Fig. 1. Schematic diagram of fiber-coupled optical system

Fig. 2. Simulation results of divergent angles of collimated beams. (a) Divergent angle of point-source QCL collimator; (b) divergent angle of extended-source QCL collimator with (0 mm, 0 mm) field of view; (c) divergent angle of extended-source QCL collimator with (-0.004 mm, -0.005 mm) field of view; (d) divergent angle of extended-source QCL collimator with (0.004 mm, 0.005 mm) field of view

Fig. 3. Simulation results of divergent angles of two collimators. (a) Point-source QCL collimator; (b) extended-source QCL collimator

Fig. 4. Simulated intensity distributions of collimated beams. (a) QCL collimator with NA of 0.68; (b) QCL collimator with NA of 0.83

Fig. 5. Simulation result of single-channel fiber-tcoupling system. (a) Laser spot on input surface of fiber; (b) laser spot at 0.1 mm away from output surface of fiber

Fig. 6. Single-mode hollow core fiber combiner. (a) Structure diagram of hollow core fiber; (b) transmission loss of single-mode hollow core fiber; (c) picture of single-mode hollow core fiber; (d) picture of single-mode 4×1 hollow core fiber combiner; (e) picture of output surface of single-mode hollow core 4 in 1 fiber combiner under microscope

Fig. 7. Schematic diagram of fiber combining experimental system

Fig. 8. Experimental setup of single-mode fiber coupling system

Fig. 9. Picture of QCL collimator and fiber coupler. (a) QCL collimator with NA of 0.83; (b) fiber coupler

Fig. 10. Experimental results of coupling of single-mode long wave infrared hollow core fiber. (a) Fiber output power; (b) fiber coupling efficiency

Fig. 11. QCL collimating spot and fiber coupling output spot. (a) QCL collimating spot; (b) fiber coupling output spot

Fig. 12. Experimental setup of 4×1 fiber combining system

Fig. 13. Experimental results of QCL 4×1 fiber combining. (a) Fiber coupling output power; (b) total fiber output efficiency and total system coupling efficiency

Fig. 14. Combined QCL beam spots at different positions along beam propagation direction. (a) -50 mm; (b) 0 mm; (c) 100 mm; (d) 150 mm

Fig. 15. Beam propagation quality factor M² of combined QCL. (a) X axis; (b) Y axis

Table 1. Performance parameters of long-wave infrared QCL

Table 2. Lens data of point-source QCL collimator

Table 3. Lens data of extended-source QCL collimator

Table 4. Lens data of QCL collimator with NA of 0.68

Table 5. Lens data of QCL collimator with NA of 0.83

Table 6. Lens data of fiber coupler

Table 7. Measurement results of QCL output properties