METHOD OF DETERMINING UNBALANCE OF TWIN-WAVE INTERFEROMETERS Russian patent published in 1994 - IPC

FIELD: microwave and infra-red technique. SUBSTANCE: method involves exciting a twin-wave interferometer by radiation, measuring signals at its output corresponding to at least different relative unbalances of its arms which differ from each other by a predetermined magnitude at which a phase difference in these unbalances is not multiple of 180 degrees, calculating a desired unbalance from the measured signals, in one of the arms of interferometer radiation being modulated and the interferometer output signals being measured by a detector non-sensitive to the components of amplitude-non-modulated signals. Furthermore, there are versions of this method which are characterized in that modulated components of signal at the output of interferometer are measured by a phase-sensitive demodulator, e.g. by synchronous detection technique. Besides, versions where radiation is modulated by phase, by amplitude, by carrier-free double-band amplitude modulation technique and so on are possible. Versions where radiation is amplitude-modulated such that a modulating function is piece-wise continuous and takes two values modulo equal but differing in a sense, particularly when modulating function represents a Walsh function are effective. Versions where radiation is modulated not only in one arm of interferometer but in the other one as well are possible, modulation frequency in the second arm of interferometer differing from the same in the first arm and measurements at the output being performed at a difference frequency or (and) sum frequency. The method permits to measure both phase and amplitude unbalances of interferometer that is, phases and amplitudes of transmission or reflection coefficients of objects being investigated. EFFECT: enhanced accuracy and reliability. 8 cl, 3 dwg