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Dr. NAVALAR NEDUNCHEZHIYAN COLLEGE OF ENGINEERING Tholudur, Cuddalore (Dt) – 606 303. DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

QUESTION BANK Subject Code/Subject: EC1011 / OPTO ELECTRONICS DEVICES Name : K.SENTHILNATHAN

Designation : ASSISTANT PROFESSOR

Dept : ECE

Semester

: VIII

UNIT I ELEMENTS OF LIGHT AND SOLID STATE PHYSICS

Wave nature of light – Polarization – Interference – Diffraction – Light source – Review of quantum mechanical concept – Review of solid state physics – Review of semiconductor physics and semiconductor junction device. PART-A (1 Mark) 1. Intrinsic semiconductor material is characterized by a valence shell of how many electrons? A)1 B)2 C)4 D)6 2. Ionization within a P-N junction causes a layer on each side of the barrier called the: A) Junction B) depletion region C) barrier voltage D) forward voltage 3. What causes the depletion region? A) doping B) diffusion C) barrier potential D)Ions 4. Silicon atoms combine into an orderly pattern called a: A) covalent bond B) crystal C) the semiconductor D) valence orbit 5. In "n" type material, majority carriers would be: A) holes B) dopants C) slower D) electrons 6. Elements with 1, 2, or 3 valence electrons usually make excellent: A) conductors B) semiconductors C) insulators D) neutral 7. A commonly used pentavalent material is: A) arsenic B) boron C) gallium D) neon 8. Which material may also be considered a semiconductor element? A) carbon B) ceramic C) mica D) argon 9. What can a semiconductor sense? A) magnetism B) temperature C) pressure D) all of the above 10. When an electron jumps from the valence shell to the conduction band, it leaves a gap. What is this gap called? A) energy gap B) hole C) electron-hole pair D) Recombination 11. Forward bias of a silicon P-N junction will produce a barrier voltage of approximately how many volts? A) 0.2 B) 0.3 C) 0.7 D) 0.8 12. Which semiconductor material is made from coal ash? Department of ECE

Opto Electronics Devices

A) germanium ANSWER:

B) silicon

C) tin

1

2

3

4

5

6

7

8

C

B

B

B

D

A

A

A

9

D

10

B

D) Carbon 11

12

C

A

PART –B

9

D

10

B

11 12

C

A

(2 MARKS)

13.What is meant by wave function?{DEC-13] Wave function is the probability amplitude of finding the electron in an energy state of the solid.It is a complex displacement of matter wave (electron wave)and we can`t measure it 14.Define depletion layer. Deflection layer is the region in the p-n junction &it contains no free charge carriers it is existing on the both sides of a p-n junction&contains immobile ions it is called space charge layer. 15.What are density of states? MAY-11 Density of states is defined as the number of energy states per unit volume in an energy interval. It is calculate the number of charge carriers per unit volume of the solid. 16.What is meant by contact potential at the p-n junction? Contact potential barrier arising due to the maintaining of constant Fermi level throughout the p-n junction. 17. What is the source of bioelectric signals? The living tissues used as a power station generating multiple electrical signals with 2 internal sources namely muscles and nerves. 18. What are the types of electrodes? • Microelectrodes • Depth and needle electrodes • Surface electrodes. 19.what is QCSE? Quantum confined stark effect refers to the bending of potential well dueto transverse applied electric field and shifting of the absorptuion edge of exciton to lower energy side and resulting absorption of photons 20. What are the needs of the electrodes? JUNE-12 • Electrodes makes a transfer from the ionic conduction in the tissue to the electronic conduction which is necessary for making measurement. • Electrodes plays an important part in the satisfactory recording of bioelectric signals and their choice requires careful consideration. 21.Mention the important semiconductors used in laser and LED’s?NOV/DEC-13 InGaAsP-to produce wavelength from 1.3µm to 1.7µm GaAlAs-to produce wavelength from 0.8µmto 0.9µm 22.What is the effect of high rise time of drive current in LEDs? If the rise time increases, carrier life time is increased and hence radiative reambination rate is decreased . these lead to decrease of bandwidth and output power of LED. PART –B

(16 Marks)

23.Derive bragg’s law in Xray diffraction. 24.Discuss the powder methed of crystal structure analysis.[NOV/DEC-12]

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25.Describe with the help of experimental set up ,how will yow determine the nature of a semiconductoer using Hall effect. 26.Describe the crystal structure of silicon and Ga As? 27.Explain the energy values of electrons in a metal.[NOV/DEC-13] 28.How does the electrical conductivity of extrinsic semiconductors vary with temperature &impurity addition? 29.Explain the frequency response of silicon photodiodes using a suitable graph. [JUNE-12]

UNIT II DISPLAY DEVICES AND LASERS

Introduction – Photo luminescence – Cathode luminescence – Electro luminescence –Injection luminescence – Injection luminescence – LED – Plasma display – Liquid Crystal Display (LCD) – Numeric displays – Laser emission – Absorption – Radiation –Population inversion – Optical feedback – Threshold condition – Laser modes – Classes of lasers – Mode locking – Laser applications. PART-B

(1 MARK)

30.When is a P-N junction formed? A) in a depletion region B) in a large reverse biased region C) the point at which two opposite doped materials come togetherD) whenever there is a forward voltage drop 31..Electron pair bonding occurs when atoms: A) lack electrons B) share holes

C) lack holes

D) share electrons

32.How many valence electrons are in every semiconductor material? A) 1 B) 2 C) 3 D) 4 33.What is a type of doping material? A) extrinsic semiconductor material B) pentavalent material C) n-type semiconductor D) majority carriers 34.Minority carriers are many times activated by: A) heat B) pressure C) dopants 35.What is the voltage across R1 if the P-N junction is made of silicon?

D) forward bias

A) 12V B) 11.7V C) 11.3V D) 0V 36.If conductance increases as temperature increases, this is known as a: A) positive coefficient B) negative current flowC) negative coefficient D) positive resistance Department of ECE


37.Which of the following cannot actually move? A) majority carriers B) ions

C) holes

D) free electrons

38.What electrical characteristic of intrinsic semiconductor material is controlled by the addition of impurities? A) conductivity B) resistance C) power D) all of the above 39.What is a varistor? A) a voltage-dependent resistor B) a voltage-dependent diode C) a current-dependent resistor D) a current-dependent diode 40.Which type of transformer is required to create a 180 degree input to a rectifier? A) center-tapped secondary B) step-down secondary C) stepped-up secondary D) split winding primary 41.What circuit activity may shift a characteristic curve so that diode operating points are different? A) higher power (heat) B) higher resistance C) lower voltage D) lower current ANSWER: 30 C

31 D

32 D

33 B

34 A

35 C

PART-B

36 C

37 C

38 A

39 A

40 A

41 A

(2 MARKS)

42.What is LED? LED is the light emitting diode &consists of a forward biased p-n junction the recombination of electrons from conduction band with the hole in the valence band,produces emission of light .the energy difference b/w the conduction electron &bound electron in the valence band is quantum as the energy of the light photon. 43.What is a cryotron? { MAY-13] Cryotron is a switching element made from two different superconductors arranged in a manner that one superconductor in the form of a straight wire is enclosed by another superconducting coiland is based on the disappearance of superconducting state in a superconductor 44.What are liquid crystals?{ MAY-12] Liquid crystals are the intermediate phases of the crystal they have both fluid &crystalline properties. During the application of electricfield , there is a change in the orientation of liquid crystal molecules. 45.What are the advantages of liquid crystal display?[MAY-13} It is very cheap.

It irequires very small power. For 1cm2 display area if requires 1micro wave It is very thin It can be viewed under avide range of lighting conditions 46.What is meant by intrinsic absorption? Intrinsic absorption means the IRabsorption and ultraviolet absorption by fiber material(SIO2). IR asorption is due to Si-O coupling .uv absorption is due to electronic absorption bands. 47.What is meant by electro-absorption? Absorption of photons whose energy is less then the bandgap energy of a semiconductor by mens of applied electric field. 48.What are high TC superconducttors? { DEC-12] High tc superconductors are the superconductors which have higher superconducting transituion temperature (>80k) their properties cannot be explained by BCS theory. 49.Why do we require IC packages? To provide electrical contact from the chip to outside To dissipate the heat produced during service.

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To protect the chip from environmental conditions To hendle the chip easily. 50.What are the laser light properties ? 1.higher monochromacity 2.high intensity ,3.high coherence,4.high directionality. The above properties are obtained by stimulated emission. 51.What is meant by laser action? Laser action means the amplification of light by stimulated emission of radiation .to get laser action there should be population inversion and stimulated emission should take place. 52.What is meant by threshold condition for laser oscillation? There should be a minimum amount of population inversion from which laser oscillation starts. This is called threshold condition for laser oscillations there to start the laser oscillation ,the gain coefficient should exceed the threshold value. 53.What are the drawbecks of homojunction laser diodes? Threshold current is very large. The output beam has large divergence Coherence and stability are poor Optical confinement is very poor 54.Define internal quantum efficiency of a laser or LED? η=Radiative recombination rate per unit volume sum of radiative recombination rate and non radiative reambination rate per unit volume 55.What are the factors that decrease the life time of laser diode? 1.increase of temperature,2.aging,3. High current density. 56.How does the LED Work? Due to higher population of injected minority carrier there is enormous radiative recombination when there is forward bias across the active layer of LED.

PART-B

(16 marks)

57.Explain the operation of LED and derive an expression for the frequency response and bandwidth of an LED. 58.What are the major advantages of LED over LCD? { MAY-12] 59.Derive expressions for gain in a level laser medium? {DEC-12] 60.Explain the basic principle of LED? { JUNE-12] 61.Explain the transient response of LEDS? 62.Discuss the different types of hetero-S structure LEDs along with diagrams? { DEC-13]

UNIT III OPTICAL DETECTION DEVICES Photo detector – Thermal detector – Photo devices – Photo conductors – Photo diodes –Detector performance.

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PART –A

(1 MARK)

63.What is wrong with this diode?

A) open B) short C) nothing D) not enough data 64.The dc current through each diode in a bridge rectifier equals: A) the load current B) half the dc load current C) twice the dc load current D) one-fourth the dc load current 65.When matching polarity connections have been made and the potential difference (PD) is above 0.7 V, the diode is considered to be: A) not working B) forward biased C) reverse biased D) an open switch 66.In a power supply diagram, which block indicates a smooth dc output? A) transformer B) filter C) rectifier D) regulator 67.If a 169.7 V half-wave peak has an average voltage of 54 V, what is the average of two full-wave peaks? A) 119.9 V B) 108.0 V C) 115.7 V D) 339.4 V 68.What is the current through the LED?

A) 0mA B) 23 mA C) 13 mA D) 18 mA 69.Electrons in the outermost orbit or shell of an atom are called A) free electrons B) negative ions C) valence electrons D) conduction band electrons 70.Shunting the ac component away from the load is the task of a: A) transformer B) filter C) regulator D) rectifier 71.A pn junction allows current flow when A) the p-type material is more positive than the n-type material B) the n-type material is more positive than the p-type material C) both the n-type and p-type materials have the same potential D) there is no potential on the n-type or p-type materials 72..What is the current through the zener diode?

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A) 0mA B) 7mA C) 8.3 mA D) 13 Ma 73.When a diode is forward biased, the voltage across it A) is directly proportional to the current B) is inversely proportional to the current C) is directly proportional to the source voltage D) remains approximately the same 74.Why is heat produced in a diode? A) due to current passing through the diode B) due to voltage across the diode C) due to the power rating of the diode D) due to the PN junction of the diode 75.The peak inverse voltage (PIV) across a nonconducting diode in a bridge rectifier equals approximately: A) half the peak secondary voltage B) twice the peak secondary voltage C) the peak value of the secondary voltageD) four times the peak value of the secondary voltage KEY: 63 C

64 A

65 B

66 D

67 B

68 D

69 C

70 C

71 B

72 A

73 B

74 A

PART-B

75 A

( 2 MARKS)

76.What is a photodiode? A photodiode is a reverse biased diode which absorbs light &converts it into charge carriers or electric current 77.What are the properties of photodiodes? { MAY-12] Every photodiode should have low dark current , wide wavelength response &high quantum efficiency .it should have low rise time &fast response. 78.What is meant by binary digital modulation? The analog signal is sampled and binary coded in the form of “ones”and “zeros. 79.State franz –keldysh effect. Franz –keldysh effect refers to the absorption of photons having energies less than the bandgap of the semiconductor by means of applying a strong electric field. 80.SWtate stark effect. Stark effect refers to the energy shift and corresponding electron tunneling by absorption of photons whose energy is less then the band gap of the semiconductor by means of applying a strong electric field 81.What are the different factors that determine the response time of photodetector? { MAY-12] (i) transit time of charge carriers (ii)diffusion time of charge carriers (iii) time constant RC of the photo detector circuit. 82.What are the condition for total internal reflection. (i) Light should travel from denser medium to rarer medium. (ii)the angle of incidence should be greater then the critical angle of the denser medium. 83.Define V-number of fiber.

V-number of fiber indicates the number of possible propagation modes in the core Department of ECE


V=2π/λa(N.A) Number of propagating modes through the step index fiber N=V2/2 84.What are the different noises present in the avalanche photodiode? { MAY-12] (i)quantum noise ,(ii)dark current noise (iii)thermal noise and (iv)avalanche multiplication. 85.What are the required properties of photo detector? (i)high quantum efficiency. (ii ) low rise time or fast response (iii)low dark current. PART –B

(16 MARKS)

86.Explain the basic principle of electro-optic modulators? { JUNE-12] 87.Describe the electro-optic amplitude modulation with neat sketch? { MAY-13] 88.Explain the quantum confined stark effect(QCSE)? 89.Explain the self-electro-optic device? 90.Discuss the different types of noises in the photodiodes{ NOV/DEC-12] 91.Give an account on the high speed and long wavelength photodiodes? { MAY-13,10,12] 92.Derive expressions for the gain of a photoconductor with dc excitation at different levels of increasing applied bias? { MAY-10,08,07]

93.Discuss the characteristic of p-i-n photodiode with energy band diagram? UNIT IV OPTOELECTRONIC MODULATOR

Introduction – Analog and digital modulation – Electro-optic modulators – Magneto optic devices – Acoustoptic devices – Optical – Switching and logic devices.

PART-A

(1 MARKS)

94.Among the fibers in which fiber the light travels a longer distance for a given fiber length A)step index single mode fiber B) graded index multimode fiber C) step index multimode fiber D) graded index fiber 95.Which fiber is preferred for long distance communication A)step index single mode fiber B) graded index multimode fiber C) step index multimode fiber D) graded index fiber 96.Among the different modes which is preferred in the optical fiber communication A)HE10 mode B) LP01 mode C) LP11 mode D) EH10 mode 97.At which wavelength the silica fiber has minimum loss and dispersion A)0.85µm B) 1.7µm C) 1.1µm D) 1.3µm 98.At a wavelength 0.8 µm which mechanism produces a high optical loss in silica fiber? A)Rayleigh scattering B) OH absorption C) ultra violet absorption D) infra red absorption 99.Among the dispersion which has higher magnitude in a silica fiber A)multimode dispersion B) material dispersion C) waveguide dispersion D) refractive index profile dispersion Department of ECE


100.In a single mode step index fiber at 1.3 µm which dispersion has higher magnitude A)multimode dispersion B) waveguide dispersion C) material dispersion D) profile dispersion 101.Modulation is necessary A)to increase data rate B) to reduce alternation C) to increase response time D) to reduce dispersion 102.In the wave length range from 1.3 µm to 1.55 µm which material is used as an optical detector A)Si B) Ga As C) In P D) In Ga As 103.Among the modulation techniques which effect will respond to electric field in a linear manner A)Kerr effect B) Stark effect C) Pockels effect D) Faraday effect 104.Hard disk in a computer is A)Permanent magnetic storage B) Temporary magnetic storage C) high capacity optical disk storage D) high capacity CDROMs 105.CCDs are A)charge storage device B) charge creation device C) temporary memory storage in a computer D) Charge compact disks 106.Magnetic bubble is a A)bubble appearing on the magnetic liquid surface B) magnetic storage element C) magnetic drive D) high capacity magnetic storage material 107.Among storages which have high storage capacity A)flexible floppy disk B) hard disk C) CDROM D) multiple disk storage 108.Which one of the material does not have covalent bond A)Silicon B) Ga As C)Ge D) NaCl KEY: 94

95

96

97

98

99

100 101 102 103

104

105

106

107

108

C

A

B

D

A

A

B

A

C

B

D

D

A

D

PART-B

C

(2 MARKS)

109.Give the merits of PCM? The non –linearities of the light source do not affect the quality of the transmitted signal. Even though the transmitted signals are highly degraded or attenuated, the original analog signals may be obtained without any error. this is free from noise and temperature effects 110.What are the demerits of PCM? { MAY-12] There is a small quantization error. There is a possibility of formation of noise during coding or decoding the signal. 111. What are the types of microelectrodes? • Metallic microelectrode • Nonmetallic or micropipet. 112.What is the necessity of cladding for an optical fiber?

To provide proper light guidance inside the core To avoid leakage of light from the fiber Department of ECE


To give mechanical strength for the fiber. 113.Define relative refractive index difference . ∆=n1 2 - n22/2n12=n1- n2/n1 Thus the relative refractive index difference is the ratio between the refractive index difference . 114.What arev skew rays? { MAY-13] Skew rays are the rays following the helical path around the fiber axis when they travel through the fiber and they would not cross the fiber axis at any time. 115.What are meridional rays? { DEC-12] Meridional rays are the rays following ZIG-Zag path when they travel through fiber and for every reflection it will cross the fiber axis. 116.What are microbending losses? These occur due to bends in the fiber axis these microbending losses occur during cabling and stresses acting on the fiber.these produce mode coupling losses also. 117.Define cutoff wavelength of the fiber. The cut off wavelength is defined as the minimum value of wavelength that can be transmitted through the fiber .the wavelengths greater than the cutoff wavelength can be transmitted. Λcutoff=2πa(N.A)/V 118.What is material dispersion? Material dispersion arises due to variation of refractive index of core with respect to wavelength of light this occur 2 when d n1/dλ2≠0 119.What is wave guide dispersion? { MAY-13] Wave guide dispersion is due to finite frequency bandwidth and the dependence of mode group velocity on the frequency of light. 120.Why do we have smaller dispersion in graded index fibers? Due to shaping the refractive index profile in the parabolic manner and by self focusing effect, the dispersion is small. 121.What is dark current noise? { NOV/DEC-13] Dark current noise is due to the flow of current through the bias circuit eventhough there is no incident light PART-B 122.Describe electro-optic amplitude modulation with neat sketch ? { JUNE-12] 123.Give the principle and design of optical amplifiers{ DEC/NOV-12] 124.Explain the quantum confined stark effect(QCSE) 125.Explain The Self –Electro-Optic Device. { DEC/NOV-13}

(16 MARKS)

UNIT V OPTOELECTRONIC INTEGRATED CIRCUITS

Introduction – Hybrid and monolithic integration – Application of opto electronic integrated circuits – Integrated transmitters and receivers – Guided wave devices.

PART-A

(1 MARK)

126.A bond which is found by the sharing of electron is A)metallic bond B) Covalent bond C)Ionic bond D) Dipole bond 127.The crystal structure of Germanium is Department of ECE


A)SC B) BCC C)FCC D) DCC 128.Silicon doped with gallium is A)intrinsic semiconductor B) PN junction diode C)P type semiconductor D) N type semiconductor 129.IC chips used in computers and microprocessors are made of A)pure semiconductor B) pure silicon C)silicon with desired impurities D) Germanium having silicon and arsenic as impurities 130.The density of charge carriers in a pure semiconductor is proportional to A)T B) T2 C)T3/2 D) T1/3 131.In silicon at 0K the forbidden gap in electro volt equals to A)1.11 B) 1.21 C) 1.51 D) 0.72 132.The depletion region in a open circuited p-n junction contains A)Electrons B) holes C) Electrons and holes D) immobile ions 133.To produce light of wavelength 0.8 µm, which material is used? A)Silicon B) Ga As C) Ge D) In P 134.In computers what kind of LEDs are used? A)homojunction LEDs B) hetero junction LEDs C) indirect bandgap LEDs D) narrow bandgap LEDs 135.Hard superconductors observe A)Incomplete Meissner effect B) breakdown by Silsbees rule C) high critical field and transition temperature D) all of the above 136The transition temperature of most low temperature superconductiong elements is in the range A)0-10 K B) 10K-20K C) 20K-50K D) above 50K 137.If the temperature of a conductor is decreased below is critical temperatute the value of critical magnetic field will A)decrease B) increase C) remain constant D) may increase or decrease 138.Nitinol is a A)conducting polymer B) shape memory alloy C) electrets D) thermo electric material 139.When the bandwidth of modulation is B Hz then in digital modulation the binary coded bits are time space about A)1/B sec B) 1/2B sec C) B sec D) 2B sec 140.Among the electro absorption modulators which will produce an efficient intensity modulation of light A)Franz-Keldysh modulator B) Stark modulator C) Quantum Well modulator D) P-I (MQW) - n diode modulator 141.Among the following materials ,which is an efficient electrooptic modulator material? A)Li Nb O3 B) Ga As C) KDP D) Li Ta O3 Department of ECE


ANSWER

126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 B

D

C

C

C

A

D

B

A

D

A

B

B

B

D

A

PART-B (2 MARKS) 142.What are modulation and demodulation? Modulation means the mixing process of low frequency signal with the high frequency signal with the high frequency carrier (laser)by changing the amplitude (or )frequency (or) phase of the carrier in accordance with the amplitude of signal. Demodulation (or) detection is the extraction of the signal from the modulated carrier. 143.What are the other sources to produce dispersion? The spectral spread of the light source and improper shaping of refractive index profile create dispersion in the fibers. 144. What is meant by Isolation? { MAY-13] (i)Improper grounding of the system is one of the most comm (ii)measurement problems and noise. Signal conditioners with (iii)prevent these problems. Such devices pass the signal from (iv)measurement device without a physical or galvanic connec (v)transformer,optical of capacitive coupling techniques. 145.What is meant by electrooptic effect? { DEC-13] Electrooptic effect refers to the change of refractive index of the medium by the applied electric field and hence modulation of light is obtained. 146.What is pockels effect? { DEC/NOV-12] The change in refractive index of the medium is directly proportional to the applied field strength. 147. What are the different component of an optical transmitter? 1.encoder or signal snaping circuit 2.modulator or driver circuit,3.optical source 148. What are the different component of an optical receiver? 1.optical detector 2.pre- amplifier,3.variable gain voltage amplifier4.fixed gain amplifier 5.decoder or demodulator. 149.Distinguish between analog storage and digital storage. In analog storage the signal recorded is a representation of the original signal in digital storage ,the signal is sampled and each sample is converted into a number through A/Dconverter .these binary numbers are written or recorded. 150.Define optical switching. Optical switching refers tonthe phenomenon in which transmission of an optical field through a device is switched among two or more possible states by optical means PART-B (16 MARKS) 151.Describe the fabrication process of an opto electronic integrated transmitter circuit by molecular beam ,epitaxy regrowth.? 152.Describe about the guided wave Mach-Zehder interferometer and arrive at the expression for half wave voltage. 153.Mention few photodetector materials and properties.? { NOV/DEC-12] 154.Describe the construction and working of PIN diode. { MAY-13] 155. Explain the different types of modulation techniques ? { JUNE/-12] 156.Explain the different modulation formets? 157.Briefly explain the different detection schemes using block diagrams? { MAY-13] 158.Describe the working of soliton laser? { MAY-10,11] 159.Discuss the PCM transmission technique and its advantages. { DEC/NOV-12]

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