Question 1: Describe the method of optical feedback to give oscillations and therefore amplification in the laser. Point out how this gives a distinctive spectral output from the device.
Question 2: Describe edge emitting and surface emitting diodes.
Question 3: With the help of schematic diagram describe the structure of Febry Parot cavity.
Question 4: Outline the general LED structures for optical fiber communication describing their relative advantages and drawbacks. In particular compare surface and edge emitting devices. Comment on the difference between multimode and single mode devices.
Question 5: A planer LED is fabricated from gallium arsenide that has a refractive index of 3.6.
a) Compute the optical power emitted into air as a percentage of internal optical power for the device when the transmission factor at the crystal-air interface is 0.68.
b) When the optical power generated internally is 50 percent of the electrical power supplied, find out the external power efficiency.
Question 6: The radiative and non-radiative recombination lifetimes of minority carriers in the active region of double hetro junction LED are 60ns and 100ns correspondingly. Find out the total carrier recombination lifetime and the power internally generated in the device when the peak emission wavelength is 0.87um at a drive current of 40mA.
Question 7: Compute the ratio of the stimulated emission rate to the spontaneous emission rate for an incandescent lamp operating at a temperature of 1000K. It might be supposed that the average operating wavelength is 0.5 micrometer.
Question 8: A ruby LASER comprises of a crystal length 4 cm with a refractive index of 1.78. The peak emission wavelength from the device is 0.55micrometer. Find out the number of longitudinal modes and their frequency separation.
Question 9: Compare the approximate radiative minority carrier lifetimes in the Gallium arsenide and Silicon if the minority carriers are electrons injected to the p-type region which consists of a hole concentration of 1018 cm-3. The injected electron density is small compared with majority carrier density.
Question 10: What do you understand by the principle of photo detector?