Chapter #17 Solutions - Introduction to Optics - Leno M Pedrotti, Leno S Pedrotti, Frank L Pedrotti - 3rd Edition

 

1. Given that the semiconductor germanium has a band-gap energy of 0.67 eV, find the longest wavelength that will be absorbed by a germanium photoconductor. Get solution

2. A certain photodiode generates one electron for every 10 photons of wavelength 0.9 μm incident on the detector.a. What is the quantum efficiency of this detector?b. What is the responsivity in A/W (at this wavelength) of this detector? Get solution

3. The responsivity of an InGaAs p-i-n photodiode is 0.8 A/W at a wavelength of 1.5 μm. What photocurrent is generated by this detector when an electromagnetic field of irradiance 0.1 μW and wavelength 1.5 μm is incident on the detector? Get solution

4. Due to quantum fluctuations, laser fields have an inherent uncertainty Δn in the number of photons n contained in the field. For an ideal laser field, this inherent uncertainty is given by ...where ... is the mean number of photons in the field. A signal cannot be extracted from noise unless the mean signal photon number ... exceeds the uncertainty in photon number .... This requirement gives ...Thus the minimum optical signal that can be extracted from the inherent quantum noise in an ideal laser field must contain, on average, at least one photon per detector sampling time. Use this relation to estimate the minimum detectable signal power in an ideal laser field of wavelength 1.5 μm using a detector with a detection observation time of 1 μs. Get solution

5. The noise equivalent power NEP (at a wavelength of 1.5 μm) of an InGaAs p-i-n photodiode using a detection observation time of 1 μs is about 4 × 10−11 W.a. Calculate the number of photons arriving at the detector in one observation time in an optical signal of wavelength 1.5 μm with a power equal to the noise equivalent power of the detector.b. Is the noise equivalent power for this detector a result of the intrinsic quantum fluctuations in the incident laser field? (Refer to the discussion in Problem 1.)Problem 1Due to quantum fluctuations, laser fields have an inherent uncertainty Δn in the number of photons n contained in the field. For an ideal laser field, this inherent uncertainty is given by ...where ... is the mean number of photons in the field. A signal cannot be extracted from noise unless the mean signal photon number ... exceeds the uncertainty in photon number .... This requirement gives ...Thus the minimum optical signal that can be extracted from the inherent quantum noise in an ideal laser field must contain, on average, at least one photon per detector sampling time. Use this relation to estimate the minimum detectable signal power in an ideal laser field of wavelength 1.5 μm using a detector with a detection observation time of 1 μs. Get solution

6. Discuss how a twisted nematic liquid crystal between crossed polarizers can be used as a voltage-controlled irradiance modulator. Get solution

7. Research and describe the manner in which a nematic liquid crystal placed between transparent glass sheets with parallel scratches can be used as a voltage-controlled phase modulator. Get solution

8. A thin lens is used to image an object 1 m from the lens onto a CCD array 10 cm from the lens. What must the pixel spacing on the CCD array be so that features 1 mm apart on the object can be distinguished in the CCD image? How many pixels would be in such a CCD array of dimensions 2 cm × 2 cm? Get solution

9. A photodetector has a saturation photocurrent of 10 μA and a responsivity of 100 m A/W. What is the optical saturation power for this detector? Get solution

10. Rotate a Polaroid sheet (Polaroid sunglasses will work) in front of a calculator display. Note and carefully explain your observations. Get solution


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