ANALYSIS AND DESIGN OF HIGHLY BROAD-BAND, PLANAR EVANESCENT COUPLERS

It is shown that by taking advantage of the maximum in the spectral de pendence of the coupling coefficient, very broad-band symmetric and as ymmetric single-mode planar couplers can be designed. The symmetric co upler allows at least 95.6% coupling between the two cores over the wa velength range 1.3-1.58 mu m, while the asymmetric coupler can act as a 3 dB splitter with only +/- 1.6% variation in the splitting ratio ov er the wavelength range 1.3-1.67 mu m. In both cases, the design inclu des the curved input-output arms, and the estimated bend loss is appro ximately 0.1 dB.