7.3 Laser diode characteristics and performance metrics
3 min read•august 7, 2024
Laser diodes are crucial in optoelectronics, converting electrical energy into light. This section dives into their key characteristics, including light output, spectral properties, and modulation capabilities. Understanding these metrics is essential for optimizing laser diode performance in various applications.
We'll explore the L-I curve, , and efficiency metrics. We'll also examine , , and beam properties. These factors impact laser diode performance in real-world scenarios, from telecommunications to high-power industrial applications.
Light Output Characteristics
L-I Curve and Threshold Current Density
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Top images from around the web for L-I Curve and Threshold Current Density
The natural critical current density limit for Li 7 La 3 Zr 2 O 12 garnets - Journal of ... View original
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An Experimental Study on the Temperature Characteristic of a 940 nm Semiconductor Laser Diode View original
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An Experimental Study on the Temperature Characteristic of a 940 nm Semiconductor Laser Diode View original
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Light-current (L-I) curve plots the output optical power as a function of the input current
Below the , the laser diode acts as an LED with low
Above the threshold current, the output power increases linearly with the input current
Threshold current density Jth is the minimum current density required for lasing action to occur
Depends on factors such as the active layer material, cavity length, and mirror reflectivity
Lower Jth leads to higher efficiency and lower power consumption
Slope Efficiency and Output Power
ηs is the ratio of the change in output optical power to the change in input current above the threshold
Measured in W/A and represents how efficiently the laser diode converts additional current into light
Higher ηs indicates better performance and is desirable for high-power applications
Output power is the maximum optical power that the laser diode can emit
Limited by factors such as the maximum current density the device can withstand and thermal effects
High-power laser diodes (HPLDs) can have output powers ranging from a few watts to several hundred watts
Wall-Plug Efficiency
ηwp is the ratio of the output optical power to the input electrical power
Measures the overall energy conversion efficiency of the laser diode
Depends on factors such as the slope efficiency, threshold current, and operating voltage
Typical values range from 30% to 70% for high-efficiency laser diodes (GaAs, InGaAs)
Spectral Properties
Spectral Linewidth
Spectral Δλ is the full width at half maximum (FWHM) of the laser diode's emission spectrum
Determines the laser's ability to resolve fine spectral features and its suitability for applications such as spectroscopy and fiber optic communication
Affected by factors such as the active layer material, cavity design, and operating conditions
The emission wavelength of a laser diode shifts with temperature at a rate of about 0.1 nm/°C
Caused by changes in the bandgap energy and refractive index of the active layer material
Requires temperature stabilization for applications that demand precise wavelength control
The threshold current and slope efficiency also vary with temperature
Higher temperatures lead to increased non-radiative recombination and reduced efficiency
Temperature-stabilized laser diode packages (butterfly, TO-can) often include a thermoelectric cooler (TEC) and thermistor for active temperature control
Modulation and Beam Properties
Modulation Bandwidth
f3dB is the maximum frequency at which the laser diode's output power can be modulated to 50% of its unmodulated value
Determines the maximum data rate for systems
Depends on factors such as the carrier lifetime, cavity photon lifetime, and parasitic capacitance