Routing and Spectrum Allocation is a complex concern in planning tools due to the many possible solutions an algorithm may provide. To avoid the wastage of spectrum, the spectrum allocation strategies rely on compacting as much as possible the slots associated with the routed optical channels while considering the bandwidth continuity and contiguity constraints. With the introduction of the last generation of coherent optical devices, the bandwidth associated with an optical channel may vary from 37.5 up to 150 GHz, generating a lot of spectrum fragmentation that yields cost inefficiency from a network management point of view. In this context, a new algorithm based on the adaptive spectrum bucket strategy is investigated and implemented.