A method to produce an optical module, in particular, a module to transmit an analog data to enhance a yield thereof is disclosed. The method comprises (a) taking an I-L characteristic and its slope efficiency, (b) taking a gradient of a linear approximation between the slope efficiency and a current applied to an LD, and (c) taking an optimum current for the CSO characteristic as varying the current. Steps (a) to (c) give a correlation between the gradient of the linear approximation and the optimum current and are performed in advance to the practical production.