Compact Polarization Research Articles

The Source Locations of Major Flares and CMEs in Emerging Active Regions

Abstract Major flares and coronal mass ejections (CMEs) tend to originate from compact polarity inversion lines (PILs) in solar active regions (ARs). Recently, a scenario named “collisional shearing” was proposed by Chintzoglou et al. to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form a compact PIL, driving the shearing and flux cancellation that are responsible for the subsequent large activities. In this work, by tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing.” We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, six from the conjoined systems of sPIL and cPIL, and two from the conjoined systems of sPIL and ePIL (external PIL between the AR and the nearby pre-existing polarities). Collision accompanied by shearing and flux cancellation is found to develop at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the more intense activities tend to originate from PILs with more severe collisions. The results suggest that “collisional shearing,” i.e., bipole–bipole interaction during the flux emergence, is a common process in driving the major activities in emerging ARs.

Polarization-Independent Circulator Based on Composite Rod of Ferrite and Plasma in Photonic Crystal Structure.

We propose a type of polarization-independent circulator based on a composite rod of ferrite and plasma materials in a two-dimensional photonic crystal (PhC) slab. Only one composite rod was set at the center of the structure to provide circulation for both TE- and TM-polarized waves. Additionally, to improve the performance of the circulator, three additional rods were inserted to improve the coupling condition between the center magneto-optical microcavity and the corresponding waveguides. Finite element method was used to calculate the characteristics of the structure and the Nelder–Mead optimization method was employed to obtain the optimum parameters. The results show that a low insertion loss (~0.22 dB) and high isolation (~14 dB) can be achieved in our structure for waves of both TE and TM polarizations. The idea presented here may be useful for designing compact polarization devices in large-scale integrated photonic circuits.

Cascaded metamaterial polarizers for the visible region

Polarizers serve many application fields such as imaging, display technology, and telecommunications. Focusing on the visible spectral region, we provide the design and fabrication of compact high-efficiency resonant polarizers in the crystalline silicon-on-quartz material system. We experimentally verify the improved efficiency attained by a cascaded dual-module polarizer assembled with building blocks of elemental subwavelength grating structures. We obtain a measured extinction ratio (ER) of ∼3000 in a 2 mm thick stacked prototype device across a bandwidth of ∼110nm in the 570-680 nm spectral domain. The ridge width of the constituent nanograting is ∼84nm. Computed results show a high ER in spite of the lossy nature of crystalline silicon in the visible region, enabling cascaded metasurfaces while preserving high transmission.

Direct-binary-search-optimized compact silicon-based polarization beam splitter using a pixelated directional coupler

In this paper, a polarization beam splitter using a pixelated directional coupler is proposed, designed, and experimentally demonstrated on silicon-on-insulator platform. According to the phase matching, structural parameters for the coupling region consisting of a straight waveguide and a pixelated waveguide are carefully selected by using direct-binary-search optimization algorithm and the finite difference time domain method, and thus the input fundamental transverse-magnetic and transverse-electric modes can be effectively separated from each other in an ultra-compact coupling length. The coupling length of our designed device is only 6 μm. Experimental results reveal that, the measured polarization extinction ratio is greater than 14.22 dB and the corresponding insertion loss is smaller than 1.36 dB within a bandwidth from 1527 to 1580 nm for the fabricated device operating in transverse-electric polarization, while the measured polarization extinction ratio and insertion loss are respectively larger than 14.47 dB and lower than 1.53 dB from 1527 to 1580 nm for the fabricated device operating in transverse-magnetic polarization.

Fabrication-tolerant and CMOS-compatible polarization splitter and rotator based on a compact bent-tapered directional coupler

In this paper, we demonstrate a broadband, low-loss, compact, and fabrication-tolerant polarization splitter and rotator (PSR) on a silicon-on-insulator platform. The PSR is based on an asymmetric directional coupler (ADC), which is covered with SiO2 from the top to make it compatible with the standard metal back end of line (BEOL) process. Conventional ADC-based PSRs suffer from stringent fabrication requirements and relatively low bandwidth, while the proposed bent-tapered design is highly insensitive to the fabrication errors (＞70 nm tolerance on the coupling gap) with an enlarged bandwidth and a compact footprint of 53 µm × 7 µm. It yields a polarization conversion loss less than 0.7 dB, a transverse electric (TE) insertion loss better than 0.3 dB, an ultra-low crosstalk with the TE extinction better than 30 dB, and the transverse magnetic extinction better than 25 dB, over a 200 nm wavelength range (1.5 µm–1.7 µm), in both ports. At the 1.55 µm wavelength, the calculated ultra-low polarization conversion loss and TE insertion loss are 0.27 dB and 0.08 dB, respectively.

A Compact Polarization Independent Power splitter for Mid IR Range

Photonic crystal based Power splitters being associated with significant advantages related to dimensions have been widely explored in literature in last few years. However these devices are associated with a serious drawback of polarization dependency which restricts their operation in various optical interconnects. This paper designs compact Photonic crystal based polarization independent Power splitter for Mid IR Range. The proposed structure has very small footprints with dimensions of 10×10μm2 shows a transmission efficiency of efficiency of 97% at wavelength of 1430 nm. Such a small footprint power splitter can help significantly while designing optical setups in areas of spectroscopy and security.

Information Resources Economy in Satellite Systems based on New Microwave Polarizers with Tunable Posts

One of the fundamental problems of modern digital telecommunications is the economy of digital information and frequency resources, which are highly limited. The introduction of novel telecommunication systems and 5G networks requires searching for principal solutions for the economy and reusing the frequency spectrum. Therefore, modern wireless mobile, terrestrial, and satellite systems use various new technologies to increase communication channels' information capacity for the economy of limited frequency resources. One of the most effective ways to reuse the information system's operating frequency band is to apply antennas with polarisation signal processing. Such systems provide the possibility to transmit and to receive simultaneously signals with different types of polarisation. Consequently, the application of electromagnetic waves with two orthogonal polarisations improves wireless systems' information characteristics for various purposes. This allows doubling the information capacity of mobile, terrestrial, and satellite communication channels. Also, polarisation processing is carried out in meteorological and radar systems to receive, transmit, and process information. The essential elements of such systems are microwave polarisers and orthomode transducers. The electromagnetic characteristics of these devices affect the aspects of the whole system significantly. Main electromagnetic factors include phase, matching, and polarisation parameters. The article presents the development of a compact tunable polarizer based on a square waveguide with three posts. The developed polariser operates in the X-band from 8.0 GHz to 8.5 GHz. Created a mathematical model of the polariser is based on the scattering and transmission matrices. To verify the developed theoretical model's correctness, the calculation of all characteristics was also performed numerically using the finite integration technique. The developed compact polariser based on a square waveguide with three posts allows tuning it's matching and polarisation characteristics by changing all posts' heights. The developed polariser's main advantages are small dimensions, tuning options, and aspects of polarisation transformation.

Recent Progress on Ultrathin Metalenses for Flat Optics.

SummaryAs technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

A compact polarization reconfigurable stacked microstrip antenna for WiMAX application

AbstractIn this paper, a stacked microstrip patch antenna with polarization reconfigurable property has been proposed for worldwide interoperability for microwave access (WiMAX) application. The proposed antenna has two substrate layers: upper and lower layers with two radiating patches connected with the coaxial probe. Without the upper layer the lower square-shaped substrate layer having regular hexagonal radiating patch with probe fed acts as a linear polarized antenna with impedance bandwidth for (S11 ≤ −10 dB) is 370 MHz 10.56% (3.32–3.69 GHz) cover WiMAX (3.4–3.69 GHz) application band. The hexagonal radiating patch is perturbed with an optimum rectangular slot to enhance the impedance bandwidth of the antenna. The lower substrate layer having hexagonal patch with the same probe position is stacked with the upper square-shaped substrate layer with same sized square patch and the upper patch soldered with the coaxial probe. The overall stacked antenna generates a circularly polarized band when the opposite corner of the top square radiating patch of the upper layer is truncated with optimum size. In order to generate another circularly polarized band and to improve the input impedance matching of the stacked antenna, the top radiating patch is perturbed with two slots and a slit. The stacked circularly polarized antenna generates impedance bandwidth of 12.75% (3.23–3.67 GHz) for (S11 ≤ −10 dB) with two circularly polarized bands (3.34–3.37 GHz) and (3.66–3.70 GHz) as per (axial ratio ≤ 3 dB) for WiMAX application. Therefore, the proposed antenna can be used as linearly polarized or dual band circularly polarized according to requirement.

Femtosecond Laser Inscribed Novel Polarization Beam Splitters Based on Tailored Waveguide Configurations

We report on a novel waveguide-based polarization beam splitter (PBS) fabricated by femtosecond (fs) laser in lithium niobate (LiNbO3) crystals. This monolithic PBS is composed of tailored waveguide configurations with different guiding properties in which linearly polarized light along extraordinary refractive index ( ne ) and ordinary index ( no ) can be well separated. At the wavelength of 1064 nm, polarization extinction ratio (PER) can reach to 16.60 dB and 16.18 dB for ne and no polarizations, with insertion loss (IL) of 3.86 dB and 4.15 dB respectively. Our work may pave a new way for designing high-performance PBS and creating compact polarization conversion systems in integrated photonics and quantum photonics.

An ultra-thin quad-band metamaterial inspired absorber using symmetric bent-arrow shaped resonator for sensing and imaging in defense applications

In this paper, a novel compact quad-band polarization insensitive metamaterial absorber has been proposed to be employable in the microwave frequency regime. The unit-cell geometry comprises of four symmetric bent-arrow shaped resonators, where each arrow has been bounded by an open ring. The resultant structure is further surrounded by a closed ring to obtain an extra resonance band. Full-wave simulation with normal incidence depicts quad-band operation with absorption peaks at 3.24 GHz (S-band), 6.55 GHz (C-band), 15.22 GHz (Ku-Band), 15.94 GHz (Ku-band) and absorptivity levels of 99.57%, 99.94%, 96.10%, 98.65% correspondingly. It also shows full width half maximum (FWHM) bandwidth of 100 MHz, 200 MHz and 1210 MHz in the first, second and third bands respectively. Furthermore, the proposed structure is based on four-fold symmetry therefore exhibits polarization-insensitive behaviour unlike conventional absorbers. The structure is fabricated on 1 mm FR4 Glass Epoxy substrate equivalent to 0.0108 λ 0 hence, can be used as absorber coating for planar surfaces. The designed absorber has been fabricated and experimental results were in good agreement with the simulated responses enabling its wide application in various technologies like stealth technology, radar cross section reduction, anechoic chambers, electromagnetic interference/electromagnetic compatibility, and radio frequency identification.

Hybrid Compact Polarimetric SAR for Environmental Monitoring with the RADARSAT Constellation Mission

Canada’s successful space-based earth-observation (EO) radar program has earned widespread and expanding user acceptance following the launch of RADARSAT-1 in 1995. RADARSAT-2, launched in 2007, while providing data continuity for its predecessor’s imaging capabilities, added new polarimetric modes. Canada’s follow-up program, the RADARSAT Constellation Mission (RCM), launched in 2019, while providing continuity for its two predecessors, includes an innovative suite of polarimetric modes. In an effort to make polarimetry accessible to a wide range of operational users, RCM uses a new method called hybrid compact polarization (HCP). There are two essential elements to this approach: (1) transmit only one polarization, circular; and (2) receive two orthogonal polarizations, for which RCM uses H and V. This configuration overcomes the conventional dual and full polarimetric system limitations, which are lacking enough polarimetric information and having a small swath width, respectively. Thus, HCP data can be considered as dual-pol data, while the resulting polarimetric classifications of features in an observed scene are of comparable accuracy as those derived from the traditional fully polarimetric (FP) approach. At the same time, RCM’s HCP methodology is applicable to all imaging modes, including wide swath and ScanSAR, thus overcoming critical limitations of traditional imaging radar polarimetry for operational use. The primary image data products from an HCP radar are different from those of a traditional polarimetric radar. Because the HCP modes transmit circularly polarized signals, the data processing to extract polarimetric information requires different approaches than those used for conventional linearly polarized polarimetric data. Operational users, as well as researchers and students, are most likely to achieve disappointing results if they work with traditional polarimetric processing tools. New tools are required. Existing tutorials, older seminar notes, and reference papers are not sufficient, and if left unrevised, could succeed in discouraging further use of RCM polarimetric data. This paper is designed to provide an initial response to that need. A systematic review of studies that used HCP SAR data for environmental monitoring is also provided. Based on this review, HCP SAR data have been employed in oil spill monitoring, target detection, sea ice monitoring, agriculture, wetland classification, and other land cover applications.

Compact, Broadband and Low-Loss Polarization Beam Splitter on Lithium-Niobate-On-Insulator Using a Silicon Nanowire Assisted Waveguide

We propose a compact, broadband, and low-loss polarization beam splitter (PBS) based on an asymmetrical directional coupler on the lithium-niobate-on-insulator platform, consisting of an amorphous silicon (a-Si) assisted waveguide, and a normal waveguide. With proper design of the a-Si nanowire, and lithium niobate waveguides, the phase-matching condition is satisfied for TE polarization, while significant mismatching exists for TM polarization. A 16- $\mu$ m-long PBS (including the s-bend region) with a 200 nm gap is achieved. Numerical simulations show that the PBS exhibits a 140-nm bandwidth for extinction ratios lager than 10 dB. Moreover, the device has an ultra-low insertion loss (IL $\sim$ 0.05 dB), and maintaining ILs $ 0.5 dB over a 170 nm wavelength range.

Silicon-based dual-mode polarization beam splitter for hybrid mode/polarization-division-multiplexed systems

This paper presents a compact dual-mode polarization beam splitter (PBS) based on silicon on insulator platform. The proposed PBS separates two lowest-order transverse magnetic (TM) modes from two lowest-order transverse electric (TE) ones by employing an optimized tapered directional coupler. To the best of our knowledge, this is the first PBS with the ability of separating two sets of modes with different polarizations, simultaneously. Such a component is an essential block in the hybrid mode/polarization-multiplexing systems. The three-dimensional finite-difference time-domain (FDTD) simulation results confirm that the designed PBS has a low loss of 1.6 dB and high extinction ratio of more than 10 dB over a broad wavelength range of 90 nm. Also, the presented PBS tolerates ±15 nm change in the coupling gap, ±30 nm waveguide width deflection, and more than ±100 nm coupling length variation with an insertion loss lower than 1 dB and extinction ratio higher than 10 dB.

High Extinction Ratio Polarization Beam Splitter Realized by Separately Coupling

A novel compact polarization beam splitter (PBS) based on a triple-waveguide directional coupler is presented. Among these three waveguides, the middle one is regarded as an input where the contrast of effective refractive index between fundamental modes is enhanced with dielectric-loaded waveguide. Confined into the waveguides with coupling lengths of $8.3~\mu \text{m}$ (TM) and $9.9~\mu $ m (TE) on both sides, the two fundamental modes are separately coupled. In virtue of the separated coupling structure, a high polarization extinction ratio (PER) of 45.6 dB together with a low insertion loss ( $1.55~\mu \text{m}$ . Furthermore, the operation bandwidth of this PBS, during which the PER is higher than 40 dB, is up to 80 nm for TE mode.

Inverse design of a single-step-etched ultracompact silicon polarization rotator.

We propose and experimentally demonstrate a novel ultracompact silicon polarization rotator based on equivalent asymmetric waveguide cross section in only single-step etching procedure for densely integrated on-chip mode-division multiplexing system. In the conventional mode hybridization scheme, the asymmetric waveguide cross section is employed to excite the hybridized modes to realize high performance polarization rotator with compact footprint and high polarization extinction ratio. However, the fabrication complexity severely restricts the potential application of asymmetric waveguide cross section. We use inverse-designed photonic-crystal-like subwavelength structure to realize an equivalent asymmetric waveguide cross section, which can be fabricated in only single-step etching process. Besides, a theory-assisted inverse design method based on a manually-set initial pattern is employed to optimize the device to improve design efficiency and device perform. The fabricated device exhibited high performance with a compact footprint of only 1.2 × 7.2 µm2, high extinction ratio (> 19 dB) and low insertion loss (< 0.7 dB) from 1530 to 1590 nm.

Design of a compact polarization beam splitter for silicon-based cross-slot waveguides

In this paper, a compact polarization beam splitter (PBS) for cross-slot waveguides is numerically proposed and designed. The device is based on the mode-coupling theory with an asymmetric directional coupler (DC) system, in which the input quasi-TM mode is fully coupled into the cross port and the quasi-TE mode remains transmitting in the through port. With properly chosen structural parameters, a compact PBS with a length of 13.2 µm, including the coupling and S-bend sections, is realized. This is much shorter than PBSs using the symmetric DC system. The numerical results show that the optimized extinction ratios (ERs) are 25.5 and 23.6 dB for the quasi-TE and quasi-TM modes, respectively. Moreover, the ERs are higher than 15 dB for both polarizations over the wavelength range from 1.5 to 1.6 µm, indicating a broad operating bandwidth.

Omnidirectional and compact transmissive chromatic polarizers based on a dielectric-metal-dielectric structure.

High-performance omnidirectional transmissive chromatic polarizers based on a one-dimensional dielectric-metal-dielectric subwavelength grating structure are proposed. The incident angle-insensitive properties, azimuthal angle-insensitive properties and polarization features are investigated thoroughly to realize the proposed omnidirectional transmissive chromatic polarizers. The color difference at different angles for the proposed yellow polarizers is less than 0.9746, and the extinction ratio at different angles for the proposed cyan polarizers exceeds 26. Analysis of the power density profiles for the transverse electric (TE) and transverse magnetic (TM) polarizations show that surface plasmon resonance and high refractive index contrast properties lead to excellent polarization features and high angular tolerance.

Compact high-performance polarization beam splitter based on a silicon photonic crystal heterojunction

A novel polarization beam splitter based on a silicon photonic crystal (PC) heterostructure operating in the optical-telecommunications band is envisaged and is configured for planar integration with other PC or waveguide structures. The small 9μm×9.4μm footprint polarization beam splitter is investigated by the plane-wave expansion and finite-difference time-domain methods. Due to the combined effects of self-collimation and the photonic band gap, self-collimation transmission and 90° beam splitting for the two orthogonal polarizations are achieved. The transmissivity exceeds 60% (78%) for TE (TM) polarization covering a 115-nm bandwidth, and it is also observed that the polarization extinction ratios of the device are higher than 13 and 31 dB, respectively. Moreover, at the wavelength of 1550 nm, TE (TM) polarization has high transmissivity 94.9% (88%) with high polarization extinction ratio of 17 dB (41 dB). A compact and efficient polarization beam splitter is successfully designed for applications in optical communications.

Numerical Investigation of a Short Polarization Beam Splitter Based on Dual-Core Photonic Crystal Fiber with As2S3 Layer.

A polarization beam splitter is an important component of modern optical system, especially a splitter that combines the structural flexibility of photonic crystal fiber and the optical modulation of functional material. Thus, this paper presents a compact dual-core photonic crystal fiber polarization beam splitter based on thin layer As2S3. The mature finite element method was utilized to simulate the performance of the proposed splitter. Numerical simulation results indicated that at 1.55 μm, when the fiber device length was 1.0 mm, the x- and y-polarized lights could be split out, the extinction ratio could reach −83.6 dB, of which the bandwidth for extinction ratio better than −20 dB was 280 nm. It also had a low insertion loss of 0.18 dB for the x-polarized light. In addition, it can be completely fabricated using existing processes. The proposed compact polarization beam splitter is a promising candidate that can be used in various optical fields.