Abstract

The determination of a single mode fiber’s cutoff wavelength, characteristic of the fiber’s index profile, is an important consideration both to verify fiber design and to avoid modal noise¹ in applications such as communication systems and sensors. The use of an effective cutoff wavelength which is characteristic of a particular fiber length, or condition of curvature, can be in error by hundreds of nanometers and can lead to system design errors. After considerable research and experimentation, three types of experiments have evolved to measure the cutoff wavelength of the LP₁₁ mode on a single mode fiber: the far-field measurement of Gambling, et al.,² the near-field transmission measurement of Murakami, et al.,³ and the refracted power measurement of Bhagavatula, et al.⁴ The far-field measurement of Ref. ² provides the normalized frequency V from experimental characterization of the lp₀₁ far-field diffraction pattern, based on the assumption of a step-index profile. The cutoff wavelength can then be obtained by extrapolating from the experimental wavelength to the wavelength which corresponds to the cutoff frequency of a step-index profile.