Photonic molecule lasing

Hara, Yoshiko; Mukaiyama, Takashi; Takeda, Kenji; Kuwata‐Gonokami, Makoto

doi:10.1364/ol.28.002437

Cited by 79 publications

(47 citation statements)

References 14 publications

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“…We also note that while absorption will degrade the strength of the resonance, microspheres containing gain materials can in principle enhance the resonant force, and the effect should be most interesting when the WGM starts lasing. 10 These would be interesting topics for further studies.…”

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confidence: 96%

“…The strength of the optical forces can be enhanced by orders of magnitude when a MDR is excited. As microsphere cavities are emerging as an alternative to the photonic crystal in controlling light, [8][9][10] the MDR-force may be deployed for the manipulation of a microsphere cluster.…”

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confidence: 99%

“…[8][9][10] Nevertheless, the MDR force is actually quite robust against size dispersion. The solid line in Fig.…”

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Strong optical force induced by morphology-dependent resonances

Chan

Sheng

et al. 2005

Opt. Lett.

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We consider the resonant optical force acting on a pair of transparent microspheres by the excitation of the Morphology Dependent Resonance (MDR). The bonding and anti-bonding modes of the MDR correspond to strong attractions and repulsions respectively. The dependence of the force on separation and the role of absorption are discussed. At resonance, the force can be enhanced by orders of magnitude so that it will dominate over other relevant forces. We find that a stable binding configuration can be induced by the resonant optical force.Optical forces are useful in the manipulation of ultra-fine particles and mesoscopic systems, and the development is rather astounding in the last three decades. The most well known types of the optical forces are the radiation pressure and the optical gradient force. There is also an inter-particle optical force, induced by the multiple scattering of light.1-7 We present here an interesting type of resonant inter-particle force. We will see that the tuning of the incident light frequency to the Morphology Dependent Resonance (MDR) of a cluster of transparent microspheres would induce a strong resonant optical force (MDR-force) between the spheres. The MDR of a pair of spheres had been observed in fluorescent 8, 9 and lasing 10 experiments. Here we study theoretically the force induced by such resonances. We will see that the MDR-induced force, derived from the coherent coupling of the whispering gallery modes (WGM's), is a strong short ranged force that can be attractive or repulsive depending on whether the bonding mode (BM) or the anti-bonding mode (ABM) is excited. The strength of the optical forces can be enhanced by orders of magnitude when a MDR is excited. As microsphere cavities are emerging as an alternative to the photonic crystal in controlling light, 8-10 the MDR-force may be deployed for the manipulation of a microsphere cluster.In this paper, we calculate the electromagnetic (EM) forces acting on microspheres when WGM's or MDR's are excited. The optical force acting on a microsphere can be computed via a surface integral of the Maxwell stress tensor, ↔ T , over the sphere's surface. The microspheres cannot respond to the high frequency component of the time varying optical force, so we calculate the time-averaged force < T is computed by the multiple scattering theory, 1, 11 which expands the fields in vector spherical harmonics. This formalism is quite possibly the most accurate method that can be applied. It is in principle exact, and the numerical convergence is being controlled by the maximum angular momentum (L max ) used in the expansion. The calculation for the resonance of dielectric microspheres near contact requires a high L max , 12 which is chosen so that further increase in L max does not change the value of the calculated force. In most of the calculations, the size parameter (kR) is between 28 and 29, and L max =63 was used. We adopt the Generalized Minimal Residual iterative solver (GMRES) for the linear system of equations.13 In the following, th...

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Strong optical force induced by morphology-dependent resonances

Chan

Sheng

et al. 2005

Opt. Lett.

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“…In the current state-of-the-art, the difficulties in collecting identical microspheres limit the experiments on tight binding photonic modes to "photonic molecules" consisting of a small number of particles. 10,11,12,13,14,15 The sorting scheme we proposed may help to collect a larger number of microspheres with size-dispersion fulfilling the stringent optical requirements, paving the way to go beyond small "photonic molecules" to extended photonic crystals, coupled resonator optical waveguides, and other structures.…”

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Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes

Chan

2008

Applied Physics Letters

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We show that when a microsphere is illuminated by an evanescent wave, the optical forces on-and off-whispering gallery mode (WGM) resonance can differ by several orders of magnitude. Such size selective force allows one to selectively manipulate the resonating particles, while leaving those particles at off-resonance untouched. As WGM resonances have very high-Q's, this kind of force could be deployed for size-selective manipulation with a very high accuracy (~1/Q), as well as simultaneous particle-sorting according to their size or resonant frequency.

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“…Recent studies of optical mode structure in small coupled spherical microcavities [1][2][3][4][5] (photonic molecules, PMs) have led to the observation of a modified electromagnetic field distribution that differs significantly from what would be obtained for a single microcavity. Experimental 2,4 and theoretical 1,3 investigations showed that, depending on the orientation of the PM, whispering gallery modes (WGMs) of a monosphere can be split into two broadened modes of lower quality factor ͑Q͒.…”

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Tunable photon lifetime in photonic molecules: a concept for delaying an optical signal

2005

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We experimentally and theoretically studied the photon lifetime spectral distribution in two coherently coupled spherical microcavities of 3-16 m diameter forming a photonic molecule, which shows a multipeak narrowband modal structure resulting from lifting of the mode degeneracy with respect to the azimuthal quantum number. The results demonstrate the feasibility of photonic molecules as a basis for a multichannel, wavelength-tunable optical delay-line device, which can be used for delay times in the range 10 ps to 1 ns. © 2005 Optical Society of America OCIS codes: 230.5750, 350.3950, 060.4230, 230.3120. Modern optical communications involve the use of short optical pulses with picosecond duration and gigahertz repetition rates to transmit data on an optical network. Synchronization of optical pulse trains within circuits in the network is provided by an optical delay-line device. Designs for compact devices with delay times in the range of 1 ps to 1 s are required that will integrate well with photonic circuits.Recent studies of optical mode structure in small coupled spherical microcavities 1-5 (photonic molecules, PMs) have led to the observation of a modified electromagnetic field distribution that differs significantly from what would be obtained for a single microcavity. Experimental 2,4 and theoretical 1,3 investigations showed that, depending on the orientation of the PM, whispering gallery modes (WGMs) of a monosphere can be split into two broadened modes of lower quality factor ͑Q͒. In analogy with the quantum mechanical formation of molecular electronic orbits, these modes have been called bonding (BN) and antibonding (ABN) states.3 More recent investigations of the internal field distribution in a PM revealed a complex distribution of photonic states within the BN and ABN modes 3,5 and therefore pointed the way toward consideration of applications of coupled microspheres (MSs). In this Letter we experimentally and theoretically demonstrate an application of a PM for the storing and buffering of optical pulses. The theoretical possibility of controlling the group velocity of optical pulses in coupled-resonator structures was studied previously. [6][7][8][9] Recently, the occurrence of a resonance with higher Q in the system of two MSs interacting through waveguides, mimicking electromagnetically induced transparency, was predicted.9 In this Letter we discuss a new and alternative method based on lifting of the WGM degeneracy with respect to the azimuthal quantum number m in a system with strong coupling of two MSs. Such a system of coupled microcavities is proposed as a versatile building block suitable for integration in communication circuits because of its the size and spectral and material compatibility with optical fiber. The focus of our work is the fine structure of the BN and ABN modes of the PM, which can be observed for off-axis excitation geometry, and which our group has recently demonstrated.5 A key feature of this modal structure is much higher Q factors and therefore longer photo...

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Photonic molecule lasing

Cited by 79 publications

References 14 publications

Strong optical force induced by morphology-dependent resonances

Strong optical force induced by morphology-dependent resonances

Size-selective optical forces for microspheres using evanescent wave excitation of whispering gallery modes

Tunable photon lifetime in photonic molecules: a concept for delaying an optical signal

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