Abstract: Method and system for constructing and testing integrity of a combination of first and second spaced apart optical fiber couplers that each receive and hold two fibers. A segment of each fiber in a separation region between the couplers is heated, twisted and elongated by selected amounts to form a fiber complex, located between the first and second couplers. The fibers in the second coupler are subjected to further controlled elongation. A spectrum analyzer receives a common light beam passed through each of the two fibers and fiber couplers and measures successive maximum and minimum values of an interferometric variable IF and pit-to-pit or peak-to-peak spacing of the IF values as fiber segment elongation is varied.

Abstract: System and method for wavelength discrimination using a DWDM (N+1)-stage fiber optic cascade tree structure with additional filtering to provide acceptable flat-top passband response, and to provide acceptable optical isolation when combined with a multilayer thin film filter. Each channel in a DWDM cascade tree structure has a conventional Mach-Zehnder interferometer (MZI) that provides wavelength discrimination. Each channel in at least one stage has an additional filter that is either (1) an inverted Fabry-Perot etalon (FPE) or (2) an inverted, non-symmetric MZI. The number of output channels may be 32, 64, 128 or more.