Reversible All-Optical Modulation Based on Evanescent Wave Absorption of a Single-Mode Fiber With Azo-Polymer Overlay

An etched single-mode fiber with azo-polymer overlay is made by the chemical etching method. The fiber´s cylindrical symmetry is maintained and the refractive index of the azo-polymer is controlled to be lower than that of the fiber to keep the waveguide structure. By altering the refractive index of the azo-polymer in course of its photoisomerization, the evanescent wave absorption is controlled, based on the penetration depth changing of the evanescent wave, and eventually modulates the optical power transmitted though the fiber. Under cyclical irradiation of UV light and visible light, reversible modulation of the transmitted optical power at 1550 nm is achieved.