Flattop all-fiber wavelength interleaver for DWDM transmission: Design analysis, parameter optimization, fabrication and characterization recipe

Abstract

Flattop response within the passband is an important desirable feature of any wavelength selective component that goes into a DWDM optical network. In this paper, we report design and fabrication recipe for realizing wavelength interleavers/slicers with flattop wavelength response, configured around unbalanced all-fiber 2-stage Mach–Zehnder interferometers (MZI). Based on a comprehensive analysis, we have developed a design process/algorithm to determine the optimum splitting ratios as well as the relationship between the splitting ratios of the couplers that constitute the 2-stage MZI, to achieve a flattop wavelength response. The implication of the second delay line with respect to its presence in the upper/lower arm of the second stage of the MZI is highlighted through an algebraic analysis. This revealed that there would be corresponding changes in the optimum splitting ratios of the couplers. These features of our design analysis were then exploited to fabricate a wavelength interleaver with a near box-like response, which validated our algorithm. The polarization dependent losses of the device were measured to be ≈ 0.4 dB. Our analysis and fabrication recipe should be useful in the realization of flattop all-fiber wavelength interleavers for deployment in DWDM networks of high spectral efficiency.