Laser Light Source Update

Speakers from Nanjing CQ Lasers, Necsel and the University College of Southeast Norway gave presentations at Display Summit China on the status of laser devices for projection applications. As expected, some parts of the supply chain are mature and some are not, but price reduction will be the key to expanding opportunities.

CQ Xu reviewed some of the laser projector applications and stated some requirements for RGB laser solutions in projection. These include high efficiency, high optical power, compactness for portable devices, low cost, high reliability and easy mass production.

He then reviewed where current red, green and blue lasers are compared to these requirements. Red lasers for example, meet the above criteria with the exceptions of cost (needs to decrease) and wavelength (need longer wavelength devices). Likewise, blue lasers generally meet these requirements as well, with many categories in the “acceptable” range meaning they are OK for current products but can be improved for future products – including price.

Things get more troublesome for green lasers. For green laser diodes, Xu said costs “have room to reduce” and that the wavelength needs to increase. The one major supplier, Nichia, offers a 520 nm device that should move to 532 nm or so to better match system needs. He did not consider Necsel as a laser diode supplier but a VECSEL supplier

For the Diode Pumped Solid State Lasers (DPSSL) type that CQ Lasers offers, the items he highlighted were cost and mass production, which need some work. This is summarized in the table below.

CQ table

He also compared the price of a RGB solution using their mGreen DPSSL laser to a conventional laser phosphor solution for a 3000 lumen projector and a ratio of optical power of 1:1:1. Using the cost of the blue laser as the baseline price (X), the laser phosphor solution would cost 32X (i.e. you need 32 blue lasers), while the RGB solution would cost 70x or more than twice. This chart provoked much debate as there was no indication of the speckle reduction level needed or many other parameters that can drive the cost.

Necsel offers an RGB laser solution that is very popular in cinema projectors today. Speaker Jun Saito reviewed some of the benefits of lasers in projection, which was nicely summarized in the chart below.

NECSEL table

He then showed the chart that Christie Digital showed at NAB suggesting that all new cinema projectors sold in 2022 will be RGB laser-based, which drew some debate following his presentation.

His chart on RGB laser pricing also drew discussion as some suggested that a simplistic focus on $/W was not sufficient as the needs of each market segment differ and you need to focus on the cost of the light source solution including despeckling, drivers and thermal management to get a better guage of true costs. But the price declines for the devices themselves was impressive.

Xuyuan Chen from the University College of Southeast Norway focused his talk on speckle reduction, which he called the bottleneck for projection applications. His presentation reviewed a number of methods that can be deployed to reduce the spatial and temporal coherence of the laser light. The available degrees of freedom are shown in the chart below.

USN chart

His paper then described a wide variety of methods for speckle reduction, which we won’t detail here. His conclusion: the optimum choice of speckle reduction methods depends greatly on the architecture of the laser projector. – CC