Single Fabry-Perot Interferometer Research Articles

Lateral Offset Single-Mode Fiber-Based Fabry-Perot Interferometers with Vernier Effect for Hydrogen Sensing.

A high-sensitive optical fiber hydrogen (H2) sensor with Vernier effect by cascading three Fabry-Perot interferometers (FPIs) has been proposed. It is prepared by welding three sections of a single-mode fiber with a lateral offset structure and coating polydimethylsiloxane (PDMS) at the offset part to form three cascaded FPIs and generate a Vernier envelope spectrum. To realize H2 sensing, the hydrogen-sensitive material Pd/WO3 is fabricated and coated on the outside of the PDMS. Pd/WO3 will generate local heat when in contact with H2, which will cause the thermal expansion and refractive index change of PDMS and finally lead to the Vernier envelope wavelength shifting with the change of H2 concentration. Due to the Vernier effect, the H2 sensor can achieve a linear measurement sensitivity of 6.214 nm/% in the concentration range of 0-1%, which is 16.11 times that of a single FPI. The proposed H2 sensor possesses advantages of high sensitivity, easy preparation, compact structure, low cost, and easy long-distance transmission.

High Sensitivity Hollow-Core Fiber Strain Sensor Based on Signal Processing Assisted Vernier Effect

A fiber strain sensor with improved sensitivity is proposed and experimentally demonstrated, based on a single Fabry–Perot interferometer (FPI) using a signal processing assisted Vernier effect. The FPI structure is simply fabricated by splicing a segment of hollow-core fiber (HCF) between two pieces of single-mode fiber (SMF) with a commercial fusion splicer. Through data processing, we do not need to precisely manufacture two interferometers with very small detuning between their optical path differences (OPDs), as in the traditional schemes based on Vernier effect, since it is difficult to control the detuning strictly. The optical spectra of the reference interferometer (RIM) are replaced by an artificial reference spectrum (ARS), which is produced by spatial frequency down-conversion of the interference spectra of the sensing interferometer (SIM) in the initial state. Then, the optical spectrum envelope of Vernier-effect can be obtained by multiplying the SIM intensity with the constructed ARS intensity. When the length of HCF is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1201\mu \text{m}$ </tex-math></inline-formula> , the sensitivity can reach 315pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> with the modulation length of 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> m. Compared with the sensitivity without signal processing, the sensitivity magnification is 188.6 times. The proposed scheme to realize sensitivity-enhancement using a single FPI based on the HCF, could simplify the sensor structure and device fabrication.

A High-Precision Method for the Determination of Cavity Length of a Fabry-Perot Interferometer

A novel method to obtain the cavity length of a Fabry-Perot interferometer (FPI) precisely based on the Vernier effect via a virtually variable reference FPI is proposed in this paper. Compared with the traditional method based on the measurement of wavelength spacing between two adjacent peaks in the spectrum of a single FPI, or enlarge the wavelength spacing with the Vernier effect by incorporating a real reference FPI in the sensor part, the present scheme is more flexible and applicable. By scanning the cavity length of the virtual reference FPI digitally, the accurate cavity length of the real FPI can be obtained when the free spectrum range (FSR) of the spectrum envelope of the combined FPIs reaches a maximum. Both theoretical analysis and experimental results show that the proposed scheme is superior to traditional methods, and with the present measurement condition, more than 20 times accuracy improvement for the determination of cavity length can be achieved.

High sensitivity temperature and pressure sensor based on cascaded Fabry-Perot and Sagnac interferometers

A sensor was proposed and experimentally demonstrated to improve temperature and pressure sensitivity by the Vernier effect. The sensor is composed of a cascaded Fabry-Perot interferometer (FPI) and a Sagnac interferometer (SI), which has almost the same free spectral range (FSR) forming the Vernier effect. The SI is a fiber-loop consisting of a segment of polarization maintaining fiber (PMF). The FPI consists of a section of quartz capillary inserted between two sections of single mode fiber. A micro-channel is drilled in the quartz capillary using a femtosecond laser to circulate air inside and outside the Fabry-Perot (F-P) cavity. SI and FPI in the sensor structure are selectively sensitive to temperature and pressure. In temperature sensing, the SI acts as the sensor and FPI as the reference, whereas in pressure measurements, the FPI is the sensing unit and SI the reference unit. Thus, in Vernier effect sensing, they perform the functions of reference or sensing units to each other. The sensor provides high sensitivity for both temperature and pressure. Experimental results show that the temperature sensitivity is ∼23.14 nm/°C, which is ∼13.4 times higher for the single SI sensor (–1.73 nm/°C), and the pressure sensitivity is ∼49.2 nm/MPa, which is ∼12.2 times higher than for the single FPI sensor (4.02 nm/MPa). The sensor has a simple structure, easy preparation, and high sensitivity of both temperature and gas pressure, and has widespread prospective application.

Ultrasensitive parallel double-FPIs sensor based on Vernier effect and Type II fiber Bragg grating for simultaneous measurement of high temperature and strain

In this work, we demonstrated an ultrasensitive parallel double Fabry–Perot interferometers (FPIs) sensor based on Vernier effect and Type II fiber Bragg grating (FBG) for simultaneous measurement of temperature and strain in the temperature range of 26 °C–1000 °C. Two FPIs are manufactured from hollow silica tube (HST), single mode fiber (SMF) and multimode fiber (MMF). The superposition of both waves from the FPIs produces an interference spectrum with a large envelope that has a temperature sensitivity of 6.98 pm/°C and a strain sensitivity of 127.32 pm/μɛ at 800 °C. This strain sensitivity is ∼7.6 times higher than that of a single FPI structure (without Vernier Effect). In addition, an FBG is inscribed in one of the FPIs using a femtosecond laser to provide additional temperature reading (temperature sensitivity ∼15.14 pm/∘C) and to serve as thermal compensation for the measurement. The FBG is encapsulated in glass capillary tube so that it is unaffected by the applied strain. The proposed sensor is robust and highly sensitive, and it is suitable for the applications under extreme temperature condition.

Negative curvature hollow core fiber sensor for the measurement of strain and temperature.

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.

Ultra-sensitive high temperature sensor based on a PMPCF tip cascaded with an ECPMF Sagnac loop

We propose a sensitivity magnified polarization maintaining photonic crystal fiber (PMPCF) Fabry-Perot probe cascaded with a Sagnac loop (SL) for high temperature measurement (up to 1000 °C). The Fabry-Perot interferometer (FPI) fabricated by fusion splicing a PMPCF tip with a single mode fiber works as a sensing interferometer. The cascaded SL consisting of a temperature insensitive elliptical core polarization maintaining fiber (ECPMF) is applied as a reference interferometer. The free spectral range of the SL is easily tailored by adjusting the ECPMF length, making it similar to that of the sensing FPI, to generate Vernier effect. Experimental results show that the temperature sensitivity of the single FPI is 13.71 pm/°C, and the sensitivities of cascaded FPI-SLs are 143.52 pm/°C, 418.7 pm/°C and 1.15 nm/°C. The measured magnification factors are about 10, 35 and 91, which are consistent with theoretical results. The linearity of temperature response is 99.94 % from room temperature to 1000 °C. The proposed ultra-sensitive sensor has promising prospects for high temperature measurement.

High temperature Vernier probe utilizing photonic crystal fiber-based Fabry-Perot interferometers.

This study proposes a highly sensitive and stable optical fiber probe based on Vernier effect for high temperature measurement (up to 1000 °C), utilizing photonic crystal fiber (PCF)-based Fabry-Perot interferometers (FPIs). The cascaded FPIs are fabricated by fusion splicing a section of polarization maintaining PCF to a lead-in single-mode fiber, and then a section of temperature-insensitive hollow core PCF is spliced between the PMPCF and a multi-mode fiber. The shift of the spectral envelope is monitored to measure the temperature variation. Experimental results show that the sensitivities of three fabricated probes are as high as 173.43 pm/ °C, 230.53 pm/ °C and 535.16 pm/ °C when operating from room temperature to 1000 °C, which are consistent with theoretical results. The sensitivities are magnified about 13, 19 and 45 times compared with the single FPI. The linearity of the temperature response is as high as 99.73%. The proposed probe has great application prospects due to compactness, high sensitivity and low cost.

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.

Sensitivity-enhanced temperature sensor with fiber optic Fabry-Perot interferometer based on vernier effect

Fiber-optic temperature sensors have gained much attention owing to their intrinsic features of light weight, immunity to electromagnetic interference, and capability for distributed measurement. Especially, temperature sensors based on Fabry-Perot interferometers (FPIs) are attractive owing to their advantages of compact size and convenient reflection measurement. However, due to the low thermal expansion or/and thermo-optic coefficient of fiber, the temperature sensitivities of these sensors are normally low (~10 pm/℃ or even lower). In order to improve the temperature sensitivity, a device with dual cascaded FPIs is proposed and demonstrated in this paper, which works on vernier effect and exhibits a much higher temperature sensitivity. The device is fabricated by splicing a short segment of large mode area (LMA) fiber to a short segment of capillary tube fused with a section of single-mode fiber to form an extrinsic Fabry-Perot interferometer with a glass cavity cascaded to an intrinsic FPI with a narrow air cavity. By setting the lengths of capillary tube and LMA fiber to allow similar free spectral ranges to be obtained, and superimposing of the reflection spectra of the two FPIs, the vernier effect can be generated. Firstly, the principle of temperature sensing based on vernier effect of this device is analyzed and simulated theoretically, and it is found that the temperature sensitivity can be improved significantly by using vernier effect compared with that of a single FPI with an air-cavity or glass cavity by directly tracing resonant dips/peaks. Then, the temperature responses of the FPI with single air-cavity and dual cascaded cavities are measured, respectively. Experimental results match well with the theoretical analysis carried out. The temperature sensitivity of the proposed sensor is improved greatly from 0.71 pm/℃ for a single FPI sensor with an air-cavity to 179.30 pm/℃ by employing the vernier effect. Additionally, the sensor exhibits good repeatability in a temperature range of 100-500℃. The proposed sensor has the advantages of compact size (1 mm in dimension) and high sensitivity, which makes it promising for temperature sensing in a variety of industries, such as food inspection, pharmacy, oil/gas exploration, environment, and high-voltage power systems.

Assimilation of thermospheric measurements for ionosphere‐thermosphere state estimation

AbstractWe develop a method that uses data assimilation to estimate ionospheric‐thermospheric (IT) states during midlatitude nighttime storm conditions. The algorithm Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) uses time‐varying electron densities in the F region, derived primarily from total electron content data, to estimate two drivers of the IT: neutral winds and electric potential. A Kalman filter is used to update background models based on ingested plasma densities and neutral wind measurements. This is the first time a Kalman filtering technique is used with the EMPIRE algorithm and the first time neutral wind measurements from 630.0 nm Fabry‐Perot interferometers (FPIs) are ingested to improve estimates of storm time ion drifts and neutral winds. The effects of assimilating remotely sensed neutral winds from FPI observations are studied by comparing results of ingesting: electron densities (N) only, N plus half the measurements from a single FPI, and then N plus all of the FPI data. While estimates of ion drifts and neutral winds based on N give estimates similar to the background models, this study's results show that ingestion of the FPI data can significantly change neutral wind and ion drift estimation away from background models. In particular, once neutral winds are ingested, estimated neutral winds agree more with validation wind data, and estimated ion drifts in the magnetic field‐parallel direction are more sensitive to ingestion than the field‐perpendicular zonal and meridional directions. Also, data assimilation with FPI measurements helps provide insight into the effects of contamination on 630.0 nm emissions experienced during geomagnetic storms.

Highly Sensitive Airflow Sensor Based on Fabry–Perot Interferometer and Vernier Effect

A novel highly sensitive airflow sensor based on Fabry–Perot interferometer (FPI) and Vernier effect is proposed and demonstrated. The sensor is fabricated by splicing a section of hollow-core fiber (HCF) between a lead-in single mode fiber (SMF) and a section of SMF, which is almost one-fifteenth the length of the HCF. Airflow changes the cavity length of the FPI, which leads to the shift of the reflection spectrum. The reflection beam from the last end of the SMF is utilized to generate the Vernier effect, which enlarges the shift of the spectrum for 9.57 times than that of a single FPI. According to the experimental results, when the airflow ranges from ${\text{0 to 7 m/s}}$ , the spectrum of the sensor shifts as high as 7.9 nm which is almost eight times more than that of the self-heating sensor based on silver-coated FBG. And the highest airflow velocity sensitivity of the sensor can reach ${\text{1.541 nm/(m/s)}}$ in the region of ${\text{3m/s} \sim {7m/s}}$ . Besides, the sensor has a series of advantages such as fast response, low cost, compact size, and reflection measurement.

The ALOMAR Rayleigh/Mie/Raman lidar: objectives, configuration, and performance

Abstract. We report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar. This instrument is one of the core instruments of the international ALOMAR facility, located near Andenes in Norway at 69°N and 16°E. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. These studies address questions about the thermal structure of the Arctic middle atmosphere, the dynamical processes acting therein, and of aerosols in the form of stratospheric background aerosol, polar stratospheric clouds, noctilucent clouds, and injected aerosols of volcanic or anthropogenic origin. Furthermore, the lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 µrad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N2 and N2+O2 molecules, respectively. Currently, up to 36 detector channels simultaneously record the photons collected by the telescopes. The internal and external instrument operations are automated so that this very complex instrument can be operated by a single engineer. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds. Due to its very effective spectral and spatial filtering, the lidar has unique capabilities to work in full sunlight. Under these conditions it can measure temperatures up to 65 km altitude and determine particle size distributions of overhead noctilucent clouds. Due to its very high mechanical and optical stability, it can also employed efficiently under marginal weather conditions when data on the middle atmosphere can be collected only through small breaks in the tropospheric cloud layers.Key words: Atmospheric composition and structure (aerosols and particles; pressure · density · and temperature; instruments and techniques)

The ALOMAR Rayleigh/Mie/Raman lidar: objectives, configuration, and performance

<strong class="journal-contentHeaderColor">Abstract.</strong> We report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar. This instrument is one of the core instruments of the international ALOMAR facility, located near Andenes in Norway at 69°N and 16°E. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. These studies address questions about the thermal structure of the Arctic middle atmosphere, the dynamical processes acting therein, and of aerosols in the form of stratospheric background aerosol, polar stratospheric clouds, noctilucent clouds, and injected aerosols of volcanic or anthropogenic origin. Furthermore, the lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 µrad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N₂ and N₂+O₂ molecules, respectively. Currently, up to 36 detector channels simultaneously record the photons collected by the telescopes. The internal and external instrument operations are automated so that this very complex instrument can be operated by a single engineer. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds. Due to its very effective spectral and spatial filtering, the lidar has unique capabilities to work in full sunlight. Under these conditions it can measure temperatures up to 65 km altitude and determine particle size distributions of overhead noctilucent clouds. Due to its very high mechanical and optical stability, it can also employed efficiently under marginal weather conditions when data on the middle atmosphere can be collected only through small breaks in the tropospheric cloud layers.<br><br><b>Key words:</b> Atmospheric composition and structure (aerosols and particles; pressure · density · and temperature; instruments and techniques)

Wavelength stabilization and control of pulsed or cw tunable dye lasers: a simple scheme

A new method for wavelength stabilization and control of pulsed or cw dye lasers using a single Fabry-Perot interferometer and a reference He-Ne laser is proposed. The performance of the system and the sources of error are discussed. It is shown that the rigorous demands on thermal, pressure, and mechanical stability usually made on such systems can be relaxed to a large extent.

Observation of molecular rotational bands with a single Fabry-Perot interferometer

A method is described for using a single Fabry-Perot interferometer to study the emissions from an entire molecular rotation band, not just a single line to determine atmospheric temperature. It is shown that if the effective line spacing of the band to free spectral range is nearly a rational number, the resulting signal is highly temperature sensitive, particularly at low temperatures. It is shown that the finesse of the instrument is not extremely important but that the instrument function must be known very precisely. The method is illustrated with the O2 atmospheric band and an interferometer flown on the Dynamics Explorer 2 satellite.

Infrared Modulator for Optical Sensors Based on a Vibrating Fabry-Perot Interferometer

The development, construction and space qualification of an IR modulator for f/1 radiation in the 14-16 pm band is described. The modulation is based on the principle of a vibrating Fabry-Perot (FP) interferometer with gap width variations of -±Am/8c,-, 2 pm (A-center wavelength) which is considered micromechanical. By connecting two such Fabry-Perot interferometers in series (with two outer CdTe plates in fixed positions and one common vibrating inner CdTe plate for harmonic gap width variation) a modulation effici-ency of about 75% is attained. CdTe is superior to other materials as far as IR absorption (0.2%/cm) within the -20°C to +60°C temperature range and the 2 to 25 11M wavelength range is concerned. Its modulation efficiency in a single FP interferometer is however too low because of its low refractive index (n = 2.5). The double FP interferometer is designed for small weight, large receiving aperture, small power consumption and high reliability in long-time space operation. The modulator is operated at a selected resonance frequency between 100 Hz and 1 kHz. It can be tuned to other wavelengths in the 2 to 25 pm range.

Brillouin Scattering Study of Gd2(MoO4)3 Using a Double Fabry-Perot Interferometer

To improve the contrast of a single Fabry–Perot interferometer, a double Fabry–Perot interferometer was designed. The contrast of this system is ∼7×104 which is ∼30 times as large as that of a single Fabry-Perot interferometer. Using this system, the Brillouin spectrum of gadolinium molybdate crystal, which has a very strong central component, could be observed. The temperature dependence of Brillouin shifts and Brillouin linewidths was measured. Brillouin shifts show softening and Brillouin linewidths show anomalous broadening near the structural phase transition point.