STUDY OF NUMERICAL APERTURE OF OPTICAL FIBER

Transcription

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2 EX.NO.: 1a DATE: STUDY OF NUMERICAL APERTURE OF OPTICAL FIBER AIM: The objective of this experiment is to measure the numerical aperture of the plastic Fiber provided with the kit using 660nm wavelength LED. EQUIPMENTS: Link-B Kit with power supply Patch chords 1-Meter Fiber Cable Numerical aperture measurement Jig Steel Ruler THEORY: Numerical aperture refers to the maximum angle at the light incident on the fiber end is totally internally reflected and is transmitted properly along the Fiber. The cone formed by the rotations of this angle along the axis of the Fiber is the cone of acceptance of the Fiber. The light ray should strike the fiber end within its cone of acceptance; else it is refracted out of the fiber core. CONSIDERATION IN A MEASUREMENT: 1. It is very important that the source should be properly aligned with the cable & the distance from the launched point & the cable be properly selected to ensure that the maximum amount of Optical Power is transferred to the cable. 2. This experiment is best performed in a less illuminated room.

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4 NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown. Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep Intensity control pot P2 towards minimum position. 3. Keep Bias control pot P1 fully clockwise position. 4. Switch ON the power supply. 5. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the 1 meter Fiber into the cap. Now tighten the cap by screwing it back. 6. Insert the other end of the Fiber into the numerical aperture measurement jig. Adjust the fiber such that its cut face is perpendicular to the axis of the Fiber. 7. Keep the distance of about 5mm between the fiber tip and the screen. Gently tighten the screw and thus fix the fiber in the place. 8. Increase the intensity pot P2 to get bright red light circular patch. 9. Now observe the illuminated circular patch of light on the screen. 10. Measure exactly the distance d and also the vertical and horizontal diameters MR and PN 11. Mean radius is calculated using the following formula r = (MR+PN)/4 12. Find the numerical aperture of the Fiber using the formula NA = sinθ max = r / d2 + r2 Where θ max is the maximum angle at which the light incident is properly transmitted through the fiber.

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6 RESULT: Thus the numerical aperture of the plastic Fiber is measured using 660nm wavelength LED. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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8 EX.NO.: 2a DATE: STUDY OF CHARACTERISTICS OF FIBER OPTIC LED AIM: To study the characteristics of Fiber Optic LEDs and plot the graph of forward current v/s output optical energy EQUIPMENTS: Link-B Kit with power supply Patch chords Jumper to Crocodile connectors 1-Meter Fiber Cable Voltmeter and Current meter 2Nos. each THEORY: In Optical Fiber communication system, Electrical signal is first converted into optical signal with the help of E/O conversion device such as LED. After this optical signal is transmitted through Optical Fiber, it is retrieved in its original electrical form with the help O/E conversion device such as photo detector. Different technologies employed in chip fabrication lead to significant variation in parameters for the various emitter diodes. All the emitters distinguish themselves in offering high output power coupled into the important peak wavelength of emission, conversion efficiency (usually specified in terms of power launched in optical Fiber peak wavelength of emission), conversion efficiency (usually specified in terms of power launched in optical Fiber for specified forward current) optical rise and fall times which put the limitation on operating frequency, maximum forward current through LED and typical forward voltage across LED.

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10 NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown. Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep switch SW8 towards VI position. 3. Keep switch SW9 towards TX1 position. 4. Keep Jumper JP8 towards sine position. 5. Keep Bias control pot P1 towards maximum position & P2 towards minimum position. 6. Insert the jumper to crocodile connecting wires (provided along with the kit) in jumper JP5, JP6, JP9 and JP10 at positions shown. 7. Connect the voltmeter and current meter with proper polarities to above mentioned jumpers. 8. Switch ON the power supply. 9. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the 1 meter Fiber into the cap. Now tighten the cap by screwing it back. 10. Vary intensity control pot P2 to control current flowing through the LED. 11. To get the V-I characteristics of LED, rotate P2 slowly and measure forward current and corresponding forward voltage. Take number of such readings for various current values and plot V-I characteristics graph for the LED. 13. For each reading taken above, find out the power, which is product of V and I. This is the electrical power supplied to the LED. Data sheets for the LED specify optical power coupled into plastic fiber when forward current was 10mA as 200uW. This means that the electrical power at 10mA current is converted into 200uW of optical energy. Hence the efficiency of the LED comes out to be approximately 1.15%. 14. With this efficiency assumed, find out optical power coupled into plastic Optical Fiber for each of the reading. Plot the graph of forward current v/s output optical power of the LED.

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12 RESULT : Thus the characteristics of Fiber Optic LEDs are studied and the graph of forward current v/s output optical energy is plotted. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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14 EX.NO.: 2b DATE: V-I CHARACTERISTICS OF LASER SOURCE AIM: CW. To study and plot the V-I characteristics for 1550nm Laser source for the EQUIPMENTS: FOM-1D module Optical Patch cords THEORY: In Optical Fiber communication system, Electrical signal is first converted into optical signal with the help of E/O conversion device such as LASER. After this optical signal is transmitted through Optical Fiber, it is retrieved in its original electrical form with the help O/E conversion device such as photo detector. Different technologies employed in chip fabrication lead to significant variation in parameters for the various emitter diodes. All the emitters distinguish themselves in offering high output power coupled into the important peak wavelength of emission, conversion efficiency (usually specified in terms of power launched in optical Fiber peak wavelength of emission), conversion efficiency (usually specified in terms of power launched in optical Fiber for specified forward current) optical rise and fall times which put the limitation on operating frequency, maximum forward current through LASER and typical forward voltage across LASER.

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16 PROCEDURE: Referring to the Block Diagram, 1. Make sure that the FOM-1D module is off. 2. Keep Intensity Control pot fully anticlockwise. 3. Keep Signal Selector 2 Switch_1550nm on CW position. 4. Connect Optical O/P 2 to Optical I/P 2, using 1meter ST-ST fiber optic cable. 5. Turn ON the FOM-1D module. The Current display should show 00.0 and voltage display should show the garbage value. 6. Turn the Intensity Control pot slightly in clockwise direction, until the Current display shows 00.1mA. 7. Record the current in ma and the corresponding voltage in volts. 8. Repeat the procedure for current readings in steps of 00.1mA upto 45mA. Record the current in ma and the corresponding voltage in volts. 9. Plot the graph for Current (ma) vs Voltage (v). 10. Find out the Threshold Current (Ith) in ma from the I-V graph.

17 TABLE: V-I CHARACTERISTICS OF LASER FORWARD VOLTAGE FORWARD CURRENT

18 RESULT: Thus the characteristic of Laser is studied and the graph of forward current v/s voltage is plotted. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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20 EX.NO.: 3 AIM: DATE: STUDY OF LOSSES IN OPTICAL FIBER The objective of this experiment is to measure propagation loss & bending losses for two different wavelengths in plastic Fiber provided with the kit. EQUIPMENTS: Link-B Kit with power supply Patch chords 20MHz Dual Channel Oscilloscope 1 MHz Function Generator 1 & 3-Meter Fiber Cable THEORY: Optical Fibers are available in different variety of materials. These materials are usually selected by taking into account their absorption characteristics for different wavelengths of light. In case of Optical Fiber, since the signal is transmitted in the form of light, which is completely different in nature as that of electrons, one has to consider the interaction of matter the radiation to study the losses in fiber. Losses are introduced in fiber due to various reasons. As light propagates from one end of Fiber to another end, part of it is absorbed in the material exhibiting absorption loss. Also part of the light is reflected back or in some other directions from the impurity particles present in the material contributing to the loss of the signal at the other end of the Fiber. In general terms it is known as propagation loss. Plastic Fibers have higher loss of the order of 180 db/km. Whenever the condition for angle of incidence of the incident lights is violated the losses are introduced due to refraction of light. This occurs when fiber is subjected to bending. Lower the radius of curvature more is the loss. Other losses are due to the coupling of Fiber at LED & photo detector ends.

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22 NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown. Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep SW9 towards TX1 position for SFH Keep jumpers & SW8 positions as shown in FIG Keep Intensity control pot P2 towards minimum position. 5. Switch ON the power supply. 6. Feed about 2Vpp sinusoidal signal of 1KHz from the function generator to the IN post of Analog Buffer. 7. Connect the output post OUT of Analog Buffer to the post TX IN of Transmitter. 8. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the 1 meter Fiber into the cap. Now tighten the cap by screwing it back. 9. Connect the other end of the Fiber to detector SFH350V (Photo Transistor Detector) very carefully as per the instructions in above step. 10. Observe the detected signal at post ANALOG OUT on oscilloscope. Adjust Intensity control pot P2 Optical Power control potentiometer so that you receive signal of 2Vpp amplitude. 11. Measure the peak value of the received signal at ANALOG OUT terminal. Let this value be V Now replace 1 meter Fiber by 3 Meter Fiber between same LED and Detector. Do not disturb any settings. Again take the peak voltage reading and let it be V If α is the attenuation of the Fiber then we have. α db = (10/L1-L2) log10 (V2/V1) where α= db / Km, L1 = Fiber Length for V1 L2 = Fiber Length for V2 This α is for peak wavelength of 660nm 17. Now switch off the power supply. 18. Keep SW9 towards TX1 position for SFH Set the jumpers to form simple analog link using LED SFH450V at 950nm

23 TABLE: BENDING LOSS S.No. BENDING DIAMETER AMPLITUDE TABLE: ATTENUATION S.No. LENGTH AMPLITUDE 1 L1= 1m 2 L2=3m

24 and phototransistor SFH350V (Photo Transistor Detector) with 1 meter Fiber Cable. 20. Switch on the power supply. 21. Repeat the same procedure as above again for this link to get α at 950nm. 22. Compare the two α values. MEASUREMENT OF BENDING LOSSES: 1. Set up the 660 nm analog link using 1-meter fiber as per procedure above. 2. Bend the Fiber in a loop. (As shown in FIG. 3.1) measure the amplitude of the received signal. 3. Keep reducing the diameter of bend to about 2 cm & take corresponding out voltage readings. (Do not reduce loop diameter less than 1 cm). 4. Plot a graph of the received signal amplitude versus the loop diameter. 5. Repeat the procedure again for second transmitter.

25 WORK SPACE: Attenuation: α db = (10/L1-L2) log10 (V2/V1) where α = db / Km, L1 = Fiber Length for V1 L2 = Fiber Length for V2

26 RESULT: Thus the propagation loss & bending losses for two different wavelengths are measured using plastic Fiber provided with the kit. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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28 EX.NO.: 4a AIM: DATE: SETTING UP A FIBER OPTIC ANALOG LINK The objective of this experiment is to set a analog communication using fiber optic cable. EQUIPMENTS: Link-B Kit with power supply Patch chords 20MHz Dual Channel Oscilloscope 1 MHz Function Generator 1 Meter Fiber Cable THEORY: Fiber Optic Links can be used for transmission of digital as well a analog signals. Basically a Fiber Optic Link contains three main elements, a transmitter, an Optical Fiber & a receiver. The transmitter module takes the input signal in electrical form & then transforms it into Optical (light) energy containing the same information. The Optical Fiber is the medium which carriers this energy to the receiver. At the receiver, light is converted back into electrical from with the same pattern as originally fed to the transmitter. TRANSMITTER: Fiber Optic transmitters are typically composed of a buffer, driver & Optical Source. The buffer electronics provides both an electrical connection & isolation between the transmitter & the electrical system supplying the data. The driver electronics provides electrical power to the Optical source in a fashion that duplicates the pattern of data being fed to the transmitter. Finally the optical source (LED) converts the electrical current to light energy with the same pattern. The LED SFH450V (950nm) supplied with this kit operates outside the visible light spectrum. Its Optical output is centered at near infrared wavelength of 950nm. The LED

29 TABLE: S.No. INPUT AMPLITUDE TIME PERIOD OUTPUT AMPLITUDE TIME PERIOD

30 SFH756V (660nm) supplied with this kit operates at the visible light spectrum. Its Optical output is centered at wavelength of 660nm. RECEIVER: The function of the receiver is to convert the optical energy into electrical form, which is then conditioned to reproduce the transmitted electrical signal in its original form. The detector SFH350V (Photo Transistor Detector) used in the kit has a transistor type output. The parameters usually considered in the case of detector are its responsivity at peak wavelength & response time. SFH350V (Photo Transistor Detector) has responsivity of about 0.8mA/10uW at 660nm. But its response time is quite large & thus has lower bandwidth of about 300KHz. When optical signal falls on the base of the transistor detector, proportional current flows through its emitter generating the voltage across the resistance connected between emitter & ground. This voltage is the duplication of the transmitted electrical signal, which can be amplified.

31 INPUT\OUTPUT GRAPH:

32 NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown. Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep switch SW8 towards TX position. 3. Keep switch SW9 towards TX1 position. 4. Keep Jumper JP5 towards +12V position. 5. Keep Jumpers JP6, JP9, JP10 shorted. 6. Keep Jumper JP8 towards sine position. 7. Keep Intensity control pot P2 towards minimum position. 8. Switch ON the power supply. 9. Feed about 2Vpp sinusoidal signal of 1KHz from the function generator to the IN post of Analog Buffer. 10. Connect the output post OUT of Analog Buffer to the post TX IN of Transmitter. 11. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the one-meter fiber into the cap. Now tighten the cap by screwing it back. 12. Connect the other end of the Fiber to detector SFH350V (Photo Transistor Detector) very carefully as per the instructions in above step. 13. Observe the detected signal at post ANALOG OUT on oscilloscope. Adjust Intensity control pot P2 Optical Power control potentiometer so that you receive signal of 2Vpp amplitude. 14. To measure the analog bandwidth of the phototransistor, vary the input signal frequency and observe the detected signal at various frequencies. 15. Plot the detected signal against applied signal frequency and from the plot determine the 3dB down frequency. 16. Repeat the same procedure as above for second transmitter SFH450V by making the following changes. Analog bandwidth of SFH350 for TX1 SFH756 is about 300KHz while for TX2 SFH450 is below 300KHz. 17. Keep switch SW9 towards TX2 position. 18. Keep Jumper JP7 towards +12V position.

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34 RESULT: Thus the analog communication is set using fiber optic link. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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36 EX.NO.: 4b AIM: DATE: SETTING UP A FIBER OPTIC DIGITAL LINK The objective of this experiment is to set a digital communication using fiber optic cable. EQUIPMENTS: Link-B Kit with power supply Patch chords 20MHz Dual Channel Oscilloscope 1 MHz Function Generator 1 Meter Fiber Cable THEORY: In the analog communication link we have seen how analog signals can be transmitted & received using LED, Fiber & Detector can be configured for the digital applications to transmit binary data over Fiber. Thus basic elements of the link remain same even for digital application. TRANSMITTER: LED, digital DC coupled transmitters are one of the most popular varieties due to their ease of fabrication. We have used a standard TTL gate to drive a NPN transistor, which modulates the LED SFH450V or SFH 756V source. (Turns it on & off). RECEIVER: SFH-551V is a digital optodetector. It delivers a digital output, which can be processed directly with little additional external circuitry. The integrated circuit inside the SFH551V optodetector comprises the photodiode device, a transimpedance amplifier, a comparator and a level shifter. The photodiode converts the detected light into a photocurrent. With the aid of an integrated lens the light emanating from the plastic Fiber is

37 TABLE: S.No. INPUT AMPLITUDE TIME PERIOD OUTPUT AMPLITUDE TIME PERIOD

38 almost entirely focused on the surface of the diode. At the next stage the trans-impedance amplifier converts the photocurrent into a voltage. In the comparator, the voltage is compared to a reference voltage. In over to ensure good synchronism between the reference and the transimpedance output voltage, the former is derived from a second circuit of a similar kind, which incorporates a blind photodiode. The comparator derives a level shifter with an open collector output stages. Here a catch diode (similar to Schottky-TTL) prevents the saturation of the output transistor, thus limiting the output voltage to the supply voltage. NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown in the figure. Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Switch ON the power supply. 3. Feed TTL Square wave signal of 1KHz from the function generator to the IN post of Digital Buffer. 4. Connect the output post OUT of Digital Buffer to the post TX IN of Transmitter. 5. Slightly unscrew the cap of SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the One Meter Fiber into the cap. Now tighten the cap by screwing it back. 6. Connect the other end of the Fiber to detector SFH551V very carefully as per the instructions in above step. 7. Observe the detected signal at post TTL OUT on oscilloscope. 8. To measure the digital bandwidth of the phototransistor vary the input signal frequency and observe the detected signal at various frequencies. 9. Determine the frequency at which the detector stops recovering the signal. This determines the maximum bit rate on the digital link. 10. Keep switch SW9 towards TX2 position. 11. Keep Jumper JP7 towards +5V position. 12. Repeat the same procedure above for second transmitter SFH450V by making the following changes. 13. The digital bandwidth of SFH551 for TX1 SFH756 is 3MHz & for SFH450 it is 1MHz.

39 INPUT\OUTPUT GRAPH:

40 RESULT: Thus the digital communication is set using fiber optic link. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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42 EX.NO.:5 DATE: WAVELENGTH DIVISION MULTIPLEXING & DEMULTIPLEXING AIM: The objective of this experiment is to perform fiber optics wavelength division multiplexing and demultiplexing. EQUIPMENTS: FOM-1D, FOM-02 & FOM-04 1 meter ST-ST glass Fiber cables - 05 Dual Channel Digital Storage Oscilloscope (DSO) 100 MHz Function Generator 1 MHz THEORY: In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colours) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to making it possible to perform bidirectional communications over a single strand of fiber. The term wavelength-division multiplexing is commonly applied to an optical carrier (which is typically described by its wavelength). Merges optical traffic onto one optical fiber Allows high flexibility in expanding bandwidth Not dependant on signal, bit rate or format Wavelength Division Multiplexing (WDM) applies to any fiber optic system where two or more signals are being transmitted, at different optical

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44 wavelengths, over a single fiber. This type of transmission increases the capacity of the optical fiber. Under WDM, the optical transmission spectrum is carved up into a number of non-overlapping wavelengths (or frequencies) with each supporting a single communication channel. WDM technology utilizes a multiplexer that accepts data from the end user's equipment and transmits this data, via lasers, onto a channel. The multiplexer simultaneously supports many end users in this way. The multiplexer then combines all of the channels into one signal and sends that signal, over one optic fiber, to another device at the destination site called a de-multiplexer. The de-multiplexer separates the signal back into channels of different frequencies and passes those channels on to their assigned destinations. NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Refer to figure, Connect Function Generator s TTL 1 KHz Signal to the Signal i/p post and 1 KHz, 1Vp-p sine wave Signal to the Signal i/p 1 post of FOM-1D, using BNC-BNC cable. 2. Set external function generator to 1 KHz, 1Vpp sine wave input and connect to Signal input 1 post of FOM-01D for 1310 nm laser source. 3. Prepare individual Analog transmission link on 1310 nm laser source. 4. Set external function generator to 1 KHz TTL input and connect to Signal input 2 post of FOM-01D for 1550 nm laser source. 5. Prepare individual digital transmission link on 1550 nm laser source. 6. SWITCH OFF the FOM-01D system. 7. Now connect Optical o/p 1 post (FOM-1D module) to Port1 of WDM 1 on FOM-02 module, using ST-ST 1 meter SM patch cord provided with modules. 8. Connect Optical o/p 2 post (FOM-1D module) to Port2 of WDM 1 on FOM- 02 module, using ST-ST 1 meter SM patch cord provided with modules. 9. Connect Port 3 of WDM on FOM-02 to optical input 1 post on FOM-01D module, using ST-ST 1 meter SM patch cord provided with modules. 10. Connect CH1 of DSO to Signal output 1 post (FOM-01 module). 11. Keep SW1 switch on Analog mode. 12. Connect the mains power cable to FOM-01 module at the back. While connecting this, ensure that the power supply is OFF.

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46 13. Now switch ON the power supply of module FOM-01, function generator and the Digital storage Oscilloscope. 14. Check and observe multiplexed output on signal output 1 post of PIN DETECTOR 1. Use OFFSET POT 1 to adjust the output. 15. Now connect WDM 1 Port3 output to Port3 of WDM 2 in FOM Connect Port1 of WDM 2 to Optical i/p 1 of Detector 1 in FOM-1D. 17. Observe the de-multiplexed Sine wave on Signal o/p 1 in FOM-1D. 18. Adjust the Offset pot 1 if required. 19. Connect Port 2 of WDM 2 in FOM-02 to Optical i/p 1 of Detector 1 in FOM-1D. 20. Put switch SW 1 to Digital position in FOM-1D. 21. Observe the de-multiplexed TTL signal on Signal o/p 1 post of FOM-1D. 22. If required adjust the Offset pot 1 in FOM-1D. RESULT: Thus, using Fiber Optic WDM2x1, 1310nm and 1550nm are multiplexed and using another WDM1x2, de-multiplexing is performed. The respective waveforms are observed on DSO. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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48 EX.NO.: 6 DATE: CHROMATIC DISPERSION AIM: The objective of this experiment is to study Chromatic dispersion using dual source of 1310nm & 1550nm laser diodes. EQUIPMENTS: FOM-1D module, FOM-2 module, Optical Power Meter, Optical Patch cords, BNC-BNC cable and a Digital Oscilloscope. THEORY: MATERIAL DISPERSION:

49 CALCULATIONS: Source 1= 1310nm Source 2= 1550nm So, = = 240 T= 44 ns from waveform. Using formula, = D0L D0= ps/km/nm for central wavelength o (1450 nm) Considering that the pulses are spread out over a spectrum of 240 nm, dispersion in the region of 7333 ps/km/nm, around 1450 nm is obtained. Verify the calculations with data sheet provided. Note: In case if you observe that the amplitude of chromatic dispersion waveform is very less (say around 1v or so), use 5dB attenuator in FOM-02 to attenuate power of 1550nm source output before connecting it to WDM.

50 PROCEDURE: 1. Make sure that the FOM-1D module is off. 2. Keep Intensity Control pot fully anticlockwise. 3. Refer to block diagram. Connect function generator TTL OUT to Signal IN 1 and Signal IN 2 post (FOM-1D module), using BNC connector. 4. Keep Function Generator TTL out frequency at 1 KHz. 5. Keep Selector switch SW1 on 30nS pulse. 6. Connect Optical Output 1 to Port-1 (1310nm port) of a WDM-1 in FOM Connect Optical Output 2 to Port-2 (1550nm port) of a WDM-1 in FOM Connect Optical Output Port-3 of FOM-02 to Port-1 of FOM-4 25Km single mode fiber optic cable module. 9. Connect Port-2 of FOM-4 module to the detected optical i/p 1 on FOM-1D module. 10. Connect Signal O/p 1 to Digital Oscilloscope. 11. Turn On the FOM-1D module. 12. Measure T (time difference between two peaks) as per the waveform.

51 RESULT: We studied the measurement of chromatic dispersion, using 1310nm and 1550nm sources. We found that, At 1300 nm, dispersion is null At 1550 nm, dispersion is in the region of ps/km/nm (7.333 * 2) This is verified with the given fiber data. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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53 EX.NO.:7 AIM: DATE: MEASUREMENT OF BIT ERROR RATE The objective of this experiment is to measure Bit error rate. EQUIPMENTS: Link-B Kit with power supply Patch chords 1 Meter Fiber cable Patch chords 20 MHz Dual Channel Oscilloscope THEORY: BIT ERROR RATE In telecommunication transmission, the bit error rate (BER) is a Ratio of bits that have errors relative to the total number of bits received in a transmission. The BER is an indication of how often a packet or other data unit has to be retransmitted because of an error. Too high BER may indicate that a slower data rate would actually improve overall transmission time for a given amount of transmitted data since the BER might be reduced, lowering the number of packets that had to be resent. Measuring Bit Error Rate A BERT (bit error rate tester) is a procedure or device that measures the BER for a given transmission. The BER or quality of the digital link is calculated from the number of bits received in error divided by the number of bits transmitted. BER= (Bits in Error) / (Total bits transmitted)

54 BER MEASUREMENT As per the definition the BER is a ratio of Errored bits (Eb) to Total bits Transmitted (Tb) in a period of time t seconds. i.e. BER = Eb / Tb For eg. in this experiment if PRBS data is transmitted at 32Kbits per second ( i.e. jumper selection at 32KHz ) for a period of 10 seconds. So total bits transmitted in 10 seconds (Tb) = 320Kbits. The TTL OUT data & data with noise is fed to BER counter which compares the two data inputs at each clock input. The counter displays the Error count (Eb) on LED in 10-bit binary form (e.g ), which has to be converted in decimal form (it becomes 10) so the BER ratio then becomes BER = 10 / (320 x 10 E 3) = i.e the channel Bit Error Rate ratio is 3.1x10E-5 ( 3 / ) or in other words we can say that out of bits transmitted through the channel the channel gives 3 bits in error.

55 Using a bench test setup, this is easily measured by means of a comparator in which the transmitted bits are matched in an XOR gate with the received bits. In Link-B, PRBS sequence is generated by using a 4-bit right shift register whose feedback is completed by the EX-OR gate. Let initially 1001 be the 4-bit switch setting on the SW7. Clock States D1 D2 D3 D4 A B C Thus the sequence repeats constantly with a period corresponding to 16 clock states. Length of sequence = 24 =16 Now the Pseudo Random Sequence pattern is C =

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57 Fig shows the schematic of the device used for the following measurements. If the bits are alike at the XOR gate input, when clocked in from the D flip flop, the output is low. If they are different, the XOR output goes high, causing an event count. The event counter can be set for various time periods. In general, the longer the time period, the more accurate is the count. A random character generator and white noise source should be used for these measurements. The number of bit errors is dependent upon the amount of noise entering the system. White noise or background noise has an average or RMS value that is exceeded periodically by peaks that rise many times that level. These peaks exist only for a very short period of time. When the peak equals or exceeds the signal level, that is noise energy = bit energy, there is a 50/50 chance of error. The peak time periods can be calculated statistically from the error function.

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59 NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown in fig Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep PRBS switch SW7 as shown in fig.11.1 to generate PRBS signal. 3. Keep switch SW8 towards TX position. 4. Keep switch SW9 towards TX1 position. 5. Keep the switch SW10 at fiber optic receiver output to TTL position. 6. Select PRBS generator clock at 32 KHz by keeping jumper JP4 at 32K position. 7. Keep Jumper JP5 towards +5V position. 8. Keep Jumpers JP6 shorted. 9. Keep Jumper JP8 towards pulse position. 10. Switch ON the power supply. 11. Connect the post DATA OUT of PRBS Generator to the IN post of Digital Buffer and also to the DATA IN post of Bit Error Rate event counter. 12. Connect the OUT post of Digital Buffer to TX IN post Transmitter. 13. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the one-meter fiber into the cap. Now tighten the cap by screwing it back. 14. Slightly unscrew the cap of RX1 Photo Transistor with TTL logic output SFH551V. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back. 15. Connect detected signal TTL OUT to post IN of Noise Source. 16. Connect post OUT of Noise Source to post RXDATA IN of Bit Error Rateevent counter. 17. Connect post CLK OUT of PRBS Generator to post CLK IN of Bit Error Rate event counter. 18. Press Switch SW11 to start counter. 19. Vary pot P3 for Noise Level to observe effect of noise level on the error count. 20. Observe the Error Count LEDs for the error count in received signal in time10 seconds as shown.

60 INPUT\OUTPUT GRAPH:

61 RESULT: Thus the bit error rate is measured using the fiber optic modules. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

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63 EX.NO.: 8 DATE: AIM: link. STUDY OF EYE PATTERN The objective of this experiment is to study eye pattern using fiber optic EQUIPMENTS: Patch chords 1 Meter Fiber cable Patch chords 20 MHz Dual Channel Oscilloscope THEORY: The eye-pattern technique is a simple but powerful measurement method for assessing the data-handling ability of a digital transmission system. This method has been used extensively for evaluating the performance of wire systems and can also be applied to optical fiber data links. The eye-pattern measurements are made in the time domain and allow the effects of waveform distortion to be shown immediately on an oscilloscope. An eye-pattern can be observed with the basic equipment. The output from a pseudorandom data pattern generator is applied to the vertical input of an oscilloscope and the data rate is used to trigger the horizontal sweep. This results in the type of pattern, which is called the eye pattern because the display shape resembles a human eye. To see how the display pattern is formed, consider the eight possible 4- bit-long NRZ combinations. When these sixteen combinations are superimposed simultaneously, an eye pattern is formed. To measure system performance with the eye-pattern method, a variety of word patterns should be provided. A convenient approach is to generate a random data signal, because this is the characteristic of data streams found in practice. This type of signal generates ones and zeros at a uniform rate but in a random manner. A variety of pseudorandom pattern generators are available for this purpose. The word pseudorandom means that the generated combination or

64 EYE PATTERN:

65 sequence of ones and zeros will eventually repeat but that it is sufficiently random for test purposes. A pseudorandom bit sequence comprises four different 2-bitlong combinations, eight different 3-bit-long combinations, sixteen different 4-bitlong combinations and so on (that is, sequences of different N-bit-long combinations) up to a limit set by the instrument. After this limit has been generated, the data sequence will repeat. A great deal of system performance information can be deduced from the eye pattern display. To interpret the eye pattern, follow the procedure ahead. NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Make connections as shown in fig Connect the power supply cables with proper polarity to Link-B Kit. While connecting this, ensure that the power supply is OFF. 2. Keep switch SW7 as shown in fig to generate PRBS signal. 3. Keep switch SW8 towards TX position. 4. Keep switch SW9 towards TX1 position. 5. Keep the switch SW10 to EYE PATTERN position. 6. Select PRBS generator clock at 32 KHz by keeping jumper JP4 at 32K position. 7. Keep Jumper JP5 towards +5V position. 8. Keep Jumpers JP6 shorted. 9. Keep Jumper JP8 towards TTL position. 10. Switch ON the power supply. 11. Connect the post DATA OUT of PRBS Generator to the IN post of digital buffer. 12. Connect OUT post of digital buffer to TX IN post. 13. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the one-meter fiber into the cap. Now tighten the cap by screwing it back. 14. Slightly unscrew the cap of RX1 Photo Transistor with TTL logic output SFH551V. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back. 15. Connect CLK OUT of PRBS Generator to EXT. TRIG. of oscilloscope.

66

67 16. Connect detected signal TTL OUT to vertical channel Y input of oscilloscope. Then observe EYE PATTERN by selecting EXT. TRIG KNOB on oscilloscope. Observe the Eye pattern for different clock frequencies. As clock frequency increases the EYE opening becomes smaller. RESULT: Thus the EYE pattern is studied using fiber optic link. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

68

69 EX.NO.: 9 DATE: EFFECT OF LATERAL, LONGITUDINAL ANGULAR DISPLACEMENT AIM: The objective of this experiment is to study effect of lateral and longitudinal displacement. In this experiment, you will study the relationship between the input signal & received signal through angular and displacement Jig. EQUIPMENTS: FG-01 with power cable 20 MHz Dual Channel Oscilloscope 0.5-meter connectorized Fiber cables Connecting Sleeve Precision Displacement Jigs Patch chords Power supply (Use only one provided) THEORY: MECHANICAL MISALIGNMENT IN FIBERS Mechanical misalignment is a major problem while joining two fibers because of their microscopic size. It results in the radiation loss because the radiation cone of the emitting fiber does not match the acceptance cone of the receiving fiber. The magnitude of the radiation loss depends upon the degree of misalignment. There are three types of mechanical misalignments as shown. These are lateral (coaxial), longitudinal (end separation) and angular. The lateral misalignment results when the axes of the fibers are separated

70 (a). The longitudinal misalignment occurs when the fibers have the same axis but have some gap between their and faces (b). The angular misalignment occurs when the fiber end faces are no longer parallel (c).the most common misalignment that occurs in practice is the lateral misalignment. This misalignment reduces the overlap area of the two fiber core end faces and consequently reduces the amount of power that can be coupled from on fiber into the other. The power loss due to this type of misalignment is usually more than that due to the other types of misalignment. In the case of step-index fibers, the loss from lateral misalignment can be found by simply calculating the overlap area of the core because the irradiance is constant over the face of a step-index fiber. The loss due to longitudinal misalignment can be calculated by comparing the area of the receiving fibers with the area of the beam from the first fiber at a distance z, where z is the separation between the end faces. The loss from the angular misalignment has the same form as the longitudinal misalignment loss with sin8/ NA replacing z/a (see Fig.8.5c). For graded index fibers, the calculation is much more complicated because the irradiance varies as a function of the position within the fiber core. In this experiment fiber loss due to mechanical misalignments are measured. The fiber could be step index or graded index type. Fiber Optic Links can be used for transmission of digital as well as analog signals. Basically, a fiber optic link contains three main elements, a transmitter, an optical fiber & a receiver. The transmitter module takes the input signal in electrical form& then transforms it into optical (light) energy containing the same information. The optical fiber is the medium, which carries this energy to the receiver. At the receiver, light is converted back into electrical form with the same pattern as originally fed to the transmitter. If we transmit signal between two fibers by putting them through coupling jig, depending on the extent of coupling, we will get appropriate signal at the detector side. NOTE: KEEP ALL SWITCH FAULTS IN OFF POSITION. PROCEDURE: 1. Refer to fig 8.1 and make the following connections. 2. Connect the power supply with proper polarity to FCL-01 and FCL-02. While connecting this, ensure that the power supply if OFF. 3. Keep the jumpers JP1, JP2, JP3 & JP4, S2 on FCL-01 as shown in fig Keep switch S2 on FCL-01 to VI position. 5. Keep switch SW2 in SIGNAL STRENGTH position on FCL Keep pot P3 fully anticlockwise &P4 fully clockwise position. 7. Connect the output of Photo Diode detector post OUT to post IN of Signal Strength Indicator block. 8. Switch on the power supply. 9. Take two fibers of 0.5meters length after connectrorization as explained in

71 Exp.No.1. Slightly unscrew the cap of LED SFH756V (660nm). Do not remove the cap from the connector. Once the cap is loosened, insert the 0.5meter fiber into the cap. Now tighten the cap by screwing it back. 10. Connect 0.5meter fiber with plug form receiver to part A of Precision Displacement Jig. 11. Connect 0.5meter fiber with plug form receiver to part B of Precision Displacement Jig. 12. Check that vertical and horizontal alignment is proper as shown in fig Place the other end of this fiber into Photo Diode SFH250V of FCL-02 by Slightly unscrewing the cap. Do not remove the cap from the connector. Once the cap is loosened, insert the other end of fiber into the cap. Now tighten the cap by screwing it back. 14. Observe the signal strength LEDs, adjust the TRANSMITTER LEVEL using Intensity control pot P3 until you get the reading of all LEDs glow.

72

73 LATERAL DISPLACEMENT: 15. Introduce some lateral misalignment with the help of adjusting screws. For horizontal displacement fix the vertical displacement screw SC1, vary the horizontal displacement between part A & part B from 0 to 2 mm in steps of mm.Also For vertical displacement fix the horizontal displacement screw SC1, Vary the vertical displacement by adjusting screw SC2 between part A & part B from 0 to 2 mm in steps of 0.5mm. 17. The amount of misalignment effect can be observed with the help of signal strength meter coupled into the second fiber. Measure the detected signal at every step and compare it with the earlier reading. And realign the fiber ends. LONGITUDINAL DISPLACEMENT: 18. Check that the alignment of part A and part B of the precision jig is proper, if not make it proper by adjusting appropriate screws. 19. Now introduce longitudinal misalignment with the help of looseningtightening screw at the upper end of the precision jig. Then move the front end of fiber connecting plug away from each other around 1 to 2 mm. 20. The amount of misalignment effect can be observed with the help of signal strength meter coupled into the second fiber. Measure the detected signal at every step and compare it with the earlier reading and then realign the fiber ends. ANGULAR DISPLACEMENT: 21. Now replace the precision jig no.1 with precision jig no Do the connections as shown in fig Now introduce angular misalignment by 5,10,15 degree with the help of part A & part B of the precision jig no.2. The amount of misalignment effect can be observed with the help of signal strength meter coupled into the second fiber. Measure the excess loss as a function of angular misalignment, using the rotational stage to change the angular orientation of fiber ends and observe the detected signal on signal strength meter at every angle.

74 RESULT: Thus the The objective of this experiment is to study effect of lateral and longitudinal displacement. In this experiment, you will study the relationship between the input signal & received signal through angular and displacement Jig. Pre lab test (20) Remarks & Performance (50) Signature with Date Result (10) Post-lab test (20) Total (100)

75 Microwave Lab

76 Power Supply Klystron Oscillator Reflex Klystron Characteristics Isolator Variable Attenuator Frequency Meter CRO / VSWR Matched Detector

77 EX. NO.: 1a DATE: CHARACTERISTICS OF REFLEX KLYSTRON AIM: To obtain the reflex klystron mode characteristics. EQUIPMENTS: THEORY: 1. Klystron power supply 2. Klystron Oscillator 3. Isolator 4. Attenuator 5. Frequency Meter 6. Matched detector 7. CRO The reflex klystron makes use of velocity modulation to transform a continues electron beam into micro power. Electron emitted from the cathode are accelerated and passed through the positive resonator towards negative reflector, which retards and finally, reflex the electron and the electrons turns back through the resonator. Suppose HF field exists between the resonators, the electron traveling forward will be accelerated or retarded as the voltage at the resonator changes in amplitude. The accelerated electrons leave the resonator at an increased velocity. The electrons leaving the resonator will need different time to return, due to change in velocities. As a result, returning electrons group together in bunches. As the electron bunches pass through resonator, they interact with

78 TABULATION: Repeller voltage (volts) Output signal amplitude (volts) Frequency (GHz) MODEL GRAPH:

79 voltage resonator grids. If the bunches pass the grid at such time that the electrons are slowed down by the voltage, energy will be delivered to the resonator, and the klystron will oscillate. The frequency is primarily determined by the dimension of resonant cavity. Hence by changing the volume of the resonator, mechanical tuning range of klystron is possible. Also a small frequency change can be obtained by adjusting the reflector voltage.this is called electronic tuning range. PROCEDURE: 1. Set the cooling fan to blow air across the tube. 2. Set the beam voltage control knob fully anti-clockwise and repeller voltage knob clockwise. 3. Switch on the supply. Set HT/LT to HT. 4. Vary the beam voltage and set beam current to 20 ma. 5. Vary the repeller voltage slowly and ensure that the amplitude of the output square wave varies. 6. Decrease the repeller voltage in steps and note down the output signal through CRO and frequency in the frequency meter. 7. Plot the output voltage vs repeller voltage 8. Plot the frequency vs repeller voltage.

80

81 RESULT: Thus the mode characteristics of reflex klystron were obtained. Pre lab test Performance (20) (50) Remarks & Signature with Date Result (10) Post-lab test (20) Total (100)

82 Gunn Power Supply Gunn Oscillator Isolator Gunn Diode Characteristics PIN Modulator Frequency Meter Variable Attenuator CRO / VSWR Matched Detector

83 EX. NO.: 1b DATE: CHARACTERISTICS OF GUNN DIODE AIM: To obtain the Gunn diode characteristics. EQUIPMENTS: THEORY: 1. Gunn power supply. 2. Gunn Oscillator 3. PIN modulator 4. Isolator 5. Attenuator 6. Frequency Meter 7. Matched detector 8. CRO The gun oscillator is based on negative differential conductivity effect in bulk semiconductors, which has two conduction bands minima separated by an energy gap. A disturbance at the cathode gives rise to high field region, which travels towards the anode. When this high field domain reaches the anode, it disappears and another domain is formed at the cathode and starts moving towards anode and so on. The time required for domain to travel from cathode to anode gives oscillation frequency. Although Gunn oscillator can be amplitude modulated with the bias voltage, we have used separate PIN modulator through PIN diode for

84 TABULATION: Bias Voltage (volts) Current (ma) MODEL GRAPH:

85 square wave modulation. A measure of the square wave modulation capability is the modulation depth. i.e., the output ratio between ON and OFF state. PROCEDURE: 1. Keep the Gunn bias knob and PIN bias knob at minimum. 2. Switch on the Gunn supply. Put V/I switch to measure voltage. 3. Increase the Gunn bias voltage, adjust the PIN bias supply and modulation frequency to get a good demodulated square wave output. 4. Decrease the Gunn bias to 0 and increase in steps of 0.5 V and note down the corresponding current values. 5. Plot the graph between the bias voltage and current and determine the threshold voltage. RESULT: Thus the Gunn diode characteristics were obtained. Pre lab test Performance (20) (50) Remarks & Signature with Date Result (10) Post-lab test (20) Total (100)

86 BLOCK DIAGRAM:

87 EX. NO.: 2 DATE: STUDY OF POWER DISTRIBUTION IN DIRECTIONAL COUPLER AIM: To study the power distribution in a multi hole directional coupler by measuring the coupling factor, isolation and directivity. EQUIPMENTS: 1. Micro wave source 2. Isolator 3. Variable Attenuator 4. Frequency Meter 5. Slotted line section 6. VSWR meter 7. Matched load 8. Detector mount THEORY: A directional coupler is a device with which it is possible to measure the incident and reflected wave separately. It consists of two transmission lines, the main arm and the auxiliary arm, electromagnetically coupled to each other. The power entering port 1in the main arm divides between the port 2 and port 3, and almost no power comes out in port 4.Power entering port 2 is divided between port 1and 4.The coupling factor is defined as Coupling factor (db) = 10 log 10 (P1/P3) Where port 4 is terminated with built in termination and power is entering at port 1.

88 CALCULATIONS: Input Power = Output Power at port 2 = Coupling Power at port 4 = Back Power at port 3 = TABULATION: Forward Direction Repeller Amplitute Voltage Power (db) Backward Direction Repeller Amplitute Voltage Power (db)

89 The directivity of the coupler is a measure of separation between incident and reflected wave. It is measured as the ratio of two power outputs form the auxiliary line when a given amount of power is successively applied to each terminal of the main lines with other port terminated by material loads. Directivity D (db) =10 log 10 (P 3F /P 3R ) Where P 3F and P 3R is the power measured at the port 3 with equal amount of power fed to port 1 port 2 respectively. PROCEDURE: 1. Set up the experiment as shown in block diagram. 2. Energize the microwave source for particular operation of frequency. 3. Remove the multi hole directional coupler and connect the detector mount to the frequency meter. Tune the detector for the maximum output. 4. Set any reference level of power on VSWR meter with the help of variable attenuator,gain control knob of VSWR meter, and note down the reading (let reference level be x) 5. Insert the directional coupler as shown in the with figure with detector to the auxiliary port 3 and matched termination to port 2, without changing the position of variable attenuator and gain control knob of VSWR meter. 6. Note down the reading on VSWR meter, let it be Y. 7. Now calculate the coupling factor, which will be X-Y in db.