## 1 Introduction  
As is well known, there are several methods for optical communication multiplexing, including wavelength division multiplexing (WDM), optical time division multiplexing (OTDM), and polarization multiplexing (PM). Coherent optical communication based on polarization-multiplexing was extensively studied in the 1980s due to the high sensitivity of coherent receivers, which could enhance unrepeated transmission distance [1]. However, related research and development were interrupted in the 1990s due to the rapid advances in high-capacity WDM systems. In 2005, the demonstration of digital carrier-phase estimation in coherent receivers sparked renewed interest in coherent optical communications [2, 3]. This was because the digital coherent receiver allowed for a variety of spectrally efficient modulation formats, such as M-ary phase-shift keying and quadrature-amplitude modulation (QAM), which rely upon stable carrier-phase estimation in the digital domain. Additionally, linear transmission impairments, such as group-velocity dispersion (GVD) and polarization-mode dispersion (PMD) of transmission fibers, can be addressed via digital signal processing (DSP). These advantages of the born-again coherent receiver afford considerable potential for innovating existing optical communication systems. Recently, 100-Gb/s transmission systems, which employ QPSK modulation, polarization-division multiplexing, and phase diversity homodyne detection assisted with high-speed DSP at a symbol rate of 25 Gbd, have been developed and introduced into commercial networks [4]. Worldwide efforts are now underway to develop coherent receivers that can handle a bit rate of over 400 Gb/s per WDM channel. In recent decades, there has been a growing focus on enhancing the security of fiber-optic communication through the use of optical chaotic secure communications that employ various devices [5]. As these methods have become increasingly capable of high-speed and high-capacity data transmission, most of the current studies are focused on multi-channel optical chaotic secure communications, including WDM, OTDM and PM chaotic secure communications. Efforts in this area aim to develop secure communication systems that can operate over multiple channels simultaneously, with the goal of improving both the speed and security of fiber-optic communication. Several researchers have already demonstrated successful implementations of WDM and OTDM chaotic secure communications. Furthermore, as digital signal processing (DSP) becomes increasingly integrated with coherent optical communication, high-speed coherent optical transmission systems are poised to play a more significant role in the global optical network infrastructure. The ongoing evolution of fiber-optic communication promises significant enhancements in both capacity and security. As a result, coherent optical chaotic secure communication (COCSC) has generated considerable interest from researchers and industry experts who are working to explore and develop this promising technology. However, it is worth noting that to date, COCSC has not been widely reported and there are several new challenges in key areas of the technology that will need to be addressed moving forward. These new challenges include the following: first, knowing how to realize multi-channel COSCs with high-speed and high-capacity, and second, knowing how to achieve high-quality chaotic synchronization and coherent demodulation. It is anticipated that quantum dot spin vertical-cavity surface-emitting lasers (QD-Spin-VCSELs) can be employed to implement high-speed and high-capacity multi-channel coherent optical chaotic secure communications (COSCs). QD-Spin-VCSELs possess femtosecond dynamic characteristics [6], temperature stability [7], lower lasing current [8], ultra-large bandwidth [9], and independent control of output polarization [10; 11; 12], making them well-suited for the realization of multi-channel COSCs with high-speed and high-capacity.