Highly unidirectional & ultralow-threshold lasing from on ... Highly unidirectional & ultralow-threshold

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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: yfxiao@pku.edu.cn

    Tel: (86)10-62765512

    mailto:yfxiao@pku.edu.cn

  • Advantages of microcavities

     

    Q 

    22

    cav

    in

    P Q B

    P nD

      Cavity power build-up factor:

    Q ~1×108, D ~ 50m, Vm ~ 600 m 3  B ~ 105

    Cavity photon lifetime:

    WHY ultra-high-Q whispering gallery resonator?

    Pin = 1 mW 

    Pcav ~ 100 W, Icav ~ 2.5 GW/cm 2,

     ~ 100 ns, # of round trip ~ 2105.

    Experimental

    data in our

    group

    > 100 W

    “Strongly enhanced light-matter interaction”

    2

  • Cavity QED for implementation of quantum computation, quantum routers, ...

    Quantum optics, quantum information processing

    3

    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

    4

    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

    5

    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

    6

    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

    V a h a la

    , N a tu

    re , 2

    0 0 3

    7

  • 8

    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

  • 9

    From circular to deformed microcavities

  • 10

    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

    11

  • 12

    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

    13

  • Ray dynamics......Poincaré surface of section

    14

    • KAM curves

    • Islands

    • Chaos

    Disjoined nature classically

    2-D:

    f

    s in

    c

    1/n

    f

    s in

    c

  • Mechanism for the unidirectional emission

    15

    Regular mode→chaos

    Dynamical tunneling

    Chaos→refractive emission

    Short-time ray dynamics

  • 16

    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

  • 17

    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

  • 18

    0

    0 ss

    =

    1 1 1 1 1 1 1 1

    ext mat rad ext

    Q Q 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 

  • 19

    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

    20

    White boundary: circle

    Black boundary: ellipse

    Red boundary: our design

    Nanometer-scaled control

  • 21

    Transmission

    Free-space

    Fiber taper

    Q>108

    Excitation

  • 22

    Experimental Q factors

  • Lasing action

    23

  • 24

    Unidirectional-emission lasing

  • Summary

    25

     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