Fast LEDs for optical pulse generation?

[Chris Carlen]

Hi:

Anyone working with fast LED pulsers lately? I'm looking for LEDs that
can deliver 10-100ns pulses. Hopefully some SMT package can do this.
Prefer visible range, but near IR might be Ok. The closer I can get to
10ns the better.

Of course, I would like a lot of photons. I am looking into
transmission line pulsing circuits to deliver very short several amp pulses.

The purpose is to create a short optical marker pulse for setting up
gated intensified cameras.


A slightly different project would be to be able to attempt to
substitute an LED for a pulsed YAG laser to create pulses of light to
illuminate very high velocity events such as fuel injection spray
visualization.

For this a <=10us pulse is likely satisfactory, so I will be considering
something like an array of Luxeon LEDs driven by some big MOSFET drivers.

Thanks for input.


--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
[email protected]
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[John Larkin]

Hi:

Anyone working with fast LED pulsers lately? I'm looking for LEDs that
can deliver 10-100ns pulses. Hopefully some SMT package can do this.
Prefer visible range, but near IR might be Ok. The closer I can get to
10ns the better.

Of course, I would like a lot of photons. I am looking into
transmission line pulsing circuits to deliver very short several amp pulses.

The purpose is to create a short optical marker pulse for setting up
gated intensified cameras.

LEDs tend to be slow, but you might get below 100 ns driving a small
led or an array. You'd likely need a push-pull driver to blast the
diode capacitance both ways.

A cheap 850 nm VCSEL laser can deliver a milliwatt or two of optical
power with risetimes in the 200 ps range. Drive one from a TinyLogic
gate through a resistor and it should be easy to get, say, a 3 ns
light pulse. ECL, maybe an EL89, would be even faster.

How much optical power do you need? An ICCD shouldn't need a lot of
light.

Whose ICCD camera? We make the timing electronics for brand A.

John

 

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LEDs tend to be slow, but you might get below 100 ns driving a small
led or an array. You'd likely need a push-pull driver to blast the
diode capacitance both ways.

Been there, done that - with HP-2400 opto-couplers. A bit of reverse
bias (from a diode clamped inductor) helped appreciably in getting a
worst case toleranced 10Mbit/sec link running. The boss ran it it up to
18MBit/sec (over 18 metres of ribbon cable) before the one he tried
fell over. I read him the riot act - if the sales guys had ever foound
out about it, that 18MHz would have ended up in the specs.

A cheap 850 nm VCSEL laser can deliver a milliwatt or two of optical
power with risetimes in the 200 ps range. Drive one from a TinyLogic
gate through a resistor and it should be easy to get, say, a 3 ns
light pulse. ECL, maybe an EL89, would be even faster.

Sounds good to me.

Reverse biassing an LED into breakdown is reputed to give similarly
fast edges - I'll dive into my paper files next week and should be able
to find the reference. The paper didn't say anything about how long the
LED lasted when abused in this way.

 

[Chris Carlen]

LEDs tend to be slow, but you might get below 100 ns driving a small
led or an array. You'd likely need a push-pull driver to blast the
diode capacitance both ways.

Is it the lead inductance, or the semiconductor physics (large junction
C, etc.) that causes this? I suppose then that the larger the LED die
and light output capability, the slower the thing is.

A cheap 850 nm VCSEL laser can deliver a milliwatt or two of optical
power with risetimes in the 200 ps range. Drive one from a TinyLogic
gate through a resistor and it should be easy to get, say, a 3 ns
light pulse. ECL, maybe an EL89, would be even faster.

How much optical power do you need? An ICCD shouldn't need a lot of
light.

The VCSEL might be the way to go. I actually have a visible one. I
shall look in to these further.

Whose ICCD camera? We make the timing electronics for brand A.

John

We have a lot of Xybion, some Princeton Instruments, and maybe another.



--
Good day!

________________________________________
Christopher R. Carlen
Principal Laser&Electronics Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and
"BOGUS" from email address to reply.