Fabry-Perot Cavity Length Research Articles

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.

Highly Sensitive Air-Gap Fiber Fabry–Pérot Interferometers Based on Polymer-Filled Hollow Core Fibers

This letter, for the first time, investigates a novel, and ultracompact air-gap fiber Fabry-Perot interferometer (AG-FFPI), which is based on a polymer-filled hollow core fiber (HCF) endface. The proposed polymer-filled AG-FFPI has advantages of easy fabrication, high temperature sensitivity, low cost, and arbitrary length of air-gap. The variation of the Fabry-Perot cavity length can be greatly enhanced from exploiting the high thermal expansion coefficient of the elastic polymer-filled in the HCF. The proposed device exhibits a wavelength shift of the interference fringes that corresponds to temperature sensitivity of , which is equivalent to sensitivity to a change in cavity length of .

All-fiber, long-active-length Fabry-Perot strain sensor

This paper presents a high-sensitivity, all-silica, all-fiber Fabry-Perot strain-sensor. The proposed sensor provides a long active length, arbitrary length of Fabry-Perot cavity, and low intrinsic temperature sensitivity. The sensor was micro-machined from purposely-developed sensor-forming fiber that is etched and directly spliced to the lead-in fiber. This manufacturing process has good potential for cost-effective, high-volume production. Its measurement range of over 3000 µε, and strain-resolution better than 1 µε were demonstrated by the application of a commercial, multimode fiber-based signal processor.

Fiber Temperature Sensor Based on Micro-mechanical Membranes and Optical Interference Structure

A novel fiber temperature sensor is presented theoretically and experimentally in this paper. Its working principle is based on Optical Fabry-Perot interference structure that is formed between a polished optical fiber end and micro-mechanical Bi-layered membranes. When ambient temperature is varying, Bi-layered membranes will be deflected and the length of Fabry-Perot cavity will be changed correspondingly. By detecting the reflecting optical intensity from the Fabry-Perot cavity, the ambient temperature can be measured. Using finite element software ANSYS, the sensor structure was optimized based on optical Interference theory and Bi-layered membranes thermal expansion theory, and theoretical characteristics was simulated by computer software. In the end, using optical fiber 2×2 coupler and photo-electrical detector, the fabricated sample sensor was tested successfully by experiment that demonstrating above theoretical analysis and simulation results. This sensor has some favorable features, such as: micro size owing to its micro-mechanical structure, high sensitivity owing to its working Fabry-Perot interference cavity structure, and optical integration character by using optical fiber techniques.

Peculiarities in the work of laser gravitational antennas in the infra-low frequency range

We study the methodology of measuring quasistatic perturbations of geophysical nature in laser gravitational-wave interferometers. We calculate the transfer function of such an instrument in the destructive interference mode (the “dark spot” mode) taking into account the natural asymmetry of the optical Fabry-Perot cavity lengths in its arms. Formulas have been obtained for estimating the output signal power modulation at the frequency of photon circulation in the arms due to geophysical perturbations. The estimates are compared with the results of observations at the LIGO interferometer.

Conversion of stability of femtosecond mode-locked laser to optical cavity length

In this contribution we propose a scheme for a generation of precise displacements through conversion of relative stability of components of a femtosecond laser into the length of a Fabry-Perot cavity. The spacing of mirrors of a Fabry-Perot interferometer represents a mechanical length standard referenced to stable optical frequency of a femtosecond mode-locked laser. With the help of a highly selective optical filter, it is possible to get only a few discrete spectral components. By tuning and locking the Fabry-Perot cavity to a selected single component it is possible to get a mechanical length standard with the uncertainty of the repetition frequency of the femtosecond laser. To verify the method, an auxiliary single-frequency laser is locked to the resonance mode of the cavity and simultaneously it is optically mixed with an independent optical frequency standard He-Ne-I2. The stability of the beat-frequency between these 2 lasers represents the stability of the Fabry-Perot cavity length. The stability recording evaluated through Allan variances for one hour of operation is presented. The pilot experimental setup is able to generate the length standard in the order of 0.01 nm for 20 min of integration time.

Single-mode GaAs/AlGaAs quantum cascade microlasers

Single-mode edge emitting GaAs/AlGaAs quantum cascade microlasers at a wavelength of about 11.4 μm were realized by shortening the Fabry-Perot cavity length. The spacing of the longitudinal resonator modes is inversely proportional to the cavity length. Stable single-mode emission with a side mode suppression ratio of about 19 dB at 85 K for a 150-μm-long device was demonstrated.

Optical pressure/acoustic sensor with precise Fabry-Perot cavity length control using angle polished fiber

This paper presents a novel Fabry-Perot (FP) optical fiber pressure/acoustic sensor. It consists of two V-shaped grooves having different sized widths, a diaphragm on the surface of the larger V-groove, and a 45 degrees angle-polished fiber. The precision of FP cavity length is determined by the fabrication process of photolithography and anisotropic etching of a silicon crystal. Therefore, the cavity length can be controlled on the order of ten nm. Sensors were fabricated and tested. Test results indicate that the sensors' cavity lengths have been controlled precisely. The packaged sensor has demonstrated very good static and dynamic responses compared to a commercially available pressure sensor and a microphone.

Low cost optical fibre based Fabry–Perot strain sensor production

The production of Fabry–Perot-based optical fibre sensors has long been an iterative and labour-intensive process. This paper demonstrates the production of Fabry–Perot-based optical fibre strain sensors using chemical etching techniques. Utilizing hydrofluoric acid and single-mode optical fibres, a preferential etching mechanism was observed around the core portion of the fibres. These etched fibre ends were then spliced together successfully to form enclosed Fabry–Perot cavities between 18 and 60 µm in length. These sensors have then been deployed for strain monitoring and have been subjected to strains of up to 1400 με on tensile test specimens. Etched Fabry–Perot cavity lengths were monitored using a white light interferometry system based on a CCD spectrometer and an 850 nm super luminescent diode. A linear and repeatable response to these strain tests has been shown with negligible sensitivity to temperature.

Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings

In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.

Ultralow internal optical loss in separate-confinement quantum-well laser heterostructures

Internal optical loss in separate-confinement laser heterostructures with an ultrawide (>1 smm) waveguide has been studied theoretically and experimentally. It is found that an asymmetric position of the active region in an ultrawide waveguide reduces the optical confinement factor for higher-order modes and raises the threshold electron density for these modes by 10–20%. It is shown that broadening the waveguide to above 1 µm results in a reduction of the internal optical loss only in asymmetric separate-confinement laser heterostructures. The calculated internal optical loss reaches ∼0.2 cm−1 (for λ≈1.08 µm) in an asymmetric waveguide 4 µm thick. The minimum internal optical loss has a fundamental limitation, which is determined by the loss from scattering on free carriers at the transparency carrier density in the active region. An internal optical loss of 0.34 cm−1 was attained in asymmetric separate-confinement laser heterostructures with an ultrawide (1.7 µm) waveguide, produced by MOCVD. Lasing in the fundamental transverse mode has been obtained owing to the significant difference in the threshold densities for the fundamental mode and higher-order modes. The record-breaking CW output optical power of 16 W and wallplug efficiency of 72% is obtained in 100-µm aperture lasers with a Fabry-Perot cavity length of ∼3 mm on the basis of the heterostructures produced.

Focus on Sensors

Focus on Sensors

Self-calibrated interferometric-intensity-based optical fiber sensors

This paper presents self-calibrated interferometric-intensity-based optical fiber sensors, which combine for the first time fiber interferometry and intensity-based devices into a single sensor system. The sensor involves an extrinsic Fabry-Perot (FP) interferometric cavity. The broadband light returned from the FP cavity is split into two channels in such a way that one channel has a coherence length much longer than the doubled air-gap separation in the sensor so the FP generates effective interference, while the coherence length in the other channel is so short that no effective interference takes place. As a result, the optical signal in the channel with a long coherence length yields information about the FP cavity length while the signal in the other channel is proportional only to the source power, fiber attenuation, and other optical loss factors in the optical path. To eliminate fringe direction ambiguity and relative measurement limitations associated with interferometric sensors, the sensor is designed such that it is operated over the linear range between a valley and a peak of one interference fringe in the first channel. Moreover, the ratiometric signal-processing method is applied for the signals in the two channels to obtain self-calibrating measurement to compensate for all unwanted factors, including source power variations and fiber bending losses. Various pressure and temperature sensors based on the self-calibrated interferometric/intensity-based scheme are designed, fabricated, and tested. Experimental results show that a resolution as high as 0.02% of full scale can be obtained for both the pressure and temperature measurements.

Extrinsic Fabry-Perot interferometer fiber-optic microphone

In this paper we describe a new fiber-optic microphone developed as a passive acoustic sensor for traffic monitoring and vehicle classification. It is based on a fiber-optic extrinsic Fabry-Perot (FP) microinterferometer coupled to an external membrane for modulating the FP cavity length and a low coherent superluminescent diode as light source. The frequency characteristic as compared with a standard condenser microphone exhibits a sensitivity range of more than 80 dB between 100 Hz and 15 kHz. Initial results are presented demonstrating acoustic monitoring of aircraft via their characteristic noise spectra using downleads of km length.

White-light interferometric multimode fiber-optic strain sensor

A white-light interferometric extrinsic Fabry-Perot strain sensor that uses a multimode fiber is demonstrated. The Fabry-Perot cavity length is measured with the help of a Fizeau interferometer. The sensor is described, and some results obtained at this time are given. The strain measurements are absolute and perfectly linear, with a sensitivity of 0.25 micrometers per meter (micro). the design of a thermally autocompensated strain sensor is also presented.