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Vertical Cavity Surface Emitting Laser (VCSEL) technology is a key enabler in applications such as facial mapping, gesture recognition, proximity sensing and optical communications.

In addition to their outstanding performance characteristics, the very nature of VCSEL construction enables testing at various phases of manufacture, increasing production yields, improving product performance and reducing cost.

With an experience base spanning more than 50 years in light measurement, Gamma Scientific is uniquely positioned to deliver precise, repeatable, and high speed optical and electrical test solutions for all performance characteristics of VCSEL devices.

Unmatched Performance in VCSEL Test Solutions

VCSEL Test & Characterization Solutions

• Near field spot size and emission angles

• Far field spot size and emission angles

• Spatial uniformity and hotspot determination for regulatory & safety compliance

• Absolute power measurement

• Spectral parameters including peak, centroid & dominant wavelength

• Electrical parameters including LIV, VF, VR and IR

• Wall plug efficiency

• Chromaticity and CCT values including CIE x,y

Key when purchasing metrology equipment is knowing that the correct information is being collected. Our experience operating an ISO 17025 compliant company and 3rd party NVLAP testing facility has allowed us to better anticipate the needs of users and eliminate common causes of measurement inaccuracy.

The resulting systems leverage this knowledge to make software and hardware as universal as possible, with wafer level multi-channel test & characterization solutions for measurement in CW or pulsed operating modes.

VCSEL 170 x 170 µm

Electrical Parameters

Sample Test Parameters

• Open Short Test – 200 – 1500 mV typical range

• Leakage Current Test – maximum of 10µA

• NTC Thermistor Test – user defined

• VF, IF, VR & IR – forward & reverse current & voltages, user defined

• Wall Plug Efficiency – light power/electrical power, minimum of 35%

VCSEL Test & Characterization Solutions

LEDInput Current (I)

Forward Voltage (V)

Light Output (L)

LIV for is an acronym for light flux, current and voltage measurement. Optical parameters and Forward voltage are collected as device input current is ramped over a predefined range.

The total light output is collected using an integrating sphere, and the input current & device voltage is collected using an SMU (source-meter unit) or a digital multi-meter.

Some applications require VCSELs to be held at a specific temperature. In such cases and optional thermoelectric cooler (TEC) is used to regulate the package temperature.

LIV curve, 850nm sample pulsed at 30Hz (pulse width of 3ms)

Regulating A Single-Pulse System:

The control software operates the instrumentation and lets the user define the scope of testing to perform. For VCSEL measurements, the required optical and electrical inspection may vary between manufacturers, so a custom recipe development tool is there to help the user select what data they wish to report.

Using external hardware triggering, the system software synchronizes the electrical turn-on time with the spectrometer scan time in order to measure a single pulse. By maintaining physical timers, the measurement is highly reproducible to isolate just the performance of the VCSEL from the results.Example process flow a single LIV scan. The total test time depends on

user settings for electrical vs optical data points and pulse width

START

END

Trigger SMU

SMU turns VCSEL onSMU triggers Spectrometer SMU measure electrical data

and spectrometer scansSpectrometer ends scan

SMU turns VCSEL off

• Optical Power

• Peak & Centroid Wavelength

• Spectral Bandwidth (FWHM)

• Spectral Width (RMS)

• LIV Slope Efficiency – dL/dI – W/A, user defined

• LIV Slope Efficiency – dV/dI – V/A, user defined

Collecting LIV data using an SMU & integrating sphere

An integrating sphere with 3 ports in the configuration

shown to the left is used to collect the total light

output (L) from the VCSEL sample. The device is

attached to the sample port on a sphere and total light

output (L) is measured using a spectrometer. Power is

applied to the VCSEL by the SMU and the input

current (I) and device voltage (V) can be measured. In

this configuration, the electronic data can be collected

for the rest of the efficiency parameters like open

short and leakage current.

VCSEL

sample,

on PCB

2601 SMU

Power

Input

Voltage

Sense

Integrating

Sphere

Spectrometer

Reference

LampDetector

Port

The Gamma Scientific VCSEL Test System leverages proprietary calibration process and absolute verification and correlation via a goniometer system.

Beam Distribution Test Parameters:

• Beam Angle

• Beam Uniformity

• Hot Spot Checking – photobiologic safety inspection

• Emitter Uniformity

Optical Parameters

Example Beam Angle Data

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VCSEL Test & Characterization Solutions

Rev 8.18.1

Nominal SpecificationsDUT Form Factor Chip on Carrier, Chip on Submount, Wafer Level

Short-pulse Duty Cycle Typically 1 msec, options to 100 µsec

Spectroradiometer

Spectral Range 200 to 1100 nm (Custom ranges available on request)

Wavelength Repeatability 0.03 nm

Wavelength Accuracy ± 0.2 nm

Spectral Sensor Temperature stabilized back-thinned 1024 x 128 element CCD array

Electrical Resolution 16 bit

Dynamic Range 64,000:1 (single scan)

Optical Power Meter

Sensor Type InGaAs (Si or Ge available, specifications may differ)

Dynamic Range -8.5 to + 3.5 dBm

Typical Response 9.5 x 10-1 A/W at 1550 nm

Calibration Range 800 to 1750nm

Current Ranges

Current Range 100 nA to 10A

Current Resolution As low as 2 pA (current range dependent)

Typical Noise (peak to peak) As low as 5 pA (current range dependent, 0.1 Hz to 10 Hz)

Voltage Ranges

Compliance Voltage Range 100 mV to 40 V

Programming Resolution As low as 5 µV (voltage range dependent)

Typical Noise (peak to peak) As low as 20 µV (voltage range dependent, 0.1 Hz to 10Hz)

Emission Angle Measurement Error < 1°Calibration Accreditation ISO/IEC 17025 by NVLAP (NVLAP lab code 200823-0)

Control SoftwareLight Touch LED software for Windows via USB 2.0 interfaceIncludes binning and batch tracking functions

Specifications are subject to change without notice.

Precision I/V Source

Spectroradiometer

System Controller

Calibration Light Source

• Absolute Power• Spectral Properties• LIV, Vf, Vr, WPE

• Spot Size• Emission Angles• Spatial Uniformity

DUT

Integrating Sphere

RadOMAcam

Typical System Configuration