26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Joint gas-line sensing and resilience in optical communications

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Description

Spectroscopy of gasses is a key detection technique for identifying both the type and concentration of gas. Gas absorption lines are typically on the order of ~1 GHz (8 pm) wide, and so detecting these reliably requires precision optical instrumentation. Recent progress in hollow-core optical fibers (HCFs), which present the lowest-loss waveguides for light propagation at attenuations below 0.1 dB/km, has brought gas absorption features into optical communications research. Here, a ~GHz wide gas absorption feature can have an outsized impact on optical signals, since it is not resolved by common digital signal processing techniques. To fully exploit these ultralow-loss fibers for ultrahigh-capacity transmission, new digital signal processing techniques are required to resolve and counter gas absorption features, while also providing information on their wavelength locations and shapes.

We investigate performance degradation due to gas absorption with a) single-carrier modulation, where each message occupies the full signal bandwidth, and b) multi-carrier modulation, where the signal bandwidth is divided into multiple subcarriers carrying independent messages. Current optical fiber communication systems typically favour single-carrier modulation because of its simpler implementation and stronger tolerance to fiber non-linearities. For HCF transmission, multi-carrier systems may offer an advantage as fiber non-linearities are minimized and the impact of gas absorption can be contained to subcarriers around the absorption frequency.

To experimentally validate this advantage, we emulate HCF with conventional optical fibers and gas cells. We show a performance gap between single-carrier and multi-carrier systems at different absorption depths. Moreover, we can infer the location, depth, and width of the dips during the digital processing of signals even if the transmitter has no knowledge of the absorption dips. This shows that new tools developed for optical communications systems may also provide a mass-producible technique for tomography of gas lines, enabling a new generation of environmental monitoring systems.