Patent ID: 7233721

Claim:
A method of producing a low-loss spectrally periodic all fiber filter, the method comprising the steps of: providing a multi-mode fiber capable of propagating an LP01 mode and an LP02 mode at wavelengths of interest; providing a single-mode fiber capable of propagating a fundamental mode at the wavelengths of interest; and splicing a selected length of the multi-mode fiber between first and second lengths of the single-mode fiber, wherein the properties of the multi-mode fiber and the single-mode fiber are related such that the optical field distribution resulting from the coherent superposition of the optical field of the LP01 mode and the optical field of the LP02 mode in the multi-mode fiber is sufficiently similar to the optical field distribution of the fundamental mode in the single-mode fiber at the wavelengths of interest, such that transmission across the two splices taken together at the wavelengths of interests is at least 70%, and the extinction of the resulting filter is at least 10 dB.