Modifications to condenser microphone theory yield new expressions for the membrane deflections at its center, which provide the basic theory for the fiber optic microphone. The theoretical analysis for the membrane amplitude and the phase response of the fiber optic microphone is given in detail in terms of its basic geometrical quantities. A relevant extension to the original concepts of the optical microphone includes the addition of a backplate with holes similar in design to present condenser microphone technology. This approach generates improved damping characteristics and extended frequency response that were not previously considered. The construction and testing of the improved optical fiber microphone provide experimental data that are in good agreement with the theoretical analysis. PACS numbers: 43.88.Kb, 43.88.Zp LIST OF SYMBOLS a CT D h J•(x) km lk m Mm M•4 N p(r,O,O) Pi t r k radius of membrane, m location of k th hole, m element of matrix A isothermal sound speed, m/s air compliance, mSN membrane compliance, mSN see Eq. (2) air gap between membrane and backplate, m nth order Bessel function of the first kind wave number of sound in air = co/cr, m-1 see Eq. (3d) wave number of sound in membrane -co(c•4/T)•/2, m-• depth of k th hole, m wave number for vector potential -( --icopo /lu ) • /2, m -• see Eq. (3e) mechanical sensitivity, m/Pa membrane mass, kg/m 4 see Eq. (14c) reaction pressure at membrane surface, Pa incident sound pressure, Pa Npi, Pa see Eq. (7) number of backplate openings quality factor, condenser microphone quality factor, optical fiber microphone radius of k th hole, m air layer resistance, Ns/m s Present address: Tacan Corp., Carlsbad, CA 92008. S k T t ZA Zc Zk T r' m 15(m ) •l( r) {•) m •m Po O' M s Matrices A I Y ¾ area ofk th opening in backplate, m 2 membrane tension, N/m see Eq. (3c) volume velocity of air displaced by membrane, m3/s U/N, m3/s volume of backchamber, m 3 input optical power, W output optical power, W element of matrix Y acoustic impedance of membrane, Ns/m s N 2ZA, Ns/m 5 acoustic impedance of backchamber, Ns/m 5 acoustic impedance ofk th opening, Ns/m • see Eq. (6) ratio of specific heats see Eq. (3f) see Eq. (3b) = 1 if m--0, =0ifm%0 membrane displacement, m see Eq. (3a) absolute viscosity of air, Ns/m 2 see Eq. (3g) static density of air, kg/m 3 membrane surface density, kg/m 2 element of matrix --1 angular frequency of sound, s see Eq. (5) identity matrix see Eq. (8) see Eq. (6) see Eq. (4) 3049 J. Acoust. Soc. Am. 91 (5),