Multicore Polymer Waveguides and Multistep 45° Mirrors for 3D Photonic Integration

Multicore, compact, and low-crosstalk polymer waveguides have been designed, fabricated, and characterized. These single-mode waveguides are arranged in five layers following a hexagonal lattice with 20-\(\mu \) m pitch. The waveguides exhibit similar propagation loss of <;1 dB/cm (at 1550 nm) without any polarization-dependent effect. The interwaveguide crosstalk remains below -40 dB at 3.8-cm propagation length. A series of multistep 45° mirrors have been introduced to extract light from each of the individual layers. The mirror loss ranges from 1.5 to 1.9 dB, with deep mirrors being gradually more loss-prone due to the free-space beam broadening.