The Faraday effect provides a mechanism for achieving unidirectional light propagation in optical isolators; however, miniaturization requires large Verdet constants. High rare-earth content glasses produce suitably large Verdet values, but intrinsic fabrication problems remain. The novel powder-intube method, or a single-draw rod-in-tube method, obviates these difficulties. The powder-in-tube method was used to make silica-clad optical fibers with a high terbium oxide content aluminosilicate core. Core diameters of 2.4 μm were achieved in 125-μm-diameter fibers, with a numerical aperture of 0.35 and a Verdet constant of −20.0 rad/(T m) at 1.06 μm. This value is greater than 50% for crystals found in current isolator systems. This development could lead to all-fiber isolators of dramatically lower cost and ease of fabrication compared with their crystalline competitors.
© 1995 Optical Society of America
Original Manuscript: November 21, 1994
Revised Manuscript: March 31, 1995
Published: October 20, 1995
John Ballato and Elias Snitzer, "Fabrication of fibers with high rare-earth concentrations for Faraday isolator applications," Appl. Opt. 34, 6848-6854 (1995)