Vincent J. Hernandez

104 MHz rate single-shot recording with subpicosecond resolution using temporal imaging.

We demonstrate temporal imaging for the measurement and characterization of optical arbitrary waveforms and events. The system measures single-shot 200 ps frames at a rate of 104 MHz, where each frame is time magnified by a factor of -42.4x. Impulse response tests show that the system enables 783 fs resolution when placed at the front end of a 20 GHz oscilloscope. Modulated pulse trains characterize the systems impulse response, jitter, and frame-to-frame variation.

High-energy (>70 keV) x-ray conversion efficiency measurement on the ARC laser at the National Ignition Facility

The Advanced Radiographic Capability (ARC) laser system at the National Ignition Facility (NIF) is designed to ultimately provide eight beamlets with a pulse duration adjustable from 1 to 30 ps, and energies up to 1.5 kJ per beamlet. Currently, four beamlets have been commissioned. In the first set of 6 commissioning target experiments, the individual beamlets were fired onto gold foil targets with energy up to 1 kJ per beamlet at 20–30 ps pulse length. The x-ray energy distribution and pulse duration were measured, yielding energy conversion efficiencies of 4–9 × 10−4 for x-rays with energies greater than 70 keV. With greater than 3 J of such x-rays, ARC provides a high-precision x-ray backlighting capability for upcoming inertial confinement fusion and high-energy-density physics experiments on NIF.

Transmitter and translating receiver design for 64-ary pulse position modulation (PPM)

This paper explores the architecture and design of an optically-implemented 64-ary PPM transmitter and direct-translating receiver that effectively translates incoming electrically-generated bit streams into optical PPM symbols (and vice-versa) at > 1 Gb/s data rates. The PPM transmitter is a cascade of optical switches operating at the frame rate. A corresponding receiver design is more difficult to architect and implement, since increasing data rates lead to correspondingly shorter decision times (slot times and frame times). We describe a solution in the form of a time-to-space mapping arrayed receiver that performs a translating algorithm represented as a code map. The technique for generating the code map is described, and the implementation of the receiver as a planar lightwave circuit is given. The techniques for implementing the transmitter and receiver can be generalized for any case of M-ary PPM.

Optical CDMA (O-CDMA) technology demonstrator (TD) for 2D codes

A technology demonstrator (TD) based on wavelength/time codes, configured to multiplex and transmit 32 asynchronous gigabit Ethernet data flows (GbE over O-CDMA), is described. The TD is user and data rate scalable.

Design of optical pulse position modulation (PPM) translating receiver

A design for a receiver that directly converts PPM pulse positions into bit sequences for arbitrary M and data rate is described in this paper. The design is enabled by lossless splitters based on EDWA/PLCs.

Virtual array receiver options for 64-ary pulse position modulation (PPM)

NASA is developing technology for 64-ary PPM using relatively large PPM time slots (10 ns) and relatively simple electronic-based receiver logic. In this paper we describe photonics-based receiver options for the case of much higher data rates and inherently shorter decision times. The receivers take the form of virtual (array or quadrant) arrays with associated comparison tests. Previously we explored this concept for 4-ary and 16-ary PPM at data rates of up to 10 Gb/s. The lessons learned are applied to the case of 64-ary PPM at 1.25 Gb/s. Various receiver designs are compared, and the optimum design, based on virtual arrays, is evaluated using numerical simulations.

Receiver architecture for 12.5 GB/S 16-ary pulse position modulation (PPM) signaling

In this paper, we extend these photonic process techniques to a 16-ary, 12.5 Gb/s (10 Gb/s plus 8B/10B line coding) PPM communications system for fiber optic avionics, wherein much of the receiver processing is enabled by techniques based on planar lightwave circuits (PLCs). The architecture is applicable to higher input data rates and M-ary PPM. In the following, we present the PPM encoding and decoding architectures and numerically simulated results.

Bit-error-rate performance of a gigabit Ethernet O-CDMA technology demonstrator (TD)

An O-CDMA TD based on 2-D (wavelength/time) codes is described, with bit-error-rate (BER) and eye-diagram measurements given for eight users. Simulations indicate that the TD can support 32 asynchronous users.

Performance Impact of Multiple Access Interference in a 4-ary Pulse Position Modulated Optical Code Division Multiple Access (PPM/O-CDMA) System

An O-CDMA system utilizing 4-ary pulse position modulation and a novel virtual quadrant receiver is described. Bit-error-rates show the impact of multiple access interference, as influenced by its proximity to the correctly decoded signal.

Dispersion compensation requirements for optical CDMA using WDM lasers

Optical code division multiple access (O-CDMA) uses very narrow transmission pulses and is thus susceptible to fiber optic link impairments. When the O-CDMA is implemented as wavelength/time (W/T) matrices which use wavelength division multiplexing (WDM) sources such as multi-frequency laser transmitters, the susceptibility may be higher due to: (a) the large bandwidth utilized and (b) the requirement that the various wavelength components of the codes be synchronized at the point of the data modulation and encoding as well as after (optical) correlation. A computer simulation based on the nonlinear Schroedinger equation (developed to study optical networking on the National Transparent Optical Network (NTON)) was modified to characterize the impairments on the propagation and decoding of W/T matrix codes over a link of the NTON. Three critical impairments were identified by the simulation: group velocity dispersion (GVD); the flatness of the optical amplifier gain; and the slope of the GVD. Subsequently, experiments were carried out on the NTON link to verify and refine the simulations as well as to suggest improvements in the W/T matrix signal processing design. The NTON link measurements quantified the O-CDMA dispersion compensation requirements. Dispersion compensation management is essential to assure the performance of W/T matrix codes.