Faculty of Engineering & Technology, Multimedia University
ETM 4106 Optoelectronics and optical communication
Tutorial 1
Solve the following problems:
Q.1 An amplifier has a higher output power of 6mW compared to its input power, which is 2mW.
Determine the power gain of the amplifier.
Ans. +4.77dB
Q.2. Alight source for a fibre optic system has an output power of -14dBm. Express this power in watts.
Ans. 39.8W
Q.3 What is the output power, in watts, for the circuit shown in the figure below?
Ans. 0.58W
Loss = 0.2dB
Input power = -12dBm
Length = 8.2km
Loss = 2.4dB/km
Output
Length = 150m
Loss = 3.0dB/km
Q.4 A silica fibre with has a core refractive index of 1.50 and a cladding refractive index of 1.47.
Determine:
(i)
the critical angle at the core-cladding interface
(ii)
the NA for the fibre
(iii)
the acceptance angle in air for the fibre.
Ans. (i) 78.5o, (ii) 0.30 , (iii) 17.4o
Q.5 A typical relative refractive index difference for an optical fiber is 1.3% and its core index is given as
1.46. Determine the NA and critical angle at the core-cladding interface within the fiber.
Ans. 0.24, 80.80
Q.6 An optical fiber has a numerical aperture of 0.20 and a cladding refractive index of 1.59. Determine:
(ii) the acceptance angle for the fiber in water. The refractive index of water is 1.33.
(ii) the critical angle at the core-cladding interface.
Ans. (i) 8.60 (ii) 83.60
Q.7 The velocity of light in the core of a step-index fiber is 2.01  108 m/ s and the critical angle at the
core cladding interface is 800 . Determine the numerical aperture and the acceptance angle for the
fiber in air, assuming it has a core diameter suitable for consideration by ray analysis. The velocity of
light in air is 2.998  108 m/ s.
Ans. 0.263, 15.20 .
Q.8 A step index fiber with a large core diameter compared with the wavelength of the transmitted light has
an acceptance angle in air of 220 and a relative refractive index difference of 3%. Estimate the
numerical aperture and the critical angle at the core-cladding interface for the fiber.
Ans. 0.243, 75.930 .
Dr. Andy L. Y. Low