Fig. 1. Schematic of the 8×3 DFB laser array. LD: laser diode; SCH-MQW: separate confinement hetero-structure-multi-quantum well; BG: Bragg grating.

Fig. 2. Schematic of equivalent π-phase shift grating.

Fig. 3. (a) Sampling grating period of LD1–LD24 designed based on REC technique. (b) Transmission spectra of the three designed series gratings (LD5, LD13, and LD21). The three transmission peaks labeled with red triangles correspond to the lasing modes of the three series laser units.

Fig. 4. Microscopic top view of the proposed DFB laser array.

Fig. 5. (a) Microscopic image of the chip-on-submount (COS) assembly. (b) Design model of the packaged device.

Fig. 6. (a) Superimposed lasing spectra of all 24 lasers with ISOA, IY, Icom, and ILD set to 180, 180, 30, and 100 mA, respectively, (b) fitted lasing wavelengths for the 24 lasers, and (c) wavelength deviations for the 24 lasers.

Fig. 7. (a) Measured output power of the three LDs located on the same waveguide when ISOA=100  mA, IY=100  mA, and Icom=30  mA, and the ILD is varied from 0 to 200 mA. (b) Measured voltage with respect to the currents of the three LDs when ISOA=100  mA, IY=100  mA, and Icom=30  mA, and the ILD is varied from 0 to 200 mA. (c) Measured output power of the three LDs when IY=180  mA, ILD=100  mA, and Icom=30  mA, and the ISOA is varied from 0 to 200 mA.

Fig. 8. Superimposed spectrogram as the 24 lasers of the proposed WSL are sequentially tuned by injecting currents varying from 50 to 200 mA in 5 mA increments, with ISOA=180  mA, IY=180  mA, and Icom=30  mA.

Fig. 9. (a) The measured RIN for LD1–LD24 when ISOA=100  mA, IY=100  mA, ILD=100  mA, and Icom=30  mA. (b) The measured RIN of LD12 when ILD is varied from 50 to 100 mA, in steps of 10 mA, with ISOA=100  mA, IY=100  mA, and Icom=30  mA. (c) The measured RIN of LD12 when ISOA is varied from 20 to 160 mA, in steps of 20 mA, with ILD=100  mA, IY=100  mA, and Icom=30  mA.

Fig. 10. Linewidth of a typical laser unit in the proposed DFB laser array when ISOA=180  mA, IY=180  mA, ILD=100  mA, and Icom=30  mA.

Fig. 11. (a) Variation of continuous wavelength sweeping optical power over time with a constant ISOA. (b) Variation of continuous wavelength sweeping optical power over time after real-time adjustment of ISOA for power equalization.

Fig. 12. Schematic of the high-precision measurement system for frequency variation over time of the WSL based on two F-P etalons. WSL: wavelength-swept laser; OS: optical splitter; VOA: variable optical attenuator; F-P etalon: Fabry–Perot etalon; PD: photodetector.

Fig. 13. Wavelength sweeping of LD12 and LD13: (a) under a linear scanning current and (b) after pre-distortion of ILD.

Fig. 14. Calculation process for the nonlinear variation of the proposed WSL’s output frequency over time. (a) Transmission spectrum information for 24 channels. (b) Method for calculating the peak distance ratio (R). (c) Transmission spectrum information at the start of the sweeping cycle. (d) Transmission spectrum information during the sweeping cycle.

Fig. 15. WSL dynamic sweeping characteristics measuring experimental system setup. OSA: optical spectrum analyzer; OS: optical splitter; CIR: optical circulator; PD: photodetector; WSL: wavelength-swept laser.

Fig. 16. Peak-hold spectrum of the continuous sweeping light from the WSL.

Fig. 17. (a) Temporal waveform of the multi-cycle FBG reflected light collected by the PD. (b) Magnified view of the FBG reflected signal in (a).

Fig. 18. (a) Schematic of the high-speed FBG sensor interrogation system based on the proposed WSL. (b) Physical photograph of the integrated high-speed FBG sensor interrogation system based on the proposed WSL. (c) Graphical interactive control program for the FBG sensor interrogation system developed with LabVIEW.

Fig. 19. 300 min real-time interrogation monitoring experiments of multiple physical parameters. (a) Temperature real-time interrogation experiment. (b) Variations in the center wavelength of FBGA are interrogated by the interrogation system with temperature. (c) Strain real-time interrogation experiment. (d) Variations in the center wavelength of FBGB are interrogated by the interrogation system with strain. λA: center wavelength of FBGA; λB: center wavelength of FBGB.

Fig. 20. Interrogation results of the vibration experiment: the time-domain interrogation distribution and frequency analysis of the interrogation results when the FBGC is under vibration conditions at (a) 2 kHz, (b) 4 kHz, and (c) 8 kHz.

Fig. 21. Interrogation system vibration and shock tests in (a) X-axis direction, (b) Y-axis direction, and (c) Z-axis direction.