Photonics Research, 2018, 6 (5): 05000A23, Published Online: Jul. 18, 2018
Parity-time-symmetric whispering-gallery mode nanoparticle sensor [Invited] 
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Fig. 1. WGM nanoparticle sensors based on (a) the single passive resonator, (b) the single active resonator, and (c) PT-symmetric coupled resonators with balanced gain and loss. The gray-colored small circle denotes a nanoparticle within the mode volume of the resonator. The spectra illustrate sensing mechanisms of the sensors. The dashed red curve shows the spectrum before the nanoparticle binding event; the solid blue curve corresponds to the spectrum after the nanoparticle binding event. The sensors in (a) and (b) exhibit a frequency splitting proportional to ϵ
Fig. 2. Evolution of the (a) real part and (b) imaginary part of eigenfrequencies in PT-symmetric coupled resonators when the coupling strength between two resonators is varied. The PT phase transition point is obtained when the coupling strength κ = κ PT = 1 GHz
Fig. 3. (a) Evolution of the real part of the eigenfrequencies Re ( ω − ω 0 ) μ R a Re ( Δ ω )
Fig. 4. (a) Dependence of sensitivity of a PT-symmetric sensor operating at the phase transition point on the perturbation strength ϵ ϵ γ γ κ ϵ ϵ γ
Fig. 5. (a) Evolution of the imaginary part of the eigenfrequencies Im ( ω − ω 0 ) μ R a 2 Im ( Δ ω )
Fig. 6. (a) Illustration of the detection of two nanoparticles in a PT-symmetric WGM nanoparticle sensor. The two nanoparticles are placed within the mode volume of the resonator with gain. (b), (c) Variation in frequency splitting as a function of the angular position of the second nanoparticle when (b) the two nanoparticles are identical with the same perturbation strength, and (c) the two nanoparticles are different and hence have different perturbation strengths. The angular position of the first nanoparticle is fixed and set to be zero. Blue squares are numerical simulation results; red solid curves are theoretical predictions. The results are normalized by the frequency splitting induced by the first nanoparticle on a single resonator sensor.
Fig. 7. (a) Illustration of the detection of multiple nanoparticles in a PT-symmetric WGM nanoparticle sensor. Ten different nanoparticles (numbered gray circles) are randomly deposited within the mode volume of the resonator with gain one by one. (b) Numerical results of frequency splitting variation for 10 nanoparticles deposited on the PT-symmetric WGM sensor (blue lines and squares) and a single WGM sensor (red lines and circles). The dashed vertical lines are used as eye guides. Results for the single WGM sensor are obtained by removing the lossy resonator in the numerical simulation. Results are normalized by the frequency splitting induced by the first nanoparticle deposited on a single WGM sensor with a value of 73 MHz.
Weijian Chen, Jing Zhang, Bo Peng, Şahin Kaya Özdemir, Xudong Fan, Lan Yang. Parity-time-symmetric whispering-gallery mode nanoparticle sensor [Invited][J]. Photonics Research, 2018, 6(5): 05000A23.
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