From: Christopher Fry <70353.3056@CompuServe.COM>
Subject: Re: Integrated laser arrays for Eyephones
Date: 30 Oct 91 22:08:43 EST



>It seems likely to me that the lasers would be run in some sort of
>pulsed mode anyhow, 

Good, this could save lots of power over continuous lasers.
>either by scanning in both horizontal and vertical
>as is done in CRT's, or maybe a whole line at a time.

The beauty of the fixed array is no moving parts and the whole thing made by 
VLSI technology. How to you make a laser scan with those constraints?

>Scanning means
>that the frame buffer storage cells don't have to be right next to the
>lasers, so you don't have to run all the random access circuitry right
>up to the lasers.  

I'm thinking just a little ahead where putting a few ram cells under each 
laser would be, fabrication-wise, easy, and oh so conveinient. That means the 
OUTPUT of the RAM is in parallel. ie right out to the laser. We wouldn't need 
any lines to carry the output of a ram cell though the ram matrix. 
The shift-register that you described is indeed a neat trick, but remember, 
for decent resolution eyephones we've got a LOT more pixels than any display 
yet made. And besides, you still have to have the frame buffer somewhere so 
you're not saving hardware in total. 

Including the RAM on the chip will increase the reliability problems,
but probably not more so than a moving part scanner.

>Well, in the not too long-term, LCD displays will be chips too (or at
>least the substrates will be).  Active-matrix LCD displays are essentially
>hybrid IC's with a transistor per pixel; making the substrates monolithic
>IC's ought to cut the cost drastically after the technology gets pushed
>through the learning curve.

Hope you're right. I believe in parallel development. Good LCD displays have 
been "just around the corner" for so long that I've lost faith. Laser arrays 
are the new kid on the block.

In a discussion with Mike Titel at VPL last night, he indicated that one way 
around the too-long wavelength of microlasers may be to coat the surface of 
them with a phosphor. This get's rid of their "laser" quality [good and bad] 
and essentially translates the laser power output into the visible spectrum.
I don't know much about how excitation of phosphor with lasers works, but it 
may also have the capability to get a white light output instead of 
monochromatic.  With a fine-screen and a phosphor deposition technique, you 
could probably put down a pattern of red, green and blue phosphors similar to 
how CRT's do it. One big advantage for the microlasers would be that you don't
have to have the shadow-mask.