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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 10 — May. 19, 2014
  • pp: 11610–11619

All-fiber fused directional coupler for highly efficient spatial mode conversion

Rand Ismaeel, Timothy Lee, Bernard Oduro, Yongmin Jung, and Gilberto Brambilla  »View Author Affiliations

Optics Express, Vol. 22, Issue 10, pp. 11610-11619 (2014)

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We model and demonstrate a simple mode selective all-fiber coupler capable of exciting specific higher order modes in two- and few-mode fibres with high efficiency and purity. The coupler is based on inter-modally phase-matching the propagation constants in each arm of the asymmetric fused coupler, formed by dissimilar fibres. At a specific coupler diameter, the launched fundamental LP01 mode is coupled into the higher order mode (LP11, LP21, LP02) in the other arm, over a broadband wave-length range around 1550 nm. Unlike other techniques, the demonstrated coupler is composed of a multimode fiber that is weakly fused with a phase matched conventional single mode telecom fiber (SMF-28). The beating between the supermodes at the coupler waist produces a periodic power transfer between the two arms, and therefore, by monitoring the beating while tapering, it is possible to obtain optimum selection for the desired mode. High coupling efficiencies in excess of 90% for all the higher order modes were recorded over 100 nm spectral range, while insertion losses remain as low as 0.5 dB. Coupling efficiency can be further enhanced by performing slow tapering at high temperature, in order to precisely control the coupler cross-section geometry.

© 2014 Optical Society of America

OCIS Codes
(060.0060) Fiber optics and optical communications : Fiber optics and optical communications
(060.1810) Fiber optics and optical communications : Buffers, couplers, routers, switches, and multiplexers

ToC Category:
Fiber Optics

Original Manuscript: February 27, 2014
Revised Manuscript: April 7, 2014
Manuscript Accepted: April 23, 2014
Published: May 6, 2014

Rand Ismaeel, Timothy Lee, Bernard Oduro, Yongmin Jung, and Gilberto Brambilla, "All-fiber fused directional coupler for highly efficient spatial mode conversion," Opt. Express 22, 11610-11619 (2014)

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