| dc.description.abstract | Silicon Photonics (SiP) has emerged as the prominent platform for Photonic
Integrated Circuits (PICs). CMOS technology compatible fabrication processes,
high index contrast of the waveguide core-cladding leading to sharp bends, and low
propagation loss are the key advantageous features of SiP circuits in Silicon on
Insulator (SOI). Various functional units are already in their mature stage where
Micro Ring Resonators (MRRs) have been widely used to realize wavelength
selective devices in a PIC. Compact design, high Q-Factor, scalable spectral
properties, and the ability to create complex higher-order signal processing
architectures are some of its basic advantages. Due to these benefits of MRR, it has
found a wide range of applications ranging from sensors, optical communication,
and filters.
MRRs resonate at particular resonance wavelengths dictated by the interference
condition. However, fabrication imperfections and parasitic coupling at various
interfaces in MRR excite undesirable degenerate cavity modes that can lead to
unpredictable resonance splitting. The extent of splitting and the shape of split
resonances are uncontrollable and unpredictable within a reasonable degree of
accuracy and are only identified during the device characterization stage. Such split
response limits the use of MRR, otherwise a versatile component in PIC. In this
work, we attempted to tackle the resonance splitting problem by engineering mode
interaction within the cavity. We proposed and demonstrated a unique Self-Coupled
MRR (SCMRR) that provides a predictable and controllable resonance split by
regulating the excitation of the degenerate cavity mode. We also worked over
multiple cavity systems like loaded MRR and quadruple resonance split MRR to
gain control over not only the extent of splitting but also the resonance shape.
Finally, the proposed devices were exploited for applications in three different
domains i.e. sensing, optical communication and RF signal processing using
photonics.
Optical Communication: we demonstrated four channel multicasting at 48Gbps (4 x12 Gbps) by selectively splitting the MRR resonance into four notches. Multicasting
is achieved using Two Photon Absorption (TPA) induced Free Carrier Dispersion
(FCD) in Silicon. To the best of our knowledge, we achieved the highest data
rate/channel of 12 Gbps using a MRR based device.
Sensing: we demonstrated an on-chip self-calibrated sensor interrogator. In this
patented technique, we used SCMRR as an interrogator to scan the shift in FBG
sensor spectrum that can automatically calibrate the system performance against
the natural decay of the SCMRR thermal tuners and fluctuations in the ambient
environment. Unlike a single MRR, SCMRR interrogator response certain spectral
characteristics that can be processed to identify the change in FBG spectrum as
well as the SCMRR resonance split. The SCMRR split is then fed back to the
system to calibrate the thermal tuners for SCMRR.
RF signal processing using photonics: we proposed a RF Phase Shifter (PS) and
generation of on-chip Single SideBand with carrier (SSB+C) for Radio over Fiber
(RoF) based applications. In PS, we achieved continuous tuning of RF phase from
00 to 1800 with a record low power penalty of sub-1dB for a wide bandwidth RF (8
GHz-43 GHz). In RoF, we proposed a method of generating SSB+C signal by
suppressing one of the sidebands of a Double SideBand with Carrier (DSB+C)
signal. We achieved a tunable suppression ratio, high dynamic range, and almost
zero dispersion-based power penalty, unlike DSB+C signals, over a transmission
length of 43 Km and a frequency range of 1 GHz-20 GHz. The suppression is
achieved using DSB+C signal from bulk modulator as well as an on-chip modulator | en_US |
