In the era of rapidly advancing global informatization, information security has emerged as a critical challenge that demands immediate attention. Conventional encryption technologies at the upper layers have proven inadequate in providing comprehensive protection against sophisticated eavesdropping threats, particularly in mission-critical sectors such as national defense, government operations, and financial systems. The imperative to ensure secure signal transmission at the physical layer has become paramount, as it serves as the fundamental safeguard for protecting sensitive data against increasingly sophisticated cyber threats. To enhance the security performance of optical communication systems, we propose a key concealment and distribution encryption optical communication system based on amplified spontaneous emission (ASE) light. Leveraging the broad bandwidth and high-noise characteristics of ASE light sources integrated with dynamic key encryption technology, a unique one-time key is generated for phase-based signal encryption in each data transmission. This approach not only effectively conceals the data and key signals but also enhances the system’s resistance to decryption by immediately updating dynamic keys. Simulation results demonstrate that an on-off keying (OOK) signal with a transmission rate of 5 Gbit/s, after transmitting 50 km, can be accurately received and decoded by authorized users at a received optical power of -10 dBm, with a bit error rate (BER) as low as 2×10^-7. In contrast, the eavesdropper’s BER remains consistently at 0.5, which proves the system’s confidentiality performance. We provide a feasible solution for photonic layer security, contributing to the enhancement of data transmission security and covertness.

The proposed ASE-based key concealment and distribution encryption optical communication system is illustrated in Fig. 1. The ASE light from two ASE light sources with different central frequencies is injected into a polarization modulator (PolM) and a Mach?Zehnder modulator (MZM), respectively. The key signal and data signal generated by an arbitrary waveform generator are loaded onto the PolM and MZM, respectively. The optical signal output from the MZM is fed into a dispersion module to broaden the signal in the time domain. Subsequently, a phase modulator (PM1) is used to perform phase encryption on the broadened optical signal. A variable optical attenuator (VOA) is employed to control the optical power output from the PolM to match that of the phase-encrypted optical signal. The phase-encrypted optical signal and the PolM-modulated optical signal are then combined into a single signal using a wavelength division multiplexer (WDM) and transmitted over single-mode fiber (SMF) to the authorized user. At the receiver, the optical signal is first compensated for dispersion using dispersion-compensating fiber (DCF), and transmission loss is compensated by an erbium-doped fiber amplifier (EDFA). Subsequently, wavelength demultiplexing is used to separate the mixed optical signal into two signals: the phase-encrypted signal and the PolM-modulated signal. The PolM-modulated optical signal passes through PC3 and enters a linear polarizer (LP). By adjusting PC3, the principal axis of the LP is set at 135° relative to the principal axis of the PolM. The signal is then converted into an electrical key signal by a photodetector (PD1). The recovered key signal is loaded onto PM2 to perform phase decryption of the data optical signal. After dispersion compensation, the data signal is recovered by PD2.

The simulation results demonstrate that the proposed ASE-based key concealment and distribution encryption optical communication system can effectively hide the transmitted information in both the frequency domain [Figs. 2(a) and (b)] and the time domain [Fig. 2(c)]. At the receiver, only legitimate authorized users can fully recover the key and data information [Figs. 3(b) and (d)]. Figure 5 illustrates that the phase modulation index should be set within the range of 0.38 to 0.63. Within this range, a balance between encryption and decryption performance can be achieved. Under the condition of a received optical power of -10 dBm, the measured BER of the data signal is 2×10^-7 (Fig. 6). The proposed encryption system supports a maximum transmission distance of 90 km (Fig. 7). To avoid affecting signal demodulation performance, the mismatch between the βPM encryption dispersion and transmission dispersion must be controlled within a specific range (Fig. 8).

To address the information security challenges in metropolitan area network (MAN) optical fiber communications for the military, government, and financial sectors, we propose an encrypted optical communication system based on ASE light sources for key concealment and distribution. Leveraging the broad bandwidth and high noise characteristics of ASE light sources, the system hides both the key and data in the frequency and time domains, achieving high levels of signal transmission concealment and confidentiality. Each transmission is accompanied by the generation and updating of a unique one-time key, effectively preventing the risk of long-term key compromise. Simulation results demonstrate that the system can stably transmit OOK signals at a rate of 5 Gbit/s over a distance of 50 km with a BER of 2×10^-7, ensuring error-free information reception. In conclusion, we not only validate the feasibility of the proposed system but also provide a viable solution for enhancing the physical layer security of optical fiber communications.