An optical accelerometer and method of determining an acceleration are disclosed. In one aspect, an accelerometer includes a light source, a substrate, a light guide attached to a first side of the substrate and configured to redirect light from the light source through the substrate. The accelerometer also includes a light detector, a proof mass attached to a second side of the substrate via one or more springs, wherein the second side is opposite the first side and wherein motion of the proof mass alters a characteristic of the light from the light source reaching the light detector, and a processor configured to determine an acceleration based on the characteristic of the light reaching the light detector.