McqMate
| 301. |
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. |
| A. | 0.61 |
| B. | 0.12 |
| C. | 0.32 |
| D. | 0.48 |
| Answer» C. 0.32 | |
| 302. |
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. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 303. |
How many types of hetero-junctions are available? |
| A. | two |
| B. | one |
| C. | three |
| D. | four |
| Answer» A. two | |
| 304. |
The ______________ system is best developed and is used for fabricating both lasers and LEDs for the shorter wavelength region. |
| A. | inp |
| B. | gasb |
| C. | gaas/gasb |
| D. | gaas/alga as dh |
| Answer» D. gaas/alga as dh | |
| 305. |
Stimulated emission by recombination of injected carriers is encouraged in |
| A. | semiconductor injection laser |
| B. | gas laser |
| C. | chemist laser |
| D. | dye laser |
| Answer» A. semiconductor injection laser | |
| 306. |
In semiconductor injection laser, narrow line bandwidth is of the order |
| A. | 1 nm or less |
| B. | 4 nm |
| C. | 5 nm |
| D. | 3 nm |
| Answer» A. 1 nm or less | |
| 307. |
Injection laser have a high threshold current density of |
| A. | 104acm-2and more |
| B. | 102acm-2 |
| C. | 10-2acm-2 |
| D. | 10-3acm-2 |
| Answer» A. 104acm-2and more | |
| 308. |
ηT Is known as slope quantum efficiency. State true or false |
| A. | true |
| B. | false |
| Answer» B. false | |
| 309. |
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. |
| A. | 7.8 % |
| B. | 10 % |
| C. | 12 % |
| D. | 6 % |
| Answer» A. 7.8 % | |
| 310. |
In a DH laser, the sides of cavity are formed by _______________ |
| A. | cutting the edges of device |
| B. | roughening the edges of device |
| C. | softening the edges of device |
| D. | covering the sides with ceramics |
| Answer» B. roughening the edges of device | |
| 311. |
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. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 312. |
Gain guided laser structure are |
| A. | chemical laser |
| B. | gas laser |
| C. | dh injection laser |
| D. | quantum well laser |
| Answer» C. dh injection laser | |
| 313. |
Laser modes are generally separated by few |
| A. | tenths of micrometer |
| B. | tenths of nanometer |
| C. | tenths of pico-meter |
| D. | tenths of millimeter |
| Answer» B. tenths of nanometer | |
| 314. |
The spectral width of emission from the single mode device is |
| A. | smaller than broadened transition line-width |
| B. | larger than broadened transition line-width |
| C. | equal the broadened transition line-width |
| D. | cannot be determined |
| Answer» A. smaller than broadened transition line-width | |
| 315. |
Single longitudinal mode operation is obtained by |
| A. | eliminating all transverse mode |
| B. | eliminating all longitudinal modes |
| C. | increasing the length of cavity |
| D. | reducing the length of cavity |
| Answer» D. reducing the length of cavity | |
| 316. |
A correct DH structure will restrict the vertical width of waveguide region |
| A. | 0.5μm. |
| B. | 0.69 μm |
| C. | 0.65 μm |
| D. | less than 0.4 μm |
| Answer» D. less than 0.4 μm | |
| 317. |
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 |
| A. | 0.198 |
| B. | 0.283 |
| C. | 0.366 |
| D. | 0.467 |
| Answer» A. 0.198 | |
| 318. |
The strip width of injection laser is |
| A. | 12 μm |
| B. | 11.5 μm |
| C. | less than 10 μm |
| D. | 15 μm |
| Answer» C. less than 10 μm | |
| 319. |
Some refractive index variation is introduced into lateral structure of laser. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 320. |
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. |
| A. | gas lasers. |
| B. | gain guided lasers. |
| C. | weak index guiding lasers. |
| D. | strong index guiding lasers. |
| Answer» D. strong index guiding lasers. | |
| 321. |
In Buried hetero-junction (BH) lasers, the optical field is confined within |
| A. | transverse direction. |
| B. | lateral direction. |
| C. | outside the strip. |
| D. | both transverse and lateral direction. |
| Answer» D. both transverse and lateral direction. | |
| 322. |
A double-channel planar buried hetero-structure (DCP BH) has a planar active region, the confinement material is |
| A. | alga as |
| B. | ingaasp |
| C. | gaas |
| D. | sio2 |
| Answer» B. ingaasp | |
| 323. |
Problems resulting from parasitic capacitances can be overcome |
| A. | through regrowth of semi-insulating material. |
| B. | by using oxide material. |
| C. | by using a planar ingaasp active region. |
| D. | by using a algaas active region. |
| Answer» A. through regrowth of semi-insulating material. | |
| 324. |
Quantum well lasers are also known as |
| A. | bh lasers. |
| B. | dh lasers. |
| C. | chemical lasers. |
| D. | gain-guided lasers. |
| Answer» B. dh lasers. | |
| 325. |
Quantum well lasers are providing high inherent advantage over |
| A. | chemical lasers. |
| B. | gas lasers. |
| C. | conventional dh devices. |
| D. | bh device. |
| Answer» C. conventional dh devices. | |
| 326. |
Strip geometry of a device or laser is important. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 327. |
Better confinement of optical mode is obtained in |
| A. | multi quantum well lasers. |
| B. | single quantum well lasers. |
| C. | gain guided lasers. |
| D. | bh lasers. |
| Answer» A. multi quantum well lasers. | |
| 328. |
Multi-quantum devices have superior characteristics over |
| A. | bh lasers. |
| B. | dh lasers. |
| C. | gain guided lasers. |
| D. | single-quantum-well devices. |
| Answer» B. dh lasers. | |
| 329. |
Dot-in-well device is also known as |
| A. | dh lasers. |
| B. | bh lasers. |
| C. | qd lasers. |
| D. | gain guided lasers. |
| Answer» C. qd lasers. | |
| 330. |
A BH can have anything from a single electron to several electrons. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 331. |
QD lasers have a very low threshold current densities of range |
| A. | 0.5 to 5 a cm-2 |
| B. | 2 to 10 a cm-2 |
| C. | 10 to 30 a cm-2 |
| D. | 6 to 20 a cm-2 |
| Answer» D. 6 to 20 a cm-2 | |
| 332. |
__________________ may be improved through the use of frequency-selective feedback so that the cavity loss is different for various longitudinal modes. |
| A. | frequency selectivity |
| B. | longitudinal mode selectivity |
| C. | electrical feedback |
| D. | dissipated power |
| Answer» B. longitudinal mode selectivity | |
| 333. |
Device which apply the frequency-selective feedback technique to provide single longitudinal operation are referred to as ________________ |
| A. | dsm lasers |
| B. | nd: yag lasers |
| C. | glass fiber lasers |
| D. | qd lasers |
| Answer» A. dsm lasers | |
| 334. |
Which of the following does not provide single frequency operation? |
| A. | short cavity resonator |
| B. | dsm lasers |
| C. | coupled cavity resonator |
| D. | fabry-perot resonator |
| Answer» D. fabry-perot resonator | |
| 335. |
Conventional cleaved mirror structures are difficult to fabricate with the cavity lengths below |
| A. | 200μmand greater than 150 μm |
| B. | 100 μm and greater than 50 μm |
| C. | 50 μm |
| D. | 150 μm |
| Answer» C. 50 μm | |
| 336. |
In the given equation, corrugation period is given by lλb/2Ne. If λb is the Bragg wavelength, then what does ‘l’ stand for? |
| A. | length of cavity |
| B. | limitation index |
| C. | integer order of grating |
| D. | refractive index |
| Answer» C. integer order of grating | |
| 337. |
The first order grating (l=1) provide the strongest coupling within the device. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 338. |
The semiconductor lasers employing the distributed feedback mechanism are classified in _________________ categories |
| A. | one |
| B. | two |
| C. | three |
| D. | four |
| Answer» B. two | |
| 339. |
DBF-BH lasers exhibit low threshold currents in the range of ________________ |
| A. | 40 to 50 ma |
| B. | 21 to 30 ma |
| C. | 2 to 5 ma |
| D. | 10 to 20 ma |
| Answer» D. 10 to 20 ma | |
| 340. |
Fabry-Perot devices with BH geometries high modulation speeds than DFB-BH lasers. State whether the given statement is true or false |
| A. | true |
| B. | false |
| Answer» B. false | |
| 341. |
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 ______________ |
| A. | π/2 radians |
| B. | 2π radians |
| C. | π radians |
| D. | 3π/2 radians |
| Answer» A. π/2 radians | |
| 342. |
The narrow line-width obtained under the CW operation for quarter wavelength shifted DFB laser is ________________ |
| A. | 2 mhz |
| B. | 10 mhz |
| C. | 3 mhz |
| D. | 1 mhz |
| Answer» C. 3 mhz | |
| 343. |
Line-width narrowing is achieved in DFB lasers by a strategy referred as _______________ |
| A. | noise partition |
| B. | grating |
| C. | tuning |
| D. | bragg wavelength detuning |
| Answer» D. bragg wavelength detuning | |
| 344. |
_________________ is a technique used to render the non-conducting material around the active cavity by producing permanent defects in the implanted area |
| A. | dispersion |
| B. | ion de-plantation |
| C. | ion implantation |
| D. | attenuation |
| Answer» C. ion implantation | |
| 345. |
The threshold temperature coefficient for InGaAsP devices is in the range of |
| A. | 10-40 k |
| B. | 40-75 k |
| C. | 120-190 k |
| D. | 150-190 k |
| Answer» B. 40-75 k | |
| 346. |
The process where the energy released during the recombination of an electron-hole event getting transferred to another carrier is known as |
| A. | inter-valence bond absorption |
| B. | auger recombination |
| C. | carrier leakage effects |
| D. | exothermic actions |
| Answer» B. auger recombination | |
| 347. |
Auger recombination can be reduced by using |
| A. | strained mqw structure. |
| B. | strained sqw structure. |
| C. | gain-guided strained structure. |
| D. | strained quantum dots lasers. |
| Answer» A. strained mqw structure. | |
| 348. |
High strain in strained MCQ structure should be incorporated. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 349. |
The parameter that prevents carrier from recombination is |
| A. | auger recombination |
| B. | inter-valence band absorption |
| C. | carrier leakage |
| D. | low temperature sensitivity |
| Answer» C. carrier leakage | |
| 350. |
Determine the threshold current density for an AlGaAs injection laser with T0=180k at 30°C. |
| A. | 6.24 |
| B. | 9.06 |
| C. | 3.08 |
| D. | 5.09 |
| Answer» D. 5.09 | |
| 351. |
The phenomenon occurring when the electron and photon population within the structure comes into equilibrium is known as |
| A. | auger recombination |
| B. | inter-valence band absorption |
| C. | carrier leakage |
| D. | relaxation oscillations |
| Answer» D. relaxation oscillations | |
| 352. |
When a current pulse reaches a laser having parasitic capacitance after the initial delay time, that pulse will |
| A. | have no effect |
| B. | will get vanished |
| C. | becomes narrower |
| D. | gets broader |
| Answer» D. gets broader | |
| 353. |
Reducing delay time and ____________ are of high importance for lasers. |
| A. | auger recombination |
| B. | inter-valence band absorption |
| C. | carrier leakage effects |
| D. | relaxation oscillations |
| Answer» D. relaxation oscillations | |
| 354. |
Dynamic line-width broadening under the direct modulation of injection current is known as |
| A. | auger recombination |
| B. | inter-valence band absorption |
| C. | carrier leakage effects |
| D. | frequency chirping |
| Answer» D. frequency chirping | |
| 355. |
A particular characteristic or parameter that occurs during analog transmission of injection lasers is |
| A. | noise |
| B. | mode hopping |
| C. | carrier leakage effects |
| D. | frequency chirping |
| Answer» A. noise | |
| 356. |
Intensity of output from semiconductor injection lasers leading to optical intensity noise is due to |
| A. | fluctuations in amplitude |
| B. | mode hopping |
| C. | carrier leakage effects |
| D. | frequency chirping |
| Answer» A. fluctuations in amplitude | |
| 357. |
In multimode lasers the optical feedback from unnecessary external reflections affecting stability of frequency and intensity is |
| A. | remains unaffected |
| B. | increased gradually |
| C. | reduced |
| D. | gets totally vanished |
| Answer» C. reduced | |
| 358. |
Reduction in the number of modes in multimode fiber increases the mode partition noise. State whether the given statement is true or false. |
| A. | false |
| B. | true |
| Answer» A. false | |
| 359. |
The behavior of laser occurring when current is increased above threshold particularly is |
| A. | mode hopping |
| B. | auger recombination |
| C. | frequency chirping |
| D. | noise |
| Answer» A. mode hopping | |
| 360. |
____________________ lasers are presently the major laser source for optical fiber communications |
| A. | semiconductor |
| B. | non-semiconductor |
| C. | injection |
| D. | solid-state |
| Answer» C. injection | |
| 361. |
Which of the following is not a property of Nd: YAG laser that enables its use as an optical fiber communication source? |
| A. | single mode operation |
| B. | narrow line-width |
| C. | long lifetime |
| D. | semiconductors and integrated circuits |
| Answer» D. semiconductors and integrated circuits | |
| 362. |
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. |
| A. | true |
| B. | false |
| Answer» B. false | |
| 363. |
Which of the following co-dopant is not employed by neodymium and erbium doped silica fiber lasers? |
| A. | phosphorus pent oxide |
| B. | germania |
| C. | nitrogen |
| D. | alumina |
| Answer» C. nitrogen | |
| 364. |
_______________ fibers include addition of lead fluoride to the core glass in order to raise the relative refractive index. |
| A. | solid-state |
| B. | gaas |
| C. | semiconductor |
| D. | zblanp |
| Answer» D. zblanp | |
| 365. |
In Fabry-perot laser, the lower threshold is obtained by |
| A. | increasing the refractive index |
| B. | decreasing the refractive index |
| C. | reducing the slope efficiency |
| D. | increasing the slope efficiency |
| Answer» C. reducing the slope efficiency | |
| 366. |
Y3Al5 O12 Is a molecular formula for _____________ |
| A. | ytterbium aluminate |
| B. | yttrium oxide |
| C. | ytterbium oxy-aluminate |
| D. | yttrium-aluminum garnet |
| Answer» D. yttrium-aluminum garnet | |
| 367. |
Which of these factors are critical in affecting the system performance in the case of coherent optical fiber transmission? |
| A. | laser line-width and stability |
| B. | refractive index and index difference |
| C. | core cladding diameter |
| D. | frequency |
| Answer» A. laser line-width and stability | |
| 368. |
_______________ occurs as a result of the change in lasing frequency with gain |
| A. | frequency multiplication |
| B. | dispersion |
| C. | attenuation |
| D. | line-width broadening |
| Answer» D. line-width broadening | |
| 369. |
Laser cavity length can be extended by |
| A. | increasing the refractive index |
| B. | reducing frequency |
| C. | introduction of external feedback |
| D. | using grin-rod lenses |
| Answer» C. introduction of external feedback | |
| 370. |
What is the purpose of wavelength dispersive element is LEC lasers? |
| A. | wavelength selectivity |
| B. | reduction of line-width |
| C. | frequency multiplication |
| D. | avalanche multiplication |
| Answer» A. wavelength selectivity | |
| 371. |
An effective method to reduce the line-width is to make the cavity longer. State whether the following statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 372. |
Which devices are used to modulate the external cavity in order to achieve the higher switching speeds? |
| A. | electromagnetic |
| B. | acousto-optic |
| C. | dispersive |
| D. | lead |
| Answer» B. acousto-optic | |
| 373. |
How many techniques are used to tune monolithic integrated devices (lasers)? |
| A. | five |
| B. | one |
| C. | two |
| D. | three |
| Answer» C. two | |
| 374. |
_________________ 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 |
| Answer» B. gcsr | |
| 375. |
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 |
| Answer» A. 0.1 to 1 nm | |
| 376. |
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 |
| Answer» A. less than 1 mhz | |
| 377. |
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 |
| Answer» C. more than 100 nm | |
| 378. |
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 |
| Answer» D. bragg wavelength control | |
| 379. |
How many sections are included in a sampling grating distributed Bragg-reflector laser (SG-DBR)? |
| A. | four |
| B. | five |
| C. | three |
| D. | two |
| Answer» B. five | |
| 380. |
Fiber based lasers provide diffraction-limited power at higher levels than solid-state laser. State whether the given statement is true or false |
| A. | true |
| B. | false |
| Answer» A. true | |
| 381. |
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 |
| Answer» A. angle recombination and optical losses | |
| 382. |
Auger current is mostly ___________________ for material with band gap providing longer wavelength emission. |
| A. | unaffected |
| B. | lesser |
| C. | larger |
| D. | vanishes |
| Answer» C. larger | |
| 383. |
Injection lasers operating in smaller wavelengths are subjected to increased carrier losses. State whether the following statement is true or false? |
| A. | true |
| B. | false |
| Answer» B. false | |
| 384. |
Devices based on quaternary PbSnSeTe and their ternary compounds, emit at wavelength ? |
| A. | between 3-4 μm |
| B. | longer than 4 μm |
| C. | between 3.5 to 4.2 μm |
| D. | between 2 to 3 μm |
| Answer» B. longer than 4 μm | |
| 385. |
Replacing Sn with Eu, Cd or Ge in some _________________ the band gap. |
| A. | remove the band gap |
| B. | does not affect |
| C. | decreases |
| D. | increases |
| Answer» D. increases | |
| 386. |
Lasing obtained in __________ when 191 mW of pump light at a wavelength of 0.477 μm is launched into laser. |
| A. | ternary pbsnsete alloy laser |
| B. | quaternary pbsnsete alloy laser |
| C. | doped fluoro-zirconate fiber |
| D. | ternary pbeute alloy laser |
| Answer» C. doped fluoro-zirconate fiber | |
| 387. |
The thulium doped fiber laser when pumped with alexandrite laser output at 0.786 μm, the laser emits at |
| A. | 0.6 μm |
| B. | 0.8 μm |
| C. | 2.3 μm |
| D. | 1.2μm |
| Answer» C. 2.3 μm | |
| 388. |
The diode-cladding-pumped Erbium praseodymium-doped fluoride device operates at wavelength. |
| A. | around 3 μm |
| B. | 4 μm |
| C. | 2.6 μm |
| D. | 1.04 μm |
| Answer» A. around 3 μm | |
| 389. |
A technique based on inter-sub band transition is known as |
| A. | auger recombination |
| B. | frequency chirping |
| C. | inter-valence band absorption |
| D. | quantum cascading |
| Answer» D. quantum cascading | |
| 390. |
In a QC laser, a same electron can emit number of photons. State the given statement is true or false? |
| A. | true |
| B. | false |
| Answer» A. true | |
| 391. |
The phenomenon resulting in the electrons to jump from one state to another each time emitting of photon is known as : |
| A. | inter-valence band absorption |
| B. | mode hopping |
| C. | quantum cascading |
| D. | quantum confinement |
| Answer» D. quantum confinement | |
| 392. |
A QC laser is sometimes referred as: |
| A. | unipolar laser |
| B. | bipolar laser |
| C. | gain guided laser |
| D. | non semiconductor laser |
| Answer» A. unipolar laser | |
| 393. |
In QC lasers, it is possible to obtain different output signal wavelengths. This can be achieved by |
| A. | inter-valence band absorption |
| B. | mode hopping |
| C. | quantum cascading |
| D. | selecting layers of different thickness |
| Answer» D. selecting layers of different thickness | |
| 394. |
QC lasers ______________ the performance characteristics. |
| A. | have negligible effects |
| B. | does not affects |
| C. | improves |
| D. | degrades |
| Answer» C. improves | |
| 395. |
An MQW cascaded laser is more advantageous because of: |
| A. | mode hopping |
| B. | auger recombination |
| C. | control over layers of material |
| D. | properties of material |
| Answer» C. control over layers of material | |
| 396. |
The absence of _______________ in LEDs limits the internal quantum efficiency. |
| A. | proper semiconductor |
| B. | adequate power supply |
| C. | optical amplification through stimulated emission |
| D. | optical amplification through spontaneous emission |
| Answer» C. optical amplification through stimulated emission | |
| 397. |
The excess density of electrons Δnand holes Δpin an LED is |
| A. | equal |
| B. | Δpmore than Δn |
| C. | Δn more than Δp |
| D. | does not affects the led |
| Answer» A. equal | |
| 398. |
The hole concentration in extrinsic materials is _________ electron concentration. |
| A. | much greater than |
| B. | lesser than |
| C. | equal to |
| D. | negligible difference with |
| Answer» A. much greater than | |
| 399. |
In a junction diode, an equilibrium condition occurs when |
| A. | Δngreater than Δp |
| B. | Δnsmaller than Δp |
| C. | constant current flow |
| D. | optical amplification through stimulated emission |
| Answer» C. constant current flow | |
| 400. |
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. |
| A. | 41.17 ns |
| B. | 35 ns |
| C. | 40 ns |
| D. | 37.5 ns |
| Answer» A. 41.17 ns | |
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