Fig. 1. Optical fiber terahertz time-domain spectral system

Fig. 2. Coupling efficiency of ideal single-mode fiber varies with β

Fig. 3. Coupling efficiency of initial single-mode fiber

Fig. 4. Spot diagram of optical system

Fig. 5. Optimized coupling efficiency of single mode fiber

Fig. 6. Spot diagram after optimization

Fig. 7. Schematic diagrams of coupling alignment error analysis. (a) Beam tilt relative to optical axis; (b) beam offset relative to optical axis; (c) beam waist radius mismatch with fiber mode field radius

Fig. 8. Relationship between coupling efficiency of Gaussian propagation single mode fiber and radial mismatch

Fig. 9. Relationship between coupling efficiency of Gaussian propagation single mode fiber and angular mismatch

Fig. 10. Relationship between coupling efficiency of physical propagation single mode fiber and radial mismatch

Fig. 11. Relationship between coupling efficiency of physical propagation single mode fiber and angular mismatch

Fig. 12. Experimental image of collimating lens coupling

Fig. 13. Relationship between fiber output power and coupling error. (a) Output power versus radial mismatch; (b) output power versusangular mismatch