We propose a spectral-mode-splitting scheme and how it can be applied to CSRZ and CSRZ-DPSK signal formats, and show that it provides both accurate chromatic dispersion detection in CSRZ application and robustness against linear cross talk and nonlinear impairment in CSRZ-DPSK applications. We propose a spectral-mode-splitting scheme and how it can be applied to CSRZ and CSRZ-DPSK signal formats, and show that it provides both accurate chromatic dispersion detection in CSRZ application and robustness against linear cross talk and nonlinear impairment in CSRZ-DPSK applications.