I'm working with an infrared emitter/detector system based on an Osram SFH 4545 IR LED collimated through a 40mm dia, 120mm fl lens and a sensor array based on three separate sets of three Vishay TSOP 34856's all running a 56kHz signal. Both emitter and detector are designed to mounted on a wide variety of fully mobile objects and so cannot be physically connected.
The issue is the mobile elements mounting the sensor arrays are typically much larger in terms of surface area then the detectors can cover, especially considering the number of components used. Also, by design the sensors must be exposed during a highly physical process thus requiring additional protection and maintenance.
Would it be possible to use fiber optic lines as a light pipe to bring the IR signal to the sensor array? I am imagining arranging multiple lines over a broad area of the target element, thus increasing the area each array can cover and also allowing the delicate sensor components to be moved to a more protected location. Ideally, I would like to be able to utilize the same detectors or at least one with similar parameters so as to avoid any redesign or reprogramming.
If this is possible, what type of cable would be required? How would the ir signal be collected at each cable? I can't imagine that you would have raw cable ends sticking out everywhere, but I can't seem to find any termination components that aren't designed to physically connect to a light source. I've researched this fairly thoroughly via Google and several other message boards and haven't found the information I need. My team and I are firmly in the DIY camp and so our knowledge base is deep only in specific areas. Fiber optics is not one of them. Any help would be appreciated.
Best Answer
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:
Fiber-Optic Coupled IR LEDs
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: