Hydrogen sensing system with dichroic element, and method employing the same

An optical gas sensing system (1) for sensing hydrogen in a fluid is provided. The system comprises: an optical sensor (100) comprising a fiber (15), the fiber including at an end portion a sensor element (21) with a sensing layer (22) configured to change its dielectric properties depending on a gas partial pressure at the sensing layer (22); at least one light source (55) for coupling light with a first spectrum into the optical sensor (100); a dichroic element (35) provided in the light path between the light source (55) and the sensor element (21); a light detection unit (58) comprising a light dispersion device (59) and at least two photodetectors (61); wherein the light detection unit is configured for detecting light reflected by the dichroic element (35) and light reflected or transmitted by the sensor element (21), after it has passed the light dispersion device (59), with the at least two photodetectors (61); and a control unit (70) operatively coupled to the light detection unit (58). Further, a respective detection method for a gas in a fluid is provided, and electrical transformers employing the gas sensing system and method.