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!