Reading bits on a CD-ROM without a photodiode

Abstract : The authors demonstrate that the bits of a Compact Disc – Read Only Memory (CD-ROM) can be read without aphotodiode (PD). A commercial CD-ROM drive was used and left unmodified except a beam splitter was removed which wouldroute the light to a PD. This allowed for the reflected light to be incident on the laser within the laser package itself. Bymonitoring fluctuations in the voltage across the laser diode under constant-current injection, it was possible to read andinterpret the bits from a spinning CD-ROM