  We experimentally study an unequally-spaced optical comb (USOC), which is
generated by a unidirectional fiber loop laser operated at low temperatures.
The underlying mechanism responsible for USOC formation is explored using both
close and open loop measurements. The role played by dispersion is investigated
using radio frequency spectrum measurements. By integrating a saturable
absorber into the loop, a lasing state is revealed, in which mode locking
coexists with the USOC.
