To reduce four-wave-mixing crosstalk in high-capacity, long-haul, repeaterless, wavelength-division multiplexing (WDM) lightwave systems, the use of unequally spaced channels has been proposed. Instead of being solved by integer linear programming, the unequal-spaced channel-allocation problem is treated by constructing suitable optical orthogonal codes in optical code-division multiple-access (CDMA). An "algebraic" framework and three algorithms on finding the frequency locations of unequally spaced WDM channels are introduced, where the constructions are based on generating optical CDMA codewords with a predetermined pulse separation and "aperiodic" autocorrelation sidelobes no greater than one. The algorithms potentially provide a fast and simple alternative to solve the problem, besides the proposed computer-search method.