Ultrahigh-resolution and ultra-simple fiber-optic sensor with resonant Sagnac interferometer.

The resonant fiber-optic sensor (RFOS) is well known for its high sensing resolution but usually suffers from high cost and system complexity. In this Letter, we propose an ultra-simple white-light-driven RFOS with a resonant Sagnac interferometer. By superimposing the output of multiple equivalent Sagnac interferometers, the strain signal is amplified during the resonance. A 3 × 3 coupler is employed for demodulation, by which the signal under test can be read out directly without any modulation. With 1 km delay fiber and ultra-simple configuration, a strain resolution of 28f ε/Hz at 5 kHz is demonstrated in the experiment, which is among the highest, to the best of our knowledge, resolution optical fiber strain sensors.

Parameter optimization of hollow-core optical fiber phase modulators.

We studied the effect of varying gas concentration, buffer gas, length, and type of fibers on the performance of optical fiber photothermal phase modulators based on C2H2-filled hollow-core fibers. For the same control power level, the phase modulator with Ar as the buffer gas achieves the largest phase modulation. For a fixed length of hollow-core fiber, there exists an optimal C2H2 concentration that achieves the largest phase modulation. With a 23-cm-long anti-resonant hollow-core fiber filled with 12.5% C2H2 balanced with Ar, phase modulation of π-rad at 100 kHz is achieved with a control power of 200 mW. The modulation bandwidth of the phase modulator is 150 kHz. The modulation bandwidth is extended to ∼1.1 MHz with a photonic bandgap hollow-core fiber of the same length filled with the same gas mixture. The measured rise and fall time of the photonic bandgap hollow-core fiber phase modulator are 0.57 µs and 0.55 µs, respectively.

Quasi-distributed fiber-optic acoustic sensor based on a low coherence light source: publisher's note.

This publisher's note contains a correction to Opt. Lett.47, 3780 (2022)10.1364/OL.464020.

Femto-strain resolution fiber-optic sensing with an ultra-simple white-light round trip filtering method.

In the past decade, laser-driven resonant fiber-optic sensors (RFOSs) have been reported touching their ultimate resolution limit. The practicability of these high-performance sensors is, however, discounted because of high system complexity and dependence on narrow-linewidth lasers. In this paper, a novel, to the best of our knowledge, white-light-driven RFOS is established based on a round trip filtering (RTF) method. Via measuring the RTF loss of an add-drop fiber ring resonator (FRR) sensor, strain signal can be read out with an ultra-simple open-loop configuration. In the sensing experiment, even a resolution of several femto-strain around 1 kHz is demonstrated, representing the highest resolution level of RFOS to date. Thanks to the obvious superiority in both resolution, simplicity, and cost over traditional laser-driven RFOSs, the proposed white-light-driven RFOS is believed to be a milestone in the development of fiber-optic strain sensors.

Quasi-distributed fiber-optic acoustic sensor based on a low coherence light source.

A quasi-distributed acoustic sensor using in-line weak reflectors and a low coherence light source is presented. The dynamic strain is retrieved from the phase change of the two interfering light beams reflected by the same weak reflector. In the experiments, two vibrations at different channels along a weak reflector array are successfully detected simultaneously. A strain resolution of 50 pɛ/H z with 20-m interval is achieved in experiments, and no cross talk is observed. With simple system configuration and low cost, this approach provides a new, to the best of our knowledge, solution for quasi-distributed acoustic sensing.

Pico-strain resolution fiber-optic sensor with white-light interferometry.

The fiber Bragg grating (FBG) sensor is well known for simple fabrication, absolute measurement, inherent multiplexing capability, etc. To date, most FBG sensors that use a broadband light source for demodulation can only achieve resolution at the µÉ› level. In this Letter, we propose a white-light-driven self-reference sensing system with FBGs, using a Mach-Zehnder interferometer (MZI) and a white light source, to realize multiplexed high-resolution vibration sensing with a very simple system configuration. A strain resolution of 35p ε/Hz at 1 kHz is demonstrated, which is several orders of magnitude better than the current FBG sensor systems with white light sources. The performance of the sensing system is analyzed, and multiplexing capability is also experimentally evaluated; there is no observable cross talk.

Ultrahigh-resolution optical vector analyzer for multiple parallel measurements based on frequency-domain analysis.

An ultrahigh-resolution optical vector analyzer (OVA) is reported for multiple parallel measurements based on frequency-domain analysis (FDA). In the proposed system, an optical linearly frequency modulated waveform generated via electro-optic modulation and optical injection locking is launched into an unbalanced Mach-Zehnder interferometer (MZI), in which multiple devices under test (DUTs) are cascaded with different time delays in one arm and a delay reference line in the other arm. The optical signals from the two arms of the MZI are sent to a balanced photo-detector, where a series of electrical signals with different frequencies is generated. With the use of the FDA, the optical spectral response of the DUTs can be separately extracted from the generated electrical signals. An experimental demonstration is performed, in which the frequency responses of a hydrogen cyanide (HCN) gas cell, a phase-shifted fiber Bragg grating, and an optical reflector are characterized simultaneously. The measurement results show that the proposed OVA has a simultaneous characterization capacity of multiple devices at a frequency resolution as high as 200 kHz, a measurement time as short as 490 µs, and a frequency measurement range as wide as 18.5 GHz.

White-light-driven resonant fiber-optic gyro based on round trip filtering scheme.

As the second generation of the fiber-optic gyro (FOG), a resonant FOG (RFOG) appears as a very viable candidate for a miniaturized optical gyro. However, due to the impediment of laser-induced parasitic noise and system complexity, the actual performance of the RFOG is well below expectations. This paper proposes a novel, to the best of our knowledge, RFOG which is driven by broadband white light rather than a narrow linewidth laser. The fiber-optic ring resonator (FRR) works as a filter, and the rotation under detection is read out from the round trip loss of the FRR. The parasitic noise is effectively avoided due to the low coherence light, and the measuring resolution can be thus improved. In the experiment, a bias instability of 0.012 ∘/h is demonstrated with a 100-m fiber coil and a very simple structure. The proposed method would be a big step forward for making the RFOG practical with high performance and low cost.

Single-exposure multi-wavelength diffraction imaging with blazed grating.

Multi-wavelength diffraction imaging is a lensless, high-resolution imaging technology. To avoid multiple exposures and enable high-speed data collection, here an innovative setup for the single-exposure multi-wavelength diffraction imaging based on a blazed grating is proposed. Since the blazed angle varies with the wavelength, the diffraction patterns for the individual wavelengths can be separated from each other and recorded in a single measurement at one time. A method of high-precision position alignment between different wavelength patterns is proposed in our system to achieve good image quality and high resolution. Experiments on a phase-only USAF resolution target and biological samples were carried out to verify the effectiveness of our proposed method. This proposed setup has such advantages as a simpler structure, fast recording, and algorithm robustness.

Complete modal decomposition of a few-mode fiber based on ptychography technology.

An exact modal decomposition method plays an important role in revealing the modal characteristics of a few-mode fiber, and it is widely used in various applications ranging from imaging to telecommunications. Here, ptychography technology is successfully used to achieve modal decomposition of a few-mode fiber. In our method, the complex amplitude information of the test fiber can be recovered by ptychography, and then the amplitude weight of each eigenmode and the relative phase between different eigenmodes can be easily calculated by modal orthogonal projection operations. In addition, we also propose a simple and effective method to realize coordinate alignment. Numerical simulations and optical experiments validate the reliability and feasibility of the approach.

Resonant fiber-optic strain and temperature sensor achieving thermal-noise-limit resolution.

In the area of fiber-optic sensors (FOSs), the past decade witnessed great efforts to challenge the thermal-noise-level sensing resolution for passive FOS. Several attempts were reported claiming the arrival of thermal-noise-level resolution, while the realization of thermal-noise-level resolution for passive FOSs is still controversial and challenging. In this paper, an ultrahigh-resolution FOS system is presented with a sensing resolution better than existing high-resolution passive FOSs. A fiber Fabry-Perot interferometer as the sensing element is interrogated with an ultra-stable probe laser by using the Pound-Drever-Hall technique. Both strain and temperature measurements are carried out to validate the performance of the sensor. The measured noise floor agrees with the theoretical thermal noise level very well.

White-light-driven resonant fiber-optic strain sensor.

Recently, laser-driven resonant fiber-optic sensors (FOSs) have been reported to reach the ultimate resolution limit, set by the thermal noise in fiber. However, they are still far away from commercialization because of their dependence on expensive and ultra-narrow-linewidth lasers. In this Letter, a white-light-driven resonant FOS is proposed for the first time, to the best of our knowledge. By using the white-light multi-beam interferometry, the resonant peaks of a fiber Fabry-Perot interferometer sensor are obtained, and the resonance drifts are tracked for sensor readout by using the Pound-Drever-Hall technique. The proposed FOS is adopted for strain measurement, and the achieved strain resolution (0.9pε/√Hz at 100 Hz) is comparable with that of laser-driven FOSs.

Miniature interrogator for multiplexed FBG strain sensors based on a thermally tunable microring resonator array.

We present a high-resolution and miniature multi-wavelength Fiber Bragg Grating (FBG) interrogator based on a thermally tunable microring resonator (MRR) array. A phase detection method using dithering signals is exploited to generate an antisymmetric error signal curve, which is utilized for the feedback locking of the MRR with the FBG sensor. Dynamic strain sensing of both single FBG and multiple FBGs are experimentally demonstrated, with a dynamic strain resolution of 30 nε/√Hz over 100 Hz to 1 kHz. The proposed interrogator shows the great improvements in both resolution and wavelength accuracy compared with the reported MRR-based interrogators and is promising for scalable multiplexed sensing applications.