The paper "Low-Loss Vertical MMI Coupler for 3D Photonic Integration" written by M. Nuck,M. Kleinert,C. Zawadzki,A. Scheu,H. Conradi,D. de Felipe,N. Keil,M. Schell is out!

In this publication a polymer vertical multi-mode interference coupler with device losses below 1.2 dB for a vertical centre-to-centre waveguide distance of 7.2 μm is presented.

You can read it at https://bit.ly/3ip2wzG.