high-Q Optical Microcavities Research Articles

Analytical Model and Solution Illustrating Classical Optical Contribution to Giant Spectral Splitting in Strongly-Coupled Micro/nanocavity-atom System

Many experimental observations have shown remarkably large or even giant spectral splitting in strongly-coupled micro/nanocavity-atom systems. Popularly, such a spectral splitting has been attributed to the Rabi splitting, a pure quantum mechanical effect. However, there are disputes regarding whether the spectral splitting caused by multiple emitters, such as excitons in J-aggregate of molecules, is a pure quantum effect or also contributed by classical optical effect. In this work, we address this difficult problem by building a model physical system of a practical Fabry-Perot high-Q optical microcavity involving Lorentz-dispersion atoms. Very interestingly, by performing evaluation and estimate upon several strongly-coupled cavity-atom systems, we have found that the classical optical splitting and quantum Rabi splitting can be in the same order of magnitude. Our studies clearly indicate that the phenomenon of “giant Rabi splitting” that has been extensively observed in many experiments can also be caused by classic optical effects in addition to quantum mechanical effect. In some cases, the contribution by classic optical effects may be comparable to or even exceeding the contribution from quantum effects. We expect that this work can constructing the true and complete physics picture underlying strong light-matter interaction in a micro/nanocavity system.

Fabrication of a rutile titanium dioxide thin film heterostructure using ion-implantation with Cu-Sn bonding

Single crystalline titanium dioxide thin film in the rutile phase (r-TiO2) is exfoliated from bulk material using a He+-implantation method, and is bonded onto SiO2 substrate to form a heterostructure using Cu-Sn bonding technology. The exfoliated r-TiO2 thin film was examined to be in good quality, and the exfoliation mechanism of ion-implanted r-TiO2 was analyzed. The obtained r-TiO2 thin film heterostructure with high refractive index contrast has a potential application in the fabrication of high-Q optical microcavities in visible wavelengths, which is useful in integrated photonic devices.

Implementation of a Two-Qubit C-NOT Quantum Gate in a System of Two Double Quantum Dots, a Microcavity, and a Laser

We study the possibility of implementing a two-qubit controlled-NOT gate operation in a structure consisting of two semiconductor double quantum dots placed in a high-Q optical microcavity and governed by a resonant laser field. The effect of relaxation processes on the dynamics of the two-electron system is discussed. The dissipation rates allowing quantum error correction algorithms to be used are determined. The existing additional excitation channel (laser pulse) is shown to weaken the effect of the nonideality of the cavity on the evolution of the states. Optimal electron coupling coefficients in the quantum dots with control fields are fitted, in which the controlled qubit is switched with the highest probability and the gate implementation takes several hundreds of picoseconds.

Saturable absorption by carbon nanotubes on silica microtoroids

Saturable absorption is a key technology for shaping the waveform of light such as in passive mode-locking. The combination of high-Q optical microcavities with a saturable absorber allows stable lasing and soliton formation. This work describes saturable absorption by carbon nanotubes (CNTs) on silica microtoroids. CNTs, which are saturable absorbers capable of a fast response time and broadband absorption, were grown on silica microtoroids by chemical vapor deposition (CVD). Raman spectroscopy revealed that the CNTs are in good quality (G/D ratio ∼ 7) and about 1.0 nm in diameter, thus confirming that a sample for use in the telecommunication band can be prepared by CVD. A counter-propagating pump-probe experiment enabled us to investigate the characteristics of CNTs as saturable absorbers while suppressing thermo-optic bistability in a microcavity system. The results revealed a saturable absorption coefficient of 0.042 cm−1, a saturable intensity of 25.9 MW/cm2, and a modulation depth of 28%. This is the first step toward the demonstration of the robust mode-locking in a silica microtoroid consisting of CNTs.

Active capture and stabilization of temporal solitons in microresonators.

Soliton mode locking and femtosecond pulse generation have recently been demonstrated in high-Q optical microcavities and provide a new way to miniaturize frequency comb systems, as well as create integrated comb systems on a chip. However, triggering the mode-locking process is complicated by a well-known thermal hysteresis that can destabilize the solitons. Moreover, on a longer time scale, thermal drifting of the cavity resonant frequency relative to the pumping frequency causes loss of mode locking. In this Letter, an active feedback method is used both to capture specific soliton states and to stabilize the states indefinitely. The capture and stabilization method provides a reliable way to overcome thermal effects during soliton formation and to excite a desired number of circulating cavity solitons. It is also used to demonstrate a low pumping power of 22 mW for generation of microwave-repetition-rate solitons on a chip.

Single nanoparticle detection using split-mode microcavity Raman lasers.

Ultrasensitive nanoparticle detection holds great potential for early-stage diagnosis of human diseases and for environmental monitoring. In this work, we report for the first time, to our knowledge, single nanoparticle detection by monitoring the beat frequency of split-mode Raman lasers in high-Q optical microcavities. We first demonstrate this method by controllably transferring single 50-nm-radius nanoparticles to and from the cavity surface using a fiber taper. We then realize real-time detection of single nanoparticles in an aqueous environment, with a record low detection limit of 20 nm in radius, without using additional techniques for laser noise suppression. Because Raman scattering occurs in most materials under practically any pump wavelength, this Raman laser-based sensing method not only removes the need for doping the microcavity with a gain medium but also loosens the requirement of specific wavelength bands for the pump lasers, thus representing a significant step toward practical microlaser sensors.

Adaptive on-chip control of nano-optical fields with optoplasmonic vortex nanogates

A major challenge for plasmonics as an enabling technology for quantum information processing is the realization of active spatio-temporal control of light on the nanoscale. The use of phase-shaped pulses or beams enforces specific requirements for on-chip integration and imposes strict design limitations. We introduce here an alternative approach, which is based on exploiting the strong sub-wavelength spatial phase modulation in the near-field of resonantly-excited high-Q optical microcavities integrated into plasmonic nanocircuits. Our theoretical analysis reveals the formation of areas of circulating powerflow (optical vortices) in the near-fields of optical microcavities, whose positions and mutual coupling can be controlled by tuning the microcavities parameters and the excitation wavelength. We show that optical powerflow though nanoscale plasmonic structures can be dynamically molded by engineering interactions of microcavity-induced optical vortices with noble-metal nanoparticles. The proposed strategy of re-configuring plasmonic nanocircuits via locally-addressable photonic elements opens the way to develop chip-integrated optoplasmonic switching architectures, which is crucial for implementation of quantum information nanocircuits.

(Invited) Silicon Nanocrystals Coupled to High-Q Optical Microcavities: Theory and Applications

not Available.

Optical Microcavities Clad by Low-Absorption Electrode Media

Four types of high-Q optical microcavities - disk, 1-D photonic crystal nanobeam, 2-D photonic crystal slab, and 3-D photonic crystal optical microresonators - clad by low-optical-loss electrode media such as indium tin oxide are designed and evaluated by the perturbation theory and 3-D finite-difference time-domain (FDTD) method. The quality (Q) factor is obtained via perturbation theory in which the imaginary part of the cladding material is regarded as a perturbation and confirmed to agree with results from the 3-D FDTD method. Although the studied designs preserve the high-Q factor, they provide the placement of low-loss conductive electrode material proximate to high-Q microcavity modes. Further enhancement of the Q factor is possible by a reduction of the electrode volume. Microlasers based on this study would provide an excellent heat sink and efficient carrier injection into a microcavity mode, thereby resulting in the realization of continuous-wave, room-temperature microlasers with low threshold.

Characterization of high-Q optical microcavities using confocal microscopy

Confocal microscopy was initially developed to image complex circuits and material defects. Previous imaging studies yielded only qualitative data about the location and number of defects. In the present study, this noninvasive method is used to obtain quantitative information about the Q factor of an optical resonant cavity. Because the intensity of the fluorescent signal measures the number of defects in the resonant cavity, this signal is a measure of the number of surface scattering defects, one of the dominant loss mechanisms in optical microcavities. The Q of the cavities was also determined using conventional linewidth measurements. Based upon a quantitative comparative analysis of these two techniques, it is shown that the Q can be determined without a linewidth measurement, allowing for a noninvasive characterization technique.

Control of light pulse propagation with only a few cold atoms in a high-finesse microcavity.

Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.

Room temperature photonic crystal defect lasers at near-infrared wavelengths in InGaAsP

Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (/spl lambda//2n)/sup 3/. Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (/spl ap/500 /spl mu/W absorbed).