Abstract
Increasing the working optical bandwidth of a photonic circuit is important for many applications, in particular chemical sensing at mid-infrared wavelengths. This useful bandwidth is not only limited by the transparency range of waveguide materials, but also the range over which a waveguide is single or multimoded for predictable circuit behaviour. In this work, we show the first experimental demonstration of "endlessly single-mode" waveguiding in silicon photonics. Silicon-on-insulator waveguides were designed, fabricated and characterised at 1.95 µm and 3.80 µm. The waveguides were shown to support low-loss propagation (1.46 ± 0.13 dB/cm loss at 1.95 µm and 1.55 ± 0.35 dB/cm at 3.80 µm) and single-mode propagation was confirmed at 1.95 µm, meaning that only the fundamental mode was present over the wavelength range 1.95 - 3.80 µm. We also present the prospects for the use of these waveguides in sensing applications.
Highlights
For many photonic integrated circuits (PICs), single-mode propagation is a requirement of the waveguides for predictable optical behaviour
The absorption from the underlying SiO2 layer limits the use of SOI at longer MIR wavelengths, the waveguide design approach that we experimentally demonstrate here could be adapted for use in other group IV material platforms, for > 4 μm
To experimentally demonstrate that the waveguides were single-moded over a broad wavelength range, the waveguides were experimentally characterised at = 1.95 μm and = 3.80 μm, covering an octave of frequency
Summary
For many photonic integrated circuits (PICs), single-mode propagation is a requirement of the waveguides for predictable optical behaviour. For a conventional rib or strip waveguide, the wavelength range for solely supporting the fundamental mode is limited. Waveguide modes are considered guided if their effective index is above the refractive index of the waveguide cladding at a given wavelength. For single-moded guidance, the higher order modes must have an effective index above this cut-off value.
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