## 2 Ultra-High-Speed MCF-Based ICS OTN Prototype System  
In this section, we present our proposed ultra-high-speed MCF-based ICS OTN prototype system, whose architecture is shown in Figure 1. The extremely high bit rate of the system is achieved through next-generation single-wavelength 1.2 Tb/s OTUs and a CDM transmission technique based on 7-core fibers. The ICS capability of the system is enabled by 200 Gb/s ICS OTUs, which can perform the real-time monitoring of environmental disturbances (e.g., shaking and striking) to optical fiber cable while transmitting data. Specifically, at the transmitter station, multiple 1.2 Tb/s OTUs are utilized to transmit ultra-high-speed modulated signals in the C-band, and a 200 Gb/s ICS OTU is employed to transmit ICS signals. The optical signals emitted by these OTUs exhibit distinct central wavelengths and are multiplexed through a wavelength selective switch (WSS). An Erbium-Doped Fiber Amplifier (EDFA) is used to amplify the multiplexed signals, which are then coupled to a fiber core of the 7-core fiber for CDM transmission via a FIFO device. The total transmission link consists of multiple CDM transmission links, each composed of a pair of FIFO devices and a span of 7-core fiber. The FIFO devices facilitate mutual coupling between the 7-core fiber and multiple SMFs. And 7 sets of single-mode (SM) EDFAs are employed between every two CDM transmission links to amplify the 7-channel CDM optical signals. After transmission over multiple CDM links, each path of received WDM signals from the FIFO device is first amplified by an EDFA at the receiver station, and another WSS is used to demultiplex the WDM signals. The demultiplexed signals are then sent to the corresponding OTUs for coherent reception. The 1.2 Tb/s OTUs at the receiver perform a real-time DSP and bit error rate (BER) calculation on the received signals to achieve ultra-high-speed data transmission. Unlike the 1.2 Tb/s OTUs, the 200 Gb/s ICS OTU simultaneously detects the optical status of received signals to sense external environmental disturbances to the MCF cable when performing DSP at the receiver. Considering the structural characteristics of MCFs, where multiple fiber cores are integrated within a single cladding, the ICS signal transmitted through one fiber core is sufficient to sense environmental disturbances affecting the entire MCF. Therefore, as illustrated in Figure 1, in our proposed MCF-based ICS prototype system, only the central core of the 7-core fiber is equipped with a pair of 200 Gb/s ICS OTUs for environmental monitoring, while the remaining six fiber cores are used to transmit ultra-high-speed 1.2 Tb/s optical signals. It should be emphasized that, as shown in Figure 1, due to the lack of sufficient ultra-high-speed 1.2 Tb/s OTUs in the field trial, we employ two pairs of 1.2 Tb/s OTUs with different central wavelengths to test the transmission performance of each fiber core channel. Other wavelength channels in the C-band are filled with white noise generated by a C-band amplified spontaneous emission (ASE) source to simulate a fully loaded C-band WDM transmission. The power of the ASE signal that filled in each wavelength channel is identical to that of each modulated signal emitted by the OTU, and the multiplexing of modulated signals and ASE signals is also performed through the WSS. In our field trial, we test the performance of each fiber core channel individually, which is achieved by manually connecting the output SM pigtail of the transmitter to different input ports of the FIFO device one by one. The remaining six fiber cores are fully populated with C-band ASE signals to simulate a CDM transmission. This is achieved by launching C-band ASE signals  
Figure 1: Architecture of the ultra-high-speed MCF-based ICS OTU prototype system. into the remaining six fiber core channels through the FIFO device. Moreover, considering the length of available MCF cables, the entire transmission link consists of two 70.76 km CDM transmission links in the field trial.