Electro-optic measurement of poled polymer-based asymmetric Fabry–Perot cavity

An easy way to determine linear electro-optic effect of poled polymer materials was demonstrated by polymer-based asymmetric Fabry–Perot multiple reflection cavity. The standing-free technique of the cavity and reflective light path configuration was adopted in the measurement. This method can convert probe beam from phase modulation to intensity modulation without the reference beam for electro-optic application of poled polymer. The polymer used was a disperse red 1 doped guest/host material. The principle of the system was analyzed by multiple reflection and index ellipsoid methods, and the voltage sensitivity about 6 mV/Hz of the system was obtained at 1 kHz input signal.     

Design of low frequency fiber optic Fabry–Perot seismometer based on transfer function analysis

We develop a low frequency fiber Fabry–Perot(F-P) seismometer based on transfer function analysis. The seismometer structure and demodulation system accuracy are limitations of low frequency seismic monitoring. The transfer function of the F-P seismometer is analyzed, and the mass displacement spectrum(MDS) is introduced. MDS provides guidance for mechanical structure design and optical interferometer analysis to achieve low noise. The F-P seismometer prototype is built. The experiment shows that the prototype has an average noise of 6.74 ng=p Hz below 50 Hz, and its noise is less than that of the global new high noise model within 0.16–50 Hz, whose potential is considerable.     

Mechanism investigation of a narrow-band super absorber using an asymmetric Fabry–Perot cavity

We propose a metal–insulator-metal super absorber based on an asymmetric Fabry–Perot cavity, by which a perfect narrow-band absorption can be achieved. In this structure, two silver layers form a cavity spaced by a lossless silicon oxide layer. The absorption of the absorber can reach about 98% and its absorption peak can be tuned by altering the thickness of the middle SiO₂ layer. We further present a deep comprehension on the physics mechanism of such high absorption. This super absorber can be easily fabricated by mature thin film technology, which make it an appropriate candidate for photodetectors, sensing, and spectroscopy.     

Microscopic theory of dipole–dipole interaction in ensembles of impurity atoms in a Fabry–Perot cavity

We develop a consistent quantum theory of the collective effects that take place when electromagnetic radiation interacts with a dense ensemble of impurity centers embedded in a transparent dielectric and placed in a Fabry–Perot cavity. We have calculated the spontaneous decay dynamics of an excited impurity atom as a specific example of applying the developed general theory. We analyze the dependence of the decay rate on the density of impurity centers and the sample sizes as well as on the characteristic level shifts of impurity atoms caused by the internal fields of the dielectric. We show that a cavity can affect significantly the pattern of collective processes, in particular, the lifetimes of collective states.     

Thermal characteristics of Fabry–Perot cavity based on regenerated fiber Bragg gratings

The Letter reports the thermal stability and strain response of Fabry–Perot(FP) cavity under different high temperatures. The FP cavity was made by thermal regeneration of two identical cascaded fiber Bragg gratings(FBGs). It is demonstrated that the FP cavity is capable of measuring temperatures from 300℃ to 900℃ with a temperature sensitivity of 15.97 pm/℃. The elongation of the fiber was observed through the drifted Bragg wavelength at 700℃ or above when weight was loaded. The elongation was further inferred by the slight change in the interference spectra of the FP cavity at 900℃.     

Reconstruction of Fabry–Perot cavity interferometer nanometer micro-displacement based on Hilbert transform

A novel reconstruction method of nanometer micro-displacement of Fabry–Perot(F-P) interference is proposed in this study. Hilbert transforms are performed for F-P interference fringes, and the obtained signal performs tangent operation with the original signal. Finally, the validity of the proposed algorithm and the structure are verified by simulation and several experimental measurements for vibration. Results from the experiments show that the maximum relative error is 4.9%.     

Enhanced chiral response from the Fabry–Perot cavity coupled meta-surfaces

The circular dichroism(CD) signal of a two-dimensional(2D) chiral meta-surface is usually weak, where the difference between the transmitted(or reflected) right and left circular polarization is barely small. We present a general method to enhance the reflective CD spectrum, by adding a layer of reflective film behind the meta-surface. The light passes through the chiral meta-surface and propagates towards the reflector, where it is reflected back and further interacts with the chiral meta-surface. The light is reflected back and forth between these two layers, forming a Fabry–Perot type resonance,which interacts with the localized surface plasmonic resonance(LSPR) mode and greatly enhances the CD signal of the light wave leaving the meta-surface. We numerically calculate the CD enhancing effect of an L-shaped chiral meta-surface on a gold film in the visible range. Compared with the single layer meta-surface, the L-shaped chiral meta-surface has a CD maximum that is dramatically increased to 1. The analysis of reflection efficiency reveals that our design can be used to realize a reflective circular polarizer. Corresponding mode analysis shows that the huge CD originates from the hybrid mode comprised of FP mode and LSPR. Our results provide a general approach to enhancing the CD signal of a chiral meta-surface and can be used in areas like biosensing, circular polarizer, integrated photonics, etc.     

Performance of Extrinsic Fabry–Perot Interferometer Based on Graded-Index Lenses for a Fabry–Perot Cavity with Surface Errors

Interference contrast is an important parameter for extrinsic Fabry–Perot interferometer (EFPI) based on graded index (GRIN) lenses. It determines the signal-to-noise ratio (SNR) and the measurement accuracy. We discuss the influence of Fabry–Perot (FP) cavity surface errors, which are inevitable in controlling the interference contrast during the manufacturing procedure. Our theoretical analysis and results of numerical simulations demonstrate that the surface errors diminish the interference contrast — the larger the surface error, the smaller the interference contrast. The results obtained contribute to the EFPI application in fiber sensors.     

Influence of intra-cavity loss on transmission characteristics of fiber Bragg grating Fabry–Perot cavity

A theoretical model of the fiber Bragg grating Fabry–Perot(FBG-FP) transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured.The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited.The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1,which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.     

Design of three-primary-color filter based on structure of three-cavity Fabry–Perot color filter

Optical and Quantum Electronics - Elastic optical network (EON) is considered as the platform for future optical transport networks. Routing and spectrum allocation (RSA) has a significant bearing...     

Electrical Control of the Frequencies of a Fabry–Perot Acoustic Resonator

The effect electronic tuning has on the frequency of the acoustic resonance of an acousto-optic modulator intended for active laser mode locking is studied theoretically and experimentally. The problem of exciting a Fabri–Perot acoustic resonator with a plate-like piezoelectric transducer is solved in the approximation of plane acoustic waves, with allowance for the real parameters of the HF generator and the matching elements of the transducer and the generator. Expressions for the basic electrical and acoustic parameters are obtained. Theoretical analysis confirms the frequency shift effect of acoustic resonances, observed earlier experimentally upon varying the matching electrical elements. The experiment is performed using an acousto-optic quartz cell and a lithium niobate transducer.     

Stabilization of a fiber Fabry–Perot interferometric acoustic wave sensor

Control of the operating point of an interferometric optical sensor to produce the highest sensitivity is crucial in the demodulation of interferometric optical sensors to compensate for Q point mismatching. A new method for operating point control of FFPI was discussed and demonstrated, the relationship of the F–P cavity length, the visibility and the interferometric fringe was analyzed. MCU was introduced to tracing the Q point by changing the laser wavelength through adjusting the light source temperature. It is proved that the dynamic range of the sensor system is surely extended; the NSR could be greatly improved because the wavelength change induced noises is greatly limited in this sensor system.     

Dynamical behaviour of birefringent Fabry–Perot cavities

In this paper we present a theoretical and experimental study of the dynamical behaviour of birefringent cavities. Our experimental data show that usual hypothesis which provides that a Fabry–Perot cavity is a first-order low-pass filter cannot explain the behaviour of a birefringent cavity. We explain this phenomenon and give the theoretical expression of the equivalent cavity filter which corresponds to a second-order low-pass filter.     

A thin wire ion trap to study ion–atom collisions built within a Fabry–Perot cavity

We report on the implementation of a thin wire Paul trap with tungsten wire electrodes for trapping ions. The ion trap geometry, though compact, allows large optical access enabling a moderate finesse Fabry–Perot cavity to be built along the ion trap axis. The design allows a vapor-loaded magneto-optical trap of alkali atoms to be overlapped with trapped atomic or molecular ions. The construction and design of the trap are discussed, and its operating parameters are determined, both experimentally and numerically, for Rb⁺. The macromotion frequencies of the ion trap for ⁸⁵Rb⁺ are determined to be f _r  = 43 kHz for the radial and f _z  = 54 kHz for the axial frequencies, for the experimentally determined optimal operating parameters. The destructive off axis ion extraction and detection by ion counting is demonstrated. Finally, evidence for the stabilization and cooling of trapped ions, due to ion–atom interactions, is presented by studying the ion-atom mixture as a function of interaction time. The utility and flexibility of the whole apparatus, for a variety of atomic physics experiments, are discussed in conclusion.     

Design of fiber Bragg grating-based Fabry–Perot sensor for simultaneous measurement of humidity and temperature

A new sensor for simultaneous measurement of humidity and temperature is proposed. The sensor consists of Fabry–Perot cavity formed by two identical uniform fiber Bragg gratings. To make the cavity serves as humidity sensor, moisture sensitive polymer, which is polyimide, is coated on the FBG and on the cavity with different thickness. When the sensor is exposed to the relative humidity change, the polyimide will expand and stretch the fiber and induces strain on the FBG and on the cavity. The induced strain alters the grating period, cavity length and effective refractive index of fiber. The simulation results show that the humidity sensitivity and thermal sensitivity are 1.92 pm/%RH and 8.87 pm/°C, respectively, for polyimide coating thickness of 10 μm on the FBG and 15 μm on the cavity.     

Parametric oscillatory instability in a Fabry–Perot cavity of the Einstein Telescope with different mirror's materials

We discuss the parametric oscillatory instability in a Fabry–Perot cavity of the Einstein Telescope. Unstable combinations of elastic and optical modes for two possible configurations of gravitational wave third-generation detector are deduced. The results are compared with the results for gravitational wave interferometers LIGO and LIGO Voyager.     

Accuracy analysis and stabilization design of the Fabry–Perot frequency discriminator in double-edge wind lidars

The measurement error of a double-edge wind lidar caused by a disturbed Fabry–Perot interferometer (FPI) is analyzed. Several error sources such as air pressure variations, temperature changes, and mechanical vibrations are considered in the measurement-error model. The simulation results show that a double-edge wind lidar is so sensitive to environmental variations that the measurement error reaches ±60 m/s if the FPI is not stabilized. In order to compensate the external disturbance acting on the FPI, a nonlinear proportional–integral–derivative (PID) control scheme is designed based on the transmission measurement of the calibration channel. An arc tangent function is used to improve the feedback gain of the usual PID control design. The results show that with the new controller the measurement accuracy of the wind lidar can be improved 4–5 times in comparison with the usual control design, and the range of the measurement error is only ±3 m/s.     

Systematical research on the characteristics of a vertical coupled Fabry–Perot plasmonic filter

A nanometric surface plasmon polariton (SPP) filter based on a vertical coupled metal–insulator–metal (MIM) Fabry–Perot resonator is proposed and analyzed. The transmission characteristics of the SPP filter are analyzed in detail by using the finite difference time domain method. And the resonance condition derived by the numerical method is consonant with the analytic model based on the Fabry–Perot model, which includes the metal loss and dispersion effects. And the simulation results show that multiple transmission dips can be formed and the resonance wavelengths of the transmission dips can be altered by the Fabry–Perot cavity length and width. Also the extinction ratio and the quality factor of the filter are affected by the barrier thickness of the coupling region. The proposed nanometric plasmonic filter is simple and very promising for the SPP waveguides platform.     

Design of a broadband μ-negative planar material with low frequency dispersion

Compared with the traditional split-ring resonator reported by Pendry et al. (IEEE Trans. Microw. Theory Tech. 47:2075, 1999), the co-directional split-ring resonator, which has inherent low mutual coupling between its outer and inner rings, can provide distinct dual-band magnetic resonances. In this paper, we analyzed and compared different types of split-ring resonator, but selected the co-directional split-ring resonator for the tri-band magnetic resonator design because of its attractive dual-band magnetic resonance characteristics. We then accommodated the rings’ resonant strengths in the co-directional split-ring resonator to be nearly equal, and added an arm-loaded ring to design a new tri-band magnetic resonator. Finally, we designed and experimentally demonstrated a broadband μ-negative planar material with low frequency dispersion, which consisted of three pairs of tri-band magnetic resonators with slightly different dimensions.