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2B- Optical Technologies

E-Photon One Curriculum. 2B- Optical Technologies. Coordinator: António Teixeira, Co-Coordinator: K. Heggarty. António Teixeira, Paulo André, Rogério Nogueira, Tiago Silveira, Ana Ferreira, Mário Lima, Ferreira da Rocha, J. Prat, J. A. Lazaro, C. Bock, J. Andrade. Basic Photonic Measurements

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2B- Optical Technologies

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  1. E-Photon One Curriculum 2B- Optical Technologies Coordinator: António Teixeira, Co-Coordinator: K. Heggarty António Teixeira, Paulo André, Rogério Nogueira, Tiago Silveira, Ana Ferreira, Mário Lima, Ferreira da Rocha, J. Prat, J. A. Lazaro, C. Bock, J. Andrade

  2. Basic Photonic Measurements Material growth and processing Semiconductor materials Transmission systems performance assessment tools Optical Amplifiers Semiconductor Optical Amplifiers (SOAs) Erbium Doped Fiber Amplifiers (EDFAs) Fiber Amplifiers- Raman Other Amplifiers Emitters Semiconductor Fiber Receivers PIN APD Modulators Mach Zehnder Electro-absorption Acoust-optic Filters Fiber Bragg gratings Fabry Perot Mach-Zehnder Isolators Couplers Switches Mechanical Wavelength converters Multiplexers/ Demultiplexers Program E1- 2b Optical technologies

  3. 10. Couplers 1.1. Optical Connectors (14) 1.2. Technologies (1) 1.3. Optical Planar Circuits (1) 1.4. Splitters and Couplers (13) E1- 2b Optical technologies

  4. 11. Isolators 1.1. Isolators (1) 1.2. Circulators (1) 1.3. Isolators and circulators (2) 1.4. Integrated Photonic Circuits (4) 1.5. Integrated Optics (8) 1.6. Sub-wavelength-diameter silica wires for low-loss optical wave guiding (1) E1- 2b Optical technologies

  5. António Teixeira, Paulo André Couplers and other components

  6. Optical Connectors Optical connectors are used for a temporal connection between two fibers or between a fiber and the transmitter or receiver. The most important characteristics of an optical connector are: • Insertion loss (aka attenuation): is the decrease in transmitted signal power caused by the connector, measured as the light goes out from one fiber and goes into the next fiber. The causes of the insertion loss are due to intrinsic and extrinsic mechanisms. • Return loss (aka Reflectivity): is the ratio of the optical power arriving at an the connector to the optical power reflected back. • Degradationand Durability: the attenuation of a connector changes due to connection and disconnections processes. • Environmental stability: the attenuation of a connector can depend on the environmental conditions as: temperature, vibrations,… Each application requires a specific type of connector. • Cost: usually related with the mechanical precision of the connector. E1- 2b Optical technologies

  7. Causes of Insertion Loss Intrinsic mechanisms(due to differences between the two fibers): • Mismatch of the core area of the two fibers • Mismatch of the numerical aperture of the two fibers • Excentricity of the cores of the fibers • Mismatch of the refractive index profiles Extrinsic mechanisms(due to the physical characteristics of the connection): • Lateral misalignment of the fibers • Angular misalignment of the fibers • Gap between the fibers • Reflections at the fiber ends (neff=1.46) E1- 2b Optical technologies

  8. Troubles with Connectors Separation Lateral Deviation Angular Deviation Reflections and Interference Concentricity Ellipsicity E1- 2b Optical technologies

  9. Connectors -Classification by Structure Connecting by proximity: Connecting by beam expansion: Ferrule End of fiber Adaptor Fiber cable Connector Lens Collimated beam E1- 2b Optical technologies

  10. Connectors - type of fixing classification SMA (screw thread): ST (tipe BNC, angular alignment): FC (screw, with angular alignment): SC (rectangular, by pressure): E1- 2b Optical technologies

  11. Connectors - type of polish classification Conventional: polish perpendicular to the optical axis • (examples: ST, FC, SC) • Typical Return loss: 14 dB _/PC (Physical Contact): concave polish • (e.g.: FC/PC, SC/PC) • Typical Return loss: 35 dB – 45 dB (SPC) _/APC (Angle PC): angled polish • (e.g.: FC/APC, SC/APC) • Typical Return loss: 60 dB E1- 2b Optical technologies

  12. Optical Connectors E1- 2b Optical technologies

  13. FC ST E2000 2.5mm ferrule 1.25mm ferrule LC MU E1- 2b Optical technologies

  14. Connector’s performance evaluation (example) FC/PC connector: • Insertion Loss: 0.3 dB typical • Return Loss: > 45 dB typical • Temperature Range: -40°C to +85°C • Durability: <0.2 dB change after 500 mating cycles E1- 2b Optical technologies

  15. Angled Physical Contact (APC) Air gap Physical Contact (PC) 8º typical insertion losses: 0.5 dB Insertion Losses: <0.25 dB InsertionLosses : 0.4 to 0.9 dB Return: > 60 dB Return: < 14 dB (Fresnel) Return: > 40 dB E1- 2b Optical technologies

  16. Mechanical Precision • Optical Axis is aligned with better precision than ±1 µm • Physical contact is necessary between connectors Cleaning the contact region is absolutely necessary Key Fiber Ferrule Sleeve E1- 2b Optical technologies

  17. Derickson, Dennis, “Fiber Optic Test and Measurement”, Prentice Hall PTR,1998, E1- 2b Optical technologies

  18. Optical splices • Permanent connections between fibers • The fiber ends will be permanently fixed (aligned) by means of chemical, mechanical solutions or by fusion of the fibers. • Main characteristics of the splice are: • Lower insertion loss than connectors, e.g.: 0.1 dB. • Lower return losses than connectors, e.g.: 80 dB. • Longer durability (with time) • Lower cost • Relative easy realization E1- 2b Optical technologies

  19. Connector Cleaning Filtered Air • alcohol isopropyl cleaning with an handkerchiefor cotton for optical applications; • filtered air cleaning; • abrasive tape cleaning. AlcoolIsopropyl E1- 2b Optical technologies

  20. Technologies • Fiber Technology Interesting due to its nature • Low connection losses to transmission media by excellence, itself • Micro-optical mounting of micro-devices (prisms, lenses, crystals, etc) in order to fulfill an objective. • This technology is now more mature and the commuter matrices are based on micro-mirrors of MEM (micro-electronic machine) technology • Planar Guide Technology (PLC - Planar Lightwave Circuit ) using the planar guides' building techniques and its treatment to obtain complex functionalities over a substrate E1- 2b Optical technologies

  21. Optical Planar Circuits Concept Advantages • Integration and interconnection of similar component sets • Higher control of interaction spaces and critical dimensions • Many functionalities, due to precision and other requirements can’t be made on another technology • Reproducibility and mass fabrication can be easily obtained E1- 2b Optical technologies IBM White Book, pags.150,151

  22. Optical Couplers and Splitters On a network, it’s necessary to part or combine signals These devices are responsible for the light distribution from one or several input fibers to one or several output fibers Types: Passive, bidirectional, coupler, power splitter Applications: • Distribution networks for CATV, • Local Area networks (e.g. Passive Optical Network, FTTH) • Wavelength Division Multiplexing systems (WDM) Important characteristics: • Return loss » A part of the signal is reflected • Insertion loss » A part of the signal is lost when transiting through the sub-system • Excess loss » Extra quantity of losses, beyond the predicted theorical value E1- 2b Optical technologies

  23. Multi-port Optical Couplers 1xN or NxN Using 2x2 optical couplers: Optical Fibers E1- 2b Optical technologies

  24. Optical Couplers and Splitters - Characteristics Characteristics to take into account: • Number of ports • Insertion loss and division ratio Insertion loss: attenuation of a signal at an import port from another input port Insertion loss (dB) = 10 log (P_1/P_3) Division (or splitting) ratio: % of the input power at each of the output ports 100 . P_3/(P_3 + P_4) % , 100 . P_4/(P_3 + P_4) % • Directivity • Wavelength dependency • Fiber type (single-mode or multi-mode) • Cost Coupler input output E1- 2b Optical technologies

  25. Optical Couplers and Splitters - Characteristics • Excess loss: signal attenuation above the minimum one required for the achieved splitting ratio. Excess loss (dB)= 10 log P_in/(∑P_out) • Directivity (aka isolation): signal attenuation at one of the input ports different from the one at which signal is being injected Directivity (dB) = 10 log P_1/P_2 input output E1- 2b Optical technologies

  26. Optical Couplers – Classification by Working Principle Type • Bylateral displacement • Beam divisionby semitransparent mirror • Fused bi-conical taper (FBT) 2x2 (fused fibers) Directional coupler Beam Splitter E1- 2b Optical technologies

  27. Resonant Coupling Two fibers are closely placed in parallel A ressonant coupling is created and where no signal could be found in the fiber, it progressivly appears • By the end of the coupling length, all energy was coupled to other guide • It carries on like this periodically • This way a 3dB coupler is defined, with half of the coupling length, and there on successively -- 1 __ 2 E1- 2b Optical technologies IBM White Book, pags.186,188

  28. Resonant Couplers The coupling length increases with the nucleus distance apart The coupling lengths strongly depend on the wavelength From one port to the port on the opposite fiber, there is phase rotation Ei,out are the output fields, Ei,in are the input fields  is the coupling factor The couplers are symmetrical, such as in the direction 1->2,3 there is an equivalence between schemes; however, in the opposite direction, joining 2 similar signals in 2 and 3, will only result in 1 signal of amplitude equal to the mean of both their amplitudes!!! E1- 2b Optical technologies IBM White Book, pag.189

  29. Practical Couplers Fused Taper Couplers • These are warmed (through heat or electrical discharge) and the contact point is stretched in a way for narrower nucleus to form, and to there be better coupling • These are the more widely diffused and present excess losses in the order of 0.2dB Double nucleus fibers • Have high potential, but are difficult to connect Polished or Etching • It’s necessary to physically part of the cladding in order to bring the nucleus closer together Planar Guides • very efficient, however they present fiber coupling problems E1- 2b Optical technologies

  30. Practical Couplers and Splitters Couplers can implement 1x2 2x2 2x1 as well as other multiples E1- 2b Optical technologies

  31. Coupler structures Based on simple couplers, more complex structures can be achieved • losses to an 8 output = 9dB 180º 90º 0º 90º 180º 90º 180º 270º We can have couplers with different coupling levels: 1%, 2%, 5%, 30% are quite common Lossless Coupling, only for different ’s signals E1- 2b Optical technologies IBM White Book , pag.191

  32. -selective Couplers and Splitters By correctly drawing he coupler’s length, a ~100% light coupling, coming from several s, can be achieved. • Typical insertion losses to these couplers are < 1.5dB • High bandwidths: 30-50nm • Operation Bands : 1300-1500, 1550-1600, etc. E1- 2b Optical technologies IBM White Book, pag.191

  33. Star Couplers It’s simply a coupler where each input is partially presented on each output Are the base to many LAN and MAN network architectures 3dB based 8x8 star E1- 2b Optical technologies IBM White Book, pag.194,195

  34. Beam-splitters Sometimes it’s needed to split two polarizations from a beam of light Based on birefringent materials, devices whose total internal reflection angle is different for both polarizações can be designed • Calcite (CaCO2), Rutile (TiO2) are examples of materials of this type E1- 2b Optical technologies IBM White Book, pags.196,197

  35. António Teixeira, Paulo André Isolators

  36. 11. Isolators 1.1. Faraday Effect (3) 1.2. Circulators (1) 1.3. Isolators and circulators (2) 1.4. Polarization of Light (4) 1.5. Polarization Controllers (1) 1.6. Integrated Photonic Circuits (4) 1.7. Integrated Optics (7) 1.8. Sub-wavelength-diameter silica wires for low-loss optical wave guiding (1) E1- 2b Optical technologies

  37. Isolators Faraday Effect For some materials, being light driven causes a rotation in polarization, at the opposite direction of the driven light. In order not to loose a given polarization, a Polarization Beam Splitter and two of these systems can be used. Insertion losses ~1dB E1- 2b Optical technologies IBM White Book, pag.199

  38. Isolators • It transmits light only in one direction • Its is used to avoid reflected signals (e.g. from connectors) that can affect to lasers, optical amplifiers,… • It is built by a Faraday rotator of 45º between two linear polarizers. Transmitted Wave Polarizer B Faraday Rotator Incident Wave Polarizer A E1- 2b Optical technologies

  39. Isolators Reflected Wave • Typical material: YIG (Yttrium-iron-garnet) • Isolation: 30 – 60 dB • Loss: 1 – 2 dB* (*using Polarization Beam Splitters) Polarizer B Polarizer A Faraday Rotator Incident Wave E1- 2b Optical technologies

  40. Circulators These devices are used in many applications (e.g.: used as reflection spectrums in some Fiber Bragg gratings devices) Can be built based on isolators, are usually micro-optical devices Low Insertion Losses <1.5dB E1- 2b Optical technologies IBM White Book, pags.200-203

  41. Isolators and circulators E1- 2b Optical technologies

  42. Applications: Laser Protection and reflection amplifiers. Insertion Losses: Low losses on the co-propagation direction: 0.2 to 2dB High losses on the counter-propagation direction: 20 to 40dB simple, 40 to 80 dB dual) Return: Better than 60 dB The circulators can be thought of as two isolators in series CIRCULATOR E1- 2b Optical technologies

  43. Polarization of Light • It describes the trajectory of the electrical field in a plane transversal to the propagation vector: State of Polarization (SOP). • Relation between X and Y components depends on module and phase mismatch • SOP: ellipse (general), lineal (H, V, 45º,..), circular Linear Circular Elliptical E1- 2b Optical technologies http://en.wikipedia.org/wiki/Polarization

  44. Polarization of Light – how to parameterize • Ellipse variables: • Ellipticity, U (the ratio of the two semi-axes). • An ellipticity of 1 corresponds to circular polarization. • Azimuth angle, V (the angle between the major semi-axis of the ellipse and the x-axis) • An ellipticity of zero corresponds to linear polarization The arctangent of the ellipticity, • Χ = tan−1 (ε) (the "ellipticity angle"), is also commonly used. • Degree of polarization • Light from a laser source is monocromatic and highly polarized E1- 2b Optical technologies

  45. Polarization of Light – Optical Components • POLARIZER: it eliminates the component perpendicular to the main axis of the polarizer. • Polarization Beam Splitter (PBS): it separates both components • RETARDER: it shifts the phase of the light wave between two perpendicular polarization components • HWP: 180º, QWP: 90º, Retarder Faraday Rotator http://en.wikipedia.org/wiki/Wave_plate • ROTATOR: It moves the azimuth angle of the SOP without modifying the ellipticity. • Faraday effect: rotation proportional to the magnetic field axial to the magneto-optic element http://en.wikipedia.org/wiki/Faraday_rotator E1- 2b Optical technologies

  46. Polarization of Light – Effects in Optical Links Polarization Dependent Loss (PDL): it measures the variation of the attenuation of the device as a function of the SOP (usually two linear orthogonal polarizations) to the input signal (similar to a Polarizer effect) • dB Polarization Mode Dispersion (PMD): variation of the group propagation velocity in an long distance optical link as a function of the SOP of the input signal (similar to a Retarder effect) • ps/km½ E1- 2b Optical technologies

  47. Polarization Controllers In many cases it’s necessary to affect a field’s polarization • Line up with the main axis in a semiconductor, etc. We can build such device, based on a bi-refringent material on a fiber loop • In a fiber loop, the suffered tensions and compressions by the fiber bending, are in many cases enough to cause bi-refringency • By rotating the axis, we can get changes on the electrical field orientation Typical devices have three loops with twice the turns and another rotated by 90º We can use this effect with piezo-electric devices that pressure the fiber on some points, altering their bi-refringency E1- 2b Optical technologies IBM White Book, pag.204

  48. Integrated Photonic Circuits Optical ICs that integrate Waveguides passive structures; Waveguides with modulation electrical signals (V/I) (switches, modulators); Waveguides with modulation gain by electrical current (SOAs, lasers). Advantages optical coupling efficiency optimization; electro-optical integration in the same substrate; manufacture cost decrease. E1- 2b Optical technologies

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