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, it 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 suppression ratio of approximately 200 was
achieved. This marks the first experimental verification of the critical function in the
BLFPI.