RCLEDs?

If you could explain what a RCLED and an ELED is it would help.

Why not a laser? The inherent collimation will result in a lot more light getting into a reasonable f-number transmit lens.

John

RCLED - Resonant Cavity Light Emitting Diode EELED - Edge-Emitting Light Emitting Diode (sorry missed an E!)

both are methods for getting higher power and switching speeds over standard LEDs.

The air gap is only 1cm and the datarate is < 200Mbps so i thought i'd try out the cheaper and easier to drive LED options. I realise that there are chips that will happily drive laser diodes, but the laser modules are quite expensive.

Andrew

850 nm VCSEL lasers cost under $20 and are blindingly fast. The driver would be a single resistor, given a CMOS logic level. LEDs are OK here if their capacitance doesn't kill the speed.

John

That sounds about right, i'll be driving from PECL, but that shouldn't be a problem. Where can i get hold of a VCSEL then? I'm in the UK, but i guess worst comes to worst i can ship.

Thanks for your help.

Andrew

Sorry i shouldn't be so lazy, i just found a Optek part (OPV315Y) in digikey thats a very reasonable price. Rise time 90pS, fall 120pS and a very fair price. Can you simply drive these from logic then? Other laser diodes require the internal photodiode to monitor the output power, hence the complication and hence the use of a driver chip. Do you have any links to articles i can read?

Thanks again for your help.

Andrew

OPV315Y non-stock OPV315YAT non-stock OPV315YBT quantity available... 1

And Mouser doesn't seem to carry it.

Jon

I have a bunch of OPV315YAT in stock that I don't plan to use, available free. They have a strange behavior that messes up my application: they act as if there's a slow PIN diode in series with the laser. As long as you use them in a standard NRZI data transmission mode, or modulate them continuously, they're fine. But if you turn them completely off, then try to switch them on, the terminal voltage overshoots and the light output ramps up slowly. The equivalent tau is 10's of microseconds. The jerks at Optek first denied the problem, then said they'd fix it, then stopped answering my emails. Did I mention that they're jerks? The new Lasermates are superb.

But the OPV315YAT is, as I recall, a ball-lens part in an ST housing. A free-space application would work better with a TO-18 with a flat lens.

They're easy to drive from PECL:

+5v | | laser

-----(pecl gate)--------+-----|

Newark usually stocks the Optek stuff.

John

Thanks for the headsup, l guess i'll avoid the Optek part . I didn't realise VCSEL's were so easy to drive, i suppose they are at this sort of data rate? I checked out the lasermate

website, are they the people you were referencing? Just wondering if there were any recommendations i could get my hands on easily . Thanks.

Andrew

The Opteks are fine as long as you keep driving them. They just get weird if you let them sit at zero current for many microseconds.

I'd offer you some parts, but all we have are ball-lens lasers in ST connector housings. They could be pulled from the housings, but the ball lens is meant for fiber coupling and will scatter light all over the place in a free-space application.

The Lasermate TST-M85A426-2H is superb: 850 nm, clean, no mode jumps, lots of power. Maybe they have a flat-lens version of it.

John

In , snipped-for-privacy@yahoo.com wrote in part:

Minimum purchase 24 of them for $507.94 plus shipping.

I find this quantity minimum purchase of parts of this price unusual for DigiKey.

- Don Klipstein ( snipped-for-privacy@misty.com)

Newark sells them in singles, or used to recently.

John

Is it an in stock item, or one they have to special order?

--
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prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida