Chris Chinnock, Insight Media
In the Nov. 18, 2021 press release from Kopin, they announced a production order for displays for the U.S. Army’s Common Helmet Mounted Display (CHMD) System. There are two important takeaways from this news. One is the performance of the display, which is a new milestone, and two, that the display has transitioned from development to mass production.
Let’s start with display performance. It is common knowledge that all pilot helmet-mounted display (HMD) solutions are monochrome. The reason is that monochrome displays can deliver super high brightness that meets the pilot HMD requirements – something that is more feasible when color filters are not used. The newest Brillian display from Kopin is full color and uses color filters – nothing extraordinary there. What is unique, however, is the brightness (34,000 nits) and the contrast (500:1) achieved with this architecture.
According to Kopin, a multi-year development was needed to be able to deliver a full-color display with this performance level – and which meets rigorous military ruggedness requirements. This new Brillian microdisplay architecture features the fabrication of the backplane on a silicon wafer with color filters on top. The thin Si circuit layer is removed from the silicon substrate and transferred to a glass substrate. A liquid crystal cell process is then used to create a transmissive microdisplay, similar to normal direct view LCDs. This direct backlight configuration is preferred compared to the more complex LCOS illumination scheme (typically with a beam splitter).
Very high brightness backlights cause issues with the display. Light can affect the transistors degrading the applied voltage and light can leak from one pixel to another decreasing contrast. Using a color filter also reduces light transmittance considerably requiring an even higher backlight to achieve the desired transmitted light value.
In talking with CEO John Fan, he would not disclose the exact details of how they solved these challenges. But he did give two hints. “The key to this performance level is better light collimation,” explained Fan.
Such a hint would normally suggest a microlens array and/or pixel-level baffle structures. But he then dropped his second hint: “We did this through a backplane innovation to increase the LC drive voltages.”
How this helps is not obvious to me, but I guess this is why the solution took a few years to develop.
The second key take away is that these displays have reached the mass production stage. As many in the display industry know, showing a prototype or even a pilot line-based demo can be a long way from an actual robust mass production process. Since this is a production order, the customer is clearly happy and satisfied Kopin can deliver increased quantities.
And as other defense agencies see that a full-color display is now possible, monochrome-only programs are likely to want to upgrade to full color as well.
While this is attractive for Kopin, they don’t have the capacity to also service the consumer electronics market with similar devices, let alone potential increases in defense demand. That’s a good problem to have.