# Nonlinearity Measurement of Optical Fibers

S-108.3110 Optical Communications

Laboratory exercises WDM, Fiber nonlinearity, [Simulation of FOP links] December 2009

Prelab exercises for the lab work session II

Solve the exercises before the coming to the laboratory. If any questions, don’t hesitate to contact assistants.

Tuomas Hieta / ahieta (ät) cc.hut.fi

Every student should return their own version. These exercises will be graded.

Experiment 3: Wavelength Division Multiplexing (WDM)

Q1: Are the output spectrums of LEDs and lasers different? Why? Use terminology related to this course!

Q2: How can you tune the wavelength of LED? How would you operate if your task is to increase the output of the LED for example by 6 dB, and maintain the same wavelength?

Experiment 4: Fiber nonlinearity (See material online!)

Q3: Calculate the threshold power of SBS for the standard single mode fiber used on this lab work. The length of the fiber is 7850m, effective diameter is 10μm and loss is 0,2dB/km. The polarization factor can be assumed to be 2 and the Brillouin gain coefficient 4x10-11 m/W.

Q4: Calculate the frequency shift of Brillouin scattering for 1,55μm signal in wavelength domain. What causes the phenomena? Again brief and accurate statement is enough…

HINT: use typical values from lecture slides

Experiment 5: Simulation of fiber optic links

Q5: Use equation BLDDl<1, where B is bit-rate, L is fiber length, D is dispersion, and Dl is bandwidth [nm] to calculate the dispersion limited maximum fiber length. The transmission uses 2.5 Gbit/s pulses at 1550 nm wavelength. The transform limited bandwidth of the pulses is ca. 4 GHz.

HINT: use standard D and remember to convert [GHz ~-> nm].

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