Tunable Fabry-Perot Interferometer Research Articles

Tunable Fabry-Perot interferometer as a dispersing element in spectral devices

Presently, tunable optical filters are widely used in optical and optoelectronic systems and complexes. Tunable optical filters are essential components in a wide range of optical systems. The developed tunable Fabry-Perot interferometer presented the article can be used in various fields of optotechnics. The design of the proposed tunable optical filter is a tunable Fabry-Perot interferometer based on the inverse piezoelectric effect. The optical characteristics of the filter will depend on the optical, electrical and physical characteristics of the components included in its design.

Implementation of a Controller for a Space-Grade, Piezo-Actuated Fabry-Perot Interferometer

A tunable Fabry-Perot interferometer (FPI) can be used as an optical band-pass filter. This type of filter is used in spectrometers and spectral imagers. The transmitted wavelength depends on the optical cavity adjusted by an electronic controller. This cavity, or the gap between the FPI mirrors, is measured using capacitive sensing. The performance of the FPI controller directly affects the FPI transmission spectrum and thus the quality of the spectral data. This work describes the design of the FPI controller for the ultraviolet channel of the ALTIUS hyperspectral imager. The ALTIUS mission is part of the Earth Watch program managed by the European Space Agency, ESA. This article presents a novel combination of building blocks to implement a low-noise, high-stability controller for piezo-actuated FPIs. Special care was taken to guarantee temperature stability and to minimize fluctuation of the FPI gap caused by the controller electronics. With the controller design presented in this paper, temperature variations ranging from –50 to +50 °C induce FPI gap deviations of less than 0.1 nm at an electrode distance of 3000 nm, corresponding to a relative temperature drift of 0.3 ppm/°C.

All-Optical Demodulation Fiber Acoustic Sensor With Real-Time Controllable Sensitivity Based on Optical Vernier Effect

In the fiber sensing research area, a pair of sharp contradictions is highlighted: high sensitivity and large dynamic range. In addition, the question of how to enable user-editable features for fiber optic sensors is gaining more and more attention. This letter presents a fiber acoustic sensor with real-time controllable sensitivity based on the optical vernier effect, which is possibly a solution to such a problem. The optical vernier structure with amplified and real-time tunable detection sensitivity is formed by cascading a Sagnac interferometer and a laboratory-made tunable Fabry–Perot interferometer (FPI). Sound pressure and frequency of the acoustic signal can be all-optically demodulated simultaneously by spectral reading and spectral scanning method, respectively. Experimental results show a real-time controllable acoustic sensitivity (1×, 5×, and 10× are demonstrated) and a maximum sensitivity is as high as 37.1 nm/Pa (10× of single FPI) within relatively large sound pressure range of 62.2–92.4 dB. By adjusting the FPI cavity length in real time, sensitivity can be controlled to meet the needs of different users or occasions. The proposed sensor has merits of controllable sensitivity in real time, high sensitivity, and large dynamic range, enabling the applications related but not limited to acoustic sensing.

New technique to measure the cavity defects of Fabry–Perot interferometers

Context. Several astronomical instruments, for both nighttime and solar use, rely on tunable Fabry–Perot interferometers (FPIs). Knowing the exact shape of the etalons’ cavity is crucial for assessing the overall instrumental transmission profile and its possible variations during the tuning process.Aims. We aim to define and test a technique to accurately measure the cavity defects of air-spaced FPIs, including distortions due to the spectral tuning process that are typical of astronomical observations. We further aim to develop a correction technique to maintain the shape of the cavity as constant as possible during the spectral scan. These are necessary steps to optimize the spectral transmission profile of a two-dimensional spectrograph (polarimeter) using one or more FPIs in series, and to ensure that the spectral transmission profile remains constant during typical observing conditions.Methods. We devised a generalization of the techniques developed for the so-called phase-shifting interferometry to the case of FPI. This measuring technique is applicable to any given FPI that can be tuned via changing the cavity spacing (z-axis), and can be used for any etalon regardless of the coating’ reflectivity. The major strength of our method is the ability to fully characterize the cavity during a spectral scan, allowing for the determination of scan-dependent modifications of the plates. We have applied the measuring technique to three 50 mm diameter interferometers, with cavity gaps ranging between 600μm and 3 mm, coated for use in the visible range.Results. The technique developed in this paper allows us to accurately and reliably measure the cavity defects of air-spaced FPIs, and of their evolution during the entire spectral scan. Our main, and unexpected, result is that the relative tilt between the two FPI plates varies significantly during the spectral scan, and can dominate the cavity defects; in particular, we observe that the tilt component at the extremes of the scan is sensibly larger than that at the center of the scan. Exploiting the capability of the electronic controllers to set the reference plane at any given spectral step, we then develop a correction technique that allows the minimization of the tilt during a complete spectral scan. The correction remains highly stable over long periods, well beyond the typical duration of astronomical observations.

Continuous tunable cavity Fabry-Perot interferometer by using potassium dideuterium phosphate with two ring electrodes.

In order to perform hyperspectral remote sensing, we present a continuous tunable cavity Fabry-Perot interferometer (FPI) by using potassium dideuterium phosphate (DKDP) with two ring electrodes. DKDP has the good performances of high transmittance in the ultraviolet band and large aperture of 20mm (the maximum aperture can be 100mm). Since the resonant frequency of an FPI can be continuously varied with the refractive index change of DKDP caused by the electro-optic effect, the influence of moving parts on resonant frequency can be eliminated. Digital holographic interferometry based on a Mach-Zehnder interferometer is employed to measure the refractive index modulation of DKDP. The parameters of FPI are characterized by using an experimental setup with frequency locking and temperature control technologies. Taking the temperature-measuring high-spectral-resolution lidar based on Rayleigh-Brillouin scattering as an example, a continuous tunable cavity FPI with the full width at half-maximum of 200MHz and free spectral range of 11.12GHz is realized. The results are in good agreement with the designed parameters.

Tunable Fabry-Perot Interferometer Designed for Far-Infrared Wavelength by Utilizing Electromagnetic Force.

A tunable Fabry-Perot interferometer (TFPI)-type wavelength filter designed for the long-wavelength infrared (LWIR) region is fabricated using micro electro mechanical systems (MEMS) technology and the novel polydimethylsiloxane (PDMS) micro patterning technique. The structure of the proposed infrared sensor consists of a Fabry-Perot interferometer (FPI)-based optical filter and infrared (IR) detector. An amorphous Si-based thermal IR detector is located under the FPI-based optical filter to detect the IR-rays filtered by the FPI. The filtered IR wavelength is selected according to the air etalon gap between reflectors, which is defined by the thickness of the patterned PDMS. The 8 μm-thick PDMS pattern is fabricated on a 3 nm-thick Al layer used as a reflector. The air etalon gap is changed using the electromagnetic force between the permanent magnet and solenoid. The measured PDMS gap height is about 2 μm, ranging from 8 μm to 6 μm, with driving current varying from 0 mA to 600 mA, resulting in a tunable wavelength range of 4 μm. The 3-dB bandwidth (full width at half maximum, FWHM) of the proposed filter is 1.5 nm, while the Free Spectral Range (FSR) is 8 μm. Experimental results show that the proposed TFPI can detect a specific wavelength at the long LWIR region.

Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser.

An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated. By the use of a tunable narrow-band fiber Fabry-Perot interferometer, the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of < 700 Hz. The laser frequency noise is less than 40 dB re Hz/Hz1/2 at low frequencies (< 100 Hz) and reaches -5 dB re Hz/Hz1/2 at around 25 kHz. The measured relative intensity noise (RIN) is less than -130 dB/Hz with regard to frequencies of over 3 MHz, while the obtained linear polarization extinction ratio (LPER) is higher than 28 dB. This ultra-narrow linewidth low-noise tunable single-frequency linear-polarization fiber laser provides a promising candidate for high-order quadrature amplitude modulation (QAM) optical communication system.

Remote Sensing of 3-D Geometry and Surface Moisture of a Peat Production Area Using Hyperspectral Frame Cameras in Visible to Short-Wave Infrared Spectral Ranges Onboard a Small Unmanned Airborne Vehicle (UAV)

Miniaturized hyperspectral imaging sensors are becoming available to small unmanned airborne vehicle (UAV) platforms. Imaging concepts based on frame format offer an attractive alternative to conventional hyperspectral pushbroom scanners because they enable enhanced processing and interpretation potential by allowing for acquisition of the 3-D geometry of the object and multiple object views together with the hyperspectral reflectance signatures. The objective of this investigation was to study the performance of novel visible and near-infrared (VNIR) and short-wave infrared (SWIR) hyperspectral frame cameras based on a tunable Fabry–Perot interferometer (FPI) in measuring a 3-D digital surface model and the surface moisture of a peat production area. UAV image blocks were captured with ground sample distances (GSDs) of 15, 9.5, and 2.5 cm with the SWIR, VNIR, and consumer RGB cameras, respectively. Georeferencing showed consistent behavior, with accuracy levels better than GSD for the FPI cameras. The best accuracy in moisture estimation was obtained when using the reflectance difference of the SWIR band at 1246 nm and of the VNIR band at 859 nm, which gave a root mean square error (rmse) of 5.21 pp (pp is the mass fraction in percentage points) and a normalized rmse of 7.61%. The results are encouraging, indicating that UAV-based remote sensing could significantly improve the efficiency and environmental safety aspects of peat production.

Development of a high spectral resolution lidar based on confocal Fabry–Perot spectral filters

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5 GHz and a finesse of 50.7 (312) at 532 nm (1064 nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.

Monolithically integrated microspectrometer-on-chip based on tunable visible light MEMS FPI

We present a novel microspectrometer-on-chip for the visible spectral region, consisting of a tunable MEMS Fabry-Perot interferometer (FPI) monolithically integrated on a PIN photodiode using IC compatible microfabrication techniques. MEMS FPI is an electrostatically (AC voltage) actuated structure consisting of two parallel atomic layer deposited Bragg mirror stacks of Al2O3/TiO2 with imbedded circular aluminum electrodes on top and the bottom for capacitive tuning capability for the wavelength range of 420–550nm. The fabrication process flow for the successful completion of the device is presented. The spectral response of the device ranges from 0.1A/W at λ=420nm to 0.2A/W at λ=550nm, with transmission peak width of 8nm at 540nm. These results indicate photodiode performance that matches the sensitivity levels typical for commercially available photodiodes in this wavelength range as well as excellent transmission properties of the integrated FPI filter structure, while the monolithical fabrication process offers increased spectrometer robustness and mass production capability.

FBG Demodulation System Based on Real-Time Correction Technology

The system error of the FBG demodulation system based on tunable fiber Fabry-Perot (F-P) interferometer increases due to the uncertain relationship of driving voltage and the scanning wave peak. So the real-time correction technology is studied here. A parallel real-time correction system is designed to correct nonlinear problems of PZT and structural errors of the tunable FP interferometer. The relation between PZT driving voltage and the peak of tunable FP interferometer is analyzed by the experiments. Then a fast segmentation algorithm is designed. Then a signal processing system is designed using FPGA, which guarantees real-time work of the system by integrating the demodulation system control, filter calculation and data compression circuits into one FPGA chip. Experimental results show that the system described here solves the accuracy problem caused by the tunable FP interferometer.

Tunable fabry-perot interferometer from ferroelectric polymer based on surface energy modification

Surface energy modification was utilized in the fabrication of hollow transmission Fabry-Perot interferometer (FPI) for the first time. Polydimethylsiloxane (PDMS) was used to modify the surface energy of substrate for the self-assembly of poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] 70/30 mol% copolymer film on given areas, which is simple and low destructive for the photoelectric device. A strain of 7.12% under a field of 22.3 MV/m was observed from the copolymer film, which led to the FPI with a tunable range of 54 nm at wavelength of 604 nm.

Wavelength-swept spectral and pulse shaping utilizing hybrid Fourier domain modelocking by fiber optical parametric and erbium-doped fiber amplifiers

We report the first Fourier domain modelocked (FDML) laser constructed using optical parametric amplifier (OPA) in conjunction with an erbium-doped fiber amplifier (EDFA), centered at approximately 1555 nm, to the best of our knowledge. We utilize a one-pump OPA and a C-band EDFA in serial configuration with a tunable Fabry-Perot interferometer to generate a hybrid FDML spectrum. Results demonstrate a substantially better spectral shape, output power and stability than individual configurations, with decreased sensitivity to polarization changes. We believe this technique has the potential to enable several amplifiers to complement individual deficiencies resulting in improved spectral shapes and power generation for imaging applications such as optical coherence tomography (OCT).

Widely tunable reflection-type Fabry-Perot interferometer based on relaxor ferroelectric poly(vinylidenefluoride-chlorotrifluoroethylene-trifluoroethylene)

A reflection-type Fabry-Perot interferometer (FPI) with a large tunability has been demonstrated on relaxor ferroelectric poly(vinylidenefluoride-chlorotrifluoroethylene-trifluoroethylene) [P(VDFCTFE-TrFE)] 78.9/13.9/7.2 mol% with a thickness of 9.2 microm. The optical path length of the FPI is modulated by the electrostrictive strain of the terpolymer under electric field, where the low-loss distributed Bragg reflector and aluminium film are employed as the mirrors in the FPI. A positive strain of 20% has been achieved in the terpolymer film under a field of 30 MV/m, which leads to the FPI with a tunable range of more than 200 nm at wavelengths around 680 nm.

Optomechanical design of tunable InP-based Fabry-Perot filters for wavelength division multiplexing applications

Micromachined tunable Fabry-Perot interferometers based on compound semiconductors have earlier been proposed for fiber optic communications employing wavelength division multiplexing (WDM) for wavelengths around 1.55 µm. The cavity length in micromachined interferometers is varied by displacing one of the two distributed Bragg reflector (DBR) mirrors by electrostatic actuation of supporting beams. The filter's optical response for varying cavity lengths is simulated by a transfer matrix method, and the optical tuning efficiency of the filter is 0.53. We investigate three conventional filter designs using the finite element method (FEM) and compare it with a new proposed filter design. Using a mathematical model, deflection is analytically calculated and compared with finite element analysis results. Due to the way in which the mirror is integrated with a suspending framework of beams, bending within the mirror during actuation cannot be averted. The filter's optical performance demands that the mirror remain so flat that the maximum bending deflection is 1 nm for the mirror of given dimensions. Using a criterion based on mechanical and optical considerations, the dimensions of the beams suspending the mirror are optimized for each filter design under investigation. Combining the optical and mechanical simulations by FEM, wavelength tuning characteristics for each filter design are determined.

Using LASCO-C1 spectroscopy for coronal diagnostics

Abstract The LASCO-C1 telescope was designed to perform spectral analysis of coronal structures by means of a tunable Fabry–Perot interferometer acquiring images at different wavelengths. Results from spectral scans of the Fe xiv 5303 A green coronal emission line are presented. Physical quantities like the ion temperature (line widths), and the flow velocity along the line of sight (Doppler shifts) are obtained over the entire corona.

Electrical tunable Fabry–Perot interferometer using a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer

Electrical tunable Fabry-Perot interferometers (FPIs) using a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer were fabricated and characterized. Using pure strain tuning, which for the terpolymer films under mechanically clamped condition is 1.3% under 100 V/μm field, we show that a tunable range of 22.5 nm can be obtained at wavelengths near 1.5 μm. Due to the opposite sign of the field-induced strain and the refractive index change from the electro-optic effect, the FPI using a terpolymer film directly as the cavity of the etalon shows a smaller tunability (0.78% under 100 V/μm).

Bulk micromachining of a MEMS tunable Fabry-Perot interferometer: effect of residual silicon on device performance

A broadband tunable filter for the infrared spectral region is desired for use as a wavelength selective element in a miniature absorption spectrometer. We present the design, fabrication, packaging, and characterization of a bulk micromachined Fabry-Perot interferometer (FPI) for meeting this need. A novel approach to fabricate a MEMS-based tunable resonant cavity using two separate wafers bonded using a "lock-and-key" spacer design is outlined, with the goal of realizing electrostatically actuated membranes from films predeposited on base substrates. This ability could enable the pursuit of MEMS devices without in-house chemical vapor deposition (CVD) capability, after overcoming the shortcomings of bulk micromachining. The FPI device was designed with a planar structure comprising two face-to-face bonded chips of overall lateral dimension 10×10 mm with deflection regions of 2×2 mm. The device employs electrostatic actuation to tune the output wavelength, for which finite element modeling predicted low (<1 V) actuation voltages for movement of the membrane. Experimental results from device testing (mechanical) were found to differ from the theoretical predictions, primarily due to fabrication issues. Specifically, the device performance was found to be greatly influenced by the amount of residual silicon on the wafer chip following inductively coupled plasma (ICP) backside etching, with high voltages (~30 times higher than modeled) required for actuation of the device. Through a combination of modeling and experimental measurements, it is demonstrated that the ability to produce MEMS devices by releasing membranes from films predeposited on substrates is highly susceptible to error in etching and packaging.

Design and experiments for tunable optical sensor fabrication using (1 1 1)-oriented silicon micromachining

The paper presents the design and the experiments performed for integration of a micromechanical voltage tunable Fabry–Perot interferometer structure with a silicon p–n photodiode in order to obtain a tunable optical sensor. The Fabry–Perot interferometer can be used as a voltage tunable filter for the input radiation or as a voltage controlled attenuator to regulate the light from a monochromatic source. In our approach, the top mirror of the Fabry–Perot cavity is an Au/SiO 2 movable membrane, formed by anisotropic etching of (1 1 1)-oriented Si wafers. The Au layer provides a good reflectivity of the upper mirror. The air–silicon surface acts as the lower mirror, as the anisotropic etching of (1 1 1)-oriented Si wafers provides very smooth surfaces. The upper movable mirror can be electrostatically actuated. This Fabry–Perot interferometer was realized on the top of a p–n photodiode.

Alignment of Fabry-Pérot Interferometer Plates in a Solar Vector Magnetograph

I describe a method for quickly and accurately determining the plate parallelism in a tunable Fabry-Perot interferometer. The method takes advantage of the fact that our Fabry-Perot is installed in a spectropolarimeter: we measure profiles of solar or telluric absorption lines in three differently polarized telescope subapertures and use the residual polarization profiles to determine the plate parallelism error. An example of the error as a function of time during the observing day is also shown; it changes in a consistent way with telescope hour angle but the drift is enough to require frequent adjustment.