Multifunctional optical sensor for simultaneous spectroscopic measurement and adaptive target tracking

(Princeton Docket # 23-4045)

Inventors: Gerard Wysocki, Michael Soskind, Felix Kleemann

This invention is a multifunctional, open-path optical sensing system that enables simultaneous high-sensitivity spectroscopic measurement (specifically methane detection) and real-time tracking of a moving retroreflector (such as one mounted on a drone) using a single, commercially available quadrant photodetector (QPD). The system leverages line-locked wavelength modulation spectroscopy (WMS) at 1653.7/1654 nm, with the QPD serving both as the position sensor for adaptive target tracking and as the detector for extracting the spectroscopic signal from the returned laser beam. The laser output is split into fiber-coupled reference arms for line-locking and calibration, and a free-space path for remote measurement and tracking. The QPD’s X/Y signals are used to actively control a motorized gimbal mirror, keeping the system aligned with the moving retroreflector, while the summed signal is demodulated at the first and second harmonics to extract methane concentration data.

This dual-functionality design eliminates the need for separate tracking and sensing detectors, reducing system complexity, size, and cost compared to traditional approaches that require precise alignment and multiple detection channels. The system achieves a methane detection sensitivity of <10 ppm-m, with an experimentally demonstrated precision of 0.77 ppm-m/Hz1/21/2 at 1-second averaging, and has been validated in both stationary and drone-assisted scenarios. Calibration against a reference instrument (LICOR LI-7810) confirmed accuracy within 3.5% of ground truth. The architecture allows for continuous, real-time data acquisition, robust operation in the presence of atmospheric turbulence, and can be adapted for other gases or optical sensing modalities by changing the laser wavelength or detection scheme.

Key Innovations

• Single-Detector Dual Functionality: Combines gas sensing (achieving 0.77 ppm-m/√Hz sensitivity) and tracking via a quadrant photodetector, eliminating separate detectors and reducing alignment complexity.
• Adaptive Tracking: Uses the detector’s positional output to dynamically adjust mirrors, enabling continuous tracking of mobile platforms like drones.
• Simplified Hardware: Merges optical paths for sensing and tracking, lowering cost and size compared to traditional multi-sensor systems

Stage of Development

• Advanced prototype and field validation stage.
• The system has progressed beyond laboratory development: it has been built, optimized, and tested both in controlled environments and in real-world scenarios, including stationary and drone-assisted field trials. The prototype demonstrated high sensitivity (0.77 ppm-m/Hz1/21/2), accurate methane detection (within 3.5% of a calibrated reference instrument), and robust performance during mobile atmospheric surveys. The technology has been validated against industry-standard instruments, confirming its accuracy and operational reliability in practical applications. While some diagnostic components were included in the proof-of-concept, the core system is ready for integration and further commercialization, with minimal remaining technical barriers to deployment.

Publication
Wavelength modulation spectroscopy for open-path drone-based methane detection

Contact
Renee Sanchez

New Ventures & Licensing Associate • (609) 258-6762 • renee.sanchez@Princeton.edu