This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Nano-Optics – Photonic Crystals – Set 2”.
1. It is generally easy to introduce defects in a woodpile structure.
a) True
b) False
View Answer
Explanation: Woodpile structure is one of the several three-dimensional photonic crystal structures. It is generally fabricated by etching using beam lithography. It is usually hard to introduce controlled defects in this structure during the process flow of its production. Hence, it is unsuitable for fabrication of waveguides and cavities.
2. Identify the correct statement with respect to 2D-photonic crystal slabs.
a) Slab material is assumed to have extremely low refractive index
b) Line defects act as ultra-large optical waveguides when introduced into these crystals
c) Regulation of pseudo-3D light is unfeasible
d) Confinement of light occurs in the in-plane direction
View Answer
Explanation: Two dimensional photonic crystal slabs are made up of material having high refractive index such as silicon (Si), while their lattice points are assumed to be composed of a low refractive index medium such as air. Introduction of a line defect into a 2D photonic crystal slab will make it act as an ultra-small optical waveguide. In these slabs, light confinement occurs in the in-plane direction by virtue of photonic band gap effect. Regulation of Pseudo-3D light is thus possible.
3. Pick out the odd one from the following:
a) Woodpile structure
b) Inverse opals
c) Yablonovite
d) Bragg grating
View Answer
Explanation: Woodpile structures, spheres in a diamond lattice, inverse opals or inverse colloidal crystals and Yablonovite are few three- dimensional photonic crystal structures types. Bragg grating, on the other hand, is an example of one-dimensional photonic crystal.
4. In which of the following animals photonic crystals are not present?
a) Elephants
b) Butterflies
c) Silvery fish
d) Dogs
View Answer
Explanation: Animals reflectors or mirrors are necessary for the survival of many animals. Scales of silvery fish, eyes of dogs or cats and wings of some butterflies contain photonic crystals. All these act as reflectors or structural coloration and function by the interference of light in multilayer structures with dimension less than a wavelength.
5. Who coined the term photonic crystal?
a) Lord Rayleigh
b) Melvin M.Weiner
c) Eli Yablonovitch
d) Vladimir P. Bykov
View Answer
Explanation: Photonic crystals are an interesting class of optical materials that have been studied since the 19th century. The term photonic crystals however were coined only after about 100 years by Eli Yablonovitch and Sajeev John. They first used the term, referring to 3D photonic crystals, in their journal published in 1987.
6. Choose the correct sequence of actions taken during the fabrication of inverse opals.
a) Creation of a transparent solid ➔ Dissolution of spheres in an acid ➔ Hardener is introduced ➔ Spheres are deposited in a closed cubic packed lattice
b) Hardener is introduced ➔ Spheres are deposited in a closed cubic packed lattice ➔ Dissolution of spheres in an acid ➔ Creation of a transparent solid
c) Dissolution of spheres in an acid ➔ Spheres are deposited in a closed cubic packed lattice ➔ Creation of a transparent solid ➔ Hardener is introduced
d) Spheres are deposited in a closed cubic packed lattice ➔ Hardener is introduced ➔ Creation of a transparent solid ➔ Dissolution of spheres in an acid
View Answer
Explanation: Inverse opals or Inverse Colloidal crystals fall under the category of 3D photonic crystals. They can be created by allowing the deposition of SiO2 or polystyrene spheres into a cubic closed packed lattice suspended in a solvent. This is followed by the introduction of a hardener which creates a transparent solid out of the volume occupied by the solvent. Finally, spheres are dissolved with an acid like hydrochloric acid (HCl).
7. How are three-dimensional photonic crystals fabricated?
a) Photolithography
b) Indirect laser writing
c) Hole drilling in substrate
d) Sticking layers together
View Answer
Explanation: Inorder to fabricate three dimensional photonic crystals various methods are employed. These involve direct laser writing, drilling under different angles, stacking multiple 2-D layers on top of each other, photolithography and etching techniques. To avoid use of complicated machineries commonly applied to nanotechnological methods, alternate approaches have been taken for 3D photonic crystal fabrication. This involves growing the crystals from colloidal crystals as self-assembled structures.
8. A 1-dimensional photonic crystal does not operate in which of the following regime?
a) Diffraction regime
b) Refraction regime
c) Sub-wavelength regime
d) Bragg reflection regime
View Answer
Explanation: A 1D photonic crystal generally operates in three main regimes depending on the ratio between the structure’s pitch (A) and the operating free-space wavelength (λ). The regimes are (i) diffraction regime where the incoming beam is scattered in different orders, (ii) Bragg reflection regime where the incoming beam is reflected backward, and (iii) the Sub-wavelength regime where the diffraction and reflection effects due to the periodicity of the structures are suppressed.
9. Bragg grating is an example of what kind of photonic crystals?
a) 0D
b) 1D
c) 2D
d) 3D
View Answer
Explanation: A fiber Bragg grating is a distributed Bragg reflector that is built in a short segment of optical fiber. It functions by reflecting particular wavelengths of light and transmitting all others. It is an example of a typical one dimensional photonic crystal that is often utilized as an inline optical filter.
10. What is the full form of RBME used in computing photonic band structure?
a) Results Based Monitoring and Evaluation
b) Regional Biomedical Engineer
c) Reusable Building Materials Exchange
d) Reduced Bloch Mode Expansion
View Answer
Explanation: RBME stands for Reduced Bloch Mode Expansion. It is used for fast periodic media band structure calculations. The expansion method employs a natural basis comprised of a discrete reduced set of Bloch eigen functions. This method can reduce the time for computing the band structure by almost two orders of magnitude.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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