This device is based in the SMTwVSL (Shrinking Matter Theory with Variable Speed of Light)(1). This is an answer to the most challenging question that can be asked about a theory, which is: How can we test this theory? In this case, we can ask: How may one test if matter shrinks or not?How can one test whether matter shrinks or not?The device for detecting matter shrinkage must be based on interferometry technology.The arrangement of the apparatus is similar to the old "Michelson-Morley experiment", but the mirrors are replaced by optical fibers with another beam splitter to join the two beams from the first beam splitter. The introduction of new technologies in the production of the coherent laser beam, in the phase and polarization control and in the photodetector is essential for the proper functioning of the equipment. A room with strict temperature control is required.The large difference in the length of the two optical fiber results in a build-up of photons inside the larger optical fiber. The shrinking of the optical fiber and wavelength at different rates, combined with the increasing light speed, result in a decreasing in the accumulation of photons, changing the interference pattern in the output of the second beam splitter.