Comparison of different control loop concepts for direct distance measurement using photonic mixing devices (PMD)

This paper presents two different control loop approaches for distance measurement with photonic mixing devices (PMD). Possible all-analog implementations are pointed out, and measurements with two different loop types using our laboratory PMD system are provided. It is shown that the PI control loop implementation reaches distance accuracy comparable to previous modulation methods, but on the other hand suffers from present offsets of the PMD. For the second method, the steepest descent algorithm, contrary results are obtained. This method is not susceptible to offset variations, but requires a fairly high SNR to converge. Finally the requirements for all-analog closed loop implementation imposed on the next generation of PMD elements are pointed out.