Fig. 1. Biological, digital, and physical RC^[21]. (a) Biological RC structure; (b) digital RC structure; (c) physical RC structure

Fig. 2. Research progress of on-chip integrated RC system^{[41-44，47，49，53，57]}

Fig. 3. Research progress on free space diffraction RC system^[59-62]

Fig. 4. Integrated passive silicon 16-node photonic RC chip^[43]

Fig. 5. Novel integrated photonic RC chip based on next-generation RC framework^[53]

Fig. 6. RC system based on SLM^[60]

Fig. 7. Research progress of delay RC systems for SLs^{[64-66,68-69,71-72,74-77,79-81]}

Fig. 8. Architecture of deep reservoir photonic computer^[77]

Fig. 9. Application of deep-latency photonic RC system in nonlinear channel tasks^[77]

Fig. 10. Research progress of delay RC systems based on SL by team from Xidian University^[82-92]

Fig. 11. Schematic diagram of photonic delay-based RC system using four-channel DFB array^[91]

Fig. 12. Performance comparison between single-channel (blue) and four-channel (red) RC systems^[91]

Fig. 13. Future application scenarios of photonic RC hardware^[95]