Insight Media first reported on the scanning fiber technology developed by the University of Washington (UW, Seattle, WA) in the June 2008 issue of Large Display Report (LDR), with more details in the June 2009 Mobile Display Report (MDR). Now one of the principal inventors of the technology, Brian Schowengerdt, is preparing to spin the technology out of the University into a start-up company. The company, to be called Enravel, currently is in the process of raising capital and has no presence on the Web. While I missed SID this year, and a promised tour of Schowengerdt’s lab, I did have a chance to have a long talk with him on the telephone.

Matt Brennesholtz
Insight Media Analyst

In operation, the fiber is driven in a spiral scan to give a circular pattern on the screen. The red, green and blue lasers are modulated at the pixel rate in order to produce the image at the screen. Currently, the system uses a fixed clock rate, but Schowengerdt discussed the use of a chirped clock rate to accommodate the change in resolution as the fiber scans outward from the center. Early versions of the system had a visible artifact at the center of the spiral scan, but Schowengerdt says this has been eliminated through improved control over the lasers.

Since all conventional video sources are based on rectangular arrays of pixels, the system uses a FPGA to reformat the pixels from the rectangular input video format to the spiral format needed by the scanner.

Schowengerdt says in the past they have used red and blue laser diodes and an argon-ion laser for green. He says current systems are using a red, green and blue laser module supplied by Citizen. While Schowengerdt discussed the Citizen laser module, he added that lasers from other vendors will be usable as well. He said that most available lasers, including green lasers from Corning or Osram, are capable of focusing on a small enough spot to couple efficiently into the 8µm core of the 80µm or 125µm single-mode fibers used in the scanning system. He says currently available lasers are sufficient for the system to produce 10 - 15 lumens when the design is used as a picoprojector. He indicated that larger, multimode fibers may be usable with LED illumination, although this would lead to reduced resolution in the image. He commented that laser illumination, not LED illumination will be the main focus for Enravel.

According to Schowengerdt, VGA resolution and 30Hz frame rate are sufficient for the medical applications the scanned fiber was originally developed for. He sees no barrier to increasing the system performance to 1080p 60Hz operation for use in HD displays and developing this higher resolution system will be a priority at Enravel. Since separate X and Y drive waveforms are used, there is no problem creating an elliptical scan instead of circular one, which would be a better match for 16:9 or other wide video formats. He also said they have experimented with Lissajou scans and other advanced scan designs. In the near term, however, he prefers the spiral scan because it is more forgiving of PZT drive frequency errors.

The scanned fiber was originally developed as a detector, not a display, for use in medical applications. The small diameter (1mm) of the assembly allows it to be used in endoscopic surgery and other procedures where the camera needs to be threaded into small diameter locations in the body such as arteries or veins.

Pentax/Hoya has the license on the technology for these types of medical endoscopic applications where the scanned fiber serves solely as a detector. Enravel has the license on the technology for all display applications, including medical display applications. Enravel also has the license on the technology for detector applications where the detector is closely tied to the display. The main application of coupled display and detector is expected to be in touch-screen applications.

According to Schowengerdt, Enravel expects to focus on the manufacturing of the scanned fiber module itself. Enravel would then sell these modules to OEMs that would incorporate them into end-products such as picoprojectors, HMDs or NTE displays. Initially, they are also likely to make VR NTE displays for the medical community based on the scanned fiber system.

For more details on Enravel, the scanning fiber display and the three SID 2010 papers describing applications of the display, see the expanded version of this article in the upcoming issue of Mobile Display Report.