141 lines
5.4 KiB
Plaintext
141 lines
5.4 KiB
Plaintext
From fork-admin@xent.com Wed Oct 2 18:18:54 2002
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To: Digital Bearer Settlement List <dbs@philodox.com>, fork@spamassassin.taint.org
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From: "R. A. Hettinga" <rah@shipwright.com>
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Subject: Re: Optical analog computing?
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Date: Wed, 2 Oct 2002 10:37:02 -0400
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--- begin forwarded text
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Date: Wed, 02 Oct 2002 01:30:24 -0400
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From: "John S. Denker" <jsd@monmouth.com>
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Subject: Re: Optical analog computing?
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Sender: jsd@no.domain.spam
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To: "R. A. Hettinga" <rah@shipwright.com>
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Cc: Digital Bearer Settlement List <dbs@philodox.com>,
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cryptography@wasabisystems.com
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"R. A. Hettinga" wrote:
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...
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> "the first computer to crack enigma was optical"
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> "the first synthetic-aperture-radar processor was optical"
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> "but all these early successes were classified -- 100 to 200 projects,
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> and I probably know of less than half."
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>
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> --> Do these claims compute?! is this really a secret history, or does
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> this mean holography, of am I just completely out of the loop?1
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Gimme a break. This is remarkable for its lack of
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newsworthiness.
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1) Bletchley Park used optical sensors, which were (and
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still are) the best way to read paper tape at high speed.
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You can read about it in the standard accounts, e.g.
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http://www.picotech.com/applications/colossus.html
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2) For decades before that, codebreakers were using optical
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computing in the form of superposed masks to find patterns.
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You can read about it in Kahn.
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3) People have been doing opto-electronic computing for
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decades. There's a lot more to it than just holography.
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I get 14,000 hits from
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http://www.google.com/search?q=optical-computing
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> Optical info is a complex-valued wave (spatial frequency, amplitude and
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> phase)
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It isn't right to make it sound like three numbers (frequency,
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amplitude, and phase); actually there are innumerable
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frequencies, each of which has its own amplitude and phase.
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> lenses, refractions, and interference are the computational operators.
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> (add, copy, multiply, fft, correlation, convolution) of 1D and 2D arrays
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>
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> and, of course, massively parallel by default.
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>
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> and, of course, allows free-space interconnects.
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Some things that are hard with wires are easy with
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light-waves. But most things that are easy with wires
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are hard with light-waves.
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> Here's a commercialized effort from israel: a "space integrating
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> vector-matric multiplier" [ A ] B = [ C ]
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> laser-> 512-gate modulator -> spread over 2D
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> "256 Teraflop equivalent" for one multiply per nanosecond.
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People were doing smaller versions of that in
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the 1980s.
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> Unclassified example: acousto-optic spectrometer, 500 Gflops equivalent
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> (for 12 watts!) doing continuous FFTs. Launched in 1998 on a 2-year
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> mission. Submillimeter wave observatory.
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Not "FFTs". FTs. Fourier Transforms. All you need for
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taking a D=2 Fourier Transform is a lens. It's undergrad
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physics-lab stuff. I get 6,000 hits from:
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http://www.google.com/search?q=fourier-optics
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> Of course, the rest of the talk is about the promise of moving from
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> optoelectronic to all-optical processors (on all-optical nets & with
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> optical encryption, & so on).
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All optical??? No optoelectronics anywhere???
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That's medicinal-grade pure snake oil, USP.
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Photons are well known for not interacting with
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each other. It's hard to do computing without
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interactions.
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--- end forwarded text
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--
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-----------------
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R. A. Hettinga <mailto: rah@ibuc.com>
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The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
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44 Farquhar Street, Boston, MA 02131 USA
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"... however it may deserve respect for its usefulness and antiquity,
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[predicting the end of the world] has not been found agreeable to
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experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
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