Fig. 1. Schematics of detection light path. (a) Multi-channel detection; (b) multi-band detection

Fig. 2. Initial spectral curve of four-pass band designed by long and short wave pass method

Fig. 3. Four-pass band transmission curve designed by optimized long and short wave pass combination method

Fig. 4. Four-pass band cutoff spectral curve designed by optimized long and short wave pass combination method

Fig. 5. Transmittance curve of film system structure 1

Fig. 6. Transmittance curve of film system structure 2

Fig. 7. Origin spectral curve of designed quad-band bandpass film system structure

Fig. 8. Spectral curves of quad-band bandpass filter after optimization . (a) Transmittance spectrum; (b) cutoff background spectrum

Fig. 9. Simulated transmittance spectrum with average error of 0.2%

Fig. 10. Comparison between designed and measured spectra before optimization

Fig. 11. Sensitivity analysis results of primary quad-band bandpass layers

Fig. 12. Comparison between designed and measured transmittance curves after optimization

Fig. 13. Measured results of re-plated quad-band bandpass films after ion beam bombardment. (a) Transmittance spectrum; (b) optical density

Fig. 14. Temperature variation curve during high-low temperature cycle

Fig. 15. Environmental adaptability of quad-band bandpass filter. (a) Transmittance spectrum after high-low temperature experiment; (b) optical density after high-low temperature experiment; (c) physical picture of product after high-low temperature experiment; (d) surface morphology after environment experiment

Table 1. Optimal process parameters