Photochromic liquid-core fibers with nonlinear input-output characteristics

Photochromic liquid-core fibers were fabricated by using benzene or 2-propanol solution of spirobenzopyran. The fiber element consisting of a benzene-solution core and a silica-glass cladding exhibited variable transmittance that was controlled by ultraviolet irradiation. When a visible laser beam (532-nm wavelength) was used as input signal, output signal power increased nonlinearly with input power due to reversed photochromism. This nonlinear input-output characteristic was observed without ultraviolet light, when a fiber was constructed with 2-propanol solution and a polymer-coated glass tube. These experimental results agreed with the theoretical prediction that was based on a simple photochromic fiber model.