Dual-polarization Quadrature Phase Shift Keying Modulator Research Articles

Numerical evaluation of bidirectional high-speed data transmission over turbulence tolerable FSO link employing WDM-OAM multiplexing and DP-QPSK modulation techniques

Orbital angular momentum (OAM) mode multiplexing is achieving utmost interest for the enhancement of transmission capacity and spectral efficiency. We have reported a (2 × 8 × 112 Gbps) 1792 Gbps bi-directional FSO link based on WDM-OAM multiplexing and dual-polarization quadrature phase-shift keying (DP-QPSK) modulation technique. An optical frequency comb lines (OFCL) generator, capable to generate 44 comb lines with flatness∼0 dB is employed as a broadband laser source. The efficiency of the system is not only checked for clear weather but also for different turbulence situations (weak, moderate, and strong atmospheric turbulence). According to the best of our knowledge, this is the first one where the effect of atmospheric turbulence on DP-QPSK data carrying OAM modes has been checked for a bidirectional link. The combination of coherent detection with digital signal processing is utilized for compensating wave-form distortion and noise cancellation due to atmospheric turbulence. A very low power penalty of 1.65 dB in clear weather and 4.91 dB in strong atmospheric turbulence at a BER∼10 −9 with open eye and clear constellation diagrams depicts the feasibility of the proposed system.

Frequency-Doubled Triangular Pulse Signal Generation with Variable Symmetry Based on a Dual-Polarization Quadrature Phase-Shift Keying Modulator

Frequency-Doubled Triangular Pulse Signal Generation with Variable Symmetry Based on a Dual-Polarization Quadrature Phase-Shift Keying Modulator

Filter-free photonics-assisted frequency translator with a tunable phase shift and amplitude based on an integrated DP-QPSK modulator.

In this paper, we propose and demonstrate a novel, to the best of knowledge, filter-free photonics-assisted microwave frequency translator with a tunable phase shift and amplitude. The pivotal component of the proposed scheme is an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator, which is applied to generate a polarization orthogonal carrier-suppressed single sideband modulation signal and frequency shifted optical carrier signal. The polarization-multiplexed optical signal outputs from the DP-QPSK modulator is then sent to a photodetector (PD) via a polarization controller (PC) and a polarizer to implement photoelectric conversion. The electrical signal output from the PD is the desired frequency translated microwave signal, and the amount of frequency shift is determined by the frequency of the sawtooth wave applied to the DP-QPSK modulator. In addition, since the PC can be used to adjust the polarization angle and introduce a phase difference between the two orthogonally polarized optical signals, the phase shift and amplitude of the obtained translated signal can also be easily tuned. A theoretical analysis and simulation experiment are carried out to verify the feasibility of the proposed scheme. The simulation results show that the novel scheme can realize frequency translation with a 360° continuously tunable phase shift and adjustable amplitude for both a single-tone signal and linearly frequency modulated signal with a 50MHz bandwidth. The spurious suppression ratios of the single-tone signal and LFM signal after frequency translation are larger than 48 and 30dB, respectively.

Microwave photonic multiform microwave frequency shift keying signal generator.

A photonic approach to realizing multiform microwave frequency shift keying (FSK) signal generation is proposed and demonstrated. In the scheme, a commercial dual-polarization quadrature phase shift keying modulator (DP-QPSKM) is employed to generate two orthogonally-polarized signals containing specific optical sidebands, and a subsequent Sagnac loop structure govern the interference results of these two signals. From a theoretical analysis, when the modulators are properly biased, microwave FSK signal with fixed double relationship or flexibly tunable subcarrier frequencies can be obtained, and high frequency multiplication can be realized in the meantime. Furthermore, a photonic-optimized coherent demodulation structure is designed to recover the binary coding data, which can effectively avoid the electronic bottleneck. Simulation has been performed to investigate the mechanism and the discussions about the robustness to non-ideal parameters including DC bias, phase shift and polarization angle are also given. In the proof-of-concept experiment, microwave FSK signal with subcarrier frequencies of 2/4, 2.2/3.8, 2.4/3.6, 2.6/3.4, 2.8/3.2 GHz are generated, and the correct binary coding data is successfully recovered with the aid of simulation platform. The simulation and experimental results can verify the feasibility of the proposed multiform microwave FSK signal generator, which may find applications in modern radar and communication systems.

Photonic Generation and Antidispersion Transmission of Background-Free Multiband Arbitrarily Phase-Coded Microwave Signals

A novel type of photonic background-free multiband arbitrarily phase-coded microwave signal generator with power fading elimination capability is reported. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarized phase modulated optical signal and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarized radio frequency (RF) modulated harmonic single-sideband (HSSB) optical signal are produced based on a dual-polarization quadrature phase shift-keying modulator (DP-QPSKM). After polarization modulation to intensity modulation conversion, a microwave signal with arbitrarily phase encoding in multiple frequency bands is generated. Benefiting from the phase modulation state of the driven electrical coded signal, the generated arbitrarily phase-coded signal has no baseband components. Moreover, the equivalent HSSB modulation ensures the system can realize antidispersion transmission of one-to-multi base stations (BSs). The main distinct highlights of our generator are multifunction. The proposed single-modulator-based photonic scheme can achieve phase encoding in arbitrary format over multiple frequency bands and transmit over long-distance single-mode fiber with the elimination of power fading simultaneously. This work is pretty promising in multiband radar systems for one-to-multi BSs transmission and can increase the detection range, range resolution, Doppler tolerance, and sensitivity of objective recognition of radars.

1000 Gbps MDM-WDM FSO link employing DP-QPSK modulation scheme under the effect of fog

In this work, a dual polarization-quadrature phase shift keying (DP-QPSK) modulation scheme has been used for analysing the performance of terrestrial MDM-WDM FSO link at a data rate of 1000 Gbps. The proposed link has been investigated considering linearly polarized (LP) 01 and 02 modes with a channel capacity and spacing of 10 × 100 Gpbs and 10 GHz respectively. The performance of the system has been evaluated in terms of received optical power and signal to noise ratio (SNR) for clear weather, light, medium and heavy fog conditions over a propagation range varying from 1.2 km to 20 km.

Wideband Tunable Frequency Converter Based on an OEO Using a DP-QPSK Modulator

Flexibility and tunability are critical for frequency conversion in antenna, radar and modern communication systems. In this study we propose and experimentally demonstrate a wideband tunable frequency converter by using an optoelectronic oscillator (OEO) to generate high-purity local oscillator (LO) signal for flexible frequency conversion. In the proposed frequency converter, a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is utilized to receive the signal to be converted and also to form a tunable OEO based on a dispersion-induced microwave photonic filter. By adjusting the bias voltage of the DP-QPSK modulator, an LO signal with accurate adjustable frequency is generated by the OEO. The measured phase noise of generated LO signal can reach -110 dBc/Hz at 10 kHz offset. An experiment is performed to verify the feasibility of this proposed frequency converter. The 7.6-GHz radio frequency (RF) signal is freely converted to different intermediate frequency (IF) signals, respectively. Moreover, the proposed microwave photonic converter is applied into wireless transmission systems. A 1-Gb/s NRZ wireless signal centered at 6.5 GHz is down-converted to baseband successfully.

Photonic generation of flexible ultra-wide linearly-chirped microwave waveforms

Thanks to the large time bandwidth product (TBWP), linearly chirped microwave waveforms (LCMWs) are widely used in modern radar systems to achieve high-resolution detection and imaging. To overcome the challenge of small unmanned aerial vehicle detection and tracking, radar systems are required to have a higher resolution and multi-function operation, in which an ultra-wideband LCMW is highly preferred with a flexible tuning in the center frequency, instantaneous bandwidth, and multi-band operation. In this paper, we propose and experimentally demonstrate an approach to generating flexible ultra-wide LCMWs based on a Fourier-domain mode-locked optoelectronic oscillator (FDML-OEO) incorporating a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. In the DP-QPSK modulator, two dual-parallel Mach-Zehnder modulators (DP-MZMs) are integrated. With the use of the upper DP-MZM, an FDML-OEO is produced to generate a wideband LCMW with a tuning in the center frequency and instantaneous bandwidth. With the injection of the generated LCMW into the lower DP-MZM, an ultra-wideband LCMW is generated via microwave frequency multiplication, and multi-band waveform generation is enabled by controlling the bias condition of the lower DP-MZM. An experiment is performed and an LCMW with a maximum bandwidth as broad as 10.8 GHz is generated. By adjusting the driving signal applied to the FDML-OEO, the generated LCMW can be tuned in the center frequency from 16.2 to 23.2 GHz and the bandwidth from 3.6 to 10.8 GHz. By controlling the bias point of the lower DP-MZM, a dual-band LCMW is also experimentally demonstrated. Thanks to the ultra-wide bandwidth and strong flexibility of the generated LCMWs in terms of tunable center frequency, instantaneous bandwidth and multiband operation, the proposed approach offers a promising LCMW generator in the next-generation high-resolution radar systems.

Switchable instantaneous frequency measurement by optical power monitoring based on DP-QPSK modulator

We propose and analyze an instantaneous frequency measurement system by using optical power monitoring technique with improved resolution. The primary component adopted in the proposal is a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which is used to modulate the microwave signal that has a designed time delay and phase shifting. The generated optical signal is sent to polarization beam splitter (PBS) in DP-QPSK modulator. Owing to the complementary transmission nature of polarization interference introduced by PBS, the frequency information is converted into the optical power and the relationship between the amplitude comparison function (ACF) and microwave frequency to be measured is established. Thus, the frequency of the microwave signal can be easily measured through monitoring the optical powers of the two output ports of the PBS. Furthermore, by adjusting the direct current (DC) biases of the DP-QPSK modulator instead of changing the electrical delay, the measurement range and resolution can be switched. In this paper, the basic principle of the instantaneous frequency measurement system is derived in detail, and simulation has been performed to investigate the resolution, the measurement range, and the influence of imperfection devices. The proposed scheme is wavelength-independent and its measurement range is switchable, which can avoid the laser wavelength drifting problem and thus greatly increasing the system flexibility.

Photonic-based analog and digital RF self-interference cancellation with high spectral efficiency.

A photonic-assisted analog and digital radio frequency (RF) self-interference cancellation (SIC) approach with high spectral efficiency is reported for base stations in in-band full-duplex radio-over-fiber systems on the basis of our previous research. One dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is used as the canceller for one base station. The two dual-parallel Mach-Zehnder modulators of the DP-QPSK modulator are both biased as carrier-suppressed single-sideband modulators and driven by the received signal and reference signal, respectively, to achieve high spectral efficiency while implementing the SIC in the optical domain. The baseband optical signal after SIC is further transmitted to the central station, where the electrical signal is recovered, sampled, and processed to further suppress the residual self-interference in the digital domain by using the recursive least-square (RLS) algorithm. An experiment is then performed. The proposed system is demonstrated by employing two independent channels. The analog cancellation depths of the 200, 500, and 800 Mbaud QPSK-modulated self-interferences are around 24, 20, and 20 dB, respectively; the total cancellation depths are around 29, 28, and 25 dB, respectively, when the analog cancellation and the RLS algorithm digital cancellation are applied. Meanwhile, the fiber distribution has no significant influence on SIC performance.

Microwave photonic frequency down-conversion with self-interference cancellation and SSBI mitigation

In this paper, we proposed a microwave photonic frequency down-conversion scheme with the functions of self-interference cancellation (SIC) and signal–signal beat interference (SSBI) mitigation. The scheme is based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. One of the dual-parallel Mach–Zehnder modulator (DP-MZM) which is located in the upper part of the DP-QPSK modulator is used to achieve SIC by properly biasing the modulator. A local oscillator signal is loaded on the other DP-MZM which is located in the lower part of the DP-QPSK modulator. After photoelectric conversion of the combined optical signal by a photo-detector (PD), the signal of interest (SOI) is down-converted to an intermediate frequency (IF) signal. The SSBI is mitigated by Kramers–Kronig (KK) detection to achieve lower IF down-conversion. Experimental results show that the SIC for a single-tone interference signal is around 53 dB, and for an interference signal with a bandwidth of 100 MHz, the SIC achieved at least 29 dB. A simulation verifies the effect which the least mean square (LMS) algorithm mitigated on the influence of multipath After SIC, we used KK algorithm to reduce error vector magnitude (EVM) of the down-converted 16-QAM signal from 17.54% to 9.07%, which indicates a remarkable SSBI mitigation effect.

Photonic generation of frequency-quadrupled triangular waveform based on a DP-QPSK modulator with tunable modulation index

In this paper, a scheme for generating frequency-quadrupled triangular waveform based on a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator is proposed. The repetition rate of the generated triangular waveform is four times the frequency of radio frequency (RF) signal. In this scheme, the modulation index of modulator is no longer a fixed value, and it can be adjusted in a certain range, which increases the flexibility of the scheme. Compared with previous frequency-quadrupled triangular waveform generation schemes, the structure of this scheme is simple, and the scheme enables good repetition rate tunability. The effect of extinction ratio and DC bias drift of modulator on the scheme is analyzed by simulation.

Reconfigurable Photonic Microwave Mixer With Mixing Spurs Suppressed and Dispersion Immune for Radio-Over-Fiber System

In this article, a reconfigurable mixer based on only one dual-polarization quadrature phase shift -keying modulator (DP-QPSKM) is proposed and comprehensively demonstrated for a radio-over-fiber (RoF) system. By changing the detection unit and adjusting the dc voltages, the single-ended, double-balanced, image (IM)-free, mixing spurs suppressed, and dispersion-immune mixing can be implemented. Experimental results show that the ~60-dB IM rejection ratio and the spur suppression ratio are achieved. Moreover, the dispersion-induced power fading is successfully compensated by the dc voltage adjustment. The spurious-free dynamic range (SFDR) is about 100.56 dB.Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> . Only one optical path is required without extra optical filters or phase-related devices, which makes the structure concise and stable. This structure would be more compact to meet the potential of integration if a dispersion medium with smaller size is available.

Linearized analog photonic down-conversion link based on a dual-polarization quadrature phase-shift keying modulator

A novel linearized analog photonic down-conversion link based on an integrated dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally verified. Radio frequency and local oscillator signals are fed into the DP-QPSK modulator via an electrical attenuator, respectively. By adjusting the ratio of the two attenuators, the third-order intermodulation distortion can be eliminated based on balanced detection. The scheme is simple and compact and it achieves full spectrum utilization because of using no filter. Experimental results show that the spurious free dynamic range is improved by 16.43 dB for a two-tone signal and the error vector magnitude is improved by 6.16% for a 100-MSym/s 16-quadrature-amplitude-modulation signal.

Photonics-based multi-band linearly frequency modulated signal generation and anti-chromatic dispersion transmission.

A photonics-based anti-chromatic dispersion transmission scheme for multi-band linearly frequency modulated (LFM) signals is proposed and experimentally demonstrated. In the central station (CS), the key component is an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator, of which the up-arm and down-arm are driven by a microwave reference signal and an intermediate-frequency (IF) LFM signal respectively. By properly adjusting the DP-QPSK modulator, optical frequency comb (OFC) and frequency shift lightwave are generated. After polarization coupling and remote transmission, the orthogonal-polarization optical signals are introduced into balanced photodetector for heterodyne detection. Thence, multi-band LFM signals are generated and transmitted to remote base stations (BS) with the largest power for the anti-chromatic dispersion ability. Experiments are conducted to verify the analysis. Multi-band LFM signals at L (1.5 GHz), C (7 GHz), X (10 GHz), Ku (15.5 GHz) and K (18.5 GHz) bands with flatness of 1.9 dB are simultaneously obtained in the CS after 50 km fiber transmission, while the normally double-sideband modulation approach experiences a significant power fading for the fiber dispersion. Tunability of the system is evaluated, and detection performances of the generated signals are also analyzed.

Simple approach for Doppler frequency shift estimation based on a dual-polarization quadrature phase shift keying (DP-QPSK) modulator.

A simple approach to estimating microwave Doppler frequency shift (DFS) based on a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is capable of estimating both the value and direction of the DFS simultaneously and precisely owing to the introduction of the reference signal. In the proposed approach, the transmitted signal (microwave carrier) and the reference signal are loaded on the upper branch of the DP-QPSK modulator to generate carrier suppression double-sideband signals, respectively, while the echo signal is loaded on the lower branch of the DP-QPSK modulator to perform carrier suppression single-sideband modulation. Then optical sidebands of two branches are combined and sent to a low-speed photodetector to heterodyne. The value of the DFS is equivalent to the frequency of the beat signal between the transmitted and reference signals; meanwhile, the direction can be distinguished by comparing the frequency of the beat signal between the transmitted and reference signals with the frequency of the beat signal between the echo and reference signals. In the experiment, the accurate measurement of DFSs from $ - {100}\;{\rm kHz}$-100kHz to $ + {100}\;{\rm kHz}$+100kHz at the carrier frequencies of 15, 20, 35, and 39 GHz is implemented with errors less than $ \pm {10}\;{\rm Hz}$±10Hz.

Photonic generation of microwave dual-band phase coded signal

A simple photonic microwave dual-band phase coded signal generation method employing an integrated dual-polarization quadrature phase shift-keying (DP-QPSK) modulator and a balanced photodetector (BPD) is proposed and experimentally demonstrated. In the proposed system, the X-DPMZM is driven by a coding signal and the Y-DPMZM is driven by two different radio frequency (RF) signals. After balanced photo-detection, a microwave phase-coded signal is obtained. The working frequency range of the scheme is only limited by the modulation frequency of the DP-QPSK modulator. The feasibility of the proposed system is verified by a proof-of-concept experiment. Microwave dual-band phase coded signals, with 11-GHz and 16-GHz carrier frequencies respectively, are simultaneously generated by our system.

Simulation Study of DP-QPSK Coherent Detection Transmission System Based on Optisystem

Dual polarization quadrature phase shift keying (DP-QPSK) is currently the main modulation format for high-speed optical fiber communications, and its simulation modeling has important implications for theoretical research and practical applications. Based on Optisystem 15 optical communication system simulation software, this paper builds a 100 Gbit/s rate DP-QPSK modulation format coherent optical transmission system simulation model, analyzes the working principles of the transmitting end, transmission link, and coherent receiver. The principle of signal recovery at the digital signal processing end is briefly explained. The simulation results show that the signal quality after DSP processing has been significantly improved.

Microwave Photonic Multifunctional Phase Coded Signal Generator

A novel phase coded signal generator is proposed and experimentally verified. The scheme consists of a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator and a phase modulator in a Sagnac loop. By properly adjusting the bias voltages of the DP-QPSK modulator and the polarization direction of the signal, two-order optical sideband is polarization separated from the carrier and −2-order sideband. We can modulate the two-order optical sideband with phase coded data and two phase coded signals will be generated which are the beating products between the modulated two-order optical sideband and the unmodulated optical sidebands in balanced detector. The distinct advantage of our approach is that we integrate multiple functions into a compact system which can simultaneously generate dual-band and multi-phase coded signal with doubled and quadrupled frequency. In the experiment, 1-Gbit/s binary and quaternary phase coded signals with 11 and 22 GHz carrier frequencies are generated by using of a 5.5 GHz local oscillator signal.

Photonic Generation of a Dual-Band Polyphase-Coded Microwave Signal With a Tunable Frequency Multiplication Factor

A photonic approach to generate dual-band polyphase-coded microwave signal with a tunable frequency multiplication factor is proposed. The scheme contains a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator, a polarization modulator (PolM), and a balanced detector. When the bias voltages of the DP-QPSK modulator is properly adjusted, a double-sideband signal will be generated with one sideband along the X polarization of the PolM, with the optical carrier and the other sideband along the Y polarization. Then, the PolM is employed to modulate the optical signal with a phase-coded microwave signal. After the photoelectric balanced detection, polyphase-coded microwave signals with frequency multiplication factors of one, two, and four can be generated. In addition, the proposed scheme can simultaneously produce two phase-coded microwave signals with different carrier frequencies. The proposed system finds a potential application in dual-band radar. In the experiment, a binary- and a quaternary-phase-coded signal with 5.5, 11, and 22 GHz carrier frequencies are generated.