SOLUTION: ICM2014 Optoelectronics | My Assignment Tutor

YSGOL CYFRIFIADUREG A PHEIRIANNEG ELECTRONIGSCHOOL OF COMPUTER SCIENCE AND ELECTRONIC ENGINEERINGArholiadau Diwedd Semester 1End of Semester 1 Examinations2018/2019ICM2014OptoelectronicsAmser a ganiateir: 1½ awrTime allowed: 1½ hoursCyfarwyddiadau / Instructions:Answer all questionsTotal marks 100Trowch y dudalen drosodd pan ddywedir wrthych / Please turn over when instructedICM2014 – OptoelectronicsPlease answer ALL questions (Total marks: 100).Note to invigilators: A basic calculator and one A4 sheet with formulas, notes, etc. on both sides is allowed.1. In the figure below the light from a green laser pointer is impinging upon the surface of a swimming pool.Assume the wavelength of the laser beam is 532 nm and the refractive index of the water is 1.33. Also assumethe refractive index of air is 1 and that the speed of light in vacuum/air is 3 × 108 m/s.a) Calculate the angles of the reflected and refracted beams. [4]b) What is the frequency, wavelength and propagation speed of the reflected laser beam (measured inair)? [4]c) What is the frequency, wavelength and propagation speed of the refracted laser beam (measuredunder water)? [4]d) Using the Fresnel equations, calculate the power reflection coefficient of the air/water interface atthe specified incidence angle, assuming TE polarisation (s-polarised). [6]e) What is the transmitted power coefficient? [2]2. A reflective metal diffraction grating with grating period Λg = 3 µm is illuminated by a perpendicularbeam from an infrared laser with a wavelength of λ0 = 1550 nm, as depicted below.a) How many beams are created as a result of the laser beam impinging upon the grating and whatare the corresponding angles? [7]b) Using the result of (a) draw a diagram showing the incoming, reflected and diffracted beams. [3]3. Two plane waves with complex electric fields given by:E~1 = ej(2πf0t- λ2π0 x)^z ; E~2 = ej(2πf0t- λ2π0 [ p23 x+ 1 2 y])^zare illuminating a screen placed at x = 0. Calculate the [power] interference pattern of these two beams onthe screen. [12]24. We have a photonic chip with a waveguide layout as shown below, with an unknown waveguide loss coefficient α, where Po = Pie-αL (L is the waveguide length). The objective is to calculate α using output powermeasurements of two waveguides segments with different lengths (with the assumption that the segmentshave equal loss and equal input powers). The splitter divides the input laser power into two equal portionsand directs the power into two different waveguide paths, W1 and W2, with lengths l1 and l2 measured frompoints a and b to each output, respectively. The measured optical power at outputs O1 and O2 are 10.5 and7.8 milliwatts, respectively.a) Assuming that the power in each waveguide at the beginning of paths W1 and W2 (at points a andb) is P0, write down the expression for the power at outputs O1 and O2. [4]b) Assuming the difference in path lengths l2 – l1 is 0.2 cm, what is the waveguide loss coefficient α incm-1? [8]5. An optical resonator at a free space wavelength of λ0 = 1550 nm has a resonance linewidth (full width athalf maximum) of 0.01 nm.a) Calculate the Q factor of the resonator? [3]b) Calculate the lifetime of a photon trapped in the cavity? [4]c) You are told the free spectral range of this resonator is 5 nm. What does this mean? [3]6. This question concerns the use of semiconductors for detecting light.a) Draw the circuit diagrams for a photodiode in the photoconductive and photovoltaic modes ofoperation. Indicate one practical application for each mode of operation. [6]b) We want to measure the power of three laser beams with wavelengths of 3000 nm, 1550 nm and632:8 nm. We have three separate photodetectors made of the following materials: Silicon (Eg =1.14 eV , Germanium (Eg = 0.67 eV and Lead Sulfide (Eg = 0.37 eV). Indicate the suitability ofeach photodetector for measuring the power of each of these laser beams. [9]7. We have two different semiconductor materials at our disposal. The band diagram of each semiconductoris shown below. Which semiconductor is suitable for building lasers and LEDs? Explain your reasoning. [6]/turn over38. An optically pumped laser converts the energy of an optical pump source into a coherent laser beam asshown in the schematic below. We intend build an optically pumped semiconductor laser using a narrow rodof Indium Phosphide (Eg = 1.344 eV) as the laser gain medium and we have a choice of the following lightsources for the pump source:– A Neodymium-YAG laser operating at 1064 nm.– A telecommunication laser operating at 1550 nm.– A green LED emitting at 532 nm.a) What is the emission wavelength of the generated laser beam? [3]b) Which of the three light sources listed above can be used for pumping the laser? [3]c) To build the laser we place the Indium Phosphide rod with length Lr into an optical cavity formedby two partially reflecting mirrors as shown above. Calculate the round trip gain of the cavityassuming a gain coefficient of g for the rod and reflectivities of R1 and R2 for the mirrors. [4]d) Assume the rod length Lc is 0.1 cm and the mirror power reflectivities are R1 = 0.95 and R2 =0.99. Calculate the threshold gain gth in cm-1 that is required for the onset of lasing. [5]4