24 Sep 2008 End-face, butt tapered coupler v. lensing for low-loss integration of disparate photonic devices Helica™ TC is 2 concentric cores and a cladding. The 2 cores: low index contrast. Outer core and cladding: high contrast. At input, low index contrast cores facilitate low-loss connectivity to standard fibers. Fiber tapers down over length, eliminating inner core by output end.
This allows low NA fiber to endface-couple to smaller mode field and higher NA. Index-matching compounds used between coupler and waveguide eliminate microlens-based coupling and air gaps. | 
