Fig. 1. Schematic of wavelength tunable laser based on optical path of Littman external cavity

Fig. 2. Gain functions of laser. (a) r₂=0.0005, ΔL_IC=0; (b) r₂=0.005, ΔL_IC=50 nm; (c) r₂=0.01, ΔL_IC=0; (d) r₂=0.01, ΔL_IC=50 nm

Fig. 3. Δλ versus ΔL_IC. (a) r₂=0.0005; (b) r₂=0.005; (c) r₂=0.01

Fig. 4. Continuous tuning of Δλ with Δθ. (a) r2=0.0005; (b) r₂=0.005; (c) r₂=0.01

Fig. 5. Tuning properties of laser. (a) Bandwidth is 0.2 nm; (b) bandwidth is 0.5 nm; (c) bandwidth is 7 nm

Fig. 6. Relationship between tilting angle of waveguide and feedback intensity in single angled facet gain chip. (a) Schematic of single angled facet gain chip; (b) feedback intensity at output end under different tilt angles

Fig. 7. Schematic of experimental setup

Fig. 8. Physical drawing of experimental setup

Fig. 9. P-I curve and fluorescence bandwidth of chip

Fig. 10. P-I curve of wavelength tunable laser based on 650 nm gain chip

Fig. 11. Laser output results at typical currents. (a) Longitudinal mode image; (b) beam quality factor

Fig. 12. Wavelength stability of laser at current of 60 mA within 6.5 h

Fig. 13. Wavelength tuning characteristics of laser. (a) Mode-hop-free range; (b) tuning resolution

Fig. 14. Response of camera to different wavelengths^[38]

Fig. 15. Interferograms. (a) Using low-order (4th-order) wave plate; (b) using zero-order wave plate

Fig. 16. Surface shape test results. (a) Surface shape; (b) repeatability of multiple measurements