Tunneling control of cavity linewidth narrowing via quantum interference in triangular quantum dot molecules

A scheme for tunneling control of cavity linewidth narrowing by quantum interference in triangular-type triple quantum dots (TQDs) is proposed. In such system, quantum interference induced by tunneling between the TQDs can result in the appearance of two transparency windows and a steep dispersion. Furthermore, when the sample is embedded in a ring cavity, an ultranarrow transmission peak is obtained within the narrowed transparency windows. And by varying the tunneling, the linewidth and the position of the ultranarrow transmission peak can be engineered. Because no coupling laser is required, the scheme proposed here is more convenient for future experiments and applications in optics, and may be useful in designing novel optoelectronic devices.     

Implementation of a loss-compensated recirculating delayed self-heterodyne interferometer for ultranarrow laser linewidth measurement

Ultranarrow laser linewidth measurement using an optimized loss- compensated recirculating delayed self-heterodyne interferometer is described. An experimental setup is constructed to measure subkilohertz laser linewidths. The system parameters are optimized to obtain the best beat signals. The experimental results agree well with the theoretical analysis. Two methods of linewidth interpretation are presented and analyzed based on the experimental results. It is proved that a loss-compensated recirculating delayed self-heterodyne interferometer is an effective tool for measuring an ultranarrow laser linewidth.     

Theory and experiments of a tunable wavelength-selective photodetector based on a taper cavity

We demonstrate a wavelength-selective photodetector that combines a Fabry-Perot filtering cavity (FPC) with a taper absorption cavity (TAC). The taper cavity shows a nonresonant effect but exhibits an absorption enhancement effect, so that high speed, high quantum efficiency, wide tuning range, and an ultranarrow spectral linewidth can be achieved simultaneously. Device performance was theoretically investigated by including key factors such as taper angle, finite-size diffracting-beam input, and lateral walk-off in the taper cavity. The device was fabricated by bonding a GaAs-based FPC, which can be tuned via thermal-optic effect, with an InP-based TAC. An integrated device with a spectral linewidth of 0.6 nm (FWHM), a wavelength tuning range of 10.2 nm(1518.0-1528.2 nm), a 3 dB bandwidth of 12 GHz, and a quantum efficiency of approximately 70% was demonstrated, and the absorption layer thickness is only 0.3 microm.     

Sub-recoil-limit laser cooling via interacting dark-state resonances

We propose a laser cooling mechanism based on velocity-selective double-dark resonance that leads to a temperature significantly lower than the one-photon recoil limit. This mechanism benefits from sharp and high-contrast spectra which are induced by the two electromagnetically induced transparency windows due to the interacting dark-state resonances. It is theoretically demonstrated that four-level atoms illuminated by two counter-propagating probe beams and two additional beams directed perpendicularly to the other two exhibit new cooling effects; for red detuned probe lasers, atoms can be subject to a strong viscous force with an extremely small diffusion, characteristic of heating caused by the stochastic nature of spontaneous emission processes. By quantum mechanical simulations, we then find that the lowest temperature in EIT windows approaches 1?nK for the case of mercury. However, the different broadening mechanisms can destroy the cooling, so that the lowest temperature can increase to the recoil temperature.     

Plasmon resonances in a gated two-dimensional electron system with lateral contacts

It is shown that strong plasmon resonances can be excited in the totally gated two-dimensional electron gas with lateral contacts by incoming electromagnetic wave. In such a structure, the plasmon resonance linewidth shrinks down to the minimal theoretical value determined by the electron scattering in two-dimensional electron system.     

Geometrical optics model of Mie resonances

The geometrical optics model of Mie resonances is presented. The ray path geometry is given and the resonance condition is discussed with special emphasis on the phase shift that the rays undergo at the surface of the dielectric sphere. On the basis of this model, approximate expressions for the positions of first-order resonances are given. Formulas for the cavity mode spacing are rederived in a simple manner. It is shown that the resonance linewidth can be calculated regarding the cavity losses. Formulas for the mode density of Mie resonances are given that account for the different width of resonances and thus may be adapted to specific experimental situations.     

Plasmonic focusing reduces ensemble linewidth of silver-coated gold nanorods

Silver coating gold nanorods reduces the ensemble plasmon line width by changing the relation connecting particle shape and plasmon resonance wavelength. This change, we term "plasmonic focusing", leads to less variation of resonance wavelengths for the same particle size distribution. We also find smaller single particle linewidth comparing resonances at the same wavelength but show that this does not contribute to the ensemble linewidth narrowing.     

Resonance Fluorescence in a Squeezed Vacuum

Abstract

Fluorescence from a coherently driven two-level atom that is damped by a squeezed vacuum is studied. We show that the mean atomic polarization depends on the relative phases of the squeezed vacuum and the coherent driving field. The fluorescent spectrum is calculated and shows several modifications over the spectrum for normal resonance fluorescence. In particular, the central peak of the Mollow triplet has a linewidth that depends on the phase of the driving field. For strong squeezing this peak can either be much narrower or much broader than the natural linewidth of the atom.     

Frequency Measurement Errors of Passive Resonators Caused by Frequency-Modulated Exciting Signals

The condition of resonance for a signal with FM is defined in this paper as the condition of maximum power transfer by the resonant device. It is shown that if the width of the signal spectrum is small compared to the resonator's linewidth, then the frequency error is proportional to the third moment of the instantaneous signal frequency about its mean. One expects that this treatment should, at least, give the leading term for a precise treatment of atomic resonances. Experimental results with a cesium beam frequency standard confirm this expectation and add caution to the idea that higher Q atomic resonances make better absolute frequency standards.     

Subgroup decomposition of plasmonic resonances in hybrid oligomers: modeling the resonance lineshape

Plasmonic resonances with a Fano lineshape observed in metallic nanoclusters often arise from the destructive interference between a dark, subradiant mode and a bright, super-radiant one. A flexible control over the Fano profile characterized by its linewidth and spectral contrast is crucial for many potential applications such as slowing light and biosensing. In this work, we show how one can easily but significantly tailor the overall spectral profile in plasmonic nanocluster systems, for example, quadrumers and pentamers, by selectively altering the particle shape without a need to change the particle size, interparticle distance, or the number of elements of the oligomers. This is achieved through decomposing the whole spectrum into two separate contributions from subgroups, which are efficiently excited at their spectral peak positions. We further show that different strengths of interference between the two subgroups must be considered for a full understanding of the resulting spectral lineshape. In some cases, each subgroup is separately active in distinct frequency windows with only small overlap, leading to a simple convolution of the subspectra. Variation in particle shape of either subgroup results in the tuning of the overall spectral lineshape, which opens a novel pathway for shaping the plasmonic response in small nanoclusters.     

Si-based tunable flattop photodetector with a stepped Fabry-Perot cavity

This paper presents the design and analysis of a Si-based tunable flattop photodetector realized by the introduction of a stepped Fabry-Perot cavity, which can be thermally tuned via applying tuning power on its tuning electrode. By using a transfer matrix method, the spectral response of the photodetector is simulated in detail, indicating a flattop line shape can be achieved with an optimum step height. A trade-off residing in this device between the free spectrum range and the ease of fabrication of step height is also revealed and analyzed. In the final design of the photodetector, 1 dB linewidth of 0.5 nm, 3 dB linewidth of 0.8 nm, 6 dB linewidth of 1.2 nm, peak quantum efficiency of 40%, tuning efficiency of 91 mW/nm are theoretically obtained. We discuss the epitaxial growth and fabrication of the photodetector in the end, exhibiting the mature technique available for this device.     

Large Coulomb blockade oscillations at room temperature in ultranarrow wire channel MOSFETs formed by slight oxidation process

We propose a new fabrication technique of room-temperature operating silicon single-electron transistors (SETs). The devices are in the form of ultranarrow wire channel MOSFETs, where a sub-10-nm channel is formed by wet etching and slight thermal oxidation. Large Coulomb blockade (CB) oscillations whose peak-to-valley current ratio at room temperature is as high as 6.8 are observed in the fabricated ultranarrow wire channel MOSFETs. It is found that larger CB oscillations are obtained in the ultranarrow wire channel SETs than in the point-contact channel SETs. It is considered that the potential fluctuations induced during the channel formation processes give rise to multiple-dot SET structures in the ultranarrow wire channel MOSFETs.     

Identical-dual-bandpass sampled fiber Bragg grating and its application to ultranarrow filters

We have theoretically proposed and experimentally demonstrated a new kind of ultranarrow identical-dual-bandpass sampled fiber Bragg gratings (SFBGs) with a pi phase shift technique. The spacing of two bandpasses of the proposed grating can be flexibly adjusted by changing the sampled period, and any desired spacing can be achieved in principle. An experimental example shows that the transmission peaks of two narrow transmission-band are near 1549.1 and 1550.1 nm. Based on the proposed SFBG, an ultranarrow identical-dual-channel filter is designed. Two channels of the proposed filter have an equal bandwidth, an even strength, and the same group delay. The bandwidth of each channel of our filter is as small as 1 pm and up to 10(-3) pm (corresponding to approximately 0.1 MHz), which is less than the bandwidth of the conventional SFBG filters by a factor of 10(2)-10(4). The proposed grating and filter can find potential applications with slow light and dual-wavelength single-longitudinal-mode fiber lasers.     

Temperature dependence of the Brillouin linewidth in water

In the frequency spectrum of light that is scattered in liquid water there is a central elastically scattered peak that is due mainly to scattering by suspended particles; and, there is a peak on each side of the central peak that is displaced by the Brillouin frequency shift. The Brillouin shift is a direct measure of sound speed. The linewidth of the Brillouin shifted lines is dependent on the bulk and shear viscosity of water as well as its density, thermal conductivity, and specific heat. The linewidth of the Brillouin peaks has been investigated in laboratory experiments over a range 1°C to 35°C. The frequency spectrum of back-scattered laser light was analysed using a scanning Fabry-Perot etalon. A strong dependence of the linewidth of the Brillouin shifted lines on temperature was found. In particular, for low temperatures in the range 10°C down to 1°C the linewidth shows an increase from 750 MHz to 1.4 GHz.     

Investigating surface wave resonances with electrons on helium

Waves on liquid⁴He were excited and detected by capacitively coupling to an electron sheet trapped at the free surface. The standing wave resonances, resulting from the finite size of the sample cell, were measured and their frequencies are in good agreement with theory. The resonant linewidth displays a nonmonotonic dependence on temperature which indicates that it is determined by viscous friction at the watts of the sample cell.     

Electro-optic sensor from high Q resonance between optical D-fiber and slab waveguide

An electro-optic sensor capable of detecting electric fields with a high degree of sensitivity and linearity is fabricated using optical D-fiber. The slab coupled optical sensor utilizes weak coupling and long evanescent interaction with a lithium niobate waveguide. Transmission dips from mode resonances have a linewidth of 0.12 nm and a Q factor of approximately 13,000. These sharp resonances improve device sensitivity and are achieved due to the unique fabrication process possible with D-shaped fibers. The sensor deviates <0.1% from linearity while monitoring fields between 200 V/m and 20 kV/m and promises high sensitivity to fields well beyond that range.     

Dark‐Exciton‐Mediated Fano Resonance from a Single Gold Nanostructure on Monolayer WS2 at Room Temperature

Strong spatial confinement and highly reduced dielectric screening provide monolayer transition metal dichalcogenides with strong many‐body effects, thereby possessing optically forbidden excitonic states (i.e., dark excitons) at room temperature. Herein, the interaction of surface plasmons with dark excitons in hybrid systems consisting of stacked gold nanotriangles and monolayer WS₂ is explored. A narrow Fano resonance is observed when the hybrid system is surrounded by water, and the narrowing of the spectral Fano linewidth is attributed to the plasmon‐enhanced decay of dark K‐K excitons. These results reveal that dark excitons in monolayer WS₂ can strongly modify Fano resonances in hybrid plasmon–exciton systems and can be harnessed for novel optical sensors and active nanophotonic devices.     

Characterization technique of optical whispering gallery mode resonators in the microwave frequency domain for optoelectronic oscillators

Optical Q factor measurements are performed on a whispering gallery mode (WGM) disk resonator using a microwave frequency domain approach instead of using an optical domain approach. An absence of hysteretic behavior and a better linearity are obtained when performing linewidth measurements by using a microwave modulation for scanning the resonances instead of the piezoelectric-based frequency tuning capability of the laser. The WGM resonator is then used to stabilize a microwave optoelectronic oscillator. The microwave output of this system generates a 12.48 GHz signal with -94 dBc/Hz phase noise at 10 kHz offset.     

测量激光线宽的一种新装置

介绍了一种新的仅用一台激光器测定激光线宽或频率稳定的测量方法，用稳定的无源腔透过曲线腰处斜率将激光的频率扰动转为电压扰动。用所研制的测量装置对自制的边疆波染料激光频率的线宽和频率稳定性进行了测量。     

On chip optical isolator based on non-linear silicon photonic crystal by using asymmetric engineering waveguide

We propose an optical isolator formed in a nanoscale structure based on non-linear silicon photonic crystal that can be easily realized on an optical integrated chip. The structure comprises an engineered waveguide that is coupled to a L₂ cavity. By using a passive ultra-compact cavity-based isolator, without changing incident characteristics such as mode or frequency in outputs, an admirable transmission contrast of 20.5 dB with a small insertion loss (in the forward direction) of ?14.8 dB is achieved. The isolator attains a broad isolating linewidth operation of 0.9 nm without bistability response that is outstanding in comparison with the currently proposed cavity-based isolators. The non-linear Fano resonances that are created by the interplay between the non-linearity and spatial asymmetry notion in the structure play a critical role in the isolator efficiency. In this study, the finite-difference time-domain and finite element methods are used for simulations.