All-optical tunable multi-channel mode conversion based on a modal interferometer using two-mode fiber.

This paper presents all-optical tunable multi-channel mode conversion based on a Norland Optical Adhesive (NOA)-coated modal interferometer constructed by two-mode fiber. The modal interferometer consists of a tapered two-mode fiber (TTMF) sandwiched between two pieces of single-mode fibers. The TTMF provides a uniform modal interferometer with LP 01 and LP 11 modes as well as a strong evanescent field on its surface. The NOA is illuminated by a 405 nm laser which changes the refractive index of the NOA, thus the output spectrum of the modal interferometer can be controlled. Due to the strong light-matter interaction between NOA and the evanescent field around the TTMF, a large wavelength shift of the output spectrum can be observed under external pump light excitation. The experimental results show the transmission spectrum exhibits a blue shift with increasing pump power. A wavelength variation rate of 289 pm/mW is obtained under external pump light excitation. The interference spectrum has multiple dips where the input LP 01 mode is converted to the LP 11 mode. Thus, the modal interferometer acts as a tunable multi-channel mode converter. The proposed device might have potential applications in all-optical controllable devices and mode division multiplexing systems, etc. • The modal interferometer exhibits a wavelength variation rate of 289 pm/mW under external pump light excitation. • The modal interferometer acts as a tunable multi-channel mode converter. • The tapered two-mode fiber provides a uniform modal interferometer with LP 01 and LP 11 modes. [ABSTRACT FROM AUTHOR]