Ph.D. Research Proposal Exam: Xiheng Ai

Tuesday, March 5, 2024
2:00 p.m.
Emily Irwin
301 405 0680

Name: Xiheng Ai
Mario Dagenais (Chair)
Thomas E. Murphy
Yanne K. Chambo
AVW 2460
Time: March 5th 2-3PM

Title: broadband integrated optical devices on the Silicon Nitride platform

Photonic Integrated circuit the silicon nitride (Si_3 N_4) integrated optical platform is a low-loss and compact platform for varies of applications. And the wide bandwidth of the fundamental optical components is desired for the high performance of the optical circuit.
In this proposal, we first present the design, optimization, and implementation of a sub-wavelength grating (SWG) multi-mode interference coupler (MMI) on the silicon nitride photonic integrated circuit (PIC) platform with a significantly enhanced bandwidth compared to the conventional MMI. We demonstrate the extension of the SWG MMI theory, previously presented for the silicon-on-insulator platform, to the Si3N4/SiO2 platform. The optimized SWG MMI exhibits a 1 dB bandwidth of 300nm for both the insertion loss and power imbalance.
Then we propose a π-phase shift multimode interferometer Mach-Zehnder interferometer (πPS MMI-MZI), conceptualized as a broadband nulling interferometer. This new configuration leverages a novel low phase shift error (PSE) broadband taper-sections phase shifter (TSPS). Our simulations predict an extraordinary low PSE, falling below 1°/0.02° in the wavelength range of 1450nm to 1650nm for three and two-section TSPS respectively. followed by an compatible experimental result with the PSE of 1^o within a 190nm bandwidth for the two section TSPS. Further refinements in the TSPS design have yielded an even lower PSE of 0.6°, albeit within a reduced bandwidth of 90nm. Compared to traditional MMI-MZI setups, the proposed πPS MMI-MZI represents a substantial enhancement, achieving an extinction ratio of 50dB within a 150nm bandwidth in simulations, and around 40dB within a 100nm bandwidth in experimental setups.
Moreover, we explore the high coupling efficiency chip-to-fiber edge coupler. Different methods used to improve the coupler performance have been discussed, including the multi-tips and SWG taper design and chip facet preparation methods such as cleaving, polishing and deep etching. Alternate silicon nitride thickness and fiber choices are also discussed. The best coupling efficiency achieved by now is 1.45dB by now.

Audience: Faculty 

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