High-finesse Fabry-Perot Interferometer Research Articles

Wavelength Locking and Calibration of Fiber-Optic Ultrasonic Sensors Using Single-Sideband-Modulated Laser

Implementation of edge-filter detection for interrogating optical interferometric ultrasonic sensors is often hindered by the lack of cost-effective laser sources with agile wavelength tunability and good noise performance. The detected signal can also be affected by optical power variations and locking-point drift, negatively affecting the sensor accuracy. Here, we report the use of laser single-sideband generation with a dual-parallel Mach–Zehnder interferometer (DP-MZI) for laser wavelength tuning and locking in edge-filter detection of fiber-optic ultrasonic sensors. We also demonstrate real-time in situ calibration of the sensor response to ultrasound-induced wavelength shift tuning. The DP-MZI is employed to generate a known wavelength modulation of the laser, whose response is used to gauge the sensor response to the ultrasound-induced wavelength shifts in real time and in situ. Experiments were performed on a fiber-optic ultrasonic sensor based on a high-finesse Fabry–Perot interferometer formed by two fiber Bragg gratings. The results demonstrated the effectiveness of the laser locking against laser wavelength drift and temperature variations and the effectiveness of the calibration method against optical power variations and locking-point drift. These techniques can enhance the operational robustness and increase the measurement accuracy of optical ultrasonic sensors.

Ultrahigh-Resolution Fiber-Optic Sensing Based on High-Finesse, Meter-Long Fiber Fabry-Perot Resonators

Ultrahigh-resolution fiber-optic sensing has found a wide range of potential applications. However, the techniques reported so far are all based on highly specialized fiber structures and interrogation lasers, which are not widely available. In this paper, we report the demonstration of ultrahigh strain resolutions using only off-the-shelf commercial components. Our method leverages the high wavelength discrimination of long, high-finesse fiber Fabry-Perot interferometers (FFPI), using two 1 m-long FFPIs, one as the sensor and the other as a frequency reference. By locking the interrogation laser to the reference interferometer, which is co-packaged with the sensor interferometer, large, environment-induced sensing background is removed. This allows the laser to reliably probe the strains applied on the sensor with very high resolutions. A nominal, noise-limited strain resolution of 800 fε/√Hz has been achieved within 1-100 Hz. Strain resolution further improves to 75 fε/√Hz at 1 kHz, 60 fε/√Hz at 2 kHz and 40 fε/√Hz at 23 kHz, demonstrating better resolutions than proven techniques such as π-phase-shifted and slow-light fiber Bragg gratings. The work lays out a cost-effective scheme to achieve ultrahigh-resolution fiber-optic sensing.

A fiber-optic bolometer based on a high-finesse silicon Fabry-Pérot interferometer.

We report a fiber-optic bolometer based on a high-finesse silicon Fabry-Perot interferometer (FPI). The silicon FPI absorbs and converts the incident radiation into temperature variations, which are interrogated by the shift of the reflection spectrum of the FPI. The FPI is a silicon pillar with one side coated with a high-reflectivity dielectric mirror and the other side coated with a gold mirror. A multimode fiber collimator is applied between the FPI and lead-in single-mode fiber to reduce the round-trip diffraction loss, giving rise to a high-finesse of 35 of the FPI. The sensor is demodulated using a low-cost distributed feedback diode laser. A dummy bolometer was used to effectively reduce the common noises from the laser wavelength drift and ambient temperature variations. Experimental results show that, compared with a previously reported fiber-optic bolometer, the one reported here has a 5-fold decrease in noise and a 7-fold increase in responsivity with a noise equivalent power density (NEPD) of 0.27 W/m2, which is comparable with the NEPDs of the state-of-the-art resistive bolometers.

Linewidth of collimated wavelength-converted emission in Rb vapour

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power cw laser radiation at 780 nm and 776 nm and an internally-generated mid-IR field at 5.23 um in Rb vapour. Using a high-finesse Fabry-Perot interferometer the spectral width of the CBL is found to be less than 1.3 MHz for a wide range of experimental conditions. We demonstrate that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom-light interaction itself. Results obtained with frequency modulated laser light allow an upper limit of several hundred kHz to be set for the linewidth of the collimated mid-IR radiation at 5.23 um, which has not been directly detected.

Monostatic coaxial 15 μm laser Doppler velocimeter using a scanning Fabry-Perot interferometer

We present a laser Doppler velocimeter (LDV) in monostatic coaxial arrangement consisting of off-the-shelf telecom-grade components: a single frequency laser (wavelength λ = 1.5 μm) and a high-finesse scanning Fabry-Perot interferometer (sFPI). In contrast to previous 1.5 μm LDV systems based on heterodyne detection, our sFPI-LDV has the advantages of having large remote sensing range not limited by laser coherence, high velocity dynamic range not limited by detector bandwidth and inherent sign discrimination of Doppler shift. The more optically efficient coaxial arrangement where transmitter and receiver optics share a common axis reduces the number of components and greatly simplifies the optical alignment. However, the sensitivity to unwanted backreflections is increased. To circumvent this problem, we employ a custom optical circulator design which compared to commercial fiber-optic circulator achieves ~40 dB reduction in strength of unwanted reflections (i.e. leakage) while maintaining high optical efficiency. Experiments with a solid target demonstrate the performance of the sFPI-LDV system with high sensitivity down to pW level at present update rates up to 10 Hz.

High sensitive extrinsic fabry-perot interferometric sensor system with low cost

A high-sensitive fiber optic strain sensor system with low cost is demonstrated. The strain sensor is a microlens based high finesse Fabry-Perot interferometer, and a low-cost wavelength division coupler is used as a wavelength discriminator. A minor fluctuation of strain is changed to a power change at the output. Static strain and dynamic strain are successfully measured using the system. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 1491-1493, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26057

Dual-frequency sweeping interferometry for absolute metrology of long distances

Frequency sweeping interferometry (FSI) is a technique where absolute distance measurements are made without ambiguity, using synthetic wavelengths resulting from frequency sweeps. Accuracy is mainly dependent on the synthetic wavelength measurement using a Fabry-Perot interferometer to count resonances as frequency sweeps. Measurement uncertainty increases with distance due to propagation of uncertainty in the synthetic wavelength measurement. For large distances, the number of fringes dominates performance, leading to a linear decrease of accuracy with range. To overcome this problem, the dual FSI concept was introduced, where the measurement process for large distances is reduced to the close-range case, by limiting the interferometer optical path difference. This is achieved by increasing the reference arm with a long reference fiber, and using an ancillary interferometer to calibrate the fiber length continuously. This dual FSI concept was implemented and fully tested in view of ESA-PROBA3 space mission. The sensor is composed of an external cavity diode laser, a high-finesse Fabry-Perot interferometer, and a dual measurement system. Accuracies better than 32 µm for a measurement range from 51 to 61 m were achieved using a reference fiber with 71 m, while maintaining the reduced complexity inherent to FSI technique, which is mandatory for space applications.

Measurement of Broadband Temperature-Dependent Ultrasonic Attenuation and Dispersion Using Photoacoustics

The broadband ultrasonic characterization of biological fluids and tissues is important for the continued development and application of high-resolution ultrasound imaging modalities. Here, a photoacoustic technique for the transmission measurement of temperature-dependent ultrasonic attenuation and dispersion is described. The system uses a photoacoustic plane wave source constructed from a polymethylmethacrylate substrate with a thin optically absorbent layer. Broadband ultrasonic waves are generated by illuminating the absorbent layer with nanosecond pulses of laser light. The transmitted ultrasound waves are detected by a planar 7-microm high-finesse Fabry-Perot interferometer. Temperature-induced thickness changes in the Fabry-Perot interferometer are tracked to monitor the sample temperature and maintain the sensor sensitivity. The measured -6 dB bandwidth for the combined source and sensor is 1 to 35 MHz, with an attenuation corrected signal level at 100 MHz of -10 dB. The system is demonstrated through temperature-dependent ultrasound measurements in castor oil and olive oil. Power law attenuation parameters are extracted by fitting the experimental attenuation data to a frequency power law while simultaneously fitting the dispersion data to the corresponding Kramers-Krönig relation. The extracted parameters are compared with other calibration measurements previously reported in the literature.

Accuracy of frequency-sweeping interferometry for absolute distance metrology

Coherent interferometric absolute distance metrology is one of the most interesting techniques for length metrology. Without movement, measurements are made without ambiguity, by using either one or several synthetic wavelengths resulting from the beating of two or more wavelengths (multiple-wavelength interferometry), or a frequency sweep (frequency-sweeping interferometry). Sensors based on the latter are relatively simple devices and can fulfill an important role in dimensional metrology. In addition, their parameterization flexibility allows trade-offs to be performed, either technology-driven or application-related. We present in detail a theoretical model of frequency-sweeping interferometry and its uncertainty budget, discuss different parameterizations, present a method for drift error compensation, and demonstrate and evaluate sensor performance and robustness with a prototype sensor composed of a mode-hop-free frequency-sweep external-cavity diode laser, a high-finesse Fabry-Perot interferometer (to measure accurately the frequency sweep range), homodyne detection, and data processing. Results have shown that the inaccuracy will not exceed 10 µm for distances up to 1 m, at an affordable degree of complexity.

High-precision absolute distance measurement using dual-laser frequency scanned interferometry under realistic conditions

In this paper, we report on new high-precision absolute distance measurements performed with frequency scanned interferometry using a pair of single-mode optical fibers. Absolute distances were determined by counting the interference fringes produced while scanning the frequencies of the two chopped lasers. High-finesse Fabry–Perot interferometers were used to determine frequency changes during scanning. Dual lasers with oppositely scanning directions, combined with a multi-distance-measurement technique previously reported, were used to cancel drift errors and to suppress vibration effects and interference fringe uncertainties. Under realistic conditions, a precision about 0.2 μ m was achieved for a distance of 0.41 m. With a precision that exceeds requirements, the frequency scanned interferometry is a promising high-precision optical alignment technique for International Linear Collider silicon tracker detector.

Experimental characterization of an Yb3+-doped fiber ring laser with frequency-shifted feedback

We present experimental characteristics of an Yb3+-doped fiber ring laser operating with frequency-shifted feedback (FSF) through an acousto-optic modulator (AOM) and seeded by both a stationary continuous-wave (CW) laser and spontaneous emission. We show the spectrum and output characteristics for operations with several effective gain bandwidths, as established by Fabry–Perot etalons inside the cavity. Observation using a high finesse Fabry–Perot interferometer shows that, as expected from earlier work, although the spectrum of the FSF laser without seeding is continuous, when seeded by a CW-laser the spectrum consists of a comb of discrete modes, each offset from the seed by an integer number of AOM frequency shifts. The experimental results are in excellent quantitative agreement with the theory developed earlier [L. Yatsenko, B.W. Shore, K. Bergmann, Opt. Commun. 236 (2004) 183].

High-precision absolute distance and vibration measurement with frequency scanned interferometry

We report high-precision absolute distance and vibration measurements performed with frequency scanned interferometry using a pair of single-mode optical fibers. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. A high-finesse Fabry-Perot interferometer was used to determine frequency changes during scanning. Two multiple-distance-measurement analysis techniques were developed to improve distance precision and to extract the amplitude and frequency of vibrations. Under laboratory conditions, measurement precision of approximately 50 nm was achieved for absolute distances ranging from 0.1 to 0.7 m by use of the first multiple-distance-measurement technique. The second analysis technique has the capability to measure vibration frequencies ranging from 0.1 to 100 Hz with an amplitude as small as a few nanometers without a priori knowledge.

Dynamic models of Fabry-Perot interferometers.

Long-baseline, high-finesse Fabry-Perot interferometers can be used to make distance measurements that are precise enough to detect gravity waves. This level of sensitivity is achieved in part when the interferometer mirrors are isolated dynamically, with pendulum mounts and high-bandwidth cavity length control servos to reduce the effects of seismic noise. We present dynamical models of the cavity fields and signals of Fabry-Perot interferometers for use in the design and evaluation of length control systems for gravity-wave detectors. Models are described and compared with experimental data.

High-sensitivity measurements of the Kerr constant in gases using a Fabry–Pérot-based ellipsometer

The dc-Kerr constant was measured with high sensitivity in several gases, using a novel ellipsometer, which is based on a high-finesse Fabry–Perot interferometer. An effective interaction length of 5.26 km was achieved by using a Fabry–Perot interferometer with intracavity electrodes, yielding a single-pass sensitivity of ≈10 nanoradian. The dc-Kerrconstants of CO2, N2, and O2 were determined with a high accuracy and with good agreement with previous measurements.

Precision stabilization of the optical frequency in a large ring laser gyroscope

Pressure-induced fractional changes of 10(-7) in the geometry of a large He-Ne ring laser gyroscope induce backscatter phase changes and thus a fractional pulling of the Sagnac frequency of ~5 x 10(-3). To counter this, the optical frequency was stabilized against an iodine-stabilized laser with a high-finesse Fabry-Perot interferometer and piezoelectric control of the ring perimeter. This scheme, although limited in principle by residual geometric asymmetry and in practice by low beam powers (10 pW), stabilized the perimeter to 2.4 nm (6 x 10(-10) or 300 kHz for the optical frequency) and the Sagnac frequency to 100 parts per million over several days.

Scanning, spherical-mirror Fabry–Perot interferometer: An upper-division optics laboratory experiment

Students in our upper-division/graduate physical optics laboratory course assemble a high-finesse Fabry–Perot interferometer (FPI) from components, mode-match it to a helium–neon (HeNe) laser, and examine some of the FPI system’s properties and uses. Here, we specify the necessary equipment and describe experimental procedures. For example, the experiments use the FPI’s high spectral resolution to monitor the laser’s behavior as it warms up; in another experimental step, they confront the issue of the photodetection system’s electronic bandwidth. We also provide a review of Gaussian beam formulas and detail their use in mode-matching calculations.

Accurate measurement of the radius of curvature of a concave mirror and the power dependence in a high-finesse Fabry–Perot interferometer

We describe the accurate measurement of the radius of curvature of a concave mirror in a Fabry-Perot interferometer with a finesse of 78,100. The radius of curvature of the concave mirror is determined by measuring the free spectral range and the transverse-mode range with the frequency response functions. The radii of curvature at two orthogonal (x and y) axes on the mirror surface resulting from the polishing nonisotropy were accurately measured to be r(x) = 1008.46 mm and r(y) = 1006.94 mm, respectively, with an accuracy of 8 × 10(-5). This accuracy is the best to our knowledge. The power dependence of the radii of curvature to the cavity internal intensity at a steady state was measured to be dr(x)/dI(c) = +60 µm/(MW/cm(2)) at the x axis and dr(y)/dI(c) = +47 µm/(MW/cm/(2)) at the y axis to an intensity of 2.1 MW/cm(2).

Accurate measurement of ultralow loss in a high-finesse Fabry-Perot interferometer using the frequency response functions

We describe the accurate measurement of ultralow loss in a high-finesse Fabry-Perot interferometer using a diode-pumped Nd:YAG laser locked to the longitudinal mode with an active frequency-stabilization technique. By measuring the resonance full width and the free spectral range with the frequency response functions, and by measuring the transmission efficiency on resonance, the finesse and the loss at 1064 nm are accurately measured to be 78100 ± 1200 (reflectance of 99.99598 ± 0.00006%) and 1 5.9 ±2.0 × 10−6 (15.9 ± 2.0 ppm), respectively.

Fiber Fabry–Perot interferometers with very low polarization sensitivity

The sensitivity to input polarization in long-cavity (1 cm to 5 m) and high-finesse (~ 100) fiber Fabry-Perot interferometers (FFPI's) is reduced from greater than 20 dB to between 0.2 and 0.6 dB in passband amplitude variation by the use of very-low-birefringence fibers. Furthermore the scanning FFPI's could allow very-high-resolution measurement of polarization-mode dispersion in short-length low-birefringence fibers.

Fiber-optic Fabry-Perot interferometer and its sensor applications

Fiber-optic Fabry-Perot interferometers using monomode fibers are fabricated and their basic properties of finesse, polarization, and thermal response are studied. Fiber-optic Fabry-Perot interferometers are applied to the sensors of temperature, mechanical vibration, acoustic wave including human voice, ac voltage, and ac and dc magnetic fields. It has been demonstrated that a fiber-optic Fabry-Perot interferometer can simplify the interferometric fiber sensor system and that high measurement sensitivity can be obtained by using a high-finesse and/or long-distance fiber Fabry-Perot interferometer.