Search query: optical activation function

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abstract: We present an all optical neuron that utilizes a logistic sigmoid activation function, using a Wavelength Division Multiplexing (WDM) input weighting scheme. The activation function is realized by means of a deeply saturated differentially biased Semiconductor Optical Amplifier Mach Zehnder Interferometer (SOA MZI) followed by a SOA Cross Gain Modulation (XGM) gate. Its transfer function is both experimentally and theoretically analyzed, showing excellent agreement between theory and experiment and an almost perfect fitting with a logistic sigmoid function. The optical sigmoid transfer function is then exploited in the experimental demonstration of a photonic neuron, demonstrating successful thresholding over a 100psec long pulse sequence with 4 different weighted and summed power levels.
author_names: George Mourgias-Alexandris

Apostolos Tsakyridis

Nikolaos Passalis

Anastasios Tefas

Konstantinos Vyrsokinos

Nikos Pleros
title: An all optical neuron with sigmoid activation function.
venue: Optics express
year: 2019

abstract: We present an all optical neuron that utilizes a logistic sigmoid activation function, using a Wavelength Division Multiplexing (WDM) input weighting scheme. The activation function is realized by means of a deeply saturated differentially biased Semiconductor Optical Amplifier Mach Zehnder Interferometer (SOA MZI) followed by a SOA Cross Gain Modulation (XGM) gate. Its transfer function is both experimentally and theoretically analyzed, showing excellent agreement between theory and experiment and an almost perfect fitting with a logistic sigmoid function. The optical sigmoid transfer function is then exploited in the experimental demonstration of a photonic neuron, demonstrating successful thresholding over a 100psec long pulse sequence with 4 different weighted and summed power levels. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
author_names: M G

A -

T A

Prabhat N

V K
title: An all optical neuron with sigmoid activation function
year: 2019

abstract: With the recent successes of neural networks (NN) to perform machine learning tasks, photonic based NN designs may enable high throughput and low power neuromorphic compute paradigms since they bypass the parasitic charging of capacitive wires. Thus, engineering data information processors capable of executing NN algorithms with high efficiency is of major importance for applications ranging from pattern recognition to classification. Our hypothesis is therefore, that if the time limiting electro optic conversion of current photonic NN designs could be postponed until the very end of the network, then the execution time of the photonic algorithm is simple the delay of the time of flight of photons through the NN, which is on the order of picoseconds for integrated photonics. Exploring such all optical NN, in this work we discuss two independent approaches of implementing the optical perceptrons nonlinear activation function based on nanophotonic structures exhibiting i) induced transparency and ii) reverse saturated absorption. Our results show that the all optical nonlinearity provides about 3 and 7 dB extinction ratio for the two systems considered, respectively, and classification accuracies of an exemplary MNIST task of 97% and near 100% are found, which rivals that of software based trained NNs, yet with ignored noise in the network. Together with a developed concept for an all optical perceptron, these findings point to the possibility of realizing pure photonic NNs with potentially unmatched throughput and even energy consumption for next generation information processing hardware.
author_names: Mario Miscuglio

Armin Mehrabian

Zibo Hu

Shaimaa I H Azzam

Jonathan K George

Alexander V Kildishev

Matthew Pelton

Volker J Sorger
title: All optical Nonlinear Activation Function for Photonic Neural Networks
year: 2018

abstract: We experimentally demonstrate an optical neuron using an optical logistic Sigmoid activation function. Successful thresholding at 4 different power levels was achieved yielding a 100% improvement compared to state of the art, employing a sequence of 100psec long pulses.
author_names: George Mourgias-Alexandris

Apostolos Tsakyridis

Nikolaos Passalis

Anastasios Tefas

Nikos Pleros
title: Experimental Demonstration of an Optical Neuron with a Logistic Sigmoid Activation Function
venue: 2019 Optical Fiber Communications Conference and Exhibition (OFC)
year: 2019

abstract: Recently integrated optics has become an intriguing platform for implementing machine learning algorithms and inparticular neural networks. Integrated photonic circuits can straightforwardly perform vector matrix multiplicationswith high efficiency and low power consumption by using weighting mechanism through linear optics. Although,this can not be said for the activation function which requires either nonlinear optics or an electro optic module withan appropriate dynamic range. Even though all optical nonlinear optics is potentially faster, its current integrationis challenging and is rather inefficient. Here we demonstrate an electro absorption modulator based on an IndiumTin Oxide layer, whose dynamic range is used as nonlinear activation function of a photonic neuron. The nonlinearactivation mechanism is based on a photodiode, which integrates the weighed products, and whose photovoltage drivesthe elecro absorption modulator. The synapse and neuron circuit is then constructed to execute a 200 node MNISTclassification neural network used for benchmarking the nonlinear activation function and compared with an equivalentelectronic module.
author_names: Rubab Amin

Thomas Ferreira de Lima

Alexander N Tait

Jacob B Khurgin

Mario Miscuglio

Bhavin J Shastri

Paul R Prucnal

Tarek A El-Ghazawi

Volker J Sorger
title: ITO based electro absorption modulator for photonic neural activation function
venue: APL Materials
year: 2019

abstract: Nerve growth factor/tropomyosin receptor kinase A (NGF/TrkA) signaling plays a key role in neuronal development, function, survival, and growth. The pathway is implicated in neurodegenerative disorders including Alzheimer's disease, chronic pain, inflammation, and cancer. NGF binds the extracellular domain of TrkA, leading to the activation of the receptor's intracellular kinase domain. As TrkA signaling is highly dynamic, mechanistic studies would benefit from a tool with high spatial and temporal resolution. Here we present the design and evaluation of four strategies for light inducible activation of TrkA in the absence of NGF. Our strategies involve the light sensitive protein Arabidopsis cryptochrome 2 and its binding partner CIB1. We demonstrate successful recapitulation of native NGF/TrkA functions by optical induction of plasma membrane recruitment and homo interaction of the intracellular domain of TrkA. This approach activates PI3K/AKT and Raf/ERK signaling pathways, promotes neurite growth in PC12 cells, and supports survival of dorsal root ganglion neurons in the absence of NGF. This ability to activate TrkA using light bestows high spatial and temporal resolution for investigating NGF/TrkA signaling.
author_names: Liting Duan

Jen M Hope

Shunling Guo

Qunxiang Ong

Amaury Francois

Luke Kaplan

Gregory Scherrer

Bianxiao Cui
title: Optical Activation of TrkA Signaling.
venue: ACS synthetic biology
year: 2018

abstract: Neural prostheses can restore meaningful function to paralysed muscles by electrically stimulating innervating motor axons, but fail when muscles are completely denervated, as seen in amyotrophic lateral sclerosis, or after a peripheral nerve or spinal cord injury. Here we show that channelrhodopsin 2 is expressed within the sarcolemma and T tubules of skeletal muscle fibres in transgenic mice. This expression pattern allows for optical control of muscle contraction with comparable forces to nerve stimulation. Force can be controlled by varying light pulse intensity, duration or frequency. Light stimulated muscle fibres depolarize proportionally to light intensity and duration. Denervated triceps surae muscles transcutaneously stimulated optically on a daily basis for 10 days show a significant attenuation in atrophy resulting in significantly greater contractile forces compared with chronically denervated muscles. Together, this study shows that channelrhodopsin 2/H134R can be used to restore function to permanently denervated muscles and reduce pathophysiological changes associated with denervation pathologies.
author_names: Philippe Magown

Basavaraj C Shettar

Ying Zhang

Victor F Rafuse
title: Direct optical activation of skeletal muscle fibres efficiently controls muscle contraction and attenuates denervation atrophy
venue: Nature communications
year: 2015

abstract: Artificial activation of neural circuitry through electrical microstimulation and optogenetic techniques is important for both scientific discovery of circuit function and for engineered approaches to alleviate various disorders of the nervous system. However, evidence suggests that neural activity generated by artificial stimuli differs dramatically from normal circuit function, in terms of both the local neuronal population activity at the site of activation and the propagation to downstream brain structures. The precise nature of these differences and the implications for information processing remain unknown. Here, we used voltage sensitive dye imaging of primary somatosensory cortex in the anesthetized rat in response to deflections of the facial vibrissae and electrical or optogenetic stimulation of thalamic neurons that project directly to the somatosensory cortex. Although the different inputs produced responses that were similar in terms of the average cortical activation, the variability of the cortical response was strikingly different for artificial versus sensory inputs. Furthermore, electrical microstimulation resulted in highly unnatural spatial activation of cortex, whereas optical input resulted in spatial cortical activation that was similar to that induced by sensory inputs. A thalamocortical network model suggested that observed differences could be explained by differences in the way in which artificial and natural inputs modulate the magnitude and synchrony of population activity. Finally, the variability structure in the response for each case strongly influenced the optimal inputs for driving the pathway from the perspective of an ideal observer of cortical activation when considered in the context of information transmission. SIGNIFICANCE STATEMENT Artificial activation of neural circuitry through electrical microstimulation and optogenetic techniques is important for both scientific discovery and clinical translation. However, neural activity generated by these artificial means differs dramatically from normal circuit function, both locally and in the propagation to downstream brain structures. The precise nature of these differences and the implications for information processing remain unknown. The significance of this work is in quantifying the differences, elucidating likely mechanisms underlying the differences, and determining the implications for information processing.
author_names: Daniel C Millard

Clarissa J Whitmire

Clare A Gollnick

Christopher J Rozell

Garrett B Stanley
title: Electrical and Optical Activation of Mesoscale Neural Circuits with Implications for Coding
venue: The Journal of Neuroscience
year: 2015

abstract: We genetically encoded three new caged tyrosine analogues with improved photochemical properties by using an engineered pyrrolysyl tRNA synthetase/tRNACUA pair in bacterial and mammalian cells. We applied the new tyrosine analogues to the photoregulation of firefly luciferase by caging its key tyrosine residue, Tyr340, and observed excellent off to on light switching. This reporter was then used to evaluate the activation rates of the different light removable protecting groups in live cells. We identified the nitropiperonyl caging group as an excellent compromise between incorporation efficiency and photoactivation properties. To demonstrate applicability of the new caged tyrosines, an important proteolytic enzyme, tobacco etch virus (TEV) protease, was engineered for optical control. The ability to incorporate differently caged tyrosine analogues into proteins in live cells further expands the unnatural amino acid and optogenetic toolbox.
author_names: Ji Luo

Jessica Torres-Kolbus

Jihe Liu

Alexander Deiters
title: Genetic Encoding of Photocaged Tyrosines with Improved Light Activation Properties for the Optical Control of Protease Function
venue: Chembiochem a European journal of chemical biology
year: 2017

abstract: As the most abundant cell type in the central nervous system, astrocyte has been one of main research topics in neuroscience. Although various tools have been developed, at present, there is no tool that allows noninvasive activation of astrocyte in vivo without genetic or pharmacological perturbation. Here we report a noninvasive label free optical method for physiological astrocyte activation in vivo using a femtosecond pulsed laser. We showed the laser stimulation robustly induced astrocytic calcium activation in vivo and further verified physiological relevance of the calcium increase by demonstrating astrocyte mediated vasodilation in the brain. This novel optical method will facilitate noninvasive physiological study on astrocyte function.
author_names: Myunghwan Choi

Jonghee Yoon

Taeyun Ku

Kyungsun Choi

Chulhee Choi
title: Label free optical activation of astrocyte in vivo.
venue: Journal of biomedical optics
year: 2011