As shown in the figure, {TAIL ~ a wave} 201 representing {HEAD ~ data} is trapped in a ring cavity 202 
As shown in the figure , { TAIL ~ a wave } 201 representing { HEAD ~ data } is trapped in a ring cavity 202
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH