A bidirectional high-speed chaotic optical communication scheme with physical layer encryption is proposed and studied theoretically. The external cavity optical feedback method is analyzed. An erbium-doped fiber amplifier is used to represent the all-optical delay feedback loop of the traditional external cavity; it can overcome the shortcomings of the traditional method such as lower precision and high equipment volume requirements. The bidirectional communication scheme is discussed; it sets the encryption device at the transmitter, uses the correlation between the two encryption signals to decrypt, and cancels the decryption device at the receiver, which not only simplifies the experimental equipment but also solves the problem that the receiver cannot decrypt synchronously due to the channel damage in remote communication. Further, it is easily applied in production and life. Finally, the simulation results show that the bit error rate is <10^−  5, and the bidirectional transmission of 10-Gb  /  s information over an 85-km single-mode fiber is successfully realized.