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Laser Diode Temperature Measurement

Fibre interconnection and data room reference Published 23 Jun 2025

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Laser diodes can be used for precise temperature measurement either as part of optical sensing systems or in combination with thermistors for controlling diode temperature.

Diode-

Based Electrical Temperature Sensing

Semiconductor diodes, including diode-connected BJTs, are widely used as temperature sensors due to their predictable forward voltage drop that varies linearly with temperature, typically around −2 mV/°C. In practice, a diode or BJT is excited with a small current, and the resulting voltage is measured. The voltage is then converted to temperature using calibration curves.

This method is low-cost, compact, and suitable for moderate-precision applications in automotive, industrial, and consumer electronics. For laser diodes, temperature control is critical because the emission wavelength shifts with temperature, affecting performance in optical communication and LiDAR systems.

NT

C thermistors are often integrated near the laser diode to provide highly accurate temperature feedback, with tolerances as tight as ±1% and operating ranges from −40 to 125 °C. These thermistors can be wire-bonded inside the laser package for precise monitoring.

Optical Temperature Measurement Using Laser Diodes

Laser diodes can also be used in non-contact optical temperature measurement through tunable diode laser absorption spectroscopy (TDLAS). In this approach, a diode laser is tuned to a specific absorption line of a target gas, such as H₂O, and the absorbance is measured. The temperature is then inferred from the ratio of integrated absorbances of lines with different lower energy levels.

This method is non-intrusive, fast, and highly sensitive, making it suitable for combustion diagnostics, aerospace, and industrial applications. Accuracy can reach a few percent over a wide temperature range, even under strong laser intensity fluctuations.

Laser Diode Thermal Characterization

For research and development, the temperature of the laser diode's active region can be determined by comparing current-voltage characteristics under continuous and pulsed operation. This allows calculation of the thermal resistance and the operating temperature at peak power, which is essential for preventing overheating and optimizing performance.

Summary

Electrical sensing: Uses diode or BJT forward voltage; simple, low-cost, moderate precision. Thermistor-assisted control: NTC thermistors near laser diodes provide precise temperature feedback for wavelength stabilization. Optical sensing (TDLAS): Non-contact, high-accuracy measurement of gas or surface temperature using laser absorption; suitable for high-temperature and industrial environments.

Thermal characterization: Current-voltage analysis allows determination of active region temperature and thermal resistance for laser diode design optimization. These methods ensure accurate temperature monitoring and control, which is critical for maintaining laser diode performance, wavelength stability, and device longevity.

Laser Diode Temperature Measurement - FD SOLUCIONES OPTICAL SYSTEMS [PDF]

Laser Diode Temperature Measurement

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