Abstract
The first demonstration of a hollow core photonic bandgap fiber (HC-PBGF) suitable for high-rate data transmission in the 2 µm waveband is presented. The fiber has a record low loss for this wavelength region (4.5 dB/km at 1980 nm) and a >150 nm wide surface-mode-free transmission window at the center of the bandgap. Detailed analysis of the optical modes and their propagation along the fiber, carried out using a time-of-flight technique in conjunction with spatially and spectrally resolved (S2) imaging, provides clear evidence that the HC-PBGF can be operated as quasi-single mode even though it supports up to four mode groups. Through the use of a custom built Thulium doped fiber amplifier with gain bandwidth closely matched to the fiber's low loss window, error-free 8 Gbit/s transmission in an optically amplified data channel at 2008 nm over 290 m of 19 cell HC-PBGF is reported.
Highlights
Since the advent and commercialization of the Erbium doped fiber amplifier and dispersion shifted fibers in the late 1980s, research and development in long-haul telecoms optical fibers has focused on the 1.55 μm wavelength region
A record capacity of 73.7 Gbit/s was demonstrated through a combination of dense wavelength division multiplexing (DWDM) and mode-division multiplexing (MDM) using the three lowest order modes of a 37 cell hollow core photonic bandgap fiber (HC-PBGF) [11]
While we have previously demonstrated that these undesirable spectral features can be eliminated by flowing dry gas through the fiber [17] or through an improved fabrication process, here we demonstrate that error-free transmission can be achieved even at these wavelengths by tuning the signal to fit between absorption lines
Summary
Since the advent and commercialization of the Erbium doped fiber amplifier and dispersion shifted fibers in the late 1980s, research and development in long-haul telecoms optical fibers has focused on the 1.55 μm wavelength region. Whilst there is substantial evidence that the limiting loss factor of HC-PBGFs is scattering from roughness at the air/silica interface, the intrinsic limit has not yet been determined conclusively It is still unclear whether losses below the conventional SMF levels, or below the current state of the art of 1.7 dB/km [5, 12] are feasible in HC-PBGFs. it is still unclear whether losses below the conventional SMF levels, or below the current state of the art of 1.7 dB/km [5, 12] are feasible in HC-PBGFs In any case, both theoretical predictions [12] and recent experimental data [13] demonstrate that the minimum loss is shifted to longer wavelengths around 2 μm in HC-PBGFs as a consequence of the infrared ‘multiphonon’ absorption being effectively decreased by the substantially reduced modal overlap with the glass. We believe that this ground-breaking result represents a fundamental step towards assessing this radically novel fiber solution for generation transmission systems
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