Flexural waves on fiber and fiber Bragg gratings generated with applied ultrasounds and loading were used for switching the reflection wavelength of fiber Bragg grating and for controlling the transmission spectra of fiber. By producing lateral vibration of a fiber Bragg grating, which has been etched in cladding, it was found that the reflection wavelength could be switched from the Bragg wavelength to other wavelengths, which corresponded to the conditions of strong coupling between core mode and cladding modes. By adjusting the applied voltage for acoustic waves, the relative strength of different reflection wavelengths could be well adjusted. Theoretical analysis of phase-matching condition indicated that the diameter of etched cladding played a key role in controlling the switched reflection wavelength. Flexural waves were also generated on fiber by applying loading with one or two periodically corrugated plates. By adjusting the orientation of the periodical corrugation, loading level, and the relative position of the two corrugated plates, depressions of transmission spectrum at various wavelengths could be well controlled. The spectral depressions were caused by the coupling between core mode and various cladding modes. Such depressions were used for gain equalization of erbium-doped fiber amplifiers. The equalization operation was more efficient with curved fiber under loading. Control of fiber curvature for various forms of spectral depression will be discussed.