We demonstrate a triple Brillouin frequency spacing, multi-wavelength Brillouin laser combined with two cavities: a single Brillouin frequency spacing cavity and a double Brillouin frequency spacing cavity. In this simple structure, the optimization of multi-wavelength lasing is done with proper adjustments of Brillouin pump (BP) power and 980-nm pump power. When setting the BP power to 3-dBm and 980-nm pump power to 27.78 dBm, up to ten channels with frequency spacing of 0.26 nm are generated. The output wavelength can be tuned in a wide range of 45 nm, from 1525 to 1570 nm. We also compared and analyzed this scheme under the condition of single linear cavity 1 and double ring cavity 2. The proposed multi-wavelength laser has the potential applications in the areas of space optical communication and optical communications and microwave signal source.

In this letter, a chaos-based nonlinear encryption scheme is presented to enhance the physical layer security and reduce the peak-to-average power ratio (PAPR) in an orthogonal frequency division multiplexing passive optical network (OFDM-PON). A four-dimensional (4D) hyper chaotic system is utilized to generate the chaotic binary sequences and construct the nonlinear substitution boxes (S-boxes). With the help of these S-boxes, nonlinear transformation bit data are generated through a cyclic XOR operation with chaotic binary data to improve the resistance against chosen-plaintext attacks (CPAs). A specially designed chaotic constant amplitude zero autocorrelation matrix is used to reduce the PAPR and allow for encryption. We verify the resistance against CPAs with completely dynamic cipher texts in an _~ 10-Gb/s encrypted OFDM-PON transmission over a distance of 25 km. Compared with the standard OFDM-PON, our proposed scheme achieves _~ 2.8-dB PAPR reduction, which compensates for any sensitivity deterioration.

In this article, the micro corner-cube reflector array (MCCRA) is considered as the optical retroreflector in the modulating retroreflector (MRR) free-space optical (FSO) channel and its wavefront compensation accompanying with the pseudo phase conjugate optical return wave in the double-pass propagation is investigated by the theoretical analysis and wave-optics (WO) simulation. By WO simulations, we show the impacts of the shape and size of the retroreflector cell, the whole aperture size of the MCCRA, the turbulence condition on the beam spot, the Strehl ratio and the scintillation index of the return wave. Also, we investigate the limitations caused by the phase errors of the MCCRA and the oblique incidence of the optical beam. Finally, the wavefront compensation is demonstrated by the experiments conducted in a laboratory atmospheric chamber.

In order to improve the complexity of optical chaotic sequence output and the encryption efficiency of bit plane encryption, an image encryption algorithm based on optical chaos and DNA Rubik’s cube scrambling is proposed. An external disturbance structure of light injection is proposed to improve the complexity of the chaotic sequence of light output from the slave laser by the external disturbance generated by the mutual injection between the driving laser and the main laser. Meanwhile, in the image algorithm, in addition to Rubik’s cube scrambling at the pixel level, this paper proposes a bit plane encryption method based on DNA plane Rubik’s cube scrambling, which reduces the amount of encrypted data and further improves the security of image encryption by using encryption selection of different DNA encoding modes. The scrambled images are diffused by DNA calculation and optical chaos sequence at the bit-level and pixel level respectively. Through the quantitative analysis of the security simulation of the proposed algorithm, the results show that the algorithm guarantees a certain encryption efficiency under the condition of good security, the key space is 10⁶⁴, the information entropy of each test ciphertext image is close to the theoretical maximum, and the test indexes of plaintext sensitivity and key sensitivity are close to ideal values. For differential attacks, chosen plaintext attacks, known plaintext attacks, exhaustive attacks, cropping attacks, and noise attacks have good robustness.

The linearity of the laser frequency modulation is a crucial factor that affects the performance of the frequency-modulated continuous wave (FMCW) LiDAR ranging. Nonlinearity can influence ranging resolution and introduce errors. This paper proposes a method for correcting frequency modulation nonlinearity based on waveform preprocessing for the modulation signal of the laser. After correction, the residual nonlinearity (1-r2) of the laser is reduced to $1.85\times 10^{-4}$ for the up-sweeping and $8.47\times 10^{-4}$ for the down-sweeping using the modulation signal with the repetition frequency of 50 kHz. The full-width at half of the maximum (FWHM) of the spectrum decreases by 86% compared to pre-correction, resulting in the ranging error of 0.37% at the distance of 38 cm. With distances of 0.90 m, 1.80 m, 2.89 m, and 4.13 m, respectively, the ranging error stabilizes at 0.2%, and the minimum deflection of distance can reach $8~\mathrm {\mu m}$ .