This paper reports a novel architecture for the design of dense wavelength-division multiplexing interleavers based on planar echelle gratings. Double astigmatic point design of the echelle grating is discussed. The important and inherent limitation of aberrations associated with the echelle grating has been eliminated by the introduction of aberration free elliptical facets. A mechanism for compensating the variations of the refractive index with wavelength is also described. The theoretical analysis was used to design and manufacture remarkably low footprint 50/100 and 100/200 GHz interleavers in silica-on-silicon with the waveguide refractive index contrast of 0.62%. The comparison between the theoretical and experimental results shows an excellent agreement. The fabricated devices based on the proposed approach showed low nonuniformity in insertion loss, high dynamic range, and precise channel periodicity over the entire C band.
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