How to Synchronize VCSEL and Photodiode Measurements

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Synchronize VCSEL And Photodiode Measurements

Light-Current-Voltage (LIV) characterization of a Vertical Cavity Surface Emitting Laser (VCSEL) requires measuring the laser drive current and the corresponding optical response. When the VCSEL operates with a narrow current pulse, the monitor photodiode (PD) current must be measured synchronously with the pulsed light output. The measurement setup therefore requires sufficient response bandwidth, high-speed sampling, and controlled timing between the VCSEL excitation and PD measurement.

The test applies a pulsed current to the VCSEL while measuring the monitor PD current within the corresponding pulse interval. Precise timing aligns the electrical excitation with the optical-response measurement, while waveform capture provides visibility into the response during the pulse. The synchronized current and PD measurements provide the data required to evaluate LIV characteristics, including optical power response, slope efficiency, and kink behavior.

Synchronized VCSEL And PD Measurement Solution

Synchronized LIV testing requires measuring the photodiode response within the same time interval as the VCSEL drive pulse. The Keysight Precision PXIe Source/Measure Unit (SMU) supports VCSEL and photodiode measurements from direct current (DC) to pulse, with low-noise measurement in short pulse measurement windows, high-speed sampling for waveform capture, and precise synchronized timing control. A pair of Keysight Precision PXIe Source/Measure Unit (SMU) can be configured for VCSEL and PD measurements, with one sourcing the VCSEL drive current and the other measuring the corresponding PD response. The solution also supports current measurement resolution as low as 100 fA in DC measurements for dark-current characterization.

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