Fig. 1. Diagrams of the SWSS topologies. (a) Switch and selective SWSS featuring MRR-based wavelength selectors. (b) Dilated Banyan topology with MRRs assisted MZI as switching elements. (c) Traditional crossbar topology and (d) dilated crosspoint topology proposed in this work.

Fig. 2. An example of crosstalk increased by interference.

Fig. 3. Permutation number and effective switching states as functions of port number N. Different permutation numbers with different wavelength channels are compared. Se>PN−H indicates that the switch meets the wide-sense non-blocking condition.

Fig. 4. Flow chart of the blocking status calculation process.

Fig. 5. Switching element number as a function of the port number N among different reported SWSSs.

Fig. 6. Design space exploration of the MRR. (a) Contour of the 3 dB bandwidth versus MRR radius and κ2. (b) Contour of the attenuation at the resonance. (c) Contour of the drop port extinction ratio. (d) Overall design of the MRR. (e) Power coupling efficiency κ2 as a function of the MRR gap.

Fig. 7. (a) Schematic of the 4×4×4λ dilated crossbar optical switch. (b) 3D model of the switching element. (c) Simulated transmission spectrum of the four wavelength channels. (d) An example showing signals in four wavelength channels are routed from I1 to O1,O2, O3, and O2, respectively. The second-order in-band crosstalk and the first-order out-band crosstalk in channel 1 are illustrated. (e) Diagram of the fully connected blocking SWSS operating under a fully loaded condition. (f) Diagram of the wide-sense non-blocking SWSS operating under a fully loaded condition.

Fig. 8. (a) Microscope photograph of the dilated crossbar optical switch. (b) Photograph of the photonic chip with wire bonding and optical coupling with ultra-high-numerical-aperture (UHNA) fiber array.

Fig. 9. Diagram of the SWSS testing setup.

Fig. 10. Measured spectra of routing path from I4 to O1. (a) Spectrum when all paths are on-state. (b) Spectrum when wavelength channel 3 is at off-state with first-order crosstalk. (c) Spectrum when wavelength channel 3 is off-state with second-order crosstalk.

Fig. 11. Measured optical power map of the optical switch for four wavelength channels.

Fig. 12. The crosstalk ratios for all routing paths with leakage to all non-target output ports. The four wavelength channels are represented by distinct colors.

Fig. 13. The superimposed spectrum of all routing permutations across four channels. Each sub-figure illustrates all 16 possible permutations within each wavelength channel.

Fig. 14. Reconfiguration time of the SWSS.

Fig. 15. Diagrams of the switching states.