1. A GaAs injection laser with an optical cavity has refractive index of 3.6. Calculate the reflectivity for normal incidence of the plane wave on the GaAs-air interface.
Correct : C. 0.32
2. A ho*mo-junction is an interface between two adjoining single-crystal semiconductors with different band-gap energies. State whether the given statement is true or false.
Correct : B. false
3. How many types of hetero-junctions are available?
Correct : A. two
4. The ______________ system is best developed and is used for fabricating both lasers and LEDs for the shorter wavelength region.
Correct : D. gaas/alga as dh
5. Stimulated emission by recombination of injected carriers is encouraged in
Correct : A. semiconductor injection laser
6. In semiconductor injection laser, narrow line bandwidth is of the order
Correct : A. 1 nm or less
7. Injection laser have a high threshold current density of
Correct : A. 104acm-2and more
8. ηT Is known as slope quantum efficiency. State true or false
Correct : B. false
9. The total efficiency of an injection laser with GaAs active region is 12%. The applied voltage is 3.6 V and band gap energy for GaAs is 2.34 eV. Determine external power efficiency.
Correct : A. 7.8 %
10. In a DH laser, the sides of cavity are formed by _______________
Correct : B. roughening the edges of device
11. A particular laser structure is designed so that the active region extends the edges of devices. State whether the following statement is true or false.
Correct : A. true
12. Gain guided laser structure are
Correct : C. dh injection laser
13. Laser modes are generally separated by few
Correct : B. tenths of nanometer
14. The spectral width of emission from the single mode device is
Correct : A. smaller than broadened transition line-width
15. Single longitudinal mode operation is obtained by
Correct : D. reducing the length of cavity
16. A correct DH structure will restrict the vertical width of waveguide region
Correct : D. less than 0.4 μm
17. The external power efficiency of an injection laser with a GaAs is 13% having band gap energy of 1.64 eV. Determine external power efficiency
Correct : A. 0.198
18. The strip width of injection laser is
Correct : C. less than 10 μm
19. Some refractive index variation is introduced into lateral structure of laser. State whether the given statement is true or false.
Correct : A. true
20. Buried hetero-junction (BH) device is a type of _____________ laser where the active volume is buried in a material of wider band-gap and lower refractive index.
Correct : D. strong index guiding lasers.
21. In Buried hetero-junction (BH) lasers, the optical field is confined within
Correct : D. both transverse and lateral direction.
22. A double-channel planar buried hetero-structure (DCP BH) has a planar active region, the confinement material is
Correct : B. ingaasp
23. Problems resulting from parasitic capacitances can be overcome
Correct : A. through regrowth of semi-insulating material.
24. Quantum well lasers are also known as
Correct : B. dh lasers.
25. Quantum well lasers are providing high inherent advantage over
Correct : C. conventional dh devices.
26. Strip geometry of a device or laser is important. State whether the given statement is true or false.
Correct : A. true
27. Better confinement of optical mode is obtained in
Correct : A. multi quantum well lasers.
28. Multi-quantum devices have superior characteristics over
Correct : B. dh lasers.
29. Dot-in-well device is also known as
Correct : C. qd lasers.
30. A BH can have anything from a single electron to several electrons. State whether the given statement is true or false.
Correct : B. false
31. QD lasers have a very low threshold current densities of range
Correct : D. 6 to 20 a cm-2
32. __________________ may be improved through the use of frequency-selective feedback so that the cavity loss is different for various longitudinal modes.
Correct : B. longitudinal mode selectivity
33. Device which apply the frequency-selective feedback technique to provide single longitudinal operation are referred to as ________________
Correct : A. dsm lasers
34. Which of the following does not provide single frequency operation?
Correct : D. fabry-perot resonator
35. Conventional cleaved mirror structures are difficult to fabricate with the cavity lengths below
Correct : C. 50 μm
36. In the given equation, corrugation period is given by lλb/2Ne. If λb is the Bragg wavelength, then what does ‘l’ stand for?
Correct : C. integer order of grating
37. The first order grating (l=1) provide the strongest coupling within the device. State whether the given statement is true or false.
Correct : A. true
38. The semiconductor lasers employing the distributed feedback mechanism are classified in _________________ categories
Correct : B. two
39. DBF-BH lasers exhibit low threshold currents in the range of ________________
Correct : D. 10 to 20 ma
40. Fabry-Perot devices with BH geometries high modulation speeds than DFB-BH lasers. State whether the given statement is true or false
Correct : B. false
41. The InGaAsP/InP double channel planar DFB-BH laser with a quarter wavelength shifted first order grating provides a single frequency operation and incorporates a phase shift of ______________
Correct : A. π/2 radians
42. The narrow line-width obtained under the CW operation for quarter wavelength shifted DFB laser is ________________
Correct : C. 3 mhz
43. Line-width narrowing is achieved in DFB lasers by a strategy referred as _______________
Correct : D. bragg wavelength detuning
44. _________________ is a technique used to render the non-conducting material around the active cavity by producing permanent defects in the implanted area
Correct : C. ion implantation
45. The threshold temperature coefficient for InGaAsP devices is in the range of
Correct : B. 40-75 k
46. The process where the energy released during the recombination of an electron-hole event getting transferred to another carrier is known as
Correct : B. auger recombination
47. Auger recombination can be reduced by using
Correct : A. strained mqw structure.
48. High strain in strained MCQ structure should be incorporated. State whether the given statement is true or false.
Correct : B. false
49. The parameter that prevents carrier from recombination is
Correct : C. carrier leakage
50. Determine the threshold current density for an AlGaAs injection laser with T0=180k at 30°C.
Correct : D. 5.09
51. The phenomenon occurring when the electron and photon population within the structure comes into equilibrium is known as
Correct : D. relaxation oscillations
52. When a current pulse reaches a laser having parasitic capacitance after the initial delay time, that pulse will
Correct : D. gets broader
53. Reducing delay time and ____________ are of high importance for lasers.
Correct : D. relaxation oscillations
54. Dynamic line-width broadening under the direct modulation of injection current is known as
Correct : D. frequency chirping
55. A particular characteristic or parameter that occurs during analog transmission of injection lasers is
Correct : A. noise
56. Intensity of output from semiconductor injection lasers leading to optical intensity noise is due to
Correct : A. fluctuations in amplitude
57. In multimode lasers the optical feedback from unnecessary external reflections affecting stability of frequency and intensity is
Correct : C. reduced
58. Reduction in the number of modes in multimode fiber increases the mode partition noise. State whether the given statement is true or false.
Correct : A. false
59. The behavior of laser occurring when current is increased above threshold particularly is
Correct : A. mode hopping
60. ____________________ lasers are presently the major laser source for optical fiber communications
Correct : C. injection
61. Which of the following is not a property of Nd: YAG laser that enables its use as an optical fiber communication source?
Correct : D. semiconductors and integrated circuits
62. In a three level system, the threshold power decreases inversely with the length of the fiber gain medium. State whether the given statement is true or false.
Correct : B. false
63. Which of the following co-dopant is not employed by neodymium and erbium doped silica fiber lasers?
Correct : C. nitrogen
64. _______________ fibers include addition of lead fluoride to the core glass in order to raise the relative refractive index.
Correct : D. zblanp
65. In Fabry-perot laser, the lower threshold is obtained by
Correct : C. reducing the slope efficiency
66. Y3Al5 O12 Is a molecular formula for _____________
Correct : D. yttrium-aluminum garnet
67. Which of these factors are critical in affecting the system performance in the case of coherent optical fiber transmission?
Correct : A. laser line-width and stability
68. _______________ occurs as a result of the change in lasing frequency with gain
Correct : D. line-width broadening
69. Laser cavity length can be extended by
Correct : C. introduction of external feedback
70. What is the purpose of wavelength dispersive element is LEC lasers?
Correct : A. wavelength selectivity
71. An effective method to reduce the line-width is to make the cavity longer. State whether the following statement is true or false.
Correct : A. true
72. Which devices are used to modulate the external cavity in order to achieve the higher switching speeds?
Correct : B. acousto-optic
73. How many techniques are used to tune monolithic integrated devices (lasers)?
Correct : C. two
74. _________________ laser can be produced when a coupler section is introduced between the amplifier and phase sections of a structure
Correct : B. gcsr
75. The rare-earth-doped fiber lasers have spectral line-width in the range of _________________
Correct : A. 0.1 to 1 nm
76. The lasing line-width of Fox-smith resonator is ____________________
Correct : A. less than 1 mhz
77. What is the widest tuning range obtained in optical fiber laser structure?
Correct : C. more than 100 nm
78. The mechanism which results from a refractive index change in the passive waveguide layer is called as
Correct : D. bragg wavelength control
79. How many sections are included in a sampling grating distributed Bragg-reflector laser (SG-DBR)?
Correct : B. five
80. Fiber based lasers provide diffraction-limited power at higher levels than solid-state laser. State whether the given statement is true or false
Correct : A. true
81. The parameters having a major role in determining threshold current of efficiency of injection laser are:
Correct : A. angle recombination and optical losses
82. Auger current is mostly ___________________ for material with band gap providing longer wavelength emission.
Correct : C. larger
83. Injection lasers operating in smaller wavelengths are subjected to increased carrier losses. State whether the following statement is true or false?
Correct : B. false
84. Devices based on quaternary PbSnSeTe and their ternary compounds, emit at wavelength ?
Correct : B. longer than 4 μm
85. Replacing Sn with Eu, Cd or Ge in some _________________ the band gap.
Correct : D. increases
86. Lasing obtained in __________ when 191 mW of pump light at a wavelength of 0.477 μm is launched into laser.
Correct : C. doped fluoro-zirconate fiber
87. The thulium doped fiber laser when pumped with alexandrite laser output at 0.786 μm, the laser emits at
Correct : C. 2.3 μm
88. The diode-cladding-pumped Erbium praseodymium-doped fluoride device operates at wavelength.
Correct : A. around 3 μm
89. A technique based on inter-sub band transition is known as
Correct : D. quantum cascading
90. In a QC laser, a same electron can emit number of photons. State the given statement is true or false?
Correct : A. true
91. The phenomenon resulting in the electrons to jump from one state to another each time emitting of photon is known as :
Correct : D. quantum confinement
92. A QC laser is sometimes referred as:
Correct : A. unipolar laser
93. In QC lasers, it is possible to obtain different output signal wavelengths. This can be achieved by
Correct : D. selecting layers of different thickness
94. QC lasers ______________ the performance characteristics.
Correct : C. improves
95. An MQW cascaded laser is more advantageous because of:
Correct : C. control over layers of material
96. The absence of _______________ in LEDs limits the internal quantum efficiency.
Correct : C. optical amplification through stimulated emission
97. The excess density of electrons Δnand holes Δpin an LED is
Correct : A. equal
98. The hole concentration in extrinsic materials is _________ electron concentration.
Correct : A. much greater than
99. In a junction diode, an equilibrium condition occurs when
Correct : C. constant current flow
100. Determine the total carrier recombination lifetime of a double heterojunction LED where the radioactive and nonradioactive recombination lifetime of minority carriers in active region are 70 ns and 100 ns respectively.