All-optically reconfigurable photonic circuits in silicon-chalcogenide hybrid integrated platform

Shen, Bin; Witzens, Jeremy (Thesis advisor); Vivien, Laurent (Thesis advisor)

Aachen (2020, 2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

This work reports on the all-optically reconfigurable frequency-selective resonance splitting in chalcogenide microring resonators in silicon (Si)-chalcogenide hybrid integrated photonics platform. Experimental results are carried out with a specifically developed automated optical probe station. We first introduce the hardware and software of the automated optical probe station, presenting then the alignment process and the wafer level automated measurement process. The extended applications of the automated optical probe station in a broad range of measurements in integrated photonics are introduced.Furthermore, we propose the design, fabrication and testing of three types of coupling structures for Si-chalcogenide hybrid integrated photonics platform. The first type is a fully etched Ge23Sb7S70 (GeSbS) grating coupler (GC) defined directly in the GeSbS film. At the wavelength of 1553 nm, the coupling loss of the fully etched GeSbS GC is as low as 5.3 dB. Its waveguide-to-waveguide back-reflections are measured as 3.4%. Moreover, we propose the hybrid GeSbS-to-Si butt couplers and the adiabatic couplers transmitting light between GeSbS and Si single-mode waveguides. Coupling losses of 2.7 dB and 9.2% back-reflection are measured in the hybrid butt couplers (HBCs). The hybrid adiabatic couplers (HACs), instead, feature coupling losses as low as 0.7 dB and negligible back-reflection. Both HBCs and HACs have broad passbands, which exceed the 100 nm measurement range of the test setup. GeSbS GCs and GeSbS-to-Si waveguide couplers can be co-fabricated in the same process flow. Additionally, GeSbS waveguides and HBC transitions have been fabricated on post-processed silicon photonics chips obtained from a commercially available foundry service, with a previously deposited 2 µm thick top waveguide cladding. This fabrication protocol demonstrates the compatibility of the developed integration scheme with standard silicon photonics technology with a complete back-end-of-line process.Finally, we propose a method to enable all optically reconfigurable frequency-selective resonance splitting in a GeSbS chalcogenide microring resonator in the Si-chalcogenide hybrid integrated photonics platform. This is accomplished by inscribing Bragg gratings in photosensitive GeSbS chalcogenide microring resonators via a novel cavity-enhanced photo-inscription process, in which injection of light at the targeted C-band resonance frequency induces a spatially-varying refractive index change. The so-formed Bragg grating precisely matches the selected resonance order without introducing optical losses. Long-term stability of resonance splitting has been verified in darkness and during operation with reduced optical power levels at room temperature. Controlled splitting of multiple resonances by inscribing superimposed Bragg gratings are also demonstrated. The resonance splitting can be reconfigured by first erasure with flood illumination of visible light at 561 nm and subsequent re-inscription. The photo-induced and the thermally induced resonance shifts of the GeSbS ring resonator are also investigated.

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