Tunable photonic differentiator via Bloch surface waves

Optical differentiation is an exceptional real-time edge detection technology that enables extracting the image features, yet current optical differentiators are still lacking a resolution tunability. Based on the Bloch surface waves excited in a prism/one-dimensional photonic crystal structure, a wavelength-tuned optical differentiator with a high sensitivity ( ∂ r s / ∂ λ = 3.5 × 10 3 ) is proposed since any minute variation of the wavelength will easily give rise to a dramatic change in the Goos–Hänchen shifts of two reflected orthogonal components. Via the polarization transformation and extinction, the reflected output field can be approximately expressed as a first-order differential of the input field, and thus, it can operate the edge detection along one orientation. Our scheme can extend to two-dimensional edge detection by rotating the object and may find potential applications in cell and molecular imaging. Graphical abstract