Fig. 1. Schematic of the 2×2 MRR switch element. Solid red and dashed red arrows outline the transmission paths when the element works at the on-state and the off-state, respectively. The insets show the cross sections of the coupling regions.

Fig. 2. (a) Electric-field intensity profile of the Si3N4 waveguide with cross-sectional dimensions of 1  μm×0.4  μm. (b) Waveguide effective refractive index and MRR resonance wavelength changing with the waveguide width deviation for both Si and Si3N4 waveguides. The dimension of the Si waveguide is 0.5  μm×0.22  μm.

Fig. 3. (a) General port arrangement of the 8×8 crossbar switch fabric. (b) Example of bidirectional path transmission. When SE54 is turned on, light from I5 (I5*) is routed to O4 (O4*).

Fig. 4. (a) Microscope image of the fabricated 8×8 switch chip. (b) Microscope image of the 2×2Si-Si3N4 switch element, with a TiN heater integrated on each SiN1 MRR. (c) Microscope image of the on-chip suspended edge couplers. (d) Photo of the switch chip after packaging.

Fig. 5. (a) and (b) Through-transmission spectra of the 8×8 crossbar switch. (c) Drop transmission spectra of eight output ports when light is launched from I1.

Fig. 6. (a), (b) Transmission spectra of the routing paths of (a) Ii→Oj and (b) Ii*→Oj*. (c), (d) Histogram of the extracted optical 3-dB bandwidth for the paths of (c) Ii→Oj and (d) Ii*→Oj* (i, j=1,2,…,8).

Fig. 7. Transmission spectra of the target path and the leakages from other input ports for (a) the routing path I8→O4 and (b) the routing path I1→O3. (c) Schematic of the ER definition of the on-state SE (ERon) and the off-state SE (ERoff). The through-port and drop-port transmissions of the on-state SE are plotted in solid lines, while those of the off-state SE are plotted in dash lines. Histograms of extracted (d) ERoff and (e) ERon.

Fig. 8. Fiber-to-fiber ILs of all target ports at the wavelength of 1563 nm; 63 solid circles represent paths of Ii→Oj (i, j=1,2,…,8), and 63 hollow diamonds represent paths of Ii*→Oj*.

Fig. 9. (a), (b) Heatmap of the on-chip ILs for path (a) I→Os and (b) I*→O*s.

Fig. 10. (a) Schematic of a non-duplicate polarization-diversity 8×8 switch. (b) Experimental verification for polarization diversity of the device under test (DUT).

Fig. 11. (a) PDLs and DGDs for eight representative paths. (b), (c) Electrical signal responses for (b) path 1→1* with the maximum DGD and (c) path 6→6* with the minimum DGD.

Fig. 12. Experimental setup for 100 Gb/s DP-QPSK signal transmission over the polarization-diversity 8×8 switch.

Fig. 13. Constellation diagrams in the back-to-back (B2B) configuration, and path of 1→1*.

Fig. 14. Curve fitting results of eight representative diagonal SEs of the switch fabric. The solid blue and red lines represent the measured transmission spectra of Ii→Oi and Ii*→Oi* (i=1,2,…,8), respectively. The dashed yellow and purple lines are the correspondingly fitted curves.

Fig. 15. (a), (c), (e) Heatmaps and (b), (d), (f) corresponding histograms of extracted (a), (b) on-state loss, (c), (d) off-state loss from the Si waveguide direction, and (e), (f) off-state loss from the SiN2 waveguide direction of all the SEs in the chip.

Fig. 16. (a), (b) Extra loss fitting for (a) the horizontal Si waveguide transmission and (b) the vertical SiN2 waveguide transmission.

Fig. 17. (a) Interlayer waveguide coupling coefficient, (b) on- and off-state IL and (c) ERoff of the MRR SE changing with the deviation of the SiN2 bus waveguide and the SiN1 MRR gap.