Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!sdd.hp.com!hplabs!hpcc05!hpsciz!peng
From: peng@hpsciz.sc.hp.com (Peng Lee)
Newsgroups: comp.arch
Subject: Re: Optical Interconnect could be rather easy!
Message-ID: <510003@hpsciz.sc.hp.com>
Date: 15 Apr 91 16:03:47 GMT
References: <12618@pt.cs.cmu.edu>
Organization: Hewlett-Packard, Santa Clara, CA
Lines: 44

> / hpsciz:comp.arch / davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) /  5:55 am  Apr 11, 1991 /
> In article <510001@hpsciz.sc.hp.com> peng@hpsciz.sc.hp.com (Peng Lee) writes:
> 
> | 	On chip A, one can use the liquid crystal to modulate the light.  On
> | chip B, one can use the CCD to detect the IR (a very bad idea, someone please
> | point out a different way to do it.).
> 
>   Why would you do this rather than use an IR LED on the sender chip,
> avoiding having to pipe the light through multiple chips? With only a
> few levels of ship there would be a power disipation saving, but with
> the cube you describe later in your posting I would think the loss of
> realestate to windows would be worse than the heat problem.

	Theoretically, since it's the energy level of the wavelength is less
then the energy level of the silicon bandgap.  The silicon dice will not absorb
any of the light energy at all. (At lease that's what I remember from school.)
So, I don't think there will be a heat problem from the laser.  And we're also
talking about micro-watt or (nano-watt) laser in 5x5 micron^2 spot, right?

	Well, I don't understand the fabrication process of IR LED, but what I
do know is that the LC (or some other light modulating materials ) can be
easily fabricated (layered?) on chip.

	The hard part maybe the detector.  People told me CCD is as thick as 25
micron.  A considerable much more processes have to apply to the dice.  With
the promise of Killer-Nano, someone will find a better way to solve the
problem.  One possible solution is putting something (Let me find my Quantum
Mechanic book) in the Si to narrow the bandgap or to create a new or a smaller
bandgap.  If the bandgap is smaller then the energy level of the light, the
light can excite the electrons from the valence(sp?) band to the conducting
band.  And the light will be detected once the electron is on the conducting
band.  Someone with the stronger QM background can verify this to see if it's
theoretically possible.

> 
>   Consider this a question rather than a criticism, I can't even
> ballpark the tradeoffs in my head, so I don't imply in any way you're
> wrong.

	I don't mind it a bit.  There are a lot more people in the net that's
much more qualify than me in this area.  (Hint: My graduate major is CS.)

-Peng
p.s.  I want to get an kill-nano (76 GIPS dragon) inside my watch by 94.