Observation of the Differential Goos‐Hänchen Shifts in Wavelength Domain Using a Helical Fiber Grating

ABSTRACT The Goos‐Hänchen shift (GHS) is a phenomenon in which an optical beam experiences a longitudinal displacement (within the plane of incidence) upon total internal reflection at an interface. Since its discovery in 1947 by Goos and Hänchen, the effect has been extensively studied and applied across various fields. However, all GHS‐related studies reported to date are limited to either the spatial or momentum (wavenumber) domains. In contrast, the direct observation and utilization of such a remarkable phenomenon in the wavelength domain have remained unexplored. In this work, we propose and experimentally demonstrate an enhanced GHS in the wavelength domain using a helical fiber grating (HFG). A dual‐split in the transmission spectrum, arising from the different GHS of the TE and TM modes, or in other words, the degeneracy splitting of the TE and TM modes in the HFG, has been clearly observed, which, to the best of our knowledge, represents the first demonstration of such a well‐known optical effect in the wavelength domain. The proposed method introduces a new degree of freedom for detecting and utilizing the GHS, paving the way for its applications in all‐fiber photonic sensors, optical switches, optical information processing, and high‐precision measurements.