Showing papers by "Lan Yang published in 2013"
TL;DR: In this article, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed.
Abstract: Whispering gallery mode (WGM) optical microresonators have attracted intense interests in the past decades. The combination of high quality factors (Q) and small mode volumes of modes in WGM resonators significantly enhances the light-matter interactions, making them excellent cavities for achieving low threshold and narrow linewidth lasers. In this Review, the progress in WGM microcavity lasers is summarized, and the laser performance considering resonator geometries and materials as well as lasing mechanisms is discussed. Label-free detection using WGM resonators has emerged as highly sensitive detection schemes. However, the resolution is mainly limited by the cavity Q factor which determines the mode linewidth. Microcavity lasers, due to their narrow laser spectral width, could greatly improve the detection resolution. Some recent developments in sensing using microcavity lasers are discussed.
482 citations
TL;DR: In this paper, two coupled optical whispering galleries (optical resonators) are modeled as a pair of coupled linear oscillators, one with gain and the other with loss, and a Hamiltonian model is proposed.
Abstract: The inspiration for this theoretical paper comes from recent experiments on a $\mathcal{PT}$-symmetric system of two coupled optical whispering galleries (optical resonators). The optical system can be modeled as a pair of coupled linear oscillators, one with gain and the other with loss. If the coupled oscillators have a balanced loss and gain, the system is described by a Hamiltonian and the energy is conserved. This theoretical model exhibits two $\mathcal{PT}$ transitions depending on the size of the coupling parameter $\ensuremath{\epsilon}$. For small $\ensuremath{\epsilon}$, the $\mathcal{PT}$ symmetry is broken and the system is not in equilibrium, but when $\ensuremath{\epsilon}$ becomes sufficiently large, the system undergoes a transition to an equilibrium phase in which the $\mathcal{PT}$ symmetry is unbroken. For very large $\ensuremath{\epsilon}$, the system undergoes a second transition and is no longer in equilibrium. The principal result presented here is that the classical and quantized versions of the system exhibit transitions at exactly the same values of $\ensuremath{\epsilon}$.
131 citations
TL;DR: In this paper, an add-drop filter using an on-chip whispering gallery mode (WGM) microtoroid resonator with ultra-high quality factor (Q) side coupled to two taper fibers, forming the bus and drop waveguides.
Abstract: We fabricated and theoretically investigated an add-drop filter using an on-chip whispering gallery mode (WGM) microtoroid resonator with ultra-high quality factor (Q) side coupled to two taper fibers, forming the bus and drop waveguides. The new device design incorporates silica side walls close to the microresonators which not only enable placing the coupling fibers on the same plane with respect to the microtoroid resonator but also provides mechanical stability, leading to an add-drop filter with high drop efficiency and improved robustness to environmental perturbations. We show that this new device can be thermally tuned to drop desired wavelengths from the bus without significantly affecting the drop efficiency, which is around 57%
110 citations
TL;DR: In this article, a high quality (Q) factor optical whispering gallery mode (WGM) microtoroid resonator together with its side coupled fiber taper was encapsulated inside a low refractive index polymer, achieving a final Q higher than 107.
Abstract: We encapsulate a high-quality (Q) factor optical whispering gallery mode (WGM) microtoroid resonator together with its side coupled fiber taper inside a low refractive index polymer, achieving a final Q higher than 107. Packaging provides stable resonator-fiber taper coupling, long-term maintenance of high-Q, a protective layer against contaminants, and portability to microtoroid resonator based devices. We test the robustness of the packaged device under various conditions and demonstrate its capability for thermal sensing.
60 citations
TL;DR: In this article, a high quality (Q) factor optical whispering gallery mode (WGM) microtoroid resonator together with its side coupled fiber taper inside a low refractive index polymer, achieving a final Q higher than 10^7.
Abstract: We encapsulated a high-quality (Q) factor optical whispering gallery mode (WGM) microtoroid resonator together with its side coupled fiber taper inside a low refractive index polymer, achieving a final Q higher than 10^7. Packaging provides stable resonator-fiber taper coupling, long-term maintenance of high-Q, a protective layer against contaminants, and portability to microtoroid resonator based devices. We tested the robustness of the packaged device under various conditions and demonstrated its capability for thermal sensing.
58 citations
TL;DR: In this article, an add-drop filter (ADF) fabricated using a whispering gallery mode resonator has different crosstalks for add and drop functions due to nonzero intrinsic losses of the resonator.
Abstract: An add-drop filter (ADF) fabricated using a whispering gallery mode resonator has different crosstalks for add and drop functions due to non-zero intrinsic losses of the resonator. Here, we show that introducing gain medium in the resonator and optically pumping it below the lasing threshold allows not only loss compensation to achieve similar and lower crosstalks but also tunability in bandwidth and add-drop efficiency. For an active ADF fabricated using an erbium-ytterbium co-doped microsphere, we achieved 24-fold enhancement in the intrinsic quality factor, 3.5-fold increase in drop efficiency, bandwidth tunability of 34 MHz, and a crosstalk of only 2%.
53 citations
TL;DR: In this article, an add-drop filter (ADF) fabricated using a whispering gallery mode resonator has different crosstalks for add and drop functions due to nonzero intrinsic losses of the resonator.
Abstract: An add-drop filter (ADF) fabricated using a whispering gallery mode resonator has different crosstalks for add and drop functions due to non-zero intrinsic losses of the resonator. Here, we show that introducing gain medium in the resonator and optically pumping it below the lasing threshold not only allows loss compensation to achieve similar and lower crosstalks but also tunability in bandwidth and add-drop efficiency. For an active ADF fabricated using an erbium-ytterbium co-doped microsphere, we achieved 24-fold enhancement in the intrinsic quality factor, 3.5-fold increase in drop efficiency, bandwidth tunability of 35 MHz and a crosstalk of only 2%.
53 citations
TL;DR: In this article, a single particle detection scheme with single particle resolution is presented, which is based on monitoring the transmitted light power which shows abrupt jumps with each particle binding to the taper surface.
Abstract: A nanoparticle detection scheme with single particle resolution is presented. The sensor contains only a taper fiber thus offering the advantages of compactness and installation flexibility. Sensing method is based on monitoring the transmitted light power which shows abrupt jumps with each particle binding to the taper surface. The experimental validation of the sensor is demonstrated with polystyrene nanoparticles of radii 120 nm and 175 nm in the 1550 nm wavelength band.
32 citations
TL;DR: The detection and the size measurement of single nanoparticles in aquatic environment using mode splitting in a whispering gallery mode (WGM) optical resonator, namely a microtoroid resonator is reported.
Abstract: We, for the first time, report the detection and the size measurement of single nanoparticles (i.e. polystyrene) in aquatic environment using mode splitting in a whispering gallery mode (WGM) optical resonator, namely a microtoroid resonator. Using this method we achieved detecting and measuring individual synthetic hemozoin nanocrystals, which are a hemoglobin degradation by-product of malarial parasites, dispersed in a solution or in air. The results of size measurement in solution and in air agree with each other and with those obtained using scanning electron microscope and dynamic light scattering. Moreover, we compare the sensing capabilities of the degenerate (single resonance) and non-degenerate (split mode, doublet) operation regimes of the WGM resonator.
29 citations
TL;DR: This work proposes a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs.
Abstract: A crucial open problem inS large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.
25 citations
TL;DR: In this article, the authors investigate numerically and experimentally the statistics of the changes in the amount of frequency splitting upon adsorption of particles one by one into the mode volume of a whispering gallery mode (WGM) microresonator.
Abstract: We investigate numerically and experimentally the statistics of the changes in the amount of frequency splitting upon adsorption of particles one by one into the mode volume of a whispering gallery mode (WGM) microresonator. This multiple-particle-induced frequency splitting (MPIFS) statistics carries information on the size and number of particles adsorbed into the mode volume, and is strongly affected by two experimental parameters: the WGM field distribution and the positions of particles within the mode volume. We show that the standard deviation and maximum value of the MPIFS are proportional to the polarizability of the particles, and propose a method to estimate particle size from the MPIFS if the only available data from experiments are frequency splitting.
TL;DR: In this article, the authors investigate numerically and experimentally the statistics of the changes in the amount of frequency splitting upon the adsorption of particles one-by-one into the mode volume of whispering gallery mode (WGM) microresonator and microlasers.
Abstract: We investigate numerically and experimentally the statistics of the changes in the amount of frequency splitting upon the adsorption of particles one-by-one into the mode volume of whispering gallery mode (WGM) microresonator and microlasers. This multiple-particle induced frequency splitting (MPIFS) statistics carries information on the size and the number of adsorbed particles into the mode volume, and it is strongly affected by two experimental parameters, namely the WGM field distribution and the positions of the particles within the mode volume. We show that the standard deviation and maximum value of the MPIFS are proportional to the polarizability of the particles, and propose a method to estimate particle size from the MPIFS if the only available data from experiments is frequency splitting.
TL;DR: Some results are reported in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7).
Abstract: With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 107. We compare experimentally measured Q factors with theoretical estimates, and find good agreement.
07 Nov 2013
TL;DR: In this article, the detection of a 12MHz ultrasound wave using a microtoroidal whispering gallery mode optical resonator, encapsulated in a low-refractive-index polymer with its coupling tapered-fiber, was demonstrated.
Abstract: We have demonstrated the detection of a 12MHz ultrasound wave using a microtoroidal whispering gallery mode optical resonator, encapsulated in a low-refractive-index polymer with its coupling tapered-fiber. The sensitivity of our device is 35 mV/KPa.
Patent•
25 Sep 2013TL;DR: The microtoroid micro-resonators as mentioned in this paper have been used to enhance the Raman signal by several orders of magnitude over the signal typically expected for Raman methods, and are particularly useful for non-labeled nanoparticle sensing.
Abstract: Embodiments of the invention provide Raman spectroscopy methods and devices that exploit high quality factor (Q) resonators to enhance Raman signal by several orders of magnitude over the signal typically expected for Raman methods. Embodiments typically include one or more resonators, typically microtoroid microresonators. Embodiments also take advantage of Rayleigh scattering using these microresonators. Embodiments may be particularly useful for non-labeled nanoparticle sensing.
09 Jun 2013
TL;DR: In this article, the authors reported real-time detection of individual nanoparticles down to R=20 nm using a high-Q whispering gallery mode (WGM) microresonator.
Abstract: We report real time detection of individual nanoparticles down to R=20 nm using a high-Q whispering gallery mode (WGM) microresonator. The detection is based on resonance enhanced particle induced reflection and does not require monitoring resonance spectra.
TL;DR: In this article, whispering gallery mode micro-resonators are used as platforms to perform sensitive particle detection by exploiting the strong, evanescent field of a resonant mode exposed on the surface of the microresonator.
Abstract: We investigate Raman spectroscopic sensing using whispering gallery microresonators as a label-free method toward single particle detection. Whispering gallery mode microresonators are used as platforms to perform sensitive particle detection by exploiting the strong, evanescent field of a resonant mode exposed on the surface
of the microresonator. Particles adhered to the microresonator surface interact with the field and scatter photons circulating within the resonator. In particular, Raman scattered photons are detected, providing
molecular-specific "fingerprint" information regarding the adhered particles. The exploitation of a resonant mode allows for enhancement of generated Raman signal over traditional methods of spontaneous Raman scattering. Preliminary proof-of-concept experimental results are shown.
TL;DR: In this paper, a layer of thin film doped with optical gain medium, which is prepared by wet chemical synthesis, is applied to WGM structures on silicon wafer to achieve arrays of ultra-low threshold on-chip microlasers.
Abstract: Whispering-Gallery-Mode (WGM) resonators are emerging as an excellent platform to study optical phenomena resulting from enhanced light-matter interactions due to their superior capability to confine photons for extended periods of time. The monolithic fabrication process to achieve ultra-high-Q WGM resonators without the need to align multiple optical components, as needed in traditional design of resonators based on precise arrangement of mirrors, is especially attractive. Here we explain how to process a layer of thin film doped with optical gain medium, which is prepared by wet chemical synthesis, into WGM structures on silicon wafer to achieve arrays of ultra-low threshold on-chip microlasers. We can adjust the dopant species and concentration easily by tailoring the chemical compositions in the precursor solution. Lasing in different spectral windows from visible to infrared was observed in the experiments. In particular, we investigated nanoparticle sensing applications of the on-chip WGM microlasers by taking advantages of the narrow linewidths and the splitting of lasing modes arising from their interactions with nano-scale structures. It has been found that a nanoparticle as small as ten nanometers in radius could split a lasing mode in a WGM resonator into two spectrally separated lasing lines. Subsequently, when these lasing lines are photo-mixed at a photodetector a heterodyne beat note is generated which can be processed to signal the detection of individual nanoparticles. We have demonstrated detection of virions, dielectric and metallic nanoparticles by monitoring the changes in this self-heterodyning beat note of the split lasing modes. The built-in self-heterodyne method achieved in this monolithic WGM microlaser provides an ultrasensitive scheme for detecting and measuring nanoparticles at single particle resolution, with a theoretical detection limit of one nanometer.
01 Sep 2013
TL;DR: In this paper, an active add-drop filter (ADF) using an erbium-ytterbium co-doped microsphere resonator has been proposed and achieved a 4-fold increase in efficiency and crosstalk of 2%.
Abstract: We have fabricated an active add-drop filter (ADF) using an erbium-ytterbium co-doped microsphere resonator and have achieved 25-fold Q-enhancement, 4-fold increase in efficiency and crosstalk of 2%. This ADF provides equal add and drop efficiencies.
09 Jun 2013
TL;DR: In this article, the authors present spectra evolution of photonic molecules upon individual or collective coupling of supermodes in one resonator with single mode in the other one by tuning the coupling strength and spectral overlap of the modes.
Abstract: We present spectra evolution of photonic molecules upon individual or collective coupling of supermodes in one resonator with single mode in the other one by tuning the coupling strength and spectral overlap of the modes.
09 Jun 2013
TL;DR: In this article, an Erbium-Ytterbium co-doped microsphere resonator side-coupled to two tapered fibers was used for add-drop filter.
Abstract: We have fabricated an Add-Drop filter using an Erbium-Ytterbium co-doped microsphere resonator side-coupled to two tapered fibers. By optically pumping this active resonator below its lasing threshold, we have demonstrated bandwidth reduction, drop-efficiency increase and crosstalk suppression.
TL;DR: In this paper, the authors reported the first experimental realization of on-chip WGM microcavities which support both highly unidirectional emission and ultra-high Q factor.
Abstract: Optical whispering gallery mode (WGM) microcavities are promising candidates for basic research and optoelectronic applications. Due to the isotropic emission property resulting from the rotational symmetry, traditional WGM microcavities have to rely on external couplers to excite the modes and collect their emission. One of the most possible solutions is to deform microcavities from rotational symmetry, which could provide directional emission instead of isotropic characteristic. Here we report the first experimental realization of on-chip microcavities which support both highly unidirectional emission and ultra-high Q factors. The demonstrated Q factor exceeds 100 million in near infrared. By doping erbium into the deformed microcavity, lasing action in 1550 nm band was observed under convenient freespace optical pumping, with the threshold as low as 2 μW. Remarkably, the lasing emission is along a single direction with a narrow divergence angle about 10 degrees.