Fabrication and experimental demonstration of on-chip diamond optical devices

Student thesis: Doctoral Thesis

Abstract

This thesis focuses on the design, fabrication, and characterization of the novel single-crystal
diamond (SCD) photonic components and devices. In recent years, integrated photonics based on synthetic SCD has gained much attention. This is due to SCD’s superior optical performance for, among others, novel nonlinear-optical, quantum-optical, and short-wavelength applications. However, the current integration
level in diamond photonics is far from mature, mainly because large-area uniform SCD membranes are not yet commercially available. Besides, today’s commercial SCD plates used for device fabrication typically have a large wafer wedge (about 300nm=mm). As a result, the on-chip devices demonstrated in recent years remained primarily restricted to small-scale single resonator structures. Furthermore,
the optical interconnect and I/O in the state-of-the-art devices are rarely realized using
monolithic coupling structures, despite that they offer more flexibility in layout design and relatively high coupling performance.
In this work, carried out in partnership between VUB, Belgium and Hewlett Packard Labs, USA, we show that even when using wedged SCD substrates, it is possible to achieve a higher integration level beyond the state-of-the-art. More specifically, we succeeded in designing, fabricating and demonstrating (1) multi millimeter long yet low-loss SCD waveguides connected to high-efficiency monolithic
grating couplers optimized for fiber telecom wavelengths in the near-infrared (NIR);
(2) SCD directional coupler devices combining two widely spaced wavelengths in the NIR; and (3) SCD waveguides with monolithic grating couplers designed for very short wavelengths in the visible-ultraviolet (VIS-UV) spectral domain.
Our NIR millimeter-length waveguides and NIR directional couplers are essential components to enable on-chip signal routing in large-scale SCD photonic integrated circuits. Also, our novel VIS-UV waveguides and grating couplers represent
an essential expansion of the existing on-chip VIS optical components which are mostly single, small-scale, and microscope objective coupled resonators. The fabrication process outlined in this thesis relies on e-beam lithography and reactive ion etching technologies. To mitigate the influence of SCD wafer wedge, we introduced
a series of improvements both in layout design and fabrication process. The latter includes a novel tilted-etching technique that effectively reduces the wedge angle.
The successful realization of the aforementioned on-chip components and devices
represent a significant advancement towards the full exploitation of the diamond’s
unique optical characteristics in photonic integrated circuits.
Date of AwardDec 2019
Original languageEnglish

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