Presentation: Large-area display technologies
Our digital society has an insatiable appetite for data – and after processing, these need to be displayed in suitable form for human beings. Today’s ubiquitous display solution consists of a large-area array of color LEDs (red-green-blue), which are found everywhere from digital watches over smartphones to TV sets and electronic billboards. However, video projectors (“beamers”) based on miniature DMD (Digital Mirror Device) or LCD (Liquid Crystal Display) devices are good examples for the creation of large imagery with small-scale, affordable systems. Hamamatsu is actively developing such cost-effective large-area display solutions, making use of several different technological approaches:
Lasers are becoming easier to produce and to package if they are manufactured wafer-scale and their emission is perpendicular to the wafer surface. Such VCSELs (Vertical Cavity Surface Emitting Lasers) are found in a large number of products these days. Hamamatsu has optimized the manufacturing of these VCSELs, such that it becomes also possible to fabricate VCSEL arrays. In this way, the output power of the emitted laser light can be increased by large factors, simply by increasing the area covered by the VCSEL array.
For the generation of images it is necessary that corresponding wave-fronts are generated, as pointed out by Nobel-prize-winner Dennis Gabor. His famous technique of holography, previously implemented with photographic emulsions, can profit substantially from novel digital technologies. A so-called Computer-Generated Hologram (CGH) is a simple yet versatile approach to generate large-area imagery with a miniature device: Just a millimetre-size projection system consisting of a laser diode and a phase-modifying CGH platelet are required.
While conventional CGH projectors are static, Hamamatsu’s LCOS-SLM system is able to create CGH patterns in real-time and to generate arbitrary wave-fronts and phase distributions – and therefore also imagery of any size. The power-handling capacity of the new generation of LCOS-SLM is so high that it can be even employed for laser marking, cutting and machining.
Hamamatsu has developed a novel projection device, consisting of a single light-emission and phase-modulation device, essentially combining distributed, side-emitting laser structures and a CGH device on a millimetre-size platelet. This so-called iPMSEL (integrated Phase-Modulating Surface-Emitting Laser) is an extremely compact light-pattern generator that can also be used to create time-varying imagery on large areas.
As demonstrated by the DMDs in video projectors, optomechanical scanning can lead to superior system performance and higher cost-effectiveness. This is true both for image generation as well as for LIDAR/TOF scanning. In particular, this required for high-accuracy 3D image acquisition under extremely high background light conditions, as is typically the case in autonomous cars driving in full daylight. Hamamatsu has developed a range of very reliable 1D and 2D micromirror modules, with a (resonant) modulation/scanning frequency of up to 50 kHz.
Although it has been known for many years that organic LEDs can be fabricated on very large (poster-size) areas at low cost, no product has made a commercial appearance until now. The problem is the operational stability of these devices that are sensitive to moisture, to oxygen and to UV light. Hamamatsu has recently made a breakthrough in the production of very stable, high-quality yet low-cost organic LEDs with operational lifetimes of many thousand hours. This could be the long-sought technology for affordable large-area color displays, for which a plethora of applications exist.