The mass production optic industry in many Asian countries frequently employs human inspection lines to assess the
yield of their volume-produced optic components. The testing of shape and radius for the quality assessment of such
lenses or prismatic elements of average accuracy specification is traditionally performed by using Fizeau
interferometers for visual inspection. This method typically does not allow the documentation and/or printing of
inspection reports due to the lack of cost-intensive computer and printer periphery. Increasing accuracy as well as the
rising importance of quality assessment in mass production requires the elimination of human error as well as the
documentation and statistical analysis of the inspection results. FISBA OPTIK developed the μPhase(R) smartgage, a
new stand-alone metrology system to address exactly this need. This instrument meets the major demands of the mass
production for touch-of-a-button inspection, reliable pass/fail analysis, storage of measurement results and low
investment costs. The compact unit is designed with the potential to replace visual human-inspection instruments for
large-volume testing of relative shape accuracy and radius of curvature. The novel, small-footprint instrument is a
stand-alone system with a fully integrated computing and display unit, sample alignment stage, touch-screen operation
and optional connectivity for data export. This instrument offers simple, fast, reliable and vibration-insensitive
measurement of shape deviation on flat and spherical optical components as well as relative radius of curvature. We
present the measurement principle, the method of use and application, the measurement data presentation and data
export capabilities. Application areas for the μPhase(R) smartgage include testing of digital camera lenses, cell phone
camera lenses, general purpose spherical lenses and flats of diameters up to one inch.
An interferometer is often recognized as a lab instrument demanding environment-controlled rooms, skilled operators
and enough space for the instrument. In the case of radius measurement of spherical and toric contact lenses we'll
demonstrate the integration of such a typical "lab instrument" into modern production lines enabling 100% inspection. A
modern LabVIEWTM interface for the instrument and intelligent alignment procedures allow the fully automated control
of the samples under test.
The paper will discuss the possibilities and solutions of automated interferometric measurements in general and its limits
regarding the range of radius measurement and positioning in special. Interfaces between the interferometer, its software
and the external controller are described.
Liquid-crystal (LC) based micro-displays can be used to modulate incoming light waves with respect to amplitude,
phase and polarization. Twisted-nematic LC displays produce a combined phase-polarization modulation so that it is
difficult to achieve pure phase modulation without amplitude modulation. We present a new phase-only modulating
LCOS (Liquid Crystal On Silicon) spatial light modulator (SLM) based on an electrically controlled birefringence
(ECB) liquid crystal mode. The device has a HDTV (1920x1080) resolution and a small pixel pitch of only 8&mgr;m (87%
fill factor) on a digital silicon back plane. The LC molecules are aligned parallel to the electrodes and an applied electric
field forces them to tilt towards the direction of the field. This leads to a pure phase modulation with a phase retardation
of 2&pgr; for wavelengths between 420 and 1064nm, with negligible polarization change (<1%) if the light is linearly
polarized parallel to the director axis of the LC molecules. The shape of the back-plane of the LCOS micro-display was
investigated using a Twyman-Green interferometer and the observed deviation from a plane surface was compensated
by addressing the inverse spatially resolved phase retardation function. The interferometer was then used to measure
wave fronts that were generated with the micro-display, representing optical elements like e.g. single lenses, lens arrays
and tilted mirrors.
Interferometric asphere testing is traditionally done using computer generated holograms (CGHs) as beam shaping optics. The great disadvantage of using CGHs is that each asphere requires its own unique CGH which is expensive and requires a certain delivery time. In many cases all you are interested in first off is a quick but rough sample conformity validation to investigate and test new asphere designs. We present a new method which allows you to test rotational-symmetrical aspheres interferometrically in a spherical or plano setup. This means without expensive auxiliary beam shaping optics. The systematic setup error is automatically removed from the measurement results, so that the displayed results correspond with the traditionally known interferometer results with adapted wave fronts. Based on this method a modification of this basic method is presented that allows you to control the manufacturing process.
Prior to any interferometric surface shape testing, it is necessary to calibrate the interferometer in order to avoid systematic measurement errors. One common calibration method employs a standard specimen which has been previously calibrated by a so-called absolute testing method. Another method is the direct application of absolute testing methods to the interferometer. The authors have in the past developed and used absolute interferometric testing methods to calibrate flat, spherical and cylindrical surfaces, as well as complete interferometers. Now they have developed new methods, suitable also for toric and conical surfaces and the interferometers. The basic principles of the calibration methods are described. The correctness of the methods and the influence which measurement errors have on the results are demonstrated by computer simulation.
Two methods of calibrating an interferometer for testing cylindrical surfaces are tested experimentally. One method uses a tilting mirror instead of the test specimen and combines at least two measurements at different angles. The other method adds together three measurements. In two of them a cylindrical specifmen is used. In the third one the specimen is replaced by a roof mirror. Results of both methods are computed. They show a reproducibility of (lambda) /50 and an accuracy of (lambda) /20 for the absolute surface deviations of a cylindrical specimen.
Based on our experiences of absolute testing of flats and spherical surfaces we are developing methods for absolute testing of cylindrical surfaces. Three methods are presented and compared with each other. Method I determines the absolute deviations of three cylindrical surfaces from a mathematical cylindrical surface by five measurements. Method II calibrates the interferometer so that afterwards it can be used for absolute testing. Method III determines the absolute deviations of one single cylindrical surface by using two known flats.
Absolute interferometric flatness testing of the three-flat type has made remarkable progress within the last few years. These developments show improved lateral as well as depth resolution and easier handling.
Testing of surface shapes by automatic interferometry is exact, quick, and comfortable, and therefore popular. It, however, suffers from drawbacks: The equipment is often quite voluminous and not exactly cheap, and the attainable accuracy is limited by the precision of the reference surface (relative testing). In cooperation with Fisba Optik AG we recently developed a matchbox-sized, cost-reduced interferometric surface shape sensor to overcome the first drawback. Furthermore we combined this sensor with methods for absolute calibration of the sensor or a reference surface resp. to clear the reference surface handicap. Absolute calibration methods are methods which measure surfaces independently from others with sufficient accuracy as compared to an ideal mathematical surface. We adapted our own developments of absolute flatness and sphericity testing for the surface shape inspection sensor. Further on we developed and adapted new methods for absolute cylindricity testing the importance of which is increasing as the usage of cylindrical surfaces of higher and certificated accuracy is rising.
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