1. 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
Explanation: Phenomenon occurring when the electron and photon population within the structure comes into equilibrium is known as Relaxation oscillations. The application of a current state to device resulting in a switch delay which is followed by high frequency damped oscillations
2. 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
Explanation: The pulse will be broadened when it will reach a laser with parasitic capacitance after initial time delay. This is because when a current pulse reaches the laser, the parasitic capacitance of laser provides a source of current over the period when there is high photon density. As electron density is repetitively built up and reduced quickly, there will be several pulses at laser output as photon density will be high resulting in relaxation oscillations.
3. 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
Explanation: For lasers generally a switch-on delay time may last for 0.5ns and relaxation oscillations behind twice that period. This behavior can produce serious deterioration in shape of laser pulse at a data rate of 100Mbits. So time delay and Relaxation oscillations are highly desirable for lasers
4. 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
Explanation: Frequency Chirping is a phenomenon which is due to Dynamic line-width broadening under direct modulation of a single longitudinal mode. Semiconductor laser cause a dynamic shifting of peak wavelength emitted from device. Strong coupling between the free carrier density and refractive index of device present in semiconductor structure results in gain-induced variations which also causes Frequency Chirping.
5. 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
Explanation: During analog transmission, noise behavior of device is main thing that affects the operation of injection laser. This noise may be due to instabilities in kinks in light output versus current characteristics, reflection of light back to device and mode partition noise
6. 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
Explanation: Fluctuations in the laser output or intensity of laser output leads to optical intensity noise. These fluctuations are generally caused by temperature variations and spontaneous emission in the laser output. This randomness in fluctuations creates a noise source known as relative intensity noise (RIN).
7. 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
Explanation: The effect due to unwanted external reflections in multimode laser is reduced. This is because the reflections are spread along any fiber modes so they are weakly coupled back into laser mode.
8. Reduction in the number of modes in multimode fiber increases the mode partition noise.
a) False
b) True
Explanation: Mode partition noise is a result of laser spectral fluctuations and so a reduce in number of modes results in low pulse-width spreading thus providing low values of intermodal dispersion in the fiber. And so, the mode partition noise is decreased in multimode fiber due to reducing the number of modes.
9. The behavior of laser occurring when current is increased above threshold particularly is?
a) Mode hopping
b) Auger recombination
c) Frequency chirping
d) Noise
Explanation: Mode hopping results in the hopping of modes to a higher wavelength. This mode hopping occurs in all injection lasers and is due to increase in temperature. Mode hopping is not a continuous function of drive current but occurs above 1 to 2 mA. Mode hopping alters characteristics of laser and results in kinks in characteristics of single mode device.
10. ____________________ lasers are presently the major laser source for optical fiber communications.
a) Semiconductor
b) Non-Semiconductor
c) Injection
d) Solid-state
Explanation:Injection laser coupling using discrete lasers have proved to fruitful. Such lenses provide for relaxation for an alignment tolerances normally required for fiber coupling. Certain non-semiconductor sources are making its lace in the optical fiber communication. At slowly present, injection lasers are mostly used as laser sources.