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VCSEL arrays are found to have numerous applications in consumer electronics, including structured light sources in time-of-flight (ToF) or 3D sensing, proximity lighting in face recognition (FR), gesture recognition (GR), etc. This study focuses on detailed and comprehensive LIV testing, spectral and beam analysis of the entire VCSEL array and each emitter within it.

Necessity of 2D LIV+λ detection for single emitters

Essential for demanding applications such as facial recognition, 3D sensing, in-cabin sensing, LiDAR and range finding
Investigating crosstalk between transmitters
Parallelize measurements to reduce overall measurement time

LIV curves are the most basic measurement method used to determine the electrical and optical operating characteristics of laser diodes. These curves establish the threshold current, slope efficiency, flip point, whether there are any kinks, etc. They are widely used at different stages because it is critical to identify faulty DUTs early in the manufacturing process.

LIV characteristics of the entire VCSEL array

Measure LI and IV curves of the entire array from 200 mA to 1.8 A
Calculate the slope efficiency, threshold current and flip current based on the LI curve
In the IV curve, the voltage increases approximately linearly with the expected current.

LIV characteristics of all emitters in the entire array

The VCSEL array used in this measurement consists of 281 emitters.
The slope efficiency and threshold current of each emitter were measured
External emitter has higher slope efficiency but lower threshold current
Internal emitters have small variations in both quantities

In addition to the LIV curves, we also measured spectra of individual emitters (15 emitters were selected for the array) at different currents, similar to the LIV curves. The spectra are shown in the figure below. Each sub-figure represents an emitter, and its spectrum is color-coded at different currents (blue at 400 mA to red at 1.8 A). We observe a shift in the spectrum at higher currents, and higher-order modes also appear as the current increases.

\\ in conclusion

We have extended the existing 1D LIV testing, spectroscopy and beam analysis to cover every single emitter in the VCSEL array. This approach not only enables parallelization of the measurements, reducing the overall measurement time, but also provides the opportunity to study the mutual influence between individual emitters.

VTC 4000: Flexible and precise single emitter analysis

Our unique measurement solution, with well-defined requirements from customers, allows identification of emitters in an array that are underperforming or out of specification. We believe that this comprehensive characterization of individual emitters is critical for demanding applications. This allows VCSEL manufacturers to ensure compliance of the final product without incurring any packaging costs and speed up the manufacturing process.