We present a numerical model based on Coupled Mode Theory for modelling and optimization of thermally tuned semiconductor lasers used in digital coherent transceivers. This modular approach allows combinations of waveguides, gratings and microrings, and enables the quick simulation of longitudinal modes. Our comparative study shows that the combination of a phase-modulated DBR and a microring results in a promising, compact tunable laser diode for telecommunication and signal processing. It requires low tuning power due to the small footprint of microring. Wavelength tuning range is controlled effectively by the finite number of peaks of phase-modulated DBR, and the envelope of its reflectivity comb can be optimized numerically.
Compensation or comparative measurement is a natural way to overcome the limited measuring range of TV holography
or digital holography. In this case the resultant displacement field is the difference of the actual deformation and a known
deformation pattern. The compensation can be digital, because these measuring techniques operate with images recorded
with digital camera.
Development of Spatial Light Modulators (SLM) enables the application of active holographic optical elements in
coherent optical metrology. These modulators are capable to reconstruct digital holograms optically; therefore they can
be used as active holographic optical elements. The goal of the project was to perform adaptive comparative
measurements, where an optically reconstructed image of a recorded or simulated single or double exposure hologram is
used for holographic illumination of another object.
In this paper conventional TV holographic or digital holographic arrangement with holographic object illumination
applied for comparative displacement measurement with adaptive features. Measurement setups were built, containing
devices performing feedback, which is capable to project the real image of the master object - using its previously
recorded or computer simulated digital holograms - onto the test object to calculate the difference deformation directly.
Development of Spatial Light Modulators (SLM) opened a new area in coherent optical metrology. These modulators are
capable to optically reconstruct digital holograms; therefore they can be used as active holographic optical elements in
Electronic Speckle Pattern Interferometry (ESPI) or in digital holographic interferometry. SLM is also capable to
generate computer calculated wave fronts (not belonging to an existing object), and multiple projections can be
performed during the measurement time. Using this feature active measuring system can be built.
In our work adaptive comparative ESPI measurement is done, where an optically reconstructed image of a computer
generated hologram is used for holographic illumination of another object, with which difference deformations can be
calculated. These active interferometers can continuously adapt themselves to the change of measuring conditions,
because the test displacement profile can be compared with a suitable arbitrary master displacement profile in a
relatively simple optical setup. This approach is a straightforward digital implementation of the analogue comparative
measuring technique, where regular hologram plates are used to store and reconstruct optical wavefronts.
The development of spatial light modulators enables the application of active holographic optical elements in electronic speckle pattern interferometry. In our work adaptive comparative measurement is done, where an optically reconstructed image of a recorded or simulated single or double exposure hologram is used for holographic illumination of another object. In this paper, we present experimental results of measuring the difference of two deformations using this technique. The displacement difference can also be obtained numerically, if the wavefront used as a coherent illuminating mask does not belong to an existing object. This type of interferometer can easily adapt to the change of measuring conditions.
Digital holography and electronic speckle pattern interferometry are promising tools for industrial applications for deformation and shape measurements. Because of the limited measuring range, compensation methods can be applied in practical measurements. They can be digital, because these measuring techniques operate with images recorded with digital camera. We develop a new measurement setup, combining two out-of-plane displacement measurements with different sensitivities and an adaptive compensation method. Using this compensation method much more precise displacement maps can be produced than would be possible from a single measurement. One major task is to perform automatic measurements even if the deformation is higher than the upper measuring range of the basic method.
Active interferometers can continuously adapt themselves to the change of measuring conditions and environment. This
type of interferometers is investigated in the article. As a major feature, the wave fronts of the interferometer are formed
by different holographic optical elements. Using this technique the fringe density at highly deformed points can be
decreased or different components of the complicated fringe pattern can be removed which results in increase of the
sensitivity and leads to easier evaluation of the fringe pattern. Selected applications in speckle metrology and digital
holography are shown demonstrating applications of computer generated and classical types of HOE-s.
Digital holography and TV holography is the most promising tool for industrial applications. For a successful industrial
measuring system automated evaluation is necessary. To develop this kind of measuring system the fringe compensation
principle can be used. Because both digital holography and TV-holography operate with images recorded with a digital
camera, several computer based compensation methods can be applied. In our investigations automated compensation
techniques were investigated to develop industrial measuring systems.
In digital holography the compensation method can be easier, using digital compensation, performing the compensation
process in the computer using the recorded complex amplitude of the scattered light from the investigated object. In this
case the compensation is based on the phase manipulation of the reconstructed waves.
Digital compensation method was chosen for TV holography too. Previously developed fringe synthesizing method was
applied in Tv holographic measurements. In this method a set of phase shifted fringe patterns of the investigated object is
recorded. Using the recorded fringe systems new contour fringe pattern can be generated.
Based on these methods, the evaluation program in digital holography or in TV holography can set the sensitivity of the
measurement, can separate different deformation components (e.g. rotation, local deformation) after the measurement
was performed. Measuring the separated deformation components new alternative output of the measurement can be
generated: a list of the deformation components with its features.
Digital holography is one of the most promising tool for industrial applications. Over a period of years a number of
effective compensating techniques have been developed. In this paper compensation and comparative techniques will be
summarized to develop more intelligent measuring systems.
Digital holography is an excellent tool for comparative measurement. Using this technique remote measurement is also
can be done, because the real or simulated digital holograms of the master object can be transferred via Internet.
We present a new measurement setup, combining two out-of-plane displacement measurements with different
sensitivities and an adaptive compensation method. Using this method we can produce much more precise displacement
map, than it would be possible by a single measurement.
In an adaptive measuring system the components of the optical arrangement may be changed automatically to adapt them
to the conditions of the measurement. One mayor task of these systems is to perform automatic measurements even if the
deformation is higher than the upper measuring range of the basic method. Also adaptive measuring system can help to
understand what happened with the object due to the load.
Digital holography and TV holography is the most promising tool for industrial applications. In our investigation
adaptive methods and optical elements were developed and investigated for these techniques.
Using these automatic evaluation procedures alternative output of the fringe system can be found.
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