Transcript Chapter Three - UniMAP Portal

Chapter 3
Optical Components/Devices
OPTICAL FIBER PASSIVE DEVICES:
COUPLERS, ATTENUATORS, ISOLATORS,
CIRCULATORS, BRAGG GRATINGS AND
ATTENUATORS
Optical Passive Devices
Passive Components
i.
Couplers
ii.
Isolators
iii.
Circulators
iv.
Fiber Bragg Gratings
v.
Attenuator
Optical Couplers
• Couplers can perform both combining and splitting.
• The devices are widely used in optical LAN and broadcasting
networks
Optical Couplers
 Couplers are bi-directional, they can carry light in
either direction.
 Used to split and combine the signals.
 A coupler with single fiber at one end and two at
the other end would be referred to as 1 x 2
Coupler ( read as one by two).
 Although 1 x 2 and 2 x 2, are the most common
sizes they can be obtained in wide range types up
to 32 x 32.
Optical Couplers
• An optical coupler is a passive (unpowered) device that diverges
(1:N) or converges (N:1) optical signals from one fibre or optical
signal path to more than one (or vice versa.)
• Configurations: Splitters, taps, combiners, directional couplers
Optical Couplers
Splitting Ratio (Coupling Ratio): The proportion of the input power at each output
is called the splitting ratio or coupling ratio.
 In a 1 x 2 coupler, the input signal can split
between the two outputs in any desired ratio. In
practice however, the common ones are 90:10 and
50:50. These are also written as 9:1 and 1:1.
 In the cases where the splitting ratio is not 1:1, the
port which carries the higher power is sometimes
called the throughput port and the other is called
the tap port.
2X2 Optical coupler
Optical Couplers
Coupling Tolerance:
 Even when the splitting ratio is quoted as 1:1, it is
very unlikely, due to manufacturing tolerances
that the input power is actually shared equally
between two outputs. The acceptable error of
between 1% and 5% is called coupling or splitting
tolerance.
Optical Couplers
Losses:a. Excess loss
(The Ratio of the input power to the total output
power). The light energy has been scattered or
absorbed within the coupler and is not available at
the output.
b. Crosstalk or directivity
When we apply power to 1, we expect it to come out
of port 2 and 3 but not out of port 4, the other input
port. Because of backscatter within the coupler, some
energy is reflected back and appear at port 4. This
backscatter is very slight and is called directionality
loss or crosstalk.
Optical Couplers
c. Insertion loss
Refers to the loss for a particular port-to-port path.
For example, for the path from input port i to
output port j. This looks at a single output power
compared with the input power. There are two
possibilities, the power coming out of port 2 and
compare it with the input power at port 1 or port 3
compared with input power port 1.
Optical Couplers: Characteristics
• COUPLING RATIO
Optical Couplers
• EXCESS LOSS
– Ratio of the input power to the total output power
Optical Couplers
• INSERTION LOSS
Optical Couplers
• DIRECTIVITY
OPTICAL COUPLER
SPECIFICATION
Standard Type
The device is capable of branching or combining an optical power having a single wavelength in
a designated ratio.
Standard specification
Applicable connector, etc
Number of ports
2x2
Wavelength
1310nm, 1480nm, 1550nm
Excess loss
0.2dB or less
Split ratio
50:50 to 95:5 in (%)
Directivity
50dB or better
Fiber type
0.25mm coated fiber, 0.9mm loose-tube
fiber, 2.0mm fiber cord
Ambient temperature
-40 to +75 deg.C, or -20 to +60 deg.C
(2.0mm fiber coad)
Length
0.5m, 1.0m, 1.5m, 2.0m
Connector
FC, SC, SC2, MU, None
End-face polishing
Flat, PC, Super-PC
WDM Coupler
WDM (wavelength division multiplexing) coupler is an optical device capable of wavelength
dividing two wavelengths on a single optical fiber into two, or vice versa; i.e., combining two
wavelengths on two optical fibers into one.
Standard specification
Applicable connector, etc
Number of ports
2x2
Wavelength
980nm/1550nm, 1310nm/1550nm
Insertion loss
Pass port: 0.2dB or less
Cut-off port: 20dB or more
Split ratio
50:50 to 95:5 in (%)
Directivity
50dB or better
Fiber type
0.25mm coated fiber, 0.9mm loose-tube fiber,
2.0mm fiber cord
Ambient temperature
-40 to +75 deg.C, or -20 to +60 deg.C
(2.0mm fiber coat)
Length
0.5m, 1.0m, 1.5m, 2.0m
Connector
FC, SC, SC2, MU, None
End-face polishing
Flat, PC, Super-PC
Optical Fibre Connectors
Type
BICONIC
D4
EC/RACE
ESCON
FC
FDDI
HMS-10
SC
SC DUPLEX
SMA
ST
Typical Insertion Loss (dB)
0.6 - 1.0
0.2 - 0.5
0.1 - 0.3
0.2 - 0.7
0.5 - 1.0
0.2 - 0.7
0.1 - 0.3
0.2 - 0.4
0.2 - 0.4
0.4 - 0.8
0.4 (SM) 0.5(MM)
Fibre Type
SM, MM
SM, MM
SM
MM
SM, MM
SM, MM
SM
SM, MM
SM, MM
MM
SM, MM
Optical Fibre Connectors
Example: 1
Calculate the output power at port 3?
Sol:
Example 2:
A product sheet for a 2x2 single-mode biconical tapered coupler with a 40/60
splitting ratio states that the insertion losses are 2.7 dB for the 40-percent channel.
a) If the input power Po =200 µw , compute P1 and P2
b) Evaluate the excess loss
c) From the calculated values of P1 and P2, verify that the splitting ratio is
40/60.
Sol:
ISOLATORS
•To allow light to propagate in one direction only
P0
P1
A
B
P2
ISOLATORS
P0
P1
A
B
P3
P2
P 
Insertion loss  10 log  0 
 P1 
P 
Isolation  10 log  2 
 P3 
ISOLATOR SPECIFICATION
CIRCULATORS
Optical circulators redirects light sequentially
from port-to-port in a unidirectional path
2
Same characteristics as isolators
by looking port 1-2 @ port 2-3
1
3
To extract the desired wavelength, a circulator is used in conjunction with the
rating
CIRCULATORS: WORKING PRINCIPLE
CIRCULATORS
Characteristics:
•high isolation
•low insertion loss
•can have more than 3 ports
Applications:
•Optical Amplifier
•Add-Drop Multiplexer
•Bi-directional transmission
•To monitor back-reflection
from devices or optical
subsystems
CIRCULATORS: APPLICATION
Fiber Bragg Gratings
A grating is a periodic structure or perturbation in a material
that creates a property of reflecting or transmitting light in a certain
direction depending on the wavelength.
External writing technique using UV light
l2
Fiber Bragg Gratings
l1
l2
l1
l3
Transmission
Reflection
l2
l2  2neff
l3
Fiber Bragg Gratings
Fiber Bragg Gratings
Figure 2: FBGs reflected power as a
function of wavelength
The reflected wavelength (λB), called the Bragg wavelength, is defined by the relationship,
,
where n is the average refractive index of the grating and Λ is the grating period.
Fiber Bragg Gratings
Characteristics:
•high reflectivity to be used as a filter
•low insertion loss
•low cost/simple packaging
Fiber Bragg Gratings
Transmission spectrum
•band-rejection filter
l2
Fiber Bragg Gratings
Reflection spectrum
•reflective filter
FBG APPLICATIONS
FBG APPLICATIONS
Gain flattening filter
-15
+
-20
-25
-30
1530
1540
1550
Wavelength (nm)
1560
1570
-15
-5
=
-10
-15
-20
1520
P ower (dBm)
-10
Insert ion loss (dB)
P ower (dBm)
-5
-35
1520
-10
0
0
-20
-25
-30
1530
1540
1550
Wavelength (nm)
1560
1570
-35
1520
1530
1540
1550
Wavelength (nm)
1560
1570
FBG APPLICATIONS
Laser diode wavelength stabilizer
FIBER BRAGG GRATING SPECS.
ATTENUATORS
Function: To decrease light intensity (power)
Working Principles
Fiber displacement
Rotating an absorption disk
ATTENUATORS
Programmable attenuator
Set @ 60 dB
Insertion loss = 2 dB
Pin = 0 dBm
Pout = 0 - 20 - 2 = -22 dBm
ATTENUATORS
Characteristics:
•low insertion loss
•dynamic attenuation range
•wide range of operating wavelength
•high return loss
Applications:
•adjust optical power to the dynamic range of receivers
•equalize power between different WDM signals
•To avoid receiver saturation
ATTENUATORS
Mechanical attenuator - by adjusting a screw
Waveguide attenuator - by adjusting biasing current