Nadav Shabairou

Bio: Nadav Shabairou is an academic researcher from Bar-Ilan University. The author has contributed to research in topics: Speckle pattern & Multi-mode optical fiber. The author has an hindex of 5, co-authored 15 publications receiving 95 citations.

A visible light RGB wavelength demultiplexer based on silicon-nitride multicore PCF

Abstract: One of the main obstacles that limited the performances in visible light networking system is the ability to transmit high data communication rate. In order to overcome this obstacle, we propose a novel design for an RGB demultiplexer based on silicon-nitride (Si3N4) multicore photonic crystal fiber (PCF) structure. The new design is based on replacing several air-holes zones with Si3N4 rods along the fiber length that enable the controlling of the coupling length size between neighboring cores. The locations of the Si3N4 rods and the geometrical parameters of the PCF were analyzed and simulated utilizing the beam propagation method (BPM) combined with Matlab codes. Results show that RGB operated wavelengths can be demultiplexed after light propagation of 5.5 mm with an excellent crosstalk of −20.766 to −23.95 dB and a large bandwidth of 5.9–16.3 nm.

Color image identification and reconstruction using artificial neural networks on multimode fiber images: towards an all-optical design.

Abstract: The rapid growth of applications that rely on artificial neural network (ANN) concepts gives rise to a staggering increase in the demand for hardware implementations of neural networks. New types of hardware that can support the requirements of high-speed associative computing while maintaining low power consumption are sought, and optical artificial neural networks fit the task well. Inherently, optical artificial neural networks can be faster, support larger bandwidth, and produce less heat than their electronic counterparts. Here we propose the design of an optical ANN-based imaging system that has the ability to self-study image signals from an incoherent light source in different colors. Our design consists of a combination of a multimode fiber and a multi-core optical fiber realizing a neural network. We show that the signals, transmitted through the multimode fiber, can be used for image identification purposes and can also be reconstructed using ANNs with a low number of nodes. An all-optical solution can then be achieved by realizing these networks with the multi-core optical neural network fiber.

All-optical, an ultra-thin endoscopic photoacoustic sensor using multi-mode fiber

Abstract: Photoacoustic endoscopy (PAE) is a method of in-vivo imaging that uses tissue absorption properties. In PAE, the main tools used to detect the acoustic signal are mechanical ultrasound transducers, which require direct contact and which are difficult to miniaturize. All-optic photoacoustic sensors can challenge this issue as they can provide contact-free sensing. Here, we demonstrate sensing of photo-acoustic signals through a multimode fiber (MMF) which can provide an ultra-thin endoscopic photoacoustic sensor. Furthermore, we show the advantage of using the optical-flow method for speckle sensing and extract the photoacoustic signal despite the mode-mixing along the MMF. Moreover, it is demonstrated for the first time that the speckle reconstruction method can be used without the need for imaging of the speckles as this enables the use of multimode fibers for the speckle method.

Non-Invasive Imaging Through Scattering Medium by Using a Reverse Response Wavefront Shaping Technique.

Abstract: Fundamental challenge of imaging through a scattering media has been resolved by various approaches in the past two decades. Optical wavefront shaping technique is one such method in which one shapes the wavefront of light entering a scattering media using a wavefront shaper such that it cancels the scattering effect. It has been the most effective technique in focusing light inside a scattering media. Unfortunately, most of these techniques require direct access to the scattering medium or need to know the scattering properties of the medium beforehand. Through the novel scheme presented on this paper, both the illumination module and the detection are on the same side of the inspected object and the imaging process is a real time fast converging operation. We model the scattering medium being a biological tissue as a matrix having mathematical properties matched to the physical and biological aspects of the sample. In our adaptive optics scheme, we aim to estimate the scattering function and thus to encode the intensity of the illuminating laser light source using DMD (Digital Micromirror Device) with an inverse scattering function of the scattering medium, such that after passing its scattering function a focused beam is obtained. We optimize the pattern to be displayed on the DMD using Particle Swarm Algorithm (PSO) which eventually help in retrieving a 1D object hidden behind the media.

Optical tissue probing: human skin hydration detection by speckle patterns analysis

Abstract: An optical approach to determine the hydration level in human skin is presented. The approach is based on temporal tracking of back-reflected secondary speckle patterns generated while illuminating the tested area with a laser and applying periodic vibrations to the surface via a controlled vibration source (CVS). This approach has already been tested successfully for other biomedical parameters such as sensing vital signs, hematology and hemodynamic processes in the body. In this paper we examine and adjust this optical technique with the aim of measuring human skin moisture. We compare the suitability and accuracy of our optical method to the commercially available device for skin moisture measurements, the Corneometer CM 825 (by Courage + Khazaka, Cologne, Germany). Preliminary experiments showing the method's suitability for hydration measurements are presented, may lead to more accurate results that may upgrade the control of the cosmetic industry as well as identifying symptoms of moisture-related skin diseases.

Videokymography : High-speed line scanning of vocal fold vibration

Abstract: A digital technique for high-speed visualization of vibration, called videokymography, was developed and applied to the vocal folds. The system uses a modified video camera able to work in two modes : high-speed (nearly 8000 images/s) and standard (50 images/s in CCIR norm). In the high-speed mode, the camera selects one active horizontal line (transverse to the glottis) from the whole laryngeal image. The successive line images are presented in real time o a commercial TV monitor, filling each video frame from top to bottom. The system makes it possible to observe left-right asymetries, open quotient, propagation of mucosal waves, movement of the upper and, in the closing phase, the lower margins of the vocal folds, etc... The technique is suitable for further processing and quantification of recorded vibration.

On the theory of optical images, with special reference to the microscope

Abstract: (1896). XV. On the theory of optical images, with special reference to the microscope. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 42, No. 255, pp. 167-195.

Prospects of Photonic Crystal Fiber as Physical Sensor: An Overview.

Abstract: Photonic crystal fiber sensors have potential application in environmental monitoring, industry, biomedicine, food preservation, and many more. These sensors work based on advanced and flexible phototonic crystal fiber (PCF) structures, controlled light propagation for the measurement of amplitude, phase, polarization and wavelength of spectrum, and PCF-incorporated interferometry techniques. In this article various PCF-based physical sensors are summarized with the advancement of time based on reported works. Some physical PCF sensors are discussed based on solid core as well as hollow core structures, dual core fibers, liquid infiltrated structures, metal coated fibers, grating incorporated fibers. With the advancement of sensing technology the possibilities of temperature, pressure, strain, twist, curvature, electromagnetic field, and refractive index sensing are discussed. Also, limitations as well as possible solutions and future hopes are outlined.

Photonic Neural Networks: A Survey

Abstract: Photonic solutions are today a mature industrial reality concerning high speed, high throughput data communication and switching infrastructures. It is still a matter of investigation to what extent photonics will play a role in next-generation computing architectures. In particular, due to the recent outstanding achievements of artificial neural networks, there is a big interest in trying to improve their speed and energy efficiency by exploiting photonic-based hardware instead of electronic-based hardware. In this work we review the state-of-the-art of photonic artificial neural networks. We propose a taxonomy of the existing solutions (categorized into multilayer perceptrons, convolutional neural networks, spiking neural networks, and reservoir computing) with emphasis on proof-of-concept implementations. We also survey the specific approaches developed for training photonic neural networks. Finally we discuss the open challenges and highlight the most promising future research directions in this field.

Optical Eigenmodes; Exploiting the quadratic nature of the energy flux and of scattering interactions

Abstract: We report a mathematically rigorous technique which facilitates the optimization of various optical properties of electromagnetic fields in free space and including scattering interactions. The technique exploits the linearity of electromagnetic fields along with the quadratic nature of the intensity to define specific Optical Eigenmodes (OEi) that are pertinent to the interaction considered. Key applications include the optimization of the size of a focused spot, the transmission through sub-wavelength apertures, and of the optical force acting on microparticles. We verify experimentally the OEi approach by minimising the size of a focused optical field using a superposition of Bessel beams.