Abstract: A pilot tone generator receives optical energy from an optical communication medium carrying a plurality of optical signals. Each optical signal carries data modulated at a unique wavelength and further modulated with a unique identification signal. The identification signal has an amplitude corresponding to an optical power of the associated optical signal. The pilot tone receiver detects each identification signal from the optical energy received and determines its corresponding amplitude. The pilot tone receiver calculates the optical power of each optical signal in the optical energy in response to the amplitude of the associated identification signal.

Abstract: A method and apparatus for measuring radiometric signals. An infrared energy signal is directed through a sample and combined with a selected signal to reduce the effect of analog-to-digital converter nonlinearity. The combined signal is processed to, for example, accurately and repeatably identify the types of and concentration of molecules within the sample.