Norbert Fürstenau

Fiber-Optic Extrinsic Fabry-Perot Interferometer Strain Sensor with <50 pm displacement resolution using three-wavelength digital phase demodulation

A fiber-optic extrinsic Fabry-Perot interferometer strain sensor (EFPI-S) of ls = 2.5 cm sensor length using three-wavelength digital phase demodulation is demonstrated to exhibit <50 pm displacement resolution (<2nm/m strain resolution) when measuring the cross expansion of a PZT-ceramic plate. The sensing (single-mode downlead-) and reflecting fibers are fused into a 150/360 microm capillary fiber where the fusion points define the sensor length. Readout is performed using an improved version of the previously described three-wavelength digital phase demodulation method employing an arctan-phase stepping algorithm. In the resent experiments the strain sensitivity was varied via the mapping of the arctan - lookup table to the 16-Bit DA-converter range from 188.25 k /V (6 Volt range 1130 k ) to 11.7 k /Volt (range 70 k ).

Fiber-Optic Extrinsic Fabry-Perot Interferometer Sensors with Three-Wavelength Digital Phase Demodulation

A three-wavelength-based passive quadrature digital phase-demodulation scheme has been developed for readout of fiber-optic extrinsic Fabry-Perot interferometer vibration, acoustic, and strain sensors. This scheme uses a superluminescent diode light source with interference filters in front of the photodiodes and real-time arctan calculation. Quasi-static strain and dynamic vibration sensing with up to an 80-kHz sampling rate is demonstrated. Periodic nonlinearities owing to dephasing with increasing fringe number are corrected for with a suitable algorithm, resulting in significant improvement of the linearity of the sensor characteristics.

Development of an augmented vision video panorama human-machine interface for remote airport tower operation

In this paper the development of a 180° high resolution video panorama system and results of initial field test at Braunschweig research airport are described. The system serves as main HMI for remote surface movement management of small airports or of movement areas not directly visible for the controller. It provides the framework for video-see-through augmented vision by integration of traffic and weather data and it allows for panorama replay. Preliminary evaluation of initial field tests quantify the visual resolution as compared to the real far view.

Modelling and simulation of spontaneous perception switching with ambiguous visual stimuli in augmented vision systems

A behavioral nonlinear dynamics model of multistable perception due to ambiguous visual stimuli is presented. The perception state is formalized as the dynamic phase variable v(t) of a recursive process with cosinuidal transfer characteristic which is created by superposition (interference) of neuronal mean fields. The two parameters μ = difference of meaning of alternative percepts and G = attention parameter, control the transition between unambiguous and ambiguous stimuli, e.g. from stimulus off to stimulus on, and attention fatigue respectively. Mean field interference with delayed phase feedback enables transitions between chaotic and limit cycle attractors v(t) representing the perception states. Perceptual reversals are induced by attention fatigue G(t) ( adaptive gain g(v)) with time constant γ, and attention bias which determines the relative duration of the percepts. The coupled attention – perception dynamics with an additive stochastic noise term reproduces the experimentally observed Γ-distribution of the reversal time statistics. Mean reversal times of typically 3 – 5 s as reported in the literature, are correctly predicted if delay T is associated with the delay of 40 ms between stimulus onset and primary visual cortex (V1) response. Numerically determined perceptual transition times of 3 – 5 T are in reasonable agreement with stimulus – conscious perception delay of 150 – 200 ms [11]. Eigenfrequencies of the limit cycle oscillations are in the range of 10 – 100 Hz, in agreement with typical EEG frequencies.

Fiber-optic polarimetric strain sensor with three-wavelength digital phase demodulation

A fiber-optic polarimetric strain sensor of l(S)=10-cm sensing length with three-wavelength passive quadrature digital phase demodulation is investigated. The demodulation unit uses a superluminescent diode light source with narrow-band interference filters in front of the photodiodes and real-time processing of the interference intensities by an arctan-phase-stepping algorithm. Quasi-static strain sensing is performed during slow periodic compression of a composite reinforced plastic rod with a sensor glued to its surface. The measured displacement sensitivity of delta?/deltal=125 mrad/mum, with a resistive strain gauge as a reference, agrees well with the value of 119 mrad/mum previously determined by fringe-distance measurement [Bock et al., Pure Appl. Opt. 5, 125 (1996)]. Despite a coherence-limited fringe contrast of only a few percent, a linearity of the phase-strain characteristic of the order of 1% and a strain resolution of 2.5muepsilon are demonstrated.

Frame Rate Effects on Visual Discrimination of Landing Aircraft Deceleration Implications for Virtual Tower Design and Speed Perception

In order to help determine the required visual frame rate for the design of remote/virtual airport towers, thirteen active air traffic controllers viewed high dynamic-fidelity simulations of landing aircraft and decided whether the aircraft would stop before the end of the runway, as if to be able to make a runway turnoff. The viewing conditions and simulation dynamics replicated visual rates and environments of transport aircraft landing at small commercial airports. Three frame rates were used: 6, 12, and 24 fps. The frame rate that would be needed to produce asymptotic performance was estimated from a model fit to perceptual discriminability (d’) of the condition in which the aircraft would stop. The required frame rate appears to range from 30-60 fps, but definitive recommendations require further testing at a higher rate in the range of 45-60 fps. Errors and reports of judgment certainty show performance was roughly steady state. Anecdotal reports of increased apparent speed due to low frame rates are objectively confirmed. Some implications for the perceptual design of a remote tower are briefly discussed.

Bistable fiber-optic Michelson interferometer that uses wavelength control

Feedback of the interference signal of an unbalanced Michelson interferometer to the current supply of the semiconductor-laser source yields bistability under input intensity variation owing to wavelength-induced phase modulation. A linear stability analysis of the systems differential equation gives the ratio of the system time constant tau to the feedback delay time T to determine the critical input intensity for the onset of self-oscillations. Input-output characteristics that exhibit bistability and self-oscillations are obtained experimentally through modulation of the input power by using an integrated-optics intensity modulator.

Double-polarization interferometer for digital force sensing by fiber tension bending.

A fiber-optic interferometric force sensor with digital readout by fringe counting is investigated. Ambiguity in fringe counting is eliminated by employing the double-polarization method. Force F(t), transverse to the fiber axis, is measured by tension-bending-induced fiber strain. A theoretical strain-force characteristic is derived, yielding an F(t)(2/3) dependence of fiber strain on the transverse force that is verified experimentally.

Discriminability of flight maneuvers and risk of false decisions derived from dual choice decision errors in a videopanorama-based remote tower work position

Future remote control of small low traffic airports (Remote Tower Operation, RTO) will rely on the replacement of the conventional control tower out-of-windows view by a panoramic digital reconstruction with high resolution and pan-tilt zoom (PTZ) video cameras as basic sensor system. This provides the required visual cues for aerodrome traffic control without a local control tower. Here we show that with a 2 arcmin-per-pixel resolution panorama system even with the use of a manually controlled (analog) PTZ camera (with PAL TV-resolution and selectable zoom factor setting) experiments under operational conditions indicate a significant increase of decision errors under RTO as compared to the conventional out-of-windows view. We quantify the corresponding discrimination difference by means of detection theory (discriminability, decision criteria) and Bayes inference (risk of false decisions) using the response errors of tower controllers with regard to dual choice decision tasks. The results extend the performance and subjective data analysis of safety related maneuvers in 11.

Computational Nonlinear Dynamics Model of Percept Switching with Ambiguous Stimuli

Simulation results of bistable perception due to ambiguous visual stimuli are presented which are obtained with a nonlinear dynamics model using delayed perception---attention---memory coupling. Percept reversals are induced by attention fatigue with an attention bias which balances the relative percept duration. Periodic stimulus simulations as a function of stimulus off-time yields the reversal rate variation in surprisingly good quantitative agreement with classical experimental results reported in the literature [1] when selecting a fatigue time constant of 1 --- 2 s. Coupling of the bias to the perception state introduces memory effects which are quantified through the Hurst parameter H, exhibiting significant long range correlations (H > 0.5) in agreement with recent experimental results [2]. Percept transition times of 150 --- 200 ms and mean percept dwell times of 3 --- 5 s as reported in the literature, are correctly predicted if a feedback delay of 40 ms is assumed as mentioned in the literature (e.g. [21]).