The optical beam deflection method using the knife edge detection technique is one of the
simplest optical sensing methods. We investigate theoretically the limit to the resolution
when sensing the displacements of a mechanical cantilever using the knife edge detection
technique implemented with a quasimonochromatic thermal-like optical source. Simple
formulas for the minimum detectable displacement of the cantilever's front end are derived
assuming all nonoptical noises negligible. It is shown that superluminiscent diodes can yield …