Spice models of laser diodes?

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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.

Re: Spice models of laser diodes?

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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:
http://www.freeda.org/doc/elements/dhld.html

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.

Re: Spice models of laser diodes?
Progress...?
http://www.avtechpulse.com/faq.html/IV.33 /

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. :)

Re: Spice models of laser diodes?

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ask over on sci.optics.fiber

Steve

Re: Spice models of laser diodes?
snipped-for-privacy@uakron.edu wrote in news:14d6e586-3ca9-44e0-b3da-
snipped-for-privacy@k1g2000yqf.googlegroups.com:

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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.

Re: Spice models of laser diodes?
On Wed, 22 Jul 2009 19:45:00 -0500, Lostgallifreyan

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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



Re: Spice models of laser diodes?

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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.

--
These are my opinions, not necessarily my employer's.  I hate spam.


Re: Spice models of laser diodes?
Definitely a communications breakdown spreading here but I'm not entirely
sure it's electro-optical in nature..

Re: Spice models of laser diodes?

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

Re: Spice models of laser diodes?
On Fri, 24 Jul 2009 04:01:01 -0500, Lostgallifreyan

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46%or an all but clueless first cut i think you would need a four
terminal device, to include the transport of emitted photons.

Re: Spice models of laser diodes?

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Yes, I was sent an Intusoft newsletter that contained just such an animal,
but it's based on a Hitachi 3mW IR diode, I think. But as a 'dead' diode with
facet damage from ESD or other surge usually behaves very similarly to a live
fresh one, electrically, AND most high power diodes have no monitor
photodiodes anyway, there's nothing wrong with only two terminals. What is
then critical, if it's to be driven hard, is to include temperature
monitoring in the model. In practise diodes will vary but the setting will be
a set-and-forget one based on a single measurement of power at maximum drive,
once the thermal compensator works. I did this once (before I ever looked
into spice) using an LM317 and some thermistors in the sense resistance
network. It sounds crude, but I calculated it in some detail, and it worked
well. Apart from that LM317, the entire driver was discrete passive parts.
(Wasn't modulated though, have to add stuff then.)

Re: Spice models of laser diodes?
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.

Re: Spice models of laser diodes?

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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?

---<(kaimartin)>---
--
Kai-Martin Knaak
Öffentlicher PGP-Schlüssel:
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Re: Spice models of laser diodes?

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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.

Re: Spice models of laser diodes?
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.

Re: Spice models of laser diodes?
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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.

--
Regards, Joerg

http://www.analogconsultants.com /

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Re: Spice models of laser diodes?

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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.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(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.

Re: Spice models of laser diodes?
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

I1 2 0
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.

Re: Spice models of laser diodes?
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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 ;-)


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"File not found" :-(

Some of the 4000 series behave more like PIN diodes.


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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.

--
Regards, Joerg

http://www.analogconsultants.com /

We've slightly trimmed the long signature. Click to see the full one.
Re: Spice models of laser diodes?

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Sorry, right file, wrong location. Try this:
http://www.edn.com/archives/1998/071698/pdf/15di.pdf

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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).

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