Is It possible that via changing a sensor voltage detecting a specific wevelength?
do we have this kind of sensor?
do we have this kind of sensor?
Varactor was my guess, too.It is common to tune a microwave resonant cavity circuit using a voltage-variable capacitance diode, but that does not detect a specific frequency, it only changes a resonant frequency.
To get any kind of useful answer you will need to provide a whole lot more information as to what you are trying to accomplish. Otherwise the responses will just be guesses.