The present invention is to provide a method applicable to a fiber-optic transceiver including a transmitter optical subassembly (TOSA) provided therein with a laser diode, but without a monitoring photodiode, a laser driver controlled by a controller IC for driving the laser diode to generate a laser beam, and a thermal sensor for sensing temperature of the laser diode. The method includes executing an approximation process to characteristic data, i.e. threshold currents of the laser diode at a plurality of specific temperatures and corresponding slope efficiencies (SE), provided by manufacturer for obtaining relationship therebetween over entire temperature range, manually adjusting operation parameters (such as bias current and modulation current) of the laser diode for generating expected optical power and extinction ratio at a normal temperature and for subsequently determining the operation parameters over the entire temperature range, and writing the relationship and operation parameters thus obtained into the controller IC.