Abstract: Apparatus, and a related method for its operation, for isolating a semiconductor laser diode physically and thermally from a drive circuit used to generate large modulating currents applied to the laser diode. Bias and modulating currents generated by the drive circuit are transmitted to the laser diode over a selected length of transmission line, such as a coaxial cable. Generation of heat close to the laser diode is minimized by a backmatching technique in which impedance matching is effected entirely at the drive circuit end of the transmission line. An impedance matching the characteristic impedance of the transmission line is connected across the line at the drive circuit end, allowing modulation currents to be transmitted to the laser diode without distortion.