Instrumentation Engineering
GATE IN Communication and Optical Instrumentation PYQs
Build your understanding with focused practice from past exam papers.
Questions 21–30 of 34. Imported answers require independent review unless marked reviewed.
Question 15
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In a single-mode optical fiber, the zero-dispersion wavelength refers to the wavelength at which the
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A signal
modulates a carrier
using the double-sideband-with-carrier (DSBWC) scheme to yield a modulated signal
. The modulation index is ______. (Answer should be rounded off to one decimal place)Log in to check the answer
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A pulsed laser emits rectangular pulses of width 1 nanosecond at a repetition rate of 1 kHz. If the average power output is 1 mW, the average power over a single pulse duration, in watts, is
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 54
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A signal
has a bandwidth
about a carrier frequency of
GHz as shown in Figure (a) below. In order to demodulate this signal, it is first mixed (multiplied) with a local oscillator of frequency
GHz, and then passed through an ideal low-pass filter (LPF) with a cut-off frequency of 2.8 GHz. The output of the LPF is sent to a digitizer ADC with a sampling rate of 1.6 GHz as shown in Figure (b) below. The maximum value of
so that the signal
can be reconstructed from its samples according to the Nyquist sampling theorem is ______ MHz. 
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Consider a Michelson interferometer as shown in the figure below. When the wavelength of the laser light source is switched from 400 nanometer to 500 nanometer, it is observed that the intensity measured at the output port P goes from a minimum to a maximum. This observation is possible when the smallest path difference between the two arms of the interferometer is ____ nanometer.
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An amplitude modulated signal is shown in the figure. The modulation index is (up to one decimal place) ______.
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An optical pulse containing
photons is incident on a photodiode and
electron-hole pairs are created. The maximum possible quantum efficiency (in %) of the photodiode is ______.Log in to check the answer
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The sampling rate for Compact Discs (CDs) is 44,000 samples/s. If the samples are quantized to 256 levels and binary coded, the corresponding bit rate (in bits per second) is _____.
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A Michelson Interferometer using a laser source of wavelength λ₀ = 500 nm, with both the mirrors (M₁ & M₂) fixed and positioned equidistant from the splitter/combiner is shown in the figure. When a dielectric plate of refractive index n = 1.5, of thickness t, is placed in front of the mirror M₂, a dark fringe is observed on the detector. If the dielectric plate is removed without changing the position of the mirrors M₁ & M₂, a bright fringe is observed on the detector. The minimum thickness t (in nm) of the dielectric is _______.
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A multi-mode optical fiber with a large core diameter has a core refractive index n₁ = 1.5 and cladding refractive index n₂ = 1.4142. The maximum value of θₐ (in degrees) for which the incident light from air will be guided in the optical fiber is ±_____.
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