[Show abstract][Hide abstract] ABSTRACT: The combination of ultrafast laser dynamics and dense on-chip multiwavelength networking could potentially address new domains of real-time signal processing that require both speed and complexity. We present a physically realistic optoelectronic simulation model of a circuit for dynamical laser neural networks and verify its behavior. We describe the physics, dynamics, and parasitics of one network node, which includes a bank of filters, a photodetector, and excitable laser. This unconventional circuit exhibits both cascadability and fan-in, critical properties for the large-scale networking of information processors based on laser excitability. In addition, it can be instantiated on a photonic integrated circuit platform and requires no off-chip optical I/O. Our proposed processing system could find use in emerging applications, including cognitive radio and low-latency control.
[Show abstract][Hide abstract] ABSTRACT: Optical encryption, key generation, and optical stealth transmission techniques for protecting the privacy of communication in optical networks are proposed and summarized. The signal processing methods based on fiber components provide ways to encrypt data and generate encryption keys at the speed of data transmission in optical fibers. Private and confidential communication is achieved without compromising the capacity and bandwidth of the optical network. Optical stealth transmission can hide the signal in plain sight. Because an eavesdropper can neither read the data nor detect the existence of the transmitted signal, optical stealth transmission provides a higher level of privacy. A hybrid system which includes both the public channels and stealth channels can effectively provide anonymous communication and defend against traffic analysis.
IEEE Journal of Selected Topics in Signal Processing 10/2015; 9(7):1-1. DOI:10.1109/JSTSP.2015.2424690 · 2.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Novel materials and devices in photonics have the potential to revolutionize optical information processing, beyond conventional binary-logic approaches. Laser systems offer a rich repertoire of useful dynamical behaviors, including the excitable dynamics also found in the time-resolved "spiking" of neurons. Spiking reconciles the expressiveness and efficiency of analog processing with the robustness and scalability of digital processing. We demonstrate that graphene-coupled laser systems offer a unified low-level spike optical processing paradigm that goes well beyond previously studied laser dynamics. We show that this platform can simultaneously exhibit logic-level restoration, cascadability and input-output isolation---fundamental challenges in optical information processing. We also implement low-level spike-processing tasks that are critical for higher level processing: temporal pattern detection and stable recurrent memory. We study these properties in the context of a fiber laser system, but the addition of graphene leads to a number of advantages which stem from its unique properties, including high absorption and fast carrier relaxation. These could lead to significant speed and efficiency improvements in unconventional laser processing devices, and ongoing research on graphene microfabrication promises compatibility with integrated laser platforms.
[Show abstract][Hide abstract] ABSTRACT: We propose and experimentally demonstrate an optical self-interference cancellation system to enable more efficient spectrum management and sensing in cognitive radios. The optical system is a radio-frequency front-end module, which cancels in-band self-interference, permitting a radio to simultaneously transmit and receive. By cancelling enough self-interference, a cognitive radio can perform continuous spectrum sensing, even while transmitting, to detect the presence of a licensed user or to scan for spectrum white spaces. The system achieves 83 dB of narrowband interference cancellation, and 60 dB of cancellation of a 50 MHz frequency-modulated signal. The center frequency of the optical canceler is freely tunable across the radio frequency spectrum, limited only by the bandwidth of the photodetector and the electro-optic modulators to 10 GHz. The system is modulation-format independent and requires only one piece of hardware to operate across a wide bandwidth.
[Show abstract][Hide abstract] ABSTRACT: We consider an optical technique for performing tunable weighted addition using wavelength-division multiplexed (WDM) inputs, the enabling function of a recently proposed photonic spike processing architecture [J. Lightwave Technol., 32 (2014)]. WDM weighted addition provides important advantages to performance, integrability, and networking capability that were not possible in any past approaches to optical neurocomputing. In this letter, we report a WDM weighted addition prototype used to find the first principal component of a 1Gbps, 8-channel signal. Wideband, multivariate techniques have immediate relevance to modern radio systems, and photonic spike processing networks enabled by WDM could open new domains of information processing that bring unprecedented bandwidth and intelligence to problems in radio communications, ultrafast control, and scientific computing.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we demonstrate how a single semiconductor optical amplifier can serve as a simultaneous variable optical weight and tunable optical delay for microwave photonics. The device weight, or power transmission, and delay can be controlled simultaneously and independently from each other by varying the input optical power and the semiconductor bias current. The dual functionality is achieved by combining the effects of slow and fast light with cross-gain modulation in the semiconductor. We experimentally demonstrate a tunable delay range of 100 ps and RF gain range of -6 to +3 dB for a 600-MHz microwave signal and show how the weight and delay of the device can be separately tuned. The delay range and bandwidth of the device are limited by the semiconductor carrier lifetime and characteristic of slow and fast light. As a simultaneous optical weight and delay, as well as a wavelength converter, a semiconductor optical amplifier operating in this manner can be a compact and versatile element in microwave photonics, radio-over-fiber, and general analog optical signal processing.
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate an optical system that uses a semiconductor optical amplifier (SOA) to perform adaptive, analog self-interference cancellation for radio-frequency signals. The system subtracts a known interference signal from a corrupted received signal to recover a weak signal of interest. The SOA uses a combination of slow and fast light and cross-gain modulation to perform precise amplitude and phase matching to cancel the interference. The system achieves 38 dB of cancellation across 60-MHz instantaneous bandwidth and 56 dB of narrowband cancellation, limited by noise. The Nelder-Mead simplex algorithm is used to adaptively minimize the interference power through the control of the semiconductor’s bias current and input optical power.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate for the first time, to the best of our knowledge, that a Sagnac interferometer can threshold the energies of pulses. Pulses below a given threshold T are suppressed, while those above this threshold are normalized. The device contains an in-loop tunable isolator and 10.4 m of a highly doped silica fiber. We derive an analytical model of the nonlinear optical loop mirror’s pulse energy transfer function and show that its energy transfer function approximates a step function for very high phase shifts (>π). We reveal some limitations of this approach, showing that a step-function transfer function necessarily results in pulse distortion in fast, nonresonant all-optical devices.
[Show abstract][Hide abstract] ABSTRACT: Wireless communications, for data services in particular, have witnessed an exponential growth, and wireless spectrum shortages necessitate increasingly sophisticated methods to use spectrum efficiently. The backhaul of nearly all wireless data networks is fiber-optic. Analog optical signal processing techniques, or microwave photonics, provides an ideal platform for processing wireless information before it is transported to data aggregation centers by fibers. It is in this context that we present recent advances in optical signal processing techniques for wireless radio frequency (RF) signals. Specifically, this chapter is devoted to the discussion of photonic architectures for wideband analog signal processing, including RF beamforming, co-channel interference cancellation, and physical layer security. Photonics offers the advantages not only of broadband operation, but reduced size, weight, and power, in addition to low transmission loss, rapid re-configurability, and immunity to electromagnetic interference. 15.1 Introduction The use of wireless communication is growing exponentially. In June 2012, more than 5.6 billion subscribers had access to and were using a wireless device, nearly 80 % of the total world population of 7.02 billion . By the end of 2017, more than 90 % of the world's population is expected to have access to mobile broadband 3G devices. This statistic demonstrates the importance of mobile wireless comB .J. Shastri and J. Chang—equal contribution.
All-Optical Signal Processing Data Communication and Storage Applications, Edited by Stefan Wabnitz, Benjamin J. Eggleton, 01/2015: chapter 15: pages 469-503; Springer International Publishing., ISBN: 978-3-319-14991-2
[Show abstract][Hide abstract] ABSTRACT: We propose an on-chip optical architecture to support massive parallel communication among high-performance spiking laser neurons. Designs for a network protocol, computational element, and waveguide medium are described, and novel methods are considered in relation to prior research in optical on-chip networking, neural networking, and computing. Broadcast-and-weight is a new approach for combining neuromorphic processing and optoelectronic physics, a pairing that is found to yield a variety of advantageous features. We discuss properties and design considerations for architectures for scalable wavelength reuse and biologically relevant organizational capabilities, in addition to aspects of practical feasibility. Given recent developments commercial photonic systems integration and neuromorphic computing, we suggest that a novel approach to photonic spike processing represents a promising opportunity in unconventional computing.
[Show abstract][Hide abstract] ABSTRACT: We propose and experimentally demonstrate a wavelength-division multiplexed (WDM) optical stealth transmission system carried by amplified spontaneous emission (ASE) noise. The stealth signal is hidden in both time and frequency domains by using ASE noise as the signal carrier. Each WDM channel uses part of the ASE spectrum, which provides more flexibility to apply stealth transmission in a public network and adds another layer of security to the stealth channel. Multi-channel transmission also increases the overall channel capacity, which is the major limitation of the single stealth channel transmission based on ASE noise. The relations between spectral bandwidth and coherence length of ASE carrier have been theoretically analyzed and experimentally investigated.
[Show abstract][Hide abstract] ABSTRACT: System performance of optical steganography is theoretically analyzed and experimentally demonstrated. The optical stealth channel is carried by amplified spontaneous emission noise, which hides the stealth data in both the time and frequency domain. Meanwhile, because the stealth channel uses noise as the signal carrier, the relation between signal-to-noise ratio (SNR) and carrier power is fundamentally different from the traditional optical channels carried by modulating lasers. To transmit and hide the stealth signal in the existing public network, the degradation principle of SNR of the stealth channel is studied. Such principle can guide the design of the stealth transmission system and optimize the carrier power of the stealth channel.
[Show abstract][Hide abstract] ABSTRACT: A novel highly scalable adaptive photonic beamformer is proposed and experimentally verified. A single-mode-to-multimode combiner allows our system to recycle the same set of wavelengths for each antenna in the array. A “blind” search algorithm called the guided accelerated random search (GARS) algorithm is shown. A maximum cancellation of ∼37 dB is achieved within 50 iterations, while the presence of a signal of interest (SOI) is maintained. Cancellation across the 900 MHz and 2.4 GHz bands are shown to prove the broadband nature of the optical beamformer.
[Show abstract][Hide abstract] ABSTRACT: We propose and simulate a novel excitable laser employing passively -switching with a graphene saturable absorber for spike processing. Our approach combines the picosecond processing and switching capabilities of both linear and nonlinear optical device technologies to integrate both analog and digital optical processing into a single hardware architecture capable of computation without the need for analog-to-digital conversion. We simulate the laser using the Yamada model-a three-dimensional dynamical system of rate equations-and show behavior that is typical of spiking processing algorithms simulated in small circuits of excitable lasers.
[Show abstract][Hide abstract] ABSTRACT: We propose an equivalent circuit model for photonic spike processing laser
neurons with an embedded saturable absorber---a simulation model for photonic
excitable lasers (SIMPEL). We show that by mapping the laser neuron rate
equations into a circuit model, SPICE analysis can be used as an efficient and
accurate engine for numerical calculations, capable of generalization to a
variety of different laser neuron types found in literature. The development of
this model parallels the Hodgkin--Huxley model of neuron biophysics, a circuit
framework which brought efficiency, modularity, and generalizability to the
study of neural dynamics. We employ the model to study various
signal-processing effects such as excitability with excitatory and inhibitory
pulses, binary all-or-nothing response, and bistable dynamics.
[Show abstract][Hide abstract] ABSTRACT: We combine advances in photonic integrated circuits (PICs) with principles from neuromorphic engineering to create a scalable, robust, and extremely high bandwidth bio-inspired computational system. We describe such a system in a wafer-bonded III-V/silicon platform , integrating the network (through passive silicon-on-insulator technology) and the computational elements (through active III-V laser devices) in a single substrate, and corroborate its underlying principles through preliminary bench-top demonstrations.
Int. Symp. on Nonlinear Theory and its Appl. (NOLTA); 09/2014
[Show abstract][Hide abstract] ABSTRACT: We discuss a novel application of a photonic circuit for integrated high-performance neuromorphic signal processing. Large fan-in is an especially important capability in distributed systems; however, electronic physics impose tradeoffs between bandwidth performance and fan-in degree. A circuit developed in the field of radio frequency (RF) photonics, wavelength(λ)-fan-in does not exhibit a corresponding tradeoff and can circumvent prior challenges to fan-in in optical distributed processing applications.
2014 IEEE/ACM International Symposium on Nanoscale Architectures (NANOARCH); 07/2014
[Show abstract][Hide abstract] ABSTRACT: An optical encryption method based on analog noise is proposed and experimentally demonstrated. The transmitted data is encrypted with wideband analog noise. Without decrypting the data instantly at the receiver, the data is damaged by the noise and cannot be recovered by post-processing techniques. A matching condition in both phase and amplitude of the noise needs to be satisfied between the transmitter and the receiver to cancel the noise. The precise requirement of the phase and amplitude matching condition provides a large two-dimensional key space, which can be deployed in the encryption and decryption process at the transmitter and receiver.