Spice models of laser diodes?

Does anyone have any spice models of DVD writer type laser diodes? Possibly anything will do, I just want to explore whether there's much point to modelling with them, or whether it's enough to set soem basic parameters. I'm totally new to spice so I have no idea. But I know that many laser diodes are very sparsely documented, so the idea alone that someone might have spice- modelled one is entertaining, if nothing else.

Reply to
Lostgallifreyan
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Lostgallifreyan wrote in news:Xns9C50420FC16Azoodlewurdle@216.196.109.145:

In case anyone's following this (and I opened it from alt.lasers to two electronics newsgroups), I'm still after laser diode spice models...

And I found this:

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I'm still very new to spice, so if anyone is feeling very helpful and can write a conversion of this I can use in LTspice, please do.

Also, a quote of my earlier posts so people in the electronics groups can see them: "I've seen a few lines specifying diode models last night and gathered some for general use, and I'll look into what the parameters mean, so even a few known ones in spice format will help me, even without a full model. But I do want to know what parameters are important to laser diodes, and what values they ought to have for a DVD writer diode. I suspect they will be similar for most if not all DVD diodes.." And: "Does anyone have access to the Journal of Lightwave Technology vol.15, no.4, april 1997, page 717? I read that there's a spice model there, but I have no access to this."

In short, I want electrical models of DVD writer type diodes. I don't need extreme accuracy, or the optical details, (didn't think spice went there anyway). They just have to be realistic electrically, and I'd like some simple direct guidance on what parameters I need to change in an LTspice model of a diode, as that's the context I'm using.

Reply to
Lostgallifreyan

Progress...?

formatting link

I'm studying that as best I can but it's fairly heavyweight, can anyone help me understand how to use it?

They mention terms like TT (apparently in microseconds, for 'transit time') but they don't say where they get it from. I don't see it in the two diode data sheets I tried to find it in, only reverse recovery time, and if it were the same thing, surely the notation would be same, and it's not. The deeper I look, the thicker looks the plot.

I'll be patient now and lay off the posting because this looks more complex than I thought, and might take time to answer. Please do though, if you know how. I don't mind doing the work but I need to be shown what must be done, and where to get the data I need to start with. Right now I don't even know if it IS possible to translate from data sheet to spice model, and it looks like it isn't.

Time for the serious boffins to duke it out in this thread, if they're interested. :)

Reply to
Lostgallifreyan

ask over on sci.optics.fiber

Steve

Reply to
osr

snipped-for-privacy@uakron.edu wrote in news:14d6e586-3ca9-44e0-b3da- snipped-for-privacy@k1g2000yqf.googlegroups.com:

For an electrical model? Fibre is specifically optical... The people who I think can answer this hang out in the groups I posted to anyway.

Reply to
Lostgallifreyan

We bought some 850 nm fiber-type laser diodes that acted as if they had a microseconds-response PIN diode built into them, in series with the actual laser. If you applied current suddenly, the voltage would overshoot almost 2:1, as if there were an inductor in series. As long as the current wasn't cut off for too many nanoseconds, it behaved like a diode. Fine for telecom and maybe for burning CDs, but terrible for sending baseband on/off digital stuff.

John

Reply to
John Larkin

The telcom guys are using baseband. They use scramblers to ensure that there are enough transitions to do clock recovery. There isn't much low freqency energy.

What sort of data were you sending? Were there long strings of

1s or 0s?

I seem to remember something about not turning something all the way off. I have forgotten the context and reasoning.

I think the idea was to modulate it from 10% to 100% rather than turn it all the way off in order to avoid transients/problems like you described.

It might have been incandescent lamps, but I don't think so. Reminds me of the time I went into a dark machine room many many years ago. (I was sleeping on the couch, babysitting for an all night run.) All the red lights on the disks were on. Wow were we in trouble! After a few seconds I figured out that it was just the keep-warm current to avoid the turn-on transient. Nothing was visible in normal room light.

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Reply to
Hal Murray

Definitely a communications breakdown spreading here but I'm not entirely sure it's electro-optical in nature..

Reply to
Lostgallifreyan

Lostgallifreyan wrote in news:Xns9C512D9705DE7zoodlewurdle@216.196.109.145:

Does anyone here know how to adapt a diode model for a laser diode?

Reply to
Lostgallifreyan

Please read the last paragraph of this post, even if you don't want to read all of it.

Ok, I tried this, and I don't think it's going to work.

I corrected some typos (very few, Marco did a good job given that the original makes it very hard to see what is or is not a space), one of which is definitely in the original text, a + beginning a line without which SPICE can't run because it needs that to indicate continuation. It's safe to say there might be more errors given the results of running it. First, my typo- edited copy, which runs in LTspice:

ibias 0 p 10m xlaser p 0 pf ltest1 rout pf 0 1e9

************************************************************************ .subckt ltest1 p n pf D1 p nt1 d1mod_ltest1 Ic1 p nt1 3.6641713e-14 Vt1 nt1 n 0 D2 p n d2mod_ltest1 Ic2 p n 3.6641713e-14 Br1 p n i=0*i(Vt1) +20701.692*i(Vt1) *i(Vt1)+28862208 *i(Vt1)*i(Vt1)*i(Vt1) Bs1 p n i=1.3785977*v(m) *v(m)*ln(1e-60 +5220.1829*i(Vt1)+ + 54033309*i(Vt1) *i(Vt1)+7.5333001e +10*i(Vt1)*i(Vt1)*i(Vt1))/ + (1+0.95928574 + *v(m)*v(m)) Rph m 0 1 Cph m 0 5.518e-12 Br2 0 m i=(0*i(Vt1) +1.0120369*i(Vt1) *i(Vt1)+0*i(Vt1) *i(Vt1)*I(Vt1))/v(m) Bs2 0 m i=0.67395059 *v(m)*ln(1e-60 +5220.1829*i(Vt1) +54033309*i(Vt1)*i(Vt1)+ + 7.5333001e +10*i(Vt1)*i(Vt1) *i(Vt1))/(1+0.95928574 *v(m)*v(m)) Bpf pf 0 v=v(m)*v(m) .ends ltest1 .model d1mod_ltest1 D Is=3.6641713e-14 n=2 .model d2mod_ltest1 D Is=3.6641713e-14 n=2 tt=1.8181818e-08 ************************************************************************

.dc ibias 0 50m 0.25m .end

Third of three vertically aligned + signs was absent from original, and is vital unless you merge that line to the end of the previous one.) I made a symbol file for LTspice to use this model:

Version 4 SymbolType CELL LINE Normal -12 -40 -12 -24 LINE Normal -20 -32 -4 -32 LINE Normal -20 32 -4 32 LINE Normal -28 32 -48 32 LINE Normal -28 -32 -48 -32 LINE Normal 76 0 96 0 LINE Normal 48 -16 -16 -16 LINE Normal 16 16 48 -16 LINE Normal -16 -16 16 16 LINE Normal 48 16 -16 16 SYMATTR Value ltest1 SYMATTR Prefix X SYMATTR ModelFile LD_TEST.sub SYMATTR Value2 ltest1 SYMATTR Description Unknown laser diode model. PIN -48 -32 NONE 0 PINATTR PinName PIN+ PINATTR SpiceOrder 1 PIN -48 32 NONE 0 PINATTR PinName PIN- PINATTR SpiceOrder 2 PIN 96 0 NONE 0 PINATTR PinName OUT PINATTR SpiceOrder 3

Ignore the terrible graphic if you try this, it was a rough edit of one of my op-amp symbols, it was the fastest way to make something useable...

Anyway, it's an odd result! If I make a simple LM317 based constant current driver circuit (I have a good LM317 model now) and set the current for 152 mA using an 8R2 resistor, the current is steady but at more current than it should be! The model appears to be generating virtual energy. :) Worse, a voltage plot of the anode end shows a rediculous curve, a relaxation oscillator type sawtooth varying once every 50 microseconds, and between 0V (Ground) and MINUS 12 KILOVOLTS! That can NOT be right...

I really don't think I'm going to use this. And I suspect we wouldn't have to be bombed back to the stone age, or even to the technical levels current when the Alexandria Library was burned, to render that document as arcane as one of Harry Potter's spells. It's obviously not meant for the purpose I'm trying to put it to even if by a wild fluke I can figure out how to make it work right, and I don't think I even have leave to SEE it, technically, so I ask yet again, please can someone help me to find how to adapt a standard diode model to emulate a laser diode, electrically, well enough to design simple drivers for? I need to see if learning SPICE is going to be useful. So far I notive very different behaviour depending on whether I use 4 series 1N4005's or 4 series 1N4148's, so clearly I do need something better than plugging in the first diodes I can find.

Reply to
Lostgallifreyan

Whatever circuit you are going to use, it shouldn't be that sensitive to the properties of the diode. Unless you intend to do some very high bandwidth modulation, any diode should do in the simulation.

There's no need to reinvent the wheel here. Did you check the collection of laser diode drivers in sam's laserfaq?

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Kai-Martin Knaak

Kai-Martin Knaak wrote in news: snipped-for-privacy@lilalaser.de:

Several times. :) I'm after trying something very specific, something I was often told wouldn't work well but has often exceeded expectations so I want to see how far it goes.. I'm modulating up to 500 MHz, DC coupled, with constant regulated current held in linear proportion to an input control voltage between 0 and 5 volts, with independent control of threshold level.

I have no illusions about spice. I've always preferred to model ideas as parts on boards, but having seen LTspice mentioned a lot, I started looking at it, and decided to learn something new because like SketchUp for basic aid in visualising hardware constructions, this should save a lot of time eventually.

I found that my FIRST attempt to model my driver showed me details I saw on a

100 MHz scope many months ago, so it's obviously damn close to the mark. I was modulating at just 100 KHz then, trying to see if I could out-do Robin Bowden's Die4drive. :) (Does 200 KHz with no overshoot but with wave peaks far less flat than I want over their duration at that speed). The spice model showed that some resistor changes were enough to increase stability to allow 500 KHz modulation with sharp transitions, flat peaks, AND no overshoot, (and well over 1 MHz if I don't mind blunting the sharp edges and rounding the peaks a bit), and at those frequencies you can bet it DOES matter what diode properties there are if you're trying to keep sharp edges... in general I notice from models that those diodes which do not vary their Vf much with sharp changes from 0 drive to full drive are also those most prone to ringing and overshoot on the rising edge.

Right now I'm about 24 hours overdue for sleep and past feeling tired but I'm going to try to get some. I've started trying some LED models that are as close as anything yet. They have forward voltage similar to a laser diode, similar average currents, and they produce roughly the expected kinds of waveforms. Maybe this is enough closeness, so if during my sleep people shower my posts liberally with spice models of high-brightness red GaAlAs LED's as well as laser diodes, I'll be very happy to see them in how ever many hours it takes me to be fit to look at them.

And as a hint, my diode driver is a modification of one I posted here often, in turn based on an idea in the LaserFAQ, posted originally by Winfield Hill. His wouldn't have accepted a control voltage though, that bit was mine.

Reply to
Lostgallifreyan

If anyone is following this and wants to try modelling their own stuff, I found what might be a way. Intusoft make a tool called SpiceMod which is part of a package they call ICAP4 though it seems the demo setup doesn't have that tool, just some very good noted on it, and modelling in general: The file WkwModels.pdf from the demo install answers a lot fo the questions I had about modelling diodes, which parameters to tweak, and extraction from data sheets.

I don't know if the lack of response to me is because of a thousand experts silently screming RTFM at me, or because it's actually asomething they DON'T KNOW. Given that Intusoft explain that this is a serious challenge for experts too, I'm assuming maybe they really don't know, so they might benefit from that file as much as I will.

Reply to
Lostgallifreyan

Most of us just use a regular diode to simulate because all one (usually) wants to know is that there definitely won't be any ever so slight spike in diode current because LDs can go poof in microseconds. Simulating the optics part would be a major challenge, I think.

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Joerg

Joerg wrote in news: snipped-for-privacy@mid.individual.net:

Thought that might provoke an expert. :) I agree, same here, that's all I usually need too, though like that EDN manual says, a more detailed model that allows models to give warning of imminent demise is useful. Modelling for ESD is likely daft, better that we just take care and put in TVS's and such, but when it comes to fast modulation, a model definitely helps. Surely you'd have a use for that, no?

While I found that a string of four 1N4148's produced a modelled overshoot almost exactly like what I saw on an oscilloscope months before I considered looking at spice, I got a very different result when trying four 1N4001's so it really does need something better than reaching for a standard diode, in a model OR as a dummy diode in a real circuit (where a optically dead laser diode is best anyway). So it really comes down to trying to get something usefully close! EDN's model seems ideal, aimed at solving this problem for general use, as opposed to the elaborate models in private university publications. EDN's is probably tested too, proofread and verified before publishing.

formatting link
(Halfway through file).

If anyone can help by making that into asy and sub files for LTspice it will help me a lot, and probably a lot of other people too. Four days of searching have found lots of other people askign questions, and very few answers, and NONE complete and verified. Someone could get well known for solving this so other people can have an easier time of it.

Reply to
Lostgallifreyan

In case anyone wants to try making a model, I typed out that netlist and checked it carefully, so this can save you a bit of time:

Vlas 100 50 1 Dlas 50 200 diode1

F1 0 1 Vlas 1 Rs 1 0 {Sm*sps}

I1 2 0 {Sm*sps*Ith*exp((T/25)-1)} G1 0 2 1 0 1 Rlim 2 0 1Meg Ds 2 3 diode Vm 3 0 0

F2 300 400 Vm 1 Dmon 300 400 diode Cmon 300 400 Cmon

.model diode d .model diode d rs=5

.ENDS

But it obviously needs more than that to build a subcircuit file. I don't know how yet, or even if the 'figure 1' in that PDF has all the required detail to make it possible.

Reply to
Lostgallifreyan

I have designed LD circuitry but I am not an expert. Senor Hobbs would be one. TVS don't work well. Their cutoff isn't terribly well defined and they have too much capacitance for this. Just handle the things with care. I've never killed one with ESD, knock on wood ;-)

"File not found" :-(

Some of the 4000 series behave more like PIN diodes.

It's going to be lots of work. You'll need to get into behavioral models and while people have modeled large chunks of jet engines with that it was a ton of work.

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Regards, Joerg

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Reply to
Joerg

Joerg wrote in news: snipped-for-privacy@mid.individual.net:

Sorry, right file, wrong location. Try this:

formatting link

I've been finding (and been sent) spice models that are in various stages of completion and complexity. Ignoring the rest for now, I'm focussing on that EDN one because it looks like it's meant to be complete. But it's NOT in a single subcircuit file that can be adapted to LTspice, or anything else. I don't think it needs modelling, just translation.

For modelling, I'll look into that too, as equations are given in that PDF file I mentioned earlier, from Intusoft. In their descriptions of how to use SpiceMod (which I learned costs 600 bucks(!) and is therefore the most expensive few tens of kilobytes I've ever heard of) they show a screen that neatly prioritises the data sheet specs for pluging into the equations. While the details for transisotrs (bar a MOSFET) are not similarly revealed, there ought to be enough there in their diode explanations to model a laser diode, electrically. But again, all I'm asking for here right now is for someone who knows how, to translate that EDN article to a subcircuit ready to plug into LTspice. (I can make my own symbol file).

Reply to
Lostgallifreyan

Joerg wrote in news: snipped-for-privacy@mid.individual.net:

Interesting. Robin Bowden didn't make strong recommendations for them either. Just a resistor/capacitor network, and a zener. I concur, though at the time I was all for varistors too as I'd found a LOT fo them cheaply on eBay at the time.. But they apparently change characteristics rapidly over time fi they see anything like the conditions they have to limit, so I'm not too keen now.

Trying not to get away from the focus of the thread because I really do want direct help with model translation as it's unlikely I can do it alone, but this IS interesting to me.. PIN are those fast photodiodes, right? Often used for detecting very short laser pulses and such? When I modelled my driver using the 1N4005 model I found, I got a lot of ringing. I also saw a correlation with the changing of Vf with hard changes between zero and full drive. I analogised it with the hitting of a hard object as opposed to a softer one that inherently damps the impact. If a PIN diode is to respond fast it seems reasonable to think that it is capable of hard brittle responses, otherwise it could not hope to react in time to register a very short laser pulse. Is this a reasonable way to view it? And if so, why so with rectifiers and not signal diodes? Or LED's which I imagine are similar to laser diodes, being usually GaAs based.

Reply to
Lostgallifreyan

Lostgallifreyan wrote in news:Xns9C57D85EDFFE4zoodlewurdle@216.196.109.145:

Meaning: Diode models with little change in Vf with current at 500 KHz square wave drive were also those which rang the most.

Reply to
Lostgallifreyan

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