Optical Carrier Phase Research Articles

Optical Carrier Phase Sweeping Based RF Signal Frequency Measurement System

Optical Carrier Phase Sweeping Based RF Signal Frequency Measurement System

High-Precision Optical Carrier Phase Measurement Technology Based on Two-Satellite Formation

High-Precision Optical Carrier Phase Measurement Technology Based on Two-Satellite Formation

Photonics-Assisted Ultrawideband RF Self-Interference Cancellation With Signal of Interest Recovery and Fiber Transmission

Self-interference and chromatic dispersion are two main limiting factors that influence the recovery of the signal of interest (SOI) in in-band full-duplex (IBFD) radio-over-fiber (RoF) links. An ultrawideband photonic-assisted approach to radio-frequency (RF) self-interference cancellation (SIC) with high-speed SOI recovery and fiber transmission capability is proposed. The key to achieve the above optimum performances in a compact system is the combined use of fiber dispersion induced RF time delay and optical carrier phase-shifted double sideband (CPS-DSB) modulation. A high precision and tunable time delay matching between the reference signal and the SI signal can be achieved by dispersion induced RF time delay. Meanwhile, the equal amplitude, phase reversal, and dispersion-induced SOI power fading compensation conditions are satisfied simultaneously by manipulating the optical carrier phase of the CPS-DSB signal. For 25 km fiber transmission, 30 dB cancellation depth over 2.7 GHz bandwidth, 160 Mbit/s 16-quadrature amplitude modulation (16-QAM) SOI recovery, and good immunity to fiber dispersion are experimentally demonstrated. In addition, the proposed scheme facilitates multipath SIC by implementing an array of tunable lasers (TLs) with a shared electro-optic modulator at the reference branch.

Coherent Detection-Based Optical OFDM, 60 GHz Radio-over-Fiber Link Using Frequency Quadrupling, and Channel and Carrier Phase Estimation

The optical orthogonal frequency division multiplexing (OFDM) is proven to be a most promising technology for the next-generation high-capacity and ultra-wide bandwidth 5G communication systems. 60 GHz millimeter-wave (mm-wave) frequency band is also becoming a most popular upcoming frequency spectrum due to today’s available dense frequency spectrum used for mobile, multimedia, and data communication, etc. We propose a system comprised of 60 GHz radio-over-fiber (RoF) model using optimized optical frequency quadrupling, coherent detection, channel estimation, and carrier phase correction techniques for ultra-wide bandwidth 16-quadrature amplitude modulation (QAM) OFDM baseband signal. The proposed RoF system’s outcomes have shown relatively better bit error rate (BER) of 3.1 × 10–3 to enable successful transmission of 110 Gbps data for more than 105 km optical link comprising of standard single-mode fiber (SSMF). System performance and obtained results show a potential to fulfill the requirements of 5G and cellular communication system.

Phase-shift laser range finder technique based on optical carrier phase modulation.

A coherent laser range finder based on optical phase modulation and phase shift measurement is presented. In the proposed laser range finder, the emitted laser is modulated by an electro-optic phase modulator using a 20 MHz sine signal, and the received laser is mixed with a local oscillator using a 90° optical hybrid. Compared with traditional laser phase shift range finders, the proposed laser range finder can measure the velocity and range at high precision simultaneously. An algorithm to calculate the range and velocity is deduced. Our preliminary experiments on moving targets indicate that when the measurement rate is 100 kHz, the root mean square errors of range and velocity, respectively, are 9.35×10-4m and 4.74×10-4m/s.

Full-duplex broadcast RoF-WDM-PON with self-coherent detection and photonic frequency up/down-conversion using SSB pilot-carrier

A novel bidirectional broadcast radio-over-fiber-wavelength division multiplexing-passive optical network (RoF-WDM-PON) based on self-coherent detection and photonic frequency up and down-conversion is presented. In the proposed scheme, a single sideband (SSB) modulated pilot-carrier is transmitted to the optical network unit (ONU), together with the downstream signal by polarization multiplexing on the same fiber link. The SSB pilot-carrier serves as a local oscillator laser to realize coherent detection and an optical carrier of the upstream signal simultaneously. In this way, the optical carrier phase noise and frequency offset in coherent detection have been efficiently eliminated in ONU. Moreover, the detection of the downstream baseband signal and millimeter wave (MMW) signal by homodyne and heterodyne detection can be simultaneously implemented in the proposed scheme. Due to the reuse of SSB light wave, the upstream radio-frequency signal is down-converted at the optical line terminal (OLT) directly by photonic-mixing technique. The performance of proposed RoF-WDM-PON system is evaluated for 20 km signal-mode fiber full-duplex transmission of a 40 Gb/s 16-QAM baseband signal and 10 Gb/s DPSK wireless signal.

Reconfigurable photonic dual‐frequency phase‐coded signals generator by using optical carrier phase shifting and polarisation selection

A novel photonic dual-frequency phase-coded signals generator based on the optical carrier phase shifting and polarisation selection techniques is proposed by using an integrated dual-polarisation quadrature phase shift keying (DP-QPSK) modulator. The key feature of the scheme is the capability to generate dual-frequency phase-coded signals with reconfigurable frequency multiplication factors. In the upper QPSK modulator, an optical binary phase shift keying (BPSK) signal and a carrier-suppressed double-sideband optical signal are generated, while in the bottom QPSK modulator, another carrier-suppressed double-sideband optical signal is generated. Thanks to the dual-polarisation property of the integrated modulator, the optical BPSK signal and different optical sidebands can be selected by using polarisation selection. As a result, two phase-coded signals with different frequencies can be achieved simultaneously. By adjusting the bias phases of the submodulators, dual-frequency phase-coded signals with frequencies of one and three, or two and four times the frequency of the RF carrier can be generated. The generation of 2.5 Gbps dual-frequency phase-coded signals with frequencies of 20 and 40 GHz, or 10 and 30 GHz are verified. The proposed scheme is simple, compact, and promising to find applications in future multi-band and multi-functional radars.

Photonically assisted microwave waveform generation by gain-transparent SBS-induced carrier processing.

We propose and experimentally demonstrate a new approach to generate microwave waveforms by phase modulation and optical carrier phase processing based on gain-transparent stimulated Brillouin scattering (SBS). By properly adjusting the SBS-induced-phase shift on the carrier and the following group velocity dispersion, microwave waveforms with controllable repetition rates and temporal profiles can be generated. In the experiment, we have successfully generated triangular waveforms at repetition rates of 5.64 and 7.87GHz, and rectangular waveforms at repetition rates of 5.04 and 7.01GHz.

Generation of a frequency-quadrupled phase-coded signal using optical carrier phase shifting and balanced detection.

A novel approach for photonic generation of a frequency-quadrupled phase-coded signal using optical carrier shifting and balanced detection is proposed and demonstrated. The key component of the scheme is an integrated dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. In the modulator, an RF signal is applied to the upper QPSK modulator to generate high-order optical sidebands, while an electrical coding signal is applied to the bottom QPSK modulator to perform optical carrier phase shifting. After that, a frequency-quadrupled phase-coded signal with an exact π-phase shift is generated through balanced detection. The proposed scheme has a simple, compact structure and good tunability. Besides, a phase-coded pulse can be directly obtained when a three-level rectangular coding signal is applied. A proof-of-concept experiment is carried out. The generation of a 2-Gbit/s phase-coded signal with a frequency tuning from 12.12 to 28 GHz is experimentally demonstrated, and the generation of a phase-coded microwave pulse is also verified.

A continuously tunable microwave photonic notch filter with complex coefficient based on phase modulation

A continuously tunable microwave photonic notch filter with complex coefficient based on phase modulation is proposed and demonstrated. The complex coefficient is generated using a Fourier-domain optical processor (FD-OP) to control the amplitude and phase of the optical carrier and radio-frequency (RF) phase modulation sidebands. By controlling the FD-OP, the frequency response of the filter can be tuned in the full free spectral range (FSR) without changing the shape and the FSR of the frequency response. The results show that the center frequency of the notch filter can be continuously tuned from 17.582 GHz to 29.311 GHz with FSR of 11.729 GHz. The shape of the frequency response keeps unchanged when the phase is tuned.

Photonic microwave phase shifter based on dual-sideband phase-control technique.

An all-optical photonic microwave phase shifter that can realize a continuous 0°-360° phase shift is presented. The phase-shifting operation is implemented by controlling the phase of the two RF phase-modulation sidebands while keeping the optical carrier phase fixed. The use of two RF modulation sidebands, instead of a single sideband used in most conventional phase shifters, has the advantage of high-output RF signal power, and consequently high signal-to-noise ratio performance. Experimental results demonstrate the full -180° to +180° phase shift over a wide microwave frequency range from 11 to 26.5 GHz, and 14 dB increase in the output RF signal power compared to a conventional phase shifter.

Microwave Photonic Filter With Complex Coefficient Based on Optical Carrier Phase Shift Utilizing Two Stimulated Brillouin Scattering Pumps

A microwave photonic filter (MPF) with complex coefficient based on the frequency transparent magnitude response by independent control of the frequency and power of two stimulated Brillouin scattering (SBS) pumps is proposed and experimentally demonstrated. The motivation of this paper lies in the fact that the operation bandwidth of the previous SBS-based complex coefficient MPFs is unavoidably limited by the Brillouin frequency shift. In our scheme, the complex coefficients are obtained by a broadband microwave photonic phase shifter based on the two SBS pumps. The two SBS pump signals are located at the same side of the optical carrier. In principle, the working bandwidth of the proposed MPF is infinite. One pump is used to introduce a controllable phase shift on the optical carrier, whereas the other pump is used to retain the power of the optical carrier invariant. By simply changing the phase shift of a complex coefficient, the frequency response of the two-tap complex coefficient MPF is continuously tuned over the full free spectral range (FSR), keeping shape and FSR invariant.

Optical-to-RF phase shift conversion-based microwave photonic phase shifter using a fiber Bragg grating

A novel microwave photonic phase shifter structure is presented. It is based on the conversion of the optical carrier phase shift into an RF signal phase shift via controlling the carrier wavelength of a single-sideband RF-modulated optical signal into a fiber Bragg grating. The new microwave photonic phase shifter has a simple structure and only requires a single control to shift the RF signal phase. It also has the ability to realize multiple phase shifts. Experimental results demonstrate a continuous 0°-360° phase shift with low amplitude variation of <2 dB and low phase deviation of <5° over a wideband microwave range.

A novel two-stage phase noise estimation algorithm for coherent optical OFDM systems

In coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) receivers, the phase noise caused by the instabilities of the local oscillator is a potentially serious problem. In order to deal with the common phase error (CPE) caused by the phase noise in actual CO-OFDM receiver, a novel two-stage Least Mean Square (LMS) phase noise adaptive estimation algorithm is proposed. In the proposed estimation algorithm, an initial coarse estimation of the optical carrier phase to exploit the knowledge of pilot symbols is followed by a fine LMS adaptive estimation. The main advantage of the proposed method is that the phase-ambiguity problem is avoided after a cycle slip and the Bit Error Rate (BER) performance is improved. Furthermore, the phase noise effect induced by the transmitter laser and receiver Local Oscillator (LO) is analyzed. A simple CO-OFDM transmission system with QPSK to apply the proposed adaptive estimation algorithm is simulated, the simulation analysis shows that the proposed adaptive estimation algorithm has a more excellent performance.

Photonic RF Phase Shifter Based on Optical Carrier and RF Modulation Sidebands Amplitude and Phase Control

A new photonic microwave phase shifter that can achieve a full 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> phase shift with very little RF signal amplitude variation, and which can operate over very wide frequency range, is presented. It is based on controlling the amplitude and phase of the optical carrier and the two RF modulation sidebands via the dc bias voltages to a dual-parallel Mach-Zehnder modulator (DPMZM). It has a simple structure, only requiring a single laser, modulator, and photodetector. A continuous 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> RF phase shift without changes in the RF signal amplitude is obtained by controlling the dc bias voltages of the DPMZM. Experimental results demonstrate a very wideband operation of the RF phase shifter over an 8:1 frequency range from 2 to 16 GHz, a continuous 0-360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> RF phase shift with very low amplitude variation of <; 3 dB of over the entire frequency band, and with a phase deviation standard deviation of <; 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> .

Multi-stage feed-forward optical carrier phase estimation based on QPSK partitioning for 64-QAM signals

We numerically investigate two multi-stage feed-forward optical carrier phase estimation (CPE) methods for coherent optical 64-QAM signals, which are QPSK partitioning with maximum likelihood (ML) method and QPSK partitioning with blind phase search (BPS) method. Both methods are proved to be possible solutions for CPE of 64-QAM signals, with good laser phase noise tolerance and simple complexity. For QPSK partitioning with ML method, we creatively introduce cascaded multi-stage ML following QPSK partitioning, which leads to further improved laser phase noise tolerance compared to 1-stage ML condition. For QPSK partitioning with BPS method, BPS with 8 or 12 test phases and test phase range of π/4 is found to be suitable for practical application, because it can achieve good laser phase noise tolerance while keeping low complexity, and the use of BPS with more test phases in this method has limited advantage over single stage BPS with the same test phases.

Improved Pilot-Aided Optical Carrier Phase Recovery for Coherent $M$-QAM

We propose an improved pilot-aided (PA) optical carrier phase recovery (CPR) method, using average operation for noise suppression in PA coherent systems. Performance of this method is investigated and compared with other CPR methods through simulations for 28 Gbaud QPSK, 16-, and 64-QAM systems. Results show that PA-CPR with averaging greatly outperforms PA-CPR without averaging, and achieves better or similar performance compared with other PAor non-PA-CPR methods. In addition, we propose a method using maximum likelihood (ML) phase estimation following PA-CPR with averaging to further improve the laser phase noise tolerance. Specifically, after optimizing the bandwidth of the pilot extraction filter, the maximum linewidth symbol duration products (Δf·T) for 1-dB optical signal to noise ratio penalty at BER of 1 × 10-3 are improved from 1 × 10-4, 3.5 × 10-5, and 1 × 10-5 (by PA-CPR without averaging) to 6.6 × 10-4, 2 × 10-4, and 3.8 × 10-5 (by PA-CPR with averaging), for 28 Gbaud QPSK, 16-and 64-QAM systems, respectively. When ML is following PA-CPR with averaging, Δf·T values for 1-dB OSNR penalty are further improved to 9 × 10-4, 4.8 × 10-4, and 6.5 × 10-5 for QPSK, 16-and 64-QAM systems, respectively.

Improved pilot-aided optical carrier phase recovery using average processing for pilot phase estimation

We propose and numerically investigate an improved pilot-aided (PA) optical carrier phase recovery (CPR) method using average processing for pilot phase estimation in order to suppress the amplified spontaneous emission (ASE) noise in PA coherent transmission systems. Extensive simulations for 28Gbuad QPSK systems are implemented. The performance of proposed PA-CPR with averaging is comprehensively investigated and compared with PA-CPR without averaging and Viterbi & Viterbi phase estimation (VVPE). Results show that, PA-CPR with averaging can significantly improve the performance of PA-CPR without averaging, and the best averaging length in the average operation is determined by trading off between ASE noise and laser phase noise (PN). By comparing the optical-signal-to-noise-ratio (OSNR) penalties at bit error rate (BER) of 1×10−3using PA-CPR without averaging, PA-CPR with averaging and VVPE, the advantage of PA-CPR with averaging is further confirmed. Quantitatively, the tolerable linewidth-symbol-duration products (Δf·T) at 1-dB OSNR penalty by using PA-CPR without averaging, VVPE, and PA-CPR with averaging are 6×10−5, 1.2×10−4, and 5×10−4, respectively.

Pilot-Symbols-Aided Carrier-Phase Recovery for 100-G PM-QPSK Digital Coherent Receivers

A feedforward pilot-symbols-aided carrier-phase recovery scheme is described. The approach relies on pilot symbols that are time-division multiplexed with the transmitted data. In the scheme, an initial coarse estimation of the optical carrier phase, exploiting the knowledge of pilot symbols, is followed by a fine nondata-aided, or blind, estimation. The main advantage of the proposed solution is that of avoiding the phase- ambiguity problem after a cycle slip. The overhead and the impact on the performance of pilot symbols are investigated for long-haul transmission of 100-Gb/s polarization-multiplexed quadrature phase-shift keying wavelength-division-multiplexing signals in different scenarios. For homogeneous transmission, the proposed scheme outperforms blind carrier recovery with differential decoding.

Broadband Phase-to-Intensity Modulation Conversion for Microwave Photonics Processing Using Brillouin-Assisted Carrier Phase Shift

We theoretically and experimentally demonstrate a novel broadband phase-to-intensity modulation conversion technique for microwave photonics processing system. The technique is based on optical carrier phase shift of a phase modulated signal using stimulated Brillouin scattering. More than 360 ° carrier phase shift can be achieved. By simply adjusting the carrier phase shift while preserving its amplitude unchanged, the phase modulation can be fully or partially converted to intensity modulation. The main advantage of the proposed method lies in its broadband nature since the SBS is only imparted on the optical carrier and the phase modulated sidebands are not affected as long as the modulating frequency is higher than the Brillouin bandwidth. In addition, as a microwave photonics processing application, we demonstrate the dispersion induced power penalty control in radio-over-fiber systems using the proposed technique. Experimental results match well with the theoretical prediction.