In {HEAD ~ another embodiment}, {TAIL ~ an optical fiber} is provided with reflective gratings , each of which are reflective at different wavelengths 
In { HEAD ~ another embodiment } , { TAIL ~ an optical fiber } is provided with reflective gratings , each of which are reflective at different wavelengths
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH