A gas turbine engine includes a combustor having a fuel nozzle assembly for delivering fuel to a combustion chamber. A sensor is at least partially housed within the fuel nozzle assembly for sensing a parameter associated with the delivery of fuel to the combustion chamber. In one example, the sensor is an optical sensor coupled to an optical decoder for ascertaining the parameter. A trim valve is in communication with the fuel nozzle assembly. A controller is in communication with the sensor and is programmed to actuate the trim valve to adjust the amount of fuel delivered through the fuel nozzle assembly in response to the parameter. In one example, an end of the optical sensor is arranged near a fuel exit of the fuel nozzle assembly. The controller actuates the trim valve for the fuel nozzle assembly to achieve a desired air/fuel ratio and/or balance the fuel delivery of the fuel nozzle assembly relative to another fuel nozzle assembly within the gas turbine engine's combustor system.