Now here's a new idea

Heterodyne the light with a laser. (Hint: it's not a new idea.)

George

It is unlikely to work, even if you could sufficiently down-convert the original signal to much lower frequencies. Optical interferometers rely heavily on signal *phase* information, not just amplitude. While such phase info might be converted as well, the necessary precision probably would not be acheived, without sending some reference wave as well. Most lasers loose coherence after a few feet, at best.

Cheers, larry g.

Actually, the real reason why it wouldn't work is because, having down- shifted the light, you'd destroy synchronization by running it through a circuit switched phone system. That's the "new" part that I didn't mention in my OP. Even if you had a tunable delay circuit that self- activated every time you redialed, the signal integrity would completely disintegrate the minute your waveform hit the telco switching machine.

And another headline making idea bites the dust.

USNO built one at Anderson Mesa aobut 6 years ago and it has been in use for several years. Go to their web site for info.

"jdb snipped-for-privacy@yahoo.com" wrote in news: snipped-for-privacy@o13g2000cwo.googlegroups.com:

Was it circuit switched or just a frequency step-down?

I really don't know since I was at USNO in DC and only hear rumors about the Flagstaff operation. Sorry. There was someone I knew out there who occasionally posted on newsgroups, but I've been retired for 4 years now and forget everything about that place. Will look his name up in my empty brain.

Try this:

If someone can repeat the question (I only see replies, not the head article) I can try to answer the question. I am an employee of USNO.

snipped-for-privacy@tantalus.cox.net (Greg Hennessy) wrote in news:d17vv2$in5$1 @tantalus.no-ip.org:

I wanted to build an optical imaging interferometer that worked over a phone line.

Vacuum pipes suggest a laser interferometer, where I wanted to use wires.

Why didn't you?

How were you planning on downconverting the terahertz frequency optical frequencies to a bandwidth a phone line could handle?

Why? What makes you think you would *ever* see any fringes?

BTW A single interferometer pair cannot form an image. So your claimed objective is impossible or an oxymoron. You need a several different baselines and a range of PA angles to stand any chance of forming even a primitive image from interferometer data. Look up aperture synthesis radio telescopes for more information at much easier wavelengths.

State of the art research optical interferometers like COAST use relatively modest path lengths and devious path compensation measures in climate controlled bunkers. I am unsure what the longest optical interferometry baseline to see useful fringes is to date but I would be surprised if it was more than 500m (the longest working optical baseline I know of is 330m at CHARA).

ADS abstracts has some of the technical details online. Try the JPL OLBIN coordinating site for an explanation of what you are up against:

Regards, Martin Brown

"R.Lewis" wrote in news: snipped-for-privacy@individual.net:

I'm already a two or three years behind schedule on my main project, and since I don't have my PhD yet, I'd never be able to get anybody to take me seriously in a grant application. I'm still in the process of thinking it through, to see if it makes sense to try, and I'll give it a priority bump if I can get a paper out of my proto-thesis.

Besides, I'm just a humble mathematician, and I really don't know as much about hardware as I'd like.

snipped-for-privacy@tantalus.cox.net (Greg Hennessy) wrote in news:d1d401$7ns$1 @tantalus.no-ip.org:

I'm not a heterodyne savant, but somebody told me that lasers might do it, although I'm still open to suggestions. Perhaps you could have a staged system, where you step it down once or twice by several dB using different methods. HeNe's would be great, because they're also dirt cheap.

I'm willing to sacrifice bandwidth for twisted pair (or shielded twisted pair) because the heart of the idea is to gain distance (which translates to aperture size) cheaply.

Martin Brown wrote in news:d1e4mt$tfj $ snipped-for-privacy@news8.svr.pol.co.uk:

Twisted pair is radially symmetrical. If that's too demanding, I can relax the constraints to shielded-twisted pair or coax. However, I'm following this idea on someone else's word that fiber optic can do it. Was that guy telling me the truth?

If each baseline is cheap enough, you can afford to install several detectors.

I'm gambling that by the time I finish this, an enabling technology for phase preserving delay lines will emerge. Hopefully somebody smart is working on that, but if they're not, then I have yet another hard problem to work on.

Climate controlled signal pipes don't seem like too much of a reach.

Let me know if you can find any hard numbers about this. For proof of concept, we just need to match the state of the art.

I guess my homework this weekend is to read up on ADS, OLBIN, COAST and aperture synthesis.

John Schutkeker wrote in news:Xns961CB0F05C55Bjohnschutkeker@151.164.30.48:

These guys just have beam conduits.

You apparently missed my point, which is no one knows how to downconvert an optical frequency to something lower.

Radio interferometers such as the VLA have detectors that make use of the wave nature of the radiation, so they mix with with a local oscillator, convert to voltages, and then combine the signals in a correlator.

Optical interferometers have vaccuum delay lines, mix the light beams physically, and then have APD or CCD detectors to measure the fringes.

The reason I asked you how you were planning on downconverting the signal was a hint that the technology of doing what you asked for doesn't exist.

What is the bandwidth you think you can get out of twisted pair? If you express that as a fraction bandwidth of an optical signal (a few hundred terahertz) what sort of fractional bandwidths are you seeing? If too low you'd need the Keck telescope to measure Sirius.

I hope you aren't putting much money on that bet.