title: Two-mode fiber modal coupler.
abstract: When a single-mode fiber is used at a wavelength below the cutoff wavelength, the fiber guides second-order modes, which travel at different phase velocities from the fundamental mode. Periodically stressing this two-mode fiber once per beat length can cause coherent coupling between the modes. Such a modal coupler has been developed and is described here. Coupling to one of the second-order modes has been achieved, leaving less than -40-dB residual power in the fundamental mode. Two couplers have been mounted on a single strand of fiber to construct a Mach-Zehnder interferometer with better than a 30-dB on/off ratio. The coupler is polarization sensitive and can be used as an in-line polarizer. A 36-dB extinction ratio between polarizations has been observed.
authors.forename: R C
authors.initials: RC
authors.lastname: Youngquist
authors.forename: J L
authors.initials: JL
authors.lastname: Brooks
authors.forename: H J
authors.initials: HJ
authors.lastname: Shaw