A fiber optic micro-probe array with wavelength-division-multiplexing technique for ultrasonic field measurements

For measuring high frequency ultrasonic fields which are often spatially distributed and transient, an array probe with small element sensors is highly required. In this report, we propose a micro-probe array which is based on wavelength division multiplexing technique. The element sensor consists of a micro optical cavity of 100 μm long made at the end of optical fiber. Optical pass length of the cavity is changed by the applied acoustic field, and the modulation of output light intensity is monitored at another end of the fiber for the information of the acoustic field. Array of sensor elements and a light source as well as a photo detector are connected together by an optical star coupler. The Fabry Perot resonance wavelength of each sensor element is designed different one another, and the outputs from the sensors are discriminated by sweeping the wavelength of injected light with the use of a tunable semiconductor laser. The fabrication technique is first described in this report, and the performance of the micro-probe array is discussed experimentally