a high data rate optical signal is inverse multiplexed into a multitude of lower - rate tributaries , each of which is coded by its unique ocdm code , and the combined coded tributaries are injected into a common phase scrambler . coherent summation of these optically encoded tributaries pass through a shared phase or phase and frequency scrambler before exiting the secure location . the setting of the scrambler acts as the key . the authorized recipient with the correct key retrieves the ones and zeros of the several decoded signals .