Download Technologies - E

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
© 2005, it - instituto de telecomunicações. Todos os direitos reservados.
This tutorial is licensed under the Creative Commons
http://creativecommons.org/licenses/by-nc-sa/3.0/
Program
1.
2.
3.
4.
Basic Photonic Measurements
Material growth and processing
Semiconductor materials
Transmission systems
performance assessment tools
5. Optical Amplifiers
a)
b)
c)
d)
Semiconductor Optical Amplifiers
(SOAs)
Erbium Doped Fiber Amplifiers
(EDFAs)
Fiber Amplifiers- Raman
Other Amplifiers
6. Emitters
a)
b)
Semiconductor
Fiber
7. Receivers
a)
b)
PIN
APD
E1- 2b Optical technologies
2 Jan 2006
8. Modulators
a) Mach Zehnder
b) Electro-absorption
c) Acoust-optic
9. Filters
a) Fiber Bragg gratings
b) Fabry Perot
c) Mach-Zehnder
10. Isolators
11. Couplers
12. Switches
a) Mechanical
b) Wavelength converters
c) Multiplexers/ Demultiplexers
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
3 Jan 2006
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
4 Jan 2006
António Teixeira, Paulo André
Couplers and other components
© 2005, it - instituto de telecomunicações. Todos os direitos reservados.
This tutorial is licensed under the Creative Commons
http://creativecommons.org/licenses/by-nc-sa/3.0/
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.
•
Degradation and 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
6 Jan 2006
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
7 Jan 2006
Troubles with Connectors
Lateral
Deviation
Angular
Deviation
Concentricity
Ellipsicity
E1- 2b Optical technologies
8 Jan 2006
Separation
Reflections and
Interference
Connectors -Classification by Structure
Connecting by proximity:
Ferrule
End of fiber
Adaptor
Fiber cable
Connector
Connecting by beam expansion:
Lens
Collimated beam
E1- 2b Optical technologies
9 Jan 2006
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
10 Jan 2006
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
11 Jan 2006
Optical Connectors
E1- 2b Optical technologies
12 Jan 2006
FC
ST
E2000
2.5mm ferrule
LC
MU
E1- 2b Optical technologies
13 Jan 2006
1.25mm ferrule
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
14 Jan 2006
Air gap
typical insertion
losses: 0.5 dB
Return: < 14 dB (Fresnel)
Physical Contact
(PC)
Angled Physical
Contact (APC)
Insertion Losses: <0.25 dB
Insertion Losses :
0.4 to 0.9 dB
Return: > 60 dB
Return: > 40 dB
 nt  ni 
R  

 nt  ni 
E1- 2b Optical technologies
15 Jan 2006
8º
2
Mechanical Precision
•
•
Optical Axis is aligned with better precision
than ±1 µm
Physical contact is necessary between
connectors
Key
Fiber
Ferrule
Cleaning the contact region is absolutely
necessary
E1- 2b Optical technologies
16 Jan 2006
Sleeve
Derickson, Dennis, “Fiber Optic Test and
E1- 2b Optical technologies Measurement”, Prentice Hall PTR,1998,
17 Jan 2006
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
18 Jan 2006
Connector Cleaning
 alcohol isopropyl cleaning with
an handkerchief or cotton for
optical applications;
Filtered Air
 filtered air cleaning;
 abrasive tape cleaning.
Alcool Isopropyl
E1- 2b Optical technologies
19 Jan 2006
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 (microelectronic 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
20 Jan 2006
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
21 Jan 2006
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 subsystem
•
Excess loss » Extra quantity of losses, beyond the predicted theorical
value
E1- 2b Optical technologies
22 Jan 2006
Multi-port Optical Couplers
1xN or NxN
Optical Fibers
Using 2x2 optical couplers:
E1- 2b Optical technologies
23 Jan 2006
Optical Couplers and Splitters - Characteristics
Coupler
input
Characteristics to take into account:
• Number of ports
• Insertion loss and division ratio
output
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
E1- 2b Optical technologies
24 Jan 2006
Optical Couplers and Splitters - Characteristics
input
output
•
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
E1- 2b Optical technologies
25 Jan 2006
Optical Couplers – Classification by Working Principle Type
•
•
By lateral displacement
Beam division by semitransparent mirror
Directional coupler
•
Beam Splitter
Fused bi-conical taper (FBT) 2x2 (fused fibers)
E1- 2b Optical technologies
26 Jan 2006
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
27 Jan 2006
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
28 Jan 2006
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
29 Jan 2006
Practical Couplers and Splitters
Couplers can implement 1x2 2x2 2x1 as well as
other multiples
E1- 2b Optical technologies
30 Jan 2006
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
31 Jan 2006
-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
32 Jan 2006
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
33 Jan 2006
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
34 Jan 2006
António Teixeira, Paulo André
Isolators
© 2005, it - instituto de telecomunicações. Todos os direitos reservados.
This tutorial is licensed under the Creative Commons
http://creativecommons.org/licenses/by-nc-sa/3.0/
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
36 Jan 2006
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
37 Jan 2006
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
38 Jan 2006
Isolators
Reflected Wave
Polarizer B
Polarizer A
Faraday Rotator
Incident Wave



Typical material: YIG (Yttrium-iron-garnet)
Isolation: 30 – 60 dB
Loss: 1 – 2 dB* (*using Polarization Beam Splitters)
E1- 2b Optical technologies
39 Jan 2006
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
40 Jan 2006
Isolators and circulators
E1- 2b Optical technologies
41 Jan 2006
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
E1- 2b Optical technologies
42 Jan 2006
CIRCULATOR
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
E1- 2b Optical technologies
43 Jan 2006
Circular
Elliptical
http://en.wikipedia.org/wiki/Polarization
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
44 Jan 2006
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.
http://en.wikipedia.org/wiki/Faraday_rotator
E1- 2b Optical technologies
45 Jan 2006
 Faraday effect: rotation proportional to the
magnetic field axial to the magneto-optic
element
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
46 Jan 2006
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 birefringency
• 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 piezoelectric devices that pressure the fiber
on some points, altering their birefringency
E1- 2b Optical technologies IBM White Book, pag.204
47 Jan 2006
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
48 Jan 2006
E1- 2b Optical technologies
49 Jan 2006
E1- 2b Optical technologies
50 Jan 2006
doped SiO2 or SiOxNy
SiO2 on Si
+ very low losses
+ cpmpatible fiber core dimensions
+ low dn/dT
+ matured technology
- only passive components
InP
SiO2
Si
InP
+ activos and passive components
InGaAsP
- small core  diffícult transition into the fiber
- polarization dependency
InP
Ti-diffusion
LiNbO3
+ passive waveguides, modulators and switches
+ very low losses
+ matured technology
- high cost
E1- 2b Optical technologies
51 Jan 2006
LiNbO3
Integrated Optics
E1- 2b Optical technologies
52 Jan 2006
P
P
L0
L0/2
P/2
P
E1- 2b Optical technologies
53 Jan 2006
P/2
E1- 2b Optical technologies
54 Jan 2006
1550 nm
E1- 2b Optical technologies http://www.cem2.univ-montp2.fr/~moreau/
55 Jan 2006
1310 nm
E1- 2b Optical technologies http://www.cem2.univ-montp2.fr/~moreau/
56 Jan 2006