Beamforming using uniform coupled waveguide sections for efficient coupling to an optical fibre

Using rigorous numerical approaches, it is shown that the highly asymmetrical and divergent modal field profile of a photonic integrated circuit (PIC) could be modified to produce a near circular beam profile, which also could be expanded as required, to achieve efficient coupling to an optical fibre. This may be achieved by incorporating a uniform spot-size converter with two non-identical, but phase matched optical waveguides. For the secondary waveguide, using a more symmetrical cross-section allows the beam shape to be tailored to match the capture area of a particular optical fibre. Numerically simulated results, for a specific and typical structure, show that the design can be improved and the 61(degree) and 26(degree) vertical and horizontal beam angles of the original PIC can be significantly reduced to only 12(degree) and 11.6(degree), respectively, by using an 8 (mu)m*8 (mu)m secondary core. The power coupling loss also can be significantly reduced from 12.3 dB to only 2.4 dB. On the other hand, by using a waveguide with a smaller core, which may be easier to fabricate, a nearly symmetrical beam shape can be produced, which can be much more readily coupled to a fibre, compared to the direct coupling of the original PIC.