Shelby J. Savage

100 Gb/s optical time-division multiplexed networks

We present ultrafast slotted optical time-division multiplexed networks as a viable means of implementing a highly capable next-generation all-optical packet-switched network. Such a network is capable of providing simple network management, the ability to support variable quality-of-service, self-routing of packets, scalability in the number of users, and the use of digital regeneration, buffering, and encryption. We review all-optical switch and Boolean logic gate implementations using an ultrafast nonlinear interferometers (UNIs) that are capable of stable, pattern-independent operation at speeds in excess of 100 Gb/s. We expand the capability provided by the UNI beyond switching and logic demonstrations to include system-level functions such as packet synchronization, address comparison, and rate conversion. We use these advanced all-optical signal processing capabilities to demonstrate a slotted OTDM multiaccess network testbed operating at 112.5 Gb/s line rates with inherent scalability in the number of users and system line rates. We also report on long-haul propagation of short optical pulses in fiber and all-optical 3R regeneration as a viable cost-effective means of extending the long-haul distance of our OTDM network to distances much greater than 100 km.

40 Gbit/s all-optical XOR using a fiber-based folded ultrafast nonlinear interferometer

Summary form only given. We have shown all-optical XOR at data rates as high as 40 Gbit/s using a novel experimental setup which allows bit error-rate testing of the pseudo-random XOR pattern at the output of the switch. To the best of our knowledge, this is the highest demonstrated rate for XOR operation on two fully-loaded pseudo-random binary streams. The folded UNI incorporating a Faraday mirror reduces polarization instabilities and provides stable performance in an all-fiber switch. Because of the high-speed nonlinear refractive index in fiber, we expect that this logic gate will readily scale to higher data rates.

All-optical pulse regeneration in an ultrafast nonlinear interferometer with Faraday mirror polarization stabilization

We demonstrate the folded ultrafast nonlinear interferometer (FUNI) as a 3R all-optical regenerator. Faraday rotation provides inherent polarization stabilization, and the optical fiber nonlinear medium provides ultrafast operation and switching window tunability. We demonstrate 3R regeneration of 10-Gbit/s data with 5-pJ pulse switching energy and 4-ps timing-jitter tolerance.

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.

All-optical pulse regeneration in an ultrafast nonlinear interferometer with Faraday mirror polarization control

Summary form only given. We present a folded ultrafast nonlinear interferometer (FUNI) optical switch that uses Faraday rotation to achieve acoustic and polarization stabilization. We experimentally demonstrate FUNI operation for 3R all-optical regeneration with a wide switching window and a low BER power penalty.

Wavelength-maintaining polarization-insensitive all-optical 3R regenerator

High-rate long-haul fiber communications systems will require high-speed efficient signal regeneration. By introducing a simple semiconductor-optical-amplifier wavelength converter into the folded ultrafast nonlinear interferometer, we demonstrate a polarization-insensitive wavelength-maintaining 3R all-optical regenerator. The extinction ratio between the on and off states is 21 dB. Bit-error rate data show no error floor and <0.3-dB power penalty when compared with a baseline measurement. Moreover, changes in input polarization cause no change in performance. The regenerator maintained a constant polarization and constant output power, independent of the input polarization.

200-pass picosecond-pulse transmission through a regenerative recirculating fiber loop

We demonstrate picosecond-pulse transmission over 20 Mm using an all-optical 3R regenerator cascaded 200 times. Bit-error rate curves and cross-correlations show good pulse quality and a 1-dB penalty compared to back-to-back.

Frequency stabilization of laser diodes in an aggressive thermal environment

Mobile free-space laser communication systems must reconcile the requirements of low size, weight, and power with the ability to both survive and operate in harsh thermal and mechanical environments. In order to minimize the aperture size and amplifier power requirements of such systems, communication links must exhibit performance near theoretical limits. Such performance requires laser transmitters and receiver filters and interferometers to maintain frequency accuracy to within a couple hundred MHz of the design frequency. We demonstrate an approach to achieving high frequency stability over wide temperature ranges by using conventional DFB lasers, tuned with TEC and current settings, referenced to an HCN molecular frequency standard. A HCN cell absorption line is scanned across the TEC set-point to adjust the DFB laser frequency. Once the center of the line is determined, the TEC set-point is offset as required to obtain frequency agility. To obtain large frequency offsets from an HCN absorption line, as well as continuous laser source operation, a second laser is offset from the reference laser and the resulting beat tone is detected in a photoreceiver and set to the desired offset using a digital frequency-locked loop. Using this arrangement we have demonstrated frequency accuracy and stability of better than 8 MHz RMS over an operational temperature range of 0ºC to 50º C, with operation within minutes following 8 hour soaks at -40º C and 70º C.