## 3 Ultra-High-Speed 1.2 Tb/s OTU and 200 Gb/s ICS OTU  
In this section, we introduce the ultra-high-speed 1.2 Tb/s OTU and 200 Gb/s ICS OTU used in our field trial. The 1.2 Tb/s OTU has a modulation rate of up to 130 Gbaud, which enables the adoption of a PCS-64 QAM modulation format to achieve the ultra-high bit rate. The central wavelength of the 1.2 Tb/s OTU is tunable from 1529.553 nm to 1566.723 nm, with a channel spacing of 150 GHz, and it can support a maximum of a 32-wavelength WDM transmission over the C-band. This OTU can also dynamically adjust its bit rate by changing the modulation format. For example, the bit rate can be adjusted to 800 Gb/s by using the PCS-16 QAM modulation format. The 200 Gb/s ICS OTU adopts the DP-QPSK modulation format with a 67 Gbaud modulation rate. Its central wavelength is also tunable over the C-band, with a channel spacing of 75 GHz. The soft-decision forward error correction (SD-FEC) limit for these OTUs is 2.88 \(\times\) 10\({}^{-2}\). Figure 2a shows an interior photo of the test site. The under-test transmission equipment, including the 1.2 Tb/s OTUs, etc., are installed in the equipment rack, and the network management system is utilized to manage the OTN equipment as mentioned before. A photograph of the 200 Gb/s ICS OTUs at the test site is also depicted in Figure 2b. The 200 Gb/s ICS OTU realizes the sensing of environmental disturbances to the MCF cable by detecting and analyzing the variations in the state of polarization (SOP) of the received optical signal during DSP processing. The SOP detection process is synchronous with the DSP and enables the system to simultaneously sense environmental disturbances while receiving transmitted data. The detected SOP is represented by normalized Stokes parameters \(S_{1}\), \(S_{2}\), and \(S_{3}\), which are defined as follows:  
\[S_{1}=\left(I_{x}-I_{y}\right)/I_{total}, \tag{1}\]  
\[S_{2}=\left(I_{+45^{\circ}}-I_{-45^{\circ}}\right)/I_{total}, \tag{2}\]  
\[S_{3}=\left(I_{R}-I_{L}\right)/I_{total}, \tag{3}\]  
Figure 2: (**a**) Interior photo of the test site. (**b**) Photograph of 200 Gb/s ICS OTUs and the signal processing flow at the receiver. where \(I_{x}\), \(I_{y}\), \(I_{+45^{\circ}}\), \(I_{-45^{\circ}}\), \(I_{R}\), and \(I_{L}\) are the intensities of the horizontally linearly polarized component, vertically linearly polarized component, linearly polarized component in the \(+45^{\circ}\) direction, linearly polarized component in the \(-45^{\circ}\) direction, right-handed circularly polarized component, and left-handed circularly polarized component of the received signal light, respectively. And \(I_{total}\) is the total intensity of the received signal light. The 200 Gb/s ICS OTU at the receiver continuously acquires the normalized Stokes parameters \(S_{1}\), \(S_{2}\), and \(S_{3}\) of the received optical signals while performing DSP, and it further analyzes the characteristics of SOP variations through a trained convolutional neural network (CNN). The CNN can determine whether the MCF cable is affected by environmental disturbances and classify the type of disturbances based on the detected SOP of the received signal. The CNN is trained using data from multiple laboratory tests. And during the training process, the focus is primarily on enabling the CNN to recognize and classify three types of environmental disturbances: shaking, periodic vibration, and striking. This CNN enables the ICS transmission system to provide early warnings for optical cable faults. By further incorporating test data involving more types of environmental disturbances such as squeezing or pulling into the training process, this CNN will gain the ability to sense and classify a wider variety of disturbances. It should be noted that the main difference between this 200 Gb/s ICS OTU and existing OTUs lies in the receiver. The polarization property of the transmitted signal is consistent with that of existing polarization-multiplexed (PM) coherent optical transmission systems.