3D nanoimprinted Fabry–Pérot filter arrays and methodologies for optical characterization

Fabry–Pérot (FP) filter arrays fabricated by high-resolution three dimensional (3D) NanoImprint technology are presented. A fabrication process to implement 3D templates with very high vertical resolution is developed. Filter arrays with 64 different cavity heights have been fabricated requiring only one single imprint step. Different optical methods are involved in this paper to characterize geometric and spectral properties. In order to investigate the transfer accuracy of the surface quality from the NanoImprint template to the filter, we use white light interferometry (WLI) measurements. Surface roughness and structure height accuracy of <1 nm for both values demonstrate the conservation of these critical parameters during the 3D NanoImprint process. Additionally, an optical characterization methodology for spectral transmission and reflection measurements of the filter arrays is introduced and applied. A compact microscope spectrometer setup which allows efficient handling, high resolution and short inspection time is verified by comparing measurement results to that of an optical bench setup used as a reference. First, this paper focuses on the foundation of the FP filter arrays, second on the technological fabrication, third on validation calibration of the setup and forth on the characterization of the filter arrays. The measurements envisage the spectral position of filter transmission lines, the full width at half maximum (FWHM) and the total spectral bandwidth of the array, i.e. the stopbands of the included Distributed Bragg Reflectors (DBRs).     

High-sensitivity CW Fabry–Pérot enhanced spectroscopy of CO2 and C2H2 using a 1064-nm Nd:YAG laser

2 (20⁰3←00⁰0) R(6), C₂H₂ (2100⁰1¹←0000⁰0⁰) R(12), and C₂H₂ (1200⁰3¹←0000⁰0⁰) P(6) near 1064 nm using CW cavity ring-down spectroscopy and CW cavity transmission. An effective interaction length of more than 30 km was achieved (cavity finesse ≈86000) and the sensitivity was ≈10^-8 cm^-1. Higher sensitivity of 3.3×10^-11 cm^-1/ was obtained by cavity-enhanced wavelength modulation spectroscopy. The absorption coefficients, pressure broadening coefficients, lineshapes, line strengths, and absolute wavelengths of those lines were determined, some of them for the first time. The measurements were carried out over a wide range of pressures from the strongly inhomogeneous to the strongly homogeneous region. Received: 25 May 1998/Revised version: 28 July 1998     

The design and preparation of a Fabry–Pérot polarizing filter

A novel single-cavity narrowband Fabry–Pe′rot(FP) polarizing filter at normal incidence,constructed from a sandwich structure with sculptured anisotropic space layer and symmetric isotropic HR mirrors,is designed and prepared.The optical performances of transmittance,phase shift,central wavelength,and bandwidth for two polarized states are analyzed with the characteristic matrix.The numerical studies accord reasonably well with the experimental results.It is demonstrated that the polarization state of the electromagnetic wave and phase shift can be modulated by employing an anisotropic space layer in the polarizing beam splitter system.The birefringence of the anisotropic space layer provides a sophisticated phase modulation by varying the incidence angles over a broad range to have a wide-angle phase shift.     

Fiber in-line Fabry–Pérot interferometer for simultaneous measurement of reflective index and temperature

A fiber in-line Fabry–Pérot interferometer is presented. The sensing head consists of a micro ellipsoidal air cavity and a small section of solid-core photonic crystal fiber. The reflective index(RI) and temperature can be interrogated simultaneously through a fast Fourier transform and by tracing the dip wavelength shift of the reflective spectrum. Experimental results show that the RI amplitude and wavelength sensitivities are 5.30/RIU and 8.46 × 10~(-1)nm∕RIU in the range from 1.34 to 1.43,and the temperature amplitude and wavelength sensitivities are 6.8×10~(-4)∕°C and 2.48×10~(-3)nm∕°C in the range from 15°C to 75°C,respectively. Easy fabrication,a simple system,and simultaneous measurement make it appropriate for dual-parameter sensing application.     

Performance comparison of Fabry–Perot and Mach–Zehnder interferometers for molecular Doppler lidar based on fringe-imaging technique

Fringe-imaging Fabry–Perot interferometer (FIFPI) and fringe-imaging Mach–Zehnder interferometer (FIMZI) used as frequency discriminator for incoherent molecular Doppler lidar were analyzed, respectively. For a pure molecular backscattered signal, performances (wind measurement sensitivity and signal-to-noise ratio) of both FIFPI and FIMZI systems were simulated based on the U.S. standard atmospheric model. Comparisons of two systems were made under the same emitting and receiving parameters with certain wind speed dynamic range. Simulated results show that, though relatively lower sensitivity to Doppler shift, the single-channel FIMZI system provides a factor of 1.3 times smaller error in the horizontal wind velocity than that of FIFPI at a range of 20 km. We expect that the FIMZI frequency discriminator would provide an effective technique to improve the measurement accuracy for incoherent molecular Doppler lidar.     

Fabry–Pérot cavities based on chemical etching for high temperature and strain measurement

In this paper, two hybrid multimode/single mode fiber Fabry–Pérot (FP) cavities were compared. The cavities fabricated by chemical etching are presented as high temperature and strain sensors. In order to produce this FP cavity a single mode fiber was spliced to a graded index multimode fiber with 62.5 μm core diameter. The Fabry–Pérot cavities were tested as a high temperature sensor in the range between room temperature and 700 °C and as strain sensors. A reversible shift of the interferometric peaks with temperature allowed to estimate a sensitivity of 0.75 ± 0.03 pm/°C and 0.98 ± 0.04 pm/°C for the sensor A and B respectively. For strain measurement sensor A demonstrated a sensitivity of 1.85 ± 0.07 pm/μ? and sensor B showed a sensitivity of 3.14 ± 0.05 pm/μ?. The sensors demonstrated the feasibility of low cost fiber optic sensors for high temperature and strain.     

Limitations and guidelines for measuring the spectral width of ultrashort light pulses with a scanning Fabry–Pérot interferometer

The measurement of the spectral width of ultrashort light pulses using a Fabry–Pérot interferometer (FPI) is investigated. It is shown, numerically and experimentally, that the measured width critically depends on the pulse properties (such as pulse shape, pulse duration, frequency chirp and wavelength) and on the properties of the FPI (such as the mirror spacing and the mirror reflectivities). The obtained results are of particular importance if the spatial length of the short light pulses is comparable or even shorter than the distance between the FPI mirrors. The derived guideline indicate that the actual spectral width of the ultrashort light pulses is measured with good accuracy only if the finesse F≥40 and the round trip time of the light pulses inside the Fabry–Pérot interferometer is approximately one to three times the pulse duration. Received: 17 December 1999 / Revised version: 14 April 2000 / Published online: 5 July 2000     

Generation of Fabry–Pérot oscillations and Dirac state in two-dimensional topological insulators by gate voltage

We investigate electron transport through Hg Te ribbons embedded by strip-shape gate voltage through using a nonequilibrium Green function technique. The numerical calculations show that as the gate voltage is increased, an edgerelated state in the valence band structure of the system shifts upwards, then hangs inside the band gap and merges into the conduction band finally. It is interesting that as the gate voltage is increased continuously, another edge-related state in the valence band also shifts upwards in the small-k region and contacts the previous one to form a Dirac cone in the band structure. Meanwhile in this process, the conductance spectrum displays as multiple resonance peaks characterized by some strong antiresonance valleys in the band gap, then behaves as Fabry–P′erot oscillations and finally develops into a nearly perfect quantum plateau with a value of 2e~2/h. These results give a physical picture to understand the formation process of the Dirac state driven by the gate voltage and provide a route to achieving particular quantum oscillations of the electronic transport in nanodevices.     

Fabry–Pérot filter cavities for wide-spaced frequency combs with large spectral bandwidth

We use low-finesse Fabry–Pérot cavities in series to generate frequency combs with a large mode spacing in a way that allows its application to a large optical bandwidth. The attenuation of laser modes closest to the pass bands of the cavity exceeds 70 dB for a filter ratio of m=20 relative to the resonant modes centered within the pass bands. We also identify the best cavity geometry to suppress spurious transmission of higher order transversal modes. Such a thinned out frequency comb can be used to calibrate traditional spectrographs for precision astronomy. In the time domain mode filtering generates a pulse train with a multiplied repetition rate. High-fidelity filtering, as described here, implies small variations of the pulse energies.     

Simultaneous measurement of strain and temperature using Fabry–Pérot interferometry and antiresonant mechanism in a hollow-core fiber

A fiber-optic sensor for the simultaneous measurement of strain and temperature is proposed and experimentally demonstrated based on Fabry–Pérot(FP) interference and the antiresonance(AR) mechanism. The sensor was implemented using a single-mode fiber(SMF)–hollow-core fiber–SMF structure. A temperature sensitivity of 21.11 pm/℃ was achieved by tracing the troughs of the envelope caused by the AR mechanism, and a strain sensitivity of 2 pm/με was achieved by detecting the fine fringes caused by the FP cavity. The results indicate that the dual-parameter sensor is stable and reliable.     

High-Sensitivity Temperature Sensor Based on Two Parallel Fabry–Pérot Interferometers and Vernier Effect

Journal of Russian Laser Research - We propose a novel sensor with its temperature sensitivity improved by the Vernier effect. The sensor comprises two parallel Fabry–Pérot...     

Reflective polarization conversion Fabry–Pérot resonator using omnidirectional mirror of periodic anisotropic stack

A reflective Fabry–Pérot (FP) etalon is demonstrated exhibiting resonance peaks with a total 90°, polarization rotation. The resonator is based on the use of anisotropic alternating dielectric layers stack at wavelengths near the edge of the photonic band gap in where it acts as omnidirectional mirror. Tunability is shown to be possible by variation of the polar tilt angle of the dielectric ellipsoid.     

Antimonide-based lasers and DFB laser diodes in the 2–2.7 μm wavelength range for absorption spectroscopy

We report on Fabry–Pérot semiconductor lasers and single frequency distributed feedback lasers based on GaInAsSb/AlGaAsSb quantum wells. The laser structures were grown by molecular beam epitaxy on GaSb substrates. The devices were etched either by wet process or by inductively coupled plasma (ICP) process. Electron-beam lithography was used to deposit a metal Bragg grating on each side of the laser ridge to fabricate the DFB lasers. The devices all operate in the continuous wave regime at room temperature with a single frequency emission above 2.6 μm and good tuning properties, making them well adapted to tunable diode laser absorption spectroscopy. PACS 42.55.Px; 42.62.Fi     

Injection-locked range and linewidth measurements at different seed-laser linewidths using a Fabry–Pérot laser-diode

In this paper we experimentally examine the dependence of the injection-locked range magnitude of a Fabry–Pérot (FP) laser on the linewidth of a seed laser. We measure the enhancement of the incident-power-dependent injection-locked range when changing the seed-light linewidth in three different ranges, starting with tens of GHz, then hundreds of MHz, and up to a few hundred kHz. We notice the progressive shrinkage of the locking range with an increase in the linewidth of the seed source. Simultaneously, the linewidth of a FP laser was measured and the cancellation of multiple longitudinal operating modes as well as a great reduction of linewidth are observed with a self-homodyne measurement.     

A low-finesse Fabry–Pérot interferometer for use in displacement measurements with applications in absolute gravimetry

A low-finesse Fabry–Pérot interferometer is used to determine long and fast displacements. Two corner cube reflectors form the traveling-wave cavity and one beam splitter couples the input collimated laser beam. Given the retro-directive property of corner cube reflectors, the cavity operates at the edge of stability over an extended scanning range. The in-line scheme with a single fixed optical component makes the proposed interferometer robust and easy to align and use. These characteristics are particularly useful in applications running in noisy environments, such as in on-field absolute gravimetry. Experimental data showing the performances reached in a transportable ballistic gravimeter are also presented.     

Fast interrogation using sinusoidally current modulated laser diodes for fiber Fabry–Perot interferometric sensor consisting of fiber Bragg gratings

A fast interrogation method using a sinusoidal modulated laser diode for a fiber Fabry–Perot interferometric sensor consisting of Bragg gratings (FBG–FPI) is proposed.. The FBG–FPI has sharp transmittance peaks in the reflection band of the FBGs. Wavelength sweep produced by current modulation of a laser diode can be used to detect the peak position. This enables high-resolution strain or temperature measurement. To precisely control the current, the current modulation is realized using a laser diode controller (LDC) with external modulation function. In the modulation by a sawtooth wave, the possible speed of wavelength sweeping is limited to 100 kHz or less due to the bandwidth limitation of an LDC and thermal effect in a laser diodeUsing a sinusoidal wave as a modulation waveform enables wavelength sweeping at speeds exceeding 100 kHz. The modulation characteristics of the laser wavelength is evaluated experimentally and the operating wavelength is monitored using an asymmetric Mach–Zehnder interferometer. The resolution of 0.2 fm/\(\sqrt{\mathrm{Hz}}\) and measurement time of 1 \(\upmu\)s were experimentally demonstrated in the present sensor.     

Analysis of chemical property for Cu–Cr complex surface by laser irradiation with different wavelength and laser mode

Modification of the metal complexes by the laser irradiation with different wavelength and beam quality is investigated. After irradiation, the structure of macromolecular metal complexes are changed, and the reducing metal crystal nucleus emerges.. In this paper, the surface of the metal complexes is irradiated by laser scanning with wavelengths of 532 nm, 1064 nm and 10.6 μm.The 1064nm laser performs the most favorably by using Scanning Electron Microscope and X-ray Photoelectron Spectroscopy. Because the change of chemical composition percentage and variation of metal chemical valence state is most evident. Furthermore, mode selection of laser cavity by adding a pinhole aperture further improves the surface topography, fineness of modification and reducing ability. The appropriate wavelength and mode selection should be utilized together with other influencing laser parameters to achieve the most favorable consequence of metal complexes surface modification.     

A Brillouin lidar system using F–P etalon and ICCD for remote sensing of the ocean

A Brillouin lidar using F–P etalon and intensifier CCD (ICCD) for remote sensing of the ocean is developed. The spectrum of Brillouin scattering in the open ocean can be obtained in real time and can be used for real-time measurement of sound velocity, bulk viscosity, temperature in the ocean, as well as real-time detection of a submerged object. PACS 42.68.Wt; 42.79.Qx; 78.35.+c