Experimental demonstration of 25 GHz wideband chaos in symmetric dual port EDFRL

We study dynamics of chaos in dual port erbium-doped fiber ring laser (EDFRL). The laser consists of two erbium-doped fibers, intracavity filters at 1549.30 nm, isolators, and couplers. At both ports, the laser transitions into the chaotic regime for pump currents greater than 100 mA via period doubling route. We calculate the Lyapunov exponents using Rosenstein’s algorithm. We obtain positive values for the largest Lyapunov exponent (≈0.2) for embedding dimensions 5, 7, 9 and 11 indicating chaos. We compute the power spectrum of the photocurrents at the output ports of the laser. We observe a bandwidth of ≈ 25 GHz at both ports. This ultra wideband nature of chaos obtained has potential applications in high speed random number generation and communication

Erforschung und Implementierung von Zeitmess- und Zeitkontrollinstruktionen für RISC-V-Cores

Real Time Systems are integrated with physical processes such as sensors and actuators. Real Time Systems are time critical and hence they must be able to handle upper time bounds along with the correct functional behavior. The correct implementation of the functionality specified in the software is done using the Instruction Set Architecture (ISA) by the processor. But, neither the software nor ISA has a time measuring or time controlling role here and if time properties have to be guaranteed designers are required to reach beneath the abstraction layers which increases design complexity and effort. This thesis proposes a solution to bring control over time to the software by examining the Instruction Set Architecture (ISA) layer. The ISA defines the contract between software instructions and hardware implementations. But ISAs usually do not have timing properties imbibed in them. Hence, this work will investigate the instructions extension feature offered by RISC-V platform to allow programs to specify execution time properties in software. These include the ability to specify a minimum execution time for code blocks, and the ability to detect and handle missed deadlines from code blocks that exhibit variable execution times. This thesis investigates the RISC-V CPU named VexRiscV built by Charles Papon on the platform SpinalHDL where in which Custom Instructions would be added into the RISC-V ISA through the instruction extension featured allowed by the RISC-V platform. This was implemented and tested on an Arty A7-100 FPGA with the help of Xilinx tools

Interactive Concept Bottleneck Models

Concept bottleneck models (CBMs) (Koh et al. 2020) are interpretable neural networks that first predict labels for human-interpretable concepts relevant to the prediction task, and then predict the final label based on the concept label predictions.We extend CBMs to interactive prediction settings where the model can query a human collaborator for the label to some concepts. We develop an interaction policy that, at prediction time, chooses which concepts to request a label for so as to maximally improve the final prediction. We demonstrate thata simple policy combining concept prediction uncertainty and influence of the concept on the final prediction achieves strong performance and outperforms a static approach proposed in Koh et al. (2020) as well as active feature acquisition methods proposed in the literature. We show that the interactiveCBM can achieve accuracy gains of 5-10% with only 5 interactions over competitive baselines on the Caltech-UCSDBirds, CheXpert and OAI datasets.Comment: To appear at AAAI 202

A novel scheme of cascaded four-wave mixing for phase-sensitive amplification in nonlinear optical fibre

We propose and numerically verify a scheme of phase-sensitive amplifier (PSA) using four-wave mixing (FWM) in cascaded highly nonlinear fibres (HNLFs), without requiring initial phase-locking between signal and pump. The first HNLF is used to generate two phase-conjugate waves, which act as two pumps for FWM process in second HNLF. We feed the two pumps from opposite ends of second HNLF and a signal co-propagating with one of the pumps. We keep the signal frequency in the middle of two pump frequencies to obtain phase-conjugate wave at the same frequency as the signal by FWM process in second HNLF. Signal and phase-conjugate wave appear at opposite ends of the second HNLF and combined to obtain PSA. The frequency-shift-free operation of phase conjugation helps in preserving the frequency of input signal during phase-sensitive amplification. We derive the expression for PSA signal output and PSA gain and show analytically that PSA gain depends upon signal phase only, as the two pumps are phase conjugate to each other. Thus, eliminating the need of phase locking between signal and pump waves. We show that PSA provides high gain for in-phase component and almost cancellation for quadrature-phase component of signal. We show the broadband nature of PSA due to minimum effect of group velocity and group velocity dispersion owing to counter-propagating nature of signal and conjugate waves. We study the performance of PSA under the effects of pump-signal detuning, amplifier length and input signal phase. Simulation results show that PSA output is forced to attain 0 or π phase regardless of large variation of phase in the input signal. Nonlinear phase noise reduction of 100 Gbps DPSK signal transmitted over 1000-km standard single-mode fibre confirms phase regeneration by PSA

Mitigation of nonlinear effects through frequency shift free mid-span spectral inversion using counter-propagating dual pumped FWM in fiber

We propose and numerically verify a scheme of frequency-shift free mid-span spectral inversion (MSSI) for nonlinearity mitigation in an optical transmission system. Spectral inversion is accomplished by optical phase conjugation, realized by counter-propagating dual pumped four-wave mixing in a highly nonlinear fiber. We examine the performance of MSSI due to critical parameters such as nonlinear fiber length, pump and signal power. We demonstrate the near complete nonlinearity mitigation of 40 Gbps DQPSK modulated data transmitted over 1000 km standard single mode fiber using our method of MSSI. We perform simulation of bit-error rate as a function of optical signal to noise ratio to corroborate the effect of frequency-shift free MSSI

Frequency-shift free optical phase conjugation using counter-propagating dual pump four-wave mixing in fiber

We propose and numerically verify a novel scheme of frequency-shift free optical phase conjugation by counter-propagating dual pump four-wave mixing in nonlinear fiber. The two counter-propagating pumps create a Bragg grating inside the fiber, which diffracts the forward propagating signal and generates a backward propagating idler wave whose phase is conjugate of signal phase. The two pump frequencies are placed symmetrically about signal frequency to ensure that idler wave will have same frequency as that of signal wave. Since the signal and idler waves appear at opposite ends, the idler is easily filtered out from the rest of the spectrum. Using nonlinear Schrödinger equation, we derive equations of signal and idler evolution. We obtain expressions for idler phase and show that perfect phase conjugation is achieved at an optimum length of fiber for a given pump power. We study the effect of fiber length and pump power on phase conjugation. Simulation results show the perfect phase conjugation at optimum fiber length under lossless conditions and small phase-offset when fiber loss and self and cross phase modulations are included. The small phase-offset is avoided by choosing fiber length smaller than optimum fiber length. Simulation results exhibit close agreement to theoretical values, which validates our simulations

EKF for joint mitigation of phase noise, frequency offset and nonlinearity in 400 Gb/s PM-16-QAM and 200 Gb/s PM-QPSK systems

The performance of higher order modulation formats such as 16-quadrature amplitude modulation (QAM) coherent optical communication systems are limited due to several linear and nonlinear impairments such as phase noise, frequency offset, chromatic dispersion, and fiber nonlinearities. For a satisfactory system performance, these impairments need to be eliminated either by all-optical and/or electronic means. In this paper, we use the extended Kalman filter (EKF) algorithm to jointly mitigate laser phase noise, frequency offset, and nonlinear channel impairments, namely self phase modulation and nonlinear phase noise in polarization multiplexed 400 Gb/s 16-QAM and 200 Gb/s quadrature phase shift keying (QPSK) systems. We consider a two-state EKF with phase as one state and frequency offset as another. Simulation results for transmission over 1000 km (10 × 100 km) of standard single mode fiber show a Q-factor of 12 dB for PM-16-QAM at frequency offset of 1 GHz and laser linewidth of 100 kHz and a Q-factor of 18 dB for PM-QPSK at 1 MHz linewidth. Further, phase trajectories corresponding to tracked laser phase noise and frequency offset show that EKF can suppress laser phase noise up to 10 MHz and frequency offset up to 5 GHz, thereby eliminating the requirement of using separate algorithms for phase noise and frequency offset estimation

Experimental demonstration of optical phase conjugation using counter-propagating dual pumped four-wave mixing in semiconductor optical amplifier

We report optical phase conjugation in C-band by counter-propagating dual pumped non-degenerate four-wave mixing in a semiconductor optical amplifier (SOA). The co-propagating signal and pump waves create a grating inside SOA which diffracts counter-propagating pump and generates the conjugate wave. Since the signal and conjugate waves appear at opposite ends, the conjugate is easily filtered out from the rest of spectrum with minimal spectral shift of the conjugate with respect to the incoming signal. With pump powers of 3.2 dBm each and signal input power of 7 dBm, conjugate power was of 27.2 dBm, giving a conversion efficiency of 1% at 18 GHz pump-signal detuning. By modulating the signal by a periodic pattern ‘1000’ at 10 Gbps using a non-zero chirp intensity modulator and resolving the temporal profile of the electric field envelope of the conjugate wave, we demonstrate spectral in-version

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy