1- Two 1-km fibers are spliced together. Each fiber has a 3-dB loss, and the spl

Question

1- Two 1-km fibers are spliced together. Each fiber has a 3-dB loss, and the splice adds 2 dB of loss. If the power entering is 2 mW, then how much power is delivered to the end of this combined transmission line?

2- Compare the fiber used in trans-Atlantic communication systems with the one used in micro-bend sensors in terms of material, attenuation, light modes, core size, and cost.

3- When an LED has 2 V applied to its terminals, it draws 100 mA and produces 2 mW of optical power. What is the LED's conversion efficiency from electrical to optical power?


4- Consider a plastic fiber having a loss of 50dB/km. The power budget for the system allows a max 24 dB of fiber loss. Compute the maximum length of fiber permitted

5- Compute the frequencies at the edges of the visible spectrum. Also compute the bandwidth of the visible spectrum (that is, the difference between the highest and lowest visible frequencies).

6- Why do system designers choose 1550nm as the wave length of operation for transoceanic optical fiber telecommunications and 1300 nm as the wavelength of operation when designing LAN fiber optic systems? i.e. what is the main advantage of operating at each of those wavelengths?

7- Two people are talking over a glass-fiber transmission line. It takes 10s for a message to travel between the speakers. How long is the fiber?


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Explanation / Answer

1- Two 1-km fibers are spliced together. Each fiber has a 3-dB loss, and the splice adds 2 dB of loss. If the power entering is 2 mW, then how much power is delivered to the end of this combined transmission line? When Two 1km fibre are spliced together, we get a 2km long fibre. Each Fibre has a 3db loss per km. As two fibres are joined, there is one splice. Link Loss L = [fiber length (km) x fiber attenuation per km] + [splice loss x # of splices] + [connector loss x # of connectors] + [safety margin] ie Link Loss L = (2km*3db/km) + (2db*1) = 8db Also we know that Input power = 2mW = 3dBm So Output Power = Input Power - Loss = 3dBm - 8db = -5dBm SO OutPut Power = -5dBm = 0.31mW ........Ans When the output power is less than the input power, the value of this equation will always be negative. In most fiber optic applications, light power output from an optical fiber will always be less than the input light power into the optical fiber. Therefore, this value will always be negative. This negative gain can be referred to as a light loss, L(dB) above. 3- When an LED has 2 V applied to its terminals, it draws 100 mA and produces 2 mW of optical power. What is the LED's conversion efficiency from electrical to optical power? Conversion efficiency = (optical output power / electrical input power) x 100% electrical input power = Current * Voltage = [100*10^(-3)]*[2] =200mW SO COnversion efficiency % = 2mW/200mW = 1%.....Ans 4- Consider a plastic fiber having a loss of 50dB/km. The power budget for the system allows a max 24 dB of fiber loss. Compute the maximum length of fiber permitted Fibre Length = ( [Optical budget] – [link loss] ) / [fiber loss/km] ie Fibre length = (24-0)/50 = 0.48Km So Max legth of Fibre permitted is 0.48Km ......Ans

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