Optical Communications, 2nd Edition

PROBLEMS

1.1 Communication engineers deal with bandwidth in terms of frequency. Physicists deal with bandwidth in terms of wavelength.

1. (a) Determine the conversion between these two bandwidths. That is, find the frequency band Δf corresponding to a given wavelength band Δλ.
2. (b) Use this result to sketch a plot of frequency band Δf in hertz versus optical wavelength bandwidth Δλ in angstroms, assuming an optical, center wavelength of λ = 1 μm.

1.2 A laser cavity produces a lightwave by sustaining an optical field between two reflecting surfaces located a distance L apart, such that the fields reinforce after each reflection.

1. (a) Derive the relation between the field wavelength produced (there may be more than one) and the cavity length.
2. (b) Relate the change in field frequency to a change in cavity length.

1.3 A laser cavity 1-m long is to provide light at wavelength λ = 0.5 μm.

1. (a) What is the nearest wavelength to 0.5 μm at which the laser can also produce light?
2. (b) What is the required wavelength bandwidth of the lasing material propagation gain to guarantee light at only 0.5 μm?

1.4 An LED emits 10 mW of power when injected with 2.5 mA of current from a 5-V bias voltage. What is the power efficiency (power out/power in) of this LED?

1.5 A laser diode has the power characteristic shown in Figure 1.8a. Write an expression for the fraction of the output average power P_o that can be linearly modulated (equal positive and negative variations) in terms of P_o, the threshold ...