Fig. 1. Structure of TS-DW-DFB laser and partial gratings. (a) Structure of TS-DW-DFB laser; (b) grating structure of TS-DW-DFB laser; (c) grating structure in GR section

Fig. 2. Spectra of gratings in GR section and DW-DFB laser. (a) Reflection spectrum in GR section without apodization and transmission spectrum of DW-DFB laser; (b) reflection spectrum in GR section without apodization and delay spectrum of DW-DFB laser; (c) reflection spectrum in GR section with apodization and transmission spectrum of DW-DFB laser; (d) reflection spectrum in GR section with apodization and delay spectrum of DW-DFB laser

Fig. 3. Delay spectra of DW-DFB section and wavelength spacing between two main-modes of TS-DW-DFB laser for different EPSs. (a) Delay spectra of DW-DFB laser with different EPSs; (b) variation of wavelength spacing between two main-modes of TS-DW-DFB laser with different EPSs

Fig. 4. Power of two main modes of DW-DFB laser and TS-DW-DFB laser at I_DW=100 mA. (a) Power of two main modes of single-stage DW-DFB laser; (b) power of two main modes of TS-DW-DFB laser

Fig. 5. Threshold gain and output power difference for L_DW=500 μm. (a) Threshold gain versus length of GR section; (b) PDM versus length of GR section

Fig. 6. Pictures of TS-DW-DFB laser. (a) Physical image of TS-DW-DFB laser; (b) SEM image of TS-DW-DFB laser facet

Fig. 7. Optical spectra of single-section DW-DFB laser and TS-DW-DFB laser with different injection currents. (a) Optical spectrum of single-section DW-DFB laser with I_DW=60 mA; (b) optical spectrum of single-section DW-DFB laser with I_DW=90 mA; (c) optical spectrum of TS-DW-DFB laser with I_DW=60 mA and I_GR=12 mA; (d) optical spectrum of TS-DW-DFB laser with I_DW=90 mA and I_GR=12 mA

Fig. 8. Output power, PDM, and SMSR of TS-DW-DFB laser versus current of GR section. (a) Output power of TS-DW-DFB laser versus current of GR section when I_DW=80 mA; (b) PDM and SMSR of TS-DW-DFB laser versus current of GR section when I_DW=80 mA

Fig. 9. SMSR and PDM of DW-DFB laser and TS-DW-DFB laser. (a) SMSR of DW-DFB laser and TS-DW-DFB laser versus I_DW; (b) PDM of DW-DFB laser and TS-DW-DFB laser versus I_DW

Fig. 10. 2D optical spectra of TS-DW-DFB laser under different operation conditions. (a) 2D optical spectra of TS-DW-DFB laser under different temperatures when I_DW=80 mA and I_GR=12 mA; (b) 2D optical spectra of TS-DW-DFB laser during 1 h when I_DW=80 mA,I_GR=12 mA, and operation temperature is 24 ℃

Fig. 11. PDM, SMSR,wavelength of two main modes, and wavelength spacing of TS-DW-DFB laser varying with temperature. (a) SMSR and PDM of TS-DW-DFB laser varying with temperature when I_DW=80 mA and I_GR=12 mA; (b) wavelength of main modes varying with temperature when I_DW=80 mA and I_GR=12 mA; (c) wavelength spacing between two main modes varying with temperature when I_DW=80 mA and I_GR=12 mA

Fig. 12. PDM, SMSR, and wavelength spacing of TS-DW-DFB laser varying with time. (a) SMSR and PDM of TS-DW-DFB laser during 1 h when I_DW=80 mA,I_GR=12 mA, and operation temperature is 24 ℃; (b) wavelength spacing between main modes of TS-DW-DFB laser during 1 h when I_DW=80 mA, I_GR=12 mA, and operation temperature is 24 ℃