Fig. 1. (a) Proposed GC efficiency enhancing scheme with an 8° polished APF with its facet parallel to the chip surface. (b) Cross-sectional schematic of the 2D-FDTD model of a GC coupling with an 8° tilted APF. (c) Schematic of the light interferences in the air gap layer.

Fig. 2. (a) Surface plot for simulated CE with different tCOX and tgap. (b) Simulated insertion loss of the GC with 1.84μmtCOX (blue) and 1.57μmtCOX (red) coupling with an APF (solid line) and a 12° tilted SMF (dashed line) with tgap from 0.5 to 1.5μm. (c) Simulated transmission (solid line) and reflection (dashed line) spectra of APF (red) and 12° tilted SMF (blue) coupled GC with 1.84μmtCOX.

Fig. 3. (a) Simulated enhancing effect of the air gap at different tilting and polishing angles. (b) Peak CE drops 0.15 dB as tgap increases to 10μm.

Fig. 4. (a) Fiber alignment tolerance in the z direction for the APF (red) and SMF (blue). (b) Enhancing effect by directionality only and various tgap APF with different tCOX. (c) Maximum enhancing effect at various tgap (red) and directionality’s 1.06 dB enhancing effect.

Fig. 5. (a) Simulated (solid line) and measured (× mark) GC insertion loss with tcox from 1.2 to 1.9μm coupling with an APF with 5.4μmtgap. Inset: optical microscopy image of the “GC loop”. (b) Measured transmission spectra of the GC with 1.23μm COX coupling with SMF (blue) and APF (red).