SDR-ToF: Million Optical Depth Samples per Second Using Software-Defined Radio

We present a continuous-wave time-of-flight CW-ToF sensing system capable of megahertz-rate depth measurements using a free-space laser and commodity radio-frequency (RF) communication hardware. Existing high-speed optical displacement and vibration sensing systems typically rely on optical interferometry or specialized heterodyne electronics, making them complex and expensive to deploy. We instead show that commodity software-defined radios (SDRs) can serve as a programmable optical sensing backend by jointly performing laser modulation and RF demodulation of signals measured by a fast photodiode. This architecture enables direct phase-based depth estimation at megahertz temporal rates without requiring optical interferometry. Because both the modulation frequency and readout pipeline are fully programmable in software, the system allows flexible trade-offs between depth range, precision, and temporal bandwidth. The resulting sensor supports high-speed depth and vibration measurements, enabling applications such as monitoring rapidly moving mechanical systems, and reconstructing acoustic signals from vibrating surfaces. We experimentally evaluate a prototype system across multiple sensing scenarios and demonstrate sub-millimeter depth sensitivity at megahertz sampling rates, while analyzing practical limitations including noise, drift, and hardware constraints. Our results show that commodity RF hardware can enable low-cost, high-speed optical depth sensing, opening new opportunities for computational imaging and dynamic scene analysis.