Shift of zero-dispersion wavelength in bent optical fibers

The understanding of how bending modifies the dispersion of optical fibers, in particular, the zero-dispersion wavelength (λ₀), is essential in the development of compact nonlinear optical devices such as parametric amplifiers, wavelength converters, soliton lasers and frequency comb generators. Typically, substantial variations in the parametric gain and/or conversion efficiency are significant for changes in λ₀ of ~0.1 nm, which occur for variations on the bending radius (Rb) of 1 cm or less. Measuring λ₀ as a function of bending radius (Rb) is challenging, as it requires detecting changes < 0.1 nm and in short fibers. By using a method based on four-wave mixing (FWM) generated by an incoherent-pump with relatively broad spectrum and a weak laser, we report measurements of λ₀ as a function of Rb in a dispersion-shifted fiber with <0.1 nm accuracy on λ₀. This method is sensitive enough to measure small variations in λ₀ of ~0.04 nm in very short fibers (~20 m). We observe that λ₀ increases by 12 nm when Rb is decreased from 10 cm to 1 cm, and a change of 1 nm is obtained for Rb = 3 cm. We also present numerical simulations of the bent fiber that are in good agreement with our measurements, and help us to explain the observations and to predict how high-order dispersion is modified with bending. This study can provide insights for dispersion engineering, in which bending could be used as a tuning, equalization, or tailoring mechanism for λ₀, which can be used in the development of compact nonlinear optical devices based on fibers or other bent-waveguide structures.