Design of low-loss and highly birefringent hollow-core photonic crystal fiber

Abstract

A practical hollow-core photonic crystal fiber design suitable for attaining low-loss propagation is analyzed. The geometry involves a number of localized elliptical features positioned on the glass ring that surrounds the air core and separates the core and cladding regions. The size of each feature is tuned so that the composite core-surround geometry is antiresonant within the cladding band gap, thus minimizing the guided mode field intensity both within the fiber material and at material / air interfaces. A birefringent design, which involves a 2-fold symmetric arrangement of the features on the core-surround ring, gives rise to wavelength ranges where the effective index difference between the polarization modes is larger than 10 -4. At such high birefringence levels, one of the polarization modes retains favorable field exclusion characteristics, thus enabling low-loss propagation of this polarization channel.

Semi-analytical model for hollow-core anti-resonant fibers

“…To our understanding, this unambiguous and quantitative interpretation on the guidance mechanism results in the fast development of HC-PBGF in the first decade of Twenty First century. The optical attenuation has reached a record of 1.2 dB/km [7]; entire fabrication procedure of a HC-PBGF can be completed within 1 day; the anti-crossing between the core mode and the surface mode has been clearly identified [8,9] and can be deliberately engineered for specific purposes, e.g., polarization maintaining in HC-PBGF [10,11]. However, the intrinsic ∼70 Thz transmission bandwidth originating from the PBG guidance mechanism and the low damage threshold caused by large spatial overlap of the core mode with the glass cladding [7,12] limit the lab-on-a-fiber applications in this kind of HCFs.…”

Polarization maintaining single-mode low-loss hollow-core fibres

“…Much effort has focused on eliminating these phase-matching points, as they generally lead to high loss and reduced bandwidth. For a well-designed asymmetry, however, the surface modes can be highly birefringent [15][16][17][18][19] . Core modes of the two polarizations can see phase-matched coupling at different wavelengths.…”

“…Introducing stress in the core (the dominant method of making conventional, solid polarization-maintaining (PM) fibres) is clearly not possible in a hollow fibre. Thus, birefringence must be achieved by carefully controlling the asymmetry of glass webs around the core 16,17 , such that surface mode interactions shift one polarization relative to the other. As these surface mode interactions can provide suppression of higher-order modes (HOMs) in narrow wavelength ranges, this strategy has even resulted in simultaneous polarization-maintenance and singlemodedness 18,19 in small-core fibres.…”

Optical frequency standard using acetylene-filled hollow-core photonic crystal fibers

“…The C7 PM fiber differs from all the others as it is fabricated to be polarization maintaining (PM). The enhanced birefringence needed to have the PM property is introduced thanks to four anti-resonant features on the core wall [17]. At the same time, these features lead to improved mode confinement.…”