Delay of Light in an Optical Bottle Resonator with Nanoscale Radius Variation: Dispersionless, Broadband, and Low Loss

Abstract

It is shown theoretically that an optical bottle resonator with a nanoscale radius variation can perform a multinanosecond long dispersionless delay of light in a nanometer-order bandwidth with minimal losses. Experimentally, a 3 mm long resonator with a 2.8 nm deep semiparabolic radius variation is fabricated from a 19 μm radius silica fiber with a subangstrom precision. In excellent agreement with theory, the resonator exhibits the impedance-matched 2.58 ns (3 bytes) delay of 100 ps pulses with 0.44 dB/ns intrinsic loss. This is a miniature slow light delay line with the record large delay time, record small transmission loss, dispersion, and effective speed of light.

Nanophotonics of optical fibers

“…This problem was solved in [32] using the IR (CO 2 laser) and UV (248 nm excimer laser) beam exposures. It has been shown that it is possible to fabricate coupled SNAP microresonators [32][33][34][35][36] and other devices [37] at the surface of an optical fiber with sub-angstrom precision. A general method of precise variation of the effective radius of an optical fiber is based on local annealing of the fiber surface performed with a CO 2 laser beam [ Figure 8(A)].…”

“…The speed of axial propagation of these modes v is much smaller than the speed of light in the fiber material v 0 . The central idea of SNAP (Surface Nanoscale Axial Photonics) [30][31][32][33][34][35][36][37] reviewed in this section is to exploit the sensitivity of WGMs to extremely small variations of the effective fiber radius, which is proportional to the variation of the physical fiber radius Δr(z) = r(z)-r 0 and refractive index…”

“…As an example, Figure 10 shows the spectral characterization of a SNAP device, which was fabricated by the translation of the focused CO 2 laser beam along the 19 μm fiber axis with a nonlinearly varied speed to arrive at the parabolic variation of the fiber radius [37]. The deviation of the introduced radius variation from the exact parabolic (white line) was < 0.9 angstrom.…”

“…The deviation of the introduced radius variation from the exact parabolic (white line) was < 0.9 angstrom. This SNAP fiber was used in [37] to demonstrate a miniature slow light delay line with a breakthrough performance. In contrast to miniature slow light delay lines considered previously [39][40][41][42][43][44][45]54], this delay line is not based on the periodic photonic crystal or coupled microresonator structures.…”

Tunable photonic elements at the surface of an optical fiber with piezoelectric core

“…2b. The same figure shows the corresponding distribution of E z component of the WGM field given by (14) for r 0 = 20 µm. Notice that in order to avoid losses the thickness of the region in the vicinity of fiber surface in which the WGM power is concentrated has to be smaller than the silica layer thickness.…”