Optical Time Division Multiplexing System Research Articles

300-Gb/s Transmission Using OTDM System Implemented With Sinusoidally Modulated Input Light Source

The recently proposed 2-channel optical-time-division-multiplexing (OTDM) technique utilizing a sinusoidally modulated input light source provides an attractive solution to double the per-wavelength data rate of the short-reach intensity-modulation/ direct-detection system. However, to maximize the transmission speed of such an OTDM system, it is necessary to generate the sinusoidal input light operating at the frequency much faster than the modulator’s bandwidth. As a result, the extinction ratio (ER) of the generated sinusoidal input light can be significantly reduced, which, in turn, causes a large crosstalk in this OTDM system. To solve this problem, we propose to enhance the ER of the sinusoidal input light simply by decreasing the bias voltage applied to the Mach-Zehnder modulator (MZM) used for its generation (from the quadrature point toward the null point). We estimate that, by using this technique, it is possible to increase the ER from 3.1 dB to 14.9 dB when the required sinusoidal frequency is three times faster than the MZM’s bandwidth. To verify the effectiveness of this ER enhancement technique, we realize the 2-channel OTDM system with a sinusoidally modulated input light source by using the MZMs having a 3-dB bandwidth of 17.2 GHz and demonstrate the transmission of the 300-Gb/s PAM8 signal. Thus, the ratio between the achieved data rate and the 3-dB bandwidth of the MZM is as high as ~17.4.

Proposal for optical TDM system for digital payload in next generation high throughput satellites

The digital payload for next generation high throughput communication satellites is expected to reduce the operators’ CAPEX and OPEX. Photonic technologies, which have a great affinity with digital signals, have been studied in order to increase the data throughput and reduce the mass of the satellites. Here, we propose an optical time division multiplexing system for routing the signals in the digital channelizer and have conducted a feasibility study on the transmission efficiency. This system has the potential to reduce the cost, mass, and power consumption, and to improve reliability by cleaning up the switches used for routing the signals within the satellites.

FWM Mitigation in DWDM Optical Networks

In this paper, three optical communication systems have been proposed to mitigate Four Wave Mixing (FWM). Three techniques are used, namely; low input power with high gain amplifier, a collective Optical Time Division Multiplexing (OTDM) and Dense Wavelength Division Multiplexing (DWDM) system, and the use of alternative circular polarization. The first technique involves reduction in input power to -20 dBm and then amplifying it 40 dB before demultiplexing. The second technique divides the input signal into four time slots and then combine them with a power combiner. In the third technique, the polarization of light coming from input channels is changed after modulation into right and left handed circular polarization. Exhaustive sets of simulations are performaed using Optisys. The performance analysis includes Q-factor, Optical Signal to Noise Ratio (OSNR), received optical power, minmum Bit Error Rate (BER) and eye diagram.

A Cost-Effective 2-Channel OTDM System Implemented With Sinusoidally Modulated Light Source

We propose to implement a 2-channel optical-time-division-multiplexed (OTDM) system for short-reach optical interconnects by using a sinusoidally modulated light source instead of a complicated mode-locked laser as an input pulse source. In this system, the OTDM signal is obtained by bit-interleaving two optical return-to-zero (RZ) signals generated by using the sinusoidally modulated light. We operate these RZ signals in the orthogonal in-phase and quadrature domains to avoid the unwanted beat components. After the transmission, the OTDM signal is detected by using single photodetector, and then processed by a 2 × 2 multiple-input multiple-output equalizer. For a demonstration, we generate 150-Gb/s OTDM signal operating in the 8-level pulse-amplitude modulated (PAM-8) format by using commercial LiNbO 3 Mach-Zehnder modulators and transmit this OTDM signal over 1.9 km of the standard single-mode fiber (SSMF). In addition, we fabricate the proposed OTDM transmitter in an integrated silicon-photonics chip and use it to demonstrate the transmission of the 64-Gb/s OTDM PAM-4 signal over 2.2 km of SSMF.

Demonstration of an [formula omitted]-Gb/s optical time-division multiplexing system

An 8×25-Gb/s optical time-division multiplexing (OTDM) system is demonstrated experimentally. The optical pulse source is based on optical frequency comb (OFC) generation and pulse shaping, which can generate nearly chirp-free 25-GHz 1.6-ps optical Gaussian pulse. The eightfold optical time-division demultiplexer consists of a single-driven dual-parallel Mach–Zehnder modulator (DPMZM) and a Mamyshev reshaper. Error-free demultiplexing of 8×25-Gb/s back-to-back (B2B) signal with a power penalty of 4.1 dB to 4.4 dB at a bit error rate (BER) of 10−9 is achieved to confirm the performance of the proposed system.

Pedestal Free Pulse Source for Ultrahigh Data Rate Optical Time Division Multiplexing Systems Self-Phase Modulation Based

Pedestal Free Pulse Source for Ultrahigh Data Rate Optical Time Division Multiplexing Systems Self-Phase Modulation Based

Demonstration of flexible optical time-division multiplexing system for high-speed free-space optical communications

A high-speed free-space optical communication scheme based on optical time-division multiplexing (OTDM) is experimentally demonstrated. By multiplexing eight 2.5Gb/s base-rate signals, which is generated from a repetition-tunable actively mode-locked fiber ring laser modulated by pseudo-random binary sequence data stream, a 20Gb/s OTDM packet is obtained. After 50 m high-speed FSO system transmission, the 20Gb/s OTDM packet is injected into a highly nonlinear fiber (HNLF) loop to realize polarization-insensitive de-multiplexing based on four-wave mixing (FWM). Experimental results show that the OTDM de-multiplexer bit error rate (BER) can achieve 10−9 level with steady operation over 24 h, proving the practicality of this system.

Performance optimization of ultra-short optical pulse generation based on Mamyshev reshaping and its application in 100-Gb/s and 200-Gb/s optical time-division multiplexing

A robust, cost-effective external-modulated ultra-short pulse generator based on chirp compression and Mamyshev reshaper is simulated numerically and demonstrated experimentally. We investigated the quality of the pulse with numerical calculation, demonstrating that the pulsewidth and pulse pedestal can be significantly improved after optimization. The role of out-of-band suppression ratio of the optical filter in reducing the pulse pedestal is explained. Using the numerical analysis as a guideline, 25-GHz 1.9-ps pedestal-free nearly transform-limited optical pulse with an extinction ratio of 29dB and a root-mean square timing jitter of 120fs (100Hz to 10MHz) is experimentally generated. The pulse source is then successfully applied in 100-Gb/s and 200-Gb/s optical time-division multiplexing (OTDM) system with 100-km transmission, which is a strong proof that such pulse generator is a simple, practical, low-cost, power efficient solution for OTDM applications.

Statistical Modeling and Performance Characterization of Ultrashort Light Pulse Communication System Using Power-Cubic Optical Nonlinear Preprocessor

In this paper, we present an analytical approach in obtaining the probability density function (pdf) of the random decision variable Y, which is formed at the output of the power-cubic all-optical nonlinear preprocessor followed by the photodetector, with applications in ultrafast optical time-division multiplexing and optical code-division multiple-access systems. Our approach can be used to accurately evaluate the performance of ultrafast pulse detection in the presence of Gaussian noise. Through rigorous Monte Carlo simulation, the accuracy of the widely used Gaussian approximation of decision variable Y is refuted. However, in this paper, we show that the so-called log-Pearson type-3 (LP3) pdf is an excellent representation for the decision variable Y. Three distinguishable parameters of the LP3 pdf are obtained through an analytical derivation of three moments of the decision variable Y. Furthermore, toward a more realistic model, in addition to amplified spontaneous emission Gaussian noise, the effects of shot and thermal noises are also included. Finally, using the presented analytical approach, it is shown that the power-cubic preprocessor outperforms its quadratic counterparts, i.e., second-harmonic-generation and two-photon-absorption devices, in the high-power regime where shot and thermal noises can be neglected.

Design of optical time-division multiplexed systems using the cascaded four-wave mixing in a highly nonlinear photonic crystal fiber for simultaneous time demultiplexing and wavelength multicasting

This paper reports a new design of optical time-division multiplexed (OTDM) systems that possess a functionality of simultaneous time demultiplexing and wavelength multicasting based on the cascaded four-wave mixing in a dispersion-flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF). A module of OTDM demultiplexing and wavelength multicasting can be feasibly implemented by using a 3 dB optical coupler, a high-power erbium-doped fiber amplifier, a short-length DF-HNL-PCF, and a wavelength demultiplexer in the simple configuration. We also carry out an experiment on the proposed system to demonstrate the 100–10 Gbit s−1 OTDM demultiplexing with wavelength conversion simultaneously at 4 multicast wavelengths. It is shown that error-free wavelength multicasting is achieved on two wavelength channels with the minimum power penalty of 3.2 dB relative to the 10 Gbit s−1 back-to-back measurement, whereas the bit error rates of other two multicasting channels are measured to be about 10−6–10−5. Moreover, we propose the use of a proper error-correcting code to improve the multicasting performance of such an OTDM system, and our work reveals that the resulting system can theoretically support error-free multicasting of the OTDM-demultiplexed signal on four wavelength channels.

25-GHz dual-wavelength pedestal-free pulse source based on single-driven dual-parallel Mach-Zehnder modulator and Mamyshev reshaper

A dual-wavelength optical Gaussian pulse generation scheme based on a single-driven dual-parallel Mach-Zehnder modulator with subsequent Mamyshev reshaping is proposed. Experimental results show that nearly chirp-free Gaussian pulses with a full width at half maximum of 2.7-ps and a repetition rate of 25-GHz on 2 wavelengths are achieved simultaneously. By changing the central wavelengths of the continuous wave light and the optical bandpass filter, nearly transform-limited optical Gaussian pulses are obtained over the C-band. The pulse source is further employed in a 100-Gbit/s on–off keying optical time division multiplexing transmission system. Error-free bit error rate performance is also achieved, which confirms the high pulse quality.

Performance comparison of dispersion compensation techniques on 40 Gbps OTDM system at S-band and C-band over different fibre standards

Optical time division multiplexed (OTDM) technology has made a lot of progress towards increasing capacity and transmission distance for future optical communication networks. This paper demonstrates the comparison between three dispersion compensation techniques: pre-, post- and symmetrical- for different fibres (Alcatel, ITU G.652a and ITU G.653) on 40Gbps OTDM system operating at S-band and C-band. It has been investigated that the ITU G.653 combines with DCF to make total dispersion zero exhibits good performance in S-band as compared to C-band where the ITU G.653 is found to be worst fibre. ITU G.653 cover 1200km using symmetrical-compensation method with acceptable BER (2.39×10−9) and Q value 5.95dB.

Investigation of Modulators in OTDM System

With the ever-increasing demand for higher speeds and larger capacity brought about by rapid data growth on the Internet, interest in optical time division multiplexing has been growing rapidly in recent years due to its high speed and ability to overcome the “electronic bottleneck” offered by today’s electronic components. Optical time division multiplexing (OTDM) transmits multiple data channels in the form of ultra-short duration optical pulses which are interleaved into a single high-speed data stream by accurate control of their relative delay in the time domain. OTDM transmission system has been a topic of continuous research due to their unique advantages over conventional Pulse sources based transmissions. Among various key high repetition rate, limited pulse source, pulse range still remains as the issues that require further optimization. The performance of OTDM system is analyzed by using BER analyzer in which Q factor is to be measured. In OTDM system the maximum Q factor can be achieved by using different methods which are increasing laser power, using various.. We will focus on performance metrics and parameters used in the topology. We also focused on various modulators related to the topology.

Performance comparison of pre-, post- and symmetrical-dispersion compensation techniques using DCF on 40 Gbps OTDM system for different fibre standards

Various factors like polarization mode dispersion, non-linear effects, Kerr effect, second and third order dispersion impose limit on the performance (transmission distance, pulse broadening) of Optical Time Division Multiplexed (OTDM) transmission system. In this paper, the performance comparison of 40Gbps OTDM transmission system with pre-, post-, and symmetrical-dispersion compensation techniques for different fibre standards has been carried out. It has been observed that for pre compensation, ITU 655 [D=3.78ps/nm/km] came to be best suitable fibre with the dispersion compensating fibre length of 2.36km for maximum reach of 3000km. For post- and symmetrical-compensation, the behaviour of alcatel [D=8ps/nm/km] is almost similar with maximum transmission distance of 3200 and 3050km respectively.

Quasi-Soliton Pulse-Train Propagation in Dispersion-Managed Silicon Rib Waveguides

Dispersion-managed soliton-like pulse-train propagation in silicon rib waveguides is theoretically investigated by means of the nonlinear Schrodinger equation. A vectorial formulation is employed taking rigorously into account all relevant phenomena. For the purpose of minimizing pulse broadening, the waveguide width is precisely engineered (tapered) along the propagation direction by demanding that the soliton formation condition is locally satisfied. For typical carrier lifetimes (3 ns), bit rates up to 160 Gb/s can be transmitted with negligible pulse broadening and less than 3 dB of free-carrier-induced loss. The application of a carrier-sweep bias allows for the extension of the transmission rate beyond 1.28 Tb/s, matching current trends in silicon-photonic optical time-division multiplexing systems.

Simultaneous clock recovery and demultiplexing of a 320 Gb/s OTDM system using an optoelectronic oscillator based on cascaded MZM and PolM

An improved optoelectronic oscillator scheme for an optical time division multiplexing (OTDM) system based on cascaded Mach-Zehnder modulator (MZM) and polarization modulator (PolM) is experimentally investigated. The system can simultaneously realize clock recovery and demultiplexing. With the MZM working at peak point to generate return-to-zero-33 optical pulses and the PolM working as an equivalent intensity modulator, a high-quality clock signal with 35-fs timing jitter is extracted from the 160-GBaud OTDM-differential quaternary phase-shift keying signal. Narrow short optical switch gates (4 ps) are also generated to demultiplex 160-GBaud signals to 40-GBaud signals. Error-free performance is achieved with 2.4-dB power penalty in the worst case.

Wavelength conversion, time demultiplexing and multicasting based on cross-phase modulation and four-wave mixing in dispersion-flattened highly nonlinear photonic crystal fiber **The work was supported in part by the CAS/SAFEA International Partnership Program for Creative Research Teams.

We propose the use of cross-phase modulation (XPM) and four-wave mixing (FWM) in dispersion-flattened highly nonlinear photonic crystal fibers (HNL-PCFs) to implement the functionalities of wavelength conversion, simultaneous time demultiplexing and wavelength multicasting in optical time-division multiplexing (OTDM) systems. The experiments on wavelength conversion at 80 Gbit s−1and OTDM demultiplexing from 80 to 10 Gbit s−1 with wavelength multicasting of two channels are successfully demonstrated to validate the proposed scheme, which are carried out by using two segments of dispersion-flattened HNL-PCFs with lengths of 100 and 50 m, respectively. Moreover, the bit error rate (BER) performance is also measured. The results show that our designed system can achieve a power penalty of less than 4.6 dB for two multicasting channels with a 24 nm wavelength span at the BER of 10−9 when compared with the 10 Gbit/s back-to-back measurement. The proposed system is transparent to bit rate since only an ultrafast third-order nonlinear effect is used. The resulting configuration is compact, robust and reliable, benefiting from the use of dispersion-flattened HNL-PCFs with short lengths. This also makes the proposed system more flexible in the operational wavelengths than those based on dispersion-shifted fibers and traditional highly nonlinear fibers.

Wavelength-tunable linear-cavity passively mode-locked Yb-doped fiber laser based on volume Bragg grating

The linear-cavity all-normal-dispersion Yb-doped fiber laser based on semiconductor saturable absorber mirror and reflection type volume Bragg grating (VBG) is demonstrated. A passively mode-locked pulse stable output with a 0.32 nm spectral bandwidth, a 10.2 mW maximum average output power, a single pulse energy of 0.63 nJ and a 16.42 MHz repetition rate is achieved, when the central wavelength of pulse is 1030 nm. The central wavelength of the pulse can be tuned approximately from 1011.9 nm to 1050.6 nm by the spectral separation and mode selection effect of VBG with a tuning range of 38.7 nm at room temperature. Q-switched, second harmonic mode-locked, simultaneous dual wavelength and triple wavelength output are observed. This mode-locked fiber laser can be used as the optical source in wave division multiplexing optical time division multiplexing communication system and optical source of optical coherence tomography due to its tunable wavelength.

Generation of 40 GHz phase stable optical short pulses using intensity modulator and two cascaded phase modulators

Pulse sources based on lithium niobate modulators are very attractive for optical time division multiplexing (OTDM) transmission systems because the modulators are now commercially available, qualified for system use, and can operate up to very high speeds and over a wide wavelength range. In this paper, we describe the principles of operation and performance of the pulse source based on lithium niobate modulators. The pulse source is based on a Mach-Zehnder intensity modulator (IM) and two phase modulators (PMs). The continuouswave (CW) light is modulated in an IM and then strongly phase modulated in two cascaded PMs. The chirped pulses are subsequently compressed to desired width using dispersion compensation technology. This method has the advantage of acquiring larger chirp using normal PM rather than that special designed PM of very low Vπ. It can also generate shorter pulses than conventional methods incorporating only one PM driving by a radio frequency (RF) signal with the power larger than 1 W which may damage the device. Generation of 40 GHz optical pulses shorter than 2 ps is theoretically illustrated, simulated and experimentally verified. Experimental results show that 40 GHz phase stable optical pulses with pulse-width of 1.88 ps, extinction ratio (ER) larger than 20 dB, the timing jitter of 57 fs and signal-to-noise ratio (SNR) of 32.8 dB can be achieved. This is also a cavity-less pulse source whose timing jitter is determined only by the RF source rather than by the actively controlled cavity. In the experiment, the phase noise of the RF source we used is as low as −98.13 dBc/Hz at a 10 kHz offset frequency which resulting very low timing jitter of generated pulses. The pulses are then modulated at 40 Gbaud/s with an inphase/quadrature (I/Q) modulator and multiplexed to 160 Gbaud/s with less interference between each other. After back-to-back demultiplexing by an electro-absorption modulator (EAM) to 40 Gbaud/s and demodulation by a delay interferometer (DI), clear and opened eye diagrams of 40 Gbaud/s I and Q tributary signals are obtained which verify the good performance of generated pulses in the 160 Gbaud/s differential quadrature phase shift keying (DQPSK) OTDM system and further prove the phase stability and high quality of generated pulses.

Evaluate the Performance of Optical Time Division Demultiplexing with the Gain Saturation effect of Semiconductor Optical Amplifier

Optical Time Division Multiplexing (OTDM) system technique is the extend time division multiplexing by optically combining a number of lower speed electronic baseband digital channels. In addition, the Semiconductor Optical Amplifiers (SOA's) are important components for optical networks. In this paper, we propose a novel model for an OTDM demultiplexer based on Cross Gain Modulation in a SOA. Analysis are extended to find the output of an optical IM/DD receiver to receive the demultiplexed optical signal and to find the output signal to noise ratio (SNR) taking into account the amplified spontaneous emission (ASE) noise. The results are evaluated in terms of BER, SNR and pump power for various input signal power level. It is found that, at a given signal input power the BER can be reduced by increasing the pump power and the required pump power is higher at higher level of input power.