Title: Interfacing nanophotonic waveguides with the macro and the nano scales
Description: Silicon photonics is a powerful technological platform that has advanced with gigantic steps during the past 20 years. Its applications range from the nanoscale, with biosensing and spectroscopy, all the way to the macroscale, with optical fiber communications and on-chip Lidar. However, its commercialization is still hindered by the lack of a cost-effective and automatable chip packaging approaches. At the same time, the current multiplexing techniques to increase the bandwidth density of optical communication networks are hitting their theoretical capacity limits. This has pushed the community to look for additional spatial data transmission paths through a common optical fiber. At the smaller end of the size scale, the controlled self-assembly of nanoparticles is the holy grail of nanotechnologists around the globe. Great advances towards this goal have been demonstrated, but most of the time it is hard to simultaneously control the many variables involved in the self-assembly processes.

Silicon photonics and compatible wave guiding techniques are the ideal platform to address these issues thanks to their ability of controlling light in the nanoscale. Regarding the macroscale, this dissertation presents approaches based on micro 3D printing to overcome the silicon photonics packaging bottleneck and to access additional spatial channels to increase the bandwidth density of optical communication channels. Section 2.2 presents the plug-and-play coupling of fibers to waveguides, where a 3D printed optical-mechanical micro connector is defined directly on top of a silicon photonics chip. This connector has such a relaxed alignment tolerance, that even the coarse precision of industrial automated assembly tools is enough to automatically couple a fiber to the waveguide in a robust and passive way. Section 2.3 shows another 3D printed micro coupler design. This coupler optically bridges between the higher order modes of a multimode silicon waveguide and those of a few-mode fiber.

These higher order modes can carry different streams of information at the same wavelength, effectively increasing the amount of data transmitted through the same physical channel. Regarding the nanoscale world, there is a very popular but not completely well understood self-assembly technique called evaporative self-assembly. For the past couple of decades scientists have been trying to harness it to deposit controlled patterns of nanostructures (ranging from inorganic nanoparticles to biological elements). The problem with this technique is that several of the physical variables involved in the evaporative self-assembly process are coupled to each other, making it difficult to precisely control the particle deposition. Section 3.3 shows a way of depositing a periodic pattern of gold nanoparticle clusters along the top of a silicon photonics waveguide by assisting the evaporative self-assembly process with optofluidic transport of particles. The particle trapping and transport along a waveguide is possible thanks to the strong optical forces in the immediate vicinity of the waveguide core.

With this approach, the evaporative self-assembly deposition pattern periodicity can be controlled simply by tuning only one knob: the input laser power.