Landobasa Y. M. Tobing

Deep subwavelength fourfold rotationally symmetric split-ring-resonator metamaterials for highly sensitive and robust biosensing platform

Metamaterials provide a good platform for biochemical sensing due to its strong field localization at nanoscale. In this work, we show that electric and magnetic resonant modes in split-ring-resonator (SRR) can be efficiently excited under unpolarized light illumination when the SRRs are arranged in fourfold rotationally symmetric lattice configuration. The fabrication and characterization of deep subwavelength (~λ/15) gold-based SRR structures with resonator size as small as ~ 60 nm are reported with magnetic resonances in Vis-NIR spectrum range. The feasibility for sensing is demonstrated with refractive index sensitivity as high as ~ 636 nm/RIU.

Direct patterning of high density sub-15 nm gold dot arrays using ultrahigh contrast electron beam lithography process on positive tone resist

Ultrahigh density nanostructure arrays with controlled size and position have promised a variety of potential applications. However, their practical realization is often hindered by the amount of resources required for large-scale fabrication. Using an ultrahigh contrast electron beam lithography process, we show ultrahigh resolution and high aspect ratio patterning capability which can be done at an exposure dose lower than 100 μC cm(-2). In particular, the high aspect ratio of dot arrays on 110 nm thick resist is confirmed by a standard lift-off process of 20 nm thick gold nanodots at sub-15 nm feature size and 40 nm pitch. The smallest gold nanodot size from our experiment is 11 nm.

Boxlike filter response based on complementary photonic bandgaps in two-dimensional microresonator arrays

We propose that a boxlike filter response can be obtained by utilizing complementary photonic bandgap properties of the column and row configurations in two-dimensional microresonator arrays. The filters are fabricated using deep-UV lithography in silicon-on-insulator technology. The observed sidelobes reduction is approximately 10 dB, and the usable bandwidth can be as high as 500-750 GHz.

Finesse enhancement in silicon-on-insulator two-ring resonator system

We demonstrate experimentally the finesse enhancement in a pair of mutually coupled ring resonators coupled to two buses fabricated in silicon-on-insulator technology, as proposed theoretically in an earlier paper. A finesse close to 100 (or Q=30000) is obtained in a two-ring system, with the outer ring double the size of the inner ring, and an external coupling coefficient of 34%. The maximum finesse enhancement relative to the single-ring structure is 14 times, in good agreement with the theoretical prediction.

Experimental demonstration of coupled-resonator-induced-transparency in silicon-on-insulator based ring-bus-ring geometry

We experimentally demonstrate coupled-resonator-induced-transparency (CRIT) phenomenon in ring-bus-ring (RBR) geometry synergistically integrated with Mach-Zehnder interferometer (MZI). The RBR consists of two detuned resonators indirectly coupled through a center bus waveguide. The transparency is obtained by increasing the light intercavity interaction through tailoring the RBR phase response while ensuring balanced MZI operation. In this work, a CRIT resonance with a quality factor of ~18,000 is demonstrated with cavity size detuning of ~0.035% and power coupling of ~60%, which are in good agreement with the theory.

Coupling-induced phase shift in a microring-coupled Mach-Zehnder interferometer

We experimentally study the effects of the coupling-induced phase shift (CIPS) in silicon-on-insulator microring-coupled Mach-Zehnder interferometer (MZI) devices for the flat-top filter application. Excellent agreement is obtained between the theoretical modeling and the experiment. It is demonstrated that width offset of the uncoupled MZI arm can compensate the CIPS and approximate a box-like filter with only 0.02% deviation from its ideal requirement.

Large contrast enhancement by sonication assisted cold development process for low dose and ultrahigh resolution patterning on ZEP520A positive tone resist

The authors demonstrate a robust, low dose, high contrast, and ultrahigh resolution patterning process based on sonication assisted development of ZEP520A positive tone resist in both room and cold temperature. The contrast as high as γ ∼ 25 and γ ∼ 9.14 can readily be achieved in 6 °C and room temperature development, respectively, in diluted n-amyl acetate solution. The high contrast is demonstrated on 90 nm thick ZEP resist at 20 kV acceleration voltage, from which 20 nm thick titanium lift-off of 60 nm pitch lines and 50 nm pitch dots can be successfully achieved.

Demonstration of low-loss on-chip integrated plasmonic waveguide based on simple fabrication steps on silicon-on-insulator platform

We report the experimental realization of a robust silicon-based plasmonic waveguide structure which can theoretically provide sub-wavelength confinement for Ex- and Ey-polarized surface plasmon polariton modes. Our waveguides exhibit propagation loss as low as 0.2 dB/μm with ∼50% coupling efficiency.

Groove-structured metasurfaces for modulation of surface plasmon propagation

An alternative metasurface design based on a nonresonant mechanism is proposed and demonstrated. Using the effective medium theory and finite element calculation, we show the relationship between the effective refractive index and the metasurface geometrical parameters, which potentially can be used for tuning the wavelength and wavefront of the surface plasmon polariton (SPP). Experimental studies of our metasurface were conducted by near-field scanning optical microscopy of subwavelength gold grooves fabricated using a focused ion beam (FIB). The metasurfaces give us an alternative method for manipulating SPP propagation.

Fundamental Principles of Operation and Notes on Fabrication of Photonic Microresonators

Light confining microresonators based on evanescent wave propagation and whispering gallery (WG) modes have received much attention in the past decades, due to their conceptual similarity with their standing wave counterparts, improvements in fabrication technology, and their versatility in realizing various functions in telecommunications, sensing, measurement, and instrumentation. In this chapter the general concepts, design principles, and practical realizations of optical microresonators are briefly introduced. Using a simple but generic model, important design parameters such as the Q-factor, the finesse, the free spectral range, the intensity buildup, and the effects of loss are derived in general terms from basic principles. The discussion on cavity design is completed by reviewing several intrinsic properties of available material systems, such as the refractive index contrast, which is essential for field confinement, which limits the resonator geometrical size, contributes to material loss, and influences the nonlinear response. Finally, fabrication techniques of microring and WG resonators are also outlined, from the surface tension-mediated processes in silica microspheres and microtoroids to the wafer-based technologies such as deep ultraviolet (DUV), electron beam, and nanoimprint lithography. Some notable examples of fabricated resonators are discussed and compared.