The LDT-5910C and LDT-5940C easily control the temperature of your laser diode in one of three modes: (1) Constant Temperature, (2) Constant Sensor or (3) Constant Current. Temperature stability of <+0.003°C ensures device performance and highly reliable test measurements. With <+0.003°C stability, the controllers are ideal for R&D applications, eliminating mode hopping and significantly reducing noise due to temperature fluctuations.

The above figure figure shows that the threshold current and differential responsivity of a laser diode are strongly affected by the laser’s temperature. The laser threshold will increase exponentially with temperature as exp(T/T0), where T is the laser temperature and T0 is the “characteristic temperature” of the laser (typically between 60 to 150°C). T0 is a measure of the temperature sensitivity of the device with higher values implying that the device is more thermally stable. T0 is an important laser diode characteristic and is commonly extracted from multiple L-I curves. Changes in temperature also affect the bandgap of the semiconductor junction and therefore, the peak wavelength of the gain profile. This results in a linear relationship between temperature and the center wavelength of the laser diode (see above figure) with typical temperature tuning coefficients of 0.3 nm/°C. As a result, a temperature controller plays a key role in determining the laser wavelength. Please see Fundamentals of Laser Diode Control for additional information.

In addition to thermistor temperature sensor compatibility, the controllers accommodate RTD, current and voltage IC sensors. The type of temperature sensor is selected through the front panel or by remote command. An auto-sensing thermistor current mode selects thermistor current based on measured resistance. By using the appropriate calibration constants, +0.2°C absolute accuracy can be achieved. A unique linearized thermistor mode allows a standard 10kΩ thermistor to be used over the range from -30°C to 85°C in the 100 µA setting.

The LDT-5910C and LDT-5940C feature a fully programmable PID loop with manually adjustable PID constants, twelve preset PID values, and an auto-tuning mode. The different PID modes allow for fast and easy instrument configuration or precise PID adjustment. The first six presets feature the original gain values of the LDT-5910C and the second six presets offer optimal performance for the compatible ILX Lightwave mounts. In addition to selecting the optimum PID value for ILX Lightwave mounts, when a preset is chosen, the correct TE current limit and sensor of the mount is automatically set in the instrument. The two auto-tune functions provide the ideal auto-tuning algorithm in varying applications and automatically determine the optimal PID control constants for your particular thermal load.

The front panel features a large 7-segment LED display with integrated dot matrix display. The 7-segment display enables easy viewing of temperature, sensor resistance, or TE current across the lab depending on the control mode. The dot matrix display can display TE current, TE voltage, sensor resistance or temperature, as well as the control set point and errors. The front panel buttons are grouped by function for easy setup. With ILX interconnect cabling and a wide variety of laser diode mounts, you can set up and control temperature within minutes. New to ILX Lightwave is the ability to upgrade the firmware of the controllers on-site via the USB 2.0 interface. For detailed instructions, on upgrading the firmware, contact ILX Lightwave.

The LDT-5910C and LDT-5940C provide peace of mind with normally open and normally closed interlocks that open or close when the output is disabled. The interlocks are designed to connect to your current source and will disable the output of the current source if the controllers are disabled. The current, temperature, and temperature sensor control loops are bound by programmable limits. The current limit includes independent heating and cooling current limits that provide not only device protection, but a heat only mode. Adjustment of the limit settings is easy and precise, even with the instrument’s output enabled.