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