We characterize an approach to make ultra-low-loss waveguides using stable and reproducible stoichiometric Si3N4 deposited with low-pressure chemical vapor deposition. Using a high-aspect-ratio core geometry, record low losses of 8-9 dB/m for a 0.5 mm bend radius down to 3 dB/m for a 2 mm bend radius are measured with ring resonator and optical frequency domain reflectometry techniques. From a waveguide loss model that agrees well with experimental results, we project that 0.1 dB/m total propagation loss is achievable at a 7 mm bend radius with this approach.

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Ultra-low-loss high-aspect-ratio Si3N4 waveguides.

Planar waveguides with ultra-low optical propagation loss enable a plethora of passive photonic integrated circuits, such as splitters and combiners, filters, delay lines, and components for advanced modulation formats. An overview is presented of the status of the field of ultra-low loss waveguides and circuits, including the design, the trade-off between bend radius and loss, and fabrication rationale. The characterization methods to accurately measure such waveguides are discussed. Some typical examples of device and circuit applications are presented. An even wider range of applications becomes possible with the integration of active devices, such as lasers, amplifiers, modulators and photodetectors, on such an ultra-low loss waveguide platform. A summary of efforts to integrate silicon nitride and silica-based low-loss waveguides with silicon and III/V based photonics, either hybridly or heterogeneously, will be presented. The approach to combine these integration technologies heterogeneously on a single silicon substrate is discussed and an application example of a high-bandwidth receiver is shown.

Ultra‐low loss waveguide platform and its integration with silicon photonics

Nanoimprint lithography is gaining rapid acceptance in fields as diverse as microelectronics and microfluidics due to its simplicity high resolution and low cost. These properties are critically important for the fabrication of photonic devices, where cost is often the major inhibiting deployment factor for high volume applications. We report here on the use of nanoimprint technology to fabricate low loss broadband high index contrast waveguides in a Polysiloxane polymer system for the first time.

https://openresearch-repository.anu.edu.au/bitstream/10440/963/1/Han_Low2009.pdf

Low loss high index contrast nanoimprinted polysiloxane waveguides

Methods of film deposition using metals and metal oxides. A thin film of germanium oxide and an oxide of a non-germanium metal is deposited by ALD by alternating deposition of first and second precursor compounds, wherein the first precursor compound includes a metal other than germanium, and the second precursor compound includes germanium.

Codeposition of hafnium-germanium oxides on substrates used in or for semiconductor devices

Highly nonlinear planar glass waveguides have been shown to be useful for all optical signal processing. However, the typical SMF-28 fiber to waveguide coupling loss of ~5dB/end remains a barrier to practical implementation. Low loss coupling to a fiber using vertical tapering of the waveguide film is analyzed for rib and nanowire waveguides and experimentally demonstrated for ribs showing polarization and wavelength independence over >300nm bandwidth. Tapers with essentially zero excess loss led to total losses from the waveguide to fiber core of 1.1dB per facet comprising only material absorption (0.75dB) and mode overlap loss (0.36dB), both of which can be eliminated with improvements to processing and materials.

Low loss coupling to sub-micron thick rib and nanowire waveguides by vertical tapering

A plasma enhanced chemical vapor deposition process was developed to deposit SiO 2 -GeO 2 films suitable for high index contrast planar waveguides. These films were deposited in a standard parallel plate reactor from silane, germane, nitrous oxide, and a nitrogen carrier. The germania content of the film was equal to the mole fraction germane of the hydride precursors in the gas stream, and the refractive index of the film varied linearly with the mole fraction of germania. Low loss guides ranging from 1.5-4.0% Δ were fabricated. With standard photolithographic patterning, a 0.05 dB/cm propagation loss and minimum bend radius of 1.5 mm were measured for 2.0% A. Improvements to the photolithographic patterning to reduce sidewall roughness were required to achieve low propagation loss at higher Δ. This reduced the propagation loss for 3.5% Δ cores to 0.086 dB/cm. An average minimum bend radius of 570 μm was measured for 3.5% A, but modeling suggests the bend radius could be reduced below 500 μm with offsets to reduce transition loss. Ring resonator, fabricated from 3.5% A waveguides, exhibited a free spectral range as large as 62.7 GHz and a very low round trip insertion loss of 0.06 dB.

L. Guiziou

Papers

Ultralow Loss High Delta Silica Germania Planar Waveguides