Fig. 1. Schematic diagram of encrypted optical communication system for key hiding and distribution based on ASE (ASE: amplified spontaneous emission; PC: polarization controller; AWG: arbitrary waveform generator; PolM: polarization modulator; MZM: Mach‒Zehnder modulator; OF: optical filter; VOA: variable optical power attenuator; D: dispersion; PM: phase modulator; WDM: wavelength division multiplexer; LP: linear polarizer; SMF: single mode fiber; DCF: dispersion compensation fiber; EDFA: erbium-doped fiber amplifier; PD: photodetector; LPF: low pass filter; CDR: clock and data recovery; BER: bit error rate)

Fig. 2. Transmitted signal spectrum diagram and time domain diagram. (a) Key optical spectrum after PolM modulation; (b) data optical spectrum after PM modulation; after WDM modulation, (c) spectrum of optical signal, (d) detected electrical spectrum, and (e) detected electrical time-domain waveform

Fig. 3. Receive signal spectrum diagrams. (a) Key signal spectrum without polarizer; (b) key signal spectrum with polarizer; (c) data signal spectrum without phase decryption and dispersion compensation; (d) data signal spectrum with phase decryption and dispersion compensation

Fig. 4. Eye images under different βPM. (a)‒(d) Authorized users; (e)‒(h) eavesdroppers

Fig. 5. Influence of βPM on BER of authorized users and eavesdroppers

Fig. 6. Influence of received optical power on BER

Fig. 7. Influence of transmission distance on BER

Fig. 8. Influence of mismatch on BER. (a) βPM mismatch; (b) cryptographic dispersion mismatch; (c) transmission dispersion mismatch