A SNAP coupled microresonator delay line

A delay line fabricated of a chain of SNAP (Surface Nanoscale Axial Photonics) coupled microresonators is demonstrated. In contrast to resonant delay lines demonstrated to date, the slow light in this structure is enhanced by the 2R (Rotation + Reflection) effect realized due to the 3D propagation of light along the surface of a SNAP fiber. Here, the delay line coupled to a single input/output waveguide (i.e., operating in the reflection mode) is considered. Depending on the coupling parameters and loss, the delay time in this device is either proportional to the density of resonances averaged over the pulse spectrum or tends to zero. The delay line is fabricated of 20 coupled microresonators with the total length of 1.2 mm and footprint area of 0.05 mm2. It exhibits the record low insertion loss (< 3 dB), small speed of light (1 ns) delay time along the 0.1 nm bandwidth achieved for the miniature microresonator delay lines. The feasibility of significant improvement of the SNAP delay line characteristics (larger delay time and bandwidth, smaller losses and dimensions, and anti-reflecting apodization) is discussed.