  We demonstrate the first active optical isolator and circulator implemented
in a linear and reciprocal material platform using commercial Mach-Zehnder
modulators. In a proof-of-principle experiment based on single-mode
polarization-maintaining fibers, we achieve more than 12.5 dB isolation over an
unprecedented 8.7 THz bandwidth at telecommunication wavelengths, with only 9.1
dB total insertion loss. Our architecture provides a practical answer to the
challenge of non-reciprocal light routing in photonic integrated circuits.
