Dependence of silicon position-detector bandwidth on wavelength, power, and bias

We have developed a two-LED wobbler system to generate the spatial displacement of total light intensity on a detector surface, facilitating the acquisition of frequency responses up to 600 kHz with high accuracy. We have used this setup to characterize the low-pass filtering behavior of silicon-based position detectors for wavelengths above 850 nm by acquiring the frequency responses of several quadrant detectors and position-sensitive detectors as functions of wavelength, applied bias voltage, and total light power. We observed an increase in bandwidth for an increase in applied bias voltage and incident-light intensity. The combined effect of these parameters is strongly dependent on the detector used and has significant implications for the use of these detectors in scanning probe and optical tweezers applications.