Unfair comparison; Earlier research revealed 'liquid light'...

Unfair comparison

The comment in "Falling prices push manufacturers to join forces" that EDFAs will see 90% price reductions is very misleading (Market Watch, August, p. 69).

It is certainly true that most commercial EDFAs cost at least $16,000. However, these are fairly high-end devices primarily aimed at long-haul markets. Further, the $1500 price you projected for EDFAs in 2003 is for a very different component, a bare-bones EDFA for the highly cost-sensitive metro market.

The point is that the $1500 EDFA does not provide the same level of performance (power, gain, gain flatness, and so on) as a $16,000 EDFA, and the direct cost comparison is unfair.

David Rockwell
Director, Advanced Technology
fSONA Communications
[email protected]

Earlier research revealed 'liquid light'

Concerning "Laser beam condensed state resembles liquid" (September, p. 17), I would like to mention that we investigated mathematically as well experimentally the relationship of laser light and liquids in much detail in the 1990s. The number of publications from my group in which the similarities between lasers and liquids were theoretically predicted and subsequently demonstrated experimentally exceeds 30, beginning in the early 1990s and continuing to date.

All the things mentioned in the article such as vortices in light, vortex street behind an obstacle, droplets, and much more (such as pair creation of vortices relating optics further to elementary particle physics, and phase transition or "melting" of vortex crystals) have been demonstrated experimentally by us. I discussed the possibility of using a laser-light fluid to model black-hole physics with astrophysicists back in 1991.

Our work was published mostly in Physical Review Letters or Physical Review A, not in obscure journals. We have also written a number of reviews about this subject, one of which appeared as an invited paper in Applied Physics1 in 1999 and is accompanied by and references videos to be found as Supplementary Electronic Material at: http://link.springer.de/journals/apb. These videos vividly demonstrate in model calculations and in real experiments all the phenomena "predicted" in the Laser Focus World cover story and with a much deeper understanding of even more interesting possible phenomena.

The similarities between laser fields and fluids occur basically because resonator optics (or other coherent optics) has at its core a nonlinear Schroedinger equation, (and with that a linear Schroedinger equation). With respect to the latter, it has been known since 1926 (Madelung) that it relates very closely to Navier Stokes equations as used in fluid dynamics. Of course, the high intensities given in the September article as necessary for the experimental observations are not at all necessary. We have done all experimental demonstrations with milliwatt-level continuous lasers using the proper nonlinear materials.

In conclusion, I hope I can be forgiven for raising my voice here and pointing to our own work. I believe our work, starting almost 10 years ago, vastly exceeds the "predictions" in the article. I realize of course that one can be "too early" in research with a subject. That is, at the time when one produces the research results the research community is still interested in older subjects. I have experienced this phenomenon in my research so frequently that I have devised for myself a strategy: Once the scientific public finally develops interest in the subject previously researched in my own work, I resume publishing in this field and I cite our previous work so that it does not get forgotten. It is for this latter purpose that I write here—to draw attention to our results from the last decade. I would hope as a possible byproduct that you might become interested in these or previous results so that we might report more, and more interesting, results.

C. O. Weiss
Braunschweig, Germany
[email protected]


Appl. Phys. B 68, 151 (1999).


In "Optical-fiber sensor measures relative humidity" (October, p. 13) the contact information was incorrect. The correct e-mail address for Pascal Kronenberg is [email protected]

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