The development of cryptographic keys for traditional and quantum cryptographic systems depends on random numbers. Numerous studies have been conducted on high-bandwidth chaotic semiconductor lasers for high-speed random number generation.
Traditional methods for chaotic lasers with external feedback have limitations, including a time delay signature, sensitivity to perturbation parameters, and complicated modifications for realizing chaotic outputs.
Due to its simple and reliable design, a chaotic solitary laser without external disturbances is a popular arrangement for generating random numbers.
A group of researchers led by Professor Yong-Zhen Huang from the State Key Laboratory of Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China, and the Center of Material Science and Optoelectronic Engineering, University of Chinese Academy of Sciences, Beijing, China has proposed a new approach to control the temporal output of a single semiconductor microlaser by nonlinear means in a new paper published in Science of light and application.
With no external optical or electrical disturbances, the full output of the warped microcavity laser produces a chaotic output, allowing the creation of a simple, manageable, and reliable random signal generator.
It was intended for the Circular Sided Hexagonal Microresonator (CSHM) to improve the Q factors of the passive mode to implement the dual mode laser with the adjustable frequency range. Using a single CSHM laser, nonlinear dynamical states such as chaotic and period oscillation states were achieved.
Directly from the total output intensity of the microlaser, which was limited to 10 Gb/s by the tools used, physical random numbers were derived and verified by statistical tests. A single microcavity laser with a chaotic total output intensity provides a practical and reliable method for generating random numbers rapidly.
To consider the internal modal interaction, including modal coupling, a rate equation model based on field equations is established. Due to mode beating, which enhances mode interaction, the dual-mode laser of fundamental and first-order transverse modes ensures significant oscillation of the carrier within the laser cavity.
The rate equation can be used to predict chaotic dual-mode lasers without the use of external perturbations.
The study team stated: “In a dual-mode laser microlaser, mode pulsing can cause photon density and carrier density oscillations caused by stimulated emission, especially since the mode gap is close to the relaxation oscillation frequency of the laser. The carrier density oscillation will result in side peaks for the laser emission modes as under the external electrical modulation, and will lead to non-linear coupling for the two laser emission modes because the frequency of oscillation is the frequency interval of the two laser emission modes.”
They added, “The procedure to reveal the underlying mechanism of the internal interaction between two transverse modes provides a new understanding of the nonlinear dynamical process in semiconductor microlasers.”
“Although the random bits generated at a bit rate of 10 Gbit s-1 (5GS-1 × 2 bits) is not very high, which is limited mainly by the instruments used in the test, we expect to obtain a higher bandwidth of random bits”, the team also stated.
The team concluded: “There is still a lot of room to improve the random number rate of spontaneous chaotic microcavity lasers. we have effectively improved the chaotic bandwidth of chaotic lasers through optimal design of the resonant cavity, which is expected to generate higher speed physical random numbers under higher bandwidth chaotic signals. In the future, with the development of optoelectronic integration technology, spontaneous chaotic lasers are expected to generate convenient and portable miniaturized random number generators.”
Ma, C.G., et al. (2022) Chaotic microlasers caused by internal mode interaction for random number generation. Light: science and applications. doi:10.1038/s41377-022-00890-w.