A Personal Review of 25 Years of Fiber Grating Sensor Development

Early efforts developing smart structures started with strain sensors based on interferometeric techniques. It immediately became apparent that structural engineers were used to dealing with conventional electrical strain gages and thermocouples with much shorter gage lengths. The fiber grating offered a competitive solution for the measurement of strain and temperature with the advantages of electrical isolation and improved ruggedness. The principal draw back was cost. So early applications involved high value projects where the unique capabilities of the technology offered superior performance. One area of particular interest involved the usage of fiber gratings to sensor more than one parameter simultaneously. Multi-dimensional strain and the measurement of pressure and temperature were two key examples of multi-parameter sensing. In parallel efforts were conducted to operate at high speed. Early examples in aerospace and civil structures were at speeds in the range of 10 kHz. Ballistic work later dictated increasing speeds to 5 MHz. Much more recent work with burn, deflagration and detonation has involved measurements from more than 100 MHz to multiple GHz. This paper provides a personal history of some of these developments and how fiber grating sensor technology is moving into the future.