An improved delayed self-heterodyne interferometer for linewidth measurements

The authors demonstrated a delayed self-heterodyne interferometer with a recirculating delay, in which loss was partially compensated by an erbium-doped fiber amplifier. A resolution limit of 606 Hz was achieved with an 11-km fiber delay line, as compared to 18.2 kHz for the standard single-pass case. The possible effect of spectral broadening due to amplifier noise is considered and found to have a negligible effect on the system performance.<
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