Nonlinear Fourier transform (NFT)-based nonlinear frequency division multiplexing (NFDM) system has the potential to overcome the limit of fiber nonlinearity. We have meticulously designed a b-modulated dual-polarization (DP) full-spectrum NFDM system with 128 subcarriers for continuous spectrum and 7 eigenvalues for discrete spectrum. By using probabilistic shaping (PS) and linear minimum mean square error (LMMSE), NFDM system transmits 960km distance with bit error rate (BER) lower 3.8 × 10−3, and the data rate achieves approximately 203.7Gb/s.
We propose a single-channel photonic compressed sampling scheme. The program is composed of 4 MZMs and each MZM is set at an appropriate working point. The sparse microwave signal is modulated onto an optical carrier coded by a pseudo-random sequence, so that the microwave signal randomly distributed in the broadband range can be measured. The numerical analysis shows that a multi-tone signal in 40 GHz range can be located and reconstructed with 4.2 GHz sampling rate with high probability.
A novel elliptical ring fiber structure mode selective coupler is proposed and it can convert LP01 mode to higher-order modes (LP11a,LP11b,LP21a,LP21b) with the maximum coupling efficiency 99% in wavelength range from 1530nm to1625nm (C+L band).
We propose a novel filterless approach to generate high-quality optical frequency 16-tupling millimeter-wave based on only two MZMs. OSSR higher than 30.34 dB and RFSSR not less than 23.79 dB are achieved in this scheme.
Implement of Kalman scheme for RSOP equalization is investigated from hardware perspective and simulation results show that Kalman scheme is superior to CMA in terms of hardware resources utilization and recovery capacity.
In order to eliminate the error introduced by noise from fixed analyzer method when measuring polarization mode dispersion of optical fiber and improve the accuracy of the polarization mode dispersion measurement system, a novel denoising approach based on wavelet threshold denoising is proposed in this paper. This paper presents the algorithm flow chart based on wavelet threshold denoising and discusses the selection principles of wavelet threshold, wavelet threshold function, mother wavelet and the number of wavelet decomposition layers. We built an experimental platform and compare the measurement results with Fourier transform algorithm and the commercial polarization mode dispersion measurement instrument. Experimental results show that the proposed wavelet threshold denoising method can effectively reduce impact of noise on the measurement results effectively, which is suitable for different types and lengths of test fiber samples. Taking the commercial instrument as the standard reference, the maximum error of the measurement result of this scheme is 2.27%, which improves the accuracy significantly of the polarization mode dispersion measurement results measure by the fixed analyzer.
In this work, we propose a novel approach to generate high-quality optical millimeter-wave signals using frequency 12-tupling without an optical filter. The proposed approach is comprised of one dual parallel Mach- Zehnder modulators. The two sub-MZMs, biased at the maximum optical transmission point, which is only used for even-order optical harmonic generation, and introduces a phase shift on the optical output signal between the sub- MZMs. By properly adjusting the MZM biasing point, RF LO voltages and phases shift, sixth order optical sidebands only are generated which can result in 12-tupled mm-wave at the photo detector. Optical sideband suppression ratio (OSSR) higher than 37.65 dB and radio frequency spurious sideband suppression ratio (RFSSR) not less than 32.08 dB are achieved in this scheme. The performance of the signal in terms of OSSR and RFSSR is discussed, and the effects of non-ideal factors on OSSR and RFSSR are analyzed.
An optical frequency comb generator using a modified single-sideband recirculating frequency shifter scheme adopting a linear IQ modulator as the kernel device (SSB-RFS-LIQM) is proposed. The optical comb lines generated by the proposed scheme possess good features such as extreme flatness and high optical signal-to-noise ratio (OSNR), compared to the quality we can obtain when we use a conventional IQ modulator in the SSB-RFS structure (called SSB-RFS-CIQM scheme). The mechanism of how the SSB-RFS-LIQM works is carefully analyzed with analytical and numerical methods. With the capability of strong suppression of high-order crosstalk and less demand of the gain of erbium-doped fiber amplifiers (and hence less amplified spontaneous noise induced) in the loop, 5.5 dB OSNR improvement can be achieved when 100 extreme flat comb lines are generated using the SSB-RFS-LIQM scheme compared to using the SSB-RFS-CIQM scheme.
We propose and analyze a photonic method of generating frequency-quadrupling millimeter-wave signal. This scheme is realized by using a single LiNbO3 intensity modulator (IM) and a Faraday mirror based transverse-electrical and transverse-magnetic mode converter in a Sagnac loop without using an optical filter or an electrical microwave phase shifter. Making use of the intrinsic polarization dependence and the velocity phenomenon of the IM, a special double sideband modulation is implemented, which ensures that the optical carrier can be effectively cancelled employing polarization manipulation. A linear polarizer is used as the polarization selection element to choose the second-order sidebands from the modulated light. After beating at the photodiode, a frequency-quadrupled millimeter-wave signal with >30 dB radio frequency spurious suppression ratio is generated. The imperfection of the devices is considered when estimating the system performance.
We propose a design of a multi-OAM-modes ring-core fiber with two guided modes regions which possesses relatively large effective index separations required for the vector modes. This fiber can support 28 information states bearing OAM spanning 8 OAM orders with large effective mode area by using polarization multiplexing and both signs of topological charge in the ring region, combined with two degenerate fundamental polarization modes in the core region which can hold the whole C bands. There is a high isolation between the modes in these two regions. These designed features have potential applications in the next generation fiber communication systems either in the quantum domain or in the classical domain.
KEYWORDS: Modulators, Frequency combs, Telecommunications, Optical communications, Polarization, Optical amplifiers, Linear filtering, Signal to noise ratio, Modulation, Interference (communication)
A comprehensive investigation is done on a high-quality frequency comb or multicarrier generation using a single-sideband modulation based recirculating frequency shifter (SSB-RFS), which has shown a good capability to provide a large number of frequency-locked carriers for terabits transmission. The dominant factors, such as I/Q modulator, direct current-bias, radio-frequency signal, and band pass filter, are analyzed theoretically and experimentally in terms of the metrics such as flatness, signal-to-noise ratio, and stability. The achieved 69 flat tones by noise suppressed SSB-RFS are presented. An example of SSB-RFS based 2.56 Tb/s PDM-RZ-16QAM 792 km transmission is illustrated, which is enabled by the 20 high-quality carrier tones generated with the optimally operated SSB-RFS source.
We propose an optical domain pilot-aided carrier phase recovery (PA-CPR) scheme used in a single-carrier Nyquist system. A comprehensive mathematical description of the proposed PA-CPR scheme is presented. Optimal parameters for the system are obtained through optimizations. Furthermore, we propose the two-stage PA-CPR algorithm combinations which use the maximum likelihood or constellation transformation phase estimation as the second stage just after the pilot phase compensation. We also make the evaluation and comparison of the linewidth tolerance performances among the proposed two-stage PA-CPR algorithm combinations and other typical CPR algorithms in a 28-Gbaud Nyquist polarization-division multiplexed (PDM)-16QAM optical communication system. The calculation results show that the proposed two-stage PA-CPR algorithm combinations, which have lower complexities, show better performances than others.
By applying recirculating frequency shifter technology to generate optical comb as neighboring channels, we have experimentally investigated the interchannel nonlinear tolerance of 256-Gbit/s polarization-division multiplexing return-to-zero 16-ary quadrature amplitude modulation (PDM-RZ-16QAM) in a co-propagation with 32-Gbaud on-off keying, binary phase-shift keying, quadrature phase-shift keying (QPSK) signals in 792-km large-area fiber transmission system. The results show that the experimental back-to-back optical signal-to-noise ratio requirement of 256-Gbit/s (32-GBaud) PDM-RZ-16QAM signal is shifted by 4.8-dB penalty in comparison with the theoretical limits. The cross-phase modulation (XPM) tolerance for 256-Gbit/s PDM-RZ-16QAM in 32-Gbaud phase-modulated neighboring channels is better than in 32-Gbaud intensity-modulated neighbors. Moreover, the performance of XPM tolerance for 256-Gbit/s PDM-RZ-16QAM in 32-Gbaud QPSK neighboring channels is the best among other kinds of modulation neighboring formats.
Based on recirculating frequency shifter, we generate 20 high-quality multicarrier optical combs with a tone-to-noise ratio >25 dB . We also experimentally demonstrate 2.56-Tb/s , polarization division multiplexing return-to-zero 16-ary quadrature amplitude modulation, coherent optical wavelength division multiplexing transmission over 800 km standard single-mode fiber with 25-GHz channel spacing, and the spectrum efficiency is 5.1 b/s/Hz .
In this paper, a novel dual-polarization differential quadrature phase shift keying (DQPSK) system is proposed,
which does not need polarization de-multiplexing like the conventional polarization division multiplexing QPSK, but
bases on just one receiver. Its performance including the tolerance to chromatic dispersion (CD) and to polarization mode
dispersion (PMD) is analyzed. The result shows that the tolerance to CD and PMD of the novel system is nearly same to
that of DQPSK system with the same bit rate, but it can bring down the electrical signals rate at the transmitter.
A modified phase recovery algorithm with overlap controlled adaptively used for squared 16-QAM is proposed, which is
based on the 4th-power algorithm and relieve the problem of block-size-choosing. By using this modified algorithm,
1.8MHz linewidth tolerance for 25G Baud 16-QAM is improved on traditional 4th-power algorithm.
This paper reports the prototype of optical polarization mode dispersion compensator (OPMDC) we have made to
compensate the polarization mode dispersion (PMD) in fibers. The OPMDC prototype designed was tested in a 43Gb/s
RZ-DQPSK system either in the back-to-back case, or in a 1200km transmission testbed. It showed a good performance
under the tests of fast SOP and PSP rotation, DGD variation, and moderate knock on the testbed in a period of 12 hours.
We report an experiment of de-multiplexing automatically in a polarization division multiplexing system using a DSP
based de-multiplexer. The searching algorithm was a modified Particle Swarm Optimization. We successfully
demonstrated the de-multiplexing scheme both in a 2x10-Gb/s PolMux-NRZ-OOK system and a 40-Gb/s PolMux-RZ-DQPSK
system.
Polarization mode dispersion (PMD) is one of the major obstacles in high-speed (above 100 Gbits rate)
and long-haul optical communication system. In order to meet the requirements of high-sped optical
communication quality, some PMD compensation and mitigation schemes had been developed. Forward error
correction (FEC) is useful to increasing the system margin. The combination of distributed fast polarization
scrambler (D-FPS) and FEC is an effective method to improving the optical system's PMD tolerance. The
fundamental reason is that D-FPS can accelerate the redistribution of the link PMD to enable FEC to be more
effective during the periods that would otherwise have PMD outages. Another advantage of this scheme is that it
can mitigate the influence of PMD in multichannel system without feedback control and compensation based on
each channel. The principle and performance of scrambling is introduced in this paper and the fundamental idea of
improving PMD mitigation by using D-FPS combined with FEC is proposed. Some key factors such as scrambling
speed and the number of scrambler which affecting the performance of this scheme are also introduced. Finally,
proposing an assumption that the impact for system performance caused by the style of FPSs is distributed along
the fiber link, and the mathematical estimation model is established. The combination of D-FPS and FEC would be
a promising approach for performance improvement in ultra-high-speed optical communication system.
In this paper, a novel phase regenerator with semiconductor optical amplifier is proposed. By theoretical analysis and
simulation, the optimum parameters of phase regenerator are obtained. By comparing the phasor diagrams, received data
and Q-factors before and after regeneration, the effectiveness of the phase regenerator is proved. The results show that
nearly ideal regeneration is achieved and Q-factors are gotten great improvement.
The detailed origin of phase jitter in fiber-optic communication systems was firstly reviewed. An overview of
distribution of received phase jitter was presented. By contrasting the phase difference of sample pulses, variance of
phase noise of an DPSK system in dispersion-managed finite fiber spans was calculated and simulated by Matlab, and
the Gaussian shaped possibility density function (p.d.f.) was obtained. The performance of signal was analyzed by
estimating BER, which was calculated from the p.d.f.. By adding ASE noise of different power into the signal at each
EDFA, we found that the suppression of ASE noise contributing considerably to the improvement of signal performance.
The effect of PMD on the three axes of the degree of the polarization (DOP) ellipsoid is discussed in the different
modulation format systems. The results show that the minimum axis of DOP ellipsoids is suitable for a feedback signal
in the compensation systems. In addition, the mitigation performances of DPSK formats are superior to that of OOK
format.
Nonlinear Mach-Zehnder interferometers, when driven by a phase-locked local oscillator pump, provide phase-sensitive
amplification to input signals. So phase-sensitive amplifier(PSA) can be used to realize phase regeneration of phase
modulated signals. In the paper, we adopt kerr media-based nonlinear Mach-Zehnder interferometer to form a PSA to
regenerate DPSK signals, and we propose a structure for the phase regenerating of DQPSK signals using two balanced
PSAs. Theoretical analyses of all-optical phase regenerations of DPSK/DQPSK signals based on phase-sensitive
amplification are presented. Simulations show that nearly ideal phase regeneration can be achieved for the
DPSK/DQPSK signals.
Automatically controlled polarization controllers (PC) are the essential integral parts in an automatic compensator for
polarization mode dispersion (PMD). It is suggested by Prof. M. Karsson et al. at Charlmers University of Technology,
and afterward widely accepted that we need to adjust only two waveplate PC (two degrees of freedom, DOF) for each
stage PMD compensator to complete PMD compensation. It is equivalent to say that only two of degrees of freedom for
each PC are needed to complete the state of polarization (SOP) transformation from any input state into any other state
covering the entire Poincare Sphere. In this paper will take two types of commercial available PC as examples to prove
theoretically and experimentally that except for the reset-free problem it is necessary to adjust at least three instead of
two waveplates in order to transform any input state into any other state covering the entire Poincare Sphere. Therefore
we can achieve complete PMD compensation at least using 3 DOF instead 2 PC in each stage PMD compensator.
We study the polarization mode dispersion (PMD) compensation performance of different modulation formats. Firstly,
we analyze the relationship between the signal's degree of polarization (DOP) and differential group delay (DGD) of
different modulation formats. The results show that the differential phase-shift keyed (DPSK) modulation formats are
more suitable for PMD compensation system than the ON-OFF keying (OOK) modulation formats because the DOP-DGD
curves of DPSK signals are monotonic and it is easy to search the global maximum. Secondly, we study the PMD
compensation performance of the mentioned modulation formats with DOP as feedback signal. It is shown that the
modulation formats with smaller bandwidth have better PMD compensation performance, and that PMD compensation
performance of DPSK formats are better than that of OOK formats. CSRZDPSK combines the carrier-suppressed
characteristic of CSRZ format and specific spectrum characteristic of DPSK format, thereby it has the best performance
of PMD compensation.
In this paper we report a successful experiment of adaptive polarization mode dispersion (PMD) compensation up to second-order in a 40Gb/s optical time-division multiplexed (OTDM) communication system by using two-stage compensator. In the experiment the PMD monitoring technique based on degree of polarization (DOP) was adopted. And the Particle Swarm Optimization (PSO) algorithm was introduced in adaptive PMD compensation, with the desirable features of fast convergence to the global optimum point for compensation without being trapped in local sub-optima and with good robustness to noise. The comparison was made to estimate the performance effectiveness between PSO algorithms with global neighborhood structure (GPSO) and with local neighborhood structure (LPSO). The LPSO algorithm is shown to be more effective to search global optimum for PMD compensation than GPSO algorithm. The ability of tracking changed PMD using PSO algorithm was also investigated. The two-stage PMD compensator is shown to be effective for both first- and second-order PMD, and the compensator is shown to be bit rate independent. The compensation time is within several hundreds of milliseconds. The response time for recovery from a sharp disturbance is about 11ms.
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