Phase-coding Method Research Articles

A modified phase-coding method for absolute phase retrieval

Fringe projection technique is one of the most robust tools for three dimensional (3D) shape measurement. Various fringe projection methods have been proposed for addressing different issues in profilometry and phase-coding is one such technique employed to determine fringe orders for absolute phase retrieval. However this method is prone to fringe order error, while dealing with high-frequency fringes. This paper studies phase error introduced by system non-linearity in phase-coding and provides a mathematical model to obtain the maximum number of achievable codewords in a given scheme. In addition, a modified phase-coding method is also proposed for phase error compensation. Experimental study validates the theoretical analysis on the maximum number of achievable codewords and the performance of the modified phase-coding method is also illustrated.

Hybrid frequency and phase coding for a high-speed SSVEP-based BCI speller.

Steady-state visual evoked potential (SSVEP)-based brain-computer interfaces (BCIs) have potential to realize high-speed communication between the human brain and the external environment. Recently, multiple access (MA) methods in telecommunications have been introduced into the system design of BCIs and showed their potential in improving BCI performance. This study investigated the feasibility of hybrid frequency and phase coding methods in multi-target SSVEP-based BCIs. Specifically, this study compared two hybrid target-coding strategies: (1) mixed frequency and phase coding, and (2) joint frequency and phase coding. In a simulated online BCI experiment using a 40-target BCI speller, BCI performance for both coding approaches were tested with a group of six subjects. At a spelling speed of 40 characters per minute (1.5 seconds per character), both approaches obtained high information transfer rates (ITR) (mixed coding: 172.37±28.67 bits/min, joint coding: 170.94±28.32 bits/min) across subjects. There was no statistically significant difference between the two approaches (p>0.05). These results suggest that the hybrid frequency and phase coding methods are highly efficient for multi-target coding in SSVEP BCIs with a large number of classes, providing a practical solution to implement a high-speed BCI speller.

Optical manipulation of microobjects using binary diffractive elements

The paper describes the computation of binary diffractive optical elements (DOE) producing specific complex light patterns. The approach is based on amplitude and phase coding methods. The experimental complex light distributions are shown to agree with the computer simulation results. Due to the phase gradient this kind of light beams can be used for moving microscopic particles along a particular path. The light fields like that have been used successfully to trap and move tiny transparent polystyrol spheres 5 micrometer in diameter.

Integration of quantum cryptography into fiber-optic telecommunication systems

The prototype of a new quantum cryptosystem is described. Such a cryptosystem is naturally called time-shift quantum cryptography. It realizes all basic quantum-cryptography protocols [BB84, B92, BB84(4+2)] in a common fiber-optic system. This scheme does not involve Mach-Zehnder interferometers, which enables one to naturally realize the multiplex mode of secure key distribution and to naturally integrate this quantum-cryptography scheme into traditional fiber-optic telecommunication systems. The proposed time coding method in quantum cryptography makes it possible to significantly simplify experimental schemes and to exclude the finest fiber-optic part, the interferometer. In essence, the fundamental difference of the time coding method from the phase coding method is that the part using phase relations in superposition between “parts” of a quantum state is eliminated from the phase-coding method, and only the part using the time division principle is retained. The time division principle is common for both methods and is minimally necessary, in contrast to the phasecoding method, which can be excluded altogether. The proposed scheme is briefly compared with the two most developed phase-coding schemes (without self-compensation and with passive self-compensation).

Auditory inspection time and intelligence

The relationship of intelligence to auditory inspection time (AIT) was investigated using tasks derived from the spatial-location method reported by Parker, Crawford, and Stephen (1999). Stereo tone bursts were phase-shifted to create lateralized auditory stimuli, and a high-efficiency staircase was used to systematically vary the duration of the stimulus and determine reliable identification thresholds. As reported by Parker et al., all subjects could complete the task and log(AIT) correlated significantly with the general ability (assessed using Ravens Matrices: r=−0.53). This was independent of pitch discrimination ability. A second experiment examined the reliability of the task in a test–retest design. Test–retest reliability was 0.88, and there was no evidence for learning or practice effects on the task. A modified version of the task was constructed which cued location using binaural differences in volume instead of phase. While the volume and phase-coding methods derive from distinct brain systems, volume IT correlated with phase IT ( r=0.75). It is concluded that auditory inspection time for spatial location is able to be assessed rapidly, reliably, and with high precision, and lends support to the role of processing speed differences as basic to differences in intelligence.

Simple computer-generated holograms displayed by an x-y plotter

New simple computer-generated holograms displayed by an x-y plotter are proposed and investigated. In the construction of holograms by computer, phase coding methods are used in order to distribute the Fourier-transform values of an original object over the whole of the receiving plane where the hologram is to be constructed. It is found that relatively good images are reconstructed from the computer-generated holograms proposed here.