Optical Metrology

Optical metrology systems are being implemented across an array of diverse applications that include: 3D biometrics inspection equipment forensics engineering design alignment equipment cosmetics biomedical applications product manufacturing

Specific parameters being measured in these applications include two and three-dimensional surface shapes, contours, roughness, and discontinuities.

Structured lighting is a form of optical metrology based on illuminating an object and measuring a series of well defined light bands or stripes. A high resolution camera, located at some pre-defined angle different from the illumination angle, records these bands or stripes on the object. Then high level processing of the acquired images using optical triangulation principles and sophisticated phase shifting algorithms are used to define a multidimensional image.

From a projection standpoint, the resulting measurement accuracy of these systems is a function of how accurately and repeatedly you can control light band (or stripe width) and gray scale. If the control is precise, measurement accuracy down to 1/10 bandwidth can be controlled (<1 micron).

There are a number of methods for creating light bands or stripes on objects including projection methods or fixed gratings. The Fringe Projection Method is gaining in popularity and is being driven by DLP® technology. The Digital Micromirror Device (DMD) is the heart of DLP® technology and has an array of micromirrors fabricated on top of a semi-conductor chip that can be controlled independently. The DMD also offers high fidelity in gray scale bit depth. With high resolution and precise control of individual pixels and gray scale, DLP® technology makes it possible to repeatedly project fringe patterns with varying widths, orientations, and phase shift values, enabling high accuracy 3D optical measurement systems.

DLP® Technology has many advantages in Fringe Projection applications including:

• Each pixel is digitally controlled
• High reflectivity
• Polarization independent which increases light efficiency
• Ability to work with IR, Visible, and UV light
• Proven technology with over 18 million chipsets shipped
• Can use PWM to achieve a very linear gray scale
• Fast switching speed in the microseconds

End Equipments Solutions

• 3D Optical Metrology