x=Range[10]

y=RandomReal[{0,1},10]

{0.6783303268841356`,0.8544302792621852`,0.21137756384277662`,0.1537254657647673`,0.703558,0.0841558952426511`,0.5658538579334338`,0.3129629071193434`,0.0883717151778236`,0.11628763097720896`}

Example:

wavelength=Range[1.5,1.6,0.02]

modeindex=RandomReal[{1.4,1.5},Length[wavelength]]

ListLinePlot[Transpose[{wavelength,modeindex}]
,PlotStyle->{Thickness[0.01],Hue[0.35,1,1]}
,Filling->{1-> {0,Hue[0.27,1,1,0.3]}}
,Frame->True, GridLines->Automatic
,FrameStyle->White, GridLinesStyle->GrayLevel[0.5]
,FrameLabel->(Style[#,18,White,FontFamily->"Calibri"] & /@ {"wavelength (μm)", "mode refractive index"})
,Background->Black]