  The back-linked Fabry-Perot interferometer (BLFPI) is an interferometer
topology proposed for space gravitational wave antennas with the use of
inter-satellite Fabry-Perot interferometers. The BLFPI offers simultaneous and
independent control over all interferometer length degrees of freedom by
controlling the laser frequencies. Therefore, BLFPI does not require an active
control system for the physical lengths of the inter-satellite Fabry-Perot
interferometers. To achieve a high sensitivity, the implementation must rely on
an offline signal process for subtracting laser frequency noises. However, the
subtraction has not been experimentally verified to date. This paper reports a
demonstration of the frequency noise subtraction in the frequency band of 100
Hz-50 kHz, including the cavity pole frequency, using Fabry-Perot cavities with
a length of 46 cm. The highest reduction ratio of approximately 200 was
achieved. This marks the first experimental verification of the critical
function in the BLFPI.
