Most optical packet buffers are constructed with FDLs（Fiber Delay Lines）. However

the FDL efficiency

i.e. the ratio of total FDL length to buffer depth is rather low in current optical buffer designs （normally 2/N

where Nis the number of input port）. In this paper

two novel FDL structures

linear structure and tree structure

are proposed to substitute equivalent while wasteful FDL modules. The substitution can be made in many optical buffer designs and improve the FDL efficiency to a constant value or 1/log

2

N

resulting in significant FDL economizing.