| 摘要 |
PURPOSE:To suppress optical fluctuation due to temperature and to prevent an excess current at a high operating temperature by selecting a parameter of a bias circuit of a laser diode as specified and controlling a gate of a current source FET with a reference voltage generating source. CONSTITUTION:A gate of a depletion FET 14 being a current source FET of a bias circuit for a laser diode 3 is controlled by a reference voltage generating source comprising a reference resister 15 or the like connecting to a drain of the FET 14 similar to a FET 16 whose one drain connects to a power supply terminal 102 and whose gate and source are connected together and whose source connects to the power supply terminal. When a parameter of the bias circuit at a room temperature and a parameter of a diode 3 at a maximum operating temperature are selected to satisfy the condition of expressions I, II respectively, a current of the FET 16 is increased as temperature rises, the current is maximum at the operating highest temperature, the light fluctuation by temperature rise is suppressed and excess current at the maximum operating temperature is prevented. In equations, Vt, K are threshold voltage and mutual conductance of the FET 16, R is a resistance of the resistor 15, W is a gate width of the FET 14 and Vf is a Scottky leading voltage of the FET 16. |
