This document discusses various optical components used in fiber optic communication systems. It describes passive components like couplers, isolators, filters, and multiplexers/demultiplexers. It also covers active components such as modulators, switches, optical amplifiers, and wavelength converters. Different technologies for implementing these components are presented, including micro-optics, integrated optics, fiber-based, and hybrid approaches. Key parameters and requirements for optical components are also outlined.

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 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
 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)
Couplers

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)
1550 nm
(pump)
Amplified
Signal
Wavelength-dependent
coupler
Multiple signals combined and
broadcast to many outputs

8. Couplers
6x6 coupler1x2 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)
MUX/DEMUX using DTF filtersDTF 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
Cross-phase modulation
Four-Wave mixing
Cross-gain
Cross-phase
Four-Wave
mixing
OE/EO

32. Gain Equalizers

33. Gain/Power Equalizers

34. Gain/Power Equalizers