A Georgiou

Liquid crystal over silicon device characteristics for holographic projection of high-definition television images

We discuss some fundamental characteristics of a phase-modulating device suitable to holographically project a monochrome video frame with 1280 x 720 resolution. The phase-modulating device is expected to be a liquid crystal over silicon chip with silicon area similar to that of commercial devices. Its basic characteristics, such as number of pixels, bits per pixel, and pixel dimensions, are optimized in terms of image quality and optical efficiency. Estimates of the image quality are made from the noise levels and contrast, while efficiency is calculated by considering the beam apodization, device dead space, diffraction losses, and the sinc envelope.

Aspects of hologram calculation for video frames

This paper presents a modified version of the Fienup algorithm that can compute an image projecting hologram significantly faster. The proposed method, referred to as Fienup with don’t-care (Fidoc), is sufficiently fast to enable real-time hologram calculation for video projection purposes. It achieves high speed and excellent image quality by dispersing noise in ‘don’t-care’ areas around the image. Through simulations it was shown that for the same amount of computation, reconstruction quality is significantly better when using the Fidoc method instead of the simple GS (Gerchberg‐Saxton) and Fienup algorithms.

Hologram Optimisation Using Liquid Crystal Modelling

ABSTRACT Beam steering liquid crystal devices employed in telecommunication networks suffer from high crosstalk. This is due to the limited resolution arising from the finite extent of the liquid crystal elastic deformation and the electric field fringing. In this paper we show how non-periodic phase elements (holograms) can reduce crosstalk. A new model is devised to evaluate the approximate liquid crystal phase profile that is many times faster than the finite element method, enabling its evaluation millions of times as it is required by the hologram iterative design algorithms. Holograms designed using the new model had improved performance and flexibility compared to periodic gratings.

Liquid crystals in telecommunications systems

The first liquid crystal devices have recently been installed in the fibre optic networks that provide the backbone of the modern telecommunications system. Most optical network devices are concerned with the manipulation of the amplitude and phase of the optical signal. Liquid crystals have the highest figure of merit for field addressed electro-optic response and can have excellent transparency in the optical telecommunications window. Here we consider the importance of liquid crystals in controlling the phase and the state of polarisation of light in these systems. We also consider arrays of liquid crystal phase modulators, fabricated using LCOS technology, in holographic switches and multifunction devices.

An algorithm for computing spot-generating holograms

This paper describes a computationally efficient algorithm suitable for designing spot-generating holograms many times faster that existing techniques without compromise in the reconstruction quality. This algorithm is best suited for applications where the spatial light modulator has many pixels and phase levels while the reconstruction plane contains a relatively small number of spots.

PROJECTION OF HOLOGRAMS FROM PHOTOREFRACTIVE OASLMs

Liquid crystals doped with fullerenes and carbon nanotubes (CNTs) act as good optical nonlinear materials. We have used these materials to build optically-addressed spatial light modulators (OASLMs). The devices comprise a single layer of doped liquid crystal acting as an active layer. Undoped LC devices with surfaces coated with fullerenes are also studied. Such OASLMs allow recording of phase holograms, and we record by imaging pre-calculated pre-recorded holograms. Writing is performed at normal incidence and reading at 45° oblique incidence. Both transmission and reflection modes of operation are used. Experimental results as well as comparison with commercially available OASLMs are presented.

Multicasting optical interconnects using liquid crystal over silicon devices

This work presents the characteristics and expected capabilities of an optical interconnect that uses a diffractive liquid crystal over silicon (LCOS) device as a routing element. Such an interconnect may be used in a neighborhoods optical network to distribute high definition television, thus avoiding an electronic or optical transmitter for each user. The optimal characteristics of the LCOS device are calculated in terms of pixel number and silicon area and found to be feasible with todays technology. Finally, its performance in terms of optical efficiency and number of output ports is evaluated and found suitable for a neighborhood with hundreds of households.

Noise formation in Fourier phase-only holograms

This paper presents what is to the author’s knowledge a new theory for phase-only holograms. It explains many phenomena observed in the reconstruction of phase-only Fourier holograms and in particular the existence and nature of noise. Using this theory it was demonstrated that any reconstruction is the convolution of the target reconstruction with a two-dimensional set of impulses. The nature of this convolution function depends on the target reconstruction and in particular the spacing between the spots. In the simplest case of a two-spot generating hologram the convolution function was calculated analytically. The theory is also verified with examples from spot generating holograms, symbology, and image projection holograms.

Simulation of the functionality of liquid crystal phase holograms for applications in optical telecommunication networks

Liquid crystal phase holograms can (in principle) route light without losing photons. Here, we simulate their functionality when used in an optical network as optical switches, variable optical attenuators and phase equalisers.

Quantization effects on the deflection angles of digital holograms

Phase holograms can, in principle, route light with zero photon loss. This property makes them ideal for applications with tight power constraints such as free space interconnects and optical tweezers. Both applications require that the deflection angle is varied accurately and smoothly over a certain range. For example, in a free space switch, the output would be a single mode fibre with core diameter of 9μm and the beam has to be centred accurately on it. If an adaptive link is used the beam will be scanned near the output and the optimum position will be determined. Any quantisation effects on the deflection angle may cause instabilities in the feedback loop of the link. In optical tweezers the quantisation effects on the deflection angle will cause the particle to move in discrete steps. This may release the particle from the optical tweezers due to the large acceleration. The quantisation effects on the deflection angle may be difficult to observe because of the very small changes involved. However, these effects can be very important. In this paper we derive the quantisation effects introduced to the deflection angle due to hologram quantisation. We evaluate the minimum number of pixels required in order to achieve a certain resolution on the deflection angle, and finally we suggest methods for enhancing the performance of the hologram by taking into account these effects.