Abstract: A transistor, such as a FET or bipolar transistor, may be gate or base coupled to a laser driver output stage to receive a varying voltage from a driver output stage. The transistor converts the varying voltage to a varying current. The transistor, in series with the laser, may be coupled to a supply voltage on one side and ground on the other side. Thus, the current supplied to the laser diode is a function of the drive supplied to the transistor's base or gate.

Abstract: A system for encoding digital data with an M-ary (d,k) code to provide multi-level coded data where M>2 comprises an M-ary (d,k) encoder for accepting digital input data. The M-ary (d,k) coder encodes the digital input data to produce a plurality of code symbols, where each code symbol is at one of M levels and each pair of non-zero code symbols is separated by at least d but no more than k zeros. A waveform encoder converts the code symbols into waveform signal amplitudes compatible with a multi-level channel. Each waveform signal amplitude is generated by modulo M addition of a current code symbol with a previous waveform signal amplitude. A specific M-ary (d,k) code provides high density recording to a multi-level storage medium. The M-ary (d,k) encoder is implemented using a M-state encoder and a modulo M waveform encoder.