This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Expanded Beam Connectors”.
1. What is the use of interposed optics in expanded beam connectors?
a) To achieve lateral alignment less critical than a butt-joined fiber connector
b) To make a fiber loss free
c) To make a fiber dispersive
d) For index-matching
Explanation: Expanded beam connector utilize interposed optics at the joint in order to expand the beam from transmitting fiber end before reducing it to a size compatible with the receiving fiber end. It helps to achieve lateral alignment less critical than a butt-jointed connector. Also, the longitudinal separation is critical in expanded beam connectors.
2. The expanded beam connectors use ____________ for beam expansion and reduction.
a) Square micro-lens
b) Oval micro-lens
c) Spherical micro-lens
d) Rectangular micro-lens
Explanation: Expanded beam connectors use the principle of transmission of digital data to the receiver. It uses spherical micro-lens to first expand the beam from the transmitting end and reduces the beam at the receiving end.
3. Lens-coupled expanded beam connectors exhibit average losses of _________ in case of single mode and graded index fibers.
a) 0.3 dB
b) 0.7 dB
c) 0.2 dB
d) 1.5 dB
Explanation: Lens-coupled expanded beam connectors use spherical micro-lenses. The average losses are in the range of 1dB. With the antireflection coating on the lenses, the losses are reduced to 0.7 dB in case of single mode fibers.
4. Sapphire ball lens expanded beam design is successful than spherical lens coupled design.
Explanation: Spherical lens coupled design exhibits losses in the range 0.7 dB to 1dB. Sapphire ball lens expanded beam design achieved successful single mode fiber connection with losses as low as 0.4dB.
5. The fiber is positioned at the ________ of the lens in order to obtain a collimated beam and to minimize lens-to-lens longitudinal misalignment effects.
b) Focal length
d) Exterior circumference
Explanation: The expanded beam connector also uses a molded spherical lens. A lens alignment sleeve is used to minimize the effects of angular misalignment. The fiber is positioned at the focal length of the lens to achieve losses as low as 0.7dB.
6. ___________ exhibits a parabolic refractive index profile with a maximum at the axis similar to graded index fiber.
a) Lens coupled design
b) Sapphire ball lens
c) Spherical micro-lens
d) GRIN-rod lens
Explanation: GRIN-rod lens geometry has a parabolic refractive index profile. It facilitates efficient beam expansion and collimation within expanded beam connectors. It finds its applications in fiber couplers and source-to-fiber coupling.
7. The GRIN-rod lens can produce a collimated output beam with a divergent angle αof between _____________ from a light source situated on, or near to, the opposite lens face.
a) 1 to 5 degrees
b) 9 to 16 degrees
c) 4 to 8 degrees
d) 25 to 50 degrees
Explanation: GRIN-rod lens comprises of a cylindrical glass rod typically 0.2 to 2 mm in diameter. It exhibits a parabolic refractive index profile. It facilitates efficient beam expansion and collimation with an angle in the range 1 to 5 degrees.
8. In the given equation, if r is the radial distance, n is the refractive index; what does z stands for?
dr2/dz2 = (1/n) (d n/dr)
a) Focal length
b) Distance along the optical axis
c) Axial angle
Explanation: The above equation is known as paraxial ray equation which governs the ray propagation through the GRIN-rod lens. GRIN-rod lens geometry is parabolic in nature. Thus z is the distance along the optical axis of a parabolic profile.
9. The majority of the GRIN-rod lenses have diameters in the range of ____________
a) 2 to 2.5 mm
b) 3 to 4 mm
c) 0.1 to 0.4 mm
d) 0.5 to 2 mm
Explanation: The GRIN-rod lenses performance directly depends on the radial distance. The diameters in the range of 0.5 to 2 mm may be employed with either single mode or multimode fibers. They are available with numerical apertures of 0.37, 0.46 and 0.6.
10. Which of the following factors does not cause divergence of the collimated beam from a GRIN-rod lens?
a) Lens cut length
b) Size of fiber core
c) Refractive index profile
d) Chromatic aberration
Explanation: Various factors contribute to the divergence of the collimated beam from a GRIN-rod lens. Error in lens cut length, finite size of the fiber core and chromatic aberration are the factors that cause divergence.
11. GRIN-rod lens connectors have loss characteristics that are independent of the modal power distribution in the fiber.
Explanation: GRIN-rod lens geometry is analogous to butt-jointed multimode fiber connectors. The loss characteristics of butt-jointed connectors are dependent on modal power distribution in the fiber.
Sanfoundry Global Education & Learning Series – Optical Communications.
To practice all areas of Optical Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.
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