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Vandermeiren W.,Laboratory for Micro and Photonelectronics | Stiens J.,Laboratory for Micro and Photonelectronics | De Tandt C.,Laboratory for Micro and Photonelectronics | Shkerdin G.,Russian Academy of Sciences | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Laser induced temperature distributions inside doped semiconductor materials are used to derive laser beam profiles by means of the thermo-electric Seebeck effect. Thermal diffusion will lead to a discrepancy between the optical intensity profile of the laser beam and the measured temperature distribution inside the semiconductor. An advanced numerical 4D finite element model describing the laser induced spatial temperature distribution in function of time in a layered GaAs based structure was developed in Comsol Multiphysics. Non-linearities as the temperature dependence of the absorption coefficient, the thermal conductivity and the Seebeck coefficient were taken into account. This model was used to investigate the optical chopper frequency dependence on the spatial thermal cross-talk level and the responsivity near the illuminated surface of the detector structure. It was shown that the frequency dependent cross-talk level can be reduced significantly by applying short chopping periods due to the dependence of the thermal diffusion length on the frequency. The thermal cross-talk is reduced to -21 dB and -38.6 dB for the first and second neighboring pixel respectively for a lock-in frequency of 140 Hz. Experimental results of the spatial thermal cross-talk level and the responsivity were compared with simulations and satisfactory agreements between both were achieved. High power CO2 laser profile measurements obtained with our thermo-electric detector and a commercially available Primes detector were compared. © 2010 Copyright SPIE - The International Society for Optical Engineering. Source


Stiens J.,Laboratory for Micro and Photonelectronics | Vandermeiren W.,Laboratory for Micro and Photonelectronics | Shkerdin G.,Russian Academy of Sciences | Kotov V.,Russian Academy of Sciences | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We present a new modulation concept for medium infrared (8 - 12 μm) wavelengths. The operation principle of the presented modulator is based on evanescent wave absorption by means of a bulk, single or multiple quantum well structure. A sub-wavelength grating ensures efficient coupling of the optical field to the absorption medium. Modulation is then achieved by depletion of this absorption medium. We present an analysis of concept parameters and point out their respective advantages and disadvantages with respect to the modulation performance. In this context, we investigated the impact of different absorption media as bulk, single and multiple quantum well structures and found that single quantum well structures are best suited for modulation purposes. Simulations pointed out that an absolute modulation depth of the order of 60% can be achieved. We also investigated the impact of the diffraction order on the modulation performance. Furthermore, some preliminary experimental results on this modulation concept are presented and compared with simulations. © 2010 Copyright SPIE - The International Society for Optical Engineering. Source


Vandermeiren W.,Laboratory for Micro and Photonelectronics | Stiens J.,Laboratory for Micro and Photonelectronics | De Tandt C.,Laboratory for Micro and Photonelectronics | Ranson W.,Laboratory for Micro and Photonelectronics | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Anomalistic behavior in diffraction responses of grating can be easily detected and can indirectly provide information about the grating parameters such as the grating period, height, duty-cycle and profile. More precisely, the absorption resonance (Wood's anomaly) which arises from the excitation of a surface plasmon polariton (SPP) in reflective sub-wavelength diffraction gratings are of interest as well as Rayleigh's anomaly which takes the form of a discontinuity in the diffraction response and which is the consequence of the excitation of a new propagating mode. In this paper we describe how these anomalies can be used as a non-destructive metrology tool to estimate the grating parameters by an IR spectral scatterometry measurement. We briefly describe the theoretical conditions for which SPP are excited. We investigate the wavelength sensitivity of Wood's anomaly in the zeroth order diffraction response to individual grating parameter variations at CO2 laser wavelengths. A numerical electromagnetic grating solver software package "Gsolver" was used for the theoretical modeling. We show that this non-destructive IR spectral scatterometry measurement based on feature extraction allows us to measure grating parameter variations with nanometer resolution. The measurement time needed to scan a 4" wafer has been shown to be of the order of a few minutes. This is much faster as compared to traditional techniques as (deconstructive) SEM inspection or white light interferometry. Furthermore, the extension of this technique to larger wafers does not impose any difficulties. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Source


Vandermeiren W.,Laboratory for Micro and Photonelectronics | Stiens J.,Laboratory for Micro and Photonelectronics | Shkerdin G.,RAS Institute of Radio Engineering and Electronics | De Tandt C.,Laboratory for Micro and Photonelectronics | Vounckx R.,Laboratory for Micro and Photonelectronics
Journal of Physics D: Applied Physics | Year: 2014

An infrared modulator of which the working principle is based on evanescent wave generation and intersubband transitions in a single AlGaAs/GaAs quantum well is presented here. CO2 laser light at normal incidence is coupled to an evanescent wave by means of a sub-wavelength diffraction grating. Modulation of the zeroth order reflective mode is achieved by applying an electric field across the quantum well. The model for deriving the complex refractive index of the quantum well region is presented and used for numerical diffraction efficiency simulations as a function of the groove height and period. Two specimens with different groove heights were fabricated. Experiments are conducted at a wavelength of 10.6 ;m. At this wavelength a relatively strong absolute modulation depth of about 20% could be observed. The experimental results are in good agreement with our model and diffraction efficiency calculations. © 2014 IOP Publishing Ltd. Source


Vandermeiren W.,Laboratory for Micro and Photonelectronics | Stiens J.,RAS Institute of Radio Engineering and Electronics | Shkerdin G.,RAS Institute of Radio Engineering and Electronics | De Tandt C.,Laboratory for Micro and Photonelectronics | Vounckx R.,Laboratory for Micro and Photonelectronics
Journal of Physics D: Applied Physics | Year: 2011

A non-linear numerical finite element method model of a thermo-electric focal plane array detector is presented here.Laser induced thermo-voltage profiles tend to spread out for small lock-in frequencies as the thermal diffusion length is inversely proportional to the square-root of the lock-in frequency. This leads to a frequency and spatial dependent thermal cross-talk level. In this paper we investigate the thermal cross-talk level quantitatively as a function of spatial coordinates and lock-in frequency. Experimental data are provided at an optical power level of 1W. The impact of non-linear thermal parameters as the temperature dependence of the absorption coefficient, the thermal conductivity, the heat transfercoefficient and the Seebeck coefficient on the thermal profile and cross-talk level generated inside the detector materialis studied in detail. Heat losses that are included in the model are conduction and laminar free convection. The relative importance of the above-mentioned non-linear thermal parameters in terms of thermal cross-talk for steady-state solutions is discussed as well. © 2011 IOP Publishing Ltd. Source

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