Arijit Bera

Polarization independent integrated filter based on a cross-slot waveguide

We investigate an in-line band pass filter, working both for TE and TM polarizations, based on a cross-slot waveguide merged with a Bragg grating and an optical cavity. Different types of cavities (C₂- and C₄-symmetric) are presented in order to optimize the filtering and make the device dependent or independent on the polarization. We show a strong light confinement in an extremely small volume, which offers an advantage for further sensing applications. Moreover, we show how the inclusion of a silicon nanowire in the cavity helps the guiding and increases the amplitude of the resonance. In this study we make use of both the Fourier Modal Method and the Finite Difference Time Domain method to perform the numerical simulations.

Slow-light enhanced electro-optic modulation with an on-chip silicon-hybrid Fano system.

We present the theoretical study of a coupled cavity system yielding a Fano response on a fully on-chip silicon platform hybridized with an electro-optic polymer. This novel Fano system is based on a slot waveguide Bragg grating geometry, enabling a huge enhancement of the electro-optic properties due to slow light effects at the resonance. The modulator shows a high resonance tunability of 1.75 nm/V and a low switching power of 0.63 V. Such a versatile system shows the promise for various nonlinear and active devices only by using suitable cover material.

Parabolic opening in atomic layer deposited TiO(2) nanobeam operating in visible wavelengths.

We investigate the feasibility of developing a one dimensional photonic crystal cavity on a TiO2 platform operating in the visible. The atomic layer deposition technique is used to finely adjust the parameters of the structure. We present the experimental demonstration of a nanobeam cavity with a quadratically tapered row of holes, in which a parabolic window is opened in order to facilitate the infiltration of gas, liquid, nonlinear material, or quantum emitters. The structure exhibits a photonic band gap between λ = 635 nm and λ = 690 nm and several resonances within the photonic band gap.

Silicon slot waveguide Fano resonator

The growing interest for Fano resonators during the past decade is due to the narrow line shape observable in their optical spectra. The drastic phase shift occurring at the resonance yields a steep drop from a high to low amplitude. Fano resonances can be obtained by a combination of nanostructures. Such a system is extremely sensitive in terms of both geometrical parameters and environmental conditions. Here we study a complex arrangement of photonic crystal cavities and slot waveguides on a silicon chip. Our structure, composed of several cavities in parallel, has a particular response superimposing a shallow photonic bandgap and a resonance with a Fano line shape. It provides a low noise and a clear asymmetric resonance. We demonstrate it experimentally and show the potential of such a device for sensing. A sensitivity of 92 nm/RIU is measured.

Transfer and patterning of chemical vapor deposited graphene by a multifunctional polymer film

Graphene is seeking pathways towards applications, but there are still plenty of unresolved problems on the way. Many of those obstacles are related to synthesis and processing of graphene. Chemical vapor deposition (CVD) of graphene is currently one of the most promising techniques that enable scalable synthesis of high quality graphene on a copper substrate. From the transient metal substrate, the CVD graphene film is transferred to the desired dielectric substrate. Most often, the transfer process is done by using a supporting poly(methyl methacrylate) (PMMA) film, which is also a widely used electron beam resist. Conventionally, after graphene is transferred to the substrate, the supporting PMMA film is removed by organic solvents. Hence, the potential of using the same PMMA layer as a resist mask remains unexplored. Since PMMA is an electron beam resist, the same polymer film can be useful both for transferring and for patterning of graphene. In this work, we demonstrate simultaneous transfer and patterning of graphene by using the same PMMA film. With our demonstrated method, we are able to receive sub-micron resolution very easily. The graphene transfer and its subsequent patterning with the same resist layer may help developing device applications based on graphene and other 2D materials in the near future.Graphene is seeking pathways towards applications, but there are still plenty of unresolved problems on the way. Many of those obstacles are related to synthesis and processing of graphene. Chemical vapor deposition (CVD) of graphene is currently one of the most promising techniques that enable scalable synthesis of high quality graphene on a copper substrate. From the transient metal substrate, the CVD graphene film is transferred to the desired dielectric substrate. Most often, the transfer process is done by using a supporting poly(methyl methacrylate) (PMMA) film, which is also a widely used electron beam resist. Conventionally, after graphene is transferred to the substrate, the supporting PMMA film is removed by organic solvents. Hence, the potential of using the same PMMA layer as a resist mask remains unexplored. Since PMMA is an electron beam resist, the same polymer film can be useful both for transferring and for patterning of graphene. In this work, we demonstrate simultaneous transfer and pat...

Strip-loaded horizontal slot waveguide.

We introduce a novel concept for an optical waveguide called a strip-loaded slot waveguide. It allows an extraordinary confinement of the field in a waveguide with an extremely tiny (vertical) cross section. Unlike conventional slot waveguides, the proposed configuration has potential for very low propagation losses. Its operation is demonstrated at telecommunication wavelengths and, in addition, it is fabricated by means of mass production compatible techniques: atomic layer deposition and nanoimprint replication. The possibility to fabricate the proposed structure with such low-cost techniques opens a new path for a variety of nanophotonics applications.

Strip-loaded slot waveguide: a step beyond integrated photonics limits (Conference Presentation)

We propose a novel waveguide type based on the concept of strip-loaded waveguide. A strip-loaded waveguide is composed of a thin-film slab waveguide allowing a vertical confinement of the electromagnetic field. A lower refractive index strip provides the lateral confinement by inducing a slight modification of the effective index in the slab. By using such a generic device we will demonstrate how the limits of integrated photonics can be extended, especially, in terms of propagation losses while adding complex structure on the waveguide. Since light sees only a slight variation of effective index, and not an abrupt change of material, propagation losses of the device are fully determined by the film rather than by the structuration. Different micro- and nano-structures will be presented through simulation and experimental results. We will focus especially on the study of Y-junctions, ring resonators, interferometers, and Bragg gratings. Another advantage of strip-loaded waveguides is the simplicity of fabrication. In order to fabricate the devices we employed nano-imprinting of polymer, a fabrication technique suitable for mass production. The low refractive index of the polymer allows a large panel of materials for the slab waveguide, e.g., silicon, titanium dioxide, and lithium niobate. This diversity in the choice of the materials gives to the platform the potential to operate on a wide wavelength range from UV to IR, for multiple applications in telecommunications, sensing and bio-sensing, and medical devices.

Slow-light enhanced sensing with an on-chip Fano system (Conference Presentation)

Integrated silicon photonics promises efficient on-chip solutions for chemical and bio-molecule sensing for faster and reliable disease diagnostics. By integrating a sensor with a light source and a detector, a compact lab-on-chip sensing device is possible to realize. To increase the sensing efficiency, slot waveguide geometry is preferable due to the high confinement of the mode within the cover material. When two different light-paths in a structure interfere with each other, causing the superposition of a Lorenzian response with the background radiation continuum, a Fano lineshape occurs. This sharp resonance leads to a superior refractive index sensing capability. To develop a compact on-chip Fano-resonant platform for chemical sensing, we used a merged photonic crystal – slot waveguide (MPCSW) structure as the basic building block. It contains slot waveguides merged with Bragg gratings, formed by periodic patterning of the rails. A defect between the two Bragg grating sections forms a resonant cavity. In addition to the enhancement due to the confinement of light in the slot waveguide, the highly dispersive nature of the Bragg grating leads to slow light effect at the resonance. Three MPCSW structures are parallel-coupled to form an on-chip Fano system. By changing the refractive index of the cover material, we found a sensitivity as high as 775 nm/RIU. Moreover, the group index at the resonance of our Fano system is as high as ng = 500, due to the effect of slow light. We obtain vast increase in the refractive index sensitivity of the device.

Dynamic control of a Fano resonance with a fully integrated silicon nanostructure

We present the theoretical analysis and design of a novel slotted photonic crystal geometry to demonstrate an on-chip Fano resonance. The device employs three parallel-coupled slotted photonic crystal cavities on an SOI wafer. We present a systematic analysis of the evolution of the Fano line-shape, while the geometric parameters of the structure and the inter-cavity distances vary. To achieve the dynamic tunability of the Fano resonance, we have considered an active electro-optic chromophore as the cover material of our slot-based geometry. This paves a novel way towards the demonstration of a fully-integrated, electrically-controllable Fano resonant geometry on a silicon-polymer platform.

ALD-tuned titanium dioxide nanophotonics

We demonstrate the possibilities of atomic layer deposition technology to fabricate and improve the quality of nanowaveguide devices of a different kind in TiO2 platform. In particular, we present an original re-coating method of improving the quality of amorphous TiO2 strip waveguides, which reduces the propagation losses significantly. Then we demonstrate how atomic layer deposition technology makes it possible to fabricate very precise slot waveguides and to tune the geometrical parameters of nanobeam cavities operating with visible light. The main fabrication methods of the presented structures are electron beam lithography, reactive ion etching and atomic layer deposition.