View
1.039
Download
0
Category
Tags:
Preview:
DESCRIPTION
visible silicon photonics
Citation preview
High Quality Factor Microdisk Resonators for Chip-scale Visible Sensing
overview
2
Introduction and motivation High Q SiN microcavities on substrateCritical Coupling to SiN waveguides Experimental demonstrationConclusions
SiN for Visible Sensing
3
Multi-modal sensing in visible Low water absorption [2]Fluorescence sensingRaman sensing :nanoparticles’ plasmon
Silicon Nitride High index, low loss, low auto-fluorescence background Ease of fabrication (Planar/multilayer) (LPCVD)Source/detector integration (CMOS)
[2] lsbu.ac.uk/water/
Fabrication of SiN Microdisks
4
Stoichiometric SiN on thermal oxide Electron beam lithography on ZEP reflow of ZEP ICP etching with CF4 gas (85deg, 5nm
roughness)
1 mm
200 nm
Critical Coupling
5
Conventional straight WG Short coupling length-> narrow gaps
Pedestal[1]Controlled etching time Increasing field overlap
Pulley CouplingWaveguide looping around the diskIncreasing coupling length
R=20mm
Straight waveguide
6
Semi-phase-matching Short coupling length-> narrow gaps
-5 0 5 10 1510
6
107
coupling Q vs limit
Coupling vs. Waveguide Width
7
Pulley Scheme
8
PulleySignificant increase in coupling lengthLess coupling induced lossPhase matching -> mode selectiveSensitive to waveguide width Large gap -> ZEP reflow for smooth sidewalls
Pulley Scheme’s Phase Matching
9
Long coupling lengthStrict phase matching requirements Sensitive to waveguide width for phase matching nwg=nd [R/(R+g+w/2)]
order
neff FSR (rad/c
m)
TE 1 1.704 490
TE 2 1.626 498
TM 1 1.577 486
TE 3 1.559 504
TM 2 1.500 498
TE 4 1.503 509
140 145 150 155 160 165 1708.5
9
9.5
10
Ko (
rad/
um)
Azimuthal mode number m
Resonant modes of a 10 um radius disk
r=10 mm
Disk-Waveguide Phase Matching
10
Phase matching optimized by choosing the waveguide width
100 200 300 400 500 600
1.5
1.55
1.6
1.65
1.7
1.75
Effe
ctiv
e in
dex
of W
G
Waveguide width (nm)
Waveguide 100nm away from the disk
100 200 300 400 500 600
1.5
1.55
1.6
1.65
1.7
1.75
Effe
ctiv
e in
dex
of W
G
Waveguide width (nm)
Waveguide place farther at 400nm coupling gap
TETE
TM
TM
g= 100 nm
g= 400 nm
TE1
TE2
TE2
TE1
TM1
r=10 mm
Pedestal and Pulley Coupling to R=100 mm disk
11
Phase matchinglarger gaps, single mode operation
653 654 655 656 657 658 659 660-20
-15
-10
-5
0
653 654 655 656 657 658 659 660-12
-10
-8
-6
-4
-2
0
Pulley CouplingPedestal=40 nm
Wavelength (nm) Wavelength (nm)
Nor
mal
ized
tra
snm
issi
on
(dB
) Gap=400 nm
Effect of Phase Matching
12
-30 -20 -10 0 10 20 30-200
-100
0
100
200phase difference
-30 -20 -10 0 10 20 3010
4
106
108
1010
1012 coupling Q vs limit
-30 -20 -10 0 10 20 30-200
-100
0
100
200phase difference
-30 -20 -10 0 10 20 3010
0
105
1010
1015 coupling Q vs limit
m and W for phase matching
13
Splitting
143 3.1 3.2 3.3 3.4
x 10-7
8.3
8.4
8.5
8.6
8.7
x 106
250 260 270 280 290
7.6
7.8
8
8.2
8.4
8.6
x 106
1.68 1.7 1.72
x 10-7
8.105
8.11
8.115
8.12
x 106
Conclusions
15
SiN is an excellent material for visible and NIR photonics applications.
By optimizing the fabrication process, microdisks with Qs as high as 8M can be achieved.
Critical coupling to adjacent waveguides is achieved by using pedestal and pulley coupling schemes.
Pulley coupling also enables critical coupling to selected mode(s) of the cavity without sacrificing Q.
16
Recommended