Self-exciting optical strain gage

An optical strain gage comprising:

• first and second bridges, each bridge extending between first and second end supports, said bridges and supports having been cut from a single, uniformly doped silicon wafer;
• said first bridge including a reflective wall facing the second bridge;
• said second bridge including a reflective wall parallel to and facing the first bridge wall, the parallel bridge walls defining cavity therebetween;
• means for transmitting light transversely into the first bridge, wherein the transmitted light is reflected between the first bridge wall and the second bridge wall, resulting in a buildup of the intensity of light energy within the cavity, aid buildup inducing vibration in said first and second bridges, the frequency of vibration being related to the strain imposed on the wafer, and
• means, disposed adjacent the bridges, for sensing the vibration frequency of the bridges by measuring the frequency of the variation in the intensity of light energy within the cavity.