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 = 2neff

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

1533.8

1534.0

1534.2

1534.4

1534.6

1534.8

1535.0

1535.2

-5 15 35 55 75

Temperature (℃)

Cen

ter

Wav

elen

gth

(n

m)

Athermal

Normal

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

Typical FBG Production Procedures

SelectProperfiber

H2loading

Laserwriting

AnnealingAthermal

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

MultiplexerDispersion control EDFA

OADM

SwitchEDFADemux

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 … nFBG at 1

1 2

Circulator CirculatorFBG at 2

3

CirculatorFBG at 3

...

1, 2 … nFBG at 1

1 2

Circulator CirculatorFBG at 2

3

CirculatorFBG at 3

...

Multiplexer

De-multiplexer

ITU FBG Filter for OADM

Circulator Circulator

FBG

Through signal

Dropped signal Added signal

Outgoing signalIncoming signal

Dispersion Compensation Filter

Dispersedpulse

circulator

Chirp

ed

FBG

Pump Laser Stabilizer

980spectrum

Focal lens

Fiber 980 Stabilizer

+

-Pump Laser

Gain Flattening Filter

1 5 0 0 1 5 2 0 1 5 4 0 1 5 6 0 1 5 8 0 1 6 0 0W av e len g th (n m )

-1 5

-1 0

-5

0

5

1 0

1 5

2 0

Gai

n (d

B)

Gain profile

GFF profile

Output

Broptics Roadmap

Ceramic athermal package

100G FBG

2001 2002

50G FBG

Pump laser stabilizerWavelength lock

Gain flattening filterTunable filter

Dispersion compensation

Remote monitor sensor

Mechanical athermal package

25G FBG

Raman Amp Filter