Posted in | Photodetectors

NIR Intensity Lens for Radiant Intensity Measurements

Three-dimensional (3D) sensing technology forms the basis for numerous new applications, such as:

  • Eye tracking and iris detection
  • Gesture and facial recognition
  • Multimodal sensing for gesture and motion control of vehicles
  • Automotive LiDAR for sensing autonomous vehicles
  • Other near-infrared 3D sensing applications

Measurement methods for NIR LEDs and lasers guarantee the performance of 3D sensing and Time-of-Flight (ToF) light-based proximity sensing using dot patterns created by diffractive optical elements (DOE). An effective test and measurement solution is required to guarantee the accuracy and performance of systems and devices that use NIR sensing.

Near-Infrared Intensity Lens Solution

The Near-Infrared (NIR) Intensity Lens system from Radiant Vision Systems is an integrated camera/lens solution capable of measuring the radiant intensity and angular distribution of 850 or 940 nm near-infrared (NIR or near-IR) emitters. The NIR Intensity Lens system makes use of Fourier optics to record a full cone of data in a single measurement to ±70°, offering users very fast, precise results suitable for in-line quality control.

Makers of 3D sensing technology can utilize the NIR Intensity Lens solution for angular measurement of lasers, NIR LEDs, and structured light patterns formed by Diffractive Optical Elements (DOE). The lens can be positioned directly to a ProMetric® Imaging Radiometer from Radiant Vision Systems. It includes ProMetric or TrueTest™ Software for intuitive system arrangement as well as customizable automated measurement sequences. Further, tests dedicated to NIR emission measurements are available.

High-Resolution Angular Measurement

The NIR Intensity Lens from Radiant Vision Systems captures the entire angular distribution of a NIR light source (to ±70°) in one image, and realizes an angular resolution of about 0.05° image sensor pixel. Combined with the ProMetric® Imaging Radiometer, the NIR Intensity Lens has the ability to determine radiant flux, radiant intensity, and power with a high level of accuracy at all view angles.

This guarantees accurate intensity and distribution of NIR emissions for object sensing, and safe levels of NIR output for use in human-machine interface applications like facial and eye sensing.

Safety Considerations

The human eye does not react to invisible wavelengths of NIR light the same way it does to bright visible light, and thus can be damaged by NIR emissions. For instance:

  • IEC 60825-1 standard for lasers, comprising any NIR lasers
  • IEC 62471 standard for all light sources, mandatory in America, Europe, and Asia
  • American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs) for Physical Agents (including “lasers, light, and near-infrared radiation”)

Near-IR measurement solutions from Radiant Vision Systems characterize the NIR source’s output, offering producers with data that may be beneficial when testing to these standards.

Structured Light Dot Pattern Analysis

DOE spread NIR laser emissions in a structured light pattern (mostly tens of thousands of dots) over a broad spatial area. This pattern is created when a single beam of NIR laser light is produced through a DOE “screen”, which divides it into numerous emission points, usually forming thousands of dots. This pattern is cast on the 3D surface of a target object, for example, a face.

When the laser light interacts with the object, each of the dots in the pattern is reflected back to the NIR sensor of the device at a different angular location, intensity, and size representing curvature and depth. By measuring the deviation of distributed light against received reflected light, the sensing device can build a 3D “map” of the object.

All the dots in a structured light pattern has to be accurately placed (correct angle, azimuth, inclination) to make sure it is correctly reflected back and “understood” by the infrared sensor in the emitting device. In order to accurately map the contours of the target object, manufacturers need to regulate the position and output of each dot for the device.

It is also essential to regulate the radiant intensity (W/sr) of each point to ensure accurate levels of NIR output in applications like iris tracking and facial recognition, where the human eye is open to NIR emissions.

The NIR Intensity Lens from Radiant Vision Systems can detect points of interest across the image, measuring point-by-point values for maximum peak inclination/azimuth, maximum peak solid angle, location at x,y, spot power uniformity (between dots), maximum peak (strongest emitter), maximum peak averages, number of pixels as maximum peak point, total flux, and DOE flux (subtracting the background peak).

“Flood” Source Analysis

Object sensing may depend on a robust flash of NIR light (occasionally called “flood” distribution) for proximity detection through ToF measurement. For instance, in facial recognition, flood emitters can be used to spot the presence of a face and establish focus distance, even in darkness.

The NIR Intensity Lens offers Flood Source Analysis to assess diffuse NIR sources to make sure that they adhere to proposed performance parameters, and to identify and rectify any abnormalities such as intensity fall-off or hot spots.

Complete Measurement Solution

The NIR Intensity Lens offers an application-dedicated solution for complete NIR source characterization and emission measurement. Coupled and calibrated with a ProMetric Y Imaging Radiometer, the NIR Intensity Lens offers a turnkey radiometric imaging solution that satisfies the measurement efficiency, form factor, and cost requirements for numerous applications.

The Radiant NIR solution software offers tests dedicated to the assessment of angular distributions of NIR light, and also dot patterns formed by DOE. Users can sequence tests for quick evaluation of all applicable display features within seconds, applying particular tests to a single image recorded by the camera.

Exceptional tests for NIR analysis comprise:

  • POI Total Power
  • Total Flux (mW or W)
  • Max Power
  • Dot Source Analysis
  • Pixel Solid Angle
  • Flood Source Analysis
  • Image Export
  • Points of Interest

Radiant solutions are combined software/hardware systems designed for precise application requirements. This allows manufacturers to realize more efficient measurement processes using one provider with end-to-end support.

Key Features and Highlights of NIR Intensity Lens

  • Compact form factor
  • High angular resolution (about 0.05° per image sensor pixel)
  • Precise and dependable measurement of radiant intensity to ±70° angle
  • Efficient operation, recording data for all angles concurrently. Faster than goniometric systems for examining angular data
  • Combination of high performance, low cost, and flexibility
  • User-friendly measurement control and analysis software

Typical Applications

The NIR Intensity Lens offers an efficient measurement solution for NIR sources like lasers and LEDs. This camera/lens solution delivers high-resolution imaging to address both in-line and off-line applications:

  • Measurement of NIR LEDs, lasers, and structured light patterns formed by DOE
  • Angular measurement for devices used for 3D sensing applications such as multimodal human-machine interface (HMI), gesture recognition, facial recognition, eye tracking, and automotive LiDAR
  • Quick operation for in-line measurement for quality control of production process
  • Assessment of 850 or 940 nm light sources for precise radiant intensity output at every angle

NIR Intensity Lens for Radiant Intensity Measurements

Near-Infrared Intensity Lens Solution
Near-Infrared Intensity Lens Solution
High-Resolution Angular Measurement
Cross-section radar plot showing radiant intensity (as a function of angle) of a near-infrared LED, captured by the NIR Intensity Lens and output by TrueTest Software.
Structured Light Dot Pattern Analysis
Dot emissions created using a diffractive optical element (DOE) are captured by the Radiant NIR Intensity Lens solution and analyzed for angular location, maximum radiant intensity, uniformity, and flux.
Analyze flood distribution of diffuse NIR light sources to evaluate uniformity across angular emissions (in terms of intensity at each degree), center values, angular fall-off, or hot-spots.
Complete Measurement Solution

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