Sarah D. Dods

Optical performance monitoring technique using delay tap asynchronous waveform sampling

We propose an asynchronous sampling monitor based on a two-tap delay line. Plotting the joint distribution of the sample pairs provides a representation of waveform distortion containing similar information to an eye diagram, without clock extraction

Performance of WDM ring and bus networks in the presence of homodyne crosstalk

This paper examines the effects of coherent and incoherent homodyne crosstalk in wavelength division multiplexed (WDM) ring and bus networks using reconfigurable optical add-drop multiplexers (OADMs). It is widely understood that incoherent homodyne crosstalk causes power penalties at the receivers in these networks. We show that coherent homodyne crosstalk causes a range of possible received powers, and that coherent and incoherent crosstalk together lead to a range of possible power penalties. A Monte Carlo simulation is used to examine the probability distribution of power penalties due to homodyne crosstalk under various conditions. We find that increasing the switch and multiplexer crosstalk within each OADM, and increasing the number of WDM channels, all produce increased probabilities of large power penalties. However, the number of nodes through which a signal is transmitted does not affect the power penalty distribution.

Multi Impairment Monitoring for Optical Networks

As optical networks become more complex, the need for in-line monitoring of more than just channel wavelength, power and OSNR becomes compelling. In this paper we describe an asynchronous delay tap sampling technique coupled with statistical machine learning that enables a single monitor to measure multiple simultaneous impairments on multiple formats. We demonstrate the technique for simultaneous measures of CD and 1st order PMD on a 40 Gbit/s NRZ-DPSK signal.

Asynchronous Sampling for Optical Performance Monitoring

We present two novel performance monitoring techniques for optically switched networks, based on asynchronous multi-tap sampling. We show that multiple simultaneous impairments can be separated and quantified by a single monitor.

Homodyne crosstalk in WDM ring and bus networks

We examine the combined effects of coherent and incoherent crosstalk in wavelength-division multiplexed (WDM) ring and bus networks which use add-drop multiplexers. It is widely understood that incoherent crosstalk in these networks causes a fixed bit-error-rate (BER) door at the receiver. We show that coherent crosstalk causes a range of possible received powers. In combination with incoherent crosstalk, this leads to a range of possible BER floor positions. We use a Monte Carlo simulation to show that when both coherent and incoherent crosstalk are considered, BER floors are likely to be higher than previously appreciated. Satisfactory network performance can be ensured by careful network management, or by reducing component leakage.

Calculation of bit-error rates and power penalties due to incoherent crosstalk in optical networks using Taylor series expansions

A new calculation method is presented for bit-error rates and power penalties due to incoherent crosstalk from up to eight interferers of different powers, based on a truncated Taylor series approximation of the crosstalk contribution to the noise probability density function. Formulae are provided for bit-error rates and power penalties in both thermal and ASE limited systems, with average-power and optimized decision thresholds, and include extinction ratio effects. The technique forms an excellent complement to the Gaussian approximation.

A comparison of the homodyne crosstalk characteristics of optical add-drop multiplexers

We compare the homodyne crosstalk characteristics of a number of different optical add-drop multiplexer (OADM) structures, in the context of wavelength-division multiplexed (WDM) ring or bus network links. Nine fixed-wavelength and rive reconfigurable OADM structures are examined. For the fixed-wavelength structures, we find considerable variation in the levels of incoherent crosstalk, and generally low coherent crosstalk levels. For the reconfigurable structures, incoherent crosstalk levels are quite similar, but the coherent crosstalk levels differ considerably. The range of homodyne crosstalk-induced power penalties is calculated for all structures, and the probability distribution is found for each reconfigurable OADM. The effects of the number of OADMs in the link and the number of wavelength channels in the network are also studied. We find that the best choice of OADM depends on the application.

Robust, Low Cost, In-Band Optical Signal to Noise Monitoring Using Polarization Diversity

We demonstrate a robust in-band OSNR monitor using polarization diversity and low-cost opto-electronics. The proposed technique offers relaxed manufacturing tolerances and is insensitive to extinction ratio, bit rate, chromatic dispersion and first order PMD.

Cross modulation of pump-signals in distributed Raman amplifiers, theory and experiment

Cross modulation of the pump and signal in a backward pumped distributed Raman amplifier (DRA) is investigated theoretically and experimentally. An analytical theory describing the frequency response of cross modulation in a DRA with pump perturbation is developed for the first time. The corner frequency of this response is simply determined by the walkoff parameter of the two counterpropagation lights and the loss coefficient of the Raman fiber. This theory was confirmed by the agreement of theoretical results and experimental measurements.

Asynchronous measurement of chromatic dispersion from waveform distortion

We propose a new method to monitor chromatic dispersion, based on two-tap asynchronous sampling. We experimentally demonstrate sensitivity to dispersion between 160 and 800 ps/nm, which matches the tolerances of typical commercial 10 Gbit/s receivers.