I have a RF signal at L-Band, 950-2150 MHz. with bandwidth up to 100 MHz.
this signal needs to be converted to optics.
Does single mode or multi mode fiber have frequency/bandwidth limitations after conversion?
RF to Fiber Optics Conversion
opticsRF
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I think you need to talk to a filter vendor instead of stackexchange. For 4GHz you'll probably need some form of waveguide resonator-based bandpass filter. But I don't know if you can get that wide of bandwidth with such a steep 50Mhz transition band without paying a small fortune. Here's an IEEE article on a 4Ghz 500Mhz BP filter.
So you just want to use fiber optics to expand the coverage area of the sensors. It's entirely possible for IR to travel through fiber optic cables, it just depends on the type of cable, and the transmission wavelength. Have a look at this, specifically the diagram showing scattering and absorbtion by wavelength in fiber optic cable.
Understanding Wavelengths in Fiber Optics
And as they say on that page, the prime wavelengths are 850, 1300, and 1550, because they fall between the absorption bands, and it seems like 1550 > 1300 > 850 because of the scattering curve. Fiber optics are used with IR LEDs for example in products like this:
However that's obviously different from what you're doing, since your IR source isn't directly at one end. I imagine it will come down to is the IR detector sensitive enough, and that'll depend on how much of the light makes it into the cable, or how far apart is the cable and LED.
And it looks like your detector is sensitive from 850 - 1050nm, and your LED is 940nm so that's good, but if you're going to be using this during the day, you have to worry about solar irradiance, and atmospheric absorption. It looks like there's about 0.75 W/m^2 at 940nm of irradiance, and the absorption band is around one of those plateaus:
Or on this image, it's the first peak above 50% from the left, at about 65%, mostly due to water vapor:
So since I don't actually know whether you plan to use this in broad daylight or not, I'd say if it's a night only device, go for it. If not, it might still be possible, but it might be difficult. If you try it out and it doesn't work, there are 3 things I can think of that might help:
- Get a more powerful IR LED -It looks like you already have the most powerful IR at 940nm at least on digi-key, but it couldn't hurt to look around.
- Get more sensitive detectors
- Move to a different wavelength. --I actually have some IR LEDs from OSRAM as well. Your 4545 has a peak of 500mW/sr radiant intensity. The ones I have are the 4751, which peaks at 1250 mW/sr. Those look to be discontinued, but they do have the 4750, which has essentially the same specs. 1250 mW/sr, at a wavelength of 850nm
Best Answer
Any limitation in your fibre will be inconsequential compared to those in your optical modulation/demodulation processes.
You will have to look critically at the characteristics of your incoming signal to decide what sort of optical modulation scheme will best preserve the parameters you want to keep, and which you can allow to degrade.
If it's a data signal, you may want to throw away weak carriers. If it's a spectrum scan, you may want to keep weak ones, and ensure that strong nearby signals generate don't obscure them with intermodulation.
The most conceptually straightforward way to encode an RF signal onto optics is to analogue AM modulate a subcarrier, which has a frequency of several times your bandwidth. However, the linearity of this could vary between bad and very bad, which would affect your EVM slightly, and your co-channel hugely, if such things are of consequence in your original signal.
An ideal route would be to fully demodulate your signal, assuming it to be data, and ship the data along the fibre, using a standard data format and end-point chipsets.
There is not enough use-case information in your question to answer more than very generally at the moment. Depending on your field of employment, you may not be able to give out use case information!