Will Green Laser Diodes Revoltionize the World?
First red, then blue, and now green. It is light (specifically: the light of laser diodes) which makes the world smarter.
The first success stories involving green laser diodes reached the market in 2009. A research group from the Japanese company Sumitomo Electric Industries developed a “real green laser diode” based on GaN [1]: the efficiency was low but the enthusiasm high. Osram Opto Semiconductors continued this success and won the Beckurt’s Award for 515 nm laser diodes with optical power levels of 50 mW [2], which have been available commercially since 2012.
Light Mixtures
How Colors Are Created
With the primary valences of red, green, and blue, (almost) any other light color can be created. This is referred to as an additive mixture in the RGB color space.
White light is created by mixing all three colors at the same intensity. Yellow can be created, for example, by mixing red and green light at the same intensity.
The human eye distinguishes color as soon as light shines on an object. Depending on the object, part of the light is reflected (returned) while the other part is absorbed (swallowed).
SSI projectors are based on these two principles: light mixture and surface projection. SSI stands for solid state illumination (i.e., for semiconductor-based light sources).
The Future Market of Miniature Projectors
Beyond Borders
There is a large market for miniature projectors: Used in the projection of (moving) images from smartphones and head-up displays, they will soon become an indispensable part of everyday life. The demands placed on projectors for the mass market are great: they have to be small and consume low amounts of power.
LED or Laser Diode?
It’s the Small Differences
The light in LEDs and laser diodes is produced in a similar way, and the colors are similar; however, the properties are completely different.
The main difference between these technologies is the emission behavior of the light sources. LEDs have a divergent emission (i.e., originating from the source in a cone shape). The light of laser diodes, however, is directed, and the beam is narrow.
An image projected using laser diodes is, therefore, always sharp – on both flat and curved surfaces [3]. Furthermore, projectors with laser diodes can be built that are even smaller than LED versions [4].
[1] Heise Online Newsticker, „Erstmals ¬echte grüne Laserdiode“, 29.07.2009
[2] Osram Opto Semiconductors, Pressemeldungen, 10.12.2010
[3] Photonikforschung, „Pikoprojekte auf dem Vormarsch“, 09.04.2013
[4] PICOLO - Förderinitiative „Optische Komponenten und Systeme für Volumenmärkte“
