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

2. Outline Types of optical components Wavelength Selectivity Parameters
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 fused optical 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 Parameters of interest Type
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 Filter: Variety of technologies are available
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. Diffractive optical element
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-Zehnder Interferometer
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 effect Electro-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
OE/EO
Cross-gain
Cross-phase
Four-Wave mixing

32. Gain Equalizers

33. Gain/Power Equalizers

34. Gain/Power Equalizers