VCSELs seem to have an upper limit on the frequency they are modulated somewhere above 20GHz. If you are modulating it below that frequency, you won't be limited by any funamental limit of the VCSEL technology.
The leadframe may work as a low pass filter leading to the actual VCSEL device. If you keep the legs short, you shouldn't have too much trouble modulating it.
I've had terrible experiences with the Optek parts. I think they buy their lasers from random guys in overcoats in the back alleys of Taiwan. They keep changing, and they don't seem to know much about them. The last batch we bought had a really bizarre time-domain response, as if a very slow-recovery PIN diode were in series with the laser.
But in general a small cheap 850 laser will deliver a milliwatt or two of power at maybe 10-20 mA and is easily modulated up to a GHz at least.
Could these be used effectively for free air transmission?
I'll explain my application. I built a security system which includes a dual beam IR barrier. I'm using a dual beam with a 25ms delay,i.e if both beams are obstructed simultaneously for 25ms trip the alarm. I'm currently using tsal6100 emitters, and spectral matching detector from Panasonic. I can easily obtain the range (70ft) I need with this setup. The problem is I have to separate the emitters and detectors by a couple of feet (vertically) or one emitter will flood both detectors. I know the solution is using a collimation system with optics, these aren't readily available though. There are some budget optics on the internet but they lack datasheets.
If these LD's can be used for this application I could fit everything in one enclosure, with 5 or 6 inches of vertical separation.
Before I order a couple I thought I'd ask and see if anyone has any experience with them, and could tell me if it's practical to sub out the TSAL6100 with the LD's? With a closely matched detector the TSOP7000.
Garden-variety cleaved-cavity diode lasers can be modulated up to ~1 GHz, and VCSELs are generally faster than that. The packaging on this one doesn't look too promising for multi-GHz modulation, but for IRDA you should definitely be in the clear.
There is no reason you can't pulse the Lasers at, lets say, 10KHz with a 25% duty cycle. Since they are diven by the same electronics, it is easy to make them alternate. The detection circuit can be fairly simple.
At the photo detector, a 10Khz band pass filter will have a large output if one Laser is blocked. A 20KHz filter will have at least a fairly large output unless both are blocked.
If you need to know which Laser is blocked, you need to make the pulse pattern different or bring the information about which is on from the transmitter to the receiver. Alternating one pulse on Laser #1 and then two on Laser #2 would be a simple way to do the different patterns.