VCSEL Production Testing Complete characterization of pulsed VCSELs

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Sturdy complete system for VCSEL in-process inspection

In-process inspection of laser diodes/VCSELs calls for a high level of precision and stability when choosing a measuring system. Reliable and precise measurement of optical properties and temporal pulse performance is a prerequisite for the reproducible characterization and sorting of laser diodes in the production process.

Based on the high-resolution variants of the CAS series of spectroradiometers, in addition to the VCSEL lab measuring station Instrument Systems offers several complete solutions that are optimally tuned to VCSEL characterization in production, including the PVT 200 with a measuring system specifically for time-resolved measurement of nanosecond pulses.

The modular setup of measurement solutions from Instrument Systems and the excellent spectral resolution of the CAS-HR series (CAS 140CT-HR, CAS 120-HR) enables a wide range of applications. With the integration of a traceable, absolutely calibrated photo diode the radiant flux is output as a direct measurand– of critical importance for measurement accuracy.

Furthermore, a direct view fast photodiode can be integrated for measuring the trace of a single pulse or a complete pulse train. This requires additional driver and readout electronics which operates in the gigahertz range.

Key Features:

  • Array spectroradiometer specially for pulsed laser diodes/VCSELs
  • High spectral resolution up to 0.12 nm
  • Reliable and cost-efficient solution for production and lab
  • Optional performance measurement with a calibrated photodiode
  • Optional measurement of extremely short pulses as low as 1 ns


It is of paramount importance in the production environment to maintain a high throughput rate (UPH) with short cycle times. Laser diodes typically have high power in a very narrow spectral range, ensuring adequate modulation of the detector with short integration times. A measuring system with the shortest possible measuring time is thus necessary for cycle-precise capture of the relevant readings with high throughput.

Sophisticated electronics are required, in particular for the characterization of very short and high frequency pulses, as the short pulses must be generated at currents of 10 A and more, and the measurement data must be captured with sampling rates of several gigahertz.

System configuration

The all-in-one system from Instrument Systems for fast and precise measurement of radiant flux of laser diodes/VCSELs in production typically comprises the following components:



Array spectroradiometer

High-resolution CAS 140CT-HR with up to 0.2 nm spectral resolution as a high-end measurement solution with a cooled CCD detector for the highest stability, e.g. in a reference system.

High-resolution CAS 120B-HR with up to 0.12 nm spectral resolution as a high performant yet cost-efficient alternative to the CAS 140CT-HR.

Integrating spheres

ISP 75 and ISP 100 with small internal diameters. The small form factor is particularly suitable for installation in handler and prober systems. 

Optional: ISP 100 with variable port configuration for the connection of spectrometers and photodiodes, for determining the power or pulse form of laser diodes and with the capability of detecting extremely short pulses as low as 1 ns pulse duration (System PVT 200).

Alternative: ISP 150L with 150 mm internal diameter and 50 mm diameter of the measurement port for larger laser modules/arrays and self-absorption correction capability with the aid of an integral auxiliary light source.

Calibration Calibration traceable to national standards as PTB or NIST.


Driver electronics for generating short pulses (  1 ns) with high currents (up to 15A). Sampling electronics (or oscilloscope) for signal detection of the fast photodiode.


CAS.dll and SDK for integration into the customer’s production flow.

IR reference LEDs

Reference LEDs ACS-570-15, 570-17 with 860 nm and 950 nm. In combination with the in-house PSU 10 power source, this makes for a highly stable reference system.

Individual configuration

Our system experts will be pleased to provide competent advice on your particular application. Our global Service guarantees fast set-up and full support over the entire lifetime of the system. Together we will find the right solution – just ask us!

Examples of applications