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Chapter 3

Chapter 3. Optical Components/Devices. OPTICAL FIBER PASSIVE DEVICES : COUPLERS, ATTENUATORS, ISOLATORS, CIRCULATORS, BRAGG GRATINGS AND ATTENUATORS. Optical Passive Devices. Passive Components i. Couplers ii. Isolators iii. Circulators iv. Fiber Bragg Gratings v. Attenuator.

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Chapter 3

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  1. Chapter 3 Optical Components/Devices

  2. OPTICAL FIBER PASSIVE DEVICES: COUPLERS, ATTENUATORS, ISOLATORS, CIRCULATORS, BRAGG GRATINGS AND ATTENUATORS

  3. Optical Passive Devices Passive Components i. Couplers ii. Isolators iii. Circulators iv. Fiber Bragg Gratings v. Attenuator

  4. Optical Couplers • Couplers can perform both combining and splitting. • The devices are widely used in optical LAN and broadcasting networks

  5. Optical Couplers • Couplers are bi-directional, they can carry light in either direction. • Used to split and combine the signals. • A coupler with single fiber at one end and two at the other end would be referred to as 1 x 2 Coupler ( read as one by two). • Although 1 x 2 and 2 x 2, are the most common sizes they can be obtained in wide range types up to 32 x 32.

  6. Optical Couplers • An optical coupler is a passive (unpowered) device that diverges (1:N) or converges (N:1) optical signals from one fibre or optical signal path to more than one (or vice versa.) • Configurations: Splitters, taps, combiners, directional couplers

  7. Optical Couplers Splitting Ratio (Coupling Ratio):- • The proportion of the input power at each output is called the splitting ratio or coupling ratio. • In a 1 x 2 coupler, the input signal can split between the two outputs in any desired ratio. In practice however, the common ones are 90:10 and 50:50. These are also written as 9:1 and 1:1. • In the cases where the splitting ratio is not 1:1, the port which carries the higher power is sometimes called the throughput port and the other is called the tap port. 2X2 Optical coupler

  8. Optical Couplers Coupling Tolerance: • Even when the splitting ratio is quoted as 1:1, it is very unlikely, due to manufacturing tolerances that the input power is actually shared equally between two outputs. The acceptable error of between 1% and 5% is called coupling or splitting tolerance.

  9. Optical Couplers Losses:- a. Excess loss (The Ratio of the input power to the total output power). The light energy has been scattered or absorbed within the coupler and is not available at the output. b. Crosstalk or directivity When we apply power to 1, we expect it to come out of port 2 and 3 but not out of port 4, the other input port. Because of backscatter within the coupler, some energy is reflected back and appear at port 4. This backscatter is very slight and is called directionality loss or crosstalk.

  10. Optical Couplers c. Insertion loss Refers to the loss for a particular port-to-port path. For example, for the path from input port i to output port j. This looks at a single output power compared with the input power. There are two possibilities, the power coming out of port 2 and compare it with the input power at port 1 or port 3 compared with input power port 1.

  11. Optical Couplers: Characteristics • COUPLING RATIO

  12. Optical Couplers • EXCESS LOSS • Ratio of the input power to the total output power

  13. Optical Couplers • INSERTION LOSS

  14. Optical Couplers • DIRECTIVITY

  15. OPTICAL COUPLERSPECIFICATIONStandard TypeThe device is capable of branching or combining an optical power having a single wavelength in a designated ratio.

  16. WDM CouplerWDM (wavelength division multiplexing) coupler is an optical device capable of wavelength dividing two wavelengths on a single optical fiber into two, or vice versa; i.e., combining two wavelengths on two optical fibers into one.

  17. Optical Fibre Connectors

  18. Optical Fibre Connectors

  19. Example: 1 Calculate the output power at port 3? Sol:

  20. Example 2: • A product sheet for a 2x2 single-mode biconical tapered coupler with a 40/60 splitting ratio states that the insertion losses are 2.7 dB for the 40-percent channel. • If the input power Po =200 µw , compute P1 and P2 • Evaluate the excess loss • From the calculated values of P1 and P2, verify that the splitting ratio is 40/60. Sol:

  21. P0 P1 A B P2 ISOLATORS • To allow light to propagate in one direction only

  22. P0 P1 P2 P3 A B ISOLATORS

  23. ISOLATOR SPECIFICATION

  24. 2 1 3 CIRCULATORS Optical circulators redirects light sequentially from port-to-port in a unidirectional path Same characteristics as isolators by looking port 1-2 @ port 2-3 To extract the desired wavelength, a circulator is used in conjunction with the rating

  25. CIRCULATORS: WORKING PRINCIPLE

  26. CIRCULATORS • Characteristics: • high isolation • low insertion loss • can have more than 3 ports • Applications: • Optical Amplifier • Add-Drop Multiplexer • Bi-directional transmission • To monitor back-reflection • from devices or optical • subsystems

  27. CIRCULATORS: APPLICATION

  28. External writing technique using UV light l2 Fiber Bragg Gratings A grating is a periodic structure or perturbation in a material that creates a property of reflecting or transmitting light in a certain direction depending on the wavelength.

  29. l1 l3 l1 l3 l2 Transmission Reflection l2 Fiber Bragg Gratings

  30. Fiber Bragg Gratings

  31. Fiber Bragg Gratings Figure 2: FBGs reflected power as a function of wavelength • The reflected wavelength (λB), called the Bragg wavelength, is defined by the relationship, •              , • where n is the average refractive index of the grating and Λ is the grating period.

  32. Fiber Bragg Gratings • Characteristics: • high reflectivity to be used as a filter • low insertion loss • low cost/simple packaging

  33. l2 Fiber Bragg Gratings • Transmission spectrum • band-rejection filter

  34. Fiber Bragg Gratings • Reflection spectrum • reflective filter

  35. FBG APPLICATIONS

  36. Gain flattening filter + = FBG APPLICATIONS

  37. Laser diode wavelength stabilizer FBG APPLICATIONS

  38. FIBER BRAGG GRATING SPECS.

  39. Working Principles Rotating an absorption disk Fiber displacement ATTENUATORS Function: To decrease light intensity (power)

  40. Programmable attenuator Set @ 60 dB Insertion loss = 2 dB Pout = 0 - 20 - 2 = -22 dBm Pin = 0 dBm ATTENUATORS

  41. ATTENUATORS • Characteristics: • low insertion loss • dynamic attenuation range • wide range of operating wavelength • high return loss • Applications: • adjust optical power to the dynamic range of receivers • equalize power between different WDM signals • To avoid receiver saturation

  42. Mechanical attenuator - by adjusting a screw Waveguide attenuator - by adjusting biasing current ATTENUATORS

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