From: Jian Zheng ([email protected])
Date: Tue Nov 02 1999 - 11:11:17 PST
Hi all:
Regarding the question 1, I would like to make a comment:
Generating high frequency resonance is not a problem. People can even create
X-ray which is much higher in frequency than the visible light. The problem
is more on how we can deliver it. For signals below couple hundred GHz, we
can use PCB or GaAs circuits to build the transmission lines to deliver the
power. For light signals, we use optical fibers or other types of optical
waveguides to deliver it. The requirement for the waveguides or transmission
lines is that its cross-section must be much smaller than the wavelength. If
the cross-section is not much smaller than the wavelength, it will create
radiation and high order modes (with dispersion). That is the reason why, in
my last e-mail, I mentioned about the limitation from substrate thickness in
GaAs. This limitation is not on the generation of the high frequency
signals. It is more on the transmission of the high frequency signals.
Thanks!
Best regards,
----------------------------------------------------------------------------
------------
Jian-X. Zheng, Ph.D
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Balaji
> Lakshminarayanan
> Sent: Tuesday, November 02, 1999 6:22 AM
> To: [email protected]
> Subject: RE: [SI-LIST] : Interesting theoretical questions
>
>
>
> Hi,
>
> I would like to give a different answer to 1 and 3.
>
> 1. I partially agree that the frequeny is limited by substrate thickness.
> But there are published papers in MTT and other journals that talks about
> generating frequency upto several hundred tera hertz using GaAs or InP
> devices. The frequency is limited predominantly by the size of the device
> (gate) than the substrate thickness.
>
> 3. An asynchronous machine has been developed at MIT which is called the
> Data Flow Machine (i think proposed by Arvind). The instructions such as
> addition or subtraction is triggered only when the signal arrives and it
> is not operational otherwise. The effenciency of the machine is very low
> and people are researching on improving the effenciency and
> commercializing
> it.
>
> Thanks
>
> --Bala
>
>
> On Mon, 1 Nov 1999, Jian Zheng wrote:
>
> > Following are my answers to the questions (check keyword ANSWER in the
> > following attached context):
> >
> >
> ------------------------------------------------------------------
> ----------
> > ------------
> > Jian-X. Zheng, Ph.D
> > Zeland Software, Inc., 39676 Mission Blvd., Fremont, CA 94539, U.S.A.
> > Tel: 510-797-8109, Fax: 510-797-8241, Web: http://www.zeland.com
> >
> ------------------------------------------------------------------
> ----------
> > ------------
> > Special Announcement: (1) We will be offering a training class
> on using the
> > IE3D/FIDELITY on December 2 and 3 of 1999. Please check our web site for
> > more information. (2) IE3D 6.0 is released. The IE3D 6.0 will be about
> > 50-300% faster than the IE3D 5.X. If you have the ZELAND.EXE
> 5.2, you will
> > be able to use the IE3D 6.0. (3) IE3D 7.0 beta should be released before
> > December 1999. It is a big step from IE3D 6.0 according to its
> optimization
> > capability. It has the implementation of symbolic optimization goals. It
> > also features integrated IE3D+CURVIEW+PATTERNVIEW for automated pattern
> > calculation and pattern optimization. Interested IE3D users can
> request the
> > IE3D 7.0B for a try after it is released.
> > > -----Original Message-----
> > > From: [email protected]
> > > [mailto:[email protected]]On Behalf Of subas
> > > Sent: Monday, November 01, 1999 4:24 PM
> > > To: '[email protected]'
> > > Subject: [SI-LIST] : Interesting theoretical questions
> > >
> > >
> > > Hi all,
> > >
> > > I have some theoretical questions regarding high frequency signals:
> > >
> > > 1) What is the maximum frequency you can generate
> electronically by our
> > > current technology (GaAs???)? Can we have an oscillator that
> can oscillate
> > > in the frequency of the visible light, for example?
> >
> > ANSWER: For planar circuits (PCB or millimeter wave IC), from
> what I know,
> > people can produce circuits as high as 100-400 GHz. It is not
> easy to go to
> > much higher. The reason for it is that the frequency is limited by the
> > substrate thickness for the GaAs circuits. Some people may be using
> > substrate as thin as 25 microns. For 25 micron thick substrate,
> the maximum
> > frequency you can go is about 300 GHz. When the substrate gets thin, the
> > GaAs circuits become fragile and it is very hard to process.
> The 2nd problem
> > involved is the high metallic loss.
> >
> > To go to higher frequency, people have to use optical waveguide such as
> > optical fibers.
> >
> > >
> > > 2) The way light gets reflected from a metal (silver in a mirror)
> > > is that it
> > > first induces current (as a receiving antenna) and again
> radiates (as a
> > > transmitting antenna) the EM wave instantly so that we get
> the impression
> > > that the light is being reflected by the metal surface. Then how come
> > > different metals can have different colors (gold - yellow)
> when we expect
> > > them all to reflect light of all colors?
> >
> > ANSWER: At low frequency (compared to the frequency of light),
> plane waves
> > hits the metal and will get total reflection from the metal. At high
> > frequency, it is not true. How big a reflection is depends upon
> the complex
> > permittivity (EPS):
> >
> > EPS = EPSr - j SIGMA / ( OMEGA * EPS0 )
> >
> > EPSr is the relative permittivity of the material. SIGMA is the
> conductivity
> > of the material. OMEGA is the angular frequency. EPS0 is the
> permittivity in
> > free space: (8.86e-12).
> >
> > Typical copper's EPSr is about 1 and SIGMA = 5.8e7 s/m. At 1
> MHz, we have,
> >
> > EPS = 1 - j 5.8e7 / ( 2.0 * 3.14159 * 1.0e6 * 8.86e-12 )=1-j1.042e+12
> >
> > The refraction coefficient N is:
> >
> > N = SQRT(EPS) = 7.2e+5 - j 7.2e+5
> >
> > When light hit the copper, the reflection coefficient is:
> >
> > (1-N)/(1+N)and it is almost -1.
> >
> > At light frequency, the wavelength is about 7.0e-6 m. The
> frequency should
> > be 4.0e+5 GHz (or 4.0e+14 Hz). Assuming the EPSr and SIGMA do
> not change, we
> > still have,
> >
> > EPS = 1 - j 5.8e+7 / ( 2.0 * 3.14159 * 4.0e+14 * 8.86e-12) = 1-j2600.
> >
> > N = SQRT(EPS) = 36 - j 36.
> >
> > The reflection coefficient is still high. However, it is quite different
> > from -1. With increased frequency, normally the SIGMA should
> decrease. The
> > reflection from metal should be significantly lower than the total
> > reflection, and it will differ with different frequencies. I
> think that is
> > the reason why we will have differnt colors, at least from the
> > electromagnetic point of view.
> >
> > >
> > > 3) Has there been any computer made without any clocks
> (asynchronous)? How
> > > fast is this computer?
> >
> > ANSWER: I have no idea about it. However, it seems to me it is
> impossible.
> > For a computer without a clock, it has to be analog. When I was
> in school, I
> > learnt that there were analog computers. However, you can not
> guarantee the
> > accuracy because analog signals are affected by noise. In order
> to guarantee
> > the accuracy, we have to digitize the signals. When we digitize it, we
> > should need the clocks for synchronization.
> >
> > >
> > > 4) Why is optical computing getting no where? Is this because
> lasers are
> > > expensive? Or because of the lack of fast optical switch
> any non-linear
> > > optical device)?
> >
> > ANSWER: I think it is more of the minimization and integration
> of optical
> > switch.
> >
> > >
> > > Thank you very much.
> > >
> > > Subas
> > >
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> >
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