2. introdution
Photonic crystal (PhC)-based circuits provide many
attractive features for on-chip manipulation of light.
A key ingredient to realizing planar integrated PhC
circuits is a compact wavelength division multiplexer
(WDM) used for separating different wavelengths of
light.
3. A key word in PhCs
• periodic items of dielectric materials
• photonic band gap
• Defects
• Filter
• super cell
• Brillion zone
6. 1.Generating Point defect
1. By removing a pillar from the lattice, we create a cavity
that is effectively surrounded by reflecting walls [a].
2. grow or shrink in radius of pillar [b].
(a) (b)
7. Function of Point defect
If the cavity has the proper size to support a mode in the
band gap, then
light cannot escape and we can pin the mode to the defect.
In fact, a resonant cavity would be useful whenever one
would like to control radiation within a narrow frequency
range.
8. “important feature of PhCs”
we can “tune” the defect frequency or later called
resonant frequency to any value within the band gap
with a judicious choice of radius defect(rdef).
9. plot of the TM modes rectangular silicon
pillars
a. The defect pillar is surrounded by perfect lattice at r=0.18a
and lattice constant = 570nm.
b. The photonic band gap frequency 0.30 to 0.445.
the bigger the defect pillar the great quantity of
localized modes
10. 2.Generating Line defects
by removing a row of pillars in the direction of the crystal.
a.Macro-porous silicon material
with incorporated defect line
b.Sharp band waveguide
channel in 2D photonic crystal
11. Function of line defect
We can use cavities defects in photonic crystals to
trap light, as we have seen in point defect. By using
extended defects or line defects, we can also guide
light from one location to another.
12. Line defect Band gap
the band structure for the guide created by removing a row of
pillars in the direction of the crystal. We find a single guided
mode inside the band gap.
number of bands inside the band gap == the number of rows
of pillars removed
13. Couple cavity waveguide
what happen if we removed single row of pillar and then we
put defect along the waveguide???
16. Crystal photonic MUX/DMUX
PhCs are particularly interesting, in all-optical systems to
transmission and processing information due to the effect of
localization of the light in the defect region of the periodic
Structure.
by breaking the alternative period of photonic crystal, we can
engineer light diffusion into it
For example, we can make some changes in band structure of
photonic crystal by defect to make optical waveguide with
less loss , optical switches , filters , resonators , multiplexers
and optical demultiplexers for wavelength division
multiplexer (WDM) networks .
17. Designing 2 wavelength mux/dmux
These DEMUX/MUXs consist of circular pillars in
rectangular lattice surrounded by air.
Device A:
Radius of circular scatterers == 0.18a
Lattice constant (a) == 570nm
refractive index == 3.4
Mode == TM
Dimension: 15*15
Radius of right filter == 0.25a
Radius of left filter == 0.11a
20. Operation of device A
Device A which is 1310 nm / 1550 nm DEMUX/MUX device is
based on splitting the wavelength channel using wide band
filters.
left Filter only filter wavelength of 1310 nm
right filter only emit wavelength of 1310 nm inside it
Conclude:
left filter == DMUX
right filter == MUX
24. conclude
an optimum design is proposed to split two wavelengths into
two different output channels. The proposed design for
splitting the wavelength 1310 nm and 1550 nm is using full
defect pillars with diameter 124 nm in filter 1 and three pillars
defect pillars with diameter of 285 nm in filter 2. With this
design, it was found that it help to reduce reflectivity and
boost up the power transmission in the device.
27. “importatnt”
At the three target frequencies of ω =0.3857,
0.3863, and 0.3868 × 2πc/a, incident light
from the input waveguide is routed into the
three output waveguides. At these three
frequencies there is very little reflection in the
input waveguide, as well as very little cross
talk.
