Patent ID: 7512237

Claim:
A method of secure optical communication between a transmit-node operably coupled to a receiver-node, said transmit-node and said receiver-node having a shared secret key, said method comprising the steps of: generating a transmit-side plaintext digital data word at a transmit-side current time and synchronously generating a receiver-side plaintext digital data word at a receiver-side current time, said transmit-side plaintext digital data word dependent on a first time value indicative of said transmit-side current time, said receiver-side plaintext digital data word dependent on a second time value indicative of said receiver-side current time adjusted by an optical signal transmission time; encrypting said transmit-side plaintext digital data word to generate a transmit-side ciphertext digital data word and synchronously encrypting the receiver-side plaintext digital data word to generate a receiver-side ciphertext digital data word, said transmit-side plaintext digital data word and said receiver-side plaintext digital data word being encrypted with the shared secret key; converting said transmit-side ciphertext digital data word into a transmit-side ciphertext analog data signal and synchronously converting the receiver-side ciphertext digital data word into a receiver-side ciphertext analog data signal; modulating a transmit-side carrier signal having a first frequency with said transmit-side ciphertext analog data signal to output a first transmit-side frequency modulated privacy signal and synchronously modulating a receiver-side carrier signal having said first frequency with said receive-side ciphertext analog data signal to output a first receiver-side frequency modulated privacy signal; combining a first transmit-side frequency modulated information bearing signal with said first transmit-side frequency modulated privacy signal to obtain an encrypted transmit-side frequency multiplexed electronic information bearing signal; generating a transmit-side optical frequency modulated signal by frequency modulating a transmit-side optical carrier signal with said encrypted transmit-side frequency multiplexed electronic information bearing signal; transmitting said transmit-side optical frequency modulated signal to said receiver-node; detecting said transmit-side optical frequency modulated signal at said receiver-node; converting said transmit-side optical frequency modulated signal detected at said receiver-node into said encrypted transmit-side frequency multiplexed electronic information bearing signal; and extracting said first transmit-side frequency modulated information bearing signal from said encrypted transmit-side frequency multiplexed electronic information bearing signal by using said first receiver-side frequency modulated privacy signal to cancel out the first transmit-side frequency modulated privacy signal.