Electrical and Electronics Engineering MS Thesis Defense by Ongun Arısev

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KOC UNIVERSITY
GRADUATE SCHOOL OF SCIENCES & ENGINEERING
ELECTRICAL AND ELECTRONICS ENGINEERING
MS THESIS DEFENSE BY ONGUN ARISEV

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Title: Plasmonic Stripe Waveguide Coupler with Integrated Wavelength Division Multiplexer 

Speaker: Ongun Arısev 

Time: May 16, 2017, 9:00 

Place: ENG 208
Koç University
Rumeli Feneri Yolu
Sarıyer, Istanbul

Thesis Committee Members:

Asst. Prof. Şükrü Ekin Kocabaş (Advisor, Koç University)
Prof. İrşadi Aksun (Koc University)
Asst. Prof. Alexandr Jonas (Istanbul Technical University)

Abstract:

Plasmonics is the research field concerned with the interaction between free electrons on a metal surface and electromagnetic waves. It is possible to design nanostructures which exploit these interactions to manipulate light at the nanoscale -much beyond the diffraction limit- with the advent of new techniques and devices. Integration with electronic circuits, plasmonic lasers, biosensors, chemical sensors, surface-enhanced Raman spectroscopy and plasmonic lenses are among the ever increasing applications of the field.

Coupling from free-space electromagnetic waves to surface plasmon polaritons (SPP) and decoupling from SPPs back to free-space electromagnetic waves is one of the main considerations while designing a nanophotonic chip. Directing and routing the generated SPP beams are also another concern, and usually coupling and direction of SPPs are realized with the same structure. These structures are usually an array of scatterers, but a single scatterer might be sufficient. There is on-going research on various scatterer geometries, designs and fabrication techniques to optimize the efficiency of SPP generation. Furthermore, there are various wavelength demultiplexer designs featuring periodic or aperiodic arrays of scatterers.

In this thesis the aim is to direct optical signals of different wavelengths to three 1 μm wide stripe waveguides whose centers are separated by 4 μm at the end of a gold film. To achieve this aim we first experimented with an SPP beam launcher which excites an SPP beam with a predefined amplitude and phase. However, we were unable to couple into the stripe waveguide mode, because this approach is limited in the sense that it cannot accommodate for a variation in the amplitude and phase that are smaller than the dimensions of the scatterer. Thus we decided to use a different method.

Moving on to an established wavelength demultiplexer design utilizing nanoslits was the new starting point. After mastering the iterative algorithm stripe waveguides were put at the focal positions to study the coupling of SPPs of different wavelengths into corresponding stripe waveguide modes. Simulations were done for two types of scatterers: ∆-antennas and nanoslits. It was observed that owing to the unidirectionality ∆-antennas outperformed their nanoslit counterparts in coupling efficiency by nearly two folds. This design may be generalized for different wavelengths and a larger number of focal points.