The NanoOpto group is affiliated with the Applied Physics Department at the Hebrew University of Jerusalem, Israel. Our research is mainly focused on Silicon Photonics, Polarization Optics, Plasmonics and Opto-Fluidics.

Research highlights:


Silicon Photonics
In this work we study the optimization of interleaved Mach-Zehnder silicon carrier depletion electro-optic modulator. Following the simulation results we demonstrate a phase shifter with the lowest figure of merit (modulation efficiency multiplied by the loss per unit length) 6.7V-dB. This result was achieved by reducing the junction width to 200 nm along the phase-shifter and optimizing the doping levels of the PN junction for operation in nearly fully depleted mode. The demonstrated low FOM is the result of both low VπL of ~0.78 Vcm (at reverse bias of 1V), and low free carrier loss (~6.6 dB/cm for zero bias). Our simulation results indicate that additional improvement in performance may be achieved by further reducing the junction width followed by increasing the doping levels. (read more)

Light vapor interactions on a chip
Alkali vapours, such as rubidium, are being used extensively in many important fields of research. Recently, there is a growing effort towards miniaturizing traditional centimetre-size vapour cells. Owing to the significant reduction in device dimensions, light– matter interactions are greatly enhanced, enabling new functionalities due to the low power threshold needed for nonlinear interactions. Here, we construct an efficient and flexible platform for tailored light–vapour interactions on a chip, and demonstrate efficient interaction of the electromagnetic guided mode with absorption saturation at powers in the nanowatt regime. (read more)

Active Silicon Plasmonics
In this work, we experimentally demonstrate an on-chip nanoscale silicon surface-plasmon Schottky photodetector based on internal photoemission process and operating at telecom wavelengths. The responsivity of the nanodetector to be 0.25 and 13.3mA/W for incident optical wavelengths of 1.55 and 1.31 μm, respectively. The presented device can be integrated with other nanophotonic and nanoplasmonic structures for the realization of monolithic opto-electronic circuitry on-chip. (read more)

Plasmonics
Planar plasmonic devices are becoming attractive for myriad applications. Mitigating the challenges of using plasmonics in on-chip configurations requires precise control over the properties of plasmonic modes, in particular their shape and size. Here we achieve this goal by demonstrating a planar plasmonic graded index lens focusing surface plasmons propagating along the device. Focusing and divergence of surface plasmons is demonstrated experimentally. The demonstrated approach can be used for manipulating the propagation of surface plasmons, e.g. for beam steering, splitting, cloaking, mode matching and beam shaping applications (read more)

Metamaterials
The interaction of an incident plane wave with a metamaterial periodic structure consisting of alternating layers of positive and negative refractive index with average zero refractive index is studied. We show that the existence of very narrow resonance peaks for which giant absorption - 50% at layer thickness of 1% of the incident wavelength - is exhibited. Maximum absorption is obtained at a specific layer thickness satisfying the critical coupling condition. This phenomenon is explained by the Rayleigh anomaly and excitation of Fabry Perot modes. (read more)

Plasmonics
Great hopes rest on surface plasmon polaritons’ (SPPs) potential to bring new functionalities and applications into various branches of optics. In this work, we demonstrate a pin cushion structure capable of coupling light from free space into SPPs, split them based on the polarization content of the illuminating beam of light, and focus them into small spots. We also show that for a circularly or randomly polarized light, four focal spots will be generated at the center of each quarter circle comprising the pin cushion device. Furthermore, following the relation between the relative intensity of the obtained four focal spots and the relative position of the illuminating beam with respect to the structure, we propose and demonstrate the potential use of our structure as a miniaturized plasmonic version of the well-known four quadrant detector. (read more)

Silicon Photonics
We demonstrate a nanoscale mode selector supporting the propagation of the first antisymmetric mode of a silicon waveguide. The mode selector is based on embedding a short section of PhC into the waveguide. On the basis of the difference in k-vector distribution between orthogonal waveguide modes, the PhC can be designed to have a band gap for the fundamental mode, while allowing the transmission of the first antisymmetric mode. The device was tested by directly measuring the modal content before and after the PhC section using a near field scanning optical microscope. Extinction ratio was estimated to be ~23 dB. Finally, we provide numerical simulations demonstrating strong coupling of the antisymmetric mode to metallic nanotips. On the basis of the results, we believe that the mode selector may become an important building block in the realization of on chip nanofocusing devices. (read more)

Plasmonics
We experimentally demonstrate the focusing of surface plasmon polaritons by a plasmonic lens illuminated with radially polarized light . The field distribution is characterized by near-field scanning optical microscope. A sharp focal spot corresponding to a zero-order Bessel function is observed. For comparison, the plasmonic lens is also measured with linearly polarized light illumination, resulting in two separated lobes. Finally, we verify that the focal spot maintains its width along the optical axis of the plasmonic lens. The results demonstrate the advantage of using radially polarized light for nanofocusing applications involving surface plasmon polaritons. (read more)