Tactation is the sensation perceived by the sense of touch, and is based on the skin's receptors. Touch is a common medium used by the general population and the sensory impaired. Tactile substitution can be used by the blind or deaf in order to: (a) enhance access to computer graphical user interfaces and (b) enhance mobility in controlled environments.The skin nerves can be stimulated through six types of receptors by mechanical, electrical, or thermal stimuli. Modalities, such as vibration and pressure, can stimulate these receptors. Advances in tactile communication using implementations of the actuating devices have been developed via several new technologies. These technologies include static or vibrating pins, focused ultrasound, electrical stimulation, surface acoustic waves, and other. This paper is a review of the state-of-the-art in the physiological and technological principles, considerations and characteristics, as well as latest implementations of microactuator-based tactile graphic displays. We also review fabrication technologies, in order to demonstrate the potential and limitations in tactile applications.

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In this paper, we demonstrate a novel RAM cell based only on three traveling waveguide semiconductor optical amplifier-cross gain modulation (SOA-XGM) switches. The RAM cell features wavelength diversity in the incoming bit signals and provides Read/Write operation capability with true random access exclusively in the optical domain. Two of the SOA-XGM switches are coupled together through an 70/30 coupler to form an asynchronous flip-flop, which serves as the memory unit. Random access to the memory unit is granted by a third SOA-ON/OFF switch and all three SOAs together form the proposed RAM cell. Proof-of-principle operation is experimentally demonstrated at 8 Mb/s using commercial fiber-pigtailed components. The distinctive simplicity of the proposed RAM cell architecture suggests reduced footprint. The proposed flip-flop layout holds all the credentials for reaching multi-Gb/s operational speeds, if photonic integration technologies are employed to obtain wavelength-scale waveguides and ultrashort coupling lengths. This is numerically confirmed for 10 Gb/s using a simulation model based on the transfer matrix method and a wideband steady-state material gain coefficient. Index Terms-Optical flip-flop, optical memory, optical signal processing, semiconductor optical amplifier (SOA), transfer matrix method (TMM).

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