## 1 Introduction  
With the rapid development of high-speed data applications such as 5G, cloud computing, the Internet of Things, and smart cities, fiber-optic communication networks are heavily utilized. The area covered by optical fiber deployment and the density of networks have surged in the past decade, extending across rural areas, towns, and metropolitan regions [1, 2]. Polarization shift keying (PolSK) is a well-known digital modulation technique in the field of communications. Compared to other modulation formats, PolSK has two advantages: (1) It uses the state of polarization (SOP) as a carrier for transmitting information. This greatly reduces nonlinear effects caused by fluctuations in optical intensity within the optical fiber. (2) It supports higher-order modulation and multiple polarization state encoding, which can increase the capacity of transmission [3]. The structural health of communication optical cables and the condition assessment of civil engineering structures hosting these cables are of critical concern for long-term operation and strategic maintenance planning. Distributed fiber-optic sensing (DFOS) technologies utilize the optical fiber as both the signal transmission medium and the sensing element [4]. By detecting variations in the intensity, phase, and polarization state of the propagating optical signals, DFOS enables continuous distributed measurement of perturbations along the fiber [5; 6; 7]. Consequently, it has become an ideal non-destructive structural health monitoring method for large-scale infrastructures in various fields such as energy, power, aerospace, telecommunications, transportation, and security. The reported schemes for fiber-optic communication and sensing integration can be categorized by backscattered light [8; 9; 10] and forward-transmitted light [11; 12; 13; 14]. The former approach results in different optical propagation characteristics, which requires the separate treatment of the communication and sensing signals. This often leads to the deployment of new optical cables and supporting hardware, raising the cost. The latter approach features very similar optical propagation characteristics, which means that optical fiber and hardware (laser source, amplifiers, and demodulator) can be shared, giving rise to lower-cost deep integration. The deep integration of forward transmission distributed sensing and communication facilitates the sharing of the same laser source, optical fiber, wavelength channel, optical signal, and demodulator. Furthermore, sensing is non-intrusive since it only analyzes the vibration information that already exists within the received communication signal, without changing any hardware or taking up additional communication bandwidth. In 2021, researchers from the California Institute of Technology proposed a polarization-demodulation-based sensing system based on Google's Curie submarine optical cable. This system realized earthquake and tidal monitoring over a 10,500 km multi-span optical cable by monitoring the state of polarization (SOP) of optical communication traffic [15]. However, this demonstration did not support vibration positioning or distributed vibration mapping. In the same year, collaborating researchers from the University of L'Aquila in Italy presented an analytical interpretation of the mechanisms behind SOP monitoring [16]. [PERSON] et al. also reported long-distance distributed vibration sensors based on forward transmission [17]. Unlike the polarization demodulation used in this work, their work used the FS-ODL method based on frequency shift and coherent detection. To address the lack of positioning ability for polarization-based forward-transmission distributed fiber-optic vibration sensors, which can be used to realize PolSK communication-sensing integration, we demonstrate a new sensing scheme based on polarization demodulation, forward transmission, and phase-spectrum time delay.