Low-loss microwave photonics links using hollow core fibres

Abstract

There are a host of applications in communications, sensing, and science, in which analogue signal transmission is preferred over today’s dominant digital transmission. In some of these applications, the advantage is in lower cost, while in others, it lies in superior performance. However, especially for longer analogue photonics links (up to 10 s of km), the performance is strongly limited by the impairments arising from using standard single-mode fibres (SSMF). Firstly, the three key metrics of analogue links (loss, noise figure, and dynamic range) tend to improve with received power, but this is limited by stimulated Brillouin scattering in SSMF. Further degradation is due to the chromatic dispersion of SSMF, which induces radio-frequency (RF) signal fading, increases even-order distortions, and causes phase-to-intensity-noise conversion. Further distortions still, are caused by the Kerr nonlinearity of SSMF. We propose to address all of these shortcomings by replacing SSMFs with hollow-core optical fibres, which have simultaneously six times lower chromatic dispersion and several orders of magnitude lower nonlinearity (Brillouin, Kerr). We demonstrate the advantages in this application using a 7.7 km long hollow-core fibre sample, significantly surpassing the performance of an SSMF link in virtually every metric, including 15 dB higher link gain and 6 dB lower noise figure.

Comparison of nonlinear properties in silica-core and hollow-core fibers

“…Recently, hollow-core fibers (HCFs) with an air core have attracted considerable attention because they can dramatically reduce nonlinearity compared to silica-core optical fibers [3,4,5,6,7,8,9,10,11]. In addition dramatically improving the transmission capacity of optical fiber communications, HCFs are extremely advantageous for high-power transmission applications, such as passive optical networks [12] and power-over-fiber [13,14].…”

“…Although various types of HCFs have been reported, there are generally two types of HCFs. The former is a photonic bandgap fiber (PBGF) [3,4,5,6,7] and the latter is a nested anti-resonant nodeless fiber (NANF) [8,9,10,11]. Several experiments have been conducted to demonstrate the ultralow nonlinearity of these fibers and their utilization [9,11].…”

“…The former is a photonic bandgap fiber (PBGF) [3,4,5,6,7] and the latter is a nested anti-resonant nodeless fiber (NANF) [8,9,10,11]. Several experiments have been conducted to demonstrate the ultralow nonlinearity of these fibers and their utilization [9,11]. However, compared with conventional silica-core optical fibers, no clear evaluation of the differences in various types of nonlinear effects has been reported.…”