Konstantin Kravtsov

Simple nonlinear interferometer-based all-optical thresholder and its applications for optical CDMA

We present an experimental demonstration of an ultrafast all-optical thresholder based on a nonlinear Sagnac interferometer. The proposed design is intended for operation at very small nonlinear phase shifts. Therefore, it requires an in-loop nonlinearity lower than for the classical nonlinear loop mirror scheme. Only 15 meters of conventional (non-holey) silica-based fiber is used as a nonlinear element. The proposed thresholder is polarization insensitive and is good for multi-wavelength operation, meeting all the requirements for autocorrelation detection in various optical CDMA communication systems. The observed cubic transfer function is superior to the quadratic transfer function of second harmonic generation-based thresholders.

Optical FFT/IFFT circuit realization using arrayed waveguide gratings and the applications in all-optical OFDM system

Arrayed waveguide gratings (AWG) are widely used as wavelength division multiplexers (MUX) and demultiplexers (DEMUX) in optical networks. Here we propose and demonstrate that conventional AWGs can also be used as integrated spectral filters to realize a Fast Fourier transform (FFT) and its inverse form (IFFT). More specifically, we point out that the wavelength selection conditions of AWGs when used as wavelength MUX/DEMUX also enable them to perform FFT/IFFT functions. Therefore, previous research on AWGs can now be applied to optical FFT/IFFT circuit design. Compared with other FFT/IFFT optical circuits, AWGs have less structural complexity, especially for a large number of inputs and outputs. As an important application, AWGs can be used in optical OFDM systems. We propose an all-optical OFDM system with AWGs and demonstrate the simulation results. Overall, the AWG provides a feasible solution for all-optical OFDM systems, especially with a large number of optical subcarriers.

Ultrafast all-optical implementation of a leaky integrate-and-fire neuron

In this paper, we demonstrate for the first time an ultrafast fully functional photonic spiking neuron. Our experimental setup constitutes a complete all-optical implementation of a leaky integrate-and-fire neuron, a computational primitive that provides a basis for general purpose analog optical computation. Unlike purely analog computational models, spiking operation eliminates noise accumulation and results in robust and efficient processing. Operating at gigahertz speed, which corresponds to at least 108 speed-up compared with biological neurons, the demonstrated neuron provides all functionality required by the spiking neuron model. The two demonstrated prototypes and a demonstrated feedback operation mode prove the feasibility and stability of our approach and show the obtained performance characteristics.

Incoherent Method of Optical Interference Cancellation for Radio-Frequency Communications

In this paper, we describe a system for cancelling radio-frequency (RF) interference using optical techniques. Specifically, we attempt to receive a weak RF signal-which we assume to be of the order of microwatts-in the presence of high-power local RF interference. This local interference is a signal whose power is of the order of 100 W and is generated in close proximity to the receiver. We wish to emphasize that the nature of the interfering signal is completely known to us in practice, since we are generating it for communications purposes. This knowledge of the interfering signal will prove to be useful in our attempts to cancel it, as will be shown. We refer to this technique as optical interference cancellation, or opto-cancellation. We have demonstrated that this opto-cancellation system can cancel a simple sinusoid at 3 GHz, as well as broadband interference of approximately 100-MHz bandwidth centered at 3 GHz. We have also demonstrated cancellation of sinusoids and broadband signals at other center frequencies as well. In the case of sinusoidal signals, we have demonstrated optical cancellation over 70 dB; and in the case of the ~ 100-MHz signal, we have demonstrated optical cancellation over 30 dB.

Stealth Transmission over a WDM Network with Detection Based on an All-Optical Thresholder

An experimental demonstration of stealth transmission over a public WDM network is presented. An all-optical thresholder is utilized to minimize the power in the stealth channel, enabling efficient channel hiding in both time and spectral domains.

All-Optical Asynchronous Detection for a Compact Integrable Incoherent Optical CDMA System

In this paper, we investigate all-optical truly asynchronous detection without global clocking in an incoherent optical code-division multiple-access (CDMA) system. The implemented system is designed with an integrable optical source consisting of an electro-absorption modulator for pulse carving, compact coders consisting of fiber Bragg grating arrays for encoding and decoding, and receiver consisting of an all-optical thresholder for data and clock recovery. We compare three detection schemes: (1) synchronous detection with data from a photodetector and clock from an external source; (2) asynchronous detection with data and clock from the all-optically thresholded signal received by a clock and data recovery (CDR) unit; and (3) asynchronous detection with data from a photodetector and clock extracted from the all-optically thresholded signal using CDR. Error-free transmission is obtained for detection schemes (1) and (3). A combination of all-optical thresholding and CDR technology is demonstrated in an optical CDMA system for the first time.

A high performance photonic pulse processing device.

This paper presents an all optical fiber based implementation of a hybrid analog-digital computational primitive that provides a basis for complex processing on high bandwidth signals. A natural implementation of a hybrid analog/digital photonic processing primitive is achieved through the integration of new nonlinear fiber, and exploitation of the physics of semiconductor device to process signals in unique ways. Specifically, we describe the use of a semiconductor optical amplifier to implement leaky temporal integration of a signal and a highly Ge-doped nonlinear fiber for thresholding. A straightforward correspondence between our computational primitive and leaky-integrate-and-fire neurons permits leveraging of a large body of research characterizing the computational capabilities of these devices and the emerging pulse processing computational paradigm as a means to implement practical signal processing algorithms in hybrid computing platforms. An experimental demonstration of the behavior of the pulse processing primitive is presented.

Demonstration of an All-Optical OCDMA Encryption and Decryption System With Variable Two-Code Keying

We demonstrate the first all-optical optical code-division multiple-access (OCDMA) encryption and decryption system with variable two-code keying. The nonlinear optical loop mirror (NOLM)-based exclusive or (xor) employed in encryption utilizes the shortest length silica-based nonlinear fiber element to date, enabling a compact architecture. Fiber Bragg grating arrays create wavelength-hopping time-spreading OCDMA codes from broadband pulses at output ports of the xor resulting in variable two-code keying, a code-switching modulation format characterized by a random alternation in bit representation and immunity to differential analysis unlike fixed two-code keying. The terahertz optical asymmetric demultiplexer employed in decryption shows mutual compatibility of nonlinear fiber-based and semiconductor optical amplifier-based NOLM configurations. Our architecture can potentially perform one-time pad encryption and decryption for unconditional security.

Ultrashort Optical Pulse Detection for High-Speed Asynchronous Optical CDMA Networks

Like its wireless counterpart, optical code-division multiple access (optical CDMA) offers greater scalability than other optical multiplexing schemes and provides flexible quality of service, physical layer privacy and asynchronous access. However, unlike wireless CDMA, high bit-rate optical CDMA networks use much higher bandwidth, which cannot be effectively processed with modern electronics rendering many earlier developed detection schemes inapplicable. In this paper we show both theoretically and experimentally that conventional electronics-based detection is inefficient in optical CDMA networks and limits the total network throughput by the bandwidth of the photodetector used. As a solution, we show that network performance can be greatly improved using ultrafast all-optical signal processing for signal detection. Recently developed all-optical thresholding devices performing cubic transformation allow for more than seven times increase in throughput for typical network parameters. A comprehensive comparison of different detection methods for optical CDMA including optimized electronics-based and all-optical signal processing-based is given for the first time.

Securing data networks using optical signal processing

We propose and demonstrate the use of optical signal processing to enhance the security of data networks. Optical steganography is used to inhibit the observation and analysis of data traffic. With the use of optical CDMA, service interruption is prevented in the presence of infrastructure attacks. The soft blocking capability provides protection paths without the need of permanently reserving the bandwidth. Optical CDMA also provides a large size of code set that reduces the probability of interception of the secure signal by an eavesdropper. Finally, all-optical data encryption is demonstrated that prevents side-channel attacks and enables real-time encryption.