The present invention provides a compact analog directly modulated laser
configuration that is suitable for use in the field that uses electrical
feedback to compensate for non-linearity in real time, such that no
matter how the LI curve changes, the electrical feedback compensates for
non-linearity by amplifying a portion of the output analog optical signal
and combining it with the input analog electrical signal using the
standard control method of negative feedback. When the gain of the
feedback loop is relatively high, the overall transfer function of the
system is primarily dependent on the feedback loop gain block, which is
substantially linear. This is accomplished by incorporating a relatively
large bandwidth photo-detector at the back facet of the laser that both
monitors the output power of the system and provides a feedback signal to
the linearization control circuit, as well as an amplifier. The amplified
signal from the relatively large bandwidth photo-detector is used to
correct for various undesirable effects, such as non-linearity and
relative intensity noise (RIN) of the laser. The signal from the
relatively large bandwidth photo-detector also allows the laser to
operate effectively close to threshold.