Taper shapes for sidelobe suppression and bandwidth minimization in distributed feedback optical reflection filters

Abstract

Improvements in distributed feedback optical reflection filters are described. In particular, taper shapes for the optical reflection couplers are determined by a design method based on a variational optimization theory, to provide an out-of-band sidelobe suppression ratio of greater than -30 dB, and a reduced width of the filtered bandwidth for a specified side lobe suppression level. These filter characteristics were determined by specifying the interaction strength reflection function along the length of the coupler, by the design formula K.sub.S (z)=L.sub.o (z)+SL.sub.1 (z)+S.sup.2 L.sub.2 (z)+S.sup.3 L.sub.3 (z ) where K.sub.S (z) is the interaction strength; S is the desired sidelobe level in .vertline.dB.vertline. L.sub.i (z) (i=0,1,2,3) are functions of the propagation distance z. The functions L.sub.i (z) are given by: ##EQU1## where L.sub.c is the physical length of the coupler, and the set of constant coefficients b.sub.i,j are given by: ______________________________________ b.sub.i,j 1 2 3 4 ______________________________________ b.sub.0,j 1.316 -0.4430 2.839e-1 -1.902e-1 b.sub.1,j 1.308e-2 1.906e-2 -1.778e-2 1.229e-2 b.sub.2,j -1.540e-4 -1.136e-4 2.736e-4 -2.359e-4 b.sub.3,j 7.10e-7 1.541e-7 -1.397e-6 1.414e-6 ______________________________________ j b.sub.i,j 5 6 ______________________________________ b.sub.0,j 1.337e-1 -9.33e-2 b.sub.1,j -8.188e-3 5.436e-3 b.sub.2,j 1.615e-4 -1.048e-4 b.sub.3,j 1.0279e-6 6.680e-7 ______________________________________ In practice, the specified interaction strength is produced by modulating one of the physical parameters of the DFB filter for example, the vertical depth of horizontal width of corrugations of the reflection grating; the index contrast ratio; the duty cycle of the reflection grating; or by defining the on-off sample rate of the grating corrugations.

Dependencies are inferred from the claim text.