Realization of planar integrated silicon-on-insulator photonic platforms harnessing unguided beams
Creators: name: Ren, Guanghui
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400909
subject: Photonic and electro-optical devices, sensors and systems (excl. communications)
classificationCode: 510204
subject: Photonics, optoelectronics and optical communications

description: Single mode waveguides dominate the integrated silicon photonic chips for both passive and active components. Wide Gaussian beams, however, are needed for some applications, such as large area gas sensing, bio-imaging, microfluidic optics and among others. Therefore, how to manipulate Gaussian beams on-chip and interface them with traditional and novel integrated components is an interesting and useful topic.<br><br> The aim of this thesis is to create a planar silicon on insulator (SOI) photonic platform to harness unguided beams. This work mainly focuses on generating, controlling and collecting laterally unguided beams in slabs to realize applications for lateral leakage in thin-ridge waveguides and hybrid integration of plasmonic structures. These outcomes can be achieved by using the fabrication capability for silicon photonic chips developed by myself in RMIT University.<br><br> In this thesis, a platform which can generate and manipulate Gaussian beams on-chip is firstly studied. According fundamental optics, an integrated optical lens is proposed and experimentally demonstrated which can launch, expand, collimate and focus Gaussian beams. Approaches for varying the propagation angles of Gaussian beams are also studied. In addition, the factors that can affect the transmission loss and the beam width achievable with optical lenses are investigated.<br><br> Utilizing the integrated optical lenses system, a novel optical resonator based on lateral leakage on thin-ridge SOI waveguide is experimentally demonstrated for the first time. The optical resonator is based on the TE to TM modes conversion. The resonant reflection from a thin-ridge waveguide has been predicted previously, but it is not possible to experimentally demonstrate due to the need for wide, coherent optical beams. In the experiment, the optical lens is used to launch and collect the transmitted TE slab beam. The dependence of the resonance on waveguide width, incident angles and launched beam widths are investigated both numerically and experimentally.<br><br> Another previous study has theoretically predicted strong coupling between plasmonic crystal and beams of light trapped within a silicon slab. Again, this previous study has been limited to theoretical investigation only due to the need to illuminate the structure with a wide coherent beam of light. In this thesis, the experiments are carried out using the optical lenses to launch and collect Gaussian beams. The second Bragg resonance is firstly demonstrated which agrees with the theoretical prediction. Then the asymmetric transmission is theoretically and experimentally demonstrated, which shows its potential application on the optical diode if active components or nonlinear materials used on to the metal surface. After that, the stop-band of the hybrid plasmonic crystal is experimentally demonstrated, and the dependence of the stop-band on the pitch size and gap size is also investigated.<br><br> From the theoretical study, it is known that the hybrid plasmonic crystal has very strong optical field enhancement on the surface gaps. By utilizing transmission based NSOM, the optical field enhancement is visualized. Based on the sharp transmission change on the stop-band edge and the strong optical field enhancement on the surface, the sensitivities of the device on the environmental refractive index change and the monolayer thiol molecule are investigated, which shows very high sensitivities compared with dielectric devices. In summary, an optical lens which can launch and collect collimated Gaussian beam is realized. Based on the lens system, the single waveguide resonator and hybrid plasmonic crystal are experimentally demonstrated, paving the way for new devices and novel experimental explorations harnessing unguided beams in integrated photonic chips.<br>