Fig. 1. Research progress of on-chip modulators in 2 μm waveband^[19-23,25]

Fig. 2. Research progress of on-chip detectors with different material systems at 2 μm waveband^[27-37]

Fig. 3. (a) SEM image of cascaded MMI and SEM image of a single MMI^[38]; (b) Test image of cascaded MMI^[38]; (c) Schematic diagram of a power beam splitter based on subwavelength grating structure^[46]; (d) Experimental result of the beam splitter based on the subwavelength grating, the inset is the SEM image of the device^[46]

Fig. 4. (a) and (b) are AWG electron microscope images and experimental results images based on SOI with a top silicon thickness of 500 nm, respectively^[48]; (c) and (d) are AWG electron microscope images and experimental results images based on SOI with a top silicon thickness of 220 nm, respectively^[50]

Fig. 5. (a)-(d) correspond to the transmission spectra of the four output ports of the mode division multiplexer TE₀, TE₁, TE₂, and TE₃, respectively^[53]

Fig. 6. (a) Electron microscope and SEM of multimode waveguide grating filter^[55]; (b) Transmission spectrum under different grating periods^[55]

Table 1. Reported performance of on-chip lasers and optical amplifiers at 2 μm band

Table 2. Performance comparison of reported 2 μm band grating couplers

Table 3. Reported performance of optical switches at 2 μm waveband

Table 4. Application comparison of on-chip devices based on various material systems