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

US5668900A · kind A · utility

Assignee

• Nortel Networks Limited · CA

Inventors

• Brent E. Little · Boston, US
• Chi Wu · Ottawa, CA

Key dates

• Filing date: Nov 1, 1995
• Grant date: Sep 16, 1997
• Expiry date: Nov 1, 2015

Classification

• Technology area (CPC G): Physics
• CPC primary: G02B2006/12195
• WIPO field: Optics
• WIPO sector: Instruments

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 EQU 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-…