Siamak Amiralizadeh

Mode division multiplexing using orbital angular momentum modes over 1.4 km ring core fiber

Mode division multiplexing (MDM) systems using orbital angular momentum (OAM) modes can recover the data in D different modes without recourse to full (2D × 2D) multiple input multiple output (MIMO) processing. One of the biggest challenges in OAM-MDM systems is the mode instability following fiber propagation. Previously, MIMO-free OAM-MDM data transmission with two modes over 1.1 km of vortex fiber was demonstrated, where optical polarization demultiplexing was employed in the setup. We demonstrate MDM data transmission using two OAM modes over 1.4 km of a specially designed ring core fiber without using full MIMO processing or optical polarization demultiplexing. We demonstrate reception with electrical polarization demultiplexing, i.e., minimal 2 × 2 MIMO, showing the compatibility of OAM-MDM with current polarization demultiplexing receivers.

Single-fiber lightwave centralized WDM-OFDMA-PON with colorless optical network units

We propose and experimentally demonstrate a carrier-reuse, single-feeder, wavelength-division-multiplexed, orthogonal frequency-division-multiple-access passive optical network (WDM-OFDMA-PON) with colorless direct-detection optical network units and coherent detection optical line terminals. We examine two strategies by adjusting the frequency occupancy and the modulation format of the uplink (UL) and downlink (DL) signals. We investigate the impact of the DL signal-to-carrier ratio on the performance of both the UL andDLsignals via simulations and identify impairments limiting system performance. As a proof of concept,we demonstrate on a single wavelength channel a realization of each of the two scenarios investigated using orthogonal frequency division- multiplexing (OFDM). A quadrature phase-shift keying approachwith a wide spectrum and a narrow guard band achieves 21.6 Gb/s.A32-aryquadrature amplitudemodulation approach with a narrow spectrum and a wide guard band achieves 14.5 Gb/s and a span of over 80 km.

Error vector magnitude based parameter estimation for digital filter back-propagation mitigating SOA distortions in 16-QAM.

We investigate the performance of digital filter back-propagation (DFBP) using coarse parameter estimation for mitigating SOA nonlinearity in coherent communication systems. We introduce a simple, low overhead method for parameter estimation for DFBP based on error vector magnitude (EVM) as a figure of merit. The bit error rate (BER) penalty achieved with this method has negligible penalty as compared to DFBP with fine parameter estimation. We examine different bias currents for two commercial SOAs used as booster amplifiers in our experiments to find optimum operating points and experimentally validate our method. The coarse parameter DFBP efficiently compensates SOA-induced nonlinearity for both SOA types in 80 km propagation of 16-QAM signal at 22 Gbaud.

Modeling and compensation of transmitter nonlinearity in coherent optical OFDM

We present a comprehensive study of nonlinear distortions from an optical OFDM transmitter. Nonlinearities are introduced by the combination of effects from the digital-to-analog converter (DAC), electrical power amplifier (PA) and optical modulator in the presence of high peak-to-average power ratio (PAPR). We introduce parameters to quantify the transmitter nonlinearity. High input backoff avoids OFDM signal compression from the PA, but incurs high penalties in power efficiency. At low input backoff, common PAPR reduction techniques are not effective in suppressing the PA nonlinear distortion. A bit error distribution investigation shows a technique combining nonlinear predistortion with PAPR mitigation could achieve good power efficiency by allowing low input backoff. We use training symbols to extract the transmitter nonlinear function. We show that piecewise linear interpolation (PLI) leads to an accurate transmitter nonlinearity characterization. We derive a semi-analytical solution for bit error rate (BER) that validates the PLI approximation accurately captures transmitter nonlinearity. The inverse of the PLI estimate of the nonlinear function is used as a predistorter to suppress transmitter nonlinearity. We investigate performance of the proposed scheme by Monte Carlo simulations. Our simulations show that when DAC resolution is more than 4 bits, BER below forward error correction limit of 3.8 × 10(-3) can be achieved by using predistortion with very low input power backoff for electrical PA and optical modulator.

Experimental validation of digital filter back-propagation to suppress SOA-induced nonlinearities in 16-QAM

We experimentally demonstrate the performance of a computationally efficient digital filter back-propagation scheme for post-compensating SOA nonlinearities in coherent detection of 16-QAM signal at 16 Gbaud, and compare the results with simulations.

Comparison of 100 Gb/s O-band PAM-4 vs. C-band DMT for different laser linewidths and fiber lengths

We simulate 100 Gb/s systems using PAM-4 (O-band without chromatic dispersion) and DMT (C-band with less attenuation). We find the tolerance of each to laser linewidth, and discuss the fiber reach of each system.

Discrete Multi-Tone Transmission With Optimized QAM Constellations for Short-Reach Optical Communications

We investigate performance of optimized M-ary quadrature amplitude modulation (M-QAM) constellations in short-reach single-polarization (SP) and dual-polarization (DP) discrete multitone (DMT) with direct detection. The constellations are obtained by using an iterative gradient-search algorithm. For the nonsquare constellations, we find bit-to-symbol mappings with a blind search method. Our experiments show that the data rate can be improved in both SP and DP DMT systems by using optimized constellations instead of square M-QAM. Net data transmission rates of 165 and 152 Gb/s are respectively achieved for back-to-back and 2.2 km in a direct-detection DP DMT system assuming forward error correction threshold of 3.8×10-3.

Experimental study of M-QAM constellation options for short-reach dual-polarization optical OFDM with direct detection

We find optimized M-QAM constellations for short-reach DDO-OFDM using an iterative gradient-search method and evaluate their performance. With the optimized constellations, capacity is increased by 12 Gb/s compared to square constellation achieving data rate of 168 Gb/s for 16-QAM.

Transmitter Sensitivity to High PAPR in Coherent Optical OFDM Systems

We investigate degradation of QPSK CO-OFDM system due to components most susceptible to high PAPR. We vary transmitter design parameters and uncover appropriate working conditions and clipping effectiveness regions.