Xiaosheng Huang

Hollow core anti-resonant fiber with split cladding.

An improved design for hollow core anti-resonant fibers (HAFs) is presented. A split cladding structure is introduced to reduce the fabrication distortion within design tolerance. We use numerical simulations to compare the Kagome fibers (KFs) and the proposed split cladding fibers (SCFs) over two normalized transmission bands. It reveals that SCFs are able to maintain the desired round shape of silica cladding walls, hence improving the confinement loss (CL) compared to the KF and is comparable to that of the nested antiresonant nodeless fiber (NANF) with the same core size. In addition, the SCF allows stacking multiple layers of cladding rings to control the CL. The influences of the number of cladding layers and the cladding gap width on the CL of the SCFs have been studied. SCF with three cladding rings is fabricated by the stack-and-draw technique. A measured attenuation spectrum matches well with the calculation prediction. The measured near field mode patterns also prove the feasibility of our fiber design.

Function of second cladding layer in hollow core tube lattice fibers

Modes attenuation of the tube lattice fiber (TLF) is characterized by D/λ, where D is the core diameter and λ is the wavelength. Hence, the TLF is structured with a large core to ensure a low attenuation loss. A small core, on the other hand, facilitates the gas-filled TLF applications, but at the expense of the increased mode attenuation. We show that adding a second cladding layer to the conventional one layer TLF (1TLF) can resolve the contradicting requirements. The mode attenuation of TLF with two cladding layers (2TLF) is less influenced by the D/λ value as compared to 1TLF, thus realizing a low loss small core TLF. Furthermore, we found that adding the second layer brings another advantage to a bending performance. With a determined core size, D, a 1TLF with smaller capillary hole size, d, experiences less bending loss. However, the reduced d increases the confinement loss that counteracts the bending loss improvement. This confliction is substantially alleviated in 2TLF thanks to the second cladding layer. Theoretical investigations and experimental demonstrations are presented to evidence the important role of the second cladding ring in the TLF, which has been overlooked in prior studies.

Hollow-core air-gap anti-resonant fiber couplers

We design, fabricate, and demonstrate the first hollow-core air-gap anti-resonant fiber coupler in a dual hollow-core anti-resonant fiber (DHAF) structure. The coupling takes place through an air gap between air cores, promising a limitless operation window beyond material transmission. The DHAF follows the same waveguide mechanism as the hollow-core anti-resonant fiber (HAF). The coupling is attainable over the entire transmission bands determined by a resonant frequency of a HAF. A coupling length, thus coupling strength, is controllable by adjusting fiber design parameters. In addition, at a fixed design and length, the coupling strength linearly responds to longitudinal mechanical tension, enabling continuous variable coupling ratio in a single coupler. Furthermore, we confirm that the coupler is polarization insensitive, and does not require precise polarization alignment of an input beam. We demonstrate its robust coupling performance and applicability in forming a fiber laser ring cavity, and delivering and power splitting ultrafast laser pulse. The air-core air-gap coupling promises applications in mid-infrared and ultraviolet regions where the current coupling technology is limited.

Double layer hollow core anti-resonant fiber for small core and low loss characteristics

We study the function of second cladding layer of the tube lattice fiber (TLF) and experimentally demonstrate the important role of the second layer in the reduction of both confinement loss (CL) and bending loss.

Hollow core anti-resonant fibres with split cladding

A split cladding fibers (SCF) is proposed as an additional design to the anti-resonant type fiber. The introduced split cladding helps to reduce the fabrication distortion. We use numerical simulations to compare the Kagome fibers (KFs) and the proposed split cladding fibers (SCFs) over two normalized transmission bands. It reveals that SCFs are able to maintain the desired round shape of silica cladding walls, hence improving the confinement loss (CL) compared to the KF. Fabrication of the SCF is demonstrated by the stack-and-draw technique. The near filed mode patterns are measured to prove the feasibility of this fiber design.

Microstructured Inline Optical Fiber Structure for Dispersion Control and Coherent Supercontinuum Generation

A microstructured optical fiber (MOF) structure with longitudinal dispersion variation is theoretically investigated for broad, coherent supercontinuum (SC) generation in the infrared (IR) region. The MOF possesses anomalous dispersion at 1550 nm but changes its dispersion to normal dispersion by a tapering process. The inline dispersion controlled structure provides a linear chirp and the subsequent pulse compression without additional components. The compressed pulse then seamlessly enters a short normal dispersion section for the coherent SC generation. Our simulation suggests that the inline structure can be as short as around 11.6 cm to realize the pulse compression and the SC generation. In particular, only 0.5-cm-long final normal dispersion section is required for the coherent SC generation, hence avoiding high background loss particularly in the spectral region above 2 μm, where silica glass absorption becomes considerably high. In the structure, the peak power of a pulse is enhanced by 14 times in the compression process, and the corresponding generated SC spectrum has a bandwidth of 1260 nm, extending to wavelengths above 2 μm. The simulation also shows that the generated spectrum is highly coherent. We experimentally demonstrated the dispersion shift from anomalous to normal dispersion with the microstructure fiber fabricated in-house.