In the Optics and Photonics Lab we develop and study advanced photonic methods involving optical fibers. In recent years we have been focusing primarily on large scale distributed fiber optic sensing systems

Fields of Interest:
An optical fiber can be described as a glass pipeline which can guide light over great distances with very little loss. The role of optical fibers in today’s communication networks is well known and, indeed, the information era that we live in, could not have been materialized if it wasn’t for optical fibers which serve as the main routes for conveying data all over the globe.

Another very interesting application of optical fibers, which is much less known, is distributed sensing. By launching into the fiber specially designed pulse sequences of light and analyzing resulting light waves which are reflected from different positions along the fiber, it is possible to measure various physical parameters such as temperature and acoustic signals at these positions. During recent years the use of distributed fiber-optic sensing systems has become ubiquitous for a variety of applications such as intrusion detection, monitoring of transportation, leak detection in oil and gas pipelines, border defense and more.

Research:
Broad-bandwidth, long-haul, underwater fiber-optic sensing system
Underwater applications of distributed fiber-optic sensors comprise seismic sensing, earthquakes and tsunami monitoring and early warning, pipeline defense and leak detection, harbor security, monitoring the sounds used by marine animals for navigation and communication and more.

The technology that is being developed in our lab allows achieving simultaneously both very high sensitivity and very long range of operation. This is achieved by working with sensing fibers that comprise arrays of weak mirrors in their core and a pulse sequence which is accurately tailored to the sensing fiber. The careful design of the pulse sequence ensures that the returns from the fiber will not overlap even when the sampling rate increases by a factor of more than 50. 

Single-core optical fiber shape sensing and imaging
Optical fibers are used nowadays in many fields including structural health monitoring and medicine for purposes of shape sensing and imaging. In our research, we study methods for using a single-core optical fiber as an endoscope that can deliver shape information as well as images of the inspected object. For this purpose we mostly use speckle patterns acquired either at the proximal facet or at the distal facet of the fiber, and analyze them using deep learning algorithms.

Pulse compression comparison in Q-DAS system: Ternary codes vs. Binary codes
Pulse compression techniques became popular in the last decade in many optical fields such as Laser Range Finders (LRF), Quasi and fully Distributed Acoustic Sensing (Q-DAS and DAS), Brillouin Sensing and more. In general, it allows increasing the transmitted energy while keeping the spatial resolution the same as that of a single pulse. A promising approach for implementing pulse compression is via Perfect Periodic Autocorrelation codes (PPA). Ideally, the autocorrelation of PPA codes is a sequence delta functions. This is a manifestation of the codes ability to achieve perfect compression. Therefore, replacing each transmitted pulse by a PPA code and compressing the received returns, leads to a significant improvement in the SNR. Out of the binary PPA codes, i.e. codes whose basic elements (bits) are two complex numbers, the largest families are the M-sequence and the Legendre code.

For more information:
Email: avishay1@tauex.tau.ac.il
Site: https://www.opticsandphotonics…
Phone: +972 3 640 7365