Chapter 3 Optical Components/Devices
Oct 22, 2015
Chapter 3Optical Components/Devices
OPTICAL FIBER PASSIVE DEVICES:
COUPLERS, 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 CouplersSplitting 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 CouplersCoupling 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 CouplersLosses:- 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.
2X2 Optical coupler
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 COUPLERSPECIFICATION
Standard TypeThe device is capable of branching or combining an optical power having a single wavelength
in a designated ratio.
Standard specification 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)
Applicable connector, etc 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 Number of ports 2x2
Wavelength 980nm/1550nm, 1310nm/1550nm
Insertion loss Pass port: 0.2dB or lessCut-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)
Applicable connector, etc 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
Optical Fibre ConnectorsType Typical Insertion Loss (dB) Fibre Type
BICONIC 0.6 - 1.0 SM, MMD4 0.2 - 0.5 SM, MM
EC/RACE 0.1 - 0.3 SMESCON 0.2 - 0.7 MM
FC 0.5 - 1.0 SM, MMFDDI 0.2 - 0.7 SM, MM
HMS-10 0.1 - 0.3 SMSC 0.2 - 0.4 SM, MM
SC DUPLEX 0.2 - 0.4 SM, MMSMA 0.4 - 0.8 MMST 0.4 (SM) 0.5(MM) SM, MM
Optical Fibre Connectors
Example 1,
Sol:
Example: 2
Calculate the output power at port 3?
Sol:
P0
P2
P1
A B
•To allow light to propagate in one direction only
ISOLATORS
3
2log10P
PIsolation
1
0log10lossInsertion P
P
P0
P3P2
P1
A B
ISOLATORS
ISOLATOR SPECIFICATION
CIRCULATORS
1
2
3
Optical circulators redirects light sequentiallyfrom port-to-port in a unidirectional path
Same characteristics as isolatorsby looking port 1-2 @ port 2-3
To extract the desired wavelength, a circulator is used in conjunction with the
rating
Applications:
•Optical Amplifier•Add-Drop Multiplexer•Bi-directional transmission •To monitor back-reflection from devices or optical subsystems
Characteristics:
•high isolation•low insertion loss•can have more than 3 ports
CIRCULATORS
CIRCULATORS: APPLICATION
Fiber Bragg GratingsA grating is a periodic structure or perturbation in a materialthat creates a property of reflecting or transmitting light in a certaindirection depending on the wavelength.
2
External writing technique using UV light
21 3
2
1 3
Reflection
Transmission
effn22
Fiber Bragg Gratings
Fiber Bragg Gratings
Fiber Bragg Gratings
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.
Figure 2: FBGs reflected power as a function of wavelength
Characteristics:
•high reflectivity to be used as a filter
•low insertion loss
•low cost/simple packaging
Fiber Bragg Gratings
FBG APPLICATIONS
FIBER BRAGG GRATING SPECS.
ATTENUATORSFunction: To decrease light intensity (power)
Working Principles
Fiber displacement Rotating an absorption disk
Set @ 60 dB
Pin = 0 dBm
Insertion loss = 2 dB
Pout = 0 - 20 - 2 = -22 dBm
Programmable attenuator
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
ATTENUATORS