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EE 606: 2010-2011 Spring

Home Assignment 2Feb.24, 2011 1.

A certain optical fiber has an attenuation of 0.6 dB/km at 1310 nm and 0.3 dB/km at 1550nm. Suppose the following two optical signals are launched simultaneously into the fiber:an optical power of 150 W at 1310 nm and an optical power of 100 W at 1550 nm. What

are the power level in W of these two signals at (a) 8 km and (b) 20 km? (Ref. GerdKeiser, 4 th ed., Prob.3.2).

2.

An optical signal at a specific wavelength has lost 55 percent of its power after traversing7.0 km of fiber. What is the attenuation in dB/km of this fiber? (Ref. Gerd Keiser, 4 th ed.,Prob.3.3).

3.

A continuous 40 km-long optical fiber link has a loss of 0.4 dB/km.a) What is the minimum optical power level that must be launched into the fiber to

maintain an optical power level of 2.0 W at the receiving end?b) What is the required input power if the fiber has a loss of 0.6 dB/km?(Ref. Gerd Keiser, 4 th ed., Prob.3.4).

4.

An LED operating at 850 nm has a spectral width of 45 nm. What is the pulse spreading inns/km due to material dispersion? What is the pulse spreading when a laser diode having a2 nm spectral width is used (Ref. Gerd Keiser, 4 th ed., Prob.3.13a).

5.

A double-heterojunction InGaAsP LED emitting at a peak wavelength of 1310 nm hasradiative and nonradiative recombination times of 25 and 90 ns, respectively. The drivecurrent is 35 mA.

a)

Find the internal quantum efficiency and the internal power level.b)

If the refractive index of the light source material is n= 3.5, find the poweremitted from the device.

(Ref. Gerd Keiser, 4 th ed., Prob.4.6).

6.

(a) A GaAlAs laser diode has a 500 m cavity length which has an effective absorptioncoefficient of 10 cm -1. For uncoated facets the reflectivities are 0.32 at each end. Whatis the optical gain at the lasing threshold?

(b) If one end of the laser is coated with a dielectric reflector so that its reflectivity is now90 percent, what is the optical gain at the lasing threshold? (Ref. Gerd Keiser, 4th ed.,Prob.4.9).

(Ref. Gerd Keiser, 4 th ed., Prob.4.9). 7.

A GaAs laser emitting at 800 nm has a 400 m cavity length with a refractive index n =3.6. If the gain g exceeds the total loss t throughout the range 750 nm < < 850 nm, howmany modes will exist in the laser? (Ref. Gerd Keiser, 4 th ed., Prob.4.12).

8.

A GaAs laser operating at 850nm has a 500 m length and a refractive index of n = 3.7.What are the frequency and wavelength spacings? If, at the half-power point, ( 0) =2 nm, what is the spectral width of the gain? (Ref. Gerd Keiser, 4 th ed., Example 4.8).