An optical interferometric range sensor (10; 100; 200; 300), comprising: a light source (51; 110) configured to emit light with a changing wavelength; a plurality of interferometers (130a to 130c; 230a to 230c) configured to receive the light emitted from the light source (51; 110), each of the plurality of interferometers (130a to 130c; 230a to 230c) being configured to generate interference light based on measurement light and reference light, the measurement light being light reaching a measurement target and reflected from the measurement target, the reference light being light traveling on an optical path at least partially different from an optical path of the measurement light; optical couplers (54a to 54c; 120a to 120c; 220a to 220c) in a plurality of stages, each of the optical couplers (54a to 54c; 120a to 120c; 220a to 220c) being configured to receive the light emitted from the light source (51; 110) from an optical coupler in a preceding stage to split the light to be incident on a corresponding interferometer of the plurality of interferometers (130a to 130c; 230a to 230c) and an optical coupler in a subsequent stage; a light receiver (56a to 56c, 58a to 58c; 71a to 71c, 74a to 74c; 140a to 140c; 240a to 240c) configured to receive the interference light from each of the plurality of interferometers (130a to 130c; 230a to 230c) to convert the interference light to an electric signal; a processor (59, 75; 150) configured to calculate a distance to the measurement target based on the electric signal resulting from conversion performed by the light receiver (56a to 56c, 58a to 58c; 71a to 71c, 74a to 74c; 140a to 140c; 240a to 240c); and a plurality of isolators (53a, 53b, 221a, 221b) configured to guide light from the optical coupler (54a to 54c; 120a to 120c; 220a to 220c) in the preceding stage to the optical coupler (54a to 54c; 120a to 120c; 220a to 220c) in a subsequent stage of the optical couplers in the plurality of stages and configured to block light from a subsequent stage of the optical couplers to the optical coupler in the preceding stage of the optical couplers in the plurality of stages, wherein the light received by each of the optical couplers (54a to 54c; 120a to 120c; 220a to 220c) in the plurality of stages is split based on a first split ratio (1 - X) for a corresponding interferometer and a second split ratio for an optical coupler in a subsequent stage subsequent to a stage including the optical coupler receiving the light, and the first split ratio (1 - X) and the second split ratio are set at least based on the first split ratio (1 - X) of the optical coupler receiving the light and a product of a first split ratio (1 - Y) and a second split ratio of the optical coupler in the subsequent stage. a light source (51; 110) configured to emit light with a changing wavelength; a plurality of interferometers (130a to 130c; 230a to 230c) configured to receive the light emitted from the light source (51; 110), each of the plurality of interferometers (130a to 130c; 230a to 230c) being configured to generate interference light based on measurement light and reference light, the measurement light being light reaching a measurement target and reflected from the measurement target, the reference light being light traveling on an optical path at least partially different from an optical path of the measurement light; optical couplers (54a to 54c; 120a to 120c; 220a to 220c) in a plurality of stages, each of the optical couplers (54a to 54c; 120a to 120c; 220a to 220c) being configured to receive the light emitted from the light source (51; 110) from an optical coupler in a preceding stage to split the light to be incident on a corresponding interferometer of the plurality of interferometers (130a to 130c; 230a to 230c) and an optical coupler in a subsequent stage; a light receiver (56a to 56c, 58a to 58c; 71a to 71c, 74a to 74c; 140a to 140c; 240a to 240c) configured to receive the interference light from each of the plurality of interferometers (130a to 130c; 230a to 230c) to convert the interference light to an electric signal; a processor (59, 75; 150) configured to calculate a distance to the measurement target based on the electric signal resulting from conversion performed by the light receiver (56a to 56c, 58a to 58c; 71a to 71c, 74a to 74c; 140a to 140c; 240a to 240c); and a plurality of isolators (53a, 53b, 221a, 221b) configured to guide light from the optical coupler (54a to 54c; 120a to 120c; 220a to 220c) in the preceding stage to the optical coupler (54a to 54c; 120a to 120c; 220a to 220c) in a subsequent stage of the optical couplers in the plurality of stages and configured to block light from a subsequent stage of the optical couplers to the optical coupler in the preceding stage of the optical couplers in the plurality of stages, wherein the light received by each of the optical couplers (54a to 54c; 120a to 120c; 220a to 220c) in the plurality of stages is split based on a first split ratio (1 - X) for a corresponding interferometer and a second split ratio for an optical coupler in a subsequent stage subsequent to a stage including the optical coupler receiving the light, and the first split ratio (1 - X) and the second split ratio are set at least based on the first split ratio (1 - X) of the optical coupler receiving the light and a product of a first split ratio (1 - Y) and a second split ratio of the optical coupler in the subsequent stage.