Chains of these devices are used as multiplexers and demultiplexers in WDM systems. In one type of these devices, the quantity “pi times the square root of R all over one minus R” defines the finesse. Gyroscopes such as RLGs and FOGs are examples of these devices that operate (10[1])using the Sagnac (“sahn-YAHK”) effect. A type of these devices called an etalon consisting (10[1])of a cavity that filters out waves not in resonance is named (10[1])for Fabry and Pérot. (10[2])One of these optical devices consisting of a stone slab in a pool of mercury failed to detect (-5[1])a 0.04 fringe shift induced by the Earth’s motion. For 10 points, name these devices that split (10[1])a beam of light and later recombine them to form patterns, which (10[1])include (10[1])one used to disprove the luminiferous aether in the Michelson–Morley experiment. ■END■ (10[1]0[2])