Dual-polarization Modulator Research Articles

High-speed independent polarization modulation based on dual channel 2DEG anisotropic terahertz metasurfaces.

In communication and imaging systems, anisotropic metasurfaces bring new degrees of freedom for the independent control of electromagnetic waves with different polarizations. This paper proposes a dual-polarization modulation metasurface (DPMM) operating in the terahertz (THz) frequency range, which can effectively and independently modulate two orthogonally linearly polarized electromagnetic waves. The metasurface unit adopts an anisotropic structure, and by integrating multiple GaN-based high electron mobility transistors (GaN-HEMTs) into the anisotropic structure, independent control of the two-dimension electron gas (2DEG) carrier concentration in the dual-polarization channel is achieved, enabling selective modulation of x-polarization and y-polarization waves. Simulation and static experimental results demonstrate the excellent modulation isolation performance of the DPMM, with a maximum isolation exceeding 45 dB. Dynamic experiments further highlight the high-speed modulation effect, with modulation speeds exceeding 1 GHz for a single channel and an overall modulation speed of 2 GHz for dual polarization, highlighting its potential for enhancing channel capacity and information throughput in THz communication and imaging systems.

Electrohydrodynamic drying of pollens based on a dual-polarization induction mode triboelectric nanogenerator

Drying pollen and other powders are important procedures of the food industry. Here we demonstrate a self-powered cold plasma drying system for collecting and drying pollen powders based on a dual-charge-induction mode triboelectric nanogenerator (TENG). The charge accumulation strategy of TENG has been modified by a dual-polarized module, where both ultra-high voltage output (over 30 kV) and sufficient output charge density could be generated to enhance drying efficiency. Comparing with all the other direct-current TENGs with an output voltage over 15 kV, this as-fabricated TENG can provide the highest transferred charge density so far. The electrohydrodynamic forces generated by the high-voltage TENG can be used to evaporate moisture from pollen. Within 20 min, it can lower the moisture content of fresh pollen from 35% to 7%, presenting a straightforward design for storing pollen at present. As for the same electrohydrodynamic drying process, the energy consumption of this self-powered TENG-based drying system for evaporating 1 kg water is about 5.36 kJ, which is only 36.4% of energy consumption of commercial high-voltage power source. This design provides a simple yet effective low-power consumption drying system for current pollen storage, which can be a promising environment-friendly alternative for food industry.

Photonic joint radar and communication system using a chirp-polarity coded LFM waveform

A photonic joint radar and communication system using a frequency improved, bandwidth doubled, chirp-polarity coded linear frequency modulation (LFM) waveform is proposed and demonstrated. In the scheme, a dual-polarization modulator is driven by a repetitive LFM waveform and an RF signal to generate different optical sidebands in two orthogonal polarization directions. Then, the orthogonally polarized optical sidebands are filtered and polarization modulated to achieve chirp-polarity coding. The generated signal is employed to simultaneously perform dual functions. Both the radar echo and the communication reception are processed based on optical de-chirping. The approach is demonstrated by simulation. A chirp-polarity coded LFM waveform with central frequency of 24 GHz, bandwidth of 8 GHz, bit rate of 10 Mbit/s is generated and processed for dual functions. The radar range resolution, unambiguous range, and range-Doppler resolution are investigated. The optical demodulation of the communication is verified, and the speed improvement of communication is discussed.

30.7 Tb/s Transmission over 400 km using 40 WDM channels of DP-16 QAM and Raman amplification without inline repeaters

Forty wavelength-division multiplexing (WDM) channels of 96 Gbaud (768 Gb/s) were transmitted over 400 km of SMF using only a Raman amplifier, which was accomplished through numerical simulations. Each WDM channel comprised eight electrical subcarriers of single sideband Nyquist-pulse-shaping. 16 quadrature amplitude modulation and dual polarization modulation were applied to each subcarrier channel and so one data symbol carried eight bits. The roll-off factor in the optical subcarrier spectrum was investigated from 2% to 11%, and the change in roll-off was analyzed according to the subcarrier channel in a single WDM channel. The spectral linewidth of the light source in the transmitter was changed up to 10 MHz, and the effect on the performance was examined for a coherent transmission system with constellation analysis. The optical input power per WDM channel was optimized and the wavelength spacing between WDM channels were analyzed using nonlinear effects from adjacent WDM channels. A transmission experiment for total 30.7 Tb/s over 400 km was performed using the obtained optimal values. BER evaluation was achieved by DSP algorithms including Kramers–Kronig detection and Nyquist filtering. All 40 WDM channels exhibited sufficient transmission performance using only the Raman backward pumping of the four pump wavelengths. The proposed system can be applied to unrepeatered metro‐networks or data-center interconnects.

Broadband and linearized photonic time-stretch analog-to-digital converter based on a compact dual-polarization modulator.

A broadband linearization scheme for a photonic time-stretch (PTS) analog-to-digital converter (ADC) is proposed based on a dual-polarization binary phase-shift keying (DP-BPSK) modulator with complementary parallel single-sideband (SSB) modulation. In this system, two stretched radio frequency signals, corresponding to the two orthogonal polarizations of the DP-BPSK modulator, are complementary, which can realize differential operation to eliminate the second-order harmonic distortion and pulse envelope distortion. Meanwhile, SSB modulation is used to avoid dispersion-induced power fading. Theoretical analysis and simulation results show that the proposed scheme can effectively improve the linear performance of PTS ADC, even considering the polarization-dependent delay deviation and amplitude offset.

Wideband Microwave Phase Noise Analyzer Based on All-Optical Microwave Signal Processing

An approach for wideband phase noise measurement of microwave signal sources is proposed based on all-optical microwave signal processing. In the proposed scheme, an optical carrier is sequentially modulated by the signal under test (SUT) in a phase modulator and a dual-polarization modulator to generate two +1st-order sidebands with orthogonal polarizations. A time delay is introduced between two sidebands by a span of low-loss optical fiber. Combined with a polarization controller and a polarizer, photonic microwave downconversion with a desired phase shift and time delay can be realized after photodetection, and the phase noise of the SUT can be calculated thereafter. Since all the microwave signal processing functions in the conventional photonic-delay-line-based phase noise measurement system are implemented in the optical domain, the proposed scheme has a large operational bandwidth and a high measurement sensitivity. In the experimental demonstration, accurate phase noise measurement of SUTs is achieved in a frequency range of 10-35 GHz, and a phase noise floor as low as −132.16 dBc/Hz at 10 kHz is obtained.

Graphene-Based Optically Transparent Metasurface Capable of Dual-Polarized Modulation for Electromagnetic Stealth.

Microwave stealth technology with optical transparency is of great significance for solar-powered aircrafts (e.g., satellites or unmanned aerial vehicles) in increasingly complex electromagnetic environments. By coating them with optically transparent absorbing materials or devices, these large-sized solar panels could avoid detection by radar while maintaining highly efficient collection of solar energy. However, conventional microwave-absorbing materials/devices for solar panels suffer from bulky volume and fixed stealth performance that significantly hinders their practicality or multifunctionality. Particularly, dynamic modulation of microwave absorption for dual polarization remains a challenge. In this paper, we propose the design, fabrication, and characterization of an optically transparent and dynamically tunable microwave-absorbing metasurface that enables dual modulations (amplitude and frequency) independently for two orthogonal linearly polarized excitations. The tunability of the proposed metasurface is guaranteed by an elaborately designed anisotropic meta-atom composed of a patterned graphene structure whose electromagnetic responses for different polarizations can be dynamically and independently controlled via bias voltages. The dual tunability in such a graphene-based absorbing metasurface is experimentally measured, which agrees well with those numerical results. We further build an equivalent lumped circuit model to analyze the physical relation between the tunable sheet resistance of graphene and the polarization-independent modulations of the metasurface. Taking into account the advantages of optical transparency and flexibility, the proposed microwave-absorbing metasurface significantly enhances the multitasking stealth performance in complex scenarios and has the potential for advanced solar energy devices.

Implementation of Soft Decoding Mechanism for Addressing Nonlinearities in Long-Distance Optical Transmission System

A soft decoding technique is discussed in this paper to improve the performance of long-distance optical networks (LDOTNs). LDOTNs are affected by phase noise and nonlinearities generated inside the fiber. The investigations of the proposed LDOTN were carried out by dual-polarization 16-quadrature amplitude modulation (DP-16QAM), DP-64QAM over single-mode fiber (SMF) and digital signal processing (DSP) methodologies. The improved performance of the presented mechanism is discussed over SMF based on constellation shaping (CS). The CS of the presented LDOTN is then compared to the standard 16-QAM and 64-QAM using international telecommunication union-telecommunication (ITU-T) standard G-652.D and G-657.A1 SMF. The soft detecting procedure enables the LDOTNs to attain significant outcomes.

A Simple Photonic Generation of a Microwave Waveforms Scheme Based on a Dual-Polarization Dual-Drive Mach-Zehnder Modulator

In this paper, a simple scheme for the generation of sawtooth, triangular, and square waveforms using an integrated dual-polarization dual-drive Mach-Zehnder modulator (Dpol-DDMZM) is proposed. By properly setting the working point and the modulation index of the Dpol-DDMZM, the desired microwave waveforms are easily obtained after photodetection. The proposed scheme for the photonic generation of microwave waveforms is analyzed both by simulation and experiment. The periodical sawtooth, triangular, and square waveforms with repetition rates of 8 GHz are successfully generated. The root-mean-square errors (RMSE) are 0.190, 0.168, and 0.135, respectively. The system features flexible tunability.

Brillouin-assisted frequency-tuning-range-extended and passband-selected microwave photonic filter based on DPol-DPMZM

A frequency-tuning-range-extended and passband-selected microwave photonic filter (MPF) based on dual-polarization dual-parallel Mach-Zehnder modulator (DPol-DPMZM) is proposed and experimentally demonstrated. The upper DPMZM is biased to serve as an equivalent phase modulator, while the lower DPMZM is selectively biased to generate different modulated sideband for pump wave, and then different passband frequency response is selectively realized based on the stimulated Brillouin scattering effect. By using the upper and lower sidebands of carrier-suppression single sideband for pump wave successively, the frequency tuning range of the single-passband MPF can be extended by a value of Brillouin frequency shift, comparing with only one sideband is used. A single-passband MPF with a frequency tuning range of 1.43–19.43 GHz is experimentally obtained, while only a single-tone RF with a frequency range of DC-9 GHz is used. The double-passband MPF with equal passband magnitude and frequency interval tuned is also experimentally achieved.

Miniaturization and performance enhancement of Vivaldi antenna based on ultra-wideband metasurface lens

In this paper, the gradient elliptical slots (ES) are designed to enhance the operating bandwidth of the Vivaldi antenna (VA) in the relatively low frequency band. The antenna EVA is implemented by integrating the elliptical slots to the edge of the VA, which extends the low frequency operating point from 7.4 GHz to 5.4 GHz while obtaining the miniaturized design of the antenna. To address the problem of the gain deterioration, we design ultra-wideband metasurface lens (ML) and integrate it into the aperture of the EVA. The lens has a simple structure that can perform dual polarization modulation on electromagnetic waves. The propagation path of the electric field at the aperture of the EVA loaded with the ML is extended, and the electric field behaves more planar. We simulate and analyze the conventional VA, EVA, and ML integrated EVA (MLEVA). The VA and the proposed MLEVA are fabricated and measured. The results match those of the simulations. The operating bandwidth of the proposed antenna is 5.4–18 GHz that has been expanded compared with the VA. And the gain has increased by approximately 0.3–3.2 dB without changing the overall antenna sizes. The sidelobe level is significantly reduced at the same time. Generally, miniaturization and performance enhancement of the VA is achieved in the proposed MLEVA.

Polarized modulation and receivers for wireless communication

Achieving increase in spectral efficiency has always been a major aspect in communication systems. Our work emphasises the application of dual polarized modulation in a wireless environment. Our main goal is to increase the throughput of the system. We aim to increase the spectral efficiency and throughput without an increment of radiated energy without any Channel State Information at Transmitter (CSIT) and feedback at the transmitter The proposed dual Polarized Modulation (DPMOD) scheme exploits the polarization diversity reducing the required SNR (Eb/N0) and adding an extra bit and achieves the same Bit Error Rate (BER) carrying extra information.

Triangular-shaped waveform generation with variable symmetry based on dual-polarization modulation

Photonic generation of triangular-shaped waveform with variable symmetry based on dual-polarization modulation is proposed and demonstrated. Based on the external modulation method, a dual-polarization modulator is used to modulate the radio frequency signal to generate the needed optical signal. By setting the modulation index of the modulator and phase shift of phase shifters appropriately, the optical intensity of generated signal can equal approximately the first three terms of the Fourier series expansion of the ideal triangular-shaped waveform, so triangular-shaped waveforms with different symmetry factors can be generated. Most of previous triangular waveform generation schemes generate symmetrical triangular waveform or sawtooth waveform (sawtooth waveform can be regarded as an asymmetrical triangular waveform), and the symmetry factor is not tunable. The tunable range of symmetry factor of triangular-shaped waveform generated by this scheme can reach 0%–100%, which will greatly expand the application range of triangular-shaped waveforms. The root-mean-square error (RMSE) is introduced to measure the similarity between the generated waveform and the theoretical waveform. It can be found that theoretically the triangular-shaped waveform with a symmetry factor in a range from 14% to 86% has a good similarity to the ideal waveform (RMSE < 0.044), and the RMSE of the generated waveform in the simulation is also very close to the theoretical RMSE. Experimentally, the 4GHz triangular-shaped waveforms with different values of symmetry factor (20%–80%) are obtained by using 4GHz radio frequency signal.

SOP Change Robust Optical Modulation Based on Dual Polarization Modulation for Multi-Dimensional Optical Transmission

In optical transmission technique using optical polarization, the change of state of polarization (SOP) and the rotation of SOP (RSOP) during optical transmission has a significant impact on the transmission performance. We propose polarized intensity rotational frequency shift keying (PIR-FSK) as a novel modulation technique in change of SOP and RSOP-tolerant optical transmissions. The proposed PIR-FSK signal does not affect the entire intensity of the optical carrier by modulating the sinusoidal signals on each X and Y-polarized optical carrier. Therefore, the proposed PIR-FSK modulation and optical carrier intensity modulation can operate at the same time. Moreover, since the proposed technique does not modulate the signal using the SOP unlike the PolSK, PIR-FSK is not affected by SOP changes that occur during transmission, and the signal does not be degraded even with RSOP. We demonstrated that the signals modulated using the proposed PIR-FSK modulation have higher signal capacity and efficiency compared to the signal modulated using PolSK modulation.

Impact of Transceiver Noise on the Outage Probability Due to Polarization Dependent Loss

The method of threshold exceedances is used to investigate the impact of transceiver noise on the outage probability due to per-span polarization dependent loss (PDL). A simulation model that captures the distributed effect of PDL on the signal and amplified spontaneous emission noise is used to obtain bit-wise achievable information rate (BW-AIR) data for 10,000 instances of the link PDL. The outage probability is defined in terms of the BW-AIR being less than a threshold determined by the forward error correcting code rate. The dependence of the outage probability on the transceiver signal-to-noise ratio is assessed for 32 Gbaud, dual-polarization 64-ary quadrature amplitude modulation with uniform and probabilistically shaped constellations.

Estimating the Outage Probability Due to Polarization Dependent Loss Using Threshold Exceedances

The method of threshold exceedances is used to reliably estimate the outage probability due to per-span polarization dependent loss (PDL). Bit-wise achievable information rate (BW-AIR) data for 10,000 instances of the link PDL are obtained using a simulation model that accurately captures the effect of PDL on both the signal and amplified spontaneous emission noise. The root mean square error between the mean excess function and a theoretical fit to it, and the average squared absolute error are compared for the critical step of determining the threshold above which transformed BW-AIR data are represented by the generalized Pareto distribution (GPD). Four techniques are considered for determining values of the two parameters that specify the GPD. The outage probability is defined in terms of the BW-AIR being less than a threshold value for the generalized mutual information (GMI), as determined by a specified value for the normalized GMI. To thoroughly demonstrate the approach, the dependence of the outage probability on the per-span PDL, the number of spans, and the constellation entropy is considered for 32 Gbaud, dual-polarization 64-ary quadrature amplitude modulation with uniform and probabilistically shaped constellations. The extent to which the outage probability can be reduced by decreasing the constellation entropy is quantified.

Simultaneous Generation of Wired and Wireless Signals Using a DP-MZM in a RoF System

We experimentally demonstrate a simultaneous generation of independent 10-Gbit/s wired on/off keying (OOK) signal and 20-Gbit/s wireless quadrature phase shift keying (QPSK) signal by using a dual-polarization Mach-Zehnder modulator (DP-MZM) in a millimeter-wave-band radio-over-fiber system at 30 GHz. The polarization directions of two signals are orthogonal, so there is not any interference between two polarizations in the photodiode. By using a 100/200-GHz interleaver, the power penalty after 15-km fiber transmission for the wireless QPSK signal can be reduced from 3.9 to 1.9 dB. As we know, this is the first time to use QPSK modulation format for the wireless signal in the simultaneous generation and delivery of wireless and wired signals by using a dual-polarization modulator.

Impact of Equalization-Enhanced Phase Noise on Digital Nonlinearity Compensation in High-Capacity Optical Communication Systems.

Equalization-enhanced phase noise (EEPN) can severely degrade the performance of long-haul optical fiber transmission systems. In this paper, the impact of EEPN in Nyquist-spaced dual-polarization quadrature phase shift keying (DP-QPSK), dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM), and DP-64QAM optical transmission systems is investigated considering the use of electrical dispersion compensation (EDC) and multi-channel digital backpropagation (MC-DBP). Our results demonstrate that full-field DBP (FF-DBP) is more susceptible to EEPN compared to single-channel and partial-bandwidth DBP. EEPN-induced distortions become more significant with the increase of the local oscillator (LO) laser linewidth, and this results in degradations in bit-error-rates (BERs), achievable information rates (AIRs), and AIR-distance products in optical communication systems. Transmission systems using higher-order modulation formats can enhance information rates and spectral efficiencies, but will be more seriously degraded by EEPN. It is found that degradations on AIRs, for the investigated FF-DBP schemes, in the DP-QPSK, the DP-16QAM, and the DP-64QAM systems are 0.07 Tbit/s, 0.11 Tbit/s, and 0.57 Tbit/s, respectively, due to the EEPN with an LO laser linewidth of 1 MHz. It is also seen that the selection of a higher-quality LO laser can significantly reduce the bandwidth requirement and the computational complexity in the MC-DBP.

Modulation format identification of optical signals: an approach based on singular value decomposition of Stokes space projections.

In this paper, two Stokes space (SS) analysis schemes for modulation format identification (MFI) are proposed. These schemes are based on singular value decomposition (SVD) and Radon transform (RT) for feature extraction. The singular values (SVs) are extracted from the SS projections for different modulation formats to discriminate between them. The SS projections are obtained at different optical signal-to-noise ratios (OSNRs) ranging from 11 to 30 dB for seven dual-polarized modulation formats. The first scheme depends on the SVDs of the SS projections on three planes, while the second scheme depends on the SVDs of the RTs of the SS projections. Different classifiers including support vector machine (SVM), decision tree (DT), and K-nearest neighbor (KNN) for MFI based on the obtained features are used. Both simulation and experimental setups are arranged and tested for proof of concept of the proposed schemes for the MFI task. Complexity reduction is studied for the SVD scheme by applying the decimation of the projections by two and four to achieve an acceptable classification rate, while reducing the computation time. Also, the effect of the variation of phase noise (PN) and state of polarization (SoP) on the accuracy of the MFI is considered at all OSNRs. The two proposed schemes are capable of identifying the polarization multiplexed modulation formats blindly with high accuracy levels up to 98%, even at low OSNR values of 12 dB, high PN levels up to 10 MHz, and SoP up to 45°.

Channel characterization of a dual-band dual-polarized SAR with digital beamforming

AbstractThis paper presents the integration and channel characterization of a highly integrated dual-band digital beamforming space-borne synthetic aperture radar (SAR) receiver. The proposed SAR sensor is a low-cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module ready for the next-generation space-borne SAR missions. In previous works, by the authors, the design and experimental characterization of each sub-system was already presented and discussed. This work expands upon the previous characterization by providing an exhaustive experimental assessment of the fully integrated system. As it will be shown, the proposed tests were used to validate all the instrument channels in a set-up where the SAR sensor was illuminated by an external source minim the ground reflected waves. Test results demonstrate how the system channels are properly operating allowing the reception of the input signals and their processing in the digital domain. The possibility to easily implement a calibration procedure has also been validated to equalize, in the digital domain, the unavoidable amplitude differences between the different channels.