A method for non-contact 3D form testing of aspheric surfaces including determination of decenter and wedge errors and lens thickness is presented. The principle is based on the absolute measurement capability of multi-wavelength interferometry (MWLI). The approach produces high density 3D shape information and geometric parameters at high accuracy in short measurement times. The system allows inspection of aspheres without restrictions in terms of spherical departures, of segmented and discontinuous optics. The optics can be polished or ground and made of opaque or transparent materials.
A non-contact optical scanning metrology solution measuring aspheric surfaces is presented, which is based on multi wavelength interferometry (MWLI). The technology yields high density 3D data in short measurement times (including set up time) and provides high, reproducible form measurement accuracy. It measures any asphere without restrictions in terms of spherical departures. In addition, measurement of a large variety of special optics is enabled, such as annular lenses, segmented optics, optics with diffractive steps, ground optics, optics made of opaque and transparent materials, and small and thin optics (e.g. smart phone lenses). The measurement instrument can be used under production conditions.
Quality control in the fabrication of high precision optics these days needs nanometer accuracy. However, the fast
growing number of optics with complex aspheric shapes demands an adapted measurement method as existing
metrology systems more and more reach their limits.
In this contribution the authors present a unique and highly flexible approach for measuring spheric and aspheric optics
with diameters from 2mm up to 420mm and with almost unlimited spheric departures. Based on a scanning point
interferometer the system combines the high precision and the speed of an optical interferometer with the high form
flexibility of a classical tactile scanning system. This enables the measurement of objects with steep or strongly changing
slopes such as “pancake” or “gull wing” objects. The high accuracy of ±50nm over the whole surface is achieved by
using a full reference concept ensuring the position control even over long scanning paths.
The core of the technology is a multiwavelength interferometer (MWLI); by use of several wavelengths this sensor
system allows for the measurement of objects with polished as well as with ground surfaces. Furthermore, a large
absolute measurement range facilitates measuring surfaces with steps or discontinuities like diffractive structures or even
segmented objects. As all the measurements can be done using one and the same system, a direct comparison is possible
during production and after finishing an object.
The contribution gives an insight into the functionality of the MWLI-sensor as well as into the concept of the reference
system of the scanning metrology system. Furthermore, samples of application are discussed.
Sensors based on materials with high refractive indices are desirable for sensing applications where a low penetration
depth of the evanescent field into the covering analyte medium is required. To enhance the proportion of power carried
into the covering medium while keeping the penetration depth low, a waveguiding device can be coated by a high-index
film of metal oxide. We present numerical calculations as well as experimental comparisons between the evanescent
fields of titanium dioxide-coated and uncoated waveguides in lithium niobate. The experiments were performed by using
a Scanning Near-Field Optical Microscope (SNOM) in collection mode, which is an appropriate tool to measure and
characterise evanescent fields. The coating of the waveguide leads to an enhancement of the power carried out into the
covering medium by a factor 15 while the penetration depth remains the same in the range of a few 10 nm.
We review the propagation and interaction behavior of spatial screening solitons generated in a photorefractive SBN crystal in order to exploit them for new perspectives in soliton-driven photonics. We report on the successful experimental generation of an array of 5 x 5 spatial screening solitons. The waveguide properties of each channel are probed by a beam of different wavelength, and each channel is found to guide the probe beam independently. By combining the interaction and waveguide properties, we achieved channel combination and separation, thereby realizing complex waveguide couplers and dividers. Furthermore we show that image processing is possible using parallel propagating photorefractive solitons, allowing to create new features in the frame of the concept of "light is guiding light."
Three types of tunable and reconfigurable holographic filters based on photorefractive crystals were experimentally demonstrated. The filters exhibit an extremely narrow bandwidth (better than 0.1 nm) and allow reconfiguration or switching in a broad range of wavelengths and precise frequency trimming.