Changes In Transmission Spectra Research Articles

Precision measurement of single-atom trajectories in higher-order Laguerre-Gaussian transverse modes of a Fabry-Perot cavity

A coupled quantum system composed of cavity field and atoms is one of the main research contents of cavity quantum electrodynamics. It can be used to realize single atom manipulation and measurement, and has important significance for studying the interaction between light and the atom, preparing quantum states and quantum entanglement. Current research work mainly focuses on two aspects. One is to achieve the atom trapping via the feedback control of the trapping laser intensity. The other is to measure the single atomic motion in a Fabry-Perot cavity by using Hermite-Gaussian transverse modes. The detection of the atomic trajectories has been realized via the observation of transmission spectra of the strong coupling system composed of cold atoms and Hermite-Gaussian transverse modes in a Fabry-Perot cavity. In order to observe the atomic motion trajectories in the cavity, we theoretically study the transmission spectrum of a strong coupling system composed of cold atoms and Laguerre-Gaussian transverse modes in a Fabry-Perot cavity in this paper. We calculate the relationship between the coupling coefficient and the mode number of Laguerre-Gaussian transverse modes. The result shows that with the increase of Laguerre-Gaussian transverse mode number, the maximum coupling coefficient between the atoms and cavity fields is almost unchanged, so the contrast of the detected spectrum is nearly independent of the mode number. Analysis shows that Laguerre-Gaussian transverse mode provides more abundant information about atomic motion trajectory than Hermite-Gaussian transverse mode. The field distribution of Laguerre-Gaussian transverse mode is ring-shaped. Owing to the ring shape, the atoms dropped at different positions experience different electric field intensities, and the detected transmission spectra are changed. Therefore, we can implement the high precision distinguishment of the atomic trajectories by observing the features of the transmission spectra such as the number of the transmission peaks and their positions. Furthermore, a small deviation of the atomic motion trajectories, on the edges of the rings of the electric field, may induce great change in transmission spectrum, and then we can very accurately detect the atomic motion around these positions.

Transmission of asymmetric coupling double-ring resonator

Based on the asymmetry between waveguide and double ring, the transmission and phase characteristics of coupled double-ring resonators are analyzed systemically. It is shown that the initial detuning determines the shape of transmission spectrum. The transmission spectrum of all-optical analog to electromagnetic inducted transparency (EIT) is controlled by tuning the asymmetric coupled parameter and loss. With the increasing of asymmetric coupled parameter, the transmission spectrum changes from EIT-like profile to Lorenz profile. The EIT-like transmission spectrum results from the interference between two Lorenz profiles. With the increasing of the loss, the transmission spectrum full frequency width at half-maximum broadens and its peak declines. The detuning and loss also make significant influences on the phase profile.

Glucose sensing by waveguide-based absorption spectroscopy on a silicon chip.

In this work, we demonstrate in vitro detection of glucose by means of a lab-on-chip absorption spectroscopy approach. This optical method allows label-free and specific detection of glucose. We show glucose detection in aqueous glucose solutions in the clinically relevant concentration range with a silicon-based optofluidic chip. The sample interface is a spiral-shaped rib waveguide integrated on a silicon-on-insulator (SOI) photonic chip. This SOI chip is combined with micro-fluidics in poly(dimethylsiloxane) (PDMS). We apply aqueous glucose solutions with different concentrations and monitor continuously how the transmission spectrum changes due to glucose. Based on these measurements, we derived a linear regression model, to relate the measured glucose spectra with concentration with an error-of-fitting of only 1.14 mM. This paper explains the challenges involved and discusses the optimal configuration for on-chip evanescent absorption spectroscopy. In addition, the prospects for using this sensor for glucose detection in complex physiological media (e.g. serum) is briefly discussed.

Regenerable Plasmonic Biosensor Based on Gold Nanolines Pattern and Common Laboratory Spectrophotometer

Gold nanostructures can undergo plasmonic behavior without need of light couplers like in traditional surface plasmon resonance (SPR) systems. This effect, known as LSPR (localized SPR), can be exploited to develop optical biosensors in simple configuration. In this paper, an LSPR system based on gold lines nanopattern as transducer has been developed by using a common laboratory spectrophotometer as reader and an adapted flow cell. This novel system was applied to anti-immunoglobulin G (IgG) detection, as proof of concept. For this purpose, the transducer surface was covalently biofunctionalized with IgG and incubated with increasing concentrations of anti-IgG. The response was determined by measuring changes in light transmission spectra (Δλ, in nanometers). Contrary to other reported nanopatterns, biosensor features as repeatability, regeneration, and detectability have been deeply studied. Results indicate that the system can act as a robust and regenerable biosensor with a limit of detection of 5.98 ± 1.34 nM.

Optical Gaussian Notch Filter Based on Periodic Microbent Fiber Bragg Grating

In this paper, we demonstrated an optical notch filter constructed from a periodic microbent fiber Bragg grating attained by using two copper-wire-wound slabs. In the reflection spectrum, sideband peaks are created as a result of mechanically induced modulation on the grating period, and a higher number of peaks are observed when greater modulation is applied. The peak wavelength spacing depends upon the period of microbending, which can be varied by changing the diameter of the winding wire or the angle of placement of fiber Bragg grating placed in between the two wound slabs. Moreover, the trend of Bragg transmission loss (BTL) for the transmission spectrum changes with the changing of modulation period and amplitude. The proposed technique is very stable, and it can be used as an optical Gaussian notch filter.

Identifying insulating states of ultra cold atoms with cavity transmission spectrum

In this paper, we consider the transmission characteristics of an optical cavity loaded with ultracold atoms in a one-dimensional optical lattice at absolute zero temperature. In particular, we consider the situation when the many body quantum state of the ultracold atoms is an insulating state with a fixed number of atoms at each site, which can either be density wave or Mott insulator phase, each showing a different type of discrete lattice translational symmetry. We provide a general framework of understanding the transmission spectrum from a single and two cavities/modes loaded with such insulating phases. Further, we also discuss how such a transmission spectrum changes when these insulating phases make a cross over to the superfluid phase with the changing depth of the optical lattice potential.

Direct Surface Relief Formation in Polymer Films

Due to active development of nanoelectronics, the studies of methods of nanorelief surface formation in different materials, in particular polymers are very important. Organic polymer films in consequence of their dielectric and optical properties have been used as basis of these devices. In this paper, the possibility of UV optical record and electron beam lithography in different type of polymeric films was studied. Mechanisms of molecular structure changes: photoisomerization, destruction, cross-linking and oxidation have been discussed. The results of UV illumination of polyurethanes, polyacrylates, and some block-copolymers were described. The element analysis of polybutadiene block copolymer was performed before and after UV illumination, and the changes in optical transmission spectra of the polymer film were measured. The resolution of electron beam lithography on polymeric films also was studied.

CONTROLLING SINGLE-PHOTON TRANSPORT IN A ONE-DIMENSIONAL RESONATOR WAVEGUIDE BY INTERATOMIC DIPOLE–DIPOLE INTERACTION

Controlling single-photon transport in a one-dimensional resonator waveguide can be realized by the interatomic dipole–dipole interaction (DDI). Our numerical results show that the effects of the DDI act as that of a positive detuning. Because of the DDI, the period of the transmission spectrum changes, and its amplitude increases for stronger DDI intensity. We also discuss the influences of the DDI on the transport in low-energy and high-energy regimes. Besides, a cooperation dissipation, induced by the two atoms coupling to a common reservoir, can lead to the increase of the atomic total decay rates and the decrease of the reflection amplitude of the incident photon.

UV optical record and electron beam lithography in polymer films

Possibility of UV optical record and electron beam lithography in different type of organic polymer films was studied. Mechanisms of molecular structure changes: photoisomerization, destruction, cross-linking and oxidation have been discussed. The results of UV illumination of polyurethanes, polyacrilates, and some block-copolymers are described. The element analysis of polyisoprene block copolymer was performed before and after UV illumination, and the changes in transmission spectra of the polymer film were measured. The resolution of electron beam lithography on polymer films was studied. In the polyisoprene block copolymer film the oxidation polymerization was ascertain at UV-illumination.

Transmission characteristic of multi-turn microfiber coil resonator

A transmission characteristic of multi-turn microfiber coil resonator (MCR), which is assembled from an adiabatic microfiber, is demonstrated. A comb spectrum was obtained by wrapping a microfiber on a low refractive indexed rod. A resonance with a free spectral range of 0.8nm was observed with a single turn on a 0.5mm diameter low-indexed rod and the change in transmission spectrum of the MCR was evident as the number of turns increased. For every additional microfiber turn, there was an addition of an eigenmode to the system which could be observed from the addition of a new resonance for every fringe in the transmission spectrum. The FSR for every added eigenmode was measured to be close to 0.8nm.

Transmission properties of a new glass ceramic and doped with Co2+ as saturable absorber for 1.54 µm Er glass short pulse laser

The preparation and characteristics of a new transparent glass ceramic were described. Crystal phase particles with nanometer size were successfully precipitated in glass matrix, which was confirmed to be one of indium aluminum zinc oxide compounds (InxAlyZnzO). The presence of aluminum (Al) and indium (In) impurities in the zinc oxides (ZnO) crystal lattice leads to some changes of the carrier concentration in the material and then promote the sharply changes of transmission spectra in IR range wavelength. And subsequently, the IR cut-off edge blue shifted from 5.5 μm in base glass to 3 μm in transparent glass ceramic sample. Furthermore, passive Q switched 1.54 μm Er glass laser pulses with pulse energy of 10 mJ and pulse width of 800 ns were successfully obtained by using the cobalt doped transparent glass ceramic as a saturable absorber.

Crystallization Behavior of Silicon Quantum Dots in a Silicon Nitride Matrix

Silicon quantum dot superlattice was fabricated by alternating deposition of silicon rich nitride (SRN) and Si3N4 layers using RF magnetron co-sputtering. Samples were then annealed at temperatures between 800 and 1,100 degrees C and characterized by grazing incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). GIXRD and Raman analyses show that the formation of silicon quantum dots occurs with annealing above 1,100 degrees C for at least 60 minutes. As the annealing time increased the crystallization of silicon quantum dots was also increased. TEM images clearly showed SRN/Si3N4 superlattice structure and silicon quantum dots formation in SRN layers after annealing at 1,100 degrees C for more than 60 minutes. The changes in FTIR transmission spectra observed with annealing condition corresponded to the configuration of Si-N bonds. Crystallization of silicon quantum dots in a silicon nitride matrix started stabilizing after 60 minutes' annealing and approached completion after 120 minutes'. The systematic investigation of silicon quantum dots in a silicon nitride matrix and their properties for solar cell application are presented.

Fabrication of mid-infrared hollow-core Bragg fiber and it application in gas sensing

In its application of gas sensing, the transmission band of the hollow-core Bragg fiber should match the main absorption peak of the target gas. In this paper, we introduce the design method of the hollow-core Bragg fiber transmission band and develop a fabrication process supporting its transmission band control. Fiber samples with fundamental transmission bands at 10.6 m and 3.3 m are fabricated, whose transmission losses are 5.9 dB/m and 8.8 dB/m, respectively, measured by the cut-back method. Utilizing the fiber sample with a transmission band of 3.3 m, the injection and the expulsion of CH4/N2 gas are realized and observed by the change of fiber transmission spectrum. The detection limit of the experimental system is measured to be 26 ppm for CH4 by exponential dilution method, demonstrating the feasibility of hollow-core Bragg fiber in its application of gas sensing.

On the performance of label-free resonant photonic biosensors

R photonic biosensing is a powerful technique for label-free detection of biomolecules and viruses. Specifically during the past 5 years photonic biosensning using high quality factor (high-Q) optical microresonators has been the subject of intensive research and development. High-Q optical resonance in micron and sub-micron scale provides a sensitive transduction mechanism for generating a detectable signal proportional to the molecular binding events in label-free affinity based assays. A plethora of microresonator based photonic biosensors have been demonstrated that translate the surface density of bound molecules to measurable changes in optical transmission spectrum using resonant frequency shift. Although a large volume of research has been dedicated to different designs, sensitivity improvement in specific configurations and in few cases simple analysis of the performance, less effort has been spent on developing a comprehensive framework for comparing the practical performance of resonant photonic biosensors as an important class of biosensors. Here after a brief review of the fundamental principles of photonic biosensing using microresonators and related devices, we present a framework for a fair comparison of different devices and sensor configurations. Specifically we explore the detection limit, dynamic range and noise in resonant photonic biosensors. This analysis covers Whispering-Gallery microresonators, monolithic microring cavities, gratings, photonic crystals and microcapillaries. The proposed approach also lays the ground for the development of a universal framework that also includes microelectronic and micromechanical biosensors.

Collective cavity quantum electrodynamics with multiple atomic levels

We study the transmission spectra of ultracold rubidium atoms coupled to a high-finesse optical cavity. Under weak probing with $\ensuremath{\pi}$-polarized light, the linear response of the system is that of a collective spin with multiple levels coupled to a single mode of the cavity. By varying the atom number, we change the collective coupling of the system. We observe the change in transmission spectra when going from a regime where the collective coupling is much smaller than the separation of the atomic levels to a regime where both are of comparable size. The observations are in good agreement with a reduced model we developed for our system.

Magnetic-field-induced change in optical transmission spectra of Hg1 − x Cd x Te epitaxial films

The optical transmission spectra of epitaxial Hg1 − xCdxTe films with a gradient of the band gap have been studied experimentally. The possibility of transforming the spectra after exposure of the samples to a homogeneous magnetic field has been demonstrated. This effect is possibly caused by the dependence of the magnetization of the Hg1 − xCdxTe films on the composition gradient of the solid solution.

Photo-thermoinduced changes of transmission spectra of As40-xSbxS60 amorphous layers

Photo-thermoinduced changes of transmission spectra of As40-xSbxS60 amorphous layers

Single photon nonlinear optics on photonic crystal chips

The promise of quantum information processing is driving developments in several different physical implementations. Photons are attractive as carriers of quantum information because they can travel long distances without losing their information through interactions with their environment. However, their passive nature can be a problem in applications such as the construction of logic gates, where it is necessary for two or more photons to interact. This interaction requires a nonlinear optical medium. Particularly strong nonlinearities are achieved when photons drive an emitter near its resonance frequency, and this nonlinearity is even greater if the photon is confined near the emitter in an optical cavity. We work with single semiconductor quantum dots (QDs) coupled to photonic crystal nanocavities. Recently, we showed that such a system enables an optical nonlinearity1 at the single-photon level: the cavity transmission spectrum changes dramatically when the power nears one intracavity photon number 〈ncav〉 per cavity lifetime (see Figure 1). The transmission spectrum obtained in the cross-polarized configuration shown in Figure 1(a) changes as plotted in Figure 1(b) when 〈ncav〉 increases from nearly zero to 〈ncav〉 ∼ 5. This nonlinearity relies on saturation of the QD, which occurs when the photon flux reaches roughly one photon per emitter lifetime. This single-photon-level nonlinearity has many promising applications. One application of particular interest in quantum information processing concerns the realization of large phase shifts on a signal beam conditioned on the intensity of a control beam. Using a homodyne setup, we measured the phase of the transmission through the cavity near the QD resonance frequency.2 As the probe power increases to 〈ncav〉 ∼ 3 and the QD saturates, we found that the phase of the transmitted beam changes by up to 0.24π . In applications such as quantum Figure 1. Resonant probing of the quantum dot (QD)-cavity system. (a) The cavity is probed by a vertically (V) polarized laser beam. The transmission of the cavity is detected in the orthogonal polarization (H) in order to reduce direct scattering from the incident beam. We model the quantum dot as an excited (e) and ground state (g) which is coupled to the cavity mode by a rate g. (b) The transmission spectrum shows the vacuum Rabi splitting due to the strongly coupled QD. The splitting disappears as the QD is saturated at an intracavity photon number 〈ncav〉 near unity. (c) The phase of the signal beam changes by up to 0.16π when the control beam intensity is raised to an incident power of 1μW, corresponding to 〈ncav〉 ≈ 1.

Wavelength Switching Using GaInAs/InP MQW Variable Refractive-Index Arrayed Waveguides by Thermo-Optic Effect

We have successfully demonstrated a GaInAs/InP multiple quantum well (MQW)-based wavelength switch composed of the straight arrayed waveguide with linearly varying refractive index distribution by changing the refractive index using thermo-optic effect. Since optical path length differences between waveguides in the array were achieved through refractive index differences that were controlled by SiO2 mask design in selective metal-organic vapor phase epitaxy (MOVPE), wavelength demultiplexing, and the output port switching in each wavelength of light by the refractive index change in the array waveguides through the thermooptic effect were achieved. We have obtained the wavelength switching and the change of transmission spectra in each output ports.

Response of in-fiber Bragg gratings to hydrogen loading and subsequent heat treatment in H_2 ambience

The evolution of in-fiber Bragg gratings' contrast and resonance wavelengths caused by molecular hydrogen loading and subsequent heat treatment in a hydrogen atmosphere at a pressure of 8 MPa is experimentally studied. Changes in the gratings' transmission spectra brought about by room-temperature hydrogen loading followed by isochronal annealing cycles at temperatures up to 700 degrees C and at invariable hydrogen pressure are recorded in situ. The gratings' thermal decay dynamics in hydrogen ambience and in air are found to be different and dependent on the gratings' type and on the type of glass in the fiber core. In light of the data obtained, the origin of type IIa gratings is anew under discussion.