3D-printed optical probes for wafer-level testing of photonic integrated circuits

Abstract

Wafer-level probing of photonic integrated circuits is key to reliable process control and efficient performance assessment in advanced production workflows. In recent years, optical probing of surface-coupled devices such as vertical-cavity lasers, top-illuminated photodiodes, or silicon photonic circuits with surface-emitting grating couplers has seen great progress. In contrast to that, wafer-level probing of edge-emitting devices with hard-to-access vertical facets at the sidewalls of deep-etched dicing trenches still represents a major challenge. In this paper, we address this challenge by introducing a novel concept of optical probes based on 3D-printed freeform coupling elements that fit into deep-etched dicing trenches on the wafer surface. Exploiting the design freedom and the precision of two-photon laser lithography, the coupling elements can be adapted to a wide variety of mode-field sizes. We experimentally demonstrate the viability of the approach by coupling light to edge-emitting waveguides on different integration platforms such as silicon photonics (SiP), silicon nitride (TriPleX), and indium phosphide (InP). Achieving losses down to 1.9 dB per coupling interface, we believe that 3D-printed coupling elements represent a key step towards highly reproducible wafer-level testing of edge-coupled photonic integrated circuits.

Silicon photonic devices for scalable quantum information applications

“…Adapted from Ref. [166]. h. Fiber cores and different silicon waveguides connected by photonic wire bonds.…”

“…[171]. Grating coupling 0.58 dB (TE) 71 nm (3 dB) [160] End coupling (tapered fiber) 0.36 dB (TM); 0.66 dB (TE) >80 nm (1 dB) [161] End coupling (SMF) 2.0 dB (TM); 1.2 dB (TE) >120 nm (1 dB) [162] End coupling (SMF) 1.3 dB (TM); 0.95 dB (TE) >100 nm (1 dB) [165] 3D vertical coupling 1 dB (TE and TM) 170 nm (TE); 104 nm (TM) (1 dB) [166] 3D-printing 1.9 dB -- [167][168][169] Wire bonding 0.4 dB -- [171] In situ 3D nanoprinting 0.6 dB -larges the mode size of the waveguide by etching diffraction gratings on the waveguide surface [145]. The cross-section view of the uniform surface-corrugated grating structure is shown in Fig.…”

“…For example, 3D-printed optical probes on the fiber end faces (Fig. 6g), which can realize the detection of vertical cutting edge devices, were recently demonstrated with 1.9 dB coupling loss [166]. Photonic wire bonding and in situ 3D nanoprinting are other novel and promising techniques for chip-scale multi-platform interconnects (Fig.…”

Transient Tap Couplers for Wafer-Level Photonic Testing Based on Optical Phase Change Materials

“…This technique induces excess scattering loss and might not be practical for certain PIC designs and/or packaging configurations. An alternative approach uses turning mirrors attached to the end facets of fiber or planar waveguide probes. , The approach is however limited to testing through edge couplers of PICs. Topley et al pioneered a seminal wafer-level testing paradigm involving gratings and directional couplers created by germanium ion implantation in Si, which can be subsequently erased via annealing after testing.…”

“…An alternative approach uses turning mirrors attached to the end facets of fiber or planar waveguide probes. 19,20 The approach is however limited to testing through edge couplers of PICs. Topley et al pioneered a seminal wafer-level testing paradigm involving gratings 17 and directional couplers 18 testing.…”