A SENSOR FOR MEASURING A FLOW OF A FLUID

A sensor is provided for measuring a flow of a fluid in a physiological environment, such as within a vessel of a human or animal subject. The sensor comprises an interrogation light guide extending from a proximal end to a distal end of the sensor. The interrogation light guide is configured to transmit interrogation light to, and receive reflected interrogation light from, the distal end of the sensor. The sensor further comprises an excitation light guide configured to transmit excitation light to the distal end of the sensor. The excitation light is provided for heating the fluid (directly or indirectly). The sensor further comprises a sensing element located at the distal end of the sensor. The sensing element comprises at least two etalons for reflecting interrogation light back along the interrogation light guide towards the proximal end of the sensor. Each etalon has a respective optical path length and further has at least one reflective surface external to the interrogation light guide. The sensing element is configured to be in thermal contact with the fluid such that the optical path length of at least one etalon is dependent on a temperature of the fluid. The reflected interrogation light forms an interferogram which is dependent on the optical path lengths of the respective etalons.