Polarization-Independent, Multilayer Dielectrics at Oblique Incidence

Vol. 54. N o . 6. July-August 1975 Printed in U.S.A. Polarization-Independent, Multilayer Dielectrics at Oblique Incidence By A. A. M. SALEH (Manuscript received January 6, 1975) This -paper gives solutions for frequency. dielectrics given for by An exhaustive by multilayer dielectrics that yield polarizais given with for symmetric than new three-layer also layers tion-independent operation at a given angle of incidence and at a given analysis the same surrounded symmetric media. and medium. Special more solutions are three multilayer Rules are dielectrics surrounded by the same medium different and for multilayer dielectrics surrounded presented for of various obtaining solutions, polarizationdesign splitters independent solutions by cascading given solutions. Finally, for the purpose of demonstration comparison different beam examples are carried out for polarization-independent 3-dB to operate at millimeter wavelengths. I. INTRODUCTION T h e state of polarization of a plane w a v e will, in general, be changed upon transmission through or reflection by a multilayer dielectric at oblique incidence. T h e reason for this depolarization is that the t w o eigenmodes of polarization, .E-field perpendicular to the plane of incidence and i£-field parallel to the plane of incidence, generally h a v e different reflection coefficients and different transmission coefficients. T h i s is not desirable in m a n y applications. F o r example, such depolarization could cause crosstalk in dual-polarization optical or quasioptical components such as interference filters, 1 directional couplers 2 - 5 and diplexers, 6 or mode conversion in beam-splitter-type hybrids 7 ' 5 in oversized waveguides.