RZ Signals Research Articles

Multi-channel multi-task optical performance monitoring based multi-input multi-output deep learning and transfer learning for SDM

We propose a transfer learning (TL) simplified multi-input multi-output multi-task convolutional neural network (MIMO MT-CNN) to realize the optical performance monitoring (OPM) for space division multiplexing (SDM) fiber transmission systems. TL simplified MIMO MT-CNN is used for NRZ, RZ and PAM4 signal joint monitoring including modulation format identification (MFI) and optical signal-to-noise ratio (OSNR) estimation. Thanks to the TL technologies, the parameters used in single mode fiber transmission is transferred to SDM to reduce the required training data and epochs. The experiment has been demonstrated with MIMO MT-CNN for seven cores fiber systems. The results show that the accuracy of MFI can reach 100% for all signals. For NRZ, RZ, and PAM4, the root-mean-square errors (RMSE) of OSNR estimation are less than 0.6 dB, respectively. In addition, by implementing TL from simulation to experiment, the required training samples and epochs are reduced by 48% and 50%, respectively. Due to its low cost and being easy to implement, the proposed OPM solution has the potential for next-generation SDM fiber transmission systems. The model can realize short training time and multi-task multi-channel OPM for high-capacity SDM elastic optical networks, simultaneously.

Optimization and simulation of micrometre-scale ring resonator modulators based on p-i-n diodes using firefly algorithm

Field analysis of ring resonator modulators based on p-i-n diodes has been dissected in this paper. This analysis is performed in time and frequency domains. The conformal transformation method has been used for solving 3-D wave equation. Coupling coefficient between the ring and straight waveguides are obtained by developing the coupled-mode assumption. In the resonant wavelength of 1573.91nm, a drop of more than 15dB in frequency spectrum of the device has been observed. Time domain simulation shows that this modulator could support up to 0.4Gb/s and up to 1.5Gb/s for NRZ and RZ signals, respectively. Obtained simulation results in both domains have been properly complied with experimental results. Main goal of this paper is to present an optimized model from aforementioned modulator. It will be shown that frequency response could be more optimum than original device by optimizing structure parameters. In order to obtain practical values, Firefly Algorithm (FA) is used because it finds optimum points locally. In optimized modulator, extinction ratio (ER) could be increased up to 32dB which is double than original modulator.

Optical NRZ-to-RZ format conversion based on frequency chirp linearization and spectrum slicing

Abstract A flexible optical NRZ-to-RZ format converter based on a time lens followed by optical filtering is proposed and demonstrated experimentally. After frequency chirp linearization, 9-tone ultra-flat optical frequency comb of 25-GHz frequency spacing within 1 dB power variation is obtained. By changing the shape of the following optical band-pass filter, 3.4-ps Nyquist-shaped RZ signal and 3.7-ps Gaussian-shaped RZ signal are both achieved. The sensitivity improvements at a bit error rate of 10 −9 are 3.3 dB and 1.7 dB, respectively.

Design of Optical Fiber Transmission System Based on Absolute Polar Duty Cycle Division Multiplexing (APDCDM)

This paper propose a new multiplexing technique which use the bipolar RZ signal to realize duty cycle division multiplexing (DCDM) ,we call it Absolute Polar Duty Cycle Division Multiplexing (APDCDM).Multiplexing and demultiplexing principle of APDCDM are analyzed. Here we have designed a optical fiber transmission system based on APDCDM of three users by Joint simulation with Optisystem and Matlab. Simulation result shows the feasibility of this system. By the analysis of signal energy, explain APDCDM can carry more users than DCDM.

640 GBd Phase-Correlated OTDM NRZ-OOK Generation and Field Trial Transmission

We generate a 640 GBd phase-correlated optical time-division multiplexed (PC-OTDM) return-to-zero ON-OFF keying (RZ-OOK) signal based on cross-phase-modulation-induced cross-polarization rotation in an Al highly nonlinear fiber and a 640 GBd PC-OTDM nonreturn-to-zero (NRZ)-OOK signal by RZ-to-NRZ conversion using passive filtering. This is employed in a 1.19 Tb/s PDM-NRZ-OOK field transmission with BER <; 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> for all 128 tributaries. As a benefit of phase coherence between adjacent TDM channels, a PC-OTDM signal can be very tolerant to strict filtering and the bandwidth of the 640 GBd PC-OTDM NRZ-OOK signal can be restricted to 700 GHz. In addition, with a narrower spectrum a PC-OTDM NRZ-OOK signal is more tolerant to chromatic dispersion and polarization-mode dispersion compared to a conventional (i.e., phase-uncorrelated) OTDM RZ signal.

In-Line Chromatic Dispersion Measurement for NRZ and RZ Signals Using a Novel RF Spectrum Phase Detection Technique

In this paper, a novel method of in-line chromatic dispersion (CD) measurement is proposed, we theoretically and experimentally demonstrated the CD measurement of 10-Gbit/s NRZ and RZ signals by a novel RF spectrum phase detection technique, this is performed using in-band tone monitoring RF, electrically down-converted to direct current (DC) or a low intermediate-frequency (IF) of less than 1MHz through electronic mixing with local oscillator (LO) of 2.4 GHz. The measurement provides a large CD measuring range with good accuracies (±2000 ± 35 ps/nm), and independent of the bit-rate and data format. In addition, the use of electronic mixer and low-speed detectors makes it cost effective for in-line CD measurement.

A novel optical picosecond-duration NRZ-to-RZ format converter with simultaneous wavelength multicasting using a single-stage Mach–Zehnder modulator

We propose a novel and simple scheme to achieve NRZ-to-RZ format conversion and simultaneous wavelength multicasting based on a single-stage dual-arm electro-optic Mach–Zehnder modulator (MZM) and a short single mode fiber (SMF). The format conversion and wavelength multicast process are achieved by chirp compensation under the condition of generation of optical flat frequency comb. 40Gb/s NRZ-to-RZ conversion with one-to-five multiple-wavelength channel multicasting and transmission of the NRZ and the converted signals over 200km dispersion-managed fiber-link are successfully demonstrated by numerical simulation. Research results show that 40Gb/s 2ps RZ signal with wavelength-preserving can be obtained after format conversion. The converted RZ signal presents good transmission performance and can easily be multiplexed to 160Gb/s using optical time division multiplexing (OTDM) technology. All the multicast channels can be error free after 50km transmission. Besides, the conversion operation can also greatly reduce the timing jitter of the degraded NRZ signal due to the retiming function of the proposed scheme.

Investigation of FWM in dispersion-engineered GaInP photonic crystal waveguides

We report on the investigation of four-wave mixing (FWM) in a long (1.3 mm) dispersion-engineered Gallium Indium Phosphide (GaInP) photonic crystal (PhC) waveguide. A comparison with a non-engineered design is made with respect to measured FWM efficiency maps. A striking different response is observed, in terms of dependence on the pump wavelength and the spectral detuning. The benefits and the limitations of both structures are discussed, in particular the trade-off between slow-light enhancement of the FWM efficiency and the conversion bandwidth. The time-resolved parametric conversion of short pulses at 10 GHz is also shown. Finally, the transmission capability of a 40 Gbit/s RZ signal is assessed through bit-error rate measurements, revealing error-free operation with only 1dB penalty.

All-Optical 2R Regeneration With a Vertical Microcavity-Based Saturable Absorber

This paper gives an overview of recent demonstrations of optical 2R regeneration achieved by vertical microcavity mirror-based multiple-quantum-well saturable absorber (SA). The potential of the device to perform wavelength division multiplexing regeneration is first demonstrated through the first pigtailed SA chip implemented with eight independent fibers using a cost effective coupling technique. The cascadability and wavelength tunability assessment of this module associated with a power limiter fiber-based function has been experimentally demonstrated at 42.6 Gbit/s. Because this method of power limiting is not a suitable solution for all-optical multichannel 2R regeneration, a new SA structure allowing a power limiting function was proposed. We describe and characterize such a structure in this paper. This new SA opens the door to a complete passive all-optical 2R regeneration relying upon a single technology, as shown in this paper through the use of two SA: SA.0 for extinction ratio enhancement and SA.1 for high-power level equalization allowing receiver sensitivity (up to 3.5 dB) and Q-factor (up to 1.4 dB) improvement for a RZ signal at 42.6 Gbit/s. The limitation of SA.1 when the regenerator must be cascaded a large number of times is also described, leading to the observation that SA.1 should be more suitable for phase encoded formats that are more spectrally efficient than ON-OFF keying formats. A SA.1 used as a phase-preserving amplitude regenerator in a 42.6 Gbit/s RZ differential quadrature phase-shift keying transmission system is, therefore, assessed . A fiber launched power margin of 2 dB and a receiver sensitivity improvement of 5.5 dB are obtained. Finally, we use, for the first time an SA.1 as a phase-preserving amplitude regenerator of RZ differential quadrature phase-shift keying signals. The regenerator is assessed in a recirculating loop at 28 Gbaud. The system tolerance to nonlinear phase noise is enhanced by 3 dB and the distance improvement factor was 1.3 for a bit error rate = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> .

50 GHz Spaced 25 × 40 Gbit/s WDM Transmission Over 560 km Using SMF-Based Large Effective Area Fiber (LEAF)

In this paper, we present 50 GHz spaced 25 <img src=image/10.5923.j.ijoe.20120201.04_001.gif></img> 40 Gbit/s WDM transmission over 560 km using SMF-based Large Effective Area Fiber (LEAF) in a recirculating loop. The paper uses band-limited RZ signals carrying 2<SUP>31</SUP>-1 PRBS data, and shows that transmission distance of 560 km can be achieved with BER ≤ 10<SUP>-9 </SUP>using 1 mW peak power and 4 ps pulse-width for each data signal. To attain this, optical filters with sharp transmission characteristics are used in both transmitter and receiver. The results demonstrated in this paper are based on simulation, and the author believes that the propagation distance reached in the paper is the longest distance achieved for such system

Travelling wave analysis on high-speed performance of Q-modulated distributed feedback laser

The structure of a Q-modulated distributed feedback laser is designed and simulated. A large reflectivity modulation of the rear reflector is achieved by using an anti-resonant cavity formed by two deep trenches with the one between the modulator and phase section filled by a high index dielectric material. The travelling wave model is presented to analyze the high speed performance of the laser. Due to the effect of the wave propagation in the structure, the modulation extinction ratio decreases with increasing cavity length. It is shown that 40 Gb/s RZ signal modulation can be achieved with an extinction ratio of 7 dB and 10 dB, respectively, for a cavity length of 500 μm and 300 μm.

Quantitative monitoring of relative clock wander between signal and sampling sources in asynchronous optical under-sampling system

Optical performance monitoring using asynchronous optical or electrical sampling has gained considerable attention. Relative clock wander between data signal and sampling source is a typical occurrence in such systems. A method for the quantitative monitoring of the relative clock wander in asynchronous optical under-sampling system is presented. With a series of simulations, the clock wanders recovered using this method are in good agreement with the preset clock wanders of different amounts and frequencies for both RZ and NRZ signals. Hence, the reliability and robustness of the method are proven.

Wavelength remodulation scheme using DPSK downstream and upstream for DWDM-PONs

We propose a novel wavelength-division-multiplexed passive optical network (WDM-PON) architecture with enhanced tolerance toward chromatic dispersion where a DPSK-modulated downstream signal with constant intensity is remodulated at the ONU side with a return to zero (RZ-DPSK). Driving the downstream modulator with a 50% RZ data enabled us to employ the pulse carver at the ONU for both removing downstream data and generating the optical RZ signal for upstream. This offers an attractive alternative to earlier proposed schemes as it allows us to use full modulation depth (FMD) and balanced detection for downstream data restoration. We experimentally demonstrate the system with both balanced and single-ended detection at 2.5 Gb/s. Error-free operation has been achieved along a 20 Km single mode fiber without dispersion compensation.

All-optical NRZ-to-RZ format conversion with dual channel wavelength multicasting functions exploiting cross-phase modulation in a dispersion-flattened nonlinear photonic crystal fiber

All-optical single-to-dual channel format conversion from NRZ to RZ at 10 Gbit/s using cross phase modulation (XPM) in dispersion flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF) is demonstrated. Format conversion with dual channels signal multicasting function is achieved by filtering simultaneously the blue- and red-chirped components of broadened optical spectrum induced by XPM between NRZ signal and clock light. Moreover, the wavelength tunability and dynamics characteristics of proposed format converter are also exploited experimentally by using NRZ signal light with different central wavelength and varying input power. Our results show that a wide wavelength operation range of 21.2 nm, extinction ratio (ER) and Q factor of over 10.9 dB and 6.1 are obtained. Furthermore, the influence of central wavelength offset of optical bandpass filter on converted RZ signal quality is investigated. The proposed scheme is simple, robust, and transparent to bit rate, which makes it very potential for application in future photonic networks.

Optical clock recovery with dual-wavelength output from degraded RZ and NRZ signals

A novel scheme to implement clock recovery from degraded signals is proposed and demonstrated based on an optoelectronic oscillator and a dual-wavelength mode-locked fiber ring laser with distributed dispersion cavity. The scheme can obtain wavelength-tunable optical clocks at two wavelengths, which is highly desirable for composite optical logic gates, cascaded optical signal processing modules or optical signal processing modules that need synchronized pulses at multiple wavelengths. In addition, the scheme can operate in both RZ and NRZ systems. The feasibility of the method is demonstrated by an experiment, in which dual-wavelength 10-GHz optical clock with a timing jitter less than 170 fs is obtained from 10-Gb/s degraded RZ and NRZ signals. The optical clocks can be tuned from 1530 to 1565 nm.

Generation of a 640 Gbit/s NRZ OTDM signal using a silicon microring resonator

A 640 Gbit/s NRZ OTDM signal has been successfully generated for the first time by format conversion of a 640 Gbit/s OTDM signal from RZ to NRZ. First, a coherent 640 Gbit/s OTDM RZ signal is generated by wavelength conversion of the original incoherent OTDM signal utilizing Kerr switching in a highly nonlinear fiber. Second, RZ-to-NRZ format conversion is achieved in a specially designed silicon microring resonator with FSR of 1280 GHz, Q value of 638, high extinction ratio and low coupling loss to optical fiber. A 640 Gbit/s NRZ OTDM signal with very clear eye-diagram and narrower bandwidth than both the original incoherent 640 Gbit/s and the wavelength converted coherent 640 Gbit/s RZ OTDM signals has been obtained. Bit error ratio measurements show error free (<10(-9)) performance at a received power of -30 dBm for all the OTDM channels of the 640 Gbit/s NRZ signal, with very low power penalty (<0.5 dB) and improved dispersion tolerance compared to the wavelength converted RZ case.

Comprehensive Assessment of New Modulation Techniques in 40Gb/s Optical Communication Systems

In this paper, comprehensive assessments are proposed for intensity modulations and phase modulations respectively. Several key performance features, like receiver sensitivity, chromatic dispersion tolerance, nonlinearity tolerance, and noise sensitivity were compared among these modulation techniques. Results show that 66% duty cycle RZ signal so-called the carrier-suppressed return-to-zero (CSRZ) format has the best performance in the intensity modulations. In phase modulations, the most outstanding modulation is DPSK. DQPSK modulation is also a very promising choice if the effect of noise could be resolved. The combination of intensity modulation and phase modulation will compromise the performance advantages of both.

50 GHz Spaced 4 &amp;#215; 40 Gbit/s WDM Transmission over 700 km Using 6 ps Bandlimited RZ Signals

In this paper, we present 50 GHz spaced 4 ×40 Gbit/s WDM transmission over 700 km using SMF-based Effective Area Enlarged Positive Dispersion Fiber in a recirculating loop. The paper uses bandlimited RZ signals and shows that transmission distance of 700 km can be achieved with BER ≤ 10-9 using 6 ps pulsewidth for each data signal. To attain this, optical filters with sharp transmission characteristics are used in both transmitter and receiver. The results demonstrated in this paper are based on simulation, and the author believes the propagation distance reached in the paper is the longest distance achieved for such system.

Rate Equation Analysis of High Speed Q-Modulated Semiconductor Laser

Dynamic response of a Q-modulated semiconductor laser is simulated based on a rate equation model. Numerical results from both small-signal and large-signal analyses show that the Q-modulation has much higher bandwidth limit and smaller wavelength chirp than the direct modulation. It is shown that a high-extinction-ratio, low-chirp modulation of 40 GHz RZ signal can be achieved and the effects of various parameters on the Q-modulation are discussed. In addition to high-speed communications, the Q-modulated laser is particularly suitable for microwave carrier generation in radio-over-fiber systems.

Enhanced fast light in microfiber ring resonator with a Sagnac loop reflector

We fabricate a microfiber knot-type ring resonator with a Sagnac loop reflector, and control the light velocity using the device. In this structure, light is reflected by the Sagnac loop and passes through the ring resonator twice. Thus, it possesses doubled transmission and group delay comparing with the microfiber ring resonator without the Sagnac loop. We experimentally demonstrate pulse advancement in an under-coupled microfiber knot-type ring resonator with a Sagnac loop reflector. In the experiment, a maximum of approximately 25 ps pulse advancement was achieved for a 5-Gb/s RZ signal.