Nonlinear Optical Loop Mirror Demultiplexer Research Articles

Theory and numerical analysis of higher order dispersion effects on ultra‐high‐speed nonlinear optical loop mirror demultiplexer

AbstractThe effects of higher order dispersion are analyzed for the first time in ultra‐fast signal demultiplexing using a nonlinear optical loop mirror (NOLM). The results show that performance degradation of NOLM can occur when higher order dispersion is not negligible. Therefore, a loop fiber with a higher order dispersion that is as small as possible should be chosen to realize terabit/second operation of the NOLM. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 124–127, 2001.

All-optical 100-gbit/s word packet time-division-multiplexed access node in a looped-back configuration: enabling technologies for sequential add–drop functionality

We experimentally demonstrate the adding, dropping, and passing through of 100-Gbit/s word packets in a looped-back all-optical time-division-multiplexed (TDM) access node. Packets are routed with a 17-dB contrast ratio and demultiplexed with a 20-dB contrast ratio. This node uses short 100-Gbit/s words to demonstrate its potential to process data packets from multiple sources and to perform packet switching in a multinode ring network configuration. The ability to tolerate timing jitter as well as varying input signal characteristics is essential to an all-optical access node in a multinode network. For 2-ps input pulses, the header processor has a timing window of approximately 5 ps, and the demultiplexer has a timing window of approximately 5.5 ps. This allows for tolerance to bit-to-bit timing jitters or to an increase in the pulse width of as much as 3 ps. Packet-to-packet timing jitter is detected and compensated by the technique used to synchronize the local source to each packet. The key enabling technologies of an all-optical TDM packet add-drop multiplexer are discussed, including an erbium-doped fiber laser, a nonlinear optical loop mirror logic gate, self-synchronization to incoming packets with a fast-saturation/slow-recovery gain element followed by an intensity discriminator, a two-wavelength nonlinear optical loop mirror demultiplexer, and synchronization of new packets to the network packet rate with a phase-locked loop. The local source is automatically synchronized to the incoming packet, because it uses an extracted pulse from the packet, which has a contrast ratio of >20 dB to the rest of the packet. Finally, new packets are added by use of a local laser and a synchronization method, which gives a timing jitter of approximately 1 ps. Using a statistical method of measuring Q value with picosecond resolution, we show that a header processor with two cascaded logic gates has a Q value of 7.1 with a 95% confidence level.

Mathematical modelling and BER analysis of 100 Gbs NOLM demultiplexer using a soliton-shaped pulse for control and data

A mathematical model for the non-linear optical loop mirror (NOLM) demultiplexer, operating with a soliton-shaped pulse for both control and data, is presented. The model can be used: to optimise system parameters (control pulse width, walk-off time etc.) for maximising peak transmittance of the switching profile; to calculate the switching profile width; and to estimate the switching profile through a new convolution approach. The simulation results are verified by numerically solving the non-linear Schrodinger equation. The NOLM model is then integrated into an optical receiver model for a bit error rate (BER) analysis. Simulation results show that BER, timing jitter noise and cross-talk are strongly dependent on the walk-off time between control and signal pulses in NOLM demultiplexing. The dependence of the BER on walk-off time agrees qualitatively with experimental results reported elsewhere.

Analysis of Switching Characteristics of a NOLM Demultiplexer with Signal-Control Pulse Walk-off and GVD Effects

The switching characteristics of a nonlinear optical loop mirror (NOLM) demultiplexer are analyzed with the emphasis on signal-control pulse walk-off and group velocity dispersion (GVD) effects by using the split-step Fourier method. It is shown that the walk-off can broaden the switching window of NOLM, make the window profile deviate its central position, and decrease its switching efficiency. Overmuch walk-off is detrimental because it can broaden the switching window considerably and lead to crosstalk of neighboring channel signals to the demultiplexed signal. A new solution scheme, which is adjusting the initial time delay between signal pulse and control pulse and the peak power of control pulse, is proposed to overcome this adverse effect. Large GVD is harmful to a NOLM demultiplexer, for this reason, the NOLM demultiplexer should be operated near the zero-dispersion wavelength of the fiber.

Bit-error-rate analysis for a 100-Gbit/s nonlinear optical loop mirror demultiplexer employing soliton control and signal pulses

On the basis of a previously derived mathematical model, the power penalty associated with a nonlinear optical loop mirror (NOLM) demultiplexer was calculated, with timing jitter noise, bit-to-bit cross talk, and channel cross talk taken into consideration. Simulation results show that a 3-dBm improvement in the receiver sensitivity at a bit error rate of 10(-9) can be achieved by choice of the appropriate walk-off time between the control and the signal pulses within the NOLM demultiplexer.

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.

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.

Signal-to-noise ratio analysis of 100 Gb/s demultiplexing using nonlinear optical loop mirror

This paper investigates experimentally and theoretically the signal-to-noise ratio (SNR) characteristics of 100 Gb/s all-optical demultiplexing using a nonlinear optical loop mirror (NOLM). The analysis takes into account two effects that degrade the SNR associated with NOLM demultiplexing. First is channel crosstalk originating from the leakage of nontarget channels. Second is the intensity fluctuations of demultiplexed signals caused by the combined effects of timing jitter and a profile of the switching window. Considering these two effects, power penalties associated with NOLM. Demultiplexing are theoretically evaluated using the conventional noise theory of an optical receiver followed by an optical preamplifier. Experimental results of bit error rate measurements for 100 Gb/s demultiplexing using three different NOLMs with different intrinsic crosstalk values, defined by signal transmittance in the absence of control pulses, show that the power penalties are in good agreement with the evaluation based upon our proposed analysis. It can be found from our investigation in demultiplexing from 100 to 10 Gb/s that intrinsic crosstalk of less than -25 dB, corresponding to a coupling ratio, K, of |K-0.5|/spl les/0.03, is required for the power penalty of less than 1 dB. The root-mean-square (rms) value of the relative timing jitter necessary for obtaining a sufficient timing tolerance width for combining control and signal pulses is determined.

Synchronization of passively mode-locked erbium-doped fiber lasers and its application to optical communication networks

We synchronized two passively mode-locked erbium-doped fiber lasers using a phase lock loop with a large dynamic range and bandwidth, which is realized by using a novel acoustooptic-modulator-grating scheme. Cross-correlation of the two lasers shows the interlaser jitter is under 2 ps (same as the laser pulse width) for period as long as hours. To prove the quality of phase locking, we apply synchronized lasers in two all-optical network applications, one of which requires the lasers to have the same wavelength and the second requires the lasers to be at different wavelengths. In the single wavelength application, the synchronized lasers drive a cascade of two low-birefringence, polarization maintaining, optical logic gates with switching timing window of 4 and 5 ps, respectively. We obtain nonlinear transmission of /spl sim/50% at a switching energy of 8 pJ and contrast ratio of 16 dB, which are comparable performance as that obtained using a single laser. In the different wavelength application, we use 0.8 ps pulses to switch 2 ps pulses in a two-wavelength nonlinear optical loop mirror demultiplexer with timing window of 5.5 ps. Stable switching is reached at a efficiency as high as 90% at switching energy of 0.8 pJ, and a contrast ratio of 20 dB. Excellent agreement is found between the experimental data and the simulated results, which exclude the timing jitter.

Analysis of the polarization group-velocity dispersion effect in polarization-independent nonlinear-optical loop mirror demultiplexers

Polarization-independent two-wavelength nonlinear-optical loop mirrors are analyzed theoretically by use of a Jones matrix model. The model is then applied to study the effect of fiber polarization group-velocity dispersion and control duty cycle on the extinction ratio in nonlinear-optical loop mirror demultiplexing.

Impact of extinction ratio and switching efficiency of nonlinear optical loop mirror demultiplexer on error rate performance

A theory is evaluated that allows the calculation of the worst-case input power penalty of an optical demultiplexer using a nonlinear optical loop mirror (NOLM) as high-speed switch. Due to finite NOLM extinction ratio and switching efficiency reduction there exists a strong dependence of the penalty on the bitrate of the drop channel, which is investigated for different 100 Gbit/s demultiplexer configurations. Assuming a NOLM of 2 km loop fiber, a 20-dB extinction ratio, and a switching pulse EDFA of 14.5 dBm, demultiplexing with a penalty of less than 7 dB should be possible for drop rates between 2.5 GHz and 11.1 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of control-signal pulse walk-off on BER performance of nonlinear optical loop mirror demultiplexer

The effects of pulse walk-off between control and signal pulses on the BER performance of an NOLM demultiplexer are studied at 32 Gbit/s using a wavelength tunable mode-locked Er/sup 3+/-doped fibre ring laser. It is confirmed that BER degradation caused by timing errors is effectively suppressed by choosing an appropriate amount of pulse walk-off. >

64 Gb/s all-optical demultiplexing with the nonlinear optical-loop mirror

The first complete nonlinear optical-loop mirror demultiplexing experiments including error-rate measurements are reported. Broadband demultiplexing of 16-, 32-, and 64-Gb/s, 2/sup 15/-1 data was performed using only semiconductor lasers. The penalty for demultiplexing a 64-Gb/s time-division multiplexed data stream to the 4-Gb/s fundamental rate was 2.2 dB at an error rate of 10/sup -9/. The switching pulse energy was 1.1 pJ. >