Tailoring Wideband Signals With a Photonic Hardware Accelerator

Abstract

| Digital hardware accelerators are increasingly employed to speed up computation and reduce power dissipation, enabling real-time operation. Inspired by this paradigm, we propose the concept of the photonic hardware acceleratorVan analog optical processing engine that precedes optical-to-electrical conversion and alleviates the burden on subsequent electronics. We propose one specific class of photonic hardware accelerators designed to assist in acquisition, feature extraction, and storage of wideband waveforms.This fundamental unit reshapes, in real time, the spectrotemporal evolution of a wideband streaming signal based on signal's sparsity. Functioning as an information gearbox, the accelerator transforms the signal according to the nonuniform entropy of its spectrum. Nonlinear group delay dispersion modes are introduced as primitive building blocks for such transformations. Representing spectrotemporal basis functions, these modes and their corresponding time-stretch wavelets have distinct and useful properties that depend on their symmetry. We focus on polynomial basis functions, but also discuss their limitations and alternatives such as spline functions that offer more efficient representation of group delay spectra with localized features. They are used to synthesize complex warped spectrotemporal operations that are reconfigurable and can be implemented in both analog optical and digital (computational) domains. We show how these dispersion-based computational primitives reshape the wideband signal to enable nonuniform sampling, compression, and pattern recognition in real time. Additional applications including coding, signal classification, and enhancement of signal-to-noise ratio during ultrafast analog-to-digital conversion are discussed. Fig. 7. Various methods for realizing optical dispersion. (a) Dispersive optical fiber with internal Raman amplification. (b) chirped fiber Bragg grating (CFBG) used in conjunction with a circulator. (c) CMD. The CMD device offers field reconfigurability of phase and group delay dispersion through tuning of the launch angle of light into the multimode waveguide.

Progress in neuromorphic photonics

“…Neuromorphic photonic processors join a class of photonic hardware accelerators designed to assist in acquisition, feature extraction, and storage of wideband waveforms [123]. These accelerators manipulate the spectrotemporal of a wideband signal, a task difficult to accomplish in analog electronics over broad bandwidth and with low loss.…”

From self-organization in relativistic electron bunches to coherent synchrotron light: observation using a photonic time-stretch digitizer

“…Ultrafast diagnostics also recently started to use strategies from the emerging field of "photonic hardware accelerators" [34], which aims at increasing the speed of electronic devices by combining them with specially designed photonic front-ends. In particular photonic timestretch analog to digital converters [35,36] opened the way to the realization of "single-shot terahertz oscilloscopes" [30,35,[37][38][39] providing up to tens of million traces per second.…”

Design of Warped Stretch Transform

“…For example, direct frequency-to-time mapping can be replaced by phase retrieval 13 or coherent detection after the dispersion 14 followed by back propagation. Using warped group delay dispersion as a photonic hardware accelerator 15 , an optical signal's intensity envelope can be engineered to match the specifications of the data acquisition back-end [16][17][18] . One can slow down an ultra-fast burst of data, and at the same time, achieve data compression by exploiting sparsity in the original data 19 .…”