Optical Insanity: Solving the 45km Challenge

[neilgregge]

Hello,

I have been given an assignment to design an optical communication system. A 12 MHz LED (laser diode would be too easy) signal has to be sent 45km via optic fibre and read at the other end. Simple enough, you may think. however I have been told that I have to use multimodal cable, and all I have read has said that there are insane signal losses associated with multimode (one place, i read there was 2dB loss for every km, whicc was about 90% after 10km), hence its use primarily for internal networks. As repeater stations along the way are prohibited, I am at a loss (much like my signal) as to how to go about this.

Any help would be appreciated,

Neil

 

[Averagesupernova]

Treat the system as an FM radio system. Think about it. How much loss do we have between a transmitting antenna and a receiving antenna which are separated by 45 Km?

Edit: 2 db per Km is 90 db total. This has an input to output ratio (in power) of 1 billion to one.

 

[ravenprp]

Hi Neil,

Designing an optical communication system for a 45km distance can definitely be a challenging task, especially when using multimode cable. As you mentioned, there are significant signal losses associated with multimode, making it difficult to maintain a strong and clear signal over such a long distance. However, there are a few strategies you can use to overcome these challenges and successfully complete the 45km challenge.

Firstly, it's important to carefully select the components of your system. This includes the LED, optic fibre, and any connectors or splices. Make sure to choose high-quality components with low attenuation rates and good compatibility with each other. This will help minimize signal loss and maintain a strong and stable signal throughout the 45km distance.

Another strategy is to use signal amplification. This can be done by incorporating optical amplifiers along the length of the cable. These amplifiers will boost the signal and compensate for any losses, helping to maintain a strong signal until it reaches the other end. However, keep in mind that using amplifiers will also introduce some noise to the signal, so it's important to carefully calibrate and adjust them for optimal performance.

Additionally, using advanced coding techniques such as forward error correction (FEC) can also help improve the performance of your system. FEC adds redundancy to the transmitted signal, allowing for error correction and improving the overall reliability and quality of the signal.

Lastly, proper installation and maintenance of the system are crucial for success. Any bends, kinks, or damage to the optic fibre can significantly impact the signal and cause additional losses. So make sure to handle and install the cable carefully, and regularly inspect and maintain the system to ensure it is functioning at its best.

I hope these strategies help you in solving the 45km challenge. Best of luck with your project!