William A. Crossland

Holographic optical switching: the "ROSES" demonstrator

The design, assembly, and performance of a prototype 1/spl times/8 free-space switch demonstrator using reconfigurable holograms are reported. Central to the switch fabric is a ferroelectric liquid crystal (FLC) on silicon spatial light modulator (SLM) deposited with a 540/spl times/1 array of highly reflective and planar mirror strips. The input and output ports of the switch are fabricated as a linear array of silica planar waveguides connected to single-mode fibers, and the holographic beam-steerer operates without the need for adjustment or dynamic alignment. The waveguide array and the single Fourier transform lens for the 2f holographic replay system are housed in an opto-mechanical mount to provide stability. The switch operates at 1.55 /spl mu/m wavelength and has a designed optical bandwidth of >60 nm. The first measured insertion loss and crosstalk figures are 16.9 dB and -19.1 dB, respectively. Improvements in SLM performance, the use of new addressing schemes and the introduction of better alignment techniques are expected to improve these figures considerably. The preliminary performance of a 3/spl times/3 optical crossconnect is also presented to show that this technology is scalable to N/spl times/N switching fabrics.

Evolutionary development of advanced liquid crystal spatial light modulators

Taking into account recent developments and present trends in devices and component technologies, the future development of electrically addressed liquid crystal spatial light modulators is considered. In particular, the combination of single-crystal-silicon active backplane and chiral smectic C liquid crystal technologies is shown to be promising. The ultimate limitations of such technologies for producing faster devices of higher complexity and functionality are assessed, and an advanced device, presently under development, is described.

Dynamic holographic interconnects that use ferroelectric liquid-crystal spatial light modulators.

Dynamic interconnect holograms are designed by the use of a simulated annealing algorithm and written to a 128 × 128 pixel ferroelectric spatial light modulator that is used in a binary-phase mode. Dynamic holograms are used to implement a 2 × 2 crossbar with single-mode fiber inputs and outputs, which function with as high as 27 dB of isolation between output ports. The principle is extended to two-dimensional interconnection holograms, and arbitrary fan-out to as high as 64 points is demonstrated with good performance.Images of interconnection holograms are transferred from the spatial light modulator to an optically addressed spatial light modulator that is used in a binary-phase mode. The addition of a fixed array generator computer-generated hologram permits replication of the hologram image, thus creating a larger hologram with a high space-bandwidth product on the optically addressed spatial light modulator.Results of a preliminary experiment are presented.

Electrically induced scattering textures in smectic A phases and their electrical reversal

An electro-optic display mechanism is described which uses a smectic A liquid crystal of positive dielectric anisotropy. Information can be written on the display, stored there without a sustaining voltage i.e. has a memory, and subsequently can be erased electrically. The erase mechanism involves a dielectric re-orientation of the smectic molecules, and the writing mechanism involves a turbulent scattering state that resembles nematic dynamic scattering. The turbulent state is characterised by large rotating vortices whose plane of motion is orthogonal to the field direction. The conditions required to obtain scattering at the lowest practical threshold voltage are discussed.

Reconfigurable multilevel phase holograms for optical switches

A way of dynamically encoding polarization-insensitive multilevel phase holograms using nematic liquid crystals is presented. The method, using a quarter wave plate and a mirror, allows the optical efficiency of a free space single-mode fiber-to-fiber switch to be greatly enhanced. The validity of the approach has been verified experimentally by observing the power diffracted in the /spl plusmn/1 orders of a nematic liquid crystal grating as a function of input polarization and applied voltage.

Dynamic holography for optical interconnections. II. Routing holograms with predictable location and intensity of each diffraction order

An analysis of dynamic phase-only holograms, described by fractional notation and recorded onto a pixelated spatial light modulator (SLM) in a reconfigurable optical beam-steering switch, is presented. The phase quantization and arrangement of the phase states and the SLM pixelation and dead-space effects are decoupled, expressed analytically, and simulated numerically. The phase analysis with a skip-rotate rule reveals the location and intensity of each diffraction order at the digital replay stage. The optical reconstruction of the holograms recorded onto SLMs with rectangular pixel apertures entails sinc-squared scaling, which further reduces the intensity of each diffraction order. With these two factors taken into account, the highest values of the nonuniform first-order diffraction efficiencies are expected to be 33%, 66%, and 77% for two-, four-, and and eight-level one-dimensional holograms with a 90% linear pixel fill factor. The variation of the first-order diffraction efficiency and the relative replay intensities were verified to within 1 dB by performing the optical reconstruction of binary phase-only holograms recorded onto a ferroelectric liquid crystal on a silicon SLM.

The Silicon Backplane Design for an LCOS Polarization-Insensitive Phase Hologram SLM

Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematic Freedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division-multiplexing telecommunications, television multicast, and holographic projection.

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.

53.1: Real-time Binary Hologram Generation for High-quality Video Projection Applications

Presenting visual information using binary-phase holography has a number of advantages over conventional video projection techniques. However, acceptable image quality for video applications has yet to be realised. In addition, the computational complexity of hologram generation has precluded real-time operation. The authors present a new approach to hologram generation and display which allows high-quality images to be projected holographically, in real time.

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.