PYQs Based Test - 09 : Communication and Optical Instrumentation

A laser beam of 10 mm beam diameter is focused onto an optical fibre using a thin biconvex lens as shown in the figure. The refractive index of the lens is 1.5. The refractive indices of the core and cladding of the fibre are 1.55 and 1.54 respectively. The minimum value of the focal length of the lens to attain the maximum coupling to the fibre (in mm, rounded off to one decimal place) is

A signal is band-limited to 0 to 12 kHz. The signal spectrum is corrupted by additive noise which is band-limited to 10 to 12 kHz. Theoretically, the minimum rate in kilohertz at which the noisy signal must be sampled so that the UNCORRUPTED PART of the signal spectrum can be recovered, is __________kHz.

The figure shows a spot of light of uniform intensity 50 W/m² and size 10 mm × 10 mm incident at the exact center of a photo-detector, comprising two identical photo-diodes D₁ and D₂. Each diode has a sensitivity of 0.4 A/W and is operated in the photoconductive mode. If the spot of light is displaced upwards by 100 μm, the resulting difference between the photocurrents generated by D₁ and D₂ in micro amperes, is __________ μA.

A signal m(t) varies from -3.5 V to +3.5 V with an average power of 3 W. The signal is quantized using a midtread type quantizer and subsequently binary encoded. With the codeword of length 3, the signal to quantization noise ratio in dB is _______.

The signal $m\left(t\right)=\frac{\sin \left(100\pi t\right)}{100\pi t}$ is frequency modulated (FM) with an FM modulator of frequency deviation constant of 30 kHz/V. Using Carson’s rule, the approximate bandwidth of the modulated wave in kilohertz is _________.