共查询到20条相似文献,搜索用时 93 毫秒
1.
We discuss a new application of a thin-film prism as a beam separator for multimode guided waves in integrated optics. For each mode of propagation, the angle of deflection by the thin-film prism is different and each deflected beam can be processed subsequently. Deflection angles for different modes can be predicted by using the concept of effective index of refraction. The thickness and index of refraction of the guiding film are determined simultaneously by measuring the coupling angles of the laser beam and a simple graphical method. Calculated and observed angles of deflection are in good agreement. The thin-film prism is made by using preferential etching technique in order to obtain linear, well defined, tapered edges. Furthermore, silicon is used as the base material for possible future integration of optical and electronic components. 相似文献
2.
We present analytical equations based on thin-film optics with which to extract the thickness of weakly absorbing films from spectral interference measurements, using only the observed constant interference frequency. It is shown that the assumption of a constant index of refraction n for the analysis of interference frequency omega 0 introduces significant errors into the thickness calculation. Instead, the first derivative of n with respect to the energy, n', has to be included as well to yield the correct film thickness, even for small values of n'. The equations presented can be used as constraints in appropriate numerical methods to improve the film thickness iteratively. 相似文献
3.
We identify a route towards achieving a negative index of refraction at optical frequencies based on coupling between plasmonic waveguides that support backwards waves. We show how modal symmetry can be exploited in metal-dielectric waveguide pairs to achieve negative refraction of both phase and energy. Control of waveguide coupling yields a metamaterial consisting of a one-dimensional multilayer stack that exhibits an isotropic index of -1 at a free-space wavelength of 400?nm. The concepts developed here may inspire new low-loss metamaterial designs operating close to the metal plasma frequency. 相似文献
4.
Sabriye Acikgoz Bukem Bilen Mustafa Muamer Demir Yusuf Ziya Menceloglu Yani Skarlatos Gulen Aktas Mehmet Naci Inci 《Optical Review》2008,15(2):84-90
Humidity induced change in the refractive index and thickness of the polyethylene glycol (PEG) coatings are in situ investigated for a range from 10 to 95%, using an optical waveguide spectroscopic technique. It is experimentally demonstrated
that, upon humidity change, the optical and swelling characteristics of the PEG coatings can be employed to build a plastic
fibre optic humidity sensor. The sensing mechanism is based on the humidity induced change in the refractive index of the
PEG film, which is directly coated onto a polished segment of a plastic optical fibre with dip-coating method. It is observed
that PEG, which is a highly hydrophilic material, shows no monotonic linear response to humidity but gives different characteristics
for various ranges of humidity levels both in index of refraction and in thickness. It undergoes a physical phase change from
a semi-crystalline structure to a gel one at around 80% relative humidity. At this phase change point, a drastic decrease
occurs in the index of refraction as well as a drastic increase in the swelling of the PEG film. In addition, PEG coatings
are hydrogenated in a vacuum chamber. It is observed that the hydrogen has a preventing effect on the humidity induced phase
change in PEG coatings. Finally, the possibility of using PEG coatings in construction of a real plastic fibre optic humidity
sensor is discussed. 相似文献
5.
Negative refraction, which reverses many fundamental aspects of classical optics, can be obtained in systems with negative magnetic permeability and negative dielectric permittivity. This Letter documents an experimental realization of negative refraction at millimeter waves, finite magnetic fields, and cryogenic temperatures utilizing a multilayer stack of ferromagnetic and superconducting thin films. In the present case the superconducting YBa2Cu3O7 layers provide negative permittivity while negative permeability is achieved via ferromagnetic (La:Sr)MnO3 layers for frequencies and magnetic fields close to the ferromagnetic resonance. In these superlattices the refractive index can be switched between positive and negative regions using external magnetic field as tuning parameter. 相似文献
6.
The measurement accuracy of a parallel-plate interferometer for angular displacement measurement is analyzed. The measurement accuracy of angular displacement is not only related to the accuracy of phase extraction, but also related to initial incident angle, refraction index and thickness of plane-parallel plate as well as wavelength's stability of laser diode, etc. Theoretical analysis and computer simulation show that the measurement error of the angular displacement bears a minimum value when choosing an optimal initial incident angle in a large range. These analytical results serve as a guide in practical measurement. In this interferometer, reducing the refraction index or increasing the thickness of the parallel plate can improve the measurement accuracy; and the relative error of the phase measurement is 3.0×10−4 corresponding to 1 °C temperature variation. Based on these theoretical and experimental results, the measurement accuracy of the parallel-plate interferometer is up to an order of 10−8 rad. 相似文献
7.
Xing-zhi Gong 《Optics Communications》2010,283(20):3989-3993
This paper, for the first time, proposed a new sensitivity separation (SS) method for measuring thicknesses of multilayer thin-film stack with high efficiency and accuracy. Through the analysis of the relationship between the film parameters and the mean misfit error (MSE), a parameter called sensitivity is defined. With this parameter, an estimated rational thickness is assigned to a layer with lower sensitivity first, and then the layer thickness with high sensitivity is further obtained by optimization techniques. This method will greatly reduce the searching range and increase the iterating efficiency. It is a pretreatment method and it can be used with other optimization methods. Both theory and simulation results are provided in detail. The uncertainty problems are discussed and examples are given to verify the effectiveness of this method. 相似文献
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We report our experimental results on two-dimensional left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging. Transmission and reflection spectra of LHM are studied and a left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. Impedance matching is verified both with the experiments and simulations. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction; refraction through prism-shaped LHM, beam shifting method, and phase shift experiments. We further demonstrated subwavelength imaging and resolution using LHM superlenses. The effect of thickness on the resolving power is investigated experimentally. 相似文献
10.
基于正交偏振干涉法,建立了KDP晶体折射率非均匀性的检测系统,并可实现晶体相位失谐角的间接检测.波前检测系统实现了测试光偏振态的精密控制与切换,采用波长调谐相移的方法去除了测试过程中参考面倾斜引入的误差,优化了抗振动相移算法,提高了波前测试的测量准确度及重复性.通过折射率非均匀性分析算法的设计,解决了晶体厚度变化引入的误差等.小口径晶体元件的测试结果表明系统的折射率非均匀性检测准确度(均方根值)优于10-6. 相似文献
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12.
Mehdi Keshavarz Hedayati Franz Faupel Mady Elbahri 《Applied Physics A: Materials Science & Processing》2012,109(4):769-773
Metamaterials and plasmonics as a new pioneering field in photonics joins the features of photonics and electronics by coupling photons to conduction electrons of a metal as surface plasmons (SP). This concept has been implemented for a variety of applications including negative index of refraction, magnetism at visible frequency, cloaking devices amongst others. In the present work, we used plasmonic hybrid material in order to design and fabricate a broad-band perfect plasmonic metamaterial absorber in a stack of metal and Copper-PTFE (Polytetrafluoroethylene) nanocomposite showing an average absorbance of 97.5?% in the whole visible spectrum. Our experimental results showed that the absorption peak of the stacks can be tuned upon varying the thickness and type of the spacer layer due to the sensitivity of plasmon resonance to its environment. To the best of our knowledge, this is the first report of a plasmonic metamaterial absorber based on copper with absorption around 100?% in the entire visible and near-Infrared (NIR). 相似文献
13.
The power reflection coefficient (reflectance) of linear, periodically homogenous, isotropic, nonabsorbing stack filters is derived using full wave analysis. The well-known ABCD characteristic matrix is used to assess the spectral response of the stack filters. Adopting this method requires a huge number of matrix multiplications as the number of layers increases. An alternative approach of evaluating the whole matrix is suggested which is shown to save computational time. Band reject response far from ideal characteristics, due to the presence of unwanted ripples surrounding the stopband, is obtained. Equating these ripples without changing the length of the structure is undertaken by varying some design parameters related to the layers constituting the filter. Namely, the index of refraction and the physical thickness of individual layers are used as optimization variables. This process requires evaluating the derivative of the reflectance with respect to each design variable while leaving other parameters unchanged. The sensitivity of the derivatives to various design parameters is also addressed, which is sometimes required in manufacturing multilayered dielectric thin films. 相似文献
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A simple method to determine the thickness of a nonabsorbing thin film on an absorbing substrate from maxima of the ratio between the spectral reflectances of p- and s-polarized components reflected from the thin-film structure is presented. The spectral reflectance ratio, which can be measured in a simple polarimetry configuration at a fixed angle of incidence, consists of maxima whose number and positions depend on the thickness of a thin film. An approximative linear relation between the thin-film thickness and a wavelength of the maximum of the reflectance ratio for a specific angle of incidence is revealed, provided that the wavelength-dependent refractive index of the thin film is known and the substrate is weakly absorbing. The relation permits the calculation of the thickness from the measured spectral reflectance ratio by using one maximum only, as is demonstrated theoretically for a SiO2 thin film on a Si substrate. The application of this method is demonstrated experimentally for the same thin-film structure with different thicknesses of the SiO2 thin film. The results are compared with those given by the algebraic fitting method, and very good agreement is confirmed. 相似文献
16.
Techniques of spectral reflectometry and interferometry are used for measuring small changes in thickness of SiO2 thin film grown by thermal oxidation on different silicon substrates. A slightly dispersive Michelson interferometer with
one of its mirrors replaced by a thin-film structure is used to measure the reflectance and interferometric phase of the thin-film
structure at the same time. The experimental data are used to determine precisely the thickness of the SiO2 thin film on silicon wafers of two crystallographic orientations and different dopant concentrations. We confirmed very good
agreement between the experimental data and theory and revealed that the thin-film thickness, which varies with the type of
silicon substrate, depends linearly on the wavelength at which minimum in the spectral reflectance occurs. Similar behaviour
was revealed for the interferometric phase. 相似文献
17.
Coherent control of negative refraction based on local-field enhancement and dynamically induced chirality
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This paper studies the electromagnetic response of a coherently driven dense atomic ensemble to a weak probe.It finds that negative refraction with little absorption may be achieved in the presence of local-field enhanced interaction and dynamically induced chirality.The complex refractive index governing the probe refraction and absorption depends critically on the atomic density,the steady population distribution,the coherence dephasings,and the frequency detunings,and is also sensitive to the phase of the driving field because the photonic transition paths form a close loop.Thus,it can periodically tune the refractive index at a fixed frequency from negative to positive values and vice versa just by modulating the driving phase.Moreover,the optimal negative refraction is found to be near the probe magnetic resonance,which then requires the electric fields of the probe and the drive being on two-photon resonance due to the dipole synchronisation. 相似文献
18.
We report on the negative refraction and left-handed behavior of two-dimensional photonic crystals. For the triangular two-dimensional photonic crystals there are two saddle points and a key point in the first Brillouin zone for the second band, which play important role to determine the refraction phenomena. There is no determined relation between the left-handed behavior and the negative refraction. The refraction phenomena depend on the band structure and the configuration of the incident light. For the first configuration, the first Brillouin zone can be divided into three parts. In part I there are negative refraction and left-handed behaviors. In part II there are normal refraction and left-handed behaviors. In part III there are normal refraction and right-handed behaviors. For the second configuration, the first Brillouin zone can only be divided into two parts. For these complex refraction phenomena, it is meaningless to define the phase refractive index, and it is necessary to define the effective refraction index by a Snell-like formula, and the value of the effective index is determined by the configuration and the band structure. 相似文献
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