This set of Basic Optical Communications Questions and Answers focuses on “Planar Waveguides and Integrated Optical Devices”.
1. Optical fibre communications uses _______ dielectric waveguide structures for confining light.
Explanation: The use of circular dielectric waveguide structures is universally acceptable. This has been a boon for optical fibre communications.
2. __________ waveguide is formed when the film is sandwiched by layers of different refractive index.
Explanation: When the film is sandwiched between layers of same refractive index, symmetric waveguide is formed. Owing to the different refractive index, asymmetry is observed and hence asymmetric waveguide is formed.
3. When the dimensions of the guide are reduced, the number of ___________ also decreases.
a) Propagating nodes
d) Volume of photons
Explanation: The dimensions of the guide are directly proportional to the number of propagating nodes. As the dimensions are reduced, the number of propagating nodes also decreases.
4. What does hff stands for in the equation hff = h+x+x2?
a) Frequency of layer
b) Diameter of curve
c) Effective guide layer thickness
d) Space propagation
Explanation: In the above equation, h is the height, x and x2 are the evanescent field penetration depths. hff Denotes the effective guided layer thickness.
5. ___________ waveguides are plagued by high losses.
Explanation: All suitable waveguide materials are subject to limitations in the confinement. However, metal-clad waveguides are not so limited. Hence, they are plagued by high losses.
6. The planar waveguides may be fabricated from glasses and other isotropic materials such as ___________ and ______________
a) Octane and polymers
b) Carbon monoxide and diode
c) Fluorides and carbonates
d) Sulphur dioxide and polymers
Explanation: These materials are isotropic. However, their properties do not affect the fabrication of planar waveguides. Their properties cannot be controlled by external energy sources.
7. Which of the following devices are less widely used in the field of optical fibre communications?
a) Acousto-optic devices
d) Optical translators
Explanation: Acousto-optic devices are less widely used, mainly in the area of field deflection. Regenerators, reflectors form a base for the optical fibre communications.
8. Which of the following materials have refractive index near two?
a) GA As
Explanation: Two basic groups are distinguished on the basis of the respective refractive indices near two and near three. GaAs, InP, AlSb have refractive indices near 3.
9. Passive devices are fabricated by __________ technique.
b) High density integration
c) Radio-frequency sputtering
d) Lithium implantation
Explanation: Passive devices’ fabrication comes mainly from microelectronics industry. Radio frequency sputtering is used to deposit thin films of glass onto glass substrates.
10. Strip pattern in waveguide structures is obtained through ____________
c) Depletion of holes
Explanation: Field strength is an important aspect when it comes to strip patterns in waveguide structures. The electron and laser beam lithography is used to obtain stripe pattern in waveguide structures.
11. Propagation losses in slab and strip waveguides are smaller than the single mode fibre losses.
Explanation: The losses are in the range of 0.1 to 0.3 dB/cm. In case of slab and stripe waveguides, the losses are much higher whereas in case of single-mode fibres, they are much less.
12. A passive Y-junction beam splitter is fabricated from __________
Explanation: A passive Y-junction splitter is used to combine signals from separate sources or to divide a signal into two or more channels. It is fabricated from the waveguide materials such as LiNbO3.
13. A passive Y-junction beam splitter is also used as a switch.
Explanation: A passive junction beam splitter finds application where equal power division of the incident beam is required. It can be used as a switch if it is fabricated from an electro-optic material.
14. The linear variation of refractive index with the electric field is known as the ________
a) Linear implantation
c) Koppel effect
d) Pockels effect
Explanation: The change in refractive index is related by the applied field via the linear and quadratic electro-optic coefficients. The variation of R.I with the electric field is known as Pockels effect.
15. Planar waveguides are used to produce _______ coupler.
Explanation: MMI couplers are abbreviated as Multimode interference couplers. These are similar to fused fibre couplers. These are easily produced by using planar waveguides.
Sanfoundry Global Education & Learning Series – Optical Communications.
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