Abstract:
There has been tremendous advancements in silicon photonics over decades, thanks to compatibility of fabrication processes involved, with the well-developed and readily available
CMOS (Complementary Metal Oxide Semiconductor) technology already established in the
microelectronics industry. Consequently, it is possible to realize photonic integrated circuits
(PICs) on a large scale with low costs. Silicon photonics finds applications in optical
communications, quantum photonics, bio-medical sensing, security, etc. However, current
photonics circuits and devices are designed speci fically for particular functions, due to their
limited intricacy, and thus unsuitable for applications that require enormous complexity in
terms of designs and functionalities. Programmable or recon figurable integrated photonics,
on the other hand, are emerging paradigms that can transform the application-specific
present photonic devices into more flexible systems that can allow a series of applications on a common hardware.
Liquid crystals could be a promising candidate towards the development of programmable
integrated photonics because of their large anisotropy in their optical properties and electro-optic property which can be manipulated by an external electric eld. These properties
can be exploited to develop photonic circuits which can be precisely controlled by external
electrical signals. In this thesis, we studied the integration of liquid crystals on silicon-based
photonic devices.
In the first part, we studied the effects of the anisotropic properties of liquid crystals on
optical modes in guided wave systems on silicon-on-insulator and silicon nitride platforms.
Changes in the effective refractive index ) of optical modes propagating through Si and SiN
rectangular waveguides with liquid crystals in the upper cladding region are computationally
studied using commercial software Lumerical Mode solutions. We found that the effective refractive index of modes is sensitive to liquid crystal properties and waveguide geometry.
The second part of the work aimed to develop liquid crystals based on-chip integrated
tunable optical fi lters. We fabricated the passive optical fi lter based on ring resonators and
integrated the liquid crystals on top of it as upper cladding material. We characterized the
device and showed the active tuning of resonant wavelength in the presence of varying static
electric fi elds. Further study will be devoted to develop suitable designs that can fully exploit
the tunability of the device.
