Our group carries out research in the areas of fiber-optics and integrated photonic devices. We study the physics of wave propagation in these media, with emphasis on the nonlinear regime and on opto-mechanical interactions: the interplay between guided light and guided sound.
Our main interest in optical fibers is in their use as sensors of various quantities and environmental parameters. Fibers constitute an exceptional sensing medium. They support measurements from long stand-off distances of hundreds of km. They are readily embedded within any structure, with little effect on functionality. They are immune to electro-magnetic interference, and can be installed in harsh environments where the use of electricity is prohibited due to safety considerations. Last but not least, fibers are extremely low-cost. The propagation of light in fiber may be affected by a host of parameters of interest.
We investigate, demonstrate and employ optical fibers in the distributed measurements of temperature, mechanical strain, and even classification of surrounding liquids. The work-horses of the analysis are nonlinear opto-mechanical phenomena that are known collectively as Brillouin scattering: Stimulated interactions between light and ultra-sonic and hyper-sonic acoustic modes that are guided in the fiber. Both co-propagating and counter-propagating scattering phenomena are considered. Research highlights include:
• Brillouin analysis over 8.8 km of fiber with a spatial resolution of 2 cm, while addressing all 440,000 resolution points.
• The analysis of liquids outside the cladding of an unmodified, standard fiber. Measurements were performed even though the guided light never came in contact with the substance being tested!
• Brillouin analysis in standard fiber with a spatial resolution of 2 mm.
Complementary areas of interests within fiber optics include microwave photonics, laser range-finder systems, electro-optic oscillators, and more.

Our interest in integrated in photonic devices covers several areas as well. On the one hand, we look to implement integrated devices that are useful for data communication, with focus on the silicon material platform ('silicon photonics'). Examples include cascaded filters for the wavelength division multiplexing and de-multiplexing of data channels; hybrid integration of InP-based active layers for the realization of silicon-photonic light sources and amplifiers; and integration of photo-sensitive chalcogenide glasses alongside silicon waveguides. The latter platform effectively serves for the post-fabrication trimming of phase delays, group delays and coupling ratios of silicon-photonic integrated circuits.
On the more fundamental side, we are looking to implement interactions between guided light and sound within integrated photonic circuits as well. These activities, for the most part, make use of waveguides in chalcogenide glasses due to their pronounced nonlinearity. We study and implement waveguide profiles which guide both light and sound with large spatial overlap. In addition, we study opto-mechanical coupling in other circuits in which acoustic guiding is absent. An example of Brillouin scattering in a waveguide was reported in 2012, one of the first and few of its kind.

Prof. Zadok has been awarded a 1.5M Euro Starter Grant from the European Research Council (ERC) in 2015, for a research program that addresses opto-mechanical interactions in photonic integrated circuits.


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