FBG and Applications

1
FBG and Applications

• The Filter that Breaks Grading
• Broptics Communications Corp.

2
Fiber Grating

• Fiber grating is made by periodically changing
  the refraction index in the glass core of the
  fiber. The refraction changes are made by
  exposing the fiber to the UV-light with a fixed
  pattern.

Glass core
Glass cladding
Periodic refraction index change (Gratings)
Plastic jacket
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Fiber Grating Basics

• When the grating period is half of the input
  light wavelength, this wavelength signal will be
  reflected coherently to make a large reflection.
• The Bragg Condition

?
? n (refraction index difference)
?r 2neff ?
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Creating Gratings on Fiber

• One common way to make gratings on fiber is using
  Phase Mask for UV-light to expose on the fiber
  core.

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Characteristics of FBG

• It is a reflective type filter
• Not like to other types of filters, the demanded
  wavelength is reflected instead of transmitted
• It is very stable after annealing
• The gratings are permanent on the fiber after
  proper annealing process
• The reflective spectrum is very stable over the
  time
• It is transparent to through wavelength signals
• The gratings are in fiber and do not degrade the
  through traffic wavelengths, very low loss
• It is an in-fiber component and easily integrates
  to other optical devices

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Temperature Impact on FBG

• The fiber gratings is generally sensitive to
  temperature change (10pm/C) mainly due to
  thermo-optic effect of glass.
• Athermal packaging technique has to be used to
  compensate the temperature drift

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Types of Fiber Gratings
TYPES CHARACTERS APPLICATIONS
Simple reflective gratings Creates gratings on the fiber that meets the Bragg condition Filter for DWDM, stabilizer, locker
Long period gratings Significant wider grating periods that couples the light to cladding Gain flattening filter, dispersion compensation
Chirped fiber Bragg gratings A sequence of variant period gratings on the fiber that reflects multiple wavelengths Gain flattening filter, dispersion compensation
Slanted fiber gratings The gratings are created with an angle to the transmission axis Gain flattening filter
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Typical FBG Production Procedures
Select Proper fiber
H2 loading
Laser writing
Annealing
Athermal packaging
Testing
Different FBG requires different specialty fiber
Increase photo sensitivity for easier laser writing
Optical alignment appropriate laser writing condition
Enhance grating stability
For temperature variation compensation
Spec test
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Current Applications of FBG

• FBG for DWDM
• FBG for OADM
• FBG as EDFA Pump laser stabilizer
• FBG as Optical amplifier gain flattening filter
• FBG as Laser diode wavelength lock filter
• FBG as Tunable filter
• FBG for Remote monitoring
• FBG as Sensor
• .

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Possible Use of FBG in System
ITU FBG filter
Pump stabilizer Gain flattening filter
Dispersion compensation filter
Wave locker
E/O
Dispersion control
EDFA
Multiplexer
OADM
Demux
Switch
EDFA
ITU FBG filter
Tunable filter
Pump stabilizer Gain flattening filter
Monitor sensor
ITU FBG filter
Monitor
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ITU FBG Filter for DWDM
Multiplexer
De-multiplexer
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ITU FBG Filter for OADM
Circulator
Circulator
FBG
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Dispersion Compensation Filter
circulator
Dispersed pulse
Chirped FBG
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Pump Laser Stabilizer
980
spectrum
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Gain Flattening Filter
Gain profile
GFF profile
Output
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Broptics Roadmap
25G FBG
50G FBG
100G FBG
Pump laser stabilizer
Wavelength lock
Tunable filter
Gain flattening filter
Raman Amp Filter
Remote monitor sensor
Dispersion compensation
Ceramic athermal package
Mechanical athermal package
2001
2002