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This letter describes the design, fabrication and characterization of high-Q oval resonators based on slot waveguide geometries in thin silicon-on-insulator material. Optical quality factors of up to 27 000 were measured in such filters, and we estimate losses of Ϫ10 dB/cm in the slotted waveguides on the basis of our resonator measurements. Such waveguides enable the concentration of light to very high optical fields within nanoscale dimensions, and show promise for the confinement of light in low-index material with potential applications for optical modulation, nonlinear optics and optical sensing.

Abstract:We have designed, fabricated and characterized surface plasmon waveguides for near infrared light in the telecommunications spectrum. These waveguides exhibit losses of -1.2dB/µm and can guide light around 0.5 µm bends. Light can also be efficiently coupled between more conventional silicon waveguides and these plasmon waveguides with compact couplers, and we demonstrate that surface plasmon optical devices can be constructed by using planar circuit fabrication techniques. The large optical field enhancements of metallic surface plasmon devices are expected to lead to a new class of plasmonic optical devices, which will take advantage of the large field enhancements at the surfaces of the plasmon waveguides for nonlinear or sensing functionality, while utilizing the low losses available in silicon waveguides to move light longer distances on chip.

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We have fabricated high-Q microrings from thin silicon-on-insulater SOI layers and measured Q values of 45 000 in these rings, which were then improved to 57 000 by adding a PMMA cladding. The optimal waveguide designs were calculated, and the waveguide losses were analyzed. These high-Q resonators are expected to lead to interesting devices for telecommunication filters and sources as well as optical refractive index sensing. © 2004 American Institute of Physics. [DOI: 10.1063/1.1781355] Over the past several years, there has been substantial interest in the application of microring resonator structures as laser sources 1 and as optical filter elements for dense wavelength division multiplexing systems. 2 Here we describe a silicon-on-insulator (SOI) structure that is particularly advantageous. In the first place, it has low waveguide loss; from the measured Q values of 45 000 and 57 000, we can extrapolate an uncoupled Q value of 94 000 and a waveguide loss of 7.1 dB/ cm in the unclad case, and −6.6 dB/ cm in the PMMA clad case. Although higher Q values have been obtained for optical microcavities, 3 we believe that our geometry has the highest Q for a resonator based on a single mode silicon waveguide. But also noteworthy is the large amount of power contained outside the core silicon waveguide, which may be important in some applications; the modes that will be described have approximately 57% of the power outside the waveguide, as compared to 20% for a single-mode 200-nm-thick silicon waveguide, and 10% for a single-mode 300-nm-thick silicon waveguide.We chose to study wafer geometries that minimize the thickness of the SOI waveguiding layer as well as the buried oxide, but still yield low loss waveguides and bends. A number of different waveguide widths were compared by finite difference based mode solving. The geometry we chose consists of a 500-nm-wide waveguide formed in a 120-nm-thick silicon layer, atop a 1.4 m oxide layer, which rests on a silicon handle. Such a configuration supports only a single well-contained optical mode for near infrared wavelengths. The dispersion characteristics are shown in Fig. 1 for both unclad and PMMA-clad waveguides. Our interest in unclad structures stems from the ease of fabrication, as detailed in the following, as well as the flexibility an open air waveguide may provide for applications.These modes were determined by using a finite difference based 4 Hermitian eigensolver, the details of which are beyond the scope of this letter. It is possible to calculate the loss directly from the mode pattern with an analytic method valid in the low-loss limit, which the authors intend to publish in a forthcoming paper. The waveguide loss at 1.55 m calculated in such a fashion is approximately −4.5 dB. This loss figure was in agreement with the extrapolated results of FDTD simulation.It should be noted that since −4 dB/ cm loss is attributed to substrate leakage, the waveguide loss can be improved by the addition of a cladding, which tends to pull the mode upwards. This not...