Publications

Stabilized laser lines are highly desired for myriad of applications ranging from precise measurements to optical communications. While stabilization can be obtained by using molecular or atomic absorption references, these are limited to specific frequencies. On the other hand, resonators can be used as wide band frequency references. Unfortunately, such resonators are unstable and inaccurate. Here, we propose and experimentally demonstrate a chip-scale multispectral frequency standard replication operating in the spectral range of the near IR. This is obtained by frequency locking a microring resonator (MRR) to an acetylene absorption line. The MRR consists of a Si3N4 waveguides with microheater on top of it. The thermo-optic effect is utilized to lock one of the MRR resonances to an acetylene line. This locked MRR is then used to stabilize other laser sources at 980 nm and 1550 nm wavelength. By beating the stabilized laser to another stabilized laser, we obtained frequency instability floor of 4×10-9 at around 100 s in terms of Allan deviation. Such stable and accurate chip scale sources are expected to serve as important building block in diverse fields such as communication and metrology.

© 2015 Optical Society of America.In recent years, following the miniaturization and integration of passive and active nanophotonic devices, thermal characterization of such devices at the nanoscale is becoming a task of crucial importance. The Scanning Thermal Microscopy (SThM) is a natural candidate for performing this task. However, it turns out that the SThM capability to precisely map the temperature of a photonic sample in the presence of light interacting with the sample is limited. This is because of the significant absorption of light by the SThM probe. As a result, the temperature of the SThM probe increases and a significant electrical signal which is directly proportional to the light intensity is obtained. As such, instead of measuring the temperature of the sample, one may directly measure the light intensity profile. While this is certainly a limitation in the context of thermal characterization of nanophotonic devices, this very property provides a new opportunity for optical near field characterization. In this paper we demonstrate numerically and experimentally the optical near field measurements of nanophotonic devices using a SThM probe. The system is characterized using several sets of samples with different properties and various wavelengths of operation. Our measurements indicate that the light absorption by the probe can be even larger than the light induced heat generation in the sample. The frequency response of the SThM system is characterized and the 3 dB frequency response was found to be ∼1.5 kHz. The simplicity of the SThM system which eliminates the need for complex optical measurement setups together with its broadband wavelength of operation makes this approach an attractive alternative to the more conventional aperture and apertureless NSOM approaches. Finally, referring to its original role in characterizing thermal effects at the nanoscale, we propose an approach for characterizing the temperature profile of nanophotonic devices which are heated by light absorption within the device. This is achieved by spatially separating between the optical near field distribution and the SThM probe, taking advantage of the broader temperature profile as compared to the more localized light profile.

Hybrid nanostructures are attractive for future use in a variety of optoelectronic devices. Self-assembled hybrid organic/quantum dots can couple quantum properties to semiconductor devices and modify their functionality. These devices are simple to fabricate and control; however, they usually demonstrate low quantum efficiency. In this work we present experimental results of large extinction enhancement from a monolayer of colloidal quantum dots using a thin gold film evaporation forming random gold nanoparticles that act as plasmonic antennas. The random structures guarantee no sensitivity to polarization changes. The fabrication process of the plasmonic gold nanoparticles is simple and cheap and can be easily integrated with existing semiconductor devices. By matching the plasmonic resonance and the colloidal quantum dots bandgap we achieve up to 16% light extinction, which is 13-fold enhancement, compared to the reference. These results may pave the way toward realizing more efficient and sensitive photon detectors. Hybrid nanostructures are attractive for future use in a variety of optoelectronic devices. Self-assembled hybrid organic/quantum dots can couple quantum properties to semiconductor devices and modify their functionality. These devices are simple to fabricate and control; however, they usually demonstrate low quantum efficiency. In this work we present experimental results of large extinction enhancement from a monolayer of colloidal quantum dots using a thin gold film evaporation forming random gold nanoparticles that act as plasmonic antennas. The random structures guarantee no sensitivity to polarization changes. The fabrication process of the plasmonic gold nanoparticles is simple and cheap and can be easily integrated with existing semiconductor devices. By matching the plasmonic resonance and the colloidal quantum dots bandgap we achieve up to 16% light extinction, which is 13-fold enhancement, compared to the reference. These results may pave the way toward realizing more efficient and sensitive photon detectors.

© 2015 Optical Society of America. We describe a platform for the fabrication of smooth waveguides and ultrahigh-quality-factor (Q factor) silicon resonators using a modified local oxidation of silicon (LOCOS) technique. Unlike the conventional LOCOS process, our approach allows the fabrication of nearly planarized structures, supporting a multilayer silicon photonics configuration. Using this approach we demonstrate the fabrication and the characterization of a microdisk resonator with an intrinsic Q factor that is one of the highest Q factors achieved with a compact silicon-on-insulator platform.

We design, fabricate and experimentally demonstrate a novel generic method to detect flow rates and precise changes of flow velocity in microfluidic devices. Using our method we can measure flow rates of \~2 mm/s with a resolution of 0.08 mm/s. The operation principle is based on the Doppler shifting of light diffracted from a self-generated periodic array of bubbles within the channel and using self-heterodyne detection to analyze the diffracted light. As such, the device is appealing for variety of “lab on chip” bio-applications where a simple and accurate speed measurement is needed, e.g., for flow-cytometry and cell sorting.

The possibility of combining atomic and plasmonic resonances opens new avenues for tailoring the spectral properties of materials. Following the rapid progress in the field of plasmonics, it is now possible to confine light to unprecedented nanometre dimensions, enhancing light–matter interactions at the nanoscale. However, the resonant coupling between the relatively broad plasmonic resonance and the ultra-narrow fundamental atomic line remains challenging. Here we demonstrate a resonantly coupled plasmonic–atomic platform consisting of a surface plasmon resonance and rubidium (85Rb) atomic vapour. Taking advantage of the Fano interplay between the atomic and plasmonic resonances, we are able to control the lineshape and the dispersion of this hybrid system. Furthermore, by exploiting the plasmonic enhancement of light–matter interactions, we demonstrate all-optical control of the Fano resonance by introducing an additional pump beam.

This paper demonstrates experimentally the tight focusing of a 3X3 array of radially polarized diffraction orders, and the coupling of this array of spots to surface plasmon polaritons (SPPs), propagating on a uniform metal film, and effectively generating a periodic structure of plasmonic sources by the use of structured illumination pattern, rather than by structuring the plasmonic sample. Using near field measurements, we observed coherent interactions between these multiple plasmonic sources as they propagate towards each other. The demonstrated setup exploits the previously demonstrated advantages of radially polarized light in coupling to SPPs and in generating sharper plasmonic hot spots and expends its use towards mitigating parallel processing challenges. The experimental results are in good agreement with the theory, showing interference fringes having periodicity compatible with the plasmonic SPP wavelength. The demonstrated approach of generating array of hot spots on flat metallic films is expected to play a role in variety of applications, e.g. microscopy, lithography, sensing and optical memories.

Alkali vapours, such as rubidium, are being used extensively in several important fields of research such as slow and stored light nonlinear optics quantum computation, atomic clocks and magnetometers. 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, taking advantage of the mature platform of silicon photonics, we construct an efficient and flexible platform for tailored light–vapour interactions on a chip. Specifically, we demonstrate light–matter interactions in an atomic cladding waveguide, consisting of a silicon nitride nano-waveguide core with a rubidium vapour cladding. We observe the efficient interaction of the electromagnetic guided mode with the rubidium cladding and show that due to the high confinement of the optical mode, the rubidium absorption saturates at powers in the nanowatt regime.

We experimentally demonstrate for the first time a nanoscale resistive random access memory (RRAM) electronic device integrated with a plasmonic waveguide providing the functionality of optical readout. The device fabrication is based on silicon on insulator CMOS compatible approach of local oxidation of silicon, which enables the realization of RRAM and low optical loss channel photonic waveguide at the same fabrication step. This plasmonic device operates at telecom wavelength of 1.55 ?m and can be used to optically read the logic state of a memory by measuring two distinct levels of optical transmission. The experimental characterization of the device shows optical bistable behavior between these levels of transmission in addition to well-defined hysteresis. We attribute the changes in the optical transmission to the creation of a nanoscale absorbing and scattering metallic filament in the amorphous silicon layer, where the plasmonic mode resides.

We experimentally demonstrate a frequency modulation locked servo loop, locked to a resonance line of an on-chip microdisk resonator in a silicon nitride platform. By using this approach, we demonstrate real-time monitoring of refractive index variations with a precision approaching 10−7  RIU, using a moderate Q factor of 104. The approach can be applied for intensity independent, dynamic and precise index of refraction monitoring for biosensing applications.

In this paper we analyze the transmission and time delay properties of light propagating through a microring resonator (MRR) consisting of a solid core waveguide surrounded by an atomic vapor cladding. Using the atomic effective susceptibility of Rubidium we derive the complex transmission spectrum of the integrated system. We show, that when the system is under-coupled, the transmission can exceed the standalone MRR's background transmission and is accompanied by enhanced positive time delay. It is shown that in this case the contrast of the atomic lines is greatly enhanced. This allows achieving high optical densities at short propagation length. Furthermore, owing to its features such as small footprint, high tunability, and high delay-transmission product, this system may become an attractive choice for chip scale manipulations of light.