wherein {HEAD ~ the beams} focused onto {TAIL ~ the optical disc} are separated into the beam reflected by the optical member and the beam reflected by the reflecting member after being transmitted through the optical member and then generate different dual focuses on the optical disc 
focused onto
wherein { HEAD ~ the beams } focused onto { TAIL ~ the optical disc } are separated into the beam reflected by the optical member and the beam reflected by the reflecting member after being transmitted through the optical member and then generate different dual focuses on the optical disc
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH