Glossary entry

LIV curve

Light–current–voltage characteristic — simultaneous measurement of optical output power and forward voltage across a laser diode as a function of drive current.

The LIV (also L–I–V or P–I–V) measurement is the standard characterization of a semiconductor laser diode. Drive current is stepped through a range while two quantities are recorded simultaneously:

L (or P) — optical output power, measured with a calibrated photodetector, integrating sphere, or optical power meter
V — forward voltage across the diode terminals, measured by 4-wire (Kelvin) sense to eliminate lead resistance contamination

From a single-temperature LIV curve, multiple parameters can be extracted:

Threshold current $I_\text{th}$ from the L vs. I curve
Slope efficiency $\eta_s$ from the linear region above threshold
Series resistance from the $dV/dI$ slope above threshold
Wall-plug efficiency $\eta_\text{WPE}$ at any operating point
Turn-on voltage from the V–I knee

Temperature-dependent LIV (LIV-vs-T) datasets additionally yield the characteristic temperature $T_0$ and the differential efficiency temperature coefficient $T_1$ .

Standard measurement configuration:

Function	Component	Specification
Current source	SMU or pulsed current driver	$\leq 0.1\%$ resolution; pulsed at $\leq 1\%$ duty cycle for high-power devices
Voltage measurement	4-wire Kelvin sense	$\leq 100$ μV resolution
Optical detection	Calibrated photodetector or integrating sphere	Linear over the lasing power range
Temperature control	TEC with thermistor on submount	$\pm 0.1$ K stability

For continuous-wave operation at currents above $\sim 3 \, I_\text{th}$ , self-heating of the active region biases the measurement. Pulsed operation at $\leq 0.1$ % duty cycle eliminates the bias and is required for accurate high-power LIV characterization.