1. How many techniques are used to tune monolithic integrated devices (lasers)?
a) Five
b) One
c) Two
d) Three
Explanation: There are two techniques which can be employed to tune monolithic integrated devices. In the first method, the mode selectivity of a coupled cavity structure is used. Other method is used to a refractive index change in the device cavity provided by application of an electric field.
2. _________________ laser can be produced when a coupler section is introduced between the amplifier and phase sections of a structure.
a) SG-DBR
b) GCSR
c) Y 4-shifted
d) DSM
Explanation: DBR lasers are capable of wavelength tuning. Grating assisted co-directional coupler with sampled reflector (GCSR). Laser is capable of a tuning range greater than 40 nm. It consists of a co-directional coupler between the amplifier and the phase section.
3. The rare-earth-doped fiber lasers have spectral line-width in the range of _________________
a) 0.1 to 1 nm
b) 1.2 to 1.5 nm
c) 6 to 10 nm
d) 2 to 2.3 nm
Explanation: The rare-earth-doped fiber lasers have spectral line-width in the range of 0.1 to 1 nm. These line-widths are too long for high speed transmission is possible in this range.
4. The lasing line-width of Fox-smith resonator is ____________________
a) Less than 1 MHz
b) 1 MHz
c) 2 MHz
d) Greater than 3 MHz
Explanation: Fox-smith resonator employs a fused coupled fabricated from erbium-doped fiber. Narrower spectral line-width can be obtained using a resonator. It provides favorable line-widths than semiconductor laser.
5. What is the widest tuning range obtained in optical fiber laser structure?
a) 60 nm
b) 80 nm
c) More than 100 nm
d) 100 nm
Explanation: A tuning range greater than 100 nm by using an erbium-doped photonic crystal fiber. A wider tuning range greater than 100 nm is obtained at wavelength 1.55 nm.
6. How many techniques can be used to increase the injection cavity length?
a) One
b) Two
c) Three
d) Four
Explanation: Two techniques can be used to increase the injection laser cavity length. These are using laser chips and by extending a cavity with a passive medium such as air, glass etc.
7. The mechanism which results from a refractive index change in the passive waveguide layer is called as ___________
a) Absorption
b) Spontaneous emission
c) Monolithic inversion
d) Bragg wavelength control
Explanation: A wider wavelength tuning length is obtained by separating the Bragg region in the passive waveguide and by introducing a phase region within a waveguide control mechanism provides phase control. It takes place by some changes in a passive waveguide layer.
8. How many sections are included in a sampling grating distributed Bragg-reflector laser (SG-DBR)?
a) Four
b) Five
c) Three
d) Two
Explanation: In SG-DBR laser, five sections are longitudinally integrated together on a semiconductor substrate. These five sections include two diffraction Bragg grating sections, a gain, a phase and an amplifier section.
9. Fiber based lasers provide diffraction-limited power at higher levels than solid-state laser.
a) True
b) False
Explanation: In fiber lasers, the active gain medium is doped with rare earth elements. These lasers have active regions several kilometers long and thus provide high optical gain. Solid-state lasers, on the other hand, provide diffraction limited power at lower levels.
10. The parameters having a major role in determining threshold current of efficiency of injection laser are ___________
a) Angle recombination and optical losses
b) Frequency chirping
c) Relaxation oscillation
d) Mode hopping
Explanation: Optical losses due to free carrier absorption are more because of their dependence on square of the wavelength. Also irradiative recombination through Auger recombination contributes to it. Both these effects cause more problems in md-infrared wavelengths and so are of much importance art high temperature due to high concentration of free carriers. They also limit maximum operating temperatures