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Wednesday, January 6, 2010 - 6:18amSanction this postReply
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My favorite character in Atlas Shrugged is John Galt. One of the crucial traits of this character is his extraordinary technical ability. I can adore a fictional character, and part of the reason I adore this one is his possession of that trait.

Adoration is one thing, admiration is another. Galt’s technical genius is admirable only in the derivative sense that I would admire that trait in a real person. I cannot admire a fictional character. I can admire the character’s creator as creator, but not the character.

Fortunately, there are in our time many individuals whose mathematical and scientific accomplishments are at the high level of the fictional character John Galt. They are not well known to the general public. I want to tell you about one such man.

Eli Yablonovitch invented the concept of a photonic band gap. He arrived at this concept in 1987 while doing research on making telecommunication lasers more efficient. Another physicist Sajeev John arrived at the concept independently that same year. John came to the concept in the course of pure research attempting to create light localization.

Four years later, Yablonovitch was the first to create a successful photonic band-gap crystal. He used a variant of the crystal structure of diamond, a variant now called yablonovite. The structure was formed by drilling three intersecting arrays of holes, 400 nanometers in diameter, into a block of ceramic material. This structure, at this scale, was able to eliminate the propagation of electromagnetic radiation in the microwave range. Photonic band-gap crystals are yielding a new generation of optical fibers capable of carrying much more information, and they are contributing to the realization of nanoscopic lasers and photonic integrated circuits.

The name photonic crystalsounds like a crystal made of light. That is incorrect. A photonic crystal is an artificial crystal (or quasicrystal) made usually of solids such as dielectrics or semiconductors. The electrical properties of a semiconductor are intermediate between a dielectric (an insulator) and a conductor.

In a dielectric material, the valence electrons of the atoms are tightly bound to them. They are confined to energy levels within the band of levels called the valence band. Above that band of levels is a broad band of energies inaccessible to the electrons under the laws of quantum mechanics. That forbidden band is called the band gap. Above the band gap is a band in which electrons could move freely in the material if only enough energy were applied to them to raise them to that band of energy levels. This band is called the conduction band.

In a semiconductor, the valence electrons are less tightly bound to atoms than they are in a dielectric. The band gap is smaller. A smaller boost of energy is needed to induce the flow of electrons, a current. The degree of electrical conductivity of a semiconductor can be precisely controlled by doping one semiconductor chemical element with small amounts of another.

When an electron is promoted across the band gap, an effective positive charge called a hole is created in the valence levels below the gap. The holes, like the electrons, can be entrained into currents. By controlling the supply of electrons and holes above and below the band gap, carefully designed semiconductors are able to perform electronic switching, modulating, and logic functions. They can also be contrived to serve as media for photo detectors, solid-state lasers, light-emitting diodes, thermistors, and solar cells.

The properties of an electronic band gap depend on the type of atoms and their crystal structure in the solid semiconductor. To comprehend and manipulate the electronic properties of matter, electrons and their alterations must be treated not only in their character as particles, but in their character as quantum-mechanical waves. The interatomic spacing of the atoms in matter is right for wave-interference effects among electrons. This circumstance yields the electronic band gaps in semiconductors as well as the conductive ability of conductors.

A photonic band gap is a range of energies of electromagnetic waves for which their propagation through the crystal is forbidden in every direction. The interatomic spacing in semiconductors are on the order of a few tenths of a nanometer, and that is too small for effecting photonic band gaps in the visible, infrared, microwave, or radio ranges of the spectrum. Creation of photonic band gaps for these very useful wavelengths requires spatial organizations in matter at scales on the order of a few hundred nanometers and above.

In the 70’s and 80’s, researchers had been forming, in semiconductors, structures called superlattices. These were periodic variations in semiconductor composition in which repetitions were at scales a few times larger than the repetitions in the atomic lattice. The variations could consist of alternating layers of two types of semiconductors or in cyclic variations in the amount of selected impurities in a single type of semiconductor. These artificial lattices allowed designers, guided by the quantum theory of solids, to create new types of electronic band gaps and new opticoelectronic properties in semiconductors.

Photonic crystals are superlattices in which the repeating variation is a variation in the refractive index of the medium. It is by refractions and internal partial reflections that photonic band gaps are created. The array of holes that Yablonovitch and his associates drilled for the first photonic crystal formed a superlattice of air in the surrounding dielectric solid. Additional workable forms of photonic-crystal superlattice have been demonstrated since that first one. Costas Soukoulis and colleagues created a crystal of crisscrossed rods, and it has yielded photonic band gaps in the infrared part of the spectrum. Photonic crystals have been created mostly in dielectric or semiconductor media, but Shawn Yu Lin and associates have created them in tungsten. These may prove useful in telecommunications and in the conversion of infrared radiation into electricity.

In 2001 Eli Yablonovitch co-founded the company Luxtera, which is now a leading commercial developer of silicon photonic products.

Photonic crystals, manipulators of light, they are alive. They are alive “because they are the physical shape of the action of a living power—of the mind that had been able to grasp the whole of this complexity, to set its purpose, to give it form.” –AR 1957


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Wednesday, January 6, 2010 - 6:19amSanction this postReply
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References

Scientific American
1983 (Nov) “Solid-State Superlattices” –G.H. Dohler
1984 (Aug) “Quasicrystals” –D.R. Nelson
1986 (Oct) “Photonic Materials” –J.M. Rowell
1991 (Nov) “Microlasers” –J.L. Jewell, J.P. Harbison, and A. Scherer
1998 (Mar) “Nanolasers” –P.L. Gourley
2001 (Dec) “Photonic Crystals: Semiconductors of Light” –E. Yablonovitch
2007 (Feb) “Making Silicon Lase” –B. Jalali

Science News
1991 (Nov 2) “Drilling Holes to Keep Photons in the Dark” –I. Peterson
1993 (Sep 25) “A Novel Architecture for Excluding Photons” –I. Peterson
1996 (Nov 16) “Light Gets the Bends in a Photonic Crystal” –C. Wu
1998 (Oct 24) “Crystal Bends Light Hard, Saves Space” –P. Weiss
2003 (Oct 4) “Hot Crystal” –P. Weiss
2005 (Nov 5) “Light Pedaling” –P. Weiss

Nature Photonics
2007 (1:91–92) “Bandgap Engineering: Quasicrystals Enter Third Dimension” –C.T. Chan

Fundamental Papers – Physical Review Letters
1987 (May 18) “Inhibited Spontaneous Emission in Solid-State Physics and Electronics”
–E. Yablonovitch
1987 (Jun 8) “Strong Localization of Photons in Certain Disordered Dielectric Superlattices” –S. John
1989 (Oct 30) “Photonic Band Structure: The Face-Centered-Cubic Case” –E. Yablonovitch and T.M. Gmitter
1990 (Nov 19) “Full Vector Wave Calculation of Photonic Band Structures in Face-Centered-Cubic Dielectric Media” –K.M. Leung and Y.F. Liu
1990 (Nov 19) “Electromagnetic Wave Propagation in Periodic Structures: Bloch Wave Solution of Maxwell’s Equations” –Z. Zhang and S. Satpathy
1990 (Dec 17) “Existence of a Photonic Gap in Periodic Dielectric Structures” –K.M. Ho, C.T. Chan, and C.M. Soukoulis
1991 (Oct 21) “Photonic Band Structure: The Face-Centered-Cubic Case Employing Non-Spherical Atoms” –E. Yablonovitch, T.J. Gmitter, and K.M. Leung


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Wednesday, January 6, 2010 - 8:50pmSanction this postReply
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Bravo, Stephen! That was fascinating, lucid, and informative, elements that are hard to find all at once in science writing anywhere. I'd heard of, but had never yet understood, this core concept of the semiconductors that we rely upon every day.

I am inexorably reminded — yet again — of a talk of yours I attended in person nearly thirty years ago in Chicago, to about a dozen of us from Northwestern and the general community, on "Quantum Mechanics and the Objectivist Metaphysics." That set off long-enduring sparks in my brain, as this encomium of yours to a subtle piece of brilliance is doing now.

We can appreciate superlative achievements in communication, as well, methinks. And we should. They're pretty rare these days.

§ § §

... Especially in O-Land. {sigh}

I made a mistake in staying away from this venue for several months. Two of the Other Sites are engaged in yet another escalating, corrosive, internecine war. Which overblown habit has burned out Objectivist-types for over forty years, off and on.

(Mostly off, with the emphasis on how it smells up those joints enough to drive discussants away.)

I'm tired of hysterical condemnation, blithe condescension, and unsupported character slurs. Readers can attribute those elements to Other Sites as they wish. Plenty of shortcomings are being spread around.

I'm not going to bother doing that. I'll just go back to reading and posting here. And thanks to those readers who are indulging me in this digression ... one that, today, I only wanted to append to my finding and praising something genuinely inspiring.

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Thursday, January 7, 2010 - 6:03amSanction this postReply
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Steve, I just gotta tell you this. This morning I finally read an article you posted a couple of months ago at Objectivist Living. I liked it and added a comment on it. Then I clicked on this site and found this remark!

Thank you for being you.

—Stephen

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Thursday, January 7, 2010 - 6:46amSanction this postReply
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http://en.wikipedia.org/wiki/Valence_band
http://en.wikipedia.org/wiki/Photonic_crystal
http://en.wikipedia.org/wiki/Semiconductor

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Thursday, January 7, 2010 - 8:54amSanction this postReply
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Thanks, Merlin.

Further Developments

Photonic Crystal Fiber

Blazar

Photonic Crystals Improve LED Efficiency

Photonic Crystals Enable Ultrabright LEDs

Bright White

Tracking Light in Photonic Crystals

Slow Light in Photonic Crystals

Photonic Crystal Nanolasers: A, B

General Relativity and Photonic Crystals
Photonic crystal fibers are at work in laboratory tests for predicted phenomena of general relativity and quantum field theory taken together.
Science 319 – Fiber Optical Analogue of the Event Horizon
Abstract - “The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We use ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect, the blue-shifting of light at a white-hole horizon. We also show by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.”
Appendix – Wider Explanation / See also this sector of Ulf Leonhardt’s homepage.

Starlight
Photonic Crystal Fibers for the Kilo-Aperture Optical Spectrograph for the Gemini Observatory

Astrophotonics: A New Era for Astronomical Instruments


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Tuesday, June 22, 2010 - 4:40amSanction this postReply
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Other Advances in Photonics-Electronics

Better Living through Plasmonics
Science News 11/7/09

Plasmonic Solar Cells – Introduction * – Further * / #

Plasmonic Waveguides – Introduction * – Further *

Spaser

~~~~~~~~~~~~~~~~

Laser at 50

Townes at 94


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Tuesday, June 22, 2010 - 7:43amSanction this postReply
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Thanks, Stephen.  It is always nice to read about new inventions.  While I understood all of the words, I grasped few of the salient points. 
The structure was formed by drilling three intersecting arrays of holes, 400 nanometers in diameter, into a block of ceramic material. This structure, at this scale, was able to eliminate the propagation of electromagnetic radiation in the microwave range. Photonic band-gap crystals are yielding a new generation of optical fibers capable of carrying much more information, and they are contributing to the realization of nanoscopic lasers and photonic integrated circuits.
I understand what a gap is.  I have the basics down pretty good -- resistor, capactior; inductor; Ohm, Kirschoff; pnp, npn; about up to there --  how a inductor works as a choke (filter) and so on.  But I have a problem conceptualizing the bridge between:

a) "... eliminate the propagation of electromagnetic radiation..."
and
b) "... optical fibers capable of carrying much more information ..."

My ignorance does not stop there.  You mention "... wave-interference effects among electrons."  Now, I can understand that with voice or instrument or most other macro-level events what we call "wavelength" or "frequency" is something of an idealization as maybe the oboeist can generate a nice 440 cps but the wood tube, the box of the violins, the bells of the horns,... it's all very messy...  But electrons, I thought, were quantum events of discrete wavelengths and no others.  Red is red, not red with splashes of UV.  So, what is this "wave interference"?  Don't they have the orbits they do because of the energies of their frequencies.  I understand the gaps -- the voids or fields -- wherein electrons are not, but not is not.  How do they interfere in a region where existence is impossible? 

You see my limitations and I apologiize for my ignorance.  I am more comfortable with Benjamin Franklin's paradigm, which seems to have endured these past 250 years when you wrote about "holes" of "positive charge" another concept that I know from elementary electronics.  I just finished Kuhn's classic on paradigms, so this jumped out at me.  He says that old paradigms continue, as our surveyors still lay lines in an Earth centered universe.


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Tuesday, June 22, 2010 - 12:07pmSanction this postReply
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Michael, you may really have known of this part too, but maybe this refresher will help with one of your questions. Your other question will require a little review on my part.

In 1923 Louis de Broglie put forth the conjecture (strongly indicated by pulling together a couple of special-relativity relations) that it is not only light that has both a particle mode of existence and a wave mode of existence. Rather, massive particles such as electrons also have a wave mode. The wave length of an electron, whether moving freely in space or moving in a medium such as a solid lattice of atoms, would be inversely proportional to its momentum. So it could reach various wave lengths as its momentum were varied. In their wave mode, multiple moving massive entities could interfere with each other. *



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Wednesday, June 23, 2010 - 4:02amSanction this postReply
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Right, I "knew" that.  One of my favorite examples from a freshman physics course was to calculate the wavelength of a baseball, a pitch going 90 mph.  So, an electron can really have "any" wavelength, depending on its velocity. 

But a photon can also have "any" wavelength.  The speed of light is not constant, but dependent upon the medium.  The speed of light in water, air, etc., is not the same as in a "vacuum" whatever a "vacuum" might really be after all...  So that raises a metaphysical problem about the "ether" which does not exist... or does... or does not... or does...

Myself, I built crystal radios when I mentored scouts for a hands-on museum.  So, by extension, I can accept the value of any workable instrument from a sloiw-scan CRT to a PET scan -- positrons are real; what would Ben Franklin say? -- but this theory stuff is all a-jumble.  I suspect that the universe is a complicated place.

Thanks for the help.

You never fail to impress me.  I know what life is like for myself and I often wonder why really smart people like you don't explode or implode or something living on the Planet of the Apes.  Ever meet Durk Pearson? 


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Friday, July 16, 2010 - 8:14amSanction this postReply
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I think we have entered into a world that has begun to denounce the individualist benefit of the "self-made man," with regard to post-secondary education. I would never say that there is anything wrong with the attainment of a college degree; however, I would say that there is something wrong with a society in which the evaluation of one's intellectual value in any official sense is directly related to the level of degree they have attained. It seems to me that the social structure of society is regulating intelligence and offering certificates of recognized intellectual value.

The system of modern American education is such that it reflects very naturally the hierarchical system of an industrial assembly line, such that education is spitting out in mass quantities, not a society of free-thinking, intelligent, individualistic people who have learned how to study and learn, but rather an assembly-line of educated machines, people who have all learned within a vague, unacknowledged, uniform code thee same lessons from the same books.

Teachers and professors are fallible. It is a creed widely accepted in society that if a person gains a certificate in a particular subject matter, they are fit to relay the knowledge of the subject to the best of their understanding; thus, what they teach about the subject must, by corollary, be correct. This belief creates a system in which the greatest students are not the intellectual innovators, but rather the students who best reflect the contentions of their teacher like a mindless mirror. The reflection is conceded to represent their understanding of the subject that the teacher is certified to teach, and must therefor have a full understanding of.

In such a system, it is made increasingly difficult for any individual to advance the knowledge of a subject. It is my belief that the purpose of education is not to impart knowledge in a specific sense, but rather to teach individuals how to think! To teach individuals the values of seeking knowledge, and to set them to task in acquiring it on their own terms, to point them towards works of literature and impart good study practices, without having any strict universal set of factual awareness being the sole basis by which the government can test and certify [or not] a learned individual with official recognition of intelligence.

Furthermore, intelligence is not defined as what an individual knows, but rather the extent of their ability to quickly [or not] retain and apply new knowledge that comes to them. Therefor, though a teacher is certified in their attainment of facts with regard to a subject matter, it becomes difficult for a teacher to teach a student who has more raw intelligence than them. This student would only lack the practical application, the exposure. Once the teacher gave them the raw facts, they would quickly assume a higher understanding of its universal applications and deductive implications than the one who is [officially speaking] certified to know the most about it.

The social creed of education is such that, in order for a brilliant student to achieve in any official, recognized sense, he most only advance to the level of those teaching him, and must always remain within the scope of the specific matter they teach; never beyond. And they must learn facts instead of learning to individually seek intellectual growth. It is a system of the creation of fact machines with a cap on achievement. This seems dangerous to me.

I have lost count in my life of the number of times people have told me, "Son, you think too much." It is not what I know that people take issue with, but rather the act of continual assessment of the applications of what I know. How does one "think too much," and what does it mean about a society where it is generally accepted that such a thing is possible?

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Thursday, February 11, 2016 - 1:58amSanction this postReply
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Sixty years ago, 14 February 1956: 

 

Beckman, Shockley, and the Birth of Silicon Valley



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Thursday, June 30, 2016 - 5:53amSanction this postReply
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David Spergel: Find Things in which You Have an Unfair Advantage



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Monday, July 18, 2016 - 3:07amSanction this postReply
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A Glory of Diligence and Solitude



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Thursday, August 25, 2016 - 4:31pmSanction this postReply
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Nash optimization -- "David Spergel: Find Things in which You Have an Unfair Advantage"



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Thursday, March 16 - 3:13amSanction this postReply
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Incandescence plus photonic crystals yields new light bulbs: MIT & Purdue



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Sunday, March 19 - 1:59amSanction this postReply
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Who are the superlative achievers in transhumanism? This is virtually the only science field worth studying.



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Thursday, March 30 - 3:12amSanction this postReply
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I admire the researchers advancing any science, including this one touching your interest Kyrel: Geoff Hinton.



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Thursday, April 6 - 4:18amSanction this postReply
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Thanks, Stephen. One aspect of that for me is that prognostication fails to predict the unpredictable. I am sure that software will get smarter, but I am just as sure that the real changes will be revealed in surprising ways.  Right now, I am reading Men, Machines, and Modern Times by Elting Morison from 1968.  I could also point to another classic, John Kemeny's Man and the Computer (1972).  They did not see the iPhone coming and how we use them to monitor our exercise routines, listen to music and lectures, play games, share with our many "friends" instant snapshots of ourselves,  ...  I do not do any of that.  For me, my iPhone is the compass and level that I use to align my telescope. It is also the interactive map that speaks driving directions to me.  (Kemeny actually addressed traffic control, but he considered it only from the viewpoint of the transportation engineers of the local government -- and they do, indeed, use computers to improve traffic; but that is not perhaps the salient fact.

 

What I see coming - the error of prognostician being noted - is that we will incorporate "computers" into our brains. That eventually may mean "programming" our brains with knowledge. Along the way, we may wear "thinking caps."  I have a co-worker whose hearing aid is bluetoothed to his phone. It is a step on a long path. But, again, I am pretty sure that we do not know where that path leads, happy as I am to be on it...



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