Taper shapes for flatband response and sidelobe suppression in grating assisted optical coupler filters

US5710849A · kind A · utility

Assignee

• Nortel Networks Limited · CA

Inventors

• Brent E. Little · Boston, US
• Chi Wu · Ottawa, CA
• Wei-Ping Huang · Spånga, SE

Key dates

• Filing date: Nov 1, 1995
• Grant date: Jan 20, 1998
• Expiry date: Nov 1, 2015

Classification

• Technology area (CPC G): Physics
• CPC primary: G02B2006/12147
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

Improvements in grating-assisted optical filter couplers are described. In particularly, taper shapes for the gratings-assisted codirectional couplers are determined to provide an out-of-band sidelobe suppression ratio of greater than -30 dB, and a passband response that is flat and has a transmission of greater than 99.55% of the transmission at the passband center, over a wavelength range of 25% of the half-power bandwidth. The interaction strength defining the optimized spectral characteristics is given by EQU K.sub.1 (z)=A.sub.1 e.sup.-.alpha..sbsp.1.sup.(z-z.sbsp.i.sup.).spsp.2 +A.sub.2 e.sup.-.alpha..sbsp.2.sup.(z-z.sbsp.2.sup.).spsp.2 A.sub.3 e.sup.-.alpha..sbsp.3.sup.(z-z.sbsp.3.sup.).spsp.2 0<z<1 where K.sub.1 (z) is the normalized interaction strength along the propagation direction, and the constant coefficients are A.sub.1 =8.774; A.sub.2 =-3.45; A.sub.3 =1.183; .alpha..sub.1 =51.87; .alpha..sub.2 =34.49; .alpha..sub.3 =20.63; z.sub.1 =0.28; z.sub.2 =0.60; z.sub.3 =0.75. where z is the normalized distance and is related to the physical distance Z=Z/L.sub.c, where L.sub.c is the coupler length. At the positions z=0.462 and z=0.777, where the function K.sub.1 changes sign…