FBG and Applications The Filter that Breaks Grading Broptics Communications Corp.

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 Plastic jacket Periodic refraction index change (Gratings)

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  r = 2n eff  in Reflection spectrum reflect Transmission spectrum trans.  n (refraction index difference)

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.

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

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

Types of Fiber Gratings TYPESCHARACTERSAPPLICATIONS 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

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

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 ….

Possible Use of FBG in System Multiplexer Dispersion control EDFA OADM SwitchEDFA Demux ITU FBG filter Dispersion compensation filter Pump stabilizer & Gain flattening filter ITU FBG filter Tunable filter ITU FBG filter Pump stabilizer & Gain flattening filter E/O Wave locker Monitor Monitor sensor

ITU FBG Filter for DWDM 1, 2 … n FBG at Circulator FBG at 2 3 Circulator FBG at , 2 … n FBG at Circulator FBG at 2 3 Circulator FBG at 3... Multiplexer De-multiplexer

ITU FBG Filter for OADM Circulator FBG Through signal Dropped signal Added signal Outgoing signal Incoming signal

Dispersion Compensation Filter Dispersed pulse circulator Chirped FBG

Pump Laser Stabilizer 980 spectrum Focal lens Fiber 980 Stabilizer + - Pump Laser

Gain Flattening Filter Gain profile GFF profile Output

Broptics Roadmap Ceramic athermal package 100G FBG G FBG Pump laser stabilizer Wavelength lock Gain flattening filter Tunable filter Dispersion compensation Remote monitor sensor Mechanical athermal package 25G FBG Raman Amp Filter