Fig. 1. (a) Schematic diagram of the time-frequency self-injection locking. (b) Illustration of the frequency-shifted self-injection locking.

Fig. 2. Simulation results of instantaneous laser linewidth. (a) Drive current. (b) Instantaneous frequency (red) and residual error (blue) corresponding to (a). (c) Normalized spectrum of a free-running laser calculated by removing the frequency chirp. The linewidth is approximately 5 MHz. (d) Evolution of laser linewidth with feedback ratio. (e)–(l) Spectra of a self-injection locked laser with various feedback ratio and loop phase shift: (e) −70  dB, π/2; (f) −55  dB, π/2; (g) −40  dB, π/2; (h) −25  dB, π/2; (i) −70  dB, 3π/2; (j) −55  dB, 3π/2; (k) −40  dB, 3π/2; and (l) −25  dB, 3π/2. The insets are enlarged spectra.

Fig. 3. Simulation results of frequency-sweep nonlinearity. (a)–(c) Residual error of a free-running laser with the harmonic orders of 2, 20, and 100. (d)–(o) Residual error of a self-injection locked laser with various feedback ratios and harmonic orders: (d) −70  dB, m=2; (e) −70  dB, m=20; (f) −70  dB, m=100; (g) −55  dB, m=2; (h) −55  dB, m=20; (i) −55  dB, m=100; (j) −40  dB, m=2; (k) −40  dB, m=20; (l) −40  dB, m=100; (m) −20  dB, m=2; (n) −20  dB, m=20; (o) −20  dB, m=100; and (p) evolution of sweep nonlinearity with feedback ratio.

Fig. 4. Simulation results when both the laser spontaneous emission noise and the sweep nonlinearity are considered. (a) Residual frequency-sweep error of the free-running (blue) and self-injection locked (red) laser. (b) Zoom-in plot of the result of self-injection locked laser.

Fig. 5. Experimental setup of the self-injection locked frequency-swept laser. DFB, distributed feedback; AOM, acousto-optic modulator; EDFA, erbium-doped fiber amplifier; AFG, arbitrary function generator; RF, radio frequency.

Fig. 6. Laser frequency noise and linewidth measurement. (a) Schematic diagram of the setup. LUT, light under test; AOM, acousto-optic modulator; RF, radio frequency; PD, photodetector; PNA, phase noise analyzer; ESA, electrical spectrum analyzer. (b) Frequency noise of the free-running and self-injection locked laser. (c) Beat note spectra of the free-running (FR) laser and self-injection locked laser (SIL); the inset is the enlarged spectrum of the self-injection locked laser.

Fig. 7. Predistortion method and results. (a) Schematic diagram of the predistortion for frequency-sweep linearization without self-injection. AFG, arbitrary function generator; MZI, Mach–Zehnder interferometer; BPD, balanced photodetector; OSC, oscilloscope. (b) Averaged residual RMS evolution with the number of iterations. (c) Predistorted drive current. (d) and (e) Residual RMS of free-running laser driven by predistorted current in (d) down and (e) up ramp, respectively. (f) and (g) Residual RMS of free-running laser driven by initial current in (f) down and (g) up ramp, respectively.

Fig. 8. Self-injection locking results. (a) Beat signal spectra of the free-running (FR) and self-injection locked (SIL) lasers. (b) Enlarged spectra of (a); the central frequency is 2.046 MHz. (c), (d) Residual errors with and without self-injection locking in down and up ramps. (e), (f) Enlarged residual errors of injected laser in down and up ramps.

Fig. 9. Laser ranging setup and results. (a) Schematic diagram of the FMCW LiDAR. PD, photodetector; OSC, oscilloscope. (b) Range resolution versus target distance and the theoretical resolution limits with a self-injection locked laser. (c)–(e) Beat signal spectra of free-running laser (blue) and self-injection locked laser (red) at different distances: (c) 21.118 m, (d) 1018.85 m, and (e) 10,002.1 m.

Fig. 10. Range and velocity measurement accuracies. (a) Range accuracy versus target distance. (b) Velocity measurement result and accuracy versus target distance.