I think you have a speed mismatch issue.
Unlike most twisted pair ethernet equipment gigabit media converters are usually single speed devices. I'm not positive as to the reasoning but I think there were substantial changes on the fiber side that made supporting both systems in the same media converter difficult. This is a problem as the ethernet controller on Pi models up to and including the 3B is a 10/100 device while your media converters are gigabit devices.
I see four possible soloutions.
- Use a USB gigabit ethernet adaptor on the Pi.
- Use a gigabit switch between the Pi and media converter.
- Replace the media converters with 100 Mbps models.
- Replace the Pi with a "raspberry pi 3 model B+" which has a gigabit Ethernet controller.
First, when you talk about the "speed" of a signal in optical fiber, that's ambiguous. You should be clear about whether you're interested in the latency (the time it takes a signal to travel from one end of the fiber to the other) or the bit rate. In this case, it seems most likely you're interested in the latency, or propagation delay.
In my opinion if the speed of the wave is dependent on the refractive index which will be the same in the same fibre then the speed of both wavelengths will have the same speed. Is it true?
No. This is not true. The index of refraction of a material varies (at least slightly) depending on the wavelength of the light being considered.
In addition, in a dielectric waveguide like optical fiber, as the wavelength changes a different proportion of the signal power travels in the core and in the cladding, leading to (at least small) changes in the effective index of the fiber.
In fact, dispersion can be either negative or positive (also called anomolous and normal dispersion), depending on the wavelength and the design of the fiber. We can also engineer the dispersion properties of the fiber in some cases to optimize the fiber for different applications.
But all of that is irrelevant to answering the question, because the total effect is summarized in the dispersion parameter.
When you specify the dispersion as you did, D = -100ps/nm•km, you're saying we already know the effect of all those variations, and that effect is that the propagation delay through 1 km of fiber changes by -100 ps for every nanometer of change in the wavelength of the signal light.
So you don't need to worry about the physical mechanism. You just need to apply the definition of the dispersion parameter to decide whether a longer or shorter wavelength travels faster through this fiber.
Best Answer
So, considering free-space optical communication does work, anything that conducts light better than free-space path loss should generally work.
Think, for example, of the optical variant of S/PDIF, TOSLINK: certainly not high-tech by any modern means, it's cheap plastic optical fiber, about 8Mb/s according to Toshiba. Transmitter is a rather boring LED, not a laser like in high-speed optical comms.
The receiver is usually a photodiode (phototransistors are typically slower) in reverse bias with a transimpedance amplifier opamp configuration.
You can use fancy connectors, but really: it's just important that enough of your TX light power enters the fibre in a tight angle. So, there's "connectorless" TOSLINK "plugs" where you can just push in your (straightly cut off) POF.
Just a general remark: haven't worked directly with one myself, but SFP and SFP+ transceivers for fiberoptical comms are pretty "dumb"; although they are meant for hundreds of megabauds to gigabauds, I know multiple people who just connect the data pins to 10 MHz sources to have distributed clocking in their living rooms.
Since your doing comms and want to save on the connector and optical transport complexity: don't save on the channel coding :) especially if latency is not that critical, a large interleaver + block code might simply hide any unreliability of your connectors, and of course a lot of noise in general.