McqMate
| 401. |
Determine the internal quantum efficiency generated within a device when it has a radiative recombination lifetime of 80 ns and total carrier recombination lifetime of 40 ns. |
| A. | 20 % |
| B. | 80 % |
| C. | 30 % |
| D. | 40 % |
| Answer» B. 80 % | |
| 402. |
Compute power internally generated within a double-heterojunction LED if it has internal quantum efficiency of 64.5 % and drive current of 40 mA with a peak emission wavelength of 0.82 μm. |
| A. | 0.09 |
| B. | 0.039 |
| C. | 0.04 |
| D. | 0.06 |
| Answer» B. 0.039 | |
| 403. |
The Lambertian intensity distribution __________ the external power efficiency by some percent. |
| A. | reduces |
| B. | does not affects |
| C. | increases |
| D. | have a negligible effect |
| Answer» A. reduces | |
| 404. |
A planar LED fabricated from GaAs has a refractive index of 2.5. Compute the optical power emitted when transmission factor is 0.68. |
| A. | 3.4 % |
| B. | 1.23 % |
| C. | 2.72 % |
| D. | 3.62 % |
| Answer» C. 2.72 % | |
| 405. |
A planar LED is fabricated from GaAs is having a optical power emitted is 0.018% of optical power generated internally which is 0.018% of optical power generated internally which is 0.6 P. Determine external power efficiency. |
| A. | 0.18% |
| B. | 0.32% |
| C. | 0.65% |
| D. | 0.9% |
| Answer» D. 0.9% | |
| 406. |
For a GaAs LED, the coupling efficiency is 0.05. Compute the optical loss in decibels. |
| A. | 12.3 db |
| B. | 14 db |
| C. | 13.01 db |
| D. | 14.6 db |
| Answer» C. 13.01 db | |
| 407. |
In a GaAs LED, compute the loss relative to internally generated optical power in the fiber when there is small air gap between LED and fiber core. (Fiber coupled = 5.5 * 10-4Pint) |
| A. | 34 db |
| B. | 32.59 db |
| C. | 42 db |
| D. | 33.1 db |
| Answer» B. 32.59 db | |
| 408. |
Determine coupling efficiency into the fiber when GaAs LED is in close proximity to fiber core having numerical aperture of 0.3 |
| A. | 0.9 |
| B. | 0.3 |
| C. | 0.6 |
| D. | 0.12 |
| Answer» A. 0.9 | |
| 409. |
If a particular optical power is coupled from an incoherent LED into a low-NA fiber, the device must exhibit very high radiance . State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 410. |
The amount of radiance in planer type of LED structures is |
| A. | low |
| B. | high |
| C. | zero |
| D. | negligible |
| Answer» A. low | |
| 411. |
In optical fiber communication, ______________ major types of LED structures are used |
| A. | 2 |
| B. | 4 |
| C. | 6 |
| D. | 3 |
| Answer» C. 6 | |
| 412. |
As compared to planar LED structure, Dome LEDs have ______________ External power efficiency, ____________ effective emission area and _____________ radiance. |
| A. | greater, lesser, reduced |
| B. | higher, greater, reduced |
| C. | higher, lesser, increased |
| D. | greater, greater, increased |
| Answer» B. higher, greater, reduced | |
| 413. |
The techniques by Burros and Dawson in reference to ho*mo structure device is to use an etched well in GaAs structure. Determine the given statement is True or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 414. |
In surface emitter LEDs, more advantage can be obtained by using |
| A. | bh structures |
| B. | qc structures |
| C. | dh structures |
| D. | gain-guided structure |
| Answer» C. dh structures | |
| 415. |
Internal absorption in DH surface emitter Burros type LEDs is |
| A. | cannot be determined |
| B. | negligible |
| C. | high |
| D. | very low |
| Answer» D. very low | |
| 416. |
DH surface emitter generally give |
| A. | more coupled optical power |
| B. | less coupled optical power |
| C. | low current densities |
| D. | low radiance emission into-fiber |
| Answer» A. more coupled optical power | |
| 417. |
A DH surface emitter LED has an emission area diameter of 60μm. Determine emission area of source |
| A. | 1.534*10-6 |
| B. | 5.423*10-3 |
| C. | 3.564*10-2 |
| D. | 2.826*10-9 |
| Answer» D. 2.826*10-9 | |
| 418. |
Estimate optical power coupled into fiber of DH SLED having emission area of 1.96*10-5, radiance of 40 W/rcm2, numerical aperture of 0.2 and Fresnel reflection coefficient of 0.03 at index matched fiber surface. |
| A. | 5.459*10-5 |
| B. | 1.784*10-3 |
| C. | 3.478*102 |
| D. | 9.551*10-5 |
| Answer» D. 9.551*10-5 | |
| 419. |
In a multimode fiber, much of light coupled in the fiber from an LED is |
| A. | increased |
| B. | reduced |
| C. | lost |
| D. | unaffected |
| Answer» C. lost | |
| 420. |
Determine the overall power conversion efficiency of lens coupled SLED having forward current of 20 mA and forward voltage of 2 V with 170 μWof optical power launched into multimode step index fiber. |
| A. | 1.256*10-5 |
| B. | 4.417*102 |
| C. | 4.25*10-3 |
| D. | 2.14*10-3 |
| Answer» C. 4.25*10-3 | |
| 421. |
The overall power conversion efficiency of electrical lens coupled LED is 0.8% and power applied 0.0375 V. Determine optical power launched into fiber |
| A. | 0.03 |
| B. | 0.05 |
| C. | 0.3 |
| D. | 0.01 |
| Answer» A. 0.03 | |
| 422. |
Mesa structured SLEDs are used |
| A. | to reduce radiance |
| B. | to increase radiance |
| C. | to reduce current spreading |
| D. | to increase current spreading |
| Answer» C. to reduce current spreading | |
| 423. |
The InGaAsP is emitting LEDs are realized in terms of restricted |
| A. | length strip geometry |
| B. | radiance |
| C. | current spreading |
| D. | coupled optical power |
| Answer» A. length strip geometry | |
| 424. |
The active layer of E-LED is heavily doped with |
| A. | zn |
| B. | eu |
| C. | cu |
| D. | sn |
| Answer» A. zn | |
| 425. |
Intrinsically _________________ are a very linear device. |
| A. | injection lasers |
| B. | dh lasers |
| C. | gain-guided |
| D. | leds |
| Answer» D. leds | |
| 426. |
Linearizing circuit techniques are used for LEDs. State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 427. |
The internal quantum efficiency of LEDs decreasing _______________ with ________________ temperature. |
| A. | exponentially, decreasing |
| B. | exponentially, increasing |
| C. | linearly, increasing |
| D. | linearly, decreasing |
| Answer» B. exponentially, increasing | |
| 428. |
To utilize _____________________ of SLDs at elevated temperatures, the use of thermoelectric coolers is important. |
| A. | low-internal efficiency |
| B. | high-internal efficiency |
| C. | high-power potential |
| D. | low-power potential |
| Answer» C. high-power potential | |
| 429. |
For particular materials with smaller bandgap energies operating in _____________ wavelength, the linewidth tends to ______________ |
| A. | 2.1 to 2.75 μm, increase |
| B. | 1.1 to 1.7 μm, increase |
| C. | 2.1 to 3.6 μm, decrease |
| D. | 3.5 to 6 μm, decrease |
| Answer» B. 1.1 to 1.7 μm, increase | |
| 430. |
The active layer composition must be adjusted if a particular center wavelength is desired.State whether the given statement is true or false. |
| A. | true |
| B. | false |
| Answer» A. true | |
| 431. |
In optical fiber communication, the electrical signal dropping to half its constant value due to modulated portion of optical signal corresponds to _______ |
| A. | 6 db |
| B. | 3 db |
| C. | 4 db |
| D. | 5 db |
| Answer» B. 3 db | |
| 432. |
The optical 3 dB point occurs when currents ratio is equal to |
| A. | ⅝ |
| B. | ⅔ |
| C. | ½ |
| D. | ¾ |
| Answer» C. ½ | |
| 433. |
The optical bandwidth is _____________ the electrical bandwidth. |
| A. | smaller |
| B. | greater |
| C. | same as |
| D. | zero with respect to |
| Answer» B. greater | |
| 434. |
When a constant d.c. drive current is applied to device, the optical o/p power is 320 μm. Determine optical o/p power when device is modulated at frequency 30 MHz with minority carrier recombination lifetime of LED i.e. 5ns. |
| A. | 4.49*10-12 |
| B. | 6.84*10-9 |
| C. | 1.29*10-6 |
| D. | 2.29*10-4 |
| Answer» D. 2.29*10-4 | |
| 435. |
The optical power at 20 MHz is 246.2 μW. Determine dc drive current applied to device with carrier recombination lifetime for LED of 6ns. |
| A. | 3.48*10-4 |
| B. | 6.42*10-9 |
| C. | 1.48*10-3 |
| D. | 9.48*10-12 |
| Answer» A. 3.48*10-4 | |
| 436. |
Determine the 3 dB electrical bandwidth at 3 dB optical bandwidth Bopt of 56.2 MHz. |
| A. | 50.14 |
| B. | 28.1 |
| C. | 47.6 |
| D. | 61.96 |
| Answer» B. 28.1 | |
| 437. |
The 3 dB electrical bandwidth B is 42 MHz. Determine 3dB optical bandwidth Bopt: |
| A. | 45.18 |
| B. | 59.39 |
| C. | 78.17 |
| D. | 94.14 |
| Answer» B. 59.39 | |
| 438. |
Determine degradation rate βrif constant junction temperature is 17 degree celsius. |
| A. | 7.79*10-11 |
| B. | 7.91*10-11 |
| C. | 6.86*10-11 |
| D. | 5.86*10-11 |
| Answer» A. 7.79*10-11 | |
| 439. |
Determine CW operating lifetime for LED with βrt = -0.58 and degradation rate βr= 7.86*10-11 h-1. |
| A. | 32.12 |
| B. | 42 |
| C. | 22.72 |
| D. | 23.223 |
| Answer» C. 22.72 | |
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