With their lack of self-phase modulation and core optical absorption, hollow optical fibers are an excellent way to transmit high-peak-power optical pulses. Polymer-metal hollow waveguides transmit high peak powers but often with poor mode quality; conversely, air-silica hollow-core 2D photonic-crystal fibers transmit at high mode quality but have a lower damage threshold. Researchers at the Massachusetts Institute of Technology (Cambridge, MA) and Raydiance (Petaluma, CA) have developed a hollow-core 1D photonic-bandgap fiber made of a composite of arsenic sulfide glass (with a refractive index of 2.27 at 1.55 µm) and polycarbonate (with an index of 1.53). The fiber has mode qualities like that of a step-index (solid-core) single-mode fiber but suppresses optical absorption and nonlinearities by more than five orders of magnitude.
Rather than the usual arsenic trisulfide (As2S3), the glass mix was altered to As25S75 to reduce the melting temperature enough so that the glass could be co-drawn with the polycarbonate. The glass/polymer structure of the drawn fiber consisted of 22 bilayers of 521 nm thickness and a full-width at half-maximum (FWHM) thickness distribution of 27 nm. Propagation losses for the 60-µm-core fiber at 1.55 µm were less than 2 dB/m; the fiber transmitted pulses with 11.4 MW peak powers before failure. Contact Yoel Fink at[email protected].