Fig. 1. Structure of proposed system

Fig. 2. Principle of operation of diffraction waveguides

Fig. 3. Position of output light with different wavelengths at coupled-out volume grating

Fig. 4. Grating design principle. (a) Coupled-in volume grating structure; (b) coupled-out volume grating structure

Fig. 5. Distribution of the spectra on the detector from different light sources. (a) Continuous light source; (b) discrete light source

Fig. 6. Diffraction efficiency of composite grating

Fig. 7. Relationship between FSR and h

Fig. 8. Simulate structure of proposed system

Fig. 9. Simulation results of discrete wavelength points in each band to be measured. (a) Blue band,h=0.5 mm; (b) blue band, h=1 mm; (c) blue band, h=3 mm; (d) green band, h=0.5 mm; (e) green band, h=1 mm; (f) green band, h=3 mm; (g) red band, h=0.5 mm; (h) red band, h=1 mm; (i) red band, h=3 mm

Fig. 10. Simulation results of discrete wavelength points in a wide band range. (a) h=0.5 mm, L₂=8 mm; (b) h=0.5 mm, L₂=16 mm; (c) h=0.5 mm, L₂=25 mm; (d) h=1 mm, L₂=8 mm; (e) h=1 mm, L₂=16 mm; (f) h=1 mm, L₂=25 mm; (g) h=3 mm, L₂=8 mm; (h) h=3 mm, L₂=16 mm; (i) h=3 mm, L₂=25 mm