FPGA-based frequency estimation of a DFB laser using Rb spectroscopy for space missions

Stable laser light sources are necessary for atom interferometry based experiments on space platforms such as sounding rockets or satellites. Diode lasers, commonly used as light sources in these experiments, lack long term stability, therefore external frequency stabilization systems are required. Commonly used spectroscopy based systems require the correct optical atomic reference transition to be manually identified before analog circuits can start tracking this transition. For automated systems, latencies below 100 fis are required making the design of such systems challenging. In this paper a scalable architecture for an automated FPGAbased frequency estimation using correlation based matching algorithms is introduced. The architecture is variable in terms of the matching algorithm (SAD/SSD/CC) as well as the number of matching cores. Due to the selected algorithm a frequency estimation error below 0.9 MHz is reached. The scalable architecture allows the variation of the execution time between 25.5 ms and 60.1 μs depending on the number of cores between 1 and 512. To reach the latency constraint, 277 or more cores have to be used. The configuration featuring minimal latency and optimal accuracy (512 SAD cores) requires less than 60% logic elements, 35% registers and 10% memory bits of an Alters Cyclone IV (EP4CE115) FPGA. To investigate the latency as well as the FPGA resource and power consumption, a full design space exploration of the laser frequency estimation architecture is performed.