OPTICAL DEVICE COMPRISING AN APODIZED BRAGG GRATING AND METHOD TO APODIZE A BRAGG GRATING

摘要

The present invention relates to an optical device (1), i.e., a wavelength-selective filter, including a grating (2) having a finite length (L) and being capable of filtering a given first wavelength (λB) within an operating wavelength region, said grating (2) comprising a plurality of consecutive sections (Sn; n=1, 2, ...,N), each section including two sub-sections: a first sub-section (Sn,R) having a first period Λ and a second sub-section (Sn,T) having a second period Λ1, wherein said first period (Λ) satisfies the Bragg condition for said given first wavelength (λB) and the second period satisfies the Bragg condition for a second wavelength lying outside the operating wavelength region so as to form a grating with modulated coupling coefficient, wherein the succession of lengths [I1, Ι2, ....IN] of each section (Sn) is non periodic. Preferably, the first (Λ) and second period (Λ1) are such that nΛ=mΛ1 where n, m are integers and satisfy one of the following conditions: if Λ1Λ, n/m is not an integer and if Λ1Λ, m/n is not an integer. The reflection spectrum of the apodized grating according to the present invention does not exhibit Moiré replica over a relatively large operating wavelength region, e.g., the C-band.