Current record is transmission loss of 7. This level of transmission loss and BL are still far from telecom standard but some advanced NCF designs 31 , 33 , e. However, with the current pressurized fibre drawing technique and with the consideration of fluid dynamics inside the furnace 34 , realization of such delicate structures with predicted optical performance brings substantial challenges due to the difficulty of precisely controlling the size and position of each tube element 35 , 36 , How to remarkably bring down CL and BL by introducing minimum complexity in both fibre design and fabrication becomes a crucial issue for the advancement of HC-NCF in optical communication technology.
The design concept of this CTF is to conjoin twin or triplet anti-resonant AR tubes in the radial direction to efficiently confine light by multiple interfaces with sufficient consideration of fabrication simplicity. As light attempts to leak out of the core, it successively encounters five different dielectric layers 38 or six glass:air interfaces , i. Accurate numerical simulation the grey curve in Fig. The experimentally measured threefold higher losses probably originates from structural non-uniformity in both the transverse and longitudinal dimensions.
Spectral oscillations at band edges, i. Other spectral oscillations distributed over the whole transmission band are the result of Fano resonances 40 introduced by the glass web connections. Demonstration of an ultralow-loss broadband CTF. The yellow numbers label the five dielectric layers in the cladding. The spectral extension of the optical telecommunication O, E, S, C and L bands are also shown for comparison. One fundamental characteristic of an optical fibre is that it allows flexible bending of the light.
Previously reported NCFs mostly pursue low CL by sacrificing BL with the adoption of a large core diameter 30—55 times the working wavelength 32 , 41 , 42 , which represents a very small glancing angle at glass:air interfaces. Nevertheless, BL sensitivity is a crucial issue in practical applications and needs to be reduced. The increased number of AR layers combined with the reduced core diameter guarantee the simultaneous realization of ultralow CL and low BL.
The measured BLs see Methods exhibit values as low as 0. The simulated results the black curves in Fig.
However, this peak was not experimentally observed probably due to the indeterministic bending orientations and the small variations of the bending radius along the total loops. Under tighter bending e. Bending loss of the CTF. Inset: Photo images of the fibre under test with the loop numbers of , and , respectively. When the fibre is bent with a smaller radius, these HOM peaks are suppressed. Simulation shows CL values of 0. With more subtle adjustment of the position of the glass bar inside conjoined tube, few mode guidance might be achieved in CTF, which would make them compactible with SDM transmission systems.
S 2 analysis of the CTF. The typical multipath interference MPI vs. In optimal condition, this could drastically decrease the CL by In a NCF, additional influence from the shape of the glass wall should also be taken into account. In Fig. More surprisingly, a two-bar version CTF with five conjoined tubes and the same core diameter could further decrease the CL to below 0.
From a fabrication perspective, such a 2-bar CTF structure is much more feasible than previously proposed ultralow-loss NCF designs, e. Our CTF architecture offers another probably more practical route.
The minor influence to the total loss spectrum the pink curve in Fig. Comparison of simulated loss spectra of several designs. They share the same inscribed core diameter of The CLs are plotted in solid curves. The SSL and the total loss are plotted in dashed curves. The demonstrated fibre sample is far from the limit of CTF technique and can be further improved.
Similar to the single-ring NCF, CTF could further expand the transmission bandwidth as long as thinner and more uniform glass membranes are realized. Other advantages of CTF over PBGF include lower modal spatial overlap with glass thus higher laser damage threshold , lower dispersion, and higher group velocity, likening light propagation in vacuum.
The remaining issue lies on realization of polarization-maintaining fibres. Further investigation is needed but hybrid transmission bands 49 could represent a potential solution.
This makes HCF a strong contender to solid-core silica fibre for high-capacity data communication, where loss and nonlinear tolerance are of equal importance for enhancing spectral efficiency via higher order modulation formats. To make conjoined-tubes, a custom-made high purity thin slab is inserted into the centre of a thin glass tube and is drawn into capillaries. The latter is then drawn into fibres using the conventional two-stage stack-and-draw technique. The geometrical parameters were determined from the SEM image of the fibre with small adjustment within the range of uncertainties.
The SSL is calculated following the equations in ref. The bending loss spectra are demonstrated in Fig. BL is calculated by substracting the loss of a bent fibre from that of a straight fibre. The conformal mapping technique is implemented for the simulation of a bent fibre At the output cross-sectional plane, a SMF28 fibre records the spectra at different positions. The spectra were acquired by an OSA with the resolution of 0. The near filed image was also monitored by a camera.
Communication networks beyond the capacity crunch. A , Richardson, D. Filling the light pipe. Science , — Shannon, C. A mathematical theory of communication. Bell Syst. Performance limits in optical communications due to fiber nonlinearity.
Photon 9 , — Space-division multiplexing in optical fibres. Photon 7 , — Cregan, R. Single-mode photonic band gap guidance of light in air. Russell, P. Hollow-core photonic crystal fibres for gas-based nonlinear optics. Couny, F. Generation and photonic guidance of multi-octave optical-frequency combs. Balciunas, T.
A strong-field driver in the single-cycle regime based on self-compression in a Kagome fibre. Wang, Y.
Published on. In: Yin S. Both systems achieve good optical signal-to-noise ratio OSNR , approximately of 50 dB, but increasing the number of multiplexed FBG is an awkward task. Published by SciTech Publishing, Incorporated. In particular, it is not hygroscopic does not absorb water. One is to repeat the localized BGS in scanned positions along the FUT; the other is to repeat the Brillouin interaction under different frequency offset. Open in a separate window.
Hollow-core photonic crystal fibre for high power laser beam delivery. Power Laser Sci. Cubillas, A. Photonic crystal fibres for chemical sensing and photochemistry.
Sprague, M. Broadband single-photon-level memory in a hollow-core photonic crystal fibre.
Photon 8 , — Birks, T. Mangan, B. Chen, Y. Multi-kilometer long, longitudinally uniform hollow core photonic bandgap fibers for broadband low latency data transmission.
Light Technol. Roberts, P. Ultimate low loss of hollow-core photonic crystal fibres. Express 13 , — Mortensen, N. Modeling of realistic cladding structures for air-core photonic bandgap fibers. Amezcua-Correa, R. Control of surface modes in low loss hollow-core photonic bandgap fibers. Express 16 , — Yu, F. Negative curvature hollow core optical fiber. IEEE J. Quantum Electron. Benabid, F. Stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber. Low loss broadband transmission in optimized core-shape Kagome hollow-core PCF.
Low loss broadband transmission in hypocycloid-core Kagome hollow-core photonic crystal fiber. Understanding origin of loss in large pitch hollow-core photonic crystal fibers and their design simplification. Express 18 , — Pryamikov, A. Express 19 , — Express 20 , — Luan, F. All-solid photonic bandgap fiber.