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1. 1. UNIT-7 FIBER OPTICS. HOLOGRAPHY. 1
2. 2. APPLIED PHYSICS CODE : 07A1BS05 I B.TECHCSE, IT, ECE & EEE UNIT-7: CHAPTER 1.NO. OF SLIDES :19 2
3. 3. UNIT INDEXS.No. Module Lecture PPT Slide No. No. 1 Introduction. L -1 4-10 Acceptance angle. Numerical aperture 2 Types of optical L -2 11-17 fibres 3. Attenuation in optical L-3 18-19 fibres 3
4. 4. Lecture-1 INTRODUCTIONOptical fibers are long, thinstrands of very pure glass aboutthe diameter of a human hair. They are arranged in bundlescalled optical cables and used totransmit light signals over longdistances. 4
5. 5. Optical FiberThere are 3 parts in optical fiber. They are1.Core 2.Cladding. 3.Buffer coating. 5
6. 6. OPTICALFIBER STRUCTURE 6
7. 7. L e c tCore: u r - Thin glass center of the fiber where the e - light travels 1Cladding : Outer optical material surrounding the core that reflects the light back into the coreBuffer coating:Plastic coating that protects the fiber fom damage and moisture. 7
8. 8. Acceptance angle 8
9. 9. “The maximum angle of incidence at the core of the optical fiber for which the rays undergo totall internal reflections and travel along the fiber” is called acceptance angle. The acceptance angle is given by α m = Sin-1[(√n12-n22)/n0] 9
10. 10. L NUMERICAL APERTURE e c t u Numerical aperture of a fiber is a r e measure of its light gathering - 1 capacity. The numerical aperture (NA) is defined as the sin of the acceptance angle. (NA) = Sinα = (√n 2-n 2)/n m 1 2 0 10
11. 11. Lecture-2Single-mode fibers: If the core diameter is small it allows only one mode to travel through it. Then the fiber is called single mode or monomode fiber. The monomode fiber has very small core diameter less than 10micrometers. They Transmit infrared laser light (wavelength = 1,300 to 1,550 nanometers). 11
12. 12. Multi-mode fibers If a fiber allows more number of modes, then it is called multimode fiber. It has larger core diameter than single mode fiber. 12
13. 13.  The relative refractive index difference is also larger than single mode fiber. It transmits infrared light (wavelength = 850 to 1,300 nm) from light-emitting diodes (LEDs). 13
14. 14. Step index Fiber The refractive index of core is constant through out the core. Different rays reach the exit end at different times. Therefore, the pulsed signal received at the exit end gets broadened. This is called ‘intermodal dispersion’. 14
15. 15. Graded Index Fiber If the core has a non-uniform refractive index that gradually decreases from the center towards the core-cladding interface, the fiber is called graded index fiber. The light travels at different speeds in different directions. 15
16. 16.  A ray is continuously bent and travels a periodic path along the axis in the form of helical or skew rays. There is no chance of intermodal dispersion. Bandwidth is high. 16
17. 17. PlasticfibersSome optical fibers can be made from plastic. These fibers have a large core (0.04 inches or 1 mm diameter)transmit visible red light (wavelength = 650 nm) from LEDs 17
18. 18. Lecture-3 L e ATTENUATION c tuAttenuation is the loss of power r suffered by the optical signal as it e - propagates through the fiber. 2 It is also called fiber loss. Signal attenuation is defined as the ratio of the input optical power Pi into the fiber to the output received optical power Po from the fiber. 18
19. 19.  The attenuation coefficient of the signal per unit length is given as α =10/L log (Pi/Po) dB/km The mechanisms through which attenuation takes place are 1.Absorption losses 2.Scattering losses 19
20. 20. UNIT INDEXS.No. Module Lectur PPT Slide e No. No. 1 Basic principles of L -4 3-6 Holography 2 Construction and L -5 7-18 reconstruction Images On hologram. 3. Applications of L-6 19-23 Holography. 20
21. 21. Lecture-4 Holography L e• Holographyis about the photographic c t technique. u r e• The technic is called HOLOGRAPHY after - 3 the greek words HOLOS, and GRAPHOS, which mean ‘complete’, and ‘writing’ respectively.• It is the science of producing holograms.• It is a form of photography that allows an image to be recorded in three dimensions. 21
22. 22.  The technique of holography can also be used to optically store, retrieve, and process information. It is common to confuse volumetric displays with holograms, particularly in science fiction works such as Star Trek, Star Wars, Red Dwarf, and Quantum Leap. 22
23. 23. Technical description The difference between holography and photography is best understood by considering what a black and white photograph .It is a point-to-point recording of the intensity of light rays that make up an image. Each point on the photograph records just one thing, the intensity (i.e. the square of the amplitude of the electric field) of the light wave that illuminates that particular point. 23
24. 24.  In the case of a colour photograph, slightly more information is recorded (in effect the image is recorded three times viewed through three different colour filters), which allows a limited reconstruction of the wavelength of the light, and thus its colour. the holograms are recorded monochromatically. 24
25. 25. Holographic recording process To produce a recording of the phase of the light wave at each point in an image, holography uses a reference beam which is combined with the light from the scene or object (the object beam). If these two beams are coherent, optical interference between the reference beam and the object beam, due to the superposition of the light waves, produces a series of intensity fringes that can be recorded on standard photographic film. 25
26. 26.  These fringes form a type of diffraction grating on the film, which is called the hologram. The central goal of holography is that when the recorded grating is later illuminated by a substitute reference beam, the original object beam is reconstructed, producing a 3D image. 26
27. 27. Lecture-5 Construction process 27
28. 28. Holographic reconstruction process When the processed holographic film is illuminated once again with the reference beam, diffraction from the fringe pattern on the film reconstructs the original object beam in both intensity and phase (except for rainbow holograms where the depth information is encoded entirely in the zoneplate angle). 28
29. 29.  Because many viewpoints are stored, each of the viewers eyes sees the image from a slightly different angle, so the image appears three-dimensional. This is known as stereopsis . The viewer can move his or her viewpoint and see the image rotate 29
30. 30. Reconstruction process 30
31. 31.  HOLOGRAPHY-CONSTRUTION PROCESS L e c t u r e - 5 31
32. 32.  HOLOGRAPHY-CONSTRUCTION PROCESS 32
33. 33.  CONSTRUCTION PROCESS 33
34. 34. Holograms as diffraction grating A diffraction grating is a transparent or reflective sheet with thin slits, the distance between them and their diameter being on the order of the wavelength of the light. Light rays travelling towards it are bent at an angle determined by the distance between the slits and the wavelength of the light. 34
35. 35.  When holograms are constructed, the reference beam and the object beam interfere with one another and the dark and light fringes of the interference pattern are recorded. When this photograph is developed, the light parts become clear and the dark parts opaque. 35
36. 36.  The clear, light parts become like the slits of a diffraction grating, and the angle at which they bend incoming light (the reconstruction beam) is determined by the spacing between them, which in turn was determined originally by the object beam and reference beam, when the holograms interference pattern was made. Thus the slits bend the reconstruction beam to be the exact angles at each point that the object beam was going at. 36
37. 37. APPLICATIONS Lecture-6 Holography can be applied to a variety of uses other than recording images.1 Holographic data storage is a technique that can store information at high density inside crystals or photopolymers. The ability to store large amounts of information in some kind of media is of great importance, as many electronic products incorporate storage devices. 37
38. 38.  As current storage techniques such as Blu-ray reach the denser limit of possible data density (due to the diffraction-limited size of the writing beams), holographic storage has the potential to become the next generation of popular storage media. The advantage of this type of data storage is that the volume of the recording media is used instead of just the surface. 38
39. 39. APPLICATIONS2. Digital holography An alternate method to record holograms is to use a digital device like a CCD camera instead of a conventional photographic film. This approach is often called digital holography. In this case, the reconstruction process can be carried out by digital processing of the recorded hologram by a standard computer. A 3D image of the object can later be visualized on the computer screen or TV set. 39
40. 40. APPLICATIONS3.Use of holography in banknotes Holograms are used widely as a security device in many currencies such as the Brazilian real 20 note, British pound 5/10/20 notes, Canadian dollar 5/10/20/50/100 notes, Euro 5/10/20/50/100/200/500 notes, South Korean won 5000/10000 notes, Japanese yen 5000/10000 notes, etc. 40
41. 41. 4. Holography in art Early on artists saw the potential of holography as a medium and gained access to science laboratories to create their work. Holographic art is often the result of collaborations between scientists and artists, although some holographers would regard themselves as both an artist and scientist. 41