Using 3D multiphoton lithography, a method of 3D printing, researchers from Singapore University of Technology and Design (SUTD) demonstrated high-resolution 3D photonic structures capable of guiding light in a spiral and in an air-bridge configuration. The research has direct implications for photonic integrated circuits perceived as planar structures, that is, only able to guide light in a single plane. The technique overcomes the restriction of top-down exposure as a necessity for realizing PICs, enabling access to the functions availed by the third dimension. The researchers additionally demonstrated low-loss 3D waveguide couplers with 1.6-dB fiber-waveguide coupling losses, and 3-dB bandwidth exceeding 60 nm. Current industry standards require labor-intensive packaging for losses around 1 dB. The team demonstrated low losses without requiring any post-processing or post-fabrication. “Importantly, we were also able to demonstrate error-free 30-Gbit/s NRZ and 56-Gbit/s PAM4 data transmission through these waveguides. This is important because these high-speed testing formats and rates are in alignment with those used in commercial direct-detection transceiver products today,” said Dawn Tan, associate professor at SUTD and principal investigator on the project. The team managed to derive only small power penalties of 0.7 dB for NRZ (bit error rate [BER] = 10−12) and 1.5 dB for PAM4 (BER = 10−6) from the devices. The results demonstrate high-speed, error-free optical transmission through the 3D-fabricated waveguides. It also showcases the device’s suitability as low-loss waveguides and optical interconnects. “Importantly, the 3D quality of these waveguides allows us to exceed the limitations of traditional planar structures. In this way, it is possible to achieve far higher density PICs. The high-resolution, submicron feature sizes are also promising, especially to achieve advanced functions such as spectral filtering, resonator structures, and metasurfaces,” said Hongwei Gao, first author on the work describing the technology and a postdoctoral researcher at SUTD. “This work demonstrates the potential of additive manufacturing in making advanced photonic devices with superior 3D designs in high resolution,” added co-author and SUTD associate professor Hong Yee Low. In demonstrating high-resolution 3D waveguides capable of transcending the restrictions of light confinement in a single plane, the research has additional applications in optical signal processing and spectroscopy, the researchers reported. The research was published in Advanced Optical Materials (www.doi.org/10.1002/adom.202070071).