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Optical Components

Optical Components. Ajmal Muhammad, Robert Forchheimer Information Coding Group ISY Department. Outline. Types of optical components Passive (reciprocal & non-reciprocal ) Lens, couplers, isolators, circulators, filters, multiplexer, demultiplexer Active

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Optical Components

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  1. Optical Components Ajmal Muhammad, Robert Forchheimer Information Coding Group ISY Department

  2. Outline • Types of optical components • Passive (reciprocal & non-reciprocal) Lens, couplers, isolators, circulators, filters, multiplexer, demultiplexer • Active Modulator, switch, optical amplifier, wavelength converter, gain equalizer • Wavelength Selectivity • Fixed • Tunable • Parameters Temperature dependency, insertion loss (inputoutput loss) inter-channel cross-talks, fast tunability, stability and polarization dependency

  3. Requirements • Bandwidth • Low insertion loss (inputoutput loss) • High return loss (outputinput loss) • Polarization insensitivity • Low crosstalk • High extinction ratio • Temperature insensitivity • Low control power • Small size • Cost

  4. Optical Component Platform • Micro-optic components The assembly of discrete elements are placed together in an optical component. The elements require precise optical alignment to maximize the performance. • Integrated optics components Uses planar manufacturing techniques to develop devices such as Array Waveguide Grating (AWG), Variable Optical Attenuators (VOA), Electro-optic Modulators, etc. • Fiber based optical components Devices made of fibers such as fusedoptical couplers, fused WDMs, Fiber-Bragg gratings (FBG), etc. • Hybrid type

  5. Passive Components • Coupler: versatile device used as a building block for several other optical devices • Isolator: used in systems at the output of amplifiers and lasers to prevent reflections • Filter: to multiplex and demultiplex wavelengths in a WDM system, and to provide equalization of the gain and filtering of noise in optical amplifier • MUX & DEMUX: MUX combines signals at different wavelengths on its input ports onto a common output port, DEMUX performs the opposite function

  6. Couplers Couplers • Structure • NxN (e.g., 2x2) • α is proportional to l (α is coupling ratio, l is coupling length) • Parameters of interest • Coupling ratio • Coupling length • Excess loss (beyond α) • Type • Wavelength dependent (α has wavelength-dependency) • Wavelength independent (wavelength flat) • Splitting ratio • 3dB (splitting the power evenly) - α=0.5 • Taps (e.g., α ∼ 1 – thus, a very small portion is dropped)

  7. Couplers - Passive Reciprocal Device • They can combine or separate different wavelengths • The lights (different wavelengths) are coupled together • Example: 8x8 3-dB couplers 1310 (signal) Amplified Signal 1550 nm (pump) Wavelength-dependent coupler Multiple signals combined and broadcast to many outputs

  8. Couplers 1x2 coupler 6x6 coupler

  9. Isolators - Passive Non-Reciprocal Device • Transmit in one direction only • Avoid reflection of laser – or any reflection • One input, one output or multiple ports • Key parameters are insertion loss and excess loss • Example: circulator

  10. Operation of Isolators

  11. Isolators

  12. Passive Components • Coupler: versatile device used as a building block for several other optical devices • Isolator: used in systems at the output of amplifiers and lasers to prevent reflections • Filter: Variety of technologies are available

  13. Gratings Describe a device involving interference among multiple optical signals coming from the same source but having difference phase shift There are a number of gratings • Reflective • Transmission • Diffraction • Stimax (same as reflection but integrate with concave mirrors)

  14. Gratings • Transmission gratings • The incident light is transmitted through the slits • Due to diffraction (narrow slits) the light is transmitted in all direction • Each slit becomes a secondary source of light • A constructive interference will be created on the image plane only for specific WLs that are in phase  high light intensity • Narrow slits are placed next to each other • The spacing determines the pitch of the gratings • Angles are due to phase shift Transmission gratings Reflective gratings Diffraction gratings

  15. Fiber Bragg Gratings Any periodic perturbation in the propagation medium serves as a Bragg gratings Diffractive optical element

  16. Optical Add/Drop Using Fiber Bragg Grating

  17. Fabry-Perot Filters A cavity with highly reflective mirrors parallel to each other (Bragg structure) • Acts like a resonator • Also called FP Interferometer • Used in lasers

  18. Tunability of Fabry-Perot • Changing the cavity length (l) • Varying the refractive index (n) within the cavity • Mechanical placement of mirrors Not very reliable • Using piezoelectric material within the cavity Thermal instability

  19. Multilayer Dielectric Thin Film Filters • Dielectric thin-film (DTF) interference filters consist of alternating quarter-wavelength thick layers of high refractive index and low refractive index each layer is a quarter-wavelength thick. • The primary considerations in DTF design are: • Low-pass-band loss (« 0.3 dB) • Good channel spacing (> 10 nm) • Low inter-channel cross-talk (> -28 dB) DTF filters MUX/DEMUX using DTF filters

  20. Mach-ZehnderInterferometer • Uses two couplers • The coupling ratio can be different • A phase difference between two optical paths may be artificially induced • Adjusting ΔL changes the phase of the received signal • Because of the path difference, the two waves arrive at coupler 2 with a phase difference • At coupler 2, the two waves recombine and are directed to two output ports • each output port supports the one of the two wavelengths that satisfies a certain phase condition • Note: • Δf=C/2nΔL • ΔΦ=2πf.ΔL.(n/c)

  21. Tunability Can be achieved by altering n or L

  22. Arrayed Waveguide Grating (AWG) AWG is a generalization of the Mach-Zehnder interferometer

  23. AWG as DEMUX and Cross-Connect Input coupler Arrayed guides Output coupler Static Wavelength Cross-connect

  24. Multiplexer/Demultiplexer

  25. Multiplexer/Demultiplexer

  26. Active Components • Modulator, switch, and router • Optical amplifier (fiber amplifier, semiconductor amplifier) • Wavelength converter • Gain equalizer Optical switch can be used for:1) Light modulation(phase & intensity)2) Routing optical data

  27. Type of Optical Modulators/Switches

  28. Micro-Electro-Mechanical (MEMS) Switch

  29. Electro-Optic Modulator Need material with high electro-optic effectElectro-optic: refractive index change is proportional to applied electric field

  30. Wavelength Converter

  31. Different types of Wavelength Converter • OE/EO regeneration • SOA-based Cross-gain modulation Cross-phase modulation Four-Wave mixing • Fiber-based Cross-phase modulation Four-Wave mixing OE/EO Cross-gain Cross-phase Four-Wave mixing

  32. Gain Equalizers

  33. Gain/Power Equalizers

  34. Gain/Power Equalizers

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