Fig. 1. (a) Schematic structure of a phase-locked array of quantum cascade lasers; (b) Schematic diagram of total reflection mirror structure; (c) Schematic structure of seed laser; (d) Schematic structure of the semi-reflector; (e) Schematic structure of array output port; (f) Schematic structure of single-mode waveguide

Fig. 2. Schematic structure of the grating

Fig. 3. Schematic structure of multimode interference

Fig. 4. Schematic structure of bending waveguide

Fig. 5. (a) Waveguide optical limiting factor and loss versus upper InP cladding layer thickness; (b) Waveguide optical limiting factor and loss versus upper GaInAs layer thickness; (c) Waveguide optical limiting factor and loss versus lower GaInAs layer thickness; (d) Waveguide optical limiting factor and loss versus lower InP cladding layer thickness; (e) Waveguide optical limiting factor versus waveguide width; (f) The relationship between the effective refractive index of waveguide mode and the width of waveguide

Fig. 6. Transmission spectra versus different number of grating cycles

Fig. 7. (a) Comparison of transmission spectra with duty ratio of 0.6-0.9 and 0.5; (b) Comparison of transmission spectra with duty ratio of 0.1-0.4 and 0.5

Fig. 8. Transmission spectra of Bragg mirrors with different reflectivities. (a) 50% reflectivity; (b) 100% reflectivity

Fig. 9. Relation between L_MMI and transmission of output port

Fig. 10. (a) 19 μm×126 μm MMI optical field without tapered waveguide; (b) 19 μm×126 μm MMI optical field with tapered waveguide

Fig. 11. Temperature distribution for different array distances. (a) Distance is 15 μm; (b) Distance is 25 μm; (c) Distance is 35 μm; (d) Distance is 45 μm

Fig. 12. Optical field distribution of bending waveguides of different sizes. (a) 1300 μm×155.25 μm; (b) 550 μm×75.25 μm; (c) 380 μm×35.25 μm; (d) 280 μm×15.25 μm

Fig. 13. Relation between transmission and Al₂O₃ film thickness

Fig. 14. Far-field distribution of the array at different distances. (a) Far-field distribution at an array distance of 15 μm; (b) Far-field distribution at an array distance of 25 μm; (c) Far-field distribution at an array distance of 35 μm; (d) Far-field distribution at an array distance of 45 μm