO method much lower than that of the traditional Gordon’s method. Next, the multilevel technology is introduced in this work to avoid calculating the physical optics scattered fields from the considered scatterer directly, so that the proposed algorithm can significantly reduce the computational complexity. Finally, numerical results have demonstrated the accuracy and efficiency of the MLFPO method based on the quadratic patches.
TL;DR: An all-fiber parametric oscillator which is pumped by a mode-locked Er-doped picosecond fiber laser is proposed for the generation of multi-wavelength lasing pulses.
Abstract: An all-fiber parametric oscillator which is pumped by a mode-locked Er-doped picosecond fiber laser is proposed for the generation of multi-wavelength picosecond lasing pulses. The length of a fiber-coupled optical delay line is adjusted so that the first signal wavelength is tuned closer to the pump wavelength to facilitate the generation of more lasing wavelengths. 10 orders of cascaded four-wave-mixing processes are achieved and picosecond pulses at 17 lasing wavelengths from 1264.7 nm to 1842.4 nm are demonstrated. To the best of our knowledge, this is the largest number of lasing wavelengths reported so far from a fiber optical parametric oscillator pumped with an ultrashort-pulse laser.
TL;DR: In this paper, a marching-on-in-time discretization scheme is developed that fully conforms to the spatial and temporal Sobolev space properties of the integral equations.
Abstract: Potential-based integral equations are being explored to develop numerical methods that avoid low frequency breakdown issues and are better suited to couple to quantum physics computations. Important classes of quantum electrodynamics problems are typically formulated in the radiation gauge, leading to interest in efficient numerical solutions able to be performed directly in this gauge. This work presents time domain integral equations for penetrable regions that are developed in the radiation gauge. An appropriate marching-on-in-time discretization scheme is developed that fully conforms to the spatial and temporal Sobolev space properties of the integral equations. It is shown that following this approach leads to a discrete system with improved stability properties that produces accurate results down to very low frequencies. The accuracy and stability of this formulation at low frequencies are shown through numerical results.
TL;DR: In this article, the authors examined analytically classical and quantum electromagnetic field interferences in a 50/50 beam splitter in the context of the second order correlation function for various input conditions.
Abstract: The zeroing of second order correlation functions between output fields after interferences in a 50/50 beam splitter has been accepted decades-long in the quantum optics community as an indicator of the quantum nature of lights. But, a recent work [1] presented some notable discussions and experiments that classical electromagnetic fields can still exhibit the zero correlation under specific conditions. Here, we examine analytically classical and quantum electromagnetic field interferences in a 50/50 beam splitter in the context of the second order correlation function for various input conditions. Adopting the Heisenberg picture in quantum electromagnetics, we examine components of four-term interference terms in the numerator of second order correlation functions and elucidate their physical significance. As such, we reveal the fundamental difference between the classical and quantum interference as illustrated by the Hong-Ou-Mandel (HOM) effect. The quantum HOM effect is strongly associated with: (1) the commutator relation that does not have a classical analogue; (2) the property of Fock states needed to stipulate the one-photon quantum state of the system; and (3) a destructive wave interference effect. Here, (1) and (2) imply the indivisibility of a photon. On the contrary, the classical HOM effect requires the presence of two destructive wave interferences without the need to stipulate a quantum state.