PYQs Based Test - 09 : Communication and Optical Instrumentation

An angle modulated signal with carrier frequency ω${}_c$ = 2π × 10⁶ rad/s given by ϕ${}_m$ (t) = cos(ω${}_c$ t + 5 sin (1000πt) + 10 sin (2000πt)). The maximum deviation of the frequency in the angle modulated signal from that of the carrier is ___________ kHz.

Quantum efficiency of a photodiode (ratio between the number of liberated electrons and the number of incident photons) is 0.75 at 830 nm. Given Planck’s constant h = 6.624 × 10⁻³⁴ J-sec, the charge of an electron e = 1.6 × 10⁻¹⁹ C and the velocity of light in the photodiode C${}_m$ = 2 × 10⁸ m/s. For an incident optical power of 100 μW at 830 nm, the photocurrent in μA is __________.

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.

A signal x(t) has a bandwidth 2B about a carrier frequency of f${}_c$ = 2 GHz as shown in Figure (a) below. In order to demodulate this signal, it is first mixed (multiplied) with a local oscillator of frequency f${}_{LO}$ = 1.5 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 B so that the signal x(t) can be reconstructed from its samples according to the Nyquist sampling theorem is ______ MHz.

A Michelson Interferometer using a larger source of wavelength λ₀ = 500 nm, with both the mirrors (M₁ & M₂) fixed and positioned equidistant from splitter/ combiner 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. When 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 ________.