Patent ID: 7043123

Claim:
A band filter for filtering an optical signal having components in one or more passbands of the filter, comprising: a first waveguide grating router; a second waveguide grating router; and a plurality of waveguides connecting the first waveguide grating router to the second waveguide grating router, the plurality of waveguides arranged as a waveguide grating, each waveguide having a center wavelength for supporting transmission of an optical signal; wherein the plurality of waveguides is partitioned into at least two sets of waveguides, each set of waveguides corresponding to a particular passband in the band filter, the waveguides in a set having unequal path lengths, and the adjacent waveguides having a path-length difference defined as: L ⁡ ( m ) - L ⁡ ( m - 1 ) = A middle 2 ⁢ n ⁡ [ λ ⁡ ( m ) + λ ⁡ ( m - 1 ) ] where L(m) is the path length of waveguide m, λ(m) is the center wavelength supported for propagation by waveguide m, n is the waveguide refractive index, and A middle is an integer grating order of the waveguide grating, where A middle is chosen to be greater than or equal to order 5.