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Photonics

Covert Key Generation and Distribution Based on Gain Switching Laser

Yibo Liu, Huatao Zhu, Feng Jiang, Tong Xu, Hui Li, Xin Zhang, Shuyan Chen, Shisi Chen

Published Jun 29, 2026• 0 citations
Publisher

Abstract

This article proposes and experimentally demonstrates a covert key distribution scheme based on the phase fluctuation of a gain-switched laser diode (GSLD). The gain-switched pulse is used to generate the covert signal through spectral broadening and temporal spreading. The amplified spontaneous emission (ASE) light is used to generate ASE noise in the public channel. Eavesdroppers cannot perceive signals hidden in the public noise. The experimental results show that the correlation coefficient of the key waveforms reaches 0.95, and the scheme’s key generation rate (KGR) reaches 1.88 Gbit/s through a 25 km single-mode fiber (SMF). Moreover, the binary bitstreams have passed the NIST statistical test suite. The covert key distribution scheme proposed in this article provides an efficient way for the method of “one-time-pad” key distribution in high-speed optical communication systems.

DOI
10.3390/photonics13070627

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This article proposes and experimentally demonstrates a covert key distribution scheme based on the phase fluctuation of a gain-switched laser diode (GSLD). The gain-switched pulse is used to generate the covert signal through spectral broadening and temporal spreading. The amplified spontaneous emission (ASE) light is used to generate ASE noise in the public channel. Eavesdroppers cannot perceive signals hidden in the public noise. The experimental results show that the correlation coefficient of the key waveforms reaches 0.95, and the scheme’s key generation rate (KGR) reaches 1.88 Gbit/s through a 25 km single-mode fiber (SMF). Moreover, the binary bitstreams have passed the NIST statistical test suite. The covert key distribution scheme proposed in this article provides an efficient way for the method of “one-time-pad” key distribution in high-speed optical communication systems.
In this paper, a secure key generation and distribution scheme based on the phase noise of an amplified spontaneous emission source is proposed and experimentally verified. A giant key generator that contains two distribution arms is used to generate a specific beat dependent on the path length difference of the arms. Through the method of balanced subtraction of the local signals, the effect of the intensity noise has been mainly excluded, and the two legal users obtain the consistent differential signal that depended on the phase noise. Experiment results show that the correlation coefficient of the key signals reaches to about 0.89, and the bit generation rate of the scheme achieves to 3.06 Gbit/s under a length of 20 km standard single-mode optical fiber route, as the bit error rate stays under 0.02%. Moreover, the converted digital key stream has passed the NIST statistical test suite, which means that the scheme is inherently random in the statistical sense. With the excellent performance mentioned above, the proposed scheme provides a simple and efficient solution for the method of one-time pad.
The phase fluctuations that occurs during the pulse generation process in a gain-switched laser diode (GSLD) can be utilized to generate true random numbers. However, it is difficult to ensure consistency when using GSLD for key distribution. For the first time, a key distribution scheme that employs GSLD is proposed and demonstrated by a proof-of-concept experiment. By controlling the GSLD’s modulation current and bias current, optical pulses with random phase fluctuations can be generated. Using a Mach-Zehnder interferometer (MZI), the phase fluctuations of light pulses are converted into amplitude fluctuations. In order to improve the consistency of the key distribution system, the difference in the time delay between Alice’s and Bob’s MZIs is controlled to be 1 ps. A key distribution with a waveform consistency of 0.94 and a key consistency of 0.95 is achieved, providing a reference scheme for real-time secure communication.
High-speed physical-layer secure key generation and distribution (SKGD) schemes via channel reciprocity are achieved using external electro-optical modulation or random source distribution via additional fiber links. Here, we propose and demonstrate an SKGD scheme using the fluctuation of polarization states from an amplified spontaneous emission (ASE) source, without any external electro-optical modulation or additional fiber link. Experimentally, an error-free key generation rate (KGR) of 10.1 Gb/s is achieved over a 10-km standard single-mode fiber (SSMF), with true randomness originating from ASE. Moreover, the single fiber channel can be shared for SKGD as well as data transmission, allowing the integration of the proposed SKGD with the deployed fiber infrastructure.
We propose and experimentally demonstrate a stable secure optical communication system with no need for secure key distribution. In this scheme, the amplified spontaneous emission (ASE) noise is used as the optical carrier to hide the signal both in time and frequency domain. The coherence length of the ASE noise is pretty short so that it is extremely difficult for an eavesdropper to intercept the signal. Only one Mach-Zehnder interferometer exists in the receiver, and there is no need for the receiver to match the optical delay. By this way, the optical delay and the polarization fluctuation caused by the environment can be automatically counteracted in the returning path. Therefore, no key distribution is required, and the optical delay value can be changed dynamically as a secret key in the receiver. In our experiment, 1Gb/s encrypted on-off keying signal is securely transmitted over 25km standard single mode fiber and dispersion compensation fiber.
Amplified spontaneous emission (ASE) light is a common noise in optical communication systems with optical amplification, and a suitable optical carrier for optical covert communication. To deeply covert the secure signal, an in-band subnoise optical covert communication scheme is proposed and demonstrated by a proof-of-concept experiment. The power spectral density of optical secure channel is 10 dB less than the optical noise in the public channel. The covert signal is hidden in both optical and electrical domain, and can be transmitted with error-free. The trade-off between covertness and availability is discussed.
Amplified spontaneous emission (ASE) noise with inherent quantum nature is promising for true random number generator (TRNG) and secure key generation and distribution (SKGD). A high-speed TRNG and a physical-layer SKGD scheme are proposed and demonstrated using the polarization dynamics of an ASE source. The ASE-based randomness is enhanced in TRNG using digital signal processing on the two orthogonal polarization modes, while the fluctuation of the state of polarization (SOP) in ASE is applied as the random source in SKGD. A 16.8 Tb/s TRNG is successfully demonstrated with spectrum slicing of ASE. An error-free SKGD with a key generation rate (KGR) of 10.1 Gb/s is demonstrated over a 10-km standard single-mode fiber channel.