An optical system, an optocoupler, and an isolation device are provided. The disclosed optical system includes at least one photodetector that receives light energy and converts the light energy into one or more electrical signals. The disclosed optical system further includes a comparator module that receives the one or more electrical signals from the at least one photodetector and compares the one or more electrical signals against two different reference values to determine whether a power supply fault condition has occurred for a light source that emitted the light energy and to determine a logic signal conveyed to the at least one photodetector via the light energy emitted by the light source.