Optical coupling using polarization beam displacer

Abstract

An optical coupling apparatus for coupling an optical fiber to a photonic chip is described. The apparatus includes a collimating microlens for collimating light from the optical fiber; a polarization splitting beam displacer for separating the light collimated by the collimating microlens into orthogonally polarized X and Y component beams; at least one focusing microlens for directing the X and Y component beams separately onto the photonic chip; and first and second surface grating couplers (SGCs) orthogonally disposed on the photonic chip and configured for operation in a same polarization state, for coupling the X and Y component beams, respectively, to the photonic chip.

What is claimed is: 
     
         1 . A method for coupling light between an optical fiber and a photonic chip, comprising:
 collimating or re-focusing light from the optical fiber;   separating the light into orthogonally polarized X and Y component beams;   directing the X and Y component beams to separate first and second locations, respectively, on the photonic chip; and   coupling the X and Y component beams to the photonic chip respectively by first and second surface grating couplers (SGCs) orthogonally disposed on the photonic chip at the first and second locations, respectively, and configured for coupling a same polarization mode to the photonic chip.   
     
     
         2 . The method of  claim 1 , wherein directing the X and Y component beams separately onto the photonic chip comprises directing the X and Y component beams by first and second focusing microlenses, respectively, wherein at least one of the first and second focusing microlenses is disposed off-axis with respect to the X and Y component beams. 
     
     
         3 . The method of  claim 1 , wherein coupling the X and Y component beams to the photonic chip comprises coupling X and Y component beams onto the photonic chip at coupling angles of the first and second SGCs, respectively. 
     
     
         4 . The method of  claim 1 , further comprising magnifying a spot size of light from the optical fiber. 
     
     
         5 . The method of  claim 4 , wherein a spot size of at least one of the X and Y component beams at the photonic chip is larger than a spot size at the optical fiber. 
     
     
         6 . The method of  claim 1 , wherein the coupling of light between the optical fiber and the photonic chip is absent rotating polarization of any of the component beams. 
     
     
         7 . The method of  claim 1 , wherein the collimating or re-focusing comprises collimating, and wherein the separating is performed after the collimating. 
     
     
         8 . The method of  claim 1 , wherein the optical fiber is disposed substantially parallel to the photonic chip, the method further comprising reflecting the light exiting the optical fiber to propagate towards the photonic chip. 
     
     
         9 . The method of  claim 1 , wherein at least two of the collimating, the separating, and the directing is performed by a same optical element. 
     
     
         10 . A method for coupling light between a photonic chip and an optical fiber, comprising:
 emitting X and Y component beams by first and second surface grating couplers (SGCs), respectively, wherein the first and second SGCs are orthogonally disposed on the photonic chip at the first and second locations and are configured for coupling a same polarization mode from the photonic chip;   combining the X and Y component beams into a beam of light; and   re-focusing the beam of light onto the optical fiber.   
     
     
         11 . The method of  claim 10 , wherein the coupling of light between the optical fiber and the photonic chip is absent rotating polarization of any of the component beams. 
     
     
         12 . An apparatus for coupling light between an optical fiber and a photonic chip, the apparatus comprising:
 a collimator for collimating or re-focusing light from the optical fiber;   a beam separator for separating the light into orthogonally polarized X and Y component beams;   a beam director for directing the X and Y component beams to separate first and second locations, respectively, on the photonic chip, wherein the beam director is configured for coupling the X and Y component beams to the photonic chip respectively by first and second surface grating couplers (SGCs) orthogonally disposed on the photonic chip at the first and second locations, respectively, and for coupling a same polarization mode to the photonic chip.   
     
     
         13 . The apparatus of  claim 12 , wherein at least two of the collimator, the beam separator, and the beam director comprise a same optical element. 
     
     
         14 . The apparatus of  claim 12 , wherein the optical fiber, the collimator, and the beam separator comprise a first subassembly, and the beam director and the photonic chip comprise a second subassembly. 
     
     
         15 . The apparatus of  claim 12 , wherein the collimator comprises a microlens. 
     
     
         16 . The apparatus of  claim 12 , wherein the collimator and the beam director comprise a microlens. 
     
     
         17 . The apparatus of  claim 12 , wherein the beam separator comprises a polarization beam displacer.