Fig_3.

(a) The transmission spectrum shifts after injecting the index-calibrated water-glycerol solutions. Each spectrum is obtained from one of the 50 channels using a 600 lines/mm grating. (b) The refractive index sensitivity measured from spectral shift versus refractive index units (RIU) change. It shows linear increase and is very homogeneous over all 50 channels. The measured sensitivity is 470 ± 11.7 nm / RIU. (c) Spectral resolution based on the refractive index sensitivity and the standard deviation of noise (Ïf) of the experiment above. With 2.5 sec temporal resolution, the spectral noise is Ïf = 3.6×10⁻³ nm, giving ~10⁻⁶ RIU spectral resolution.