Abstract: The invention is a method for obtaining a measure of the light propagation time difference for two light-propagating-media paths. The first step consists of generating two substantially-identical frequency-modulated light waves whereby the frequency of the light waves is offset from a reference frequency by a different frequency increment for each basic time interval in each of a plurality of groups of three or more basic time intervals. Each frequency increment is the sum of a specified increment and a frequency-modulation-error increment. The frequency-modulation-error increments associated with the specified increments are independent of each other and unknown. The second step consists of feeding the two light waves into the entry points of two light-propagating-media paths having a light propagation time difference and obtaining a combination light wave by summing the light waves emerging from the exit points of the two light-propagating-media paths.

Abstract: An interferometer amplitude modulation reduction circuit coupled to receive an interferometer output signal from the output of a fiber optic interferometer sensor. The interferometer sensor is excited by a frequency modulated input light signal from a light source having an unwanted amplitude modulation and intensity noise signal component. The interferometer output signal has both wanted interference induced intensity modulation and also unwanted amplitude modulation and intensity noise from the unwanted amplitude modulation and intensity noise signal components present on the frequency modulated input light signal. The invention circuit has a sampling means for sampling a sample portion of the frequency modulated input light signal from the output of the light source. The sampling means detects and the sample portion signal to provide a detected sample intensity signal having a detected unwanted amplitude modulation and intensity noise signal component.