Abstract
Petabit data capacity is the next appropriate goal to accommodate the accelerating de-mand for data bandwidth. Growth in cloud services has resulted in increasing data center sizes, and a need for power and time e?cient mid-to-long reach optical communications. Photonics based interconnects are immune to the joule heating losses and inductive and capacitive time delay inherent in copper-based interconnects. Speci?cally, Silicon-based photonics is currently the leading platform of choice in integrated optics, as it is suitable with current Complementary Metal Oxide Semiconductor (CMOS) fabrication techniques which provide low cost and scalable solutions for the next generations demand in commu-nication and high-performance computing. However, there are unresolved issues, such as high waveguide dispersion of highly con?ned Silicon On Insulator (SOI) platform, wave-length dispersion of directional couplers, limiting the pursuit towards the Petabit goal. In this thesis, we present several innovations towards high bandwidth interconnects through a combination of CMOS and hybrid solutions. In Chapter 1, the big picture motivation and literature review on Silicon based in-tegrated optics are introduced. We have also described brie?y the theory of optical waveguiding and the Beam Propagation Method. In Chapter 2, we demonstrate a 5-order mode division multiplexing, the highest num-ber of multiplexed mode on SOI platform to date. Higher order modes can be controllably leveraged to carry larger amounts of information within a waveguide. The wavelength selective mode division multiplexing makes use of a device design that uses cross-Bragg coupling between two corrugated sidewalls waveguides placed parallel together; This allows multiple eigenmodes to be selectively excited or coupled from an adjacent waveg-uide. In the near future, this technology can be combined with Wavelength Division Multiplexing to scale the data capacity by a factor equivalent to the number of optical modes accommodated for in the design.In Chapter 3, innovations towards engineering optical dispersion are presented. Sec-ond order dispersion is the usual parameter to be accounted for particularly when the propagation distance of a light wave exceeds the dispersion length. However, with the increment of data rates well beyond 100Gbps, third order dispersion is increasingly be-coming an important factor to address in the propagation of optical wave packets. Dis-persion compensation can improve time multiplexed signals by limiting dispersive losses. Aside from compensating for second and third order dispersion, the ability to engineer second and third dispersion in varying magnitudes and signs is important for the control of nonlinear optical phenomena such as pulse compression and four-wave mixing. The non-linearly chirpping of the sidewalls gratings implemented on the silicon on insulator provided the ability in compensation (or generation) of the higher order dispersion. In this chapter, we have demonstrated the ?rst third order dispersion engineering on SOI platform. In Chapter 4, a conventional directional coupler has an inherent problem of wave-length sensitivity and hence, limited bandwidth when operating in broadband mode. The problem is alleviated through introducing a bent in the coupling region. We have designed a wavelength-desensitized directional coupler that consumes one of the smallest demonstrated footprint (20x3 µm). The measured normalized 3±1dB splitting ratio of the fabricated coupler is 88nm bandwidth over C+L band. A balanced Mach Zehnder Interferometer was fabricated using our bent coupler and yielded a ?attened drop port output even with a fabrication phase error of 11?. This a?rms the feasibility of practical implementation into higher level optics broadband devices such as a scaled switch fabric. In Chapter 5, an on-chip waveguide ampli?er is designed and implemented. Like di-rectional couplers, ampli?ers are also important basic structures in boosting the amount of signal power within a photonic integrated circuit. The direction towards on chip am-pli?cation requires the use of rare earth doped materials dispersed in polymer matrix. Problems like low host solubility and particle agglomeration inhibits the amount of am-pli?cation in integrated optics. In Chapter 5, demonstration of on chip ampli?cation was done through a tri-doped scheme. Other than Yb3+ and Er3+ , we introduce one more co-dopant, Ce3+ , which simultaneously quenches unwanted upconversion to the visible spectrum and boosting the desired downconversion to the IR spectrum. We have also modi?ed the surface property of the nanoparticle with an amphiphilic polymer, and this reduces the particle agglomeration of the nanoparticles and hence boosts emission. In this chapter, we have yielded the highest per unit gain of 6.6dB/cm in on-chip rare-earth doped ampli?ers. These demonstrated nanophotonic devices may bring forth the realization of all-optical integrated circuits, owing to the small footprint consumed and only single step lithog-raphy is required. The device fabrication is CMOS compatible, thus making large scale manufacturability necessary for many industry applications easily realizable.