Yang, Lirong

Denne afhandling udforsker forskellige aspekter af anvendelsen af topologioptimering ved design af nanofotoniske komponenter. Der anvendes enten en frekvensdomæne- eller en tidsdomænemetode i kombination med optimeringsalgoritmerne, afhængigt af de forskellige m˚al for designopgaverne. Frekvensdomænemetoderne er hensigtsmæssige til problemer hvor effekten skal maksimeres eller minimeres ved nogle f˚a frekvenser, uden at tage hensyn til den detaljerede profil af den optiske puls eller behovet for mange frekvenskomposanter. Designet af koblere til ”langsomt lys”, der forbinder normale kantbølgeledere og fotoniske krystalbølgeledere er behandlet her. Det er demonstreret b˚ade numerisk og eksperimentelt at de optimerede koblere kan forbedre koblingens effektivitet markant. Med fokus p˚a tidsdomæneoptimeringsmetoden diskuterer afhandlingen omfattende designet af pulsformgivningsfiltre, som i høj grad udnytter fordelene ved tidsdomænemetoderne. ”Finite-difference time-domain” metoden er anvendt som modelleringens fundament for det inverse problem. Filtre baseret p˚a b˚ade ´en-dimensionelle gitre og to-dimensionelle plane strukturer er blevet designet, og forskellige problemer vedrørende lokale minima, sort/hvidt design, mindste længdeskala og variable pulsforsinkelser er blevet adresseret. Hensigten er at demonstrere potentialet for tidsdomænebaseret topologioptimering ved design af komplicerede fotoniske strukturer til frembringelse af lyspulser med specifikke af tidskarakteristikker.This thesis explores the various aspects of utilizing topology optimization in designing nanophotonic devices. Either frequency-domain or time-domain methods is used in combination with the optimization algorithms, depending on various aims of the designing problems. The frequency-domain methods are appropriate for problems where the power is to be maximized or minimized at a few frequencies, without regards on the detailed profile of the optical pulse or the need of large amount of frequency samplings. The design of slow light couplers connecting ridge waveguides and the photonic crystal waveguides is showcased here. It is demonstrated both numerically and experimentally that the optimized couplers could improve the coupling efficiency prominently. With more focus on the time-domain optimization method, the thesis discusses extensively the design of pulse-shaping filters, which greatly exploits the benefits of time-domain methods. Finite-difference time-domain method is used here as the modeling basis for the inverse problem. Filters based on both one-dimensional gratings and two-dimensional planar structures are designed and different issues regarding local minima, black and white design, minimum lengthscale and flexible pulse delay are addressed to demonstrate time-domain based topology optimization’s potential in designing complicated photonic structures with specifications on the time characteristics of pulses

Online Research Database In Technology

Topology Optimization of Nanophotonic Devices

http://orbit.dtu.dk/ws/files/5625332/phdthesis_LirongYang%20CMYK.pdf

Topology Optimization of Nanophotonic Devices

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Online Research Database In Technology