This document summarizes research on optical true time delay lines conducted at the MetaPhotonics Lab. It examines various structures for achieving time delays, including Cantor V3 waveguides with 1 and 3 cells, meander lines with bending radii from 3-5 μm, and incorporating ring resonators. Simulation results show that longer structures and smaller bending radii increase the group delay. The document also discusses foundry options for fabrication, including Applied Nanotools Canada, IMEC, and Cornerstone, outlining their resolution, costs, timelines and packaging capabilities.

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2021.01.27
Optical True Time Delay Lines
MetaPhotonics Research Lab

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Outline
 Group index dispersion curve
 Time of flight method to calculate the group delay
 Explain Time of flight method
 Cantor V3
 Meander line optical delay line
 Meander line optical delay line (with Ring resonator)
 Fabrication

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Dispersion curve (Using Center frequency)
(1)
 Confinement decreases for longer wavelength
 Overall increase of group index value

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Time of flight
 Wavelength = 1400 to 1700 nm
 Pulse length = 37.054 um

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 Wavelength = 1550 nm
 Pulse length = 1.73 um
Time of flight (Narrow Bandwidth)

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 Cantor V3 (Cell number = 1)
Cell 1
Length = 34.9 um
 Objective function: max_value = group_delay*1E4 + 1*A;

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0.67ps
 Cantor V3 (Cell number = 1) Group delay
Group index = 5.74

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 Cantor V3 (Cell number = 1) (1400nm to 1700nm)
0.76 ps
0.14 ps
∇time = 0.62ps
Group index = 5.74

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 Cantor V3 (Cell number = 1) Center frequency =
1550nm, Bandwidth = 2.45nm
4.74 ps
4.13 ps
∇time = 0.61ps

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74%
 Cantor V3 (Cell number = 1)

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 Cantor V3 (Cell number = 3)
Cell 1 Cell 2 Cell 3
Length = 104.7 um
 Objective function: max_value = group_delay*1E4 + 1*A;

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1.99 ps
 Cantor V3 (Cell number = 3) (Group delay)

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 Cantor V3, cell number = 3 (1400nm to 1700nm)
2 ps
0.14 ps
∇time = 1.86 ps
Group index = 5.68

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 Cantor V3, cell number = 3 (center frequency = 1550nm, Bandwidth = 12.15nm)
3.02 ps
1.18 ps
∇time = 1.84 ps
Group index = 5.68

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36.8%

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0.72 ps 1.18 ps
∇time = 0.46 ps
 Time of Flight (Straight Waveguide)
Length = 34.9 um
Group index = 3.95 um
 Center frequency = 1550nm
 Bandwidth = 12.17nm

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Structure
Meander Lines for Optical Time Delay

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Meander Lines: Motivation
 Meander lines were chosen for analysis for 2 main reasons:
1. It’s easier to apply homogeneous heat using rectangular titanium heaters.
2. In the straight waveguide part of the meander lines, the optimized cantor waveguide
structure can be used to enhance the group delay even more.
3. Possibility of adding ring resonator (like a pulley) inside the bend region of the structure.

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Choosing the Right Bending Radius

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1) 3um Bending Radius
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1400-1700 nm

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Simulation 3um Bending Radius
Transmission in zoomed in vertical axis
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1400-1700 nm
Output Transmission

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Transmission in zoomed in vertical axis
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1548.53 – 1551.47 nm
Output Transmission
Simulation 3um Bending Radius Narrow Bandwidth

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E-field Vs Time
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1548.53 – 1551.47 nm
Simulation 3um Bending Radius Narrow Bandwidth
0.71 ps

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Simulation 3um Bending Radius
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1400-1700 nm
E-field

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2) Simulation 3.5 um Bending Radius
• Mesh Size: 20 nm, Simulation time: 7000 fs, Source Wavelength: 1400-1700 nm

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• Mesh Size: 20 nm, Simulation time: 7000 fs, Source Wavelength: 1400-1700 nm
Simulation 3.5 um Bending Radius
Output Transmission

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Transmission in zoomed in vertical axis
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Output Transmission
Simulation 3.5 um Bending Radius Narrow Bandwidth

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E-field Vs Time
• Mesh Size: 20 nm, Simulation time: 9000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation 3.5 um Bending Radius Narrow Bandwidth
0.778 ps

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• Mesh Size: 20 nm, Simulation time: 7000 fs, Source Wavelength: 1400-1700 nm
Simulation 3.5 um Bending Radius
E-field

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3) Simulation 4 um Bending Radius
• Mesh Size: 20 nm, Simulation time: 10,000 fs, Source Wavelength: 1400 - 1700 nm

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Simulation 4 um Bending Radius
• Mesh Size: 20 nm, Simulation time: 10,000 fs, Source Wavelength: 1400 - 1700 nm
Output Transmission

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Output Transmission
Transmission in zoomed in vertical axis
• Mesh Size: 20 nm, Simulation time: 10,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation 4 um Bending Radius Narrow Bandwidth

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E-field Vs Time
• Mesh Size: 20 nm, Simulation time: 10,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation 4 um Bending Radius Narrow Bandwidth
0.795 ps

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E-field
Simulation 4 um Bending Radius
• Mesh Size: 20 nm, Simulation time: 10,000 fs, Source Wavelength: 1400 - 1700 nm

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4) Simulation 5 um Bending Radius
• Mesh Size: 21 nm, Simulation time: 10,000 fs.

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Output Transmission
Transmission in zoomed in vertical axis
• Mesh Size: 21 nm, Simulation time: 10,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation 5 um Bending Radius Narrow Bandwidth

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E-field Vs Time
• Mesh Size: 21 nm, Simulation time: 10,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation 5 um Bending Radius Narrow Bandwidth
0.868 ps

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E-field
Simulation 5 um Bending Radius
• Mesh Size: 21 nm, Simulation time: 10,000 fs, Source Wavelength: 1400 - 1700 nm

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• Mesh Size: 25 nm, Simulation time: 35,000 fs, Source Wavelength: 1400 - 1700 nm
Comparison of Transmission Spectra

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4) Simulation of a Long Structure with 3.5 um Bending Radius
• Mesh Size: 25 nm, Simulation time: 35,000 fs
 Bending radius: 3.5 µm
 Length of the structure: 142 µm
 Width of the structure: 19 µm
 Area: 2698 µm2
 Total travelling distance : Approx. 479.675 µm

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• Mesh Size: 25 nm, Simulation time: 35,000 fs, Source Wavelength: 1400 - 1700 nm
Comparison of Transmission Spectra

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Output Transmission
Transmission in zoomed in vertical axis
• Mesh Size: 25 nm, Simulation time: 35,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation of a Long Structure with 3.5 um Bending Radius

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E-field Vs Time
• Mesh Size: 25 nm, Simulation time: 35,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation of a Long Structure with 3.5 um Bending Radius
Distance (um) Delay (ps)
51.9925 0.66516
122.0875 1.55062
192.1825 2.437
262.2775 3.353
332.3725 4.26
402.4675 5.163
479.2625 6.143

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• Mesh Size: 25 nm, Simulation time: 35,000 fs, Source Wavelength: 1548.53 - 1551.47 nm
Simulation of a Long Structure with 3.5 um Bending Radius

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E-field Map
Simulation of a Long Structure with 3.5 um Bending Radius

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 Increase the number of loops to increase time delay up to 200 ps.
 Add Ti heaters to implement thermo-optic effect for active time tuning.
Future Work to Do
Meander Lines for Optical Time Delay

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Pulley-type ring resonators
Ref: Chen, C. C., Cai, D. P., & Lee, C. C. Fine tune of pulley-type ring resonators.
 Achieving high Q-factor by increasing the radius of the microring
 Reduce bending loss
 Efficient coupling of light to the ring
 Tuning the bus waveguide width
 Gap width

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Pulley-type ring resonators (E field)
 Radius of the ring= 4.56 um
 Gap = 0.15 um
 Circumference = 28.65 um
 Bending radius = 4.89 um
 Group index = 61.78

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Pulley-type ring resonators (Group Delay and Transmission)

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Meander line optical delay line using ring resonator (Multiple ring) Transmission

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Applied Nanotools Canada Fabrication Characteristics
Critical Dimension (Resolution) 70 nm
Layout file accepted GDSII
Basic Passive Layout 4-5 Weeks
With addition of metal 7 weeks
With deep trenches for edge couples 9 weeks
Fabrication Timeline:

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Applied Nanotools Canada Fabrication Characteristics

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Applied Nanotools Canada Fabrication Characteristics
Device Layer Exposure Area
1 mm2 5 mm2 7 mm2
Cost [CAD (KRW)] Total [CAD (KRW)]
Basic Passive Structure 1515 (1,442,280) 1515 (1,442,280) 3515 (3,346,280) 4515 (4,298,280)
With addition of top 2.2 um oxide claddi
ng
+110 (+104,720) 1625 (1,547,000) 3625 (3,451,000) 4625 (4,403,000)
With tri-layer metallization (Ti/W, Alumin
ium, and oxide cladding)
+1100 (+1,047,200) 2725 (2,594,200) 4725 (4,498,200) 5725 (5,450,200)
With Deep Trench for Edge Coupled De
vices
+650 (+618,800) 3375 (3,213,000) 5375 (5,117,000) 6375 (6,069,000)
Fabrication Costs

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Other Characteristics
They offer a process module called "Deep Trench" that will expose edge facets for edge coupling.
They do not offer edge coupler packaging, but they can offer fiber packaging of vertical grating
couplers instead using a fiber array block.
All of the silicon should be on a single GDS layer (Layer 1). There is no partial etch available in MPW
runs, only full-etch silicon. Partial etch levels can be provided in a dedicated run.
Titanium heaters are also fabricable, except that our heater material is TiW (200 nm thickness) and
the minimum trace size is 3 microns.
Doping/Ion implantation is NOT POSSIBLE

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IMEC Fabrication Characteristics
Critical Dimension (Resolution) 130 nm
Layout file accepted GDSII
Passive Layout 9 Months
Active Layout Structure 1 Year
Fabrication Timeline:

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IMEC Fabrication Characteristics
Metal heaters are included in the passive (above) layout.
Cost:
Price
1 block (5.15mm x 5.15mm) 11,600 Euros (15,655,360 KRW)
Half Block (5.15mm x 2.5 mm) 6,100 Euros (8,232,560 KRW)

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Cornerstone Fabrication Characteristics
Critical Dimension (Resolution) 130 nm
Layout file accepted GDSII

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Cornerstone Fabrication Characteristics
Cost:
Price
Half block (5.5mm x 4.9mm) with heaters 11,700 Euros (15,790,320 KRW)
Full Block (11.47mm x 4.9 mm) with heaters 17,100 Euros (23,078,160 KRW)
Metal heaters are included in the passive (above) layout.

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Summary
Facilities Cost (won)
Chip size
(mm2)
Active device Critical dimension (nm) Period (weeks) Packaging
ANT 4.5 million 5
Ion implantation (x)
Metallization (o)
70 7 ~ 9
Provide vertical
coupling
IMEC 15 million 5
Metallization (o)
Ion implantation
(Possible but with extra
charges)
130 nm
48 Weeks (Active)
36 Weeks (Passive)
Provide Fiber
coupling
Cornerstone 15.7 million 5
Metallization (o)
Ion implantation
(Possible but with extra
charges)
130 nm N/A
Provide Fiber
coupling