Fig. 1. (a) OFMCW measurement and sensing system structure diagram; (b) Principle of OFMCW measurement

Fig. 2. Generation of beat spectrum sidebands

Fig. 3. Variation of phase noise with measurement distance

Fig. 4. Effect of sweep nonlinearity on beat signal

Fig. 5. High-order sidebands of external modulation

Fig. 6. Optical phase-locked on high-order sideband^[34]

Fig. 7. Multi-laser stitching OFMCW measurement system^[41]

Fig. 8. Recirculating frequency-shifting loop^[47]

Fig. 9. Wide-range sweep OFMCW generation based on stitching multi-mode of OFC^[51]. (a) Schematic of the FMcomb system; (b) Allocation of the channels by WDM; (c) Principle of coherent stitching(FD); (d) Principle of coherent stitching (TD signal of beat)

Fig. 10. Wideband LFM signal generation based on stitching multi-mode of OFC^[53]

Fig. 11. Schematic diagram of typical FDML laser

Fig. 12. Schematic diagram of buffered FDML laser system^[55]

Fig. 13. Flowchart of ILC algorithm^[58]

Fig. 14. Schematic diagram of typical OPLL structure. (a) Homodyne OPLL; (b) Heterodyne OPLL

Fig. 15. Schematic diagram of delayed self-interferometry OPLL structure

Fig. 16. Delayed self-heterodyne^[71]

Fig. 17. Multi-loop OPLL system block diagram^[73]

Fig. 18. Beat note spectrum^[78]. (a) Laser locked without chirping; (b) Laser frequency is chirped over 8 GHz in 50 ms