This overview covers most of the 3-D displays that are in use today and presents recent developments and advances in this field.

After the invention of lasers, in the past 50 years progress made in laser-based display technology has been very promising, with commercial products awaiting release to the mass market. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers, and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser safety issues need to be carefully evaluated in designing laser displays under different usage scenarios. Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and the requirements depend on the source specifications, modulation technique, and the scanning method being employed in the display. A variety of laser-based displays have been reported, and many products such as pico projectors and laser televisions are commercially available already.

Abstract-An autostereoscopic 3D display based on direct-view RGB laser projection via a transparent display screen is presented. Dynamic exit pupils are formed at the target eye locations with the help of a pupil tracker.

This paper presents a laser based auto-stereoscopic 3D display technique and a prototype utilizing a dual projector light engine. The solution described is able to form dynamic exit pupils under the control of a multiuser head-tracker. A prototype completed recently is able to provide a glasses-free solution for a single user at a fixed position. At the end of the prototyping phase it is expected to enable a multiple user interface with an integration of the pupil tracker and the spatial light modulator.

An autostereoscopic head-tracked back projection display that uses an RGB laser illumination source and a fast light engine is described. Images are horizontally scanned columns controlled by a spatial light modulator that directs two or more images in the directions of the apposite viewers' eyes. IntroductionThe HELIUM3D (High Efficiency Laser-Based Multi-user Multimodal 3D Display) is a European Union funded project developing an auto-stereoscopic multiview multi-user display. The project is led by De Montfort University in the UK and comprises eight partners, the others being: Philips, Nanjing University, Barco, Fraunhofer HHI, Koç University, Technische Universiteit Eindhoven and University College London.The goal of the project is the development of an auto-stereoscopic display whose capabilities exceed those of a purely stereoscopic display. The display operates in conjunction with a fast image forming device, allowing for the possibility of operating in what is referred to as the '3D+' mode where a completely different image can be presented to each viewer's eye. This enables other interesting modes of operation to be achieved, for example; motion parallax, user-determined viewpoint, secure images visible only to selected viewer/s etc. A multi-user head position tracker is an integral part of the system and in addition to being used to locate the regions in the viewing field where the images are observed (exit pupils) the display lends itself readily to interactive applications where the knowledge of head positions is utilized. 2.Operation of the HELIUM3D Display Figure 1 shows a schematic diagram of the HELIUM3D display system. The display consists of three sub-sections: the Light Engine, the Head Tracker and the Transfer Screen.The Light Engine [1] is to deliver a vertical uniform white light column with the size of 8 mm × 100 µm which is scanned using a scanning mirror across a Liquid Crystal on Silicon (LCOS) light valve. Three high power multi-emitter lasers are employed for red (640 nm), green (532 nm) and blue (465 nm) to achieve a wide color gamut and deliver enough luminance intensity at the LCOS device. Using multi emitter lasers reduces the coherence length and helps in combating speckle, which is a real concern in laser projection systems. The initial power of each laser is 3W and a color temperature of 6500°K is achieved by using a power ratio of 1: 0.49: 0.63 for red, green and blue. The three lasers are combined, homogenized and shaped using an x-cube, optical lenses and microlens arrays, and delivered as a uniform light column at the position of the LCOS device. The LCOS contains the image content thus creating a horizontally scanned columnar representation of the image.The scanned image is relayed to the transfer screen stage using a conventional multi-element projection lens (L 1 ). This lens acts as an interface between the Light Engine and the Transfer Screen sub-systems of the display. The Transfer ScreenThe transfer screen can further be sub-divided into three separate unit...