Jade P. Wang

Photonic ADC: overcoming the bottleneck of electronic jitter

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.

Demonstration of 40-Gb/s Packet Routing Using All-Optical Header Processing

We show simultaneous forwarding of two optical packets through a 2times2 spatial switch at 40 Gb/s using only two ultrafast nonlinear interferometers. This demonstrates a scalable all-optical header processing architecture applicable for general network topologies and can lead to reduced size, weight, and power requirements as compared with electronic solutions. Clear open eye diagrams were observed and a packet error rate of 10-6, comparable with current electronic router error rates, was measured for the entire system

A Performance Optimization Method for SOA-MZI Devices

We present a novel characterization method for semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) switches which combines a pump-probe measurement with an interferometer bias scan. This enables optimal bias identification and better understanding of switching dynamics.

Regeneration using an SOA-MZI in a 100-pass 10,000-km Recirculating Fiber Loop

We demonstrate all-optical regeneration in an SOA-MZI on a 10-Gb/s picosecond pulse train over 10,000 km in a 100-km recirculating loop. The bit-error rate after 100 loop-passes shows a 0.5-dB penalty.

Efficient performance optimization of SOA-MZI devices

We present a novel characterization method for semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) switches which combines a pump-probe measurement with an interferometer bias scan. In addition to a wealth of information on the switching dynamics for all operating points of the switch, we can create an extinction map to pinpoint regions of highest extinction for optimizing all-optical ultrafast switching. We experimentally verify the accuracy of this characterization method by performing a wavelength characterization at the optimal bias point and a nearby, non-optimal point. A 1-dB penalty was observed.

40-Gbit/s all-optical header processing for packet routing

We demonstrate 40-Gbit/s all-optical header processing using two ultrafast nonlinear interferometers to simultaneously forward two packets through a 2&2 spatial switch. Clear, open eye diagrams are observed, indicating low-error-rate forwarding decisions for packet routing.

Sensitive clock recovery for multi-rate DPSK optical receivers

Robust clock recovery is essential for optical receivers that can operate over a wide range of data rates. The multi-rate burst-mode DPSK format that is finding applications in NASAs Laser Communications Relay Demonstration (LCRD) leverages a single optically-preamplified receiver that can maintain nearly theoretical performance for data rates spanning more than two orders of magnitude. Clock recovery of this versatile format needs to function both in low signal-to-noise ratio (SNR) and in high-power regimes, and needs to be able to accommodate a wide variation of rate-dependent peak-to-average powers as well as operation over intermittent fading channels. This can be achieved with traditional analog phase-locked-loop techniques as well as gated approaches that offer lower jitter, which is helpful for stressing low-data-rate applications. This paper presents an overview of clock recovery approaches for multi-rate DPSK receivers, an analysis of expected performance, and measured results.

Efficient Performance Optimization for Ultrafast All-Optical Switching in SOA-MZI Devices

We present a simple method for optimization of ultrafast switching performance in semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) devices. By simultaneously measuring switching dynamics over all possible interferometer bias points, we acquire an extinction map which accurately identifies operating conditions for high extinction and optimal switching.