Fig. 1. (a) The schematic diagram of the proposed self-mode-locking OEO with ultrashort time delay and (b) the illustration of the generated time-domain square wave signals.

Fig. 2. The simulation results of the square-wave signals with different duty cycles under different phases. (a) ϕ=−0.985, (b) ϕ=−0.785, and (c) ϕ=−0.585.

Fig. 3. The experimental structure of the self-mode-locking OEO with ultrashort time delay.

Fig. 4. The MFCs (left columns) and corresponding time-domain square waves (right columns) generated by self-fundamental-mode-locking OEO with different bias voltages VBias in the MZM. (a) VBias=0.6V, (b) VBias=1.2V, (c) VBias=1.8V, (d) VBias=3.0V, and (e) VBias=4.8V.

Fig. 5. The MFCs (left columns) and corresponding time-domain square waves (right columns) generated by self-second-order harmonic-locking OEO with different bias voltages VBias in the MZM. (a) VBias=11.8V, (b) VBias=12.2V, (c) VBias=12.6V, (d) VBias=13.0V, and (e) VBias=13.4V.

Fig. 6. The MFCs (left columns) and corresponding time-domain square waves (right columns) generated by self-sixth-order harmonic-locking OEO with different bias voltages VBias in the MZM. (a) VBias=0.5V, (b) VBias=0.7V, (c) VBias=0.9V, (d) VBias=1.3V, and (e) VBias=2.0V.

Fig. 7. The measured phase noises of the fundamental frequency of the MFCs with different FSRs (blue line, 60 MHz; orange line, 120 MHz; and brown line, 360 MHz).

Fig. 8. The MFCs (left columns) and corresponding time-domain square waves (right columns) generated by self-fundamental-mode-locking OEOs with different loop lengths. (a) OEO loop is 3.4 m, (b) OEO loop is 5.5 m, and (c) OEO loop is 27.8 m.

Fig. 9. The measured periodic nonuniform square-wave signals.

Fig. 10. The composition analysis of the nonuniform square waves measured in Fig. 9. (a) Fig. 9(a-i), (b) Fig. 9(b-i), (c) Fig. 9(c-i), (d) Fig. 9(d-i), (e) Fig. 9(e-i), and (f) Fig. 9(f-i).