Deep-sea optical windows must withstand extreme hydrostatic pressure while maintaining optical transmittance, requiring a balance between mechanical rigidity and optical performance. Increasing thickness enhances structural strength but reduces transmittance. This study proposes a design method for deep-sea optical windows using domestically developed sapphire. Three-point bending tests were conducted on sapphire and silicon specimens, and B-criterion strength was derived using Weibull distribution to account for brittle material properties. Optical transmittance measurements established key design characteristics. Using theoretical formulations for rectangular planar optical windows under uniform external pressure, the initial design was based on experimentally derived sapphire properties. Finite element analysis of the optical window assembly confirmed sufficient structural stability margins above critical thresholds. Linear interpolation was applied to evaluate the continuous design space across discrete thickness values. A compromise solution was identified that satisfies both structural rigidity and transmittance objectives. By integrating experimental material characterization with numerical analysis, this study provides an effective framework for determining the optimal thickness of deep-sea optical windows and confirms the applicability of domestically developed sapphire as a reliable optical window material for high-pressure underwater environments.
