Fiber-based Interferometer Research Articles

Noise analysis of the fiber-based vibration detection system.

Detecting seismic events using a fiber-based CW laser interferometer attracts wide attention. To make the detection more effective, we analyze the system's noise level by setting up two vibration detection systems. By changing the fiber length (0∼100 km) and laser noise level, respectively, we detect the minor phase change caused by a 160 µm-fiber-length vibration. Furthermore, we use three indicators, Power Spectral Density, Background Noise Level, and Signal-to-Noise Ratio to analyze the noise level of the whole system. The relation between the system's background noise and corresponding detection result is carried out. This quantitative research can serve as a reference and help people to realize the most efficient vibration detection system.

Bias twisting in side-tapered PMF Sagnac loop interferometer for simultaneous measurement of directional torsion and temperature.

The polarization-maintaining fiber-based Sagnac loop interferometer (PSLI) is frequently applied in directional torsion measurement, but may suffer from a large temperature cross talk. In this study, a novel method was proposed for fabrication of side-tapered PSLI by a two-step arc-discharge technique at the splicing point. The energy distribution of the taper region was characterized, and comprehensive tests were performed in terms of torsion and temperature. The experimental results showed that, through bias twisting, the measuring areas were effectively gapped and highly sensitive torsion and temperature responses were gained simultaneously. With a small wavelength shift, the torsion sensitivity reached 13.54 dB/rad in the range from -30 to 30 rad/m. Moreover, the temperature sensitivity was found to be -1.579nm/∘C, with a near-zero intensity fluctuation. Therefore, the sensor fabricated herein successfully achieves simultaneous measurement of directional torsion and temperature with high sensitivity and ultralow cross talk. The proposed scheme has the merits of practicality, low cost, and ease of operation, and is very promising for multiparameter engineering monitoring.

Dual-Core Fiber-Based Interferometer for Detection of Gas Refractive Index

We demonstrate a dual-core fiber-based Mach–Zehnder interferometer that could be used for precise detection of variations in refractive indices of gaseous samples. The fiber used here have a solid germanium-doped silica core and an air core that allows gases to flow through. Coherent laser beams are coupled to the two cores, respectively, and thus excite guiding modes thereby. Interferogram would be produced as the light transmitted from the dual cores interferes. Variations in refractive index of the hollow core lead to variations in phase difference between the modes in the two cores, thus shifting the interference fringes. The fringe shifts can be then interrogated by a photodiode together with a narrow slit in front. The resolution of the sensor was found to be ~1 × 10−8 RIU, that is comparable to the highest resolution obtained by other fiber sensors reported in previous literatures. Other advantages of our sensor include very low cost, high sensitivity, straightforward sensing mechanism, and ease of fabrication.

Wide wavelength-tunable passive mode-locked Erbium-doped fiber laser with a SESAM

In this work we present a simple polarization-maintaining wavelength-tunable passive mode-locked Erbium-doped fiber laser with a semiconductor saturable absorber mirror (SESAM) as a mode locker. The cavity includes a Sagnac interferometer-based fiber optical loop mirror (FOLM) as a wide wavelength-tunable filter. Tunable mode-locking was experimentally achieved in the range of 1543.2 nm to 1569.5 nm by thermally adjustment of FOLM wavelength reflection. The output pulses have a repetition rate of 11.16 MHz with pulse duration about 0.9 ps. The experimental results were confirmed by numerical simulations.

Dynamic Imaging of Mouse Embryos and Cardiac Development in Static Culture.

Dynamic imaging is a powerful approach to assess the function of a developing organ system. The heart is a dynamic organ that undergoes quickmorphological and mechanical changes through early embryonic development. Defining the embyonic mouseheart'snormal function is important for our ownunderstanding of human heartdevelopment and will inform us on treatments and prevention of congenital heart defects (CHD). Traditional methods such as ultrasound or fluorescence-based microscopy are suitablefor live dynamic imaging, are excellent to visualize structure and connect gene expression to phenotypes, but can be of low quality in resolving fine features and lack imaging depth and scale to fully appreciate organ morphogenesis. Additionally, previous methods can be limited in accommodating a live imaging apparatus capable of sustaining whole embryo development for extended periods time. Optical coherence tomography (OCT) is unique in this circumstance because acquisition of three-dimensional images without contrast reagents, at single cell resolution make it a suitablemodality to visualize fine structures in the developing embryo. OCT setups are highly customizable for live imaging because of the tethered imaging arm, due to its setup as a fiber-based interferometer. OCT allows for 4D (3D+time) functional imaging of living mouse embryos and can provide functional and mechanical information to ascertain how the heart's pump function changes through development. In this chapter, we will focus on how we use OCT to visualize live heart dynamics at different stages of development and provide mechanical information to reveal functional properties of the developing heart.

Development of Collagen-IV Sensor Using Optical Fiber-Based Mach-Zehnder Interferometer Structure

This study presents a label-free and efficient method for the diagnosis of collagen-IV by using an optical fiber-based Mach-Zehnder interferometer (MZI) structure. The structure of MZI is fabricated by splicing a 2.3 cm long segment of single-mode fiber (SMF) between two ~ 45 cm strands of multi-mode fibers (MMF). Owing to the mismatch of core diameters, cladding of SMF guides the light. SMF's cladding is partially etched by using 40% hydrofluoric (HF) acid so that a part of propagating energy is released that can interplay with the surroundings. The etched region is immobilized with ~ 10 nm size of gold nanoparticles (AuNPs) and ~ 50 nm size of copper oxide nanoparticles (CuO-NPs) to initiate the influence of localized surface plasmon resonance (LSPR) phenomenon. For a comparative study, two different probes are developed and analyzed. In one probe, CuO NPs are immobilized over the etched part of SMF and named as CuO-NPs probe. In other probe, a monolayer of AuNPs is sandwiched between fiber surface and CuO-NPs and termed as AuNPs/CuO-NPs probe. The characterization of NPs and developed sensor probe are performed using UV-Vis spectroscopy, high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and energy distribution spectroscopy (EDS). The sensor probes are made very specific towards collagen-IV by functionalizing them with collagenase enzyme obtained from Clostridium histolyticum. A wide range of Collagen-IV solutions of concentrations from 2 μm/ml to 40 μm/ml are sensed through the collagenase functionalized probe. The specificity of the probes are analyzed by sensing other biomolecules present in the human body.

Detection of Collagen-IV Using Highly Reflective Metal Nanoparticles-Immobilized Photosensitive Optical Fiber-Based MZI Structure.

In this work, a photosensitive (PS) optical fiber-based Mach-Zehnder interferometer (MZI) structure is developed to diagnose the presence of collagen-IV in human bodies. The MZI is fabricated by sequentially splicing the single mode-multimode-photosensitive-multimode-single mode (SMPMS) fiber segments. The sensing region in MZI structure is created by partially removing the cladding of photosensitive fiber by using 40% hydrofluoric (HF) acid and depositing the layers of highly reflective metal nanoparticles (NPs) over it. The used NPs are polyvinyl alcohol stabilized silver nanoparticles (PVA-AgNPs), gold nanoparticles (AuNPs), and zinc oxide nanoparticles (ZnO-NPs). The size of AuNPs, PVA-AgNPs, and ZnO-NPs are 10 ± 0.2 nm, ∼ 4 -5 nm, and < 50 nm, respectively. In order to avoid the interference of other biomolecules in the detection of collagen-IV, the sensing region is functionalized with a collagenase enzyme. The sensing ability of the probe is ascertained by sensing a wide concentration of collagen solution ranging from 0 ng/ml to [Formula: see text]/ml. It is observed that sensing performance of probe is much better on immobilizing it with PVA-AgNPs and ZnO-NPs.

Generation of pure-state single photons with high heralding efficiency by using a three-stage nonlinear interferometer

We experimentally study a fiber-based three-stage nonlinear interferometer and demonstrate its application in generating heralded single photons with high efficiency and purity by spectral engineering. We obtain a heralding efficiency of 90% at a brightness of 0.039 photons/pulse. The purity of the source is checked by two-photon Hong-Ou-Mandel interference with a visibility of 95 ± 6% (after correcting Raman scattering and multi-pair events). Our investigation indicates that the heralded source of single photons produced by the three-stage nonlinear interferometer has the advantages of high purity, high heralding efficiency, high brightness, and flexibility in wavelength and bandwidth selection.

Angled fiber-based Fabry–Perot interferometer

Herein, we propose and experimentally demonstrate a novel, to the best of our knowledge, all-fiber Fabry–Perot (FP) interferometer that is formed by a simple angled fiber that can function as a beam splitter. According to the principle of the angled fiber, we verify the influence of an oblique angle on the light propagation path and light intensity ratio. Subsequently, angled fiber-based FP interferometers are experimentally demonstrated, and the influence of the oblique angle on the visibility of interference fringes and temperature characteristics is investigated. Finally, the temperature characteristics of this proposed FP interferometer are investigated experimentally, and the temperature sensitivity is 12.62 and 10.89 pm/°C for 42° and 40° angled fiber-based fiber FP interferometers, respectively. This proposed FP interferometer is fabricated by using a simple angled fiber, which has the advantages of ease of fabrication and all-fiber characteristics and hence can meet the requirements of mass production and high stability in various practical application areas.

The Thermal Phase Sensitivity of Both Coated and Uncoated Standard and Hollow Core Fibers Down to Cryogenic Temperatures

The thermal phase sensitivity of an optical fiber quantifies the degree to which a change in ambient temperature modifies the accumulated phase of light propagating through it. This sensitivity is often the limiting factor to the performance of fiber-based interferometers. Here we compare the thermal phase sensitivity of a hollow core fiber (HCF) and a standard single mode fiber (SMF-28) from −180 °C up to the room temperature. We report measurements on fibers both with and without acrylate coating that enables an accurate estimation of the coating contribution. The thermal phase sensitivity of fibers without any coating decreases at low temperatures. For SMF-28 it is reduced by a factor of four at −180 °C as compared to the room temperature. For HCF, the thermal phase sensitivity becomes negative at low temperatures, crossing zero around −70 °C, making the HCF operated at that temperature fully insensitive to small temperature fluctuations. The coating significantly influences a fibers overall thermal phase sensitivity, especially at low temperatures, since it goes through a phase transition from a rubbery state at room temperature to stiff glassy state at low temperatures. We quantify the coating contribution and suggest fiber coating design rules to obtain fibers with reduced or even zero thermal phase sensitivity.

Performance Optimization of Fiber Optic Interferometric Accelerometer Based on Phase Noise Analysis

The phase noise of a Michelson interferometer-based fiber optic accelerometer is analyzed to determine the optimal modulation depth of the laser light frequency and the length difference between the interference arms. The output intensity fluctuation of the interferometer, originating from the phase noise of the modulated laser source, is examined theoretically, revealing that both the interference intensity noise power and the phase modulation depth of the interferometer are proportional to the frequency modulation depth of the laser and the interference arm length difference. In addition, it is determined experimentally that the laser linewidth, or equivalently, the laser phase noise, varies approximate linearly with the light frequency. As the optimum phase modulation depth is a constant, the interference intensity noise power has a minimum value, when the light frequency modulation depth is at its maximum. The proposed theory is demonstrated experimentally, with results showing that a high-performance broadband fiber optic interferometric accelerometer achieves the lowest noise level when the light frequency modulation depth of the source laser is at its maximum value.

Development of Digital Holographic Microscopy on an All-Optical Phase Shifter

We propose an all-optical phase-shifting method using Yb-doped optical fibers and demonstrate its potential in on-axis digital holography microscopy (DHM) system. The Yb-doped optical fiber induces a phase change under optical pumping conditions. The induced phase shift shows a good linear response to applied pumping currents, and N-step phase-shifting up to 2p can be properly performed. Four-, six-, and eight-step phase-shifting methods are performed, and the phase retrievals from their phase-shifted interferograms are achieved using an interframe correlation matrix method. An 8-step phase shifting-based reconstruction, which is effective for background noise reduction, is used for 3D imaging of an indium tin oxide (ITO) thin film and an organic light-emitting diode (OLED) thin film. The reconstructed surface profile was in agreement with the step structure of the samples. The proposed all-optical phase-shifting method is expected to be applied to various optical imaging systems using fiber-based phase-shifting interferometers.

Fiber-Based Large Dynamic Range Vibration Sensing With Dual-Wavelength Phase Unwrapping

A large dynamic range vibration sensor is demonstrated with a fiber-based Mach-Zehnder interferometer, in combination with the 3 × 3 fiber coupler based phase demodulation and dual-wavelength linear regression phase unwrapping. Due to the relief of the π-phase constraint in the digital phase demodulation, the measurement range of the vibration sensor is significantly enlarged, with a phase noise level the same as that of the single-wavelength technique. A sampling rate much higher than the Nyquist rate, which is used to limit the phase change within a sampling period, is no longer necessary, and the trade-off between the dynamic range and the measurement bandwidth is eliminated. The proposed vibration sensing system is able to measure signal frequencies ranging from 10 Hz to 7.0 kHz, with almost flat frequency response, good linearity, and a dynamic range independent of frequency.

Fiber Ring Laser Directional Torsion Sensor with Ultra-Wide Linear Response.

In this paper, a comprehensive passive torsion measurement is performed firstly in a 40-cm-long polarization maintaining fiber-based Sagnac interferometer (PMF-SI), and the non-linear torsion response is found and investigated. Then, a fiber laser torsion sensor (FLTS) with a dual-ring-cavity structure is proposed and experimentally demonstrated, in which the PMF-SI is utilized as the optical filter as well as the sensing unit. In particular, the highly sensitive linear range is adjusted through fine phase modulation, and owing to the flat-top feature of fringes, an ~83.6% sensitivity difference is effectively compressed by the generated lasing. The experimental results show that, without any pre-twisting, the ultra-wide linear response from –175 to 175 rad/m is gained, and the torsion sensitivities are 2.46 and 1.55 nm/rad with high linearity (>0.99) in the clockwise and anti-clockwise directions, respectively. Additionally, a high extinction ratio (>42 dB) and small line-width (~0.14 nm) are obtained in the proposed FLTS, and the corresponding detection limit reaches 0.015 rad/m.

Research on temperature sensing characteristics with cascaded fiber Sagnac interferometer and fiber Fabry–Perot interferometer-based fiber laser

We have proposed and experimentally demonstrated a compact temperature sensor based on cascaded fiber Sagnac interferometer (FSI) and fiber Fabry–Perot interferometer (FFPI) with Vernier effect. The FSI is composed of a certain length of panda polarization-maintaining fiber and a 3-dB four-port coupler, whereas FFPI consists of two collimators and a wave plate. Both are used for temperature sensing, but where FSI is more sensitive to temperature than FFPI, the free spectral ranges of the two interferometers differ by 0.12 nm. The experimental results show that the temperature sensitivity is increased from −1.7 nm / ° C (single FSI) and 0.008 nm/°C (single FPI) to 10.28 nm/°C (cascade configuration), which is basically consistent with the theoretical analysis (10.82 nm/°C).

In vivo thickness measurement of the lipid layer and the overall tear film by interferometry.

New approaches for the simultaneous measurement of the thickness of the lipid layer (LL) and overall tear film (TF) in vivo are needed. In the current research, the interference signal from the ocular surface was analyzed and simplified as the superposition of two sinusoidal functions. One function with low frequency was modulated by LL, and the other function with high frequency was modulated by precorneal TF (PCTF). Two sinusoidal functions were separated and analyzed to retrieve the thickness of LL and PCTF. To validate the feasibility of the approach, a customized fiber-based interferometer with a related data processing program was developed and tested in vivo.

Alignment-free dispersion measurement with interfering biphotons.

Measuring the dispersion of photonic devices with small dispersion-length products is challenging due to the phase-sensitive and alignment-intensive nature of conventional methods. In this Letter, we demonstrate a quantum technique to extract the second- and third-order chromatic dispersion of a short single-mode fiber using a fiber-based quantum nonlinear interferometer. The interferometer consists of two cascaded fiber-based biphoton sources, with each source acting as a nonlinear beam splitter. A fiber under test is placed between these two sources and introduces a frequency-dependent phase that is imprinted on the biphoton spectrum (interferogram) at the output of the interferometer. This interferogram contains the dispersion properties of the test fiber. Our technique has three novel features: (1)the broadband nature of the biphoton sources used in our setup allows accurate dispersion measurements on test devices with small dispersion-length products; (2)our all-fiber common-path interferometer requires no beam alignment or phase stabilization; and (3)multiple phase-matching processes supported in our biphoton sources enable dispersion measurements at different wavelengths, which yields the third-order dispersion achieved for the first time, to the best of our knowledge, using a quantum optical technique.

Coherent optical modulation of graphene based on coherent population oscillation.

The optical modulation of graphene circumvents the "electrical bottleneck" in electrical field tuning of the Fermi level and motivates diverse graphene-based controllable photonic devices with extraordinary performances. Unfortunately, pervious optical modulation schemes are incoherent, and the Fermi-Dirac distribution formed from a strong pump laser prevents the absorption of a weak probe laser due to the Pauli blocking, making the modulation inconvenient and low in efficiency. Here we demonstrate the coherent optical modulation of graphene based on coherent population oscillation, where ground state population oscillates with a beat frequency equal to the pump and probe frequency difference. To distinguish it from the coexisting incoherent modulation in graphene, a phase-sensitive pump-probe system is constructed with a fiber-based Mach-Zehnder interferometer. Clear resonance within the burning hole of a pump laser is observed in the interference spectrum of a coherent probe laser. The discovery of highly coherent ground state population oscillation in graphene offers new possibilities for manipulating and controlling the phase response of graphene-based photonics with high efficiency.

Micro-structured fibers and their applications in fiber-optic sensors and random fiber lasers

Micro-structured fibers are important devices that have drawn intensive attentions and proved to be powerful platforms for various applications over the past decades due to their remarkable merits and advantages, such as small footprint, immunity to electromagnetic interferences, light weight, high physical flexibility, and low cost. Modifications in optical fibers can be used as light-steering elements to excite and couple back different core and cladding modes and form various in-fiber structures, including in-line fiber interferometer, fiber micro-cantilever, fiber random gratings, and so on. These micro-structures, when applied as fiber-optic sensors in the presence of external disturbances, show high sensitivity in terms of the significant changes in the guided light features. Novel micro-structured bend-insensitive fiber-based in-line fiber interferometer and micro-cantilever have been proposed to realize both static and dynamic parameter measurements, including temperature, axial strain, surrounding refractive index, and vibration. We have also developed a novel fiber random grating along with a spectral correlation algorithm for simultaneous measurement of three static measurands. To move a step forward, random fiber lasers based on fiber random grating are achieved for either improving the laser performances or sensing applications of temperature, strain, and ultrasound measurements with high sensitivity.

Improving the accuracy of a dual-comb interferometer by suppressing the relative linewidth

We present a compact system of synchronization for two fiber-based optical frequency comb lasers. We use a free-running continuous wave laser as an intermediary to obtain the relative noise of two combs and employ an intra-cavity electro-optic modulator (EOM) to achieve active phase feedback for fast synchronization. The EOM bandwidth is 150 kHz and the relative linewidth is suppressed markedly from 300 kHz to sub-hertz values. The relative effective timing jitter of the two pulse trains is also decreased from 680 fs to 25 fs. The proposed method shows promise for developing a high-performance, low-cost, fiber-based dual-comb interferometer for ranging or spectroscopy.