## 1 Introduction  
With the development of high-performance computers (HPC) and hyperscale data centers, especially driven by the rapid progress in artificial intelligence (AI) and AI-generated content (AIGC), the demands for computing capability and data interconnects are increasing significantly [1, 2, 3]. There are increasing demands for high-speed and low-latency board-level and chip-to-chip interconnects. such as all-to-all GPU communications, in order to optimize overall system performance [4, 5]. Electrical 100 Gb/s and 112 Gb/s single-lane interconnect standards are defined by IEEE 802.3 ck and OIF CEI-112G [6, 7]. However, due to the skin effect of copper itself in the printed circuit board (PCB), the loss of copper wires increases significantly with the transmission data rate [8, 9]. Optical interconnects have intrinsic advantages in terms of bandwidth, potential in data rate evolution, and power consumption in comparison with their electrical counterparts [10, 11]. Active optical devices for board-level optical interconnects with a single-lane 4-level pulse amplitude modulation (PAM4) transmission rate above 100 Gbps have been reported [12, 13, 14]. Polymer waveguides are attractive transmission media in board-level optical interconnects application due to their advantages such as low transmission loss, large bandwidth, low cost, and mass-producibility [15, 16, 17, 18, 19, 20, 21]. Interconnecting chips and pluggable optical modules with multimode waveguides instead of traditional copper wirescan significantly reduce link loss and power consumption [22; 23]. In addition, multimode polymer waveguides can be conveniently coupled to and from 50-\(\upmu\)m multimode fibers (MMFs) with a negligible coupling loss and a large alignment tolerance [24; 25]. Standardized pluggable interfaces offer significant benefits for maintaining optical circuit boards (OCBs) and adjusting their topological networks. OCBs with pluggable interfaces based on multimode polymer waveguides have been reported [26; 27]. The flexibility of polymer waveguides also provides obvious advantages in board-level optical interconnects application where space is limited [28; 29; 30]. Compared to MMF ribbons, flexible polymer waveguide films fabricated using polynorbornene by a \"Photodressing\" technology have a much slimmer thickness and show little degradation in bandwidth due to bending or twisting when they are bent three times at a bending radius of 1 mm or twisted for four full turns, respectively [31]. The meter-scale polymer waveguide can be integrated into larger-area OCBs, facilitating the accommodation of more complex interconnect topologies and more optical chips and devices with ease. A 40 Gbps non-return-to-zero (NRZ) transmission and a 56 Gbps PAM4 transmission in 1 m-long waveguide have been demonstrated [32; 33]; however, there are few reports on the meter-scale multimode polymer waveguide that support single-lane 100 Gbps transmission [34]. In this paper, we demonstrated single-lane 100 Gbps VCSEL-based PAM4 transmission at a wavelength of 850 nm over 12-channel meter-scale long connectorized paper-like flexible multimode polymer waveguide films with a large BLP to the best of our knowledge. The measured BLP of the multimode waveguide with a graded index in the horizontal direction is greater than 57.3 GHz-m at 850 nm under the strictest overfilled launch condition with a maximum length of 2.1 m and 10-dB insertion loss. The average insertion loss of the connectorized waveguides is about 0.042 dB/cm with inter-channel crosstalk as low as \(-\)46.4 dB under the overfilled launch condition. The flexible polymer waveguide has lower bending loss compared to that of the OM3 MMF ribbon when bent to a radius of less than 6 mm. The measured polarization-dependent loss (PDL) of both 1 m and 1.7 m-long waveguides is not larger than 0.05 dB under both the underfilled and overfilled conditions.