Fig. 1. Dammann grating mask patterns. (a) 2×2 Dammann grating; (b) 3×3 Dammann grating; (c) 4×4 Dammann grating;(d) 1×2 vortex Dammann grating

Fig. 2. Simulated results of Dammann grating. (a) 2×2 Dammann grating; (b) 3×3 Dammann grating; (c) 4×4 Dammann grating; (d) 1×2 vortex Dammann grating; (e) 1×2 forked grating

Fig. 3. Flow chart of fabrication of Dammann grating using femtosecond laser direct writing assisted by inductively coupled plasma etching

Fig. 4. Processing effects. (a) Microscopic images of mask plate patterns processed by femtosecond laser; (b) microscopic images of inductively coupled plasma etching results

Fig. 5. Characteristic diagrams by contour instrument. (a) Three-dimensional morphology of Dammann grating; (b) measured depth of Dammann grating

Fig. 6. Test light path and coupling results. (a) Test light path of far field intensity distribution of Dammann grating; (b) coupling results captured on CCD