Fast micro-optical components characterization

3D topography measurement with DHM® enables precise control of the shape, surface quality, and optical performance of the micro-optics , as well as uniformity of these parameters across the wafer.

Measurement of various micro-optics elements has proven that DHM® is ideal to measure different type of structures and especially micro-lenses. DHM® overcomes the limitations of alternative methods and the following challenges:

DHM® Uniqueness

  • Fast measurement of a large array of lenses in a single shot acquisition of the full field of view
  • No dependance on micro optics and therefore no need of special adaptation while alternative systems need to add a lens to compensate
  • No calibration process
  • Digital focusing
  • Insensitive to external vibrations
  • Digital compensation of movement or orientation of the specimen

DHM® enables measurement of a single lens as well as wafer level inspection with DHM® combined with a motorized stage. Moreover DHM® extended focus enables to measure, in reflection or transmission DHM® configurations, the real topography for object higher than the depth of focus of the microscope objective.



  • Transmission DHM® enables to have a larger numerical aperture and is therefore well adapted to measure the optical thickness
    Reflection DHM® is best to be used to measure the shape and the roughness
  • Single wavelength system
  • Standard objectives, magnification selected depending on needed numerical aperture and field of view
  • Optional motorized stage for wafer level inspection
  • Optional InfraRed source to measure Si lenses


  • A large amount of micro-lenses varying in sizes, shapes, types, and materials
  • Transparent material

Micro-lenses measured by DHM®


The DHM®-R1000 instrument measures with a nanometric vertical resolution the topography of any micro-lens shape such as spherical, parabolic, cylindrical, square without a calibration process. Because no autofocusing or/and scanning procedures are necessary to perform the shape measurement, the DHM®-R1000 is an ideal tool for entire micro-lens wafer investigation and quality control. Moreover, digital processing tools, included in the Koala Software, allow fast, efficient and quantitative evaluation of shape information such as slope, radius, step height, sphericity, etc. A surface fitting with different models (polynomial, Zernike, spherical, cylindrical, parabolic) allows suppression of the micro-lens form factor to increase the visibility of defects, quantify the deviation of the surface in comparison to a perfect shape, and to measure the roughness parameters of the micro-lens surface.

The DHM®-T1000 has the same advantages than the DHM®-R1000 in terms of precision and versatility, but it measures the micro-lenses in transmission, The measured phase data is now related to the optical path length of the light passing through the micro-lens (integration of the refractive index along the thickness). A patented decoupling procedure allows  the separation of  the thickness and the unknown refractive index. In the case of a known refractive index, only a single measurement is needed to obtain the shape of the lens. For quality control of the microlens, quantitative aberration coefficients in term of Zernike polynomials can be measured with digital fitting procedures applied to the phase map. The difference between this fitting surface and the phase map increases the visibility of defects.

Comparison with alternative methods have been published and successfully verified the accuracy of measurement with DHM® with the additional benefit of short time measurement of a large amount of lenses.


“Laser micromachining in 3D and large area applications”, Holmes, Andrew; Pedder, James

“Extended depth-of-focus by digital holographic microscopy”, Tristan Colomb, Nicolas Pavillon, Jonas Kühn, Etienne Cuche, Christian Depeursinge, and Yves Emery

“Characterization of microlenses by digital holographic microscopy”, F. Charrière, J. Kühn, T. Colomb, F. Montfort, E. Cuche, Y. Emery, K. Weible, P. Marquet, and C. Depeursinge

“Numerical parametric lens for shifting, magnification and complete aberration compensation in digital holographic microscopy”, T. Colomb, F. Montfort, J. Kühn, N. Aspert, E. Cuche, A. Marian, F. Charrière, S. Bourquin, P. Marquet and Ch. Depeursinge

High Aspect-ratio and large sloped optical components measurements

3D topography with DHM enables measurement of high aspect-ratio samples, common samples to be characterized in micro-optics technology. Their shape, surface quality (roughness, defects, scratches, etc.) must often be measured to certify the sample specifications. The challenges are as follow:

DHM® Uniqueness

  • Non-contact measurement
  • High lateral resolution
  • Fast acquisition of a large array
  • High aspect-ratio specimen measurements
  • One-side structure suppression
  • Refractive index determination

A critical parameter is the lateral resolution, limited by the numerical aperture (NA) of the microscope objective. Even with a high NA objective, many samples present slopes that are too steep. To reduce the phase jumps, an immersion medium with a calibrated refractive index may be used.



Transmission DHM-T1000, in conjunction with the use of immersion liquids, provides a versatile instrument to measure, in real-time and without contact, the 3D topography (with nanometric vertical resolution) and without knowing the refractive index of the sample.
Matching the refractive index of the immersion liquid to that of the sample allows the suppression of the interface structure in contact with the liquid, leaving only the second one to provide phase contrast information. This technique permits measurements of a single surface in transmission configuration. In addition to the 3D optical topographic measurements, immersion liquids allow sample refractive index determination. By changing the refractive index of the medium between two acquisitions, the average refractive index over the vertical axis of the sample can be calculated. The patented method of the adjustment of the medium refractive index extends the DHM-T1000 application field.
The samples investigated are transparent UV copies of the metal shim of micro corner cubes arrays of 25μm base dimension. Used as retroreflectors, these structures present an aspect-ratio of more than 1:1.4

DHM measurement on 25µm base corner cube with high aspect-ratio: (a) without immersion liquid, (b) with immersion liquid with refractive index close to that sample, and (c) its resulting 3D view