The technology described here enables the use of an inexpensive laser to measure an interferometric response of an optical device under test (DUT) at reflection lengths significantly greater than the coherence length of the laser. This is particularly beneficial in practical interferometric applications where cost is a concern. In other words, inexpensive lasers having shorter coherence lengths may be used to achieve very high interferometric measurements at longer DUT reflection lengths. The technology also enables the use of such inexpensive lasers to measure Rayleigh scatter in commercial-grade, single-mode optical fiber.