All-fiber noninterferometric narrow-transmission-bandpass filter.
In-fiber mode engineering based on the combination of Bragg and long-period gratings (LPGs) permits the implementation of noninterferometric transmission filters with narrow passbands using standard single-mode fiber. The design of the bandpass filter is based on the coupling between propagating and counterpropagating cladding modes in two fiber Bragg gratings. A LPG located between the Bragg gratings transfers power from the input fundamental mode to a specific cladding mode and recouples the filtered signal to the output fundamental mode. The filter produces a series of narrow passbands of about 30 pm linewidth with a maximum transmittance above 60%, 20 dB isolation, and passband separation of about 1 nm, each corresponding to the contribution of a different cladding mode.
Departament de Física Aplicada i electromagnetisme and Institut Universitari de Ciència dels Materials, Universitat de València, Carrer Dr. Moliner 50, Burjassot E-46100, Spain. d.saez‑rodriguez@aston.ac.uk
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D
Sáez-Rodríguez
J L
JL
Cruz
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Díez
M V
MV
Andrés