Instantaneous fourier frequency analyzer using an interferometer

Abstract

Abstract INSTANTANEOUS FOURIER ANALYSIS OF THE FREQUENCY COMPONENTS IN A SIGNAL IS PERFORMED BY MEANS OF THE ANALYSIS OF THE PATTERN OF INTERFERENCE FRINGES PRODUCED BY TWO COHERENT LIGHT BEAMS, WHICH ARE INTENSITY MODULATED IN ACCORDANCE WITH THE SIGNAL AND WHICH ARE PROVIDED WITH A SYSTEMATICALLY VARIED PHASE DIFFERENCE BETWEEN INTERFERING RAYS IN THE BEAMS. THE PHASE DIFFERENCE IS VARIED IN ACCORDANCE WITH A LINEAR FUNCTION OF THE ALGEBRAIC PRODUCT OF TIME AND ANY FUNCTION OF DISTANCE FROM A POINT IN THE INTERFERENCE PATTERN WHERE THE PHASE DIFFERENCE IS ALWAYS EQUAL TO ZERO. IN ONE EMBODIMENT, THIS TYPE OF VARYING PHASE IS OBTAINED BY APPLYING A SAW-TOOTH TIME VARYING ELECTRIC VOLTAGE ACROSS A PAIR OF COMPOUND PRISMS, MADE OF ELECTRO-OPTIC MATERIAL IN PART, UPON WHICH THE BEAMS ARE INCIDENT IN EACH ARM OF A MICHELSON INTERFEROMETER ARRANGEMENT, THEREBY DEFLECTING THE BEAMS THROUGH AN ANGLE WHICH IS LINEARLY PROPORTIONAL TO THE TIME AFTER EACH SAW-TOOTH HAS COMMENCED. OBSERVABLE CHANGES IN THE PATTERN OF INTERFERENCE FRINGES OCCUR WHEN THE LIGHT INTENSITY IS THUS MODULATED IN ACCORDANCE WITH THE SIGNAL, AS COMPARED WITH NO SUCH MODULATION, AND THESE CHANGES OCCUR ONLY AT POSITIONS IN THE INTERFERENCE PATTERN DETERMINED BY THE RESPECTIVE FREQUENCY COMPONENTS IN THE SIGNAL.

Inventors

• 👤 Herwig W Kogelnik

Bibliographic Details