Slow-light element for tunable time delay based on optical microcoil resonator

We propose a simple and compact slow-light element by use of an optical microcoil resonator (OMR) constituted by two microfiber coils. Based on the matrix exponential method, we solve the coupled-wave equations of the OMR with n turns of microfiber coils and obtain a general solution. Simulations indicate that a tunable slow-light propagation can be obtained by controlling the coupling coefficient between the two adjacent microfiber coils by means of regulating the voltage applied to the ferroelectric crystal. A slow-light time delay up to 62?ps with a bandwidth of 0.4?nm is performed at the wavelength around 1.5?μm.     

Slot optical waveguide usage in forming passive optical devices

We have reviewed the work on SOI slot optical waveguides followed by our work. In a slot waveguide structure, light can be confined in a low index slot guarded by high index slabs. Slot structures are being used in forming complex structures; such as ring resonator circuits. The increased round trip in ring resonator circuits signifies the importance of dispersion calculations. We did analytical and numerical investigations of slot structures' dispersion characteristics. Our dispersion tuned slot structures can help in reducing the dispersion effects on optical signal, which will in turn improve the efficiency of light-on-chip circuits. Since the advent of slot optical waveguides, SOI based slot optical waveguides have been under consideration. It has been found that glass based slot optical waveguide structures with relatively low refractive index contrast ratio can also play an important role in forming complex nano-size optical devices. We made use of power confined inside low index slot regions for a double slot structure. Opto-mechanical sensors have been proposed based upon: (a) variation in power confined inside low index slot region due to the movement of central high index slab under the action of external force (temperature, pressure, humidity, etc). vide Chinese Patent No. ZL 200710176770.1, 2007 (b) variation in power confined inside low refractive index slot regions due to movement of both slots under the action of external force (temperature, pressure, humidity, etc).     

Voltage-controlled optical precursors in quantum dot molecules

Abstract

Optical precursors generated in a quantum-dot-molecule system by an incident square-modulated pulse are theoretically investigated. Voltage-controlled electron tunneling couples two quantum dots instead of a laser field, and a narrow transparency window appears with normal dispersion. The main pulse is delayed due to slow-light effect and the precursor pulses are obtained. We examine the linear susceptibility and find that its one part exhibits normal dispersion and the other one presents anomalous dispersion. Competition between the two parts leads to normal dispersion for the linear susceptibility, which contributes to the above results. Voltage-controlled precursors may be useful to design novel optical devices for generating precursors.     

Cavity Enhanced Longitudinal Magneto-Optical Kerr Effect in Magneto-Plasmonic Multilayers Consisting of Ce: YIG Thin Films Incorporating Gold Nanoparticles

Enhanced magneto-optical rotation has been the subject of intense interest for communication technology. In this paper, we report an experimental study on the effect of Bragg reflector mirror and Au nanoparticles on the magneto-optical rotation in a new magneto-optical structure named magneto-plasmonic construction. Our results indicate sufficient longitudinal magneto-optical Kerr effect enhancement in this new structure by the aid of combination of surface plasmon resonance and light localization in magneto-optical garnet layer. The presence of Au nanoparticles leads to screening of the surface plasmon resonance, while Bragg reflector mirror reduces the group velocity in magneto-optical medium as a defect layer and thus we have sufficient enhancement in magneto-optical rotation. These structures can be addressed as a new concept in the development of magneto-plasmonic devices.     

Estimating materials parameters in thin-film BAW resonators using measured dispersion curves

The dispersion curves of Lamb-wave modes propagating along a multilayer structure are important for the operation of thin-film bulk acoustic wave (BAW) devices. For instance, the behavior of the side resonances that may contaminate the electrical response of a thin-film BAW resonator depends on the dispersion relation of the layer stack. Because the dispersion behavior depends on the materials parameters (and thicknesses) of the layers in the structure, measurement of the dispersion curves provides a tool for determining the materials parameters of thin films. We have determined the dispersion curves for a multilayer structure through measuring the mechanical displacement profiles over the top electrode of a thin-film BAW resonator at several frequencies using a homodyne Michelson laser interferometer. The layer thicknesses are obtained using scanning electron microscope (SEM) measurements. In the numerical computation of the dispersion curves, the piezoelectricity and full anisotropy of the materials are taken into account. The materials parameters of the piezoelectric layer are determined through fitting the measured and computed dispersion curves.     

Study of performance of a He-Ne laser having an annular gain zone

A He-Ne laser with an annular gain zone is studied theoretically. It is demonstrated that the He-Ne medium in the annular discharge zone possesses enough gain to maintain laser oscillation. A multipass ring resonator, which is composed of two annular spherical mirrors, is described, and it is shown that the resonator is suitable for extracting optical energy from the He-Ne medium in the annular gain zone. Considering the availability of population inversion in the traveling-wave cavity and the influence of the crossover of the folded light beam in the resonator on the output power, a calculation formula for the output power of the laser with the multipass ring resonator is given. Calculating results prove that a 1 W output of the He-Ne laser can be obtained by a 1 m length annular discharge zone.     

Analysis of reentrant two-mirror nonplanar ring laser cavity

A rigorous analysis is performed on the reentrant nonplanar ring laser cavity constructed by a Herriott-type multipass cell. Since the cavity is highly nonplanar, the angle between the incident planes at each reflection becomes different from that of the image rotation angles. The beam rotation, astigmatism, and spherical aberration are considered to obtain a self-consistent solution of the Gaussian beam. It turns out that spherical aberration is an important issue for this nonplanar resonator. Without taking into account the spherical aberration, a stable resonator would be difficult to realize. Using a self-consistent Gaussian beam propagation method, the laser beam characteristics are solved analytically. The results are compared with that of the 2 x 2 ABCD method.     

Using two-dimensional distributed feedback for the synchronization of emission from laser active media

It is shown that two-dimensional (2D) Bragg resonance structures can be used for the synchronization of emission from a spatially developed laser active medium. Analysis of the dynamics of a laser with 2D distributed feedback shows that stationary lasing with a frequency and a spatial structure of the field close to the fundamental mode of a 2D Bragg resonator is possible in the structures with large values of the Fresnel parameter.     

Dielectric constant measurement of low loss liquids using stacked multi ring resonator

The concept of dielectric constant measurement has been extended and applied in agriculture, pharmaceutical and food industry for quality control of liquids. Dielectric analysis of material at microwave frequencies can be done using novel shielded stacked multi-ring resonator (SMRR). The dielectric constant of liquids and paste has been calculated using SMRR with greater accuracy than the planar resonator, boxed resonator and stacked resonator. SMRR contains a ring resonator with fed patch and parasitic patch with different numbers and sizes of rings. The dimensions of rings on the parasitic patch are optimized to achieve Quality factor Q greater than 100 and return loss less than ?2 dB. Due to dual resonance in novel SMRR, structure losses are reduced by 50% than planar resonator structure. The behavior of SMRR structure at the 2.45 GHz frequency is studied with E field and H field. 3D model is designed in Computer Simulation Technology Microwave Studio (CST MWS) using TLM (Transmission Line Modeling) solver. Electromagnetic field analysis as well as impedance bandwidth of SMRR using CST MWS 3D model prove that electromagnetic coupling in SMRR structure increases thus improves quality factor. In SMRR quality factor increases and losses reduce help us to predict the complex permittivity of material for quality analysis.     

Electro-magneto-thermo-elastic plane waves in rotating media with thermal relaxation

A study is made of the propagation of plane electro-magneto-thermo-elastic harmonic waves in an unbounded isotropic conducting medium permeated by a primary uniform magnetic field when the entire medium rotates with a uniform angular velocity. The thermal relaxation time of heat conduction, the electric displacement current, the coupling between heat flow density and current density and that between the temperature gradient and the electric current are included in the analysis. A more general dispersion relation is obtained to determine the effects of rotation, relaxation time and the external magnetic field on the phase velocity of the waves. Perturbation techniques are used to study the influence of small magneto-elastic and thermo-elastic couplings on the phase velocity of the waves. Cases of low and high frequencies are also studied to determine the effect of rotation, thermoelastic and magneto-elastic couplings on the waves.     

Electromagnetically-induced transparency in a multi-cavity coupled waveguide system

The plasmonic analogue of electromagnetically-induced transparency (EIT) was investigated in a plasmonic waveguide system composed of a straight waveguide, with rectangular and U-shaped (split-ring resonator) cavities. An EIT-like transparency window occurs in the transmitting spectrum of the waveguide system and the magnetic field is dramatically changed due to the destructive interference between two resonance pathways. It is demonstrated that the EIT-like spectra can be modified by varying the coupling strength and tailoring the degree of asymmetry of the structure, and we study the coupling mechanisms between the elements of the structure, including magnetic coupling, electric coupling, and inductive coupling. In addition, a cascaded structure which consists of an SRR pair with 180° rotation asymmetry has been studied. It is found that the strong couplings between two asymmetric plasmonic nanostructures can lead to EIT-like transmission in both visible and near-infrared regions, simultaneously.     

Optical bistability in metal-insulator-metal plasmonic waveguide with nanodisk resonator containing Kerr nonlinear medium

We numerically investigate the optical bistability effect in the metal-insulator-metal waveguide with a nanodisk resonator containing a Kerr nonlinear medium. It is found that the increase of the refractive index, which is induced by enhancing the incident intensity, can cause a redshift for the resonance wavelength. The local resonant field excited in the nanodisk cavity can significantly increase the Kerr nonlinear effect. In addition, an obvious bistability loop is observed in the proposed structure. This nonlinear structure can find important applications for all-optical switching in highly integrated optical circuits.     

Resonance shift induced by free carriers of a silicon resonator of quadrangular shape

The nonlinear optical interaction of a silicon resonator with a quadrangular shaped smooth bend is studied with inclusion of free carriers (FCs), two-photon absorption, the Kerr effect, and loss. It is shown that for the range of input light power from zero up to 2 W, the incident light transmits between the silicon resonator and waveguide linearly. However, with an increase of light power from 2 W to higher values, the light transmission decreases very rapidly, so that it approximately vanishes at about 10 W. Furthermore, the resonance spectrum and stability condition of the silicon resonator in the nonlinear regime is studied with inclusion of FC dispersion and FC absorption for continuous wave operation. Thermal effects induced by FC absorption increase the refractive index, which causes a redshift of about 1.2 nm for 125.13 mW light power.     

COIL emission of a modified negative branch confocal unstable resonator

A modified negative branch confocal unstable resonator (MNBUR) was coupled to the chemical oxygen-iodine laser (COIL) device of the German Aerospace Center. It consists of two spherical mirrors and a rectangular scraper for power extraction. Experimentally measured distributions of the near- and far-field intensities and the near-field phase were found in close agreement to numerical calculations. The extracted power came up to approximately 90% of the power as expected for a stable resonator coupled to the same volume of the active medium. The output power revealed a considerable insensitivity towards tilts of the resonator mirrors and the ideal arrangement of the scraper was found to be straightforward by monitoring the near-field distributions of intensity and phase. The beam quality achieved with the MNBUR of an extremely low magnification of only 1.04 was rather poor but nevertheless in accordance with theory. The demonstrated consistency between theory and experiment makes the MNBUR an attractive candidate for lasers that allow for higher magnification. In particular, it promises high brilliance in application to 100 kW class COIL devices, superior to the conventional negative branch confocal unstable resonator.     

圆形金属腔旋流二氧化碳激光器

现有的工业ＣＯ２激光器,主要为横流,纵流和扩散冷却三种,章提出一种新型激光器,即圆形金属腔ＣＯ２激光器,该激光器的腔体由多个等距,同轴安装的空腔单元组成,每个腔单元有多个流道,放电在流道与腔体接口处产生,气流将放电及被其激活的粒子吹入腔内,形成增益,输电激光,章研究了电极结构,金属腔壁对工作气体的冷却作用和胺内的增益分布,研究结果表明,多通道放电吹入和腔内旋流,有利于腔内的均匀放电,金属腔壁有利于腔内对流冷却,降低对气速度的要求,从而缩小激光器的体积,相邻的腔单元相对转动适当角度,可以提高腔内增益分布的圆周均匀性,从而获得光束质量好的激光束。     

Unstable resonator with reduced output coupling

The properties of a laser beam coupled out of a standard unstable laser resonator are heavily dependent on the chosen resonator magnification. A higher magnification results in a higher output coupling and a better beam quality. But in some configurations, an unstable resonator with a low output coupling in combination with a good beam quality is desirable. In order to reduce the output coupling for a particular resonator, magnification fractions of the outcoupled radiation are reflected back into the cavity. In the confocal case, the output mirror consists of a spherical inner section with a high reflectivity and a flat outer section with a partial reflectivity coating. With the application of the unstable resonator with reduced output coupling (URROC), magnification and output coupling can be adjusted independently from each other and it is possible to get a good beam quality and a high power extraction for lasers with a large low gain medium. The feasibility of this resonator design is examined numerically and experimentally with the help of a chemical oxygen iodine laser.     

Effective dispersion in an inhomogeneously broadened single mode laser

Recently, we have been investigating the development of a superluminal ring laser, where finely tuned anomalous dispersion leads to an enhancement in the sensitivity of the laser frequency to a change in the cavity length, by as much as six orders of magnitude, for applications such as hypersensitive rotation sensing and accelerometry, as well as for gravitational wave detection. For such a laser, as well as other lasers that are used for precision metrology, the effective dispersion – manifested in the manner in which the lasing frequency varies as a function of a change in the cavity length due to the index induced by the medium under saturated gain corresponding to steady-state lasing – is of utmost significance. In determining the effective dispersion, the role of inhomogeneous broadening (IB) must be taken into consideration carefully. In this work, we consider an inhomogeneously broadened gain medium in a single mode optical cavity, and study the effective dispersion experienced by the lasing field. It is well known that the steady state index for such a laser cannot be expressed analytically. Previous studies have employed approximate models to interpret the effective dispersion, in two limits: IB is much larger than homogeneous broadening (HB), and IB is insignificant compared to HB. Here, we use an iterative but quickly converging numerical code to determine the exact behavior of the effective dispersion under all conditions, and show that the results agree with the expected behavior in these two limits. This technique paves the way for taking into account the effective dispersion in any inhomogeneously broadened laser, including the superluminal laser, in determining accurately its sensitivity to change in cavity length, as well as it quantum noise limited linewidth.     

An autostochastic system with parametric excitation

The parametric excitation of chaotic motions in a dynamic system with a resonator in a delayed feedback chain is numerically analyzed. It is shown that the structure of oscillations can be effectively controlled for a resonator parametrically pumped with both regular and chaotic signals.     

Electro-magneto-thermo-visco-elastic Plane Waves in Rotating Media with Thermal Relaxation

A study is made of the propagation of plane electro-magneto-thermo-visco-elastic harmonic waves in an unbounded isotropic conducting visco-elastic medium of Kelvin–Voigt type permeated by a primary uniform magnetic field when the entire medium rotates with a uniform angular velocity. The thermal relaxation time of heat conduction, the electric displacement current, the coupling between heat flow density and current density, and that between the temperature gradient and the electric current are included in the analysis. A more general dispersion relation is obtained to determine the effects of rotation, thermal relaxation time, visco-elastic parameters, and the external magnetic field on the phase velocity of the waves. Perturbation techniques are used to study the influence of small magneto-elastic and thermo-elastic couplings on the phase velocity of the waves. Cases of low and high frequencies are also analyzed to determine the effect of rotation, visco-elastic parameters, thermo elastic and magneto-elastic coupling, as well as thermal relaxation time of heat conduction on the waves.