written 8.1 years ago by | • modified 8.1 years ago |
Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks
Marks: 10
Years: MAY 2015
written 8.1 years ago by | • modified 8.1 years ago |
Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks
Marks: 10
Years: MAY 2015
written 8.1 years ago by |
Fiber attenuation measurements:
⇒ It measures the relative contribution from absorption, bending, scattering losses. The total attenuation is a function of the wavelength λ of the light.
⇒ The focused light is chopped using chopper at low frequency. This chopped light is fed to monochromater which utilizes prism to select required wavelength at which attenuation is measured.
⇒ The fiber is also put into mode scrambler to remove light launched in the fiber cladding.
⇒ Cut back method means taking a set of optical output power measurements over a long length fiber and then fiber is cutback maintaining same launch conditions for next set of output.
⇒ The optical attenuation/unit length is given by:
αdB=10L1−L2∙log10P02P01
Where,L1 and L2 are original lengths and cutback lengths P01 and P02 are output power from original and cutback lengths.
Fiber dispersion measurements
⇒ Dispersion measurement gives an indication of distortion to optical signals as they propagate down the fiber.
⇒ Dispersion effect may be characterized by taking measurements of impulse response of fiber in time domain or baseband frequency response in frequency domain.
⇒ Short optical pulses are launched into the fiber from suitable source. The pulse travels down the length of fiber under test and are broadened due to various dispersion mechanisms.
⇒ The pulses are received by a high speed photodetector and displayed on a fast sampling oscilloscope.
⇒ Beam splitter triggers the oscilloscope for input pulse measurement.
⇒ After initial measurement of output pulse width, fiber is cutback and pulse width is measured again and the pulse dispersion is then by comparing the measured pulses.