Fig. 1. (a) Cross-section sketch of the As2S3 strip waveguide showing the refractive indices of different layers. (b) Calculated effective refractive index of fundamental TE mode as a function of width and height of the strip waveguide at 1950 nm; the color area depicts the single-mode region. (c) SEM image of the cross section of strip waveguides. (d) Simulated electrical field of the fundamental TE mode in the 0.6  μm×1.2  μm strip waveguide.

Fig. 2. Schematic flow of ChG fabrication process.

Fig. 3. (a) Simulated and experimental results of the bending loss of bent waveguides versus the radius. (b) SEM image of the bent waveguides with different radii.

Fig. 4. (a) Measured waveguide loss and linear fitting line with the slope of 1.447 dB/cm. (b) SEM image of the spiral waveguide.

Fig. 5. (a) Simulated and measured coupling efficiency of grating coupler. (b) SEM image of the fabricated grating coupler.

Fig. 6. (a) Simulated electrical field of mode converter for TE1 (up) and TE2 (down). (b) SEM diagram of the fabricated mode converters, inset: coupling region for phase matching. (c) Calculated coupling efficiency of mode converter for TE1 and TE2. CE, coupling efficiency; XT, crosstalk. (d)–(f) Measured transmission spectra for three modes.

Fig. 7. (a) Transmission spectrum of Bragg grating filters. (b) SEM diagram of fabricated Bragg gratings.

Fig. 8. (a) Measured insertion loss of MMIs. (b) SEM diagram of fabricated MMI.

Fig. 9. (a) Measured transmission spectra of MZIs. (b) SEM image of fabricated MZI.

Fig. 10. Comparison of refractive index between SOI and As2S3 platform for C-band and 2 μm. (a) Real part of material refractive index. (b) Effective refractive index curves of strip waveguides. Symbols denote the width and corresponding neff of single-mode waveguides in the four cases.

Fig. 11. Comparison of devices’ performances between SOI and As2S3 platform for C-band and 2 μm. (a) Coupling spectrum of grating couplers. (b) Insertion loss of mode converters under different width deviations of fabricated waveguides.

Fig. 12. Experiment setup of (1) 2 μm on-chip MDM interconnection and (2) As2S3 chip broadband testing. Insets show optical spectrum of (i) modulated 2 μm signal, (ii) ASE broadband source, and (iii) the on-chip three-mode multiplexing.

Fig. 13. Measured BER curves of (a) 70 Gbps PAM4 and (b) 80 Gbps PAM4, under the BTB case and after 3 MDM channel transmission. Insets (i)–(iv): eye diagrams of PAM4 signals marked in (a) and (b).