optical filter 武倩倩 1120349023. outline introduction to silicon photonics athermal tunable...
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Optical Filter
武倩倩
1120349023
Outline
Introduction to silicon photonics
Athermal tunable silicon optical filter
• Working principle
• Fabricated device
• Experiments
• Conclusions
Introduction to silicon photonics
Silicon photonics is the study and application of photonics systems which use silicon as an optical medium.
Optical interconnects
Optical routers and signal process
Long range telecommunications using silicon photonics
Artist’ concept of 3D silicon processor chip with optical IO layer featuring on-chip nanophotonic network. Courtesy IBM.
CMOS-Compatible Athermal Tunable Silicon Optical Lattice Filters
Liangjun Lu, Linjie Zhou, Xiaomeng Sun, Jingya Xie, Zhi Zou, Xinwan Li, and Jianping Chen in proceeding of OFC, USA, 2013
Outline
Introduction to silicon photonics
Athermal tunable silicon optical filter
• Background
• Working principle
• Fabricated device
• Experiments
• Conclusions
Background
Silicon: large thermo-optic (TO) coefficient of ~1.86×10-4 K-1 around 1.55 μm wavelength
• Regular silicon devices: ~100 pm/K
Approaches:
Cons:• Increasing fabrication challenge • Not compatible with the CMOS • Unreliable at high temperature
• Requiring a complex system• Extra power consumption
J. Lee et. al, Opt. Express 16, 1645-1652 (2008) C. Qiu et. al, Opt. Express 19, 5143 (2011)
Polymer compensation(negative TO coefficient)
Active compensation(local heating)
MZI
Mach-Zehnder interferometer (MZI) structure
Figure 1. The Mach-Zehnder interferometer silicon modulator contains two reverse-biased p-n diode phase shifters (a). The splitters are
multimode interference (MMI) couplers. The radio-frequency (RF) signal is coupled to the traveling-wave electrode from the optical input side, and termination load is added to the output side. The cross-sectional view in (b) shows a p-n junction waveguide phase shifter on silicon on insulator. The refractive index modulation is based on the depletion width variation in response to the reverse bias voltage caused by the free-carrier plasma
dispersion effect in silicon. The coplanar waveguide electrode was designed to match the electrical and optical velocities. Images reprinted
with permission of Optics Express
Lattice filters: cascaded MZIs• Application: (de)multiplexing, dispersion compensation
• Advantages: flexible design, large FSRs
• Compared with a single MZI: narrower passband, faster passband roll-off
B. Guha et. al, Opt. Express 18, 1879 (2010) B. Guha et. al, Opt. Lett. 37, 2253-2255 (2012)
Lattice filters
Transmission spectra
1-stage MZI 4-stage MZI
7-stage MZI 10-stage MZI
Outline
Introduction to silicon photonics
Optical filter
Athermal tunable silicon optical filter
• Background
• Working principle
• Fabricated device
• Experiments
• Conclusions
Working principle
0T
Input Bar
CrossW2, L2
Athermal condition:
1 1 2 2
2eff neffn L n L
W1, L1
Phase difference:
Asymmetric MZI:
1 21 2
2 eff effn nL L
T T T
Temperature-induced phase difference:
filter central wavelength
p-i-p tuning structure
Si substrate
Oxide
Si
Oxide
P+P+
Al Al
2 μm
0.22 μm
Cross-sectional schematic of the p-i-p junction-based micro-heater
Thermal-optical tuning: the generated heat directly interacts with the optical mode
Advantages:•higher tuning efficiency •a faster temporal response•without adding fabrication complexity
~1020 cm-3
Outline
Introduction to silicon photonics
Athermal tunable silicon optical filter
• Background
• Working principle
• Fabricated device
• Experiments
• Conclusions
Fabricated device
InputBar
Cross
W2 = 500 nm, L2 = 100 μm
W1 = 350 nm, L1 = 106.44 μmgap =250 nm
Microscope image of the lattice filter
• 10 cascaded MZIs• standard CMOS
fabrication process• inverse tapers with a tip
width of 180 nm
Outline
Introduction to silicon photonics
Optical filter
Athermal tunable silicon optical filter
• Background
• Working principle
• Fabricated device
• Experiments
• Conclusions
Active tuning measurement
• Power is applied to the top arms
• Filtering band redshifts
• Tuning efficiency 0.17 nm/mW
Wavelength shift vs. Power
Active tuning measurement
• Power is applied to the bottom arms
• Filtering band blueshifts
• Tuning efficiency -0.22 nm/mW
Wavelength shift vs. Power
Thermal sensitivity without tuning
Bar-port
Cross-port
dλ/dT = -1.465 pm/℃
Regular silicon devices: ~100 pm/oC)
Outline
Introduction to silicon photonics
Optical filter
Athermal tunable silicon optical filter
• Background
• Working principle
• Fabricated device
• Experiments
• Conclusions
Conclusions
CMOS-compatible athermal tunable silicon optical lattice filters were proposed, fabricated and experimentally demonstrated.
Active tuning experiments show that the filter central wavelength can be be red-/blue-shifted by 13.1/21.3 nm with a power tuning efficiency of 0.17/0.22 nm/mW.
Temperature shift measurements show that the thermal-sensitivity of the filter without active tuning is -1.465 pm/℃, improved by almost two order compared to regular designs.
When the filter central wavelength is tuned in between 1535 nm to 1550 nm, the measured thermal-sensitivity varies within 30 pm/℃.
Thank you!