After posting my discovery of a Himax LCOS panel on a Google Glass prototype, I received a number of inquiries about Kopin including a request from Mark Gomes of SeekingAlpha the give my thoughts about Kopin which were published in “Will Kopin Benefit From the Glass Wars?” In this post I am adding morel information to supplement what I wrote for the Seeking Alpha article.
First, a little background on their “CyberDisplay® technology would be helpful. Back in the 1990’s Kopin developed a unique “lift-off” process to transfer transistor and other circuitry from a semiconductor I.C. onto a glass plate to make a transmissive panel which they call the CyberDisplay®. Kopin’s “lift-off” technology was amazing for that era. This technology allowed Kopin to apply very (for its day) small transistors on glass to enable small transmissive devices that were used predominantly in video and still camera viewfinders. The transmissive panel has 3 color dots (red, green, blue) that produce a single color pixel similar to a large LCD screen only much smaller. In the late 1990’s Kopin could offer a simple optical design with the transmissive color panel that was smaller than existing black and white displays using small CRTs. This product was very successful for them, but it has become a commoditized (cheap) device these many years later.
CyberDisplay pixel is large and blocks 98.5% of the light
While the CyberDisplay let Kopin address the market for what are now considered low resolution displays cost effectively, the Achilles’ heel to the technology is that it does not scale well to higher resolution because the pixels are so large relative to other microdisplay technologies. For example Kopin’s typical transmissive panel is15 by 15 microns and is made up of three 5 by 15 color “dots” (as Kopin calls them). But what makes matters worse; even these very large pixel devices have an extremely poor light throughput of 1.5% (blocks 98.5% of the light) and scaling the pixel down will block even more light!
While not listed on the website (but included in a news release), Kopin has an 8.7 x 8.7 micron color filter pixel (that I suspect is used in their Golden-i head mount display) but it blocks even more light than the 15×15 pixel as the pixel gets smaller. Also to be fair, there are CyberDisplay pixels that block “only” 93.5% of the light but they give up contrast and color purity in exchange for light throughput which is not usually desirable.
There are many reasons why the transmissive color filter LCOS light throughput is so poor. To begin with, the color filters themselves which are going to block more than 2/3rds of the light (blocking the other 3 primary colors plus other losses). Because it is transmissive, the circuitry and the transistor to control each pixel block the light which becomes significant as the pixel becomes small.
But perhaps the biggest factor (but most complex to understand, I will only touch on it here) is that the electric field for controlling the liquid crystal for a given color dot extent into the neighboring color dots thus causing the colors to bleed together and loose all color saturation/control. To reduce this problem they can use less light throughput efficient liquid crystal materials that are less susceptible to the neighboring electric fields and use black masks (which block light) surrounding the each color dot to hide the area where the colors bleed together.
Field Sequential Color – Small Pixels and 80+% light throughput
With reflective LCOS, all the wires and circuitry are hidden behind the pixel mirror so that non of the transistors and other circuitry block the light. Furthermore the liquid crystal layer is usually less than half as thick which limits the electric field spreading and allows pixels to be closer together without significantly affecting each other. And of course there are no color filters which waste more than 2/3rds of the light. The down side to field sequential color is the color field breakup where when the display move quickly relative to the eye, the colors may not line up for a split second. The color breakup effects can be reduce by going to higher field sequential rates.
Kopin’s pixesl are huge when compared to those of field sequential LCOS devices (from companies such as Himax, Syndiant, Compound Photonics, and Citizen Finetech Miyota) that today can easily have pixels 5 by 5 microns and with some that are smaller than 3 by 3 microns. Therefore FSC LCOS can have about 9 times the pixel resolution for roughly the same size device! And the light throughput of the LCOS devices is typically more than 80% which becomes particularly important for outdoor use.
So while a low resolution Kopin CyberDisplay might be able to produce a low resolution image in a headset as small as Google Glass, they would have to limit the device in the future to a low resolution device – – – not a good long-term plan. I’m guessing that the ability to scale to higher resolutions was at least one reason why Google went with a field sequential color device rather than starting with a transmissive panel that would have at least initially been easier to design with. Another important factor weight in advantage of LCOS over a transmissive panel is the light throughput so that the display is bright enough for outdoor use.
I don’t want to be accused of ignoring Kopin’s 2011 acquisition of Forth Dimension Displays (FDD) which makes a form of LCOS. This is clearly a move by Kopin move into reflective FSC LCOS. It so happens back in 1998 and 1999 I did some cooperative work with CRL Opto (that later became FDD) and they even used I design I worked on for their silicon backplane in their first product. The FSC LCOS that FDD makes is considerably different in both the design of the device and the manufacturing process required for a high volume product.
Through FDDs many years of history (and several name changes) FDD has drifted to a high end specialized display technology with a large 8+ micron pixels. For a low volume niche applications FDD is servicing, there was no need to develop more advance silicon to support a very small device and drive electronics. Other companies aiming more at consumer products (such as Syndiant where I was CTO) have put years of efforts into building “smarter” silicon that enabled minimizing the not only the size of the display; reducing the number of connection wires going between the display and the controller; and reduced the controller to one small ASIC.
Manufacturing Challenge for Kopin
To cost effectively assemble small pixel LCOS devices requires manufacturing equipment and methods that are almost totally different from what Kopin does with their CyberDisplay or FDD with their large pixel LCOS. Almost every step in the process is done with an eye to high volume manufacturing cost. And it is not like a they can just buy the equipment and be up and running, it usually takes over a year to get the yields up to an acceptable level from the time the equipment is installed. Companies such as Himax have reportedly spent around $300M in developing their LCOS devices and I know of multiple other companies having spend over $100M and many years of effort in the past.
For at least the reasons given above, I don’t see Kopin as currently positioned well to build a competitive high volume head mounted displays that are to meet the future needs of the market as I think all roads lead to higher resolution, yet small devices. It would seem to me that they would need a lot time, effort, and money to field a long-term competitive product.