Can multiple laser diodes be connected in parallel

Laser diodes should generally not be connected in parallel directly due to uneven current distribution, but multiple current sources can be paralleled to drive a single diode safely.

Why Direct Parallel Connection is Problematic

Laser diodes are current-driven devices, meaning their output power is highly sensitive to the current supplied. When two or more diodes are connected in parallel, small differences in forward voltage between the diodes can cause one diode to draw more current than the others. This imbalance can lead to overdriving some diodes, resulting in uneven output power, overheating, or permanent damage to the diodes (RPMCLasers ). Even minor variations in diode characteristics or temperature can exacerbate this effect, making direct parallel wiring unsafe for standard laser diodes.

Safe Alternatives

1. Series Connection: Multiple diodes can be connected in series, where the same current flows through each diode. The power supply must provide a voltage high enough to cover the sum of the forward voltages of all diodes. This ensures equal current sharing and stable operation (RPMCLasers ).
2. Paralleling Current Sources: Instead of connecting diodes directly in parallel, multiple laser diode current sources can be paralleled to drive a single high-power diode. Each current source contributes a portion of the total current, and careful wiring ensures accurate current delivery. This method is commonly used in high-power laser systems to achieve the required drive current without overloading a single source (MKS, GoPhotonics ).
   • Connect the outputs of all current sources as close as possible to the diode leads.
   • Use voltage sense lines if available to ensure precise current regulation.
   • Avoid running sources at maximum output to allow for efficiency drops over time.

Key Considerations

• Thermal Management: Uneven heating can worsen current imbalance in parallel setups, so proper heat sinking is essential (STMicroelectronics ).
• Current Matching: If multiple diodes must be paralleled, they should be carefully matched in forward voltage and temperature characteristics, though this is rarely practical for standard laser diodes.
• Driver Selection: Use constant current drivers rather than constant voltage sources, as laser diodes are sensitive to voltage fluctuations.

Conclusion

Directly connecting laser diodes in parallel is not recommended due to the risk of uneven current distribution and potential diode failure. Safe alternatives include series connections or paralleling multiple current sources to drive a single diode. Proper thermal management, current regulation, and driver selection are critical to ensure reliable operation.