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- Titre : Photonic%20Crystal%20Fiber_RB.pdf
- Submitted by : Anonymous
- Description : Photonic Crystal Fibers (PCF) Core Structure solid core hollow core Transmission Mechanism Index guiding Bandgap guiding HC-PCF Index + Bandgap By varying size & location of holes mode shape, dispersion, nonlinearity, etc. can be changed Λ: pitch D: diameter of core d: diameter of holes -Contains periodic pattern of micron-sized holes
Transcription
Photonic Crystal Fibres (PCFs)
Benefits & Applications
Randhir Bhatnagar, Chief Scientist
CSIR-Central Scientific Instruments Organisation, Chandigarh
email: rbh5@csio.res.in
22nd December 2017
Lecture Outline
Conventional Optical Fiber
Photonic Crystal Fibers
PCF Fabrication techniques
Application of PCF as Sensor,
Supercontinuum generation and High Power delivery
Classical Optical Fiber
Total Internal Reflection
• Total internal Reflection
• Multi-mode fibers(MMF)
– Short range
– many paths allowed
• Single-mode fibers(SMF)
– Long range
– Modal dispersion less
Limitation of Classical Optical Fiber
• Linear effects – a function of the fiber length
• Limited bend radius ~ 30 mm
• Dispersion – broadens the optical pulse over length of a fiber
• Non-Linear effects
• Self phase modulation (Nonlinear phase modulation of a
beam, caused by its own intensity via the Kerr effect)
• Guidance of high power is not possible
Bragg’s Law
• Periodic objects reflect incident waves when wavelength
and interplanar spacing, satisfy Bragg’s Law
One dimensional Photonic Crystal: Bragg grating
d
• Wavelength corresponds to the
• Wavelength does not correspond
to the period
• Reflected waves are in phase.
• Reflected waves are not in phase.
• Wave does not propagate inside.
• Wave propagates through.
period.
Yablonovitch, Sci.Am. 2001
Photonic Crystals (PhCs)
Novel class of optical media represented by natural or
artificial structures with periodic modulation of the refractive
index.
Depending on geometry of the structure, PhCs can be divided
into three broad categories:
1-D Photonic Crystal
The periodic modulation of the permittivity occurs in one
direction only, while in other two directions structure is
uniform e.g. Bragg grating and antireflecting optical coatings.
y
Bragg mirrors (1-D Photonic Crystal)
• Consists of alternating quarter
wavelength optical thickness high
and low refractive index materials
PBG
100
80
60
40
20
0
)
%
(
e
c
n
a
t
c
e
l
f
e
R
1000
1400
1800
Wavelength (nm)
Propagation of light over a
particular wavelength range is
forbidden
(called photonic
band gap – PBG)
Stopband width increases as
index ratio of nH/nL increases
700900110013001500Wavelength (nm)ReflectancenH= 2.0nH= 2.2nH= 2.4nH= 2.6nL= 1.5700900110013001500Wavelength (nm)ReflectancenH= 2.0nH= 2.2nH= 2.4nH= 2.6nL= 1.5nL= 1.5 Bragg mirrors (1-D Photonic Crystal)
Multilayer Mirrors: Number of Periods
of
high
Height
reflectance stopband
the
increases with
number of periods
Microcavities
)
%
(
e
c
n
a
t
c
e
l
f
e
R
100
80
60
40
20
0
• Defect layer breaks periodicity
function and
of dielectric
introduces allowed mode into
PBG
800
1000 1200 1400
1600
1800 2000
Wavelength (nm)