Abstract: A method to control the emission wavelength of a tunable laser diode (LD) is disclosed. The method measures the first derivative of the wavelength against the first stimulus, typically a current injected in the SG-DFB region, and the second derivative of the wavelength against the power supplied to the heater in the CSG-DBR region. The method adjusts the current so as to coincide the emission wavelength with the target wavelength, then, corrects the target power for the heater based on the derivative of the current multiplied by a ratio of two derivatives measured in advance to the control of the heater current.

Abstract: The method to change the emission wavelength of a tunable LD is disclosed. In an ordinary state, the method monitors conditions not only relating to determine the emission wavelength but conditions independent of the emission wavelength by an ordinary A/D-C implemented within the controller. Responding to an instruction to switch the emission wavelength, the controller only monitors the former conditions affecting the determination of the emission wavelength. The sampling rate of the ordinary A/D-C is equivalently enhanced without installing an additional A/D-C.

Abstract: A heater controller for controlling a heater precisely in the equi-power mode is disclosed. The controller includes a current source, a voltage monitor to detect a voltage drop caused in the heater, and a controller. The voltage drop may be converted to the digital form as refereeing to the first reference, while, the heater current is converted from the digital form as referring to the second reference. The second reference shows substantial temperature dependence, while, the first reference has lesser temperature dependence. The control corrects the temperature dependence of the second reference as referring to the first reference.

Abstract: An LD driver is disclosed where the power dissipation is reduced without enlarging the circuit scale. The LD driver, which drives a tunable LD including a SG-DGB region, a CSG-DBR region, and an SOA region, includes a DC/DC converter connected to current sources or voltage sources each coupled with at least two regions of the SG-DFB, CSG-DBR and SOA regions, and a voltage controller to control the output of the DC/DC converter which is commonly provided to the current sources or the voltage sources. The voltage controller independently monitors the bias conditions of the at least two regions above, and sets the output of the DC/DC converter so as to exceed a largest voltage among voltages currently provided to respective regions by a preset margin to operate the current sources or the voltage sources normally.

Abstract: A heater controller for controlling a heater precisely in the equi-power mode is disclosed. The controller includes a current source, a voltage monitor to detect a voltage drop caused in the heater, and a controller. The voltage drop may be converted to the digital form as refereeing to the first reference, while, the heater current is converted from the digital form as referring to the second reference. The second reference shows substantial temperature dependence, while, the first reference has lesser temperature dependence. The control corrects the temperature dependence of the second reference as referring to the first reference.

Abstract: An LD driver is disclosed where the power dissipation is reduced without enlarging the circuit scale. The LD driver, which drives a tunable LD including a SG-DGB region, a CSG-DBR region, and an SOA region, includes a DC/DC converter connected to current sources or voltage sources each coupled with at least two regions of the SG-DFB, CSG-DBR and SOA regions, and a voltage controller to control the output of the DC/DC converter which is commonly provided to the current sources or the voltage sources. The voltage controller independently monitors the bias conditions of the at least two regions above, and sets the output of the DC/DC converter so as to exceed a largest voltage among voltages currently provided to respective regions by a preset margin to operate the current sources or the voltage sources normally.