FPGA-Based Feedback Control of an Optical Tweezer for Biomedical Measurements

Optical tweezers (OTs) are a well-established technique in biology that allows to manipulate matter at the microscopic level. Using the property of focalized lasers to attract very small objects to their focal point, it is possible to estimate mechanical properties of living cells or to implement so-called information engines. We developed a full electronic setup, including custom electronic boards and signal conditioning circuits based on a field programmable gate array (FPGA) that controls the intensity of an OT based on the position of a trapped bead. In the presented setup, a quadrant photodetector (QPD) is used to encode the position, which is then reconstructed directly in the FPGA. This information can subsequently be utilized by various control algorithms. Thanks to the architecture of the FPGA firmware, the overall delay of the feedback loop is lower than the timings required by the physical system, allowing for the implementation of a positionclamp. We describe the experimental setup used to conduct two distinct case studies. For both experiments, a unique FPGA firmware is used, implementing different control methods.