The wavelength corresponding to the cutoff frequency. 2. In an uncabled single-mode optical fiber, the wavelength greater than which a particular waveguide mode ceases to be a bound mode. Note 1: The cutoff wavelength is usually taken to be the wavelength at which the normalized frequency is equal to 2. 405. Note 2: The cabled cutoff wavelength is usually considered to be a more functional parameter because it takes into consideration the effects of cabling the fiber.