Highly unidirectional & ultralow-threshold lasing from on ... · Highly unidirectional &...
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Highly unidirectional & ultralow-threshold lasing from on-chip ultrahigh-Q optical resonator
Yun-Feng Xiao (肖云峰)
Peking University, Beijing 100871, P. R. China 北京大学 物理学院 人工微结构和介观物理国家重点实验室
Email: [email protected]
Tel: (86)10-62765512
Advantages of microcavities
Q
22
cav
in
P QB
P nD
Cavity power build-up factor:
Q ~1×108, D ~ 50m, Vm ~ 600 m3 B ~ 105
Cavity photon lifetime:
WHY ultra-high-Q whispering gallery resonator?
Pin = 1 mW
Pcav ~ 100 W, Icav ~ 2.5 GW/cm2,
~ 100 ns, # of round trip ~ 2105.
Experimental
data in our
group
> 100 W
“Strongly enhanced light-matter interaction”
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Cavity QED for implementation of quantum computation, quantum routers, ...
Quantum optics, quantum information processing
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Nature 443, 671 (2006); Science 319, 1062 (2008); PRL 95, 067401 (2005); Nano Lett. 6, 2075 (2006)
g/2~50 MHz
k/2~18 MHz
g/2~2.6 MHz
Highly sensitive optical biosensing
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F. Vollmer & S. Arnold, Nature Methods 5, 591 (2008)
V. R. Dantham et al., APL 101, 043704 (2012)
J. Zhu, S. K. Ozdier, Y. F. Xiao et al.
Nature Photonics 4, 46 (2010)
X. Yi, Y.-F. Xiao* et al., Appl. Phys. Lett. 97, 203705 (2010); Phys.
Rev. A 83 , 023802 (2011); J. of Appl. Phys. 111 (11), 114702 (2012)
Mode shift Mode splitting
Cooling of mechanical motion
Radiation pressure induced
mechanical oscillation
Cavity optomechanics
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Amplification of mechanical motion
Mechanical ground state cooling
Nature 475, 359 (2011); Nature 478, 89 (2011)
~ Quantum limited measurement
~ Test of quantum mechanics at increasingly large mass and length scales
~ Implementations in quantum information processing
m
m
Low-threshold lasing
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Kippenberg group, PRL (2008)
Vahala group, Nature (2002)
Applications of whispering gallery microresonator
Important platform for
Fundamental physics:
Quantum optics
Cavity quantum electrodynamics (QED)
Quantum information
Classical and quantum chaos…
Cavity Optomechancs
Nano/micro-photonics:
Highly sensitive bio/chemical sensing
All-optical low-threshold switching
On-chip microlasing
Filtering… Ultrahigh Q, very small V,
and mass production on a chip
Vahala
, Natu
re, 2
003
7
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Traditional whispering gallery microcavities
High Q factor & small mode volume
Unfortunately, isotropic emission
Excitation and collection difficulties
Evanescent couplers: tapered fiber, prism,
Strict phase-matching
Coupling losses
Coupling instability
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From circular to deformed microcavities
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Nature
385, 45 (1997)
Quadruple “flattened”
Quadruple
Science
280, 1556 (1998) Appl. Phys. Lett.
83, 9 (2003)
Spiral
Phys. Rev. Lett.
100, 033901 (2008)
Limacon
Stadium
Phys. Rev. Lett.
90, 063901 (2003)
Phys. Rev. Lett.
104, 163902 (2010)
PNAS
107, 22404 (2010)
Phys. Rev. Lett.
105, 103902 (2010)
Typical deformed microcavities
Threshold for microlaser: Q2/V
Purcell effect: Q/V
Strong coupling for cavity QED: Q/V1/2
c(3) optical nonlinearities: Q2/V
Optical forces and trapping: Q/V
Optical biosensing: Q/V
IMPORTANT quality factor
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Outline
Physics in ultrahigh-Q, unidirectional microcavities
Realization of ultrahigh-Q, unidirectional microcavities
Ultralow-threshold and highly unidirectional behavior
in Er3+-doped microcavities
Summary
Really?
An intuitive expectation: emit from the points of highest
curvature (j=0, ) in the tangent direction
lead to peaks at q=± /2 in the far-field
Emission points & directions?
Hailin Wang group
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Ray dynamics......Poincaré surface of section
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• KAM curves
• Islands
• Chaos
Disjoined nature classically
2-D:
f
sin
c
1/n
f
sin
c
Mechanism for the unidirectional emission
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Regular mode→chaos
Dynamical tunneling
Chaos→refractive emission
Short-time ray dynamics
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Summary: Mechanism for the unidirectional emission
Clockwise and counter-clockwise modes
At least 2 × n emission points
Deformed cavity with only one symmetric axis
Emission towards the symmetric axis
Far-field unidirectionality
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Summary: The theoretical design
Deformed microcavity with only one symmetric axis
Support regular KAM curves or islands located on upper SOS (high-Q)
Dynamical tunneling between regular and chaotic modes
Refractive emission obeying short-term dynamics of chaos (directionality)
CCW
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0
0 ss
=
1 11 1 1 1 1 1
ext mat rad ext
QQ Q Q Q Q Q
Quality factors
Ultrahigh-Q modes:
• Locate in the upper in SOS: reduce radiation loss
• Minimized material absorption and surface scattering losses
Low loss medium
Small deformation
CO2 reflow process
Materials loss
Radiation loss
Surface scattering
Challenges Our solutions:
deformed microtoroid
𝑸𝒆𝒙𝒕 → ∞,𝑸 = 𝑸𝟎 Coupling loss
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Two-step dry etching and laser reflow
Fabrication of ultra-high-Q silica toroidal microcavity
• Precise control the shape of the deformed toroid
• Atomic-scale surface: ultralow scattering losses
Fabrication
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White boundary: circle
Black boundary: ellipse
Red boundary: our design
Nanometer-scaled control
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Transmission
Free-space
Fiber taper
Q>108
Excitation
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Experimental Q factors
Lasing action
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Unidirectional-emission lasing
Summary
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We experimentally realized on-chip deformed microcavities with
experimental Q factor exceeded 108, four orders of magnitude higher
than previous chip-based deformed microcavities.
By doping erbium into the deformed microcavity, the unidirectional-
emission lasing was observed in 1,550 nm band with the threshold as
low as 2 W and a narrow divergence angle about 10 degrees.
The work may open up new possibilities for investigations of fundamental
physics and applied photonics, such as single-photon sources, strong
coupling physics, and cavity optomechanics, by using a convenient free-
space coupling in chip-based ultrahigh-Q microcavities.
Thank you for your attention! www.phy.pku.edu.cn/~yfxiao/index.html
X.-F. Jiang, Y.-F. Xiao*, C.-L. Zou , L. He , C.-H. Dong ,
B.-B. Li , Y. Li , F.-W. Sun , L. Yang , and Q. Gong*
Advanced Materials 2012, 24, OP260-OP264