Don Hewitt

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.

Orthogonal Frequency Division Multiplexing using Baseband Optical Single Sideband for Simpler Adaptive Dispersion Compensation

A novel baseband OFDM optical single-sideband system is proposed for long-haul adaptive dispersion compensation. Simulations on a dispersive 420 km link show that non linear fibre effects and MZ modulator intermodulation effects will be the limiting factors on system performance.

WDM passive optical network with subcarrier transmission and baseband detection scheme for laser-free optical network units

We demonstrate a new scheme to achieve source-free optical network units (ONUs) in a wavelength-division-multiplexed passive optical network. The scheme utilizes subcarrier downlink transmission that enables penalty-free remodulation of the downstream signal for upstream transmission. The downstream data can be recovered at baseband either using an optical or electrical technique. In the optical scheme, the downstream signal is passed through a delay interferometer (DI) at the ONUs. A single variety of the DI is applicable to all ONUs that eliminates location-specific devices. Alternatively, the baseband data can be detected using a high-speed photodiode, a dc block, and a rectifier without any optical filter or phase locked loop for down-conversion. The upstream data is also detected at baseband without any modification to conventional receivers. We present experimental and simulation results for the scheme at 2-Gb/s downstream and upstream transmission over 20 km of fiber

Data-Aided Chromatic Dispersion Estimation for Polarization Multiplexed Optical Systems

We propose a full transmission link chromatic dispersion (CD) estimation technique for polarization-multiplexed coherent optical single carrier system using data-aided channel estimation and least square quadratic fit. New training sequences based on Chu sequence and Golay complementary pair are designed and compared for estimation performance against the ideal full-level Chu sequence for both QPSK and 16-QAM systems. The proposed technique is demonstrated in a 40-Gb/s coherent polarization multiplexed optical system over 2080-km fiber transmission for QPSK format and 80-Gb/s system over 1800-km fiber for 16-QAM format to verify its accurate and robust estimation performance.

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Owing to its low transmitter complexity and low sensitivity to nonlinear impairments, phase noise, and frequency offset, the single carrier system with frequency domain equalization (SC-FDE) is of interest for high-bit-rate optical transmission. In this letter, we experimentally demonstrate a 8×40-Gb/s optical coherent polarization-multiplexed SC-FDE over 2080-km fiber transmission using novel training sequences. The sequences are designed based on Chu and Golay complementary sequences to have binary levels and are fully compatible with the commercial quadrature phase-shift keying (QPSK) systems. The use of these training sequences helps achieve accurate channel estimation and equalization in full-system demonstration.

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We experimentally demonstrate full-transmission chromatic dispersion estimation with high accuracy in 40-Gb/s coherent polarization-multiplexed single-carrier system using binary complementary Golay training sequences. The technique is verified to be robust against polarization-mode-dispersion and amplified-spontaneous-emission noise.

40-Gb/s Optical Coherent Pol-Mux Single Carrier System With Frequency Domain Equalization and Training Sequences

We propose an optical signal-to-noise ratio (OSNR) estimation technique using self-equalized complementary Golay sequences for both QPSK and 16-QAM coherent optical systems. The training sequences have complementary spectra, which enable accurate channel estimation and equalization, and have length-independent constellation for high-performance estimation. Estimation performances are verified through 100- and 40-Gb/s QPSK and 200- and 80-Gb/s 16-QAM coherent polarization-multiplexed optical systems, with an accuracy of 0.4 and 0.7 dB, in both simulations and experiments, respectively.

Chromatic dispersion estimation in 40 Gb/s coherent polarization-multiplexed single carrier system using complementary Golay sequences

We study which optical parameters limit the performance of 10 Gbit/s baseband OFDM metro and access systems and demonstrate 16-QAM transmission over 240 km without dispersion compensation and extended reach of PONs using MM fibre.

Data-Aided OSNR Estimation for QPSK and 16-QAM Coherent Optical System

In this paper, we present a chromatic dispersion (CD) estimation technique based on complementary Golay sequences for systems employing single-carrier with frequency domain equalization (SC-FDE) format. By exploiting the unique correlation property of Golay sequences and using the sequences as channel estimation symbol (CES), chromatic dispersion can be estimated by measuring partial phase response and compensated using frequency domain equalization (FDE) with relatively low complexity in both the training sequences and estimation algorithm. The technique is verified by computer simulation to be able to estimate and compensate for up to 1500 km fiber with standard dispersion at high accuracy in 80 Gb/s coherent NRZ-QPSK system.

Performance and Applications of Gigabit OFDM over Optical Fibre Systems in Metro and Access Networks

We demonstrate a wavelength reuse scheme facilitated through sub-carrier downstream transmission that achieves source free optical network units in a WDM-PON. The scheme only requires baseband detection for both downstream and upstream data recovery.