Diameter measurement of nano/micro-optical fiber based on effective refractive index including uncertainty analysis with Monte Carlo simulation

Optical fibers with diameters of a few micrometers or less are essential devices in next-generation optical circuits and quantum photonics, so an accurate measurement technique of the fiber diameter is indispensable for performing their functions. Because nano/micro-optical fibers form an evanescent light field around their surface, the effective refractive index depends on the cross-sectional area of the optical fiber and the surrounding air, which also determines the propagation constant of the propagating light in the fiber. Based on the optical relationship, we proposed a principle to measure the fiber diameter by measuring the propagation constant with the scanning near field optical (SNOM) probe, and evaluated its measurement performance by means of uncertainty analysis. The proposed method is measurable in the single mode region, so that, for example, using 1550 nm, a diameter range from 350 nm to 1.1 μm can be measured. Detailed experimental evaluations of the measurement reliability were conducted, and then, the uncertainty of measurement was evaluated using Monte Carlo simulation. Based on the results of the uncertainty analysis, it was stated that the uncertainty of measurement can be minimized in diameter measurement by optimizing the working wavelength of the measurement system. It was experimentally shown that a relative uncertainty of about ±5.7 % (k = 2) was possible.