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In this paper, the development of an ultra low frequency noise laser has been presented. This laser is obtained by frequency stabilizing a fiber laser to a 1-km fiber length-unbalanced Michelson interferometer with heterodyne detection configuration. The laser frequency noise power spectral density is reduced by more than 40 dB for Fourier frequencies ranging from 1 Hz to 10 kHz, corresponding to a level well below 1 Hz2/Hz over the whole range. Between 30 Hz and 10 kHz, the frequency noise of the laser is shown to be comparable to that obtained by Pound-Drever-Hall locking of the laser to an ultra-stable cavity. Moreover this laser has the great advantage of no optical alignment and no polarization adjustment due to the utilization of an all-fiber system. It is therefore intrinsically more compact, light, robust and flexible than cavity-based systems. This stabilization technique allows the frequency tunability of the low noise laser.