## 1 Introduction  
With the unprecedented expansion of high-quality network applications such as computility networks and financial dedicated network services, there is a growing demand for high-speed highly reliable optical interconnection systems. To ensure the operational security of high-speed optical transmission networks, the transmission system needs to be capable of sensing external disturbances to the optical fiber cable, thereby providing advance warnings of potential failures and performing switching operations. In order to achieve this ability, integrated communication and sensing (ICS) techniques have attracted significant attention and been widely investigated, and they can offer a dual functionality in terms of high-speed data transmission and real-time environmental monitoring (e.g., temperature, strain, and vibration detection) [1]. The additional sensing ability of ICS systems enables the real-time acquisition of environmental parameters or the prediction of potential failures, and it can find applications in smart cities, industrial automation, and infrastructure health management [2; 3]. However, traditional optical fiber sensing methods will inevitably occupy communication channels, posing a formidable challenge to simultaneously achieving ultra-high-speed transmission in existing optical communication systems based on widely deployed single-mode fibers (SMFs) [4; 5]. Although constructing more optical fiber cables can, to some extent, solve the problem of insufficient transmission capacity and meet the bandwidth requirements for sensing, it is extremely costly and will occupy a large amount of spatial resources. Recently, space-division multiplexed (SDM) transmission techniques utilizing few-mode fibers (FMFs), multi-mode fibers (MMFs), or multi-core fibers (MCFs) have been widely investigated and are considered promising solutions for supporting capacity-consuming services in next-generation optical networks [6; 7; 8]. Similar to mature wavelength-division multiplexed (WDM) transmission systems, the multiple parallel spatial channels (e.g., fiber modes or fiber cores) within a single fiber cladding can multiply the transmission capacity of a single fiber without significantly increasing its size. In terms of the types of utilized optical fibers, there are two technical routes for achieving SDM transmission. For the mode-division multiplexed (MDM) technical route using FMFs or MMFs, a record ultra-large-capacity transmission is achievable due to the abundant mode resources [9; 10; 11]. However, costly multiple-input multiple-output digital signal processing (MIMO-DSP) is required at the receiver to eliminate the inevitable modal crosstalk induced by mode multiplexers/demultiplexers and fiber transmission to achieve ultra-high-speed long-haul transmission, which hinders direct compatibility with existing high-speed optical modules [12]. In contrast, the core-division multiplexed (CDM) approach using MCFs suppresses inter-core crosstalk easily, because different SDM signals are transmitted over separate fiber cores, enabling long-haul transmission and compatibility with existing optical modules via fan-in/fan-out (FIFO) devices [13; 14]. In the past decade, high-speed transmission and effective fiber maintenance technologies based on uncoupled MCFs have been widely investigated, and multiple remarkable breakthroughs have been made. For example, an advanced four-core fusion splicing technique utilizing a precise azimuthal alignment algorithm and a three-electrode arc-discharging splicer has been reported, demonstrating an average splicing loss of less than 0.03 dB [15]. Regarding FIFO devices, multiple precise fabrication methods, such as fiber bundle alignment or femtosecond laser direct writing, have been proposed and experimentally demonstrated, enabling the implementation of various MCFs with different numbers of fiber cores [16; 17].