ultra-wideband FM
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From: Robert Baer on 14 Jul 2010 04:26 John Larkin wrote: > > Hi, > > One of the nasty things about cheap fiber-coupled lasers is that they > have terrible amplitude stability and linearity, full of mode jumps > and such. Given that, sending a signal over a fiberoptic link using > amplitude modulation is usually done with a stable CW laser feeding a > lithium-niobate modulator. The modulator itself is nonlinear and > expensive and a nuisance to drive and bias. > > Digitizing and sending samples is OK, up to a point. It gets messy at > some point from a sheer speed standpoint. > > So the idea of using FM pops up. If my baseband analog signal were, > say, DC to 150 MHz, and I picked the highest carrier center frequency > that's reasonably easy to work with, say 1 GHz, it could maybe be > done. The laser driver and receiver aren't too difficult. The issues > are the modulator, the demodulator, and the pure signal theory > necessary to turn the time-domain behavior of the link into classic > measures like s/n and distortion of the recovered baseband signal. > Asymmetrically bandlimiting an FM signal is computationally messy. > > I'd expect that commercial VCOs wouldn't have anything like this sort > of fractional modulation bandwidth. And if they did, a varicap > modulating an LC oscillator would probably distort like mad. (Faint > echoes of the capacitor charge debate?) The modulator may have to be > some EclipsLite version of a 555 on steroids. Or a multi-GHz VCO > heterodyned down. Yuk: sounds like RF. > > On the theory side, does anyone know of (or have?) one of the high-end > math tools that could do a quantitative signal-quality analysis of > such a link, given, say, approximate experimental data on the > time-domain behavior of the laser link? Hiring a consultant to do this > would be a desirable alternate to getting and learning this stuff > ourselves. > > Any thoughts? > > John > > How about being "crazy" and FM the laser?
From: o pere o on 14 Jul 2010 05:34 John Larkin wrote: > > Hi, > > One of the nasty things about cheap fiber-coupled lasers is that they > have terrible amplitude stability and linearity, full of mode jumps > and such. Given that, sending a signal over a fiberoptic link using > amplitude modulation is usually done with a stable CW laser feeding a > lithium-niobate modulator. The modulator itself is nonlinear and > expensive and a nuisance to drive and bias. > > Digitizing and sending samples is OK, up to a point. It gets messy at > some point from a sheer speed standpoint. > > So the idea of using FM pops up. If my baseband analog signal were, > say, DC to 150 MHz, and I picked the highest carrier center frequency > that's reasonably easy to work with, say 1 GHz, it could maybe be > done. The laser driver and receiver aren't too difficult. The issues > are the modulator, the demodulator, and the pure signal theory > necessary to turn the time-domain behavior of the link into classic > measures like s/n and distortion of the recovered baseband signal. > Asymmetrically bandlimiting an FM signal is computationally messy. > > I'd expect that commercial VCOs wouldn't have anything like this sort > of fractional modulation bandwidth. And if they did, a varicap > modulating an LC oscillator would probably distort like mad. (Faint > echoes of the capacitor charge debate?) The modulator may have to be > some EclipsLite version of a 555 on steroids. Or a multi-GHz VCO > heterodyned down. Yuk: sounds like RF. I guess this will not be trivial! > On the theory side, does anyone know of (or have?) one of the high-end > math tools that could do a quantitative signal-quality analysis of > such a link, given, say, approximate experimental data on the > time-domain behavior of the laser link? Hiring a consultant to do this > would be a desirable alternate to getting and learning this stuff > ourselves. > > Any thoughts? > > John > Depending on how you are able to characterize the channel, different simulators may provide some useful data. Even with PSpice you might get sufficient info playing around with the different controlled sources available. If that is not sufficient, ADS will (almost) certainly give you whatever you want provided you invest sufficient time setting up the simulation (it is awful to use) and simulating. Pere
From: Bill Sloman on 14 Jul 2010 08:00 On Jul 14, 10:52 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Tue, 13 Jul 2010 16:35:27 -0700 (PDT), Bill Sloman > > > > <bill.slo...(a)ieee.org> wrote: > >On Jul 14, 1:29 am, John Larkin > ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> Hi, > > >> One of the nasty things about cheap fiber-coupled lasers is that they > >> have terrible amplitude stability and linearity, full of mode jumps > >> and such. Given that, sending a signal over a fiberoptic link using > >> amplitude modulation is usually done with a stable CW laser feeding a > >> lithium-niobate modulator. The modulator itself is nonlinear and > >> expensive and a nuisance to drive and bias. > > >> Digitizing and sending samples is OK, up to a point. It gets messy at > >> some point from a sheer speed standpoint. > > >> So the idea of using FM pops up. If my baseband analog signal were, > >> say, DC to 150 MHz, and I picked the highest carrier center frequency > >> that's reasonably easy to work with, say 1 GHz, it could maybe be > >> done. The laser driver and receiver aren't too difficult. The issues > >> are the modulator, the demodulator, and the pure signal theory > >> necessary to turn the time-domain behavior of the link into classic > >> measures like s/n and distortion of the recovered baseband signal. > >> Asymmetrically bandlimiting an FM signal is computationally messy. > > >> I'd expect that commercial VCOs wouldn't have anything like this sort > >> of fractional modulation bandwidth. And if they did, a varicap > >> modulating an LC oscillator would probably distort like mad. (Faint > >> echoes of the capacitor charge debate?) The modulator may have to be > >> some EclipsLite version of a 555 on steroids. Or a multi-GHz VCO > >> heterodyned down. Yuk: sounds like RF. > > >http://www.onsemi.com/PowerSolutions/parametrics.do?id=586 > > >The ECLips range of digitally programmable delays might be what yoou > >had in mind. Most of them have an analog bandwidth of up to 1GHz, up > >to 1.5GHz for the faster ones. > > Actually, no. They would require me to digitize the signal first, > which is what an FM scheme would avoid. Once it was digitized, I may > as well just ship the data. Some of the delay lines have an analogue input fine tune,and the MC10198 allows you to modulate the pulse-width by an entirely anlogue route, but since the message I was trying to pass on was that the idea of 555 on steroids wasn't exactly realistic, what you've actually said is that you have missed the point. -- Bill Sloman, Nijmegen
From: Jan Panteltje on 14 Jul 2010 08:55 On a sunny day (Tue, 13 Jul 2010 15:52:30 -0700) it happened Joerg <invalid(a)invalid.invalid> wrote in <8a491kFfqU1(a)mid.individual.net>: >I have seen CDs and DVDs that have delaminated. The last (expensive) DVD >we lost began to grow a blue cloud in the middle. It played to about >half the movie, then cut out. Most probably last a long time but if they >do delaminate it can happen within months. Tapes all lasted >10 years. >Some are 20 years and still fine. You need the righ tones. Use Verbatim. I have 100 out of 100 correct. Some older ones Tdk for example, has some sort of funghus growing in the optical layer, even teh new ones, I returned boxes full, but the ones i already burned failed shortly after. In fact Verbatim is so remarkedly reliable that it amazes me. The other thing is: Use DVD+ ,as DVD+ allwos you to intrrupt the burning process (can appen, system load for example can cause that) and jus tcarry on. I can even stop burns with ctrlZ in Linux, to continue later... And finally, do not 'author' DVDs! If you are going to to play on the PC anyways , save the file as a binary image. In Linux it is so simple: To write a mpg file to disk as a binary image: growisofs -speed 3 -Z /dev/dvd=filename.mpg To verify it byte for byte: dvdimagecmp -a /dev/dvd -b filename.mpg If no errors then remove the original filename.mpg rm filename.mpg This only takes minutes, and can use all the 4 700 000 000 bytes on a DVD. Burn at a slow speed to get very good quality (3x in the above example), even if you burner can do much faster. Then later to play it: xine /dev/dvd or, if you want to FFWD etc, copy to disk first: cp /dev/dvd filename.mpg xine filename.mpg xine has all the needed playback features, language menu selection, even separate H and V zoom in case the aspect sucks. Well, a PC these days can replace many boxes (PCI cards = TV receiver, video digitiser, audio, what not), and can be really small. Linux has a remote control project too. It can be smaller then the VCR :-) Westerns? C4 and C5 transmits westerns several times a week here FTA on satellite (they are UK based). Was one monday with Burt Reynolds 'Hard Ground' (2003). Usually record it, next day I will look at it, if it sucks I delete it, if it is good I watch it, if it is execellent I burn a DVD. They are doing all the old Startrek movies from the eighties, with Kirk, last one was startrek_IV_the_voyage_home_1986. I went ot see it in the eigties, missed the start, was late in the theatre. So now I wanted to record it, it started, a huge thunderstorm appeared, signal went to zero for about 30 minutes, recorded the first few minues and the last part. So I still have not seen that part where Kirk is supposed to hijack his own ship -he was made admiral before that-, but then degraded back to captain because of that in the end, after saving the worls of course. A great performance with late Scotty the engineer, where he invents 'transparent aluminum' on an old Mac :-) tries using the mouse as microhone for voce control ... Yes, TV can be fun. > >> But I have seen too many damaged tapes and dropouts. >> If yoy digitise with the PC, then you can also play with the PC, >> PC as media center. > > >A PC in the living room? No way. SWMBO won't be happy about that. We >have structured wiring so we could put it in the basement but then I'd >have to design an RF remote that works in our RF-unfriendly house. > > >> My 10 year old CDs with DivX and all my DVDs I burned still play fine. >> next is burn it to flash, an also to a huge harddisk. >> That is why I have the 1TB Seagate external, most movies just a few keys away. > > >We don't watch many anyway. Maybe an old Humphrey Bogart, or a Western. > >-- >Regards, Joerg > >http://www.analogconsultants.com/ > >"gmail" domain blocked because of excessive spam. >Use another domain or send PM. >
From: Jan Panteltje on 14 Jul 2010 09:01
On a sunny day (Tue, 13 Jul 2010 20:15:04 -0700) it happened John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in <oaaq36l7a18h0to93incdm6pkrgdijlanb(a)4ax.com>: >We have a request from a customer to ship some wideband data over >fiber. So we're thinking about it. It might turn into a standard >product, too, especially if we make it accurate down to DC. Most fiber >signal links are sort of ac-fuzzy... stick a signal in one end, get >something sort of similar out the other. > >John Have you contacted Intel? http://www.theregister.co.uk/2010/04/15/light_peak_to_succeed_usb_3_0/ They have Light Peak (TM) up to a hundred meters, at USB 3 speeds or higher. |