As laser diodes are highly sensitive to changes in current, the industry standard operating mode for laser diode applications is constant current mode. A laser diode’s beam intensity or light output is proportional to current change, and holding a stable operating current will allow the user to maintain a consistent beam output, while protecting the laser diode from dangerous current surges.
While less commonly used, constant power mode may be preferred by users who need a stable long-term optical output power. Constant power mode is effective for applications that require constant beam output despite temperature drifts, or diode degradation from aging/constant use. Constant power mode generally requires a more complex system, including a responsive photodiode feedback loop and fine-tuning the transfer function for a specific laser diode package. It is important to note that you may experience instability, slow responses, or potential diode damage if the system’s feedback loop is not well-tuned.
Constant voltage mode is rarely recommended for laser diode applications, and a majority of laser driver manufacturers will not offer constant voltage operating mode in their lineup of equipment. Constant voltage mode is generally dangerous for laser diodes, as a minor change in voltage could lead to a drastic change in current which results in poor optical output control and puts the laser diode at risk of catastrophic damage. However, depending on your application requirements or system simplicity, there may be a time and place for constant voltage control. Constant voltage mode allows for simple circuitry and can be useful in applications where current regulation is not critical (some LED applications, legacy setups, and applications with consistent thermal load). Constant voltage control can also be used in tandem with current limiting resistors, but overall, it is not laser diode-friendly in a vast majority of applications.