Optical sub-carrier multiplex television transmission system using a linear laser diode

A sub-carrier multiplex transmission system comprising

• means for frequency division multiplexing a plurality of channels into a multiplexed input signal;
• means for supplying a dc bias current;
• means for combining said dc bias current and the multiplexed input signal into a laser drive current;
• and
• a semiconductor laser, responsive to the laser drive current, for producing an optical output including the plurality of channels and their second-order and third-order distortion signals, the dc bias current being a current for which a line tangent at said current to a curve of first derivative of laser output power with respect to laser drive current has a slope with a magnitude less than or equal to approximately 4.times.10.sup.-4 mW/mA.sup.2.

A sub-carrier multiplex transmission system comprising

• means for frequency division multiplexing a plurality of channels into a multiplexed input signal;
• means for supplying a dc bias current;
• means for combining said dc bias current and the multiplexed input signal into a laser drive current;
• and
• a semiconductor laser, responsive to the laser drive current, for producing an optical output including the plurality of channels and their second-order and third-order distortion signals, the dc bias current to the semiconductor laser being greater than a threshold current and sufficient to cause an intercept current to be at least 500 mA greater than the threshold current so that composite distortion products in the optical output are approximately minimized, wherein the intercept current is the current for which a line tangent to a dL/dI versus current characteristic for the semiconductor laser intercepts a point at which dL/dI is approximately zero.