Modeling bending losses of optical nanofibers or nanowires

Abstract

Bending losses of nanofibers or nanowires with circular 90 degrees bends are simulated using a three-dimensional finite-difference time-domain (3D-FDTD) method. Dependences of bending losses on wavelength and polarization of guided light are investigated, as well as the diameters, refractive indices, and bending radii of nanowires. The acceptable bending losses (approximately 1 dB/90 degrees) predicted in glass, polymer, and semiconductor nanowires with bending radii down to micrometer level may offer valuable references for assembling highly compact photonic integrated circuits or devices with optical nanowires.

Optical microfibers and nanofibers

“…However, these approximation are not valid for sharply bent (a few micrometers) MNFs, which are usually high-index-contrast waveguides. Based on FDTD method, Yu et al investigated the bending losses of MNFs with circular 90° bends, with an acceptable value of 1 dB/90° for bending radii down to micrometer level (e.g., with a minimum allowable bending radius of 5 μm for a 350-nm-diameter silica MNF) [14]. For reference, based on the mathematical model shown in Figure 8A, numerical simulations of a 450-nm-diameter silica MNF with a bending radius of 5 μm and 1 μm are shown in Figure 8B-E. As one can see, there is virtually no power leakage (with calculated bending loss of 0.14 dB/90°) for the 5 μm bent silica MNF, owing to its strong optical confinement ability.…”

“…(1) Tight optical confinement Tight optical confinement bestows the MNF with small allowable bending radius (i.e., low loss when passing through sharp bends) and small mode area, which makes MNFs highly potential for compact circuits and devices with smaller footprints, faster response, and lower power consumption [11][12][13][14]. Meanwhile, small mode area and field enhancement originated from the tight confinement allow the observation of spectacular nonlinear effects [15][16][17][18] with low thresholds and power-consumption, such as supercontinuum generation and nonlinear optical switching.…”

Optical microfiber passive components

“…If r becomes very small (at the far left of C in fig. 2) bending losses start to be an issue; in fact they have an exponential dependence on the ratio ρ/r and on V -1 [9,23], which increase considerably for decreasing r. In high refractive index materials, the tighter mode confinement implies that even smaller ρ can be achieved for the same r.…”

Compact optical microfiber phase modulator

“…On the other hand, the excellent OM bending properties allow for a considerable reduction in size, permitting the construction of high bandwidth phase modulators. Although the mechanical properties of OM allow for extremely small bend radii [10], light transmission provides the main restriction to bend radius, especially when OMs are embedded in low refractive index polymers. According to [11], the relationship between the bending loss for unit length 1 meter (α) and the bend radius (R) for a single-mode OM embedded in low refractive index polymer can be expressed as α −10 log…”