Here is how you should invoke Babel to create the FORTRAN 90 stubs for an IDL file 10.1.
% babel -client=f90 file.sidlor simply
% babel -c=f90 file.sidl
This will create a babel.make file, numerous C headers, numerous C source files, and some FORTRAN 90 files. The files ending in _fStub.c are called by the FORTRAN 90 module which in turn allow FORTRAN 90 to call a SIDL method. The files ending in _type.F90 contain derived type definitions for classes and interfaces., and the other files ending in .F90 are FORTRAN 90 modules containing methods.
You will need to compile and link the files ending in _fStub.c (i.e., STUBSRCS in babel.make) and all the files ending in .F90 (i.e., STUBMODULESRCS and TYPEMODULESRCS in babel.make) into your application. Normally, the IOR files (_IOR.c) are linked together with the implementation file, so you probably don't need to compile them.