high-Q Modes Research Articles

Electrically Driven Single Microwire-Based Heterojuction Light-Emitting Devices

Semiconductor micro/nanowire is an attractive candidate for light-emitting devices (LED), especially laser diodes, due to its ideal geometric shape, excellent optical performance, and electrical transport properties. However, the realization of single micro/nanostructure semiconductor LED or lasers is still a challenge topic. In this Letter, we demonstrated a feasible route to fabricate electrically injection single microwire (MW) light-emitting devices. First, the excellent optical properties of single MW were investigated comprehensively, especially for the self-formed high-Q whisper gallery mode lasing. By properly engineering the band alignment of n-ZnO MW/p-GaN heterojunction using a dielectric MgO interlayer, the effective carrier injection and excitonic-type recombination electroluminescence was realized in the single MW active media. Our results present a significant step toward future fabrication of single micro/nanowire LED and laser diode.

Hyperuniform disordered phononic structures

We demonstrate the existence of large phononic band gaps in designed hyperuniform (isotropic) disordered two-dimensional (2D) phononic structures of Pb cylinders in epoxy matrix. The phononic band gaps in hyperuniform disordered phononic structures are comparable to band gaps of similar periodic structures, for both out-of-plane and in-plane polarizations. A large number of localized modes is identified near the band edges, as well as, diffusive transmission throughout the rest of the frequency spectrum. Very high-Q cavity modes for both out-of-plane and in-plane polarizations are formed by selectively removing a single cylinder out of the structure. Efficient waveguiding with almost 100% transmission trough waveguide structures with arbitrary bends is also presented. We expand our results to thin three-dimensional layers of such structures and demonstrate effective band gaps related to the respective 2D band gaps. Moreover, the drop in the Q factor for the three-dimensional structures is not more than three orders of magnitude compared to the 2D ones.

Refractometry-based air pressure sensing using glass microspheres as high-Q whispering-gallery mode microresonators

In this work a refractometric air pressure sensing platform based on spherical whispering-gallery mode microresonators is presented and analyzed. The sensitivity of this sensing approach is characterized by measuring the whispering-gallery mode spectral shifts caused by a change of air refractive index produced by dynamic sinusoidal pressure variations that lie between extremes of ±1.8kPa. A theoretical frame of work is developed to characterize the refractometric air pressure sensing platform by using the Ciddor equation for the refractive index of air, and a comparison is made against experimental results for the purpose of performance evaluation.

Planar photonic crystal based multifunctional sensors.

A planar photonic crystal (PPC) structure capable of simultaneous detection of multiple parameters is presented in this paper. We analytically and numerically demonstrate that the reflection spectrum of the PPC structure exhibits multiple high-Q resonant modes that could respond distinctively to different external perturbations, rendering the PPC sensor superior capabilities for multiparameter sensing. We further demonstrate simultaneous pressure and temperature sensing with a PPC sensor. Other advantages of this device include efficient free-space-to-multimode coupling, high sensitivity, on-chip integration, and wafer-scale fabrications.

Transverse mode interaction via stimulated Raman scattering comb in a silica microcavity.

Comb generation in different mode families via a stimulated Raman scattering (SRS) process is studied using a silica toroid microcavity. The broad gain bandwidth of SRS in silica allows us to excite longitudinal modes at long wavelengths belonging to mode families that are either the same as or different from the pump mode. We found through experiment and numerical analysis, that an SRS comb in a different mode family with a high quality factor (Q) is excited when we pump in a low-Q mode. No transverse mode interaction occurs when we excite in a high-Q mode resulting the generation of a single comb family. We studied the condition of the transverse mode interaction while varying the mode overlap and Q of the Raman mode. Our experimental results are in good agreement with the analysis and this enables us to control the generation of one- and two-mode combs.

Laser and cavity cooling of a mechanical resonator with a nitrogen-vacancy center in diamond

We theoretically analyse the cooling dynamics of a high-Q mode of a mechanical resonator, when the structure is also an optical cavity and is coupled with a NV center. The NV center is driven by a laser and interacts with the cavity photon field and with the strain field of the mechanical oscillator, while radiation pressure couples mechanical resonator and cavity field. Starting from the full master equation we derive the rate equation for the mechanical resonator's motion, whose coefficients depend on the system parameters and on the noise sources. We then determine the cooling regime, the cooling rate, the asymptotic temperatures, and the spectrum of resonance fluorescence for experimentally relevant parameter regimes. For these parameters, we consider an electronic transition, whose linewidth allows one to perform sideband cooling, and show that the addition of an optical cavity in general does not improve the cooling efficiency. We further show that pure dephasing of the NV center's electronic transitions can lead to an improvement of the cooling efficiency.

Optical bound states in slotted high-contrast gratings

This paper investigates the optical bound states in the continuum (BIC) supported by a slotted high-contrast grating (sHCG) structure. The sHCG structure consists of a periodic array of silicon ridges with a slot in each ridge. Given that the BICs are perfectly confined, their spectral locations are identified using a finite-element method formulated from a generalized eigenvalue problem. The real eigenvalues represent the wavelengths of BIC modes and the associated eigenvectors correspond to the electric field distributions. In the spectral and angular vicinity of the BICs, we studied the leaky waveguide modes using the rigorous coupled-wave analysis. The combination of the full-wave eigenvalue solver and the coupled-wave analysis provides an ideal setting to investigate the optical BICs of periodic structures for various applications. The simulation results show, for example, that the sHCG structures can support symmetry-protected bound states with a zero in-plane wave vector as well as high-quality-factor (high-Q) resonances for both TE and TM polarizations. By adjusting the slot, we can turn the BIC mode into high-Q modes and determine the linewidth of the mode by the degree of asymmetry.

Attenuated total reflection response to wavelength tuning of plasmon-induced transparency in a metal-insulator-metal structure.

We experimentally demonstrated a plasmon-induced transparency in a metal-insulator-metal (MIM) structure based on the attenuated total reflection (ATR) response. Here, the MIM waveguide (MIMWG) mode and the surface plasmon polariton (SPP) resonance mode acted as low- and high-Q resonance modes, respectively. The dependence of the resonance angles of SPP and MIMWG mode resonances on the incident wavelength differed, which allowed the coupling condition between the two modes to be tuned via the wavelength. When the resonance angles of the two modes coincided, the ATR response showed a symmetric plasmon-induced transparency spectrum; in contrast, when the resonance angles were detuned, the ATR exhibited a sharp asymmetric spectrum characteristic to off-resonance Fano interference.

High-Q surface modes in photonic crystal/iron garnet film heterostructures for sensor applications

A novel type of a plasmonic sensor based on a magnetophotonic plasmonic heterostructure with an ultrahigh-Q resonance is considered. A magnetoplasmonic resonance with an angular width of 0.06°, which corresponds to a Q factor of 700 and is a record value for magnetoplasmonic sensors, is experimentally demonstrated. It is shown that, owing to the excitation of long-propagation-range plasmons, the transverse magneto-optical Kerr effect is considerably enhanced and, thus, the sensitivity of the magnetoplasmonic sensor to variations in the refractive index increases to 18 RIU–1, where RIU is the refractive index unit. Numerical calculations indicate that the parameters of the magnetoplasmonic structure can be further optimized to attain sensitivities up to 5 × 103 RIU–1.

Raman scattering in dried DNA and crystalline amino acids

Raman spectrum characteristics of dried deoxyribonucleic acid (DNA) and two types of crystalline amino acids (L-lysine, D-asparagine) are compared in a wide range of frequencies, including the regions of lattice (7 to 200 cm−1) and intramolecular (200 to 4000 cm−1) vibrations. It is found that the spectral position of the low-frequency band in the Raman spectrum of DNA with a peak near 26 cm−1 correlates with the Raman spectrum of high-Q low-frequency modes that manifest themselves in the crystalline amino acids under investigation. The low-frequency band of DNA refers to a twist-like vibrational mode of nucleobases. The intensities of this DNA mode and the high-Q lattice modes of the crystalline amino acids L-lysine and D-asparagine are several times as high as those of the Raman lines corresponding to the intramolecular modes. Resonant coupling of low-frequency modes of DNA and amino acid molecular chains is analyzed.

Diffraction Theory of Two-Mirror Echelette Resonators

We develop the theory of a two-mirror resonator, in which one mirror is an echelette diffraction grating. The diffraction loss related to the finite sizes of the mirrors, the loss determined by the existence of a mirror diffraction maximum of the grating (coupling loss), and the ohmic loss are taken into account. We show the possibility of constructing a resonator with one high-Q mode in a wide frequency band. This mode can be used as the working mode of a gyrotron operated at the second gyrofrequency harmonic, which interacts efficiently with the electron beam. We also demonstrate the possibility of frequency tuning of the resonator in a frequency band of 1%, while retaining the parameters which are satisfactory for gyrotron operation, and a high degree of resonator selectivity (i.e., the presence of a single mode).

Piezoelectric tunable microwave superconducting cavity.

In the context of engineered quantum systems, there is a demand for superconducting tunable devices, able to operate with high-quality factors at power levels equivalent to only a few photons. In this work, we developed a 3D microwave re-entrant cavity with such characteristics ready to provide a very fine-tuning of a high-Q resonant mode over a large dynamic range. This system has an electronic tuning mechanism based on a mechanically amplified piezoelectric actuator, which controls the resonator dominant mode frequency by changing the cavity narrow gap by very small displacements. Experiments were conducted at room and dilution refrigerator temperatures showing a large dynamic range up to 4 GHz and 1 GHz, respectively, and were compared to a finite element method model simulated data. At elevated microwave power input, nonlinear thermal effects were observed to destroy the superconductivity of the cavity due to the large electric fields generated in the small gap of the re-entrant cavity.

Investigation of mode characteristics in rectangular microresonators for wide and continuous wavelength tuning

The mode characteristics are investigated for the rectangular microresonators with an output waveguide connected to the midpoint of the long side for wide and continuous wavelength tuning. Through adjusting the aspect ratio of the rectangular microresonator, the mode Q factors can be greatly enhanced. Furthermore, the large mode interval between the high-Q modes makes the rectangular microresonators suitable for tunable lasers. As a special case, single-mode operation is achieved with a continuous tuning range of 9.1 nm for a square microlaser with the side length of 17.8 mm and the output waveguide width of 1.8 mm.

Controllable lasing behavior enabled by compound dielectric waveguide grating structures.

The photonic density of states (PDOS) is one of the key physical quantities governing the lasing behavior for photonic band-edge lasers. The PDOS is conventionally altered by exploiting the high-Q band-edge mode within a device, which is typically achieved by increasing the contrast of periodic refractive index variation (Δn) or increasing the periodic number of the photonic crystals. In this paper, we propose a different approach to achieve a high-Q band edge mode within an active compound dielectric waveguide grating (CWDG). We demonstrate that the lasing threshold and intensity can be flexibly tuned by changing the filling factors of the CWDG. This design can effectively improve the performance of electrically pumped photonic band-edge lasers.

Localized high-Q modes in conical microcavities

We carry out three-dimensional (3D) numerical simulation on a conical microcavity with a half-angle of 11 degree, where there exists high-Q modes by introducing a thin high refractive index film on a conical surface. Our study reveals that, rather than the surface profile of the microcavity, the effective radius plays crucial role in whether the cavity may support localized modes. Specifically, the change of high refractive index film thickness creates an additional angular momentum barrier, so that the conical microcavity may sustain localized high-Q modes. Our study offers a new degree of freedom to control the properties of 3D microcavities, which is useful for microlaser or sensor applications.

Design of quasi-one-dimensional phononic crystal cavity for efficient photoelastic modulation

We propose and design a phononic crystal (PnC) cavity for efficient photoelastic modulation. A strongly confined acoustic field in the cavity enhances light-sound interaction, which results in efficient phase modulation of light. As one of the possible configurations, an acoustic cavity formed in a quasi-one-dimensional (quasi-1D) PnC was investigated. By carefully tuning geometrical parameters, we successfully designed a high-Q cavity mode for a longitudinal wave within a complete phononic band gap. The acoustic Q was calculated to be as high as 9.5 × 104. This enables efficient optical modulation by a factor of 2.5 compared with a bar-type structure without PnCs.

A batteryless temperature sensor based on high temperature sensitive material

The major challenge in wireless sensor networks is the reduction of energy consumption. Passive wireless sensor network is an attractive solution for measuring physical parameters in harsh environment for large range of applications requiring sensing devices with low cost of fabrication, small size and long term measurement stability. Batteryless temperature sensing techniques are an active research field. The approach developed in our work holds a promising future for temperature sensor applications in order to successfully reduce the energy consumption. The temperature sensor presented in this paper is based on the electromagnetic transduction principle using the integration of the high temperature sensitive material into a passive structure. Variation in temperature makes the dielectric constant of this material changing, and such modification induces variation in the resonant frequencies of high-Q whispering-gallery modes (WGM) in the millimeter-wave frequency range. Following the results achieved, the proposed device shows a linear response to the increasing temperature and these variations can be remotely detected from a radar interrogation.

Improvement in the quality factors for photonic crystal nanocavities via visualization of the leaky components.

A method that simply improves the quality (Q) factors of two-dimensional photonic crystal nanocavities using a three-dimensional finite-difference time domain calculation is described. The leaky area for a high-Q nanocavity mode is visualized in a real cavity structure by extracting the leaky components within a light cone in momentum space and by transferring them back into real space using an inverse Fourier transformation. The Q factor is remarkably improved by appropriately shifting the positions of air holes at the leaky area. We design three-missing-air-hole and zero-cell-defect nanocavities with Q factors of 5,000,000 and 1,700,000, respectively, for demonstration.

Selective excitation of high-Q resonant modes in a bottle/quasi-cylindrical microresonator

We fabricate a bottle/quasi-cylindrical microresonator by using a fusion splicer. This method does not require a real-time control of the translation stages and can easily fabricate a resonator with expected size and shape. Selective excitation of whispering gallery modes (WGMs) in the resonator is realized with a fiber taper coupled at various positions of the resonator along the bottle axis. Most importantly, we obtain a clean and regular spectrum with very high quality factor (Q) modes up to 3.1×107 in the quasi-cylindrical region of the resonator. Moreover, we package the coupling system into a whole device that can be moved freely. The vibration performance tests of the packaged device show that the coupling system with the taper coupled at the quasi-cylindrical region has a remarkable anti-vibration ability. The portability and robustness of the device make it attractive in practical applications.

Efficient telecom to visible wavelength conversion in doubly resonant gallium phosphide microdisks

Resonant second harmonic generation between 1550 nm and 775 nm with normalized outside efficiency >3.8×10−4 mW−1 is demonstrated in a gallium phosphide microdisk supporting high-Q modes at visible (Q∼104) and infrared (Q∼105) wavelengths. The double resonance condition is satisfied for a specific pump power through intracavity photothermal temperature tuning using ∼360 μW of 1550 nm light input to a fiber taper and coupled to a microdisk resonance. Power dependent efficiency consistent with a simple model for thermal tuning of the double resonance condition is observed.