How can it run out of carriers? Photons make h-e pairs, and more photons should make more, right? Does high pair density increase recombination before the charges can be collected? Is it possible that the photocurrent is limited by ohmic effects? The DC effect does need pondering.
One of the makers of GaAs photodiodes told us that their devices would limit above about a milliwatt optical input, so we got access to a multi-watt pulsed fiber source, and it turns out they were wrong.
I don't, didn't have to use SPICE on that section in my current design. But the optical folks have attenuators for that case.
This had me puzzled as well. The common DFB modules these days pump out
5mW-20mW but photodiodes tend to saturate around 1mW-2mW. So we'll attenuate in order to be able to run the DFB at reasonable current levels. I guess it's all for the telco market where they assume a mile or more of fiber.
If you come across a DFB that is really, really low in phase noise let me know ;-)
I was told that besides non-linearity there comes a point beyond which there would be irreversable damage. Also, the datasheet for the Sumitomo diode I am using here states 2mA Ir as the abs max limit.
The model would be a light controlled current source. PD's have about
0.8A/W conversion ratio. Double the light POWER and double the current output. his is a log convertsion ratio. so it is never really "linear" but always log. This continues till the voltage acrros the diode (the signal) is about 1/10 the reverse bias and then you get somne cross prodcut distortion. adign more power and then you saturate the amplifer front end, add more power and there is a power density/max current which is athe peak power limit.
"Jim Thompson" wrote in message news: email@example.com...
You'll have to give us your take on whether or not the company will make it. :-)
I have a friend who worked for a number of years as a consultant (these days he's an FAE at a big distributor) who said that of all the consulting jobs he worked one, although in the end the widget always worked and the schedules were generally close to being on time, only something like 1 in 10 ever ended up with a profitable product!
I often wonder why you don't start a manufacturing company. With your skills and background, you should do very well, especially since you already have the experience running that kind of operation.
You are probably doing very well consulting, but boy, you could make a mint making and selling your own product line. For you, the entire field is wide open. There's always the Chinese to think about. But you could start in niche areas that require an excellent technical background for support, and where sales are largely word-of-mouth. By the time they catch on, you could dominate the market and it would be difficult or impossible for them to break into it.
It may take a year or so, but I'd bet you would be a great success.
Thanks for the kudos. Well, what can I say, we live in California and when you do production or sales of OEM'd goods the bureaucrats can get in the way really fast.
I did run a division of a company for a few years until we were bought. This included manufacturing and it was great fun. But we had our bouts with strange rules being imposed (that was before the previous governor was recalled). Example: The whopper was a new law that required overtime pay after 8hrs/day instead of after 40hrs/week. Keeping 10hr shifts suddenly became a real financial problem. But we had people who needed that so they could take 4day/week turns and care for frail relatives. I had people burst into tears in my office. That might have all made sense to some union boss but it sure didn't to the workers.
Much of the stuff I designed is being produced in China. Works great.
I'm not a big Spice guy--I use it about twice a year--but the physics of what's going on is probably local forward bias caused by big lateral voltage drops in the (very thin) epi layer. That's usually the situation with modulated CW beams. Femtoseond beams can do truly evil things to photodiodes, messing up the populations etc, but for reasonable duty cycles the diode generally melts first.
Your first line of defense is a big fat reverse bias.