Generation and Bandwidth Scaling of silicon modulator based Integrated High Repetition rate Optical Frequency Combs

Abstract

Optical Frequency Combs (OFC) are laser sources that consist of discrete, equally spaced lines in frequency space, have found extensive use in metrology, spectroscopy, sensing and optical communications. Generation of frequency combs in integrated platforms is of interest due to their potential use as Wavelength Division Multiplexing (WDM)sources for transmitters in high-speed optical communication applications. In this thesis, we explore the following aspects: First, using electro-optical simulations we examine the feasibility of optical frequency comb generation using strong phase modulation of charge injection based on-chip silicon photonic modulators.We experimentally demonstrate frequency comb generation in the C-band with a 10GHz repetition rate using foundry fabricated devices. Optical frequency combs generated this way come with the advantage of having a tuneable center frequency and flexible repetition rate essential for optical communications applications. Secondly, we explore and experimentally demonstrate a technique to bandwidth scale frequency combs generated this way by linking two frequency combs generated from different optical carriers in the same modulator by setting up an optical phase locked loop to frequency lock them to each other. This technique is also investigated in the context of electro-optical frequency combs generated using bulk lithium niobate based optical modulators. Here, we experimentally realize a nonlinearly broadened optical frequency comb (at 25 GHz repetition rate) that consist of frequency locked carriers across a 2 THz band starting from widely spaced (100 GHz) dual offset frequency locked carriers. Finally, we investigate the effect of microwave power on optical frequency combs generated in silicon ring resonator modulators.We show that microwave power induced thermo-optic resonance shifts can be used to accomplish both center frequency tuneability and used to cascade multiple ring modulators to accomplish bandwidth scaling of frequency combs.