A tunable optical filter (30) includes a thin film waveguide (10) and a ring (308) surrounding the thin film waveguide. The ring can be mechanically pressed inwardly toward or pulled outwardly away from the thin film waveguide by external radial forces (306). A central wavelength of the tunable optical filter can be tuned according to the external radial forces. The thin film waveguide includes a substrate (102) and a multi-layered thin film (104) deposited on the substrate. The multi-layered thin film includes high refractive index layers (106) and low refractive index layers (108) alternately superposed on one another to form the multi-layered structure.