Integrated optical circuits are comprised of numerous discrete components that can route, amplify, and convert light. One key element is an optical microresonator, which confines light at precise resonant wavelengths (λ) determined by the material and geometric properties. By manipulating the resonator refractive index, it is possible to change λ, thus enabling on-chip devices like optical modulators. To date, it has been necessary to use electrical components to perform this task. In this work, we demonstrate an all-optical approach by combining light-activated small molecules with integrated devices. Azobenzenes are one of the most common photoswitchable organic small molecules. In general, the thermodynamically favored trans isomer can be excited to the unfavored cis isomer upon exposure of UV or visible light. Upon heating, the cis isomer can decay back to the trans isomer. As a result, a large refractive index change also occurs. Thus, a reversible, photo-activated device can be made. Here, a monolayer of 4-(4-diethylaminophenylazo)pyridine (Aazo) is assembled on integrated SiO2 microtoroid optical resonators (Aazo-MORs) via chemical vapor deposition. With methyl as a coating spacer, the surface density of the Aazo can be controlled. To study the ability of the Aazo to photoswitch Aazo-MORs, 410 nm (90 %) and 1300 nm (10 %) light are coupled into the device simultaneously. When 410 nm is coupled into Aazo-MORs, the near-IR resonant wavelength instantly blueshifts whereas only slight redshifts due to thermal effects are observed for the methyl-coated control devices. The reduction of refractive index by Aazo upon exposure of 410 nm can be confirmed by ellipsometry. The extent of blueshift is linearly proportional to coupled blue laser power. Given sufficient thermal stimulation by a CO2 laser, the λ can be completely recovered. Notably, the switching behavior is all-optically controlled.

Self-assembled azobenzene functionalized molecules for all-optical control of integrated photonics

2019 Fall National Meeting

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