Fiber-optic Interferometer Research Articles

A Fabry-Perot Fiber-Optic Interferometer for Highly Sensitive CO2 Detection Based on the Nanoparticles Self-Assembly Technology

The highly sensitive CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> detective instrument is intensively studied recently for the atmosphere protection. Fiber-optic interferometer is widely used as a gas sensor because its interference wavelength can be influenced by the environmental refractive index. In this work, by adopting the nanoparticles self-assembly technology, a spherical optical device with a primary pore width of 8.13 nm and a specific surface area as large as 74.58 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /g is fabricated. For gas detection, the larger the specific surface area of the device, the more gas molecules being adsorbed, resulting in a higher sensitivity. A Fabry-Perot fiber-optic interferometer is designed by mounting the self-assembled device on a fiber end face. In the experiment, it shows a fast response time of 21 s, a high wavelength sensitivity of 200 pm/%, and a wide detection range from 350 ppm to 36% for CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas. It also performs a high selectivity, good repeatability, and immunity to the gas flow rate. Such a Fabry-Perot interferometer, as a standard lab-on-fiber device, will have a significant application potential for trace CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> monitoring in the field of carbon capture, utilization, and storage (CCUS).

Miniaturized High-Sensitivity Temperature Sensor Based on Cascaded Fiber-Optic FPI

In letter, a cascaded fiber-optic Fabry-Perot interferometers temperature sensor with high-sensitivity and small-dimension is proposed and demonstrated. The sensor is fabricated by filling the polydimethylsiloxane (PDMS) and air between two single-mode fiber end-faces located in a section of silica capillary, thus a PDMS-based glue cavity, an air cavity and combined PDMS-air cavity are constructed. Due to the similar optical length between PDMS glue cavity and PDMS-air cavity, the conditions for Vernier effect can be easily satisfied in the sensor fabrication. The temperature sensitivity of proposed sensor is effectively improved in experiment. The research results show that the sensitivity of sensor is enhanced from 2.62 nm/°C to 23.22 nm/°C, which is about 8.86 times than that of the single PDMS-based glue cavity, and the linearity of temperature-dependent wavelength shifts is superior to 0.99 in temperature range of 32~50 °C. The sensor has advantages of high sensitivity, simplicity and easy to fabrication, and the small-dimension merit make it more suitable for point-temperature measurement.

Thermal gradients integrated on-chip by passive radiative cooling of silicon nitride nanomechanical resonators

Radiative coupling of objects with outer space, through the atmospheric spectral transparency window, allows passive cooling below ambient temperature. Such passively created cold sinks can be used for converting ambient heat into other useful forms of energy. Using this approach, conversion of ambient heat to electricity has been demonstrated in macroscopic settings, where the radiatively cooled heat sink is a macroscopic object coupled with ambient heat through a heterogeneously attached, standalone, thermoelectric generator. In contrast, miniaturization and on-chip integration of such heat engines has not been demonstrated, although it could be useful in portable remote technological applications. Such integration would first require that both the radiatively cooled heat sink and the hot (ambient temperature) side of the engine are monolithically integrated on a single chip. This first step is the focus of our work: we demonstrate the creation of a local thermal gradient on-chip by radiative cooling of a 90 nm thick freestanding silicon nitride nanomechanical resonator integrated on a silicon substrate that remains at ambient temperature. The reduction in temperature of the thin film is inferred by tracking its mechanical resonance frequency, under high vacuum, using an optical fiber interferometer. Experiments were conducted on 15 different days during fall and summer months, under various solar illumination, resulting in successful radiative cooling of the membrane in each case. Maximum temperature drops of 9.3 K and 7.1 K are demonstrated during the day and night, respectively, in close correspondence with our heat transfer model. Future improvements to the experimental setup could improve the temperature reduction to 48 K for the same membrane, while emissivity engineering potentially yields a maximum theoretical cooling of 67 K with an ideal emitter.

Recent advancements and future challenges in hybrid optical fiber interferometers

Hybrid optical fiber interferometers provide an efficient way for the detection of multiparameters with high sensitivity and resolution. They are formed by combining two or more identical or different fiber interferometers in cascade or parallel. Two interferometers in the hybrid structure are used for the detection of multiparameters. In addition, hybrid fiber interferometers provide high sensitivity measurement when the Free Spectral Range of the two interferometers satisfies the Vernier effect condition. This review summarizes the recent advancements and future challenges of the hybrid optical fiber interferometers. In the beginning, the hybrid interferometers are introduced, followed by an extensive review on the state-of-the-art sensing structures, and the discussion mainly covers the characteristics of multiparameter detection along with high sensitivity and resolution. In this article a detailed review is presented that describes the future trend for the placement of hybrid interferometers in practical applications.

Research on the Linear Demodulation Range and Background Noise of Fiber-Optic Interferometer System

The linear demodulation range and background noise of the Michelson interferometer system are investigated with a laser phase noise measurement system. We have theoretically and experimentally analyzed the performance of the interferometer system by changing the frequency modulation amplitude of the laser and the optical path difference (OPD) of the interferometer, respectively. It is shown that the linear demodulation range of the Michelson interferometer system is finite, which depends on the parameters of the system, such as the sample frequency, the delay time between two interferometer arms, and the system bandwidth. Furthermore, the experimental results indicate that the background noise of the interferometer system can be reduced by using a sufficiently long OPD so that the smaller true phase information can be detected with the demodulation system. The parameters of the measurement system could be optimized to satisfy the demand of the phase demodulation with different levels, which is of great significance for the phase monitoring interrogator, such as fiber-optical interferometer sensors and distributed acoustic sensors.

All-optical, non-contact, local measurement of both Young’s modulus and Poisson’s ratio in metals using a combination of Rayleigh and leaky surface acoustic waves

In non-destructive evaluation (NDE), measuring ultrasound (US) longitudinal and shear wave speeds is the main method to determine two independent mechanical moduli (Young’s modulus and Poisson’s ratio). Most US techniques use time-of-flight measurements. However, when the local sample thickness is unknown or the sample geometry is complex, bulk-wave propagation speeds cannot be accurately defined. Here we show that a properly shaped beam of nanosecond laser pulses can be used to efficiently excite (without material ablation) two types of surface acoustic waves. In addition to a conventional surface, or Rayleigh, wave, a leaky surface wave (LSAW) can be launched in the near field of the excitation region. We present the theoretical background, numerical simulations, and experimental results clearly showing that both elastic constants can be reconstructed locally by tracking Rayleigh and LSAW waves. Spatially resolved elastic properties can be obtained using local values of wave speeds obtained by sample scanning. Non-contact optical detection of propagating waves at the sample surface, in which a fiber-optic Sagnac interferometer was used, is a key piece of the method. It does not require acoustic coupling and allows remote measurements in the near field of the laser source with micron-scale resolution.

Microwave-photonic optical fiber interferometers for wavelength interrogation of fiber Bragg grating sensors with high sensitivity and a tunable dynamic range.

We propose and demonstrate a new, to the best of our knowledge, microwave interference-based scheme with high sensitivity and tunable measurement range, which is realized by a Mach-Zehnder interferometer (MZI). A chirped fiber Bragg grating and single-mode fiber serve as the two unbalanced arms of the RF interferometer. The induced differential chromatic dispersion transfers the wavelength shift of the fiber Bragg gratings to the change of the RF phase difference between the two interferometric carriers, which ultimately leads to the variation of the RF signal intensity. The phase sensitivity can be improved by adjusting the power ratio of the two beams in the interferometer and coarse adjustment of the optical variable delay line (OVDL). The OVDL is also employed to tune the measurement range of the system by adjusting the time delay difference between the two arms of the MZI. The system effectively solves the problem of unavoidable attenuation of the sensitivity of the optical carrier-based microwave interferometry system caused by the change of phase difference due to the change of measurement parameters, avoiding the mutual constraint between the measurement range and high sensitivity.

Optical frequency transfer with below 10−21 uncertainty using a DFB–laser-based fiber Brillouin amplifier

Exploiting the outstanding performance of optical atomic clocks for improved timekeeping, relativistic geodesy, and fundamental physics beyond the standard model demands comparing distant state-of-the-art optical clocks. Interferometric optical fiber links have been demonstrated as an eminent method for such frequency comparisons over distances up to thousands of kilometers. However, for such distances, the optical fiber attenuation mandates signal amplification. Fiber Brillouin amplification (FBA) has been proven as an efficient amplification technique for coherent frequency transfer. Demonstrated FBA schemes have been designed based on costly narrow-linewidth pump lasers and analog pump-to-signal phase locking schemes. Furthermore, the high pump power requirement of these FBAs hinders the integration of FBA-based frequency dissemination on fiber connections for shared telecommunication signals in the C-band. In this paper, we propose and experimentally demonstrate a novel FBA module (FBAM) employing cost-effective distributed feedback (DFB) pump lasers assisted by a digital phase locking scheme based on a field programmable gated array. The new FBAM is compact, cost-effective, and directly applicable to different bands, which opens up new opportunities to establish a frequency metrology infrastructure within existing telecommunication fiber networks. Additionally, the small-footprint of the DFB-FBAM allows for frequent amplification stages with lower pump power to reach continental scale optical metrology links with an optimized signal-to-noise ratio. We characterized the DFB-FBAM’s frequency transfer uncertainty using a two-way layout over an in-lab 100 km long optical fiber link and reach a fractional frequency instability of 9.3 × 10−22 at a 10 ks integration time. The DFB-FBAM characterizations show uncertainty contributions of (−2.1 ± 3.3) × 10−22 and below for averaging times &amp;gt;100 ks. For the first time, we assess the temporal Brillouin frequency shift variations in an underground fiber link and implement a scheme to track these changes in a remote FBAM.

Discrete amplified sensing of temperature and strain

In this paper, a parallel connected optical fiber interferometer is proposed, aiming to improve the strain and temperature sensitivity by using the Vernier effect (VE). The sensor is fabricated by an optimized 3 × 2 step manufacturing process, and implements simple and cost-effective techniques such as cleaving, splicing and gluing. The sensor consists of two Fabry–Perot interferometers (FPIs) with different propagation media, one is air and the other is a SiO2 suspension core, named C1 and C2 respectively. Separate FPIs are used as sensing units in temperature and strain sensing, and another FPI is used as a reference unit. It is proved that when the fine fringe of FPI is redshifted, the envelope is blueshift when the FPI with a large free spectral range (FSR) is used as the sensing unit, the envelope is redshift when the FPI with a small FSR is used as the sensing unit. The results show that the temperature and strain sensitivities are 188.38pm/°C and 201.18pm/μɛ, with amplification factors of 21.2 and 19.6, respectively. In addition, the sensor has a very low cross-sensitivity because C1 is far from the temperature environment and the free end of C2 cannot be fixed for strain measurement.

Temperature-induced inconsistency in the pressure sensitivity of polymer-diaphragm-based FP pressure sensors

Fiber optic Fabry-Perot Interferometer benefits many requirements in pressure sensing. The variation of pressure sensitivity of the polymer-diaphragm-based Fabry-Perot pressure sensor with temperature is studied by investigating the thermal effect of the cavity air and the diaphragm separately. FP cavity vacuum treatment and multi-curvature diaphragm simulation and experimental studies are conducted. Experimental results show that the sensor pressure sensitivity decreases with increasing temperature by 0.46nm/(kPa·°C). The diaphragm’s thermal effect is the leading cause of temperature-induced inconsistency in pressure sensitivity, accounting for 0.43nm/(kPa·°C).

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 105, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 105 CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Amplified Photothermal Phase Modulation for Carbon Dioxide Detection by Operating a Dual-Mode Interferometer at Destructive Interference.

Photothermal interferometry is a highly sensitive spectroscopic technique for trace gas detection. However, the performance of the state-of-the-art laser spectroscopic sensors is still insufficient for some high-precision applications. Here, we demonstrate optical phase-modulation amplification by operating a dual-mode optical fiber interferometer at destructive interference for ultrasensitive carbon dioxide detection. With a 50 cm long dual-mode hollow-core fiber, amplification of photothermal phase modulation by a factor of nearly 20 is achieved, which enables carbon dioxide detection down to 1 parts-per-billion with a dynamic range of over 7 orders of magnitude. This technique could be readily used to improve the sensitivity of phase modulation-based sensors with a compact and simple configuration.

In-fiber interferometry sensors for refractive index

Compact interferometers based on waveguiding structures have found countless applications in refractive index measurements, chemical sensing, as well as temperature and pressure measurements. The most common fiber devices are based on Mach–Zehnder interferometry and Michelson interferometry—two design concepts that can readily be implemented using simple fiber optic components, such as mode splitters and combiners, fiber optic gratings, and fiber tapers, among others. Fiber interferometry can also be conducted based on the Sagnac effect and the Young (double-slit) interferometer. In this review, we examine and compare over 400 fiber optic interferometers as well as more than 60 fiber optic refractive sensors based on fiber optic cavities. Even though many of the devices show temperature-, strain-, and pressure-sensitivity, we focus our review on refractive index measurements, as these are the most common applications. Many devices were characterized by their inventors using their sensitivity to refractive index changes. While the sensitivity is an important characteristic of the device, it does not easily relate to the smallest resolvable refractive index change or the limit of detection when applied to chemical measurements. Instead, we propose here that one should use the figure of merit, which is defined through the refractive index sensitivity and the width of an interferometer fringe. Using simple assumptions, we were able to mathematically relate the sensitivity and the figure of merit to common design parameters, such as the length of the interferometer arms, the operating wavelength, refractive indices of the fiber and the sample, as well as an overlap parameter, which describes the fraction of the guided wave in the sensing arm that interacts with the sample. We determined this overlap parameter for each reviewed device from the reported interferograms. Our meta-analysis provides for the first time simple and easily applicable guidance to increase the figure of merit of fiber optic interferometers and fiber optic cavities with regard to their ability to detect small refractive index changes. A high figure of merit allows measuring very small refractive index changes such as those of gases at different pressures or of very dilute solutions.

Polyacrylic Acid/Polyaniline-Coated Multimode Interferometer for Ammonia Detection.

A coaxial optical fiber interferometer (COFI) is proposed here for ammonia sensing, which comprises two light-carrying single-mode fibers (SMF) fused to a section of no-core fiber (NCF), thus forming an optical interferometer. The outer surface of the COFI is coated with a layer of polyacrylic acid (PAA)/polyaniline (PAni) film. The refractive index (RI) of the sensitive layer varies when PAA/PAni interacts with ammonia, which leads to the resonance wavelength shift. The surface morphology and structure of the PAA/PAni composites were characterized by using a scanning electron microscope (SEM) and Fourier-transform infrared (FTIR) spectroscopy. When the sensor was exposed to an ammonia atmosphere of different concentrations at room temperature, the sensing performance of the PAA/PAni composite film was superior to that of a sensitive film formed by single-component PAA or PAni. According to the experimental results, the composite film formed by 5 wt% PAA mixed with 2 wt% PAni shows better performance when used for ammonia sensing. A maximum sensitivity of 9.8 pm/ppm was obtained under the ammonia concentration of 50 ppm. In addition, the sensor shows good performance in response time (100 s) and recovery time (180 s) and has good stability and selectivity. The proposed optical fiber ammonia sensor is adapted to monitor leakage in its production, storage, transportation, and application.

Angular accelerometer based on a dual-polarization fiber-optic Sagnac interferometer.

High-performance angular accelerometers are essential for precise dynamics control of aircraft, satellites, etc. Here, we propose, for the first time to the best of our knowledge, an angular accelerometer based on a dual-polarization fiber-optic Sagnac interferometer, which exhibits relatively high sensitivity and a broad bandwidth. The experimental results show that the angular accelerometer achieves a flat frequency response in the bandwidth range of 0.01-100 Hz. The sensitivity reaches 6.6 × 10-8 rad/s2/Hz. In addition, the proposed fiber-optic angular accelerometer does not rely on any mechanical structure and has strong environmental adaptability. This research provides a feasible solution for the design and implementation of new high-performance angular accelerometers, which contributes to their development in the fields of inertial navigation and rotational seismology.

Self-calibration phase demodulation scheme for stabilization based on an auxiliary reference fiber-optic interferometer and ellipse fitting algorithm.

To solve the problem of light source jitter and asymmetric 3 × 3 coupler, a phase demodulation method with the combination of an auxiliary reference interferometer and elliptic fitting algorithm is proposed, which is verified by simulation and experiment. By introducing additional phase modulation in the auxiliary reference interferometer, the parameters of the sensing arm can be calibrated in real time, which ensures the effective operation of elliptic fitting algorithm in small signal measurement. Consequently, the experiments show that the self-calibration scheme enables a higher signal to noise and distortion ratio with an average increase of 1.65 dB and 10.47 dB compared with the traditional Arctan and cross multiplication differential, respectively. Meanwhile, the self-calibration scheme can also effectively suppress the harmonic distortion, with a total harmonic distortion of -33.64 dB in the case of small signal.

Phase-shifted demodulation scheme for fiber-optic interferometric sensors with combined waveform phase modulation

We propose and demonstrate a demodulation scheme for interferometric optical fiber sensing using combined waveform phase modulation. The method is based on a designed combined waveform and time-division separation technology, which moves the target signal to the sidebands of the carrier signal and eliminates the influence of residual direct current (DC) term and low-frequency intensity noise by filtering the detector signal directly. The effect of the modulation-to-target ratio (MTR) defined as the ratio of the modulation frequency to the target frequency on the demodulation results is also discussed. Both simulations and experiments verify the ability to obtain a pair of quadrature signals. The experimental results indicate that the phase resolution of the system is 1.1 × 10−6 rad/√Hz@2 kHz when the MTR is 625, and 5 × 10−6 rad/√Hz@2 kHz when the MTR is 25, while demonstrating excellent demodulation consistency. This work not only has the advantages of carrier modulation methods, but also does not need to generate analog signals for mixing, which provides guidance for high-sensitivity phase demodulation technology.

Zastosowanie światłowodowego interferometru różnicowego w pomiarach natężenia prądu elektrycznego

The article presents an electric current sensor built of a fiber-optic differential interferometer using the Faraday effect in a single-mode fiber. It was applied to measure current waveforms with large amplitudes and mains frequency. The optical sensor does not introduce additional resistance and inductance into the measured circuit, which is a desirable phenomenon in this type of measurements. The magnetosensitive element is an optical fiber coil made of a quartz single-mode telecommunications fiber. The optical fiber, in which the core is twisted around its axis, is characterized by a small influence of disturbing quantities, i.e., mechanical vibrations and pressure changes, on the working of the differential interferometer by inducing linear birefringence in the glass fiber. The methods of elimination of the quantities influencing the operation of the optical fiber current sensor were proposed by reducing the linear birefringence induced in the optical fiber from these quantities. The dependence of the normalized light intensity was plotted. The results of experimental research on a design solution of a differential interferometer based on the Faraday effect, operating at a wavelength of 1550 nm, are presented. The sensor was used for measurements of sinusoidal current with a frequency of 50 Hz and amplitudes ranging 100–1500 A. The uncertainty of measurement of the electric current amplitude was determined in the range of the measured values, which was estimated at no more than 1.5 %.

МЕТОД ГЕНЕРАЦИИ СВЕРХШИРОКОПОЛОСНЫХ СВЧ-СИГНАЛОВ С ЛИНЕЙНО-ЧАСТОТНОЙ МОДУЛЯЦИЕЙ НА ОСНОВЕ САМОГЕТЕРОДИНИРОВАНИЯ ИЗЛУЧЕНИЯ ЛАЗЕРНОГО ДИОДА

In this paper, microwave photonic technique of ultrawideband linearly frequency modulated signals generation is proposed. The proposed method based on direct modulation of the laser diode current, which provides a periodic change in the emission frequency. The Michelson interferometer summarizes laser signal and its replica with time delay exceeding 10 ms, which, in turn, is defined by time difference between arms. Optoelectronic conversion is performed in high-speed high-power photodiode. The proposed approach makes it possible to generate microwave signals with linear frequency modulation in the frequency range up to several tens of gigahertz by means of laser pump current modulation in the frequency range less than 100 MHz. The method of ultra-wideband microwave signals generation is implemented using a Michelson fiber-optic interferometer with Faraday mirrors. Such interferometer topology provides a doubling of the path length, and reduced gyroscopic effects due to a counter-propagating double pass. Changing the parameters of the generated microwave ultrawideband signals with frequency modulation is achieved by pump current shape and amplitude control. It is also proposed to use real-time oscilloscope without need of changing of the internal structure of such generator to pre-tune it. Time-frequency analysis is used to extract frequency versus time dependence. By so doing, direct impulse response estimation is performed. This method allows to characterize laser diode frequency response for arbitrary microwave waveform generation by means of pump current waveform calculation from experimental data.

Strain optical fiber sensor with modified sensitivity based on the vernier effect

An optical fiber strain sensor with adjustable sensitivity is proposed and demonstrated. The strain sensing setup employs a fiber optic Michelson interferometer (sensing element) and an extrinsic Fabry–Perot interferometer, in which both structures excited the Vernier effect. By adjusting the cavity length of the extrinsic Fabry–Perot interferometer, it is possible to control the M-factor. The set-up offers both sensitivity enhancement and magnification mode, where the maximal sensitivity is 4.38 pm/με (M-factor = 2.3). This design improves the sensor performance and its implementation is not intricate.