Polarization Misalignment Research Articles

A Burning Grass and Removing Root Immunoregulatory Strategy Toward Chronic Wounds Therapy by MnO2 Nanoparticle Incorporated Hyaluronic Acid Hydrogel

AbstractComplex immune microenvironment of diabetic wound possesses polarization misalignment of macrophages and excessive inflammatory response, which prolong the healing process. Consequently, developing hydrogel dressings with immunoregulatory ability shows huge potential in clinical management of diabetic wound. Nevertheless, recent immunoregulatory strategies are mainly focusing on switching the proinflammatory M1‐type to anti‐inflammatory M2‐type macrophages by using high‐cost dressings composed of cytokines and cells. Considering the hyperpolarized M1 macrophages of diabetic wounds as wild grass of wasteland, a burning grass and removing root immunoregulatory strategy toward wound healing is developed based on dopamine‐manganese dioxide nanoparticle incorporated high molecular weight hyaluronic acid (HHA) hydrogel. The self‐healing and injectable hydrogel is formed by boronate ester bonds between the HHA grafted with phenylboronic acid and polyvinyl alcohol. Notably, in vitro and vivo results confirm that the HHA components can burn the grass by switching M1 to M2 in the inflammatory microenvironment while the dopamine‐manganese dioxide nanoparticles can remove the root by relieving M1 polarization through eliminating reactive oxygen species. The comprehensive immunoregulation ability enables the hydrogel as effective therapeutic that improves wound healing, and shows reliable potential in clinical dressings for the management of diabetic wounds.

Polarization Misalignment Between Signal and Crosstalk in Direct Detection WC-MCF Systems

The impact of the polarization misalignment between the signal and the intercore crosstalk (ICXT) on the performance of direct detection (DD) weakly coupled multicore fiber (WC-MCF) systems is investigated by numerical simulation. It is shown that the bit-error ratio (BER) is not maximized for all time when the signal field polarization is aligned with the polarized component of the ICXT. However, this is the scenario in which higher levels of bit-error ratio (BER) occur more frequently along time. For the same outage probability, these higher BER levels lead to an incremental requirement of the ICXT level between 1 dB and 2 dB when compared with the scenario of independent polarizations of the signal and ICXT fields. These conclusions are valid for on-off-keying DD WC-MCF short-reach systems operating with arbitrary product between the skew (i. e., the relative propagation time delay between two cores) and the bit rate.

Online polarization error suppressed optical vector analyzer based on Bayesian optimization.

An optical vector analyzer (OVA) based on orthogonal polarization interrogation and polarization diversity detection is widely used to measure an optical device's loss, delay, or polarization-dependent features. Polarization misalignment is the OVA's primary error source. Conventional offline polarization alignment using a calibrator greatly reduces the measurement reliability and efficiency. In this Letter, we propose an online polarization error suppression method using Bayesian optimization. Our measurement results are verified by a commercial OVA instrument that uses the offline alignment method. The OVA featuring online error suppression will be widely used in the production of optical devices, not just in the laboratory.

Systematic Frequency Error in Laser Synchronization Circuits for Fiber-Optic Time Transfer Systems.

The paper addresses the problem of a systematic frequency error occurring in semiconductor-laser frequency-synchronization circuits based on counting the beat note between the two lasers in a reference time interval using a high-frequency prescaler. Such synchronization circuits are suitable for operation in ultra-precise fiber-optic time-transfer links, used e.g. in time/frequency metrology. The error occurs when the power of the light coming from the reference laser, to which the second laser is synchronized, is below about -50 dBm to -40 dBm, depending on the details of particular circuit implementation. The error can reach tens of MHz if left out of consideration and does not depend on the frequency difference between the synchronized lasers. Its sign can be positive or negative, depending on the spectrum of the noise at the prescaler input and the frequency of the measured signal. In the paper we present the background of the systematic frequency error, discuss important parameters allowing for predicting the error value, and describe the simulation and theoretical models being helpful for designing and understanding operation of discussed circuits. The theoretical models presented here show good agreement with the experimental data, which demonstrates the usefulness of proposed methods. Implementing polarization scrambling to mitigate the effect of polarization misalignment of the lights of the lasers used was considered and the resulting penalty was determined.

A simulator of optical coherent-state evolution in quantum key distribution systems

Quantum key distribution (QKD) is believed to represent a viable solution to achieve theoretically unconditionally secure key generation. However, the available optical systems for experimental QKD, based on photon transmission, are flawed by non-idealities that ultimately limit the achievable performance. Classical simulation of the optical hardware employed in these systems may take on a determining role in engineering future QKD networks. In this article, attempts for developing a QKD simulator based on low-computational-cost models of the employed hardware are presented. In particular, the simulation infrastructure targets polarization-based QKD setups with faint laser sources, whose behaviour can be described by semiclassical coherent states and Mean Photon Number (MPN) per beam. The effects of passive optical components on the photonic qubit evolution are described by Jones matrices, whose coefficients, for some commercial devices, are stored in an ad-hoc library. Realistic eavesdropping attacks and non-idealities, such as optical losses, fibre attenuation, polarization misalignment and limited efficiency of single-photon detectors, are also taken into account. The infrastructure allows the user to describe the desired QKD configuration and it provides in output the MPN at the receiver and two fiducial performance parameters: Quantum Bit Error Rate (QBER) and secure key rate. The comparison of the simulation results with experimental data in the state-of-the-art literature highlights that this work is a step forward towards the definition of compact models for the hardware-dependent simulation of quantum-assisted communication networks.

All-Polarized Wideband Rectenna With Enhanced Efficiency Within Wide Input Power and Load Ranges

The efficiency of a rectenna varies under the influences of receiving polarization tilt angle, operating frequency, input power, and load value in different applications. Yet, no reported rectenna can realize stable efficiency when all these factors vary within a wide range. To solve this problem, an all-polarized rectenna is proposed in this article, composed of a dual-input rectifier and a dual-polarized (DP) antenna. By introducing a novel six-port coupler, the rectifier maintains stable efficiency at wideband, wide input power, and dc load ranges. Moreover, the efficiency of the rectifier keeps stable when the antenna receives power at different polarization tilt angles. Accordingly, a DP antenna with extended bandwidth and 3-dB beamwidth is implemented. Finally, the rectenna is formed. The prototype can maintain beyond 70% of the peak efficiency from 1.7 to 2.5 GHz. At a power density as low as 1 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , efficiency can reach 24.4%. Furtherly, the rectenna is demonstrated by forming a battery-less digital clock. The clock can be powered wirelessly by a WiFi router or cellular base station with maximum distances of 1 or 70 m respectively. Besides, the clock can successfully function under significant transmitting-direction deviation or polarization misalignment between the power source and the rectenna.

Measurement of Orientation and Distance Change Using Circularly Polarized UWB Signals

The article proposes methodology to use circularly polarized (CP) ultra-wideband (UWB) signals for simultaneous measurement of orientation and distance changes between transmitter and receiver. The proposed technique uses the rotational Doppler effect on CP pulsed communication. The amplitude of a CP signal is immune to polarization misalignment in the presence of rotation; however, the phase is subjected to a frequency-invariant shift proportional to the rotation angle. This significantly distorts the pulse shape in the time domain and can be used for the measurement of the rotated angle. By combining the technique with the well-known localization capability of UWB systems, one can precisely measure not only the distance but also the orientation. This is demonstrated by both numerical and experimental studies presented in this article.

The influence of polarization misalignment for modulation transfer spectrum in atom gravimeter.

The accuracy of atom gravimeters is directly related to the Raman laser, which is used to manipulate the atomic wave packet, and the frequency of the Raman laser could be affected by temperature when the laser polarization is not along the preferred axis of the electro-optic crystal employed in the modulation transfer spectrum (MTS). This effect has been researched by modulating the laser polarization in the MTS in this work. The experimental results show that both the laser frequency and gravity measurement results have a sinusoidal dependence on temperature, and the period of the fluctuation is 0.8 °C. The systematic effect can reach 12.4 μGal when the polarization misalignment is 15°, which is a remarkable contribution to the absolute gravity measurement. The amplitude of this effect could be reduced by adjusting the laser polarization to the crystal's preferred axis. According to the result, the included angle between the laser polarization and the crystal's preferred axis should be smaller than 5° if 2 μGal accuracy is required.

BER performance evaluation of a non-Hermitian coherent-optical OFDM FSO system with SFBC and polarization diversity

An analytical model is developed for a non-Hermitian coherent-optical OFDM FSO system with space frequency block code (SFBC) and polarization diversity. Analysis is carried out for a non-Hermitian OFDM FSO link with SFBC coding to evaluate the effect of cross polarization induced crosstalk in presence of channel impairments such as atmospheric turbulence. Expressions are developed for signal to noise plus crosstalk ratio for a given amount of polarization misalignment angle. Considering the probability density function of the misalignment angle to be Maxwellian distributed and Gamma–Gamma distribution for strong atmospheric turbulence, the average bit error rate (BER) is determined. Results are evaluated without and with strong atmospheric turbulence. Computed result show that there is significant improvement on receiver sensitivity due to polarization diversity and coding gain due to SFBC. Further, system suffers power penalty due to crosstalk due to cross polarization and as well as turbulence. Results show that, there is 38 dB improvement in receiver sensitivity due to polarization diversity without SFBC in presence of strong turbulence at a BER of 10−12 considering local oscillator power is 5 mW and link distance is 2000 m. At a given BER of 10−12, penalty due to crosstalk is found to be 3.3 dB for mean misalignment angle of 40 when link distance is 2000 m. Finally, it is noticed that, the amount of coding gain due to SFBC is found to be 7.5 dB at a BER of 10−12.

Contrast analysis in two-beam laser interference lithography

Interference lithography enables large area, sub-µm, periodic patterning without photomasks or projection lithography tools. We show that optical contrast, which is the fundamental design variable of interference lithography, enforces coupled constraints on source coherence, beam pointing stability, field size, polarization state, and the intensity balance between beams. The analysis enables selection and alignment tolerance of components to meet a specific design requirement. In particular, the analysis reveals that grating beam splitters are significantly less sensitive to beam pointing and polarization misalignment than plate beam splitters.

Analytical evaluation of the cross-polarization induced crosstalk on BER performance of an OFDM FSO link with polarization diversity

Performance of a free space optical link can be improved by using polarization diversity. However, there is possibility of cross polarization induced crosstalk due to strong atmospheric turbulence. An analytical model for non Hermitian OFDM based DQPSK FSO system is developed to account for the cross polarization induced crosstalk in the presence of strong atmospheric turbulence. A closed-form expression of signal to noise plus crosstalk ratio and conditional BER for a given polarization misalignment and a given turbulence induced fading is derived. The average BER is evaluated by averaging the conditional BER over the pdf of the turbulence considering Gamma–Gamma distribution and Maxwellian distribution for random angular misalignment. Results are evaluated in terms of BER and receiver sensitivity improvement due to polarization diversity. The system power penalty for cross-polarization induced crosstalk in the presence of strong atmospheric turbulence is also found at a given BER. It is noticed that system BER performance degrades significantly and power penalty is found to almost 9.5dB, 12dB and 21dB for mean misalignment angle of 4°, 5°and 6°respectively at a BER of 10−8 and a given turbulence parameter Cn2=10−14m−2∕3 for a FSO link distance of 2000m. Finally, the analytical results with polarization diversity are compared with published results without diversity.

Polarization-state tracking based on Kalman filter in continuous-variable quantum key distribution.

Continuous-variable quantum key distribution with a real local oscillator (LO) has been extensively studied recently due to its security and simplicity. Making it operate automatically and resistant to channel interference is the key to further long-term system operation. To overcome the dynamic changes in the state of polarization (SOP) of quantum signal caused by the random birefringence effect in fiber, Kalman filter is employed to estimate the polarization misalignment, thereby achieving polarization demultiplexing at the data level, and ultimately recovering the quantum signal with the help of a two-step phase compensation. The signal transmission and processing is simulated, which verifies the SOP tracking ability and the immunity to the fast phase drift. A proof-of-principle experiment is also conducted, and results show that it can resist the interference of SOP rotation at 1 krad/s, and has the ability to distribute 8.4 kbps secret key rate within 20 km when only considering SOP tracking imperfection, confirming its feasibility under harsh channel conditions.

The performance of reference-frame-independent measurement-device-independent quantum key distribution

Reference-frame-independent measurement-device-independent quantum key distribution (RFI–MDI–QKD) is a promising approach for practical quantum communication. The detector side channel attacks could be removed without aligning the reference frames. By considering the statistical fluctuations, background counting rate and the polarization misalignment fluctuation, the performance of the RFI–MDI–QKD is analyzed under the condition of one, two and infinite decoy states. Moreover, the numerical simulation results are presented which offer significant reference for practical applications of RFI–MDI–QKD.

Wireless Power Transfer Antenna Alignment Using Intermodulation for Two-Tone Powered Implantable Medical Devices

Wireless power transfer (WPT) to the implantable medical devices (IMDs) often suffers from antenna radiation direction and polarization misalignments, which degrades the wireless power link efficiency. Although increasing the incident power density is able to solve the power hunger of IMDs, it poses safety issues to the human tissue. In this paper, an antenna alignment method using intermodulation is proposed to address WPT antenna misalignment in a safe way. Two-tone (2T) waveform excitation is employed to enhance the rectification as well as to generate intermodulation. The intermodulation power is fed back via a magnetic resonant coupling link. Due to the monotonic relation between the intermodulation power and the degree of antenna misalignments, the receiving antenna (in body) can be aligned with the transmitting one (out body). Such a scheme has the advantages of less harm to human tissue and less interference between the 2T waveform excitation and the magnetic resonant coupling link. The whole system is theoretically analyzed and experimentally validated.

Systematic effects in LOFAR data: A unified calibration strategy

Context. New generation low-frequency telescopes are exploring a new parameter space in terms of depth and resolution. The data taken with these interferometers, for example with the LOw Frequency ARray (LOFAR), are often calibrated in a low signal-to-noise ratio regime and the removal of critical systematic effects is challenging. The process requires an understanding of their origin and properties. Aim. In this paper we describe the major systematic effects inherent to next generation low-frequency telescopes, such as LOFAR. With this knowledge, we introduce a data processing pipeline that is able to isolate and correct these systematic effects. The pipeline will be used to calibrate calibrator observations as the first step of a full data reduction process. Methods. We processed two LOFAR observations of the calibrator 3C 196: the first using the Low Band Antenna (LBA) system at 42–66 MHz and the second using the High Band Antenna (HBA) system at 115–189 MHz. Results. We were able to isolate and correct for the effects of clock drift, polarisation misalignment, ionospheric delay, Faraday rotation, ionospheric scintillation, beam shape, and bandpass. The designed calibration strategy produced the deepest image to date at 54 MHz. The image has been used to confirm that the spectral energy distribution of the average radio source population tends to flatten at low frequencies. Conclusions. We prove that LOFAR systematic effects can be described by a relatively small number of parameters. Furthermore, the identification of these parameters is fundamental to reducing the degrees of freedom when the calibration is carried out on fields that are not dominated by a strong calibrator.

Analysis of polarization fluctuation in long-distance aerial fiber for QKD system design

Abstract The polarization basis misalignment caused by polarization fluctuation is the main limiting factor in the deployment of polarization-encoding quantum key distribution (QKD) in aerial fibers. In this study, we conduct further research on polarization fluctuations in aerial fibers from the perspective of QKD. We propose a method to evaluate polarization fluctuation in aerial fibers. The relation connecting the quantum bit error rate (QBER) to the components of the Stokes vector is derived. Through a field experiment, long-time data on the polarization fluctuations in a 68-km-long aerial fiber are obtained. A statistical analysis of the time-cost corresponding to a typical QBER caused by polarization misalignment is conducted. The results can be used to evaluate the required speed of polarization compensation, and they indicate that the time-cost of the polarization compensation module should ideally be lower than 1 ms. This can provide guidance for the design of polarization compensation modules and algorithms for polarization-encoding QKD systems based on long-distance aerial fibers, aiding in its deployment.

Exploiting Third Harmonic of Differential Charge Pump for Wireless Power Transfer Antenna Alignment

Wireless power transfer (WPT) always suffers from the antenna radiation direction and polarization misalignments between the base station and the WPT terminal. In this letter, the third harmonic of a differential charge pump is exploited for antenna alignment with only one pair of antennas. Due to the intrinsic nonlinearity of diodes, the third harmonic can be generated and reflected by the differential charge pump. A ring coupler is employed to distribute the received fundamental frequency power for rectification by the differential charge pump and couple the third-harmonic generation back to its input port. Such third-harmonic power is feedback by a dual-band antenna operating at the third-harmonic frequency. In consequence, the WPT antennas can be aligned by obtaining the maximum third-harmonic feedback at the base station. The whole system is theoretically analyzed and experimentally validated.

A High Dimensional Measurement-Device-Independent Quantum Key Distribution Scheme Based on Optical Quantum State Fusion and Fission

Measurement-device-independent quantum key distribution (MDI-QKD) not only eliminates all detector side channel attacks, but also doubles the secure transmission distance. To improve the performance of MDI-QKD, we propose a high dimensional encoding scheme. By a spatial-temporal mode conversion circuit and quantum state fusion operation, two polarization modes of two photons are converted into the temporal-polarization mode of one photon. Also, by adding a temporal-spatial mode conversion circuit to quantum state fission apparatus, the temporal-polarization mode of one photon can be split into two polarization modes of two photons. By these two processes, each of the two legitimate parties is able to send photons in high dimensional temporal and polarization modes, and the measurement server still performs Bell state measurements (BSMs) after states fission. Hence, the total output rate can be improved. In addition, one of the recovered polarization states keeps stable for channel noise. The numerical simulation results show that by this new scheme, the key generation rate increases by 2∼10 times and transmission distance increases by 6∼60 km for different polarization misalignment errors.

MOJAVE XVI: Multiepoch Linear Polarization Properties of Parsec-scale AGN Jet Cores

Abstract We present an analysis of the core linear polarization properties of 387 parsec-scale active galactic nuclei (AGNs) jets. Using 15 GHz VLBA data, we revisit the conclusions of the first paper in this series with multiepoch measurements and more detailed analysis of a larger AGN sample that spans a broader range of synchrotron peak frequencies. Each AGN has been observed for at least five epochs between 1996 and 2017. We find that BL Lac objects have core electric vector position angles (EVPAs) that tend toward alignment with the local jet direction; compared to flat spectrum radio quasars, their EVPAs are also less variable over time. The AGN cores that are most fractionally polarized and least variable in polarization have EVPAs that are closely aligned with the local jet direction; they also have low variability in EVPA. These results support the popular model of a standing transverse shock at the base of the jet that collimates the jet magnetic field perpendicular to the jet direction, increasing the fractional polarization and leading to greater polarization stability over time. High-synchrotron-peaked BL Lac objects form a low luminosity, low fractional polarization population. The five narrow line Seyfert 1 galaxies in our sample have low fractional polarization and large EVPA-jet misalignments. Although AGNs detected at γ-rays are thought to be more Doppler boosted than nondetected AGNs, we find no significant differences in fractional polarization based on detection by Fermi-LAT; the γ-loud AGNs are, however, more variable in core EVPAs.

Interview

Dr Saeid Karamzadeh at Istanbul Aydin University, Turkey, talks to Electronics Letters about the work behind his Letter ‘Millimeter-Wave High-Gain Circularly polarised SIW End-Fire Bow-tie Antenna by utilising Semi Planar Helix Unit Cell’, page 411. Saeid Karamzadeh Years ago, during the design of a system to rescue living people left under earthquake rubble, we found that the antenna is one of the most important parts of the system and should be studied in more detail. The next step was designing an antenna for satellite communication. Size reduction, designing a compact antenna, bandwidth improvement, gain increment and getting circularly polarisation were our goals. In the meantime, I finished my PHD degree and I won the most successful PHD thesis award of Istanbul Technical University. Recently, as mm-wave circularly polarised antennas have many benefits, we focused on designing novel works on this subject. One of the important issues is generation of circular polarisation from a linearly polarised antenna. Identifying linearly polarised antennas that have the ability to change to antennas with circularly polarised features and realising the methods for this is a challenge for antenna designers. Circularly polarised antennas have several important advantages compared to antennas using linear polarisation and are becoming a key technology for various wireless systems. Circularly polarised antennas are very effective in combating multi-path interferences or fading. The reflected radio signal from the ground or other objects will result in a reversal of polarisation, that is, right-hand circular polarisation (RHCP) reflections show left-hand circular polarisation (LHCP). An RHCP antenna will have a rejection of a reflected signal which is LHCP, thus reducing the multi-path interferences from the reflected signals. The second advantage is that a circularly polarised antenna is able to reduce the ‘Faraday rotation’ effect due to the ionosphere. The Faraday rotation effect causes a significant signal loss (about 3 dB or more) if linearly polarised signals are employed. Another advantage of using CP antennas is that no strict orientation between transmitting and receiving antennas is required. This is different from linearly polarised antennas, which are subject to polarisation mismatch losses if arbitrary polarisation misalignment occurs between transmitting and receiving antennas. We managed to create a circularly polarised antenna on a mm-wave linear polarisation antenna by employing several spiral unit cells. This is helpful because linear polarisation antennas have few limitation parameters, therefore designing them is relatively simple compared with circularly polarised antennas and by this method we can convert linearly polarised to circularly polarised antennas. The importance of CP antennas and consequently the advantage of this antenna is shown in this Letter. Undoubtedly, to report a work with a novel technique you must conquer many issues. In this work, finding a co-planer cell which enables a linearly polarised antenna to circularly polarise was a big challenge; in addition to issues such as selecting an antenna to radiate directionally. We are working on increasing the bandwidth and 3-dB axial ratio of this antenna and also concentrating on mm-wave antennas to improve their characteristics. In further steps, we would like to work on applying this to mm-wave CP array antennas. Over those years, many works about mm-wave antennas have been reported. We are hoping that as this continues over the next ten years, mm-wave antennas can be released in most countries, in order to use high data transfer in this frequency band. This could be so helpful for real-time communication as well as helping to save many lives through use in automotive radar. Additionally, this frequency band, which can achieve high accuracy in microwave imaging systems, can be used in biomedical systems for so many applications like tumour detection and prediction. By increasing the data transfer rate to allow 3-D vision, it will have an impact in the entertainment sector too.