Apparatus and method for controlling {TAIL ~ tracking} and focusing servo in {HEAD ~ a holographic digital data storage system} 
Apparatus and method for controlling { TAIL ~ tracking } and focusing servo in { HEAD ~ a holographic digital data storage system }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD