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Lin, Becky

University of British Columbia

The widespread adaptation of systems relying on optically-controlled quantum information will require reliable and efficient multi-channel fibre-to-chip connections that function at cryogenic temperatures. Contrary to the matured automated measurement systems and packaging methodologies at room temperature (RT), there are limited solutions for efficient and robust cryogenic fibre-to-chip coupling due to challenges such as thermal-induced stresses and inaccessibility of the cryogenic testing environment. In this thesis, we present two methods to realize optical coupling between fibre-to-chip at cryogenic temperature. The first method utilizes piezo stages to align to multiple devices which allows high-volume device measurements and parameter characterization per cool-down cycle. However, this method is prone to signal loss due to large misalignments stemming from mechanical contractions inside the cryostat and the lack of reliable position feedback. We show that this can be mitigated by using on-chip optical feedback and following a set of navigation strategies. For permanent coupling strategies, we study a new packaging technology, photonic wire bonding, that uses free-form 3D polymer structures to connect the fibre and the photonic chip facet. Large misalignment tolerance, high bandwidth, and low insertion loss are some of the attractive features of this emerging method. First, we examine some factors, such as the quality of the facet and power of the polymer writing laser, that can influence its performance at RT. Afterwards, we apply it to cryogenic optical packaging. Again, we will see that thermal contraction poses a challenge to the application of this method at cryogenic temperature and we show, that with adjusted assembling methodology and attention to material properties, we can overcome this challenge and achieve a coupling of 2 dB between a single mode fibre and tapered silicon waveguide down to 5 K.

Text

2024-01-19

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87330

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/