OptoLink: Breaking Memory Bandwidth Bottlenecks in FHE Accelerators with Photonic Interconnects

Fully Homomorphic Encryption (FHE) enables secure computation directly over encrypted data, making it highly valuable for domains such as healthcare, finance, and cloud services. However, its deployment is still constrained by immense computational overheads and critical memory bandwidth limitations, particularly in CKKS bootstrapping and the Number Theoretic Transform (NTT). While recent hardware accelerators have improved arithmetic throughput, they remain constrained by inefficient memory transfers and off-chip communication overhead. To overcome these limitations, we introduce OptoLink , a photonic interconnect architecture at the chiplet scale. By exploiting Wavelength Division Multiplexing (WDM) and Space Division Multiplexing (SDM), OptoLink delivers ultra-high throughput and low-latency data transfer. Our design achieves up to 1.6 TB/s of bandwidth across 128 optical channels, representing a 300 × latency reduction compared with conventional electronic network. In addition, OptoLink provides efficient broadcast and multicast capabilities, significantly reducing redundant data movement. Using an extended FHE simulation framework, we show that OptoLink improves CKKS bootstrapping throughput by up to 11 × on HEAX and 1.6 × on F1 and ARK, while reducing memory transfer delays by orders of magnitude. Furthermore, encrypted machine learning workloads, including logistic regression training and ResNet-20 inference, benefit from higher throughput and alleviated bandwidth pressure, demonstrating the potential of OptoLink to enable practical large-scale FHE acceleration.