Fiber devices using grin fiber lenses

Abstract

A mode converter includes first and second optical waveguides and a GRIN fiber lens. The GRIN fiber lens is attached to both the first and the second waveguides.

What is claimed is:  
     
         1 . An apparatus for mode converting, comprising: 
 first and second optical waveguides; and    a GRIN fiber lens attached to both the first and the second waveguides.    
     
     
         2 . The apparatus of  claim 1 , wherein the waveguides are fused or glued to the GRIN fiber lens.  
     
     
         3 . The apparatus of  claim 2 , wherein the first and second waveguides are first and second optical fibers, respectively.  
     
     
         4 . The apparatus of  claim 3 , wherein the first fiber has propagation modes with different sizes than the second fiber.  
     
     
         5 . The apparatus of  claim 3 , wherein the lens has a magnification, the magnification times the size of a fundamental propagation mode of the first fiber being about equal to the size of a fundamental propagation mode of the second fiber.  
     
     
         6 . The apparatus of  claim 3 , wherein the first and second fibers have cores with different diameters.  
     
     
         7 . The apparatus of  claim 3 , wherein each fiber has a core and a cladding; and a discontinuity in refractive index across an interface between the core and cladding, the discontinuities being different across the interfaces of the first and second fibers.  
     
     
         8 . The apparatus of  claim 3 , wherein the GRIN fiber lens comprises a series of connected GRIN fiber lenses; the first GRIN fiber lens of the series being attached to the first fiber and the last GRIN fiber lens of the series being attached to the second fiber.  
     
     
         9 . The apparatus of  claim 1 , wherein the GRIN fiber lens has a core with a graded refractive index profile, the profile having a radial second derivative whose average magnitude is less than about 2.4×10 −5  microns −2  in the core.  
     
     
         10 . An apparatus, comprising: 
 first, second, and third optical fibers;    first, second, and third GRIN fiber lenses attached to the first, second, and third optical fibers, respectively; and    an optical element configured to optically couple the first, second, and third optical fibers.    
     
     
         11 . The apparatus of  claim 10 , wherein free ends of the first, second, and third GRIN fiber lenses have separations of less than about 1 millimeter.  
     
     
         12 . The apparatus of  claim 10 , further comprising: 
 a MEM device; and    wherein the optical element is a moveable reflector whose position or orientation is controlled by the MEM device.    
     
     
         13 . The apparatus of  claim 10 , wherein the optical element includes one of an optical circulator, a polarization-selective splitter, and a wavelength-selective reflector.  
     
     
         14 . The apparatus of  claim 10 , wherein a free surface of one of the GRIN fiber lenses is cleaved at an angle of less than 8 degrees from a plane whose normal is the lens' axis.  
     
     
         15 . An optical apparatus, comprising: 
 an array of at least three optical fibers having attached GRIN fiber lenses; and    an optical device configured to direct light between selected ones of the GRIN fiber lenses of the array and another optical waveguide.    
     
     
         16 . The apparatus of  claim 15 , wherein the other waveguide is an optical fiber having an attached fiber GRIN lens.  
     
     
         17 . The apparatus of  claim 15 , wherein a free surface of one of the GRIN fiber lenses is cleaved at an angle of less than 8 degrees from a plane whose normal is the lens' axis.  
     
     
         18 . The apparatus of  claim 16 , wherein the optical device is configured to present an acceptance window for light from one of the fibers, the window having a diameter not greater than the diameter of one of the optical fibers.  
     
     
         19 . The apparatus of  claim 15 , wherein free ends of the GRIN fiber lenses have separations of less than about 1 millimeter.  
     
     
         20 . The apparatus of  claim 15 , wherein the optical device includes one of a reflector, a polarization-sensitive splitter, and a wavelength-sensitive reflector.  
     
     
         21 . The apparatus of  claim 16 , further comprising: 
 a second array of optical fibers having attached GRIN fiber lenses, the waveguide being one of the fibers in the second array; and    wherein the optical device includes a plurality of elements capable of routing light from the fibers of the first array to the fibers of the second array.    
     
     
         22 . The apparatus of  claim 21 , wherein at least one of the elements is one of a polarization-sensitive splitter and a wavelength-sensitive reflector.  
     
     
         23 . The apparatus of  claim 21 , wherein free ends of the GRIN fiber lenses of the array have separations of less than about 1 millimeter.  
     
     
         24 . The apparatus of  claim 21 , wherein a free surface of one of the GRIN fiber lenses of the array is cleaved at an angle of less than 8 degrees from a plane whose normal is the lens' axis.  
     
     
         25 . The apparatus of  claim 21 , wherein the optical device is configured to present an acceptance window for light from one of the fibers, the window having a diameter not greater than the diameter of one of the optical fibers.