Laser Diode Characterization

Laser diodes are characterized by their inherent physical properties within five distinct categories, including: electrical, spatial, spectral, optical, and dynamic properties. For a detailed discussion of these physical properties of laser diodes, the reader is referred to Optical Emission in Semiconductor Materials and Laser Diode Light Characteristics. The combination of properties within these categories determines the performance and effectiveness of a given laser diode in terms of operational characteristics such as:

• Threshold current - the current at which the device begins to lase
• Output power - the average output power generated by the device
• Peak wavelength - the wavelength at which the greatest output power is observed

Prior to integration within an optical system, the device design incorporating a laser diode must be validated and the properties of the proposed laser diode have to be analyzed using appropriate instrumentation. The available tools for testing a laser diode within the categories identified above include:

• Laser diode drivers, TEC controllers, and laser diode controllers (see Laser Diode Control Fundamentals)
• Optical power meters and detector heads (see Radiometric Measurement)
• Microscopes and vision systems
• Optical spectrum analyzers, wavelength meters or spectrometers
• Laser beam profilers (see Laser Beam Profile Measurement)

Figure 1 shows the MKS ILX Lightwave LDC-3726 laser diode controller and ILX Lightwave OMM-6810/OMH-6724B optical power and wavelength meter. They allow a user to control, manipulate, and measure the performance of an individual device. Using these instruments, laser diode output characteristics such as changes in output power and wavelength can be analyzed in a relatively simple setup. The LDC-3726 controller has unparalleled device protection, LIV (light, current, voltage) measurement capability, and repeatable output(s). It provides precise temperature control, which greatly improves the ability to analyze thermal effects and offers low noise current control up to 500 mA, optimal for telecommunications applications. The OMM-6810B/OMH-6742 power and wavelength meters have precise device output power measurements, are capable of measuring both output power and wavelength in a single instrument, and have remote control capability for automated test setups. Typical applications for these controllers include R&D of new products and validation of existing products under various conditions.