Presents a new category of optical CDMA systems which work based on spectral encoding. In such systems, that the authors refer to as frequency-encoded CDMA (FE-CDMA) systems, the coding is done in the frequency domain while in the usual CDMA systems the code multiplies the modulation signal in the time domain. They present a new type of FE-CDMA system, based on encoding noncoherent broadband sources. They discuss the advantages of the system compared to other optical CDMA systems and present its performance. They show that very efficient, low-cost, CDMA systems can be obtained with an aggregate throughput of many gigabits per second. Also, for this system, the spreading gain of CDMA is independent of the modulation bandwidth. Hence, the system can accommodate variable bit rates, naturally. >

Optical code-division-multiplexed systems based on spectral encoding of noncoherent sources

Interest in the smectic liquid-crystalline state of matter received a substantial boost with the discovery by Meyer in the mid-1970s that a chiral smectic C (SmC*) phase exhibits a spontaneous electric polarization, and with the subsequent demonstration by Clark and Lagerwall of the surface-stabilized SmC* ferroelectric liquid crystal at the beginning of the 1980s. Since then, chiral smectic phases and their plethora of polar effects have dominated the research in this field, which today has reached a mature state where the first commercial microdisplay applications are now shipping in millions-per-year quantities. In this Review we discuss some of the topics of highest interest in current smectic liquid crystal research, and address application-relevant research (de Vries-type tilting transitions without defect generation and high-tilt antiferroelectric liquid crystals with perfect dark state) as well as more curiosity-driven research (the nature and origin of the chiral smectic C subphases and their intermediate frustrated states between ferro- and antiferroelectricity).

Current topics in smectic liquid crystal research.

Different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the dielectric spectrum. Experimentally, the complex dielectric permittivity has been studied as a function of temperature and frequency in the range 5 Hz - 13 MHz for three different ferroelectric liquid crystal materials. The main problems encountered in dielectric measurements at low and high frequency are discussed in some detail. The soft mode dielectric behaviour has been studied as a function of temperature, frequency and bias electric field. The applicability of the Curie-Weiss law for the soft mode dielectric contribution in the A* phase was analyzed. In the C* phase the temperature dependence of the dielectric contribution of the Goldstone mode has been measured. By applying a bias electric field, we have been able to study the soft mode dielectric behaviour also deep into the C* phase. In the A* and C* phases ...

Dielectric studies of the soft mode and Goldstone mode in ferroelectric liquid crystals

Smart pixels are discussed in terms of the following neurally inspired functions: memory, sensors, intrapixel circuitry, interpixel communication, and optical outputs. The types of liquid crystals and electronic circuits used in VLSI/liquid crystal arrays, and their electrooptic properties are reviewed. Examples of electrically addressed and optically addressed liquid crystal smart pixels, and results from a 128*128 VLSI/FLC SLM are presented. This device has a response time of 150 mu s, a contrast ratio of 8:1 measured on a row containing more than 50 pixels, and a frame rate of 4.7 kHz. Improvements of these devices are discussed in terms of what the silicon technology can yield in the future. A few examples in which the liquid crystal on silicon technology has been applied are presented. >

Smart spatial light modulators using liquid crystals on silicon

A frame-sequential color video system and color-selective filters for use in the same The color-selective filters of the invention have fast response, and can be switched between the three primary colors of red, green, and blue Switching between the three primary colors is achieved by selective absorption, or by selective interference, which is controlled by the switching of specific device combinations A frame-sequential color display system is achieved by combining such a color-selective filter with a fast-switching black and white video display, which can be either emissive or reflective A frame-sequential color camera system is achieved by combining such a color-selective filter with a fast-responding black and white video camera

Fast switching color filters for frame-sequential video using ferroelectric liquid crystal color-selective filters

A new liquid‐crystal electro‐optic modulating device similar to the surface‐stabilized ferroelectric liquid‐crystal device is described. It uses the same kind of ferroelectric chiral smectics and the same geometry as that device (thin sample in the ‘‘bookshelf ’’ layer arrangement) but instead of using a tilted smectic phase like the C* phase, it utilizes the above‐lying, nonferroelectric A phase, taking advantage of the electroclinic effect. The achievable optical intensity modulation that can be detected through the full range of the A phase is considerably lower than for the surface‐stabilized device, but the response is much faster. Furthermore, the response is strictly linear with respect to the applied electric field. The device concept is thus appropriate for modulator rather than for display applications. We describe the underlying physics and present measurements of induced tilt angle, of light modulation depth, and of rise time.

Submicrosecond electro‐optic switching in the liquid‐crystal smectic A phase: The soft‐mode ferroelectric effect

We study the distortion of a chiral smectic C, under a shear applied parallel to the plane of the layers, using an original technique based on the modification of the conoscopic image. Both the amplitude of the distortion and the phase lag between the alternating applied shear and the deformation are found to vary like the flow induced transverse polarization (described in Ref. 7). The behaviour is understood in terms of a viscoelastic-nematic-like model and of a simplified optical description which gives account of the displacement without deformation of the conoscopic image.

P. Keller

Papers

Submicrosecond electro‐optic switching in the liquid‐crystal smectic A phase: The soft‐mode ferroelectric effect

Optical Study of a Chiral Smectic C Under Shear

Synthesis and mesomorphism of some r(-) 2-chloropropyl (p-alkyloxybenzylidene-p′-aminocinnamate)