OTDM System Research Articles

Symmetric Mach–Zehnder Demultiplexing Technique for Optical Time-Division Multiplexing: Comparison of EAM, MZM and AM

AbstractOptical time-division multiplexing (OTDM) updates the well-known technique of electrical time-division multiplexing into the optical domain. In OTDM, optical data streams are constructed by multiplexing a number of low bit-rate optical streams in time domain. In this paper, the performance of eight channel OTDM system is analyzed and compared for different modulators such as EAM, MZM and AM with Symmetric Mach–Zehnder demultiplexing switch at bit rate of 20 Gbps. The effect of input signal power on BER, Q-factor and received optical output power has been evaluated. It is observed that EAM, MZM and AM provide acceptable Q-factor of 7.70, 7.50, 6.69 and BER of 2.55×10

Theoretical Considerations in Designing Ultra-High Speed All-Optical Clock Recovery Using Fiber Optical Parametric Amplifiers

In this paper, a new all-optical phase-locked loop (OPLL) in a TDM system is proposed and analyzed. The scheme relies on using fiber optical parametric amplifier (FOPA) device models and theories. In the proposed OPLL, the local clock pulse stream and the received data signal pulses are fed into the FOPA as its pump and amplified signals, respectively. The power of the resulting, relatively, strong idler signal depends on the phase difference between the local clock and the received data signal pulses, and it is used to reveal the OPLL's error signal. We characterize the mathematical structure of the proposed OPLL and identify its three intrinsic sources of phase noises namely, randomness of received data pulses, detector's shot noise, and the FOPA noises such as amplified spontaneous emission (ASE). The ASE noise is reflected in the FOPA's noise figure parametrically. However, the effects of the other two noise sources on the proposed OPLL performance are investigated, using the power spectral densities (PSDs) of the signals involved in the OPLL. Finally, the PSDs are used to obtain a mathematical expression for the OPLL's timing jitter. From the analytical results, our proposed OPLL benefits from the FOPA's inherent large bandwidth and exhibits a very low timing jitter, which is in the order of femtosecond, for an OTDM system with 80 Gbps data rate.

Ultra-low timing-jitter 40GHz clock recovery using EAM-MZM double-loop and its application in a 640Gbit/s OTDM system

An ultra-low timing-jitter clock recovery scheme based on EAM-MZM double-loop with the ability of simultaneous time-division demultiplexing is proposed and demonstrated in a 640 Gbit/s OTDM transmission system. Compared with traditional clock recovery scheme based on OEO loop, significant timing-jitter improvement of the 40 GHz recovered clock is realized: from 58 fs to 30 fs in back-to-back configuration and from 59 fs to 35 fs after 400 km transmission in the 100 Hz to 10 MHz range, without increasing the overall system complexity and cost. Enabled by the proposed clock recovery and demultiplexing scheme, error-free performance of the OTDM system is achieved after 400 km transmission with an average power penalty of 4dB.

Performance of RZ and NRZ modulation—Format in 40–160 Gb/s OTDM system demultiplexing

With a symmetric SOA-MZI as a de-multiplexing switch we describe the performance of return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulated signals in all optical demultiplexing of an OTDM channel at data rates up to 160Gb/s. First, the effect of input signal power, control signals power and pattern length on BER and extinction value of demultiplexed channel is investigated for RZ and NRZ signals at different data rates. Second, demultiplexing of 160-Gb/s OTDM signal to the base rate of 40Gb/s was successfully demonstrated with error free operation for both modulation formats. Effect of variation of pulse width on BER has also been analyzed for 160–40Gb/s demultiplexing operation.

Performance analysis of OTDM system in the presence of FEC using symmetric Mach–Zehnder switch

Optical time division multiplexing is an emerging and promising alternative for future high-speed photonic networks because of its ability to accommodate higher bit rate and flexible bandwidth. SMZ have been found to be the most suitable switching element than all the available de-multiplexing switches because of compact size, thermal stability, and low-power operation. In this paper, we simulate four channel OTDM systems (all-channel multiplexer and de-multiplexer) with a Mach–Zehnder modulator and an SMZ de-multiplexer to investigate the impact of FEC on the OTDM system. It is observed that the presence of FEC in OTDM transmission can greatly improve the system performance.

Continuously-tunable, bit-rate variable OTDM using broadband SBS slow-light delay line

We conceptually compare the advantages of the proposed slow-light-based tunable OTDM to conventional fiber-based fixed OTDM multiplexer. We experimentally demonstrate continuously-controllable OTDM of two 2.5-Gb/s return-to-zero (RZ) signals using broadband SBS-based slow-light as the tunable optical delay line. We show that the time slot of one signal path can be manipulated relative to the other by as much as 75-ps. This continuous slow light tunability dramatically enhances the OTDM system performance which results in a power penalty reduction of 9-dB for the multiplexed data stream. We also demonstrate variable-bit-rate OTDM by dynamically adjusting the tunable slow-light delay according to the input bit-rates. We show efficient two-by-one optical time multiplexing of three different input data streams at 2.5-Gb/s, 2.67-Gb/s and 5-Gb/s.

Demonstration of feasibility of a complete 160 Gbit/s OTDM system including all-optical 3R

A complete 160Gbit/s single-channel OTDM system experiment is presented. The OTDM system includes all-optical transmitter, 3R (Retiming, Reshaping, and Reamplification), and receiver. Performance measurements of the single subsystems are also reported. Finally Q-factor measures verify the effectiveness of the whole system.

120 Gbit/s OTDM system using electroabsorption transmitter and demultiplexer operating at 30 GHz

The authors describe a 120 Gbit/s (4/spl times/30 Gbit/s) OTDM system in which the transmitter and the receiver are based on electroabsorption modulators operating at 30 GHz. Error-free operation with an average 120 Gbit/s sensitivity of -22.6 dBm is achieved.

A Regenerative Prescaled Clock Recovery for High-Bit-Rate OTDM Systems

A regenerative prescaled clock recovery device based on an optoelectronic version of the Miller divider has been tested in high-bit-rate OTDM systems. Tests at 4×2.5 and 4×10 Gbit/s have been performed to characterize the locking range and the frequency response of the device. The timing jitter of the recovered signal in the case of the 4×10 Gbit/s OTDM system does not exceed 0.5 ps. Finally, a comparison of two bit-error-rate measurements (with and without the clock recovery system) were carried out for the 4×10 Gbit/s OTDM system. The relevant penalty for each channel is negligible, while the maximum received power difference among the four channels at a bit error rate value of 10−10 is around 0.7 dB.

OTDM applications of dispersion-imbalanced fibre loop mirror

Improvement of the signal quality from 10 GHz directly-modulated sources and crosstalk suppression in an 80 Gbit/s OTDM system are demonstrated for the first fime by means of nonlinear switching in a dispersion-imbalanced fibre loop mirror (DILM).

Theoretical analysis on polarization deviation and switch window optimization in nonlinear optical loop mirror demultiplexer

This paper investigates theoretically two of the dominant issues on a nonlinear optical loop mirror (NOLM) demultiplexer: the sensibility to the polarization deviation between signal and control pulses and the optimization of the switch window width. The complete nonlinear Schrodinger equations concerning the different states of polarization between signal and control lights are firstly established to study the impact of the polarization deviation on the demultiplexed signal. Considering simultaneously the channel crosstalk and the timing jitter between signal and control pulses, the switch window width of NOLM is optimized to achieve the best demultiplexing performance. The theoretical analysis shows that the polarization deviation has to be controlled less than 20/spl deg/ within the bit error rate (BER) of 10/sup -9/ s. The optimal amount of the pulse walkoff is a little less than half of the slot width of the OTDM system.

OTDM communication system exploiting a modelocked fiber laser as the clock extractor

This paper briefly describes the WDM and OTDM techniques in large capacity and super large capacity optical communication systems. We propose a novel method of employing a modelocked fiber laser as the clock extractor in communication systems, and present the structure for a totally new all optical OTDM experimental communication system that is based on the use of a wavelength division prescaled clock pulse scheme.

80 Gbit/s OTDM using electroabsorption modulators

An 80 Gbit/s (8 × 10 Gbit/s) OTDM system, constructed entirely with electroabsorption modulators (EAM) as the active components, is presented. A tandem EAM pulse source with a simple dual frequency drive generates transform limited 4.5 ps pulses. At the receiver, the 10 Gbit/s channels are demultiplexed from 80 Gbit/s in a single step using a low polarisation sensitivity EAM. Error free operation with a sensitivity of –21.5 dBm is achieved.

Full 10 × 10 Gbit/s OTDM data generation and demultiplexing using electroabsorption modulators

Error free operation of all 10 independently modulated channels in a 100 Gbit/s OTDM system is demonstrated. Electroabsorption modulators are used to extract 10 Gbit/s channels from the 100 Gbit/s data stream, the highest speed reported for such a device.

Demonstration of the feasibility of dual frequency operation of an electroabsorption modulator for demultiplexing in a 16 channel 40 Gbit/s OTDM system

It is shown that, by driving an electroabsorption modulator with a dual-frequency RF drive, it is possible to decrease the duty cycle attainable to as little as 3.5%, making it possible to demultiplex from 40 to 2.5 Gbit/s using a single device.

Multiquantum well electroabsorption modulators for 80 Gbit/s OTDM systems

A fully packaged electroabsorption modulator is used to generate transform limited 4.1 ps pulses at a 20 GHz repetition rate. The feasibility of using this component for short pulse generation and demultiplexing in a four channel 80 Gbit/s OTDM system is discussed.

A 4*5 Gb/s transmission system with all-optical clock recovery

The authors demonstrate successful 5 Gb/s operation of an all-optical clock extraction circuit in a 20 Gb/s optical time division multiplexing OTDM system. An optical clock signal was obtained by synchronizing a self-pulsating 1.56 mu m laser diode to a 5 GB/s RZ data signal, demultiplexed from a 4*5 Gb/s OTDM transmission system. Synchronization was achieved for pseudo-random-bit sequences from 2/sup 7/-1 to 2/sup 31/-1. At 2/sup 7/-1 full system bit-error-ratio (BER) measurement on one of the 5 GB/s channels using the extracted optical clock for synchronization were made with no observed penalty over transmitter clock measurements. Such clock extraction techniques may be of great importance in a wide variety of telecommunications applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>