7-cell core hollow-core photonic crystal fibers with low loss in the spectral region around 2 μm

Hollow Core Photonic Bandgap fibers for Telecommunications: Opportunities and Potential Issues

“…As a result of the small overlap of the optical modes with glass (typically <0.1%), the infrared glass absorption contribution to the overall loss is significantly reduced and the minimum loss region in PBGFs is shifted to longer wavelengths, approximately to between 1.9 and 2.0 µm [8,10]. Although operation at these wavelengths would require major changes in the network infrastructure, no fundamental road-blocks exist in semiconductor and active fiber technology to make such a change in wavelength an impossibility.…”

“…It is finally worth mentioning that the optimum operational wavelength range of PBGFs may ultimately not be determined by the spectroscopic properties of Tm, but rather by the desire to avoid the strongest roto-vibrational absorptions lines of water vapor or other gases such as CO 2 or HCl, which have been experimentally observed inside the fibers [10] and which may or may not be a reason of concern, depending on the minimum concentration levels ultimately achievable.…”

Hollow-core photonic bandgap fibers: technology and applications

“…The combination of a thick core surround with the reduction in field intensity at the core boundary resulting from enlarging the core from 7 to 19 missing cells led to the lowest properly documented loss in a HC-PBGF to date of 1.7 dB/km at a wavelength of 1560 nm [51,58] ( Figure 5E), with mention of losses as low as 1.2 dB/km at slightly longer wavelength in a similarly structured fibre made in a further article [56]. In parallel, alternative designs incorporating antiresonant nodes in a thin core surround were also investigated and shown to provide loss improvements [59,60] although the small 7c core employed in these works did not allow any further improvements in terms of setting a new record loss. In both cases, the thicker anti-resonant features introduced on the core boundary invariably led to an increased presence of surface modes and thus, as discussed in Section 3.3, resulted in a substantial degradation in the other key transmission properties, including decreased bandwidth and polarisation stability.…”

“…According to the λ -3 dependence of the surface scattering loss, predicted initially through dimensional analysis in [56] and more recently confirmed by numerical calculations [57], shifting the operational wavelength from 1.55 to 2 µm would reduce the minimum total fibre loss by a factor of ~2. An experimental demonstration of this was provided in [59], in which several 7c HC-PBGFs with a very similar cladding structure but different scale factors (and thus operating at different wavelength from 1400 to 2400 nm) were investigated. A minimum loss of 9.5 dB/km at 1990 nm was measured in these experiments.…”

Thulium-doped Fiber Amplifier for Optical Communications at 2µm

“…HC-PBGFs are predicted to exhibit their minimum loss window in the waveband around 2 µm [20,21], and provide realistic prospects for achieving similar loss levels to conventional fibers at 1.5 µm while maintaining a large transmission bandwidth of more than 100 nm [17,18]. Moreover, HC-PBGFs possess the advantages of a very low nonlinearity and low latency compared with conventional fibers [17].…”