Hi,
For more information on unequal channel spacing wdm system, I would suggest you to get some focus on research papers , i share some links of that:
http://link.springer.com/chapter/10.1007%2F978-1-4020-8741-7_1#page-1
https://www.researchgate.net/publication/261320396_Duobinary_modulation_format_and_unequal_channel_spacing_integration_to_suppress_four-wave_mixing_crosstalk_in_WDM_systems
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=5876926&abstractAccess=no&userType=inst
http://www.ijarcsse.com/docs/papers/Volume_3/12_December2013/V3I12-0112.pdf