Intermodal Interference Research Articles

High-sensitivity humidity sensor based on Mach-Zehnder interferometer in seven-core fiber

A Mach-Zehnder Interferometer (MZI) based on seven-core fiber (SCF) for humidity sensing is proposed and experimentally demonstrated. The MZI is formed by sandwiched a section of SCF in between two single mode fibers (SMFs), while a fiber taper and a brief multimode fiber (MMF) act as fiber couplers to excite and couple the intermodal interference in the SCF. The optical field distribution and coupling efficiency of the MZI with different SCF lengths are analysed. The theoretical results show that the MZI is sensitive to SCF lengths, and it is expected to obtain highly sensitive humidity response. Humidity sensing experiments shows a high sensitivity of 0.6603 nm/%RH over a relative humidity (RH) range of 44–83 %RH, and the maximum measurement uncertainty introduced by the long-term stability is 0.0006 %RH. Human respiration measurement exhibits the response time and recovery time of the MZI are 0.44 s and 1.24 s respectively. The temperature effect is also experimentally investigated. Such an all-fiber MZI presents advantages of simple configuration, high sensitivity and good stability, making it has potential in humidity measurement fields.

A fiber optic refractive index sensor with temperature compensation based on cascaded Mach-Zehnder interference and Intermodal interference

Optical fiber refractive index (RI) sensor with temperature (T) compensation has important application values in biomedicine and environmental monitoring. In order to solve the problem that the detection accuracy of liquid RI is affected by T in practical applications, a T-compensated RI fiber sensor based on cascaded Mach-Zehnder interference (MZI) and multimode interference (IMI) is proposed in this paper. Experimental results showed the proposed sensor achieved a sensitivity of 797.41 nm/RIU for the measurement of RI in the range of 1.3333–1.3640, and a sensitivity of 0.120 nm/°C for the measurement of T in the range of 0–60 °C. The resolution (R) of RI and T measurements reached 2.5 × 10−5 RIU and 0.167 °C, respectively. The detection limits (DL) of RI and T measurements are 3.135 × 10−8 RIU and 1.392 °C, respectively. A matrix is obtained to demodulate the cross-sensitivity in RI and T measurements. The proposed sensor shows the advantages of simple structure, low hysteresis, and good stability.

A 1024-Channel Simultaneous Electrophysiological and Electrochemical Neural Recording System with In-Pixel Digitization and Crosstalk Compensation.

Simultaneous electrophysiological and chemical recording allows for multi-modal neural instrumentation and provides insights into chemical synapses and ion channels across the cell membrane. However, intermodal interference can hinder highly synchronized recording in large-scale systems with high temporal and spatial resolution. In this work, we propose a 1024-channel lab-on-CMOS system for dual-modal neural recording with in-pixel digitization and interference suppression. A foreground calibration scheme with tunable capacitance is implemented in-pixel to compensate for the crosstalk between electrical and chemical recording. Active pixels for both electrical and chemical modalities are designed based on a pulse width modulation (PWM) analog-to-digital conversion scheme. CMOS-compatible post-processing is implemented to realize in-pixel electrodes and chemical sensing membranes. The prototype, implemented in a 180nm CMOS technology, occupies a total area of 33mm2 with 1024 pixels, and each unit pixel includes one electrical recording site and two chemical recording sites, with dimensions of 150μm×130 μm. The total system power consumption is 19.68mW at a frame rate of 9k and 3k for electrical and chemical imaging respectively. The in-vitro experiment demonstrated the concurrent high density electrophysilogical and electrochemical recording with sub millisecond temporal resolution.

Accurate segmentation of liver tumor from multi-modality non-contrast images using a dual-stream multi-level fusion framework

The use of multi-modality non-contrast images (i.e., T1FS, T2FS and DWI) for segmenting liver tumors provides a solution by eliminating the use of contrast agents and is crucial for clinical diagnosis. However, this remains a challenging task to discover the most useful information to fuse multi-modality images for accurate segmentation due to inter-modal interference. In this paper, we propose a dual-stream multi-level fusion framework (DM-FF) to, for the first time, accurately segment liver tumors from non-contrast multi-modality images directly. Our DM-FF first designs an attention-based encoder–decoder to effectively extract multi-level feature maps corresponding to a specified representation of each modality. Then, DM-FF creates two types of fusion modules, in which a module fuses learned features to obtain a shared representation across multi-modality images to exploit commonalities and improve the performance, and a module fuses the decision evidence of segment to discover differences between modalities to prevent interference caused by modality’s conflict. By integrating these three components, DM-FF enables multi-modality non-contrast images to cooperate with each other and enables an accurate segmentation. Evaluation on 250 patients including different types of tumors from two MRI scanners, DM-FF achieves a Dice of 81.20%, and improves performance (Dice by at least 11%) when comparing the eight state-of-the-art segmentation architectures. The results indicate that our DM-FF significantly promotes the development and deployment of non-contrast liver tumor technology.

SCF-MMF based Michelson interferometer for ethanol multi-parameter measurements

A optical fiber Michelson interferometer (MI) for multi-parameter ethanol measurements is proposed and experimentally demonstrated. The sensor consists of a brief seven-core fiber (SCF) and a section of multimode fiber (MMF). With the SCF, multiple high-order modes are coupled into MMF, while the core fundamental mode and high-order modes are reflected back by the MMF end face and recoupled to the SMF by the SCF. When the surrounding ethanol changes, the reflection spectrum of the MI shift for the intermodal interference strongly integrates with the surrounding medium. Experimental results show that the sensor has an ethanol concentration sensitivity of −0.041 dB/% over the range of 0–90 %. The level sensitivities are −0.0795 nm/mm and −0.1052 nm/mm in the 0–5 mm range for 5 % and 10 % ethanol solutions, respectively, while in the 5–20 mm range, the sensitivities are −0.2773 nm/mm and −0.2243 nm/mm, respectively. Moreover, the volatilization time and volatilization stability are tested under different concentrations of ethanol, and the volatilization sensitivity is 0.071 dB/% in the range of 0–60 %. Response and recovery time of 1.008 s and 0.514 s for 15 % ethanol volatilization molecules is achieved. This MI has advantages of compact structure, easy fabrication, good stability and dominant ability to achieve multi-parameter ethanol measurement via reflective operation.

Transverse mode switchable mode-locked laser with narrow bandwidth

Transverse mode switchable ultrashort optical pulses with narrow bandwidths can create potential for exploring what we believe are new physical effects. We demonstrate the generation of transverse mode switchable ultrashort pulses with narrow bandwidths in an all-fiber mode-locked laser by exploring a mode-selective photonic lantern (MSPL). The laser cavity serves not only as a ring resonator but also as an intrinsic spectral filter. For mode-locking with the LP01, LP11a, and LP11b modes, the bandwidths are 3.0 nm, 86.7 pm and 101.7 pm, respectively. The narrowband pulses with higher-order modes are generated by an intrinsic spectral filter due to the spectral-domain intermodal interference. Mode-locked pulses with a signal-to-noise ratio better than 60 dB for LP01, LP11a, and LP11b modes are independently generated, i.e., transverse mode switchable by changing the input port of the MSPL. The mode-locked wavelength can be tuned for the LP11a mode and LP11b mode by adjusting the state of polarization. Furthermore, our experimental results also show that, the slope efficiency of LP11a and LP11b modes can be improved, by the use of LP11 mode pump scheme. We anticipate that, narrowband pulses with complex mode profiles can be generated by simultaneously phase-locked transverse and longitudinal modes.

Weak Faraday Effect Measurement in Anti-Resonant Fiber Based on Intermodal Interference Suppression

Anti-resonant fiber (ARF) works well in a relatively strong magnetic field due to its weak Faraday effect, which results from the fundamental mode mainly transmitting in the air core. Accurately measuring the Faraday effect strength, i.e., the effective Verdet constant, of an ARF determines its applicable scenarios. However, the effective Verdet constant of ARF is ~3 orders of magnitude lower than that of a standard single-mode fiber, which is very difficult to measure. In this paper, we reveal that intermodal interference is the main obstacle to measuring the ultralow effective Verdet constant of ARF and propose using a narrow-band low-coherence light to suppress it. The measured effective Verdet constant of ARF is 0.423 ± 0.005 mrad/T/m at 1550 nm.

A Micro-Mach–Zehnder Interferometer Temperature Sensing Design Based on a Single Mode–Coreless–Multimode–Coreless–Single Mode Fiber Cascaded Structure

In this paper, a temperature sensing scheme with a miniature MZI structure based on the principle of inter-mode interference is proposed. The sensing structure mainly comprises single mode–coreless–multimode–coreless–single mode fibers (SCMCSs), which have been welded together, with different core diameters. The light beam has been expanded after passing through the coreless optical fiber and is then coupled into a multimode optical fiber. Due to the light passing through the cladding and core mode of the multimode optical fiber with different optical paths, a Mach–Zehnder interferometer is formed. Moreover, due to the thermo-optic and thermal expansion effects of optical fibers, the inter-mode interference spectrum of a multimode fiber shifts when the external temperature changes. Through theoretical analysis, it is found that the change in the length of the sensing fiber during temperature detection has less of an effect on the sensitivity of the sensing structure. During the experiment, temperature changes between 20 and 100 °C are measured at sensing fiber lengths of 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, and 4.0 cm, respectively, and the corresponding sensitivities are 65.98 pm/°C, 72.70 pm/°C, 67.75 pm/°C, 66.63 pm/°C, 74.80 pm/°C, and 72.07 pm/°C, respectively. All the corresponding correlation coefficients are above 0.9965. The experimental results indicate that in the case of a significant change in the length of the sensing fiber, the sensitivity of the sensing structure changes slightly, which is consistent with the theory that the temperature sensitivity is minimally affected by a change in the length of the sensing fiber. Therefore, the effect of the length on sensitivity in a cascade-based fiber structure is well solved. The sensing scheme has an extensive detection range, small size, good linearity, simple structure, low cost, and high sensitivity. It has a good development prospect in some detection-related application fields.

Highly sensitive magnetic field sensor using magnetic fluid filled dual-core photonic crystal fiber

A high sensitivity fiber optic magnetic field sensor that utilizes a dual-core photonic crystal fiber (DC-PCF) filled with magnetic fluid (MF) has been proposed and validated to simultaneously detect magnetic field intensity and temperature. DC-PCF is a multimode fiber that supports various modes of light transmission and induces intermodal interference within fiber core. The numerical analysis of the mode characteristics of DC-PCF is conducted. The sensing structure relies on the use of a DC-PCF with air holes filled with a suitable material, such as MF substance. The analysis of the working principle of the DC-PCF for sensing and measurement is conducted by considering its structural characteristics and mode characteristics. The effective refractive index (ERI) of MF is affected by external magnetic field intensity and temperature. To extract the effective frequency points, the fast Fourier transform (FFT) method can be employed. Additionally, the inverse fast Fourier transform (IFFT) method can be utilized to determine the magnetic field sensitivity, which can reach up to 1.562 nm/mT. Furthermore, the temperature sensitivity can be as high as −1.043 nm/°C. The sensor demonstrates excellent repeatability and showcases low detection limits of 0.0128 mT and 0.0192 °C, respectively. Additionally, the proposed sensor exhibits substantial potential for further development in the field of high sensitivity magnetic field detection applications.

Optimal fiber-optical sensing element selection on multimode interferometer

The paper presents the results of model and experimental search for optimal configuration of sensing element based on fiber-optical multimode interferometer with intermode interference in the phase-amplitude filter. Simulation results are presented. Based on them, combinations of multimode fiber light guides with single-mode ones are selected, the most suitable for constructing the sensitive part. Laboratory tests of the selected configurations were carried out. The requirements for the necessary components have been developed. The dynamic characteristics of the sensing elements are obtained depending on the variable parameters for different methods of welding fiber light guides.

Investigation on fabrication and VOC sensing properties of PDMS fiber based optical sensor

In this paper, a method for preparing polydimethylsiloxane (PDMS)-based fiber structure was reported and its performance for volatile organic compound (VOC) gas sensing was demonstrated. The PDMS fiber prepared by the physical stretching method was coupled at the end faces of two multimode fibers by adhesion, forming an inter-mode interferometer. The PDMS was not easily dislodged after curing, which contributes to the strong robustness of the whole structure. When the PDMS optical fiber is exposed to VOC gas environment, PDMS will adsorb VOC gas molecules, resulting in changes in its refractive index and volume, which shifts the wavelength of inter-mode interference. Experiments show that the sensor has good sensitivity to VOC gases such as acetone, ethanol, and methanol. In the concentration range of 0–400 ppm, the sensitivity reaches 14.84 pm/ppm, 13 pm/ppm, 4.39 pm/ppm, 7.37 pm/ppm, and 5.99 pm/ppm for acetone, ethanol, methanol, toluene, and ether respectively. The proposed sensor has excellent characteristics such as simple preparation, high sensitivity, good tensile properties, and humidity resistance, which indicates that the sensor has some potential for VOC gas detection.

In-line open-cavity Mach-Zehnder interferometric refractive-index sensors based on inter-mode and inter-core-mode interferences

We experimentally demonstrated in-line Mach-Zehnder interferometric sensors based on inter-mode interference (IMI) and inter-core-mode interference (ICMI) for refractive index (RI) measurements. The structure of the IMI-based sensor consisted of a C-shaped fiber spliced between two multi-mode fibers (MMF) with the opposite ends spliced to lead-in and lead-out single-mode optical fibers. The ICMI-based sensor has a similar structure as the IMI-based sensor but with an additional in-house fabricated three-core multi-core fiber (MCF) spliced between the MMF and C-shaped fiber. The performance of the two RI sensors was evaluated and compared using water-glycerol solutions with RI values ranging from 1.333 to 1.338. The RI sensitivity, as well as other characteristic properties such as free spectral range and extinction ratio in relation to three lengths of the C-shaped fiber of 2, 2.5 and 3 mm, were investigated in both structures. The open-cavity characteristic of the C-shaped fiber allows the solution to interact with the optical path of the sensors, hence improving their RI measurement sensitivities. Both types of sensors exhibit linear wavelength responses with variation in RI. The RI sensitivity of the IMI-based sensor exhibits minor variations when the length of the C-shaped fiber is altered, with a maximum sensitivity of -7999.76 nm/RIU. In contrast, the RI sensitivity of ICMI-based sensor exhibits variability when changing the C-shaped fiber length, potentially due to variations in the RI distribution among the cores within the MCF, with its maximum sensitivity being -6211.98 nm/RIU. The temperature sensitivity of all the tested sensors was around 0.7 nm/ °C, denoting a low temperature cross-sensitivity of -7.427 × 10−5 RIU/ °C. This work experimentally exhibits a comparison of two sensing effects in the same configuration. The long length (longer than 2 mm) of the sensing element facilitates the fabrication process, and the open-cavity present in the proposed sensors yields a high sensitivity, which is in the same order of magnitude as the IMI-based sensors and is one order of magnitude higher than the ICMI-based sensors, emphasizing their promising candidacy for label-free optical sensing of chemical and biological samples.

Image camouflage and encryption scheme employing multimode fibers specklegram and polarization multiplexing technology

An image camouflage encryption scheme based on fiber specklegram and polarization multiplexing technology is proposed and demonstrated via simulation. The camouflaged original image is coupled into the multimode fiber (MMF) through different polarized light fields, and the specklegram caused by strong intermodal interference provides excellent chaos and randomness required for encryption. Since the optical fiber specklegram has a strong dependence on the configuration, transmission matrixes used as the key have high security and unpredictability. The results demonstrate the huge keyspace and excellent key sensitivity of the scheme. The ability to resist key disclosure and differential attack is analyzed. In addition, the scheme shows great security and reliability in several common noise attacks.

Mathematical model of radiation scattering on a quasi – periodic structure in an optical fiber

The paper considers a quasi – periodic microheterogeneity structure formed under the effect of optical fiber melting, which can be used as a sensitive element for an optical sensor based on a Fabry – Perot interferometer or an optical radiation scatterer with improved flexibility and strength parameters. Mathematical modeling of the process of transmission and reflection of radiation on the microcavities of the intrafiber structure will make it possible to predict the characteristics of the developed sensors. The simulation was carried out in the COMSOL Multyphysics simulation package. A section of a single – mode SMF-28e fiber with microinhomogeneities located in the core, the dimensions of which were measured in the course of an empirical study, is considered. To solve the problem, a system of equations was compiled that describes the propagation of a plane electromagnetic wave in matter. The results obtained showed that the calculated reflection spectrum qualitatively coincides with the measured value, but does not describe it with high accuracy. This may be due to the fact that the model does not take into account intermode interference in the fiber, and does not have an introduced melt zone around microcavities, since such a melt zone has a complex refractive index distribution and composition

Directional Bending Sensor and Multiparameter Sensor Based on D-Core Multimode Fiber

For the sensor with interference between fiber core mode and cladding mode, the directional bending sensor can be realized by processing asymmetric structure on the cladding or using eccentric fiber, but the temperature and strain crosstalk of the sensor with interference between fiber core mode and cladding mode is large. In this article, a kind of fiber intermode interference sensor with asymmetric structure is proposed, which can realize vector bending sensing and reduce temperature and strain crosstalk. The designed D-core multimode fiber has cladding and air on both sides of the fiber core. When 0° and 180° bending are applied to it, the interference spectrum moves in different directions, thus realizing the recognition of bending direction. For curvature detection, in the curvature range of 0–0.62 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> , the sensitivity of 0° bending is 11.00 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> , and that of 180° bending is −11.40 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> . For liquid level detection, the sensing sensitivity is 234 pm/mm with the range of 0–4 cm, and the linearity is 0.993. In addition, the temperature sensitivity is as low as 10 pm/°C, and the strain sensitivity is as low as −1.28 pm/ <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> . The proposed sensor realized the directional bending sensing and liquid level sensing of intermodal interference. Its low sensitivity to temperature and strain can be used to avoid the cross-sensitivity problems. In the field of water flow detection, the simultaneous detection of water level and water flow direction can be realized by the proposed sensor.

In Situ DNA Detection Using a Phase-Demodulated High-Order Intermodal Interferometer Based on an Exposed-Core Microstructure Fiber

In this paper, we demonstrate a phase-demodulated high-order intermodal interference based on exposed-core microstructure fiber (ECF), and it is applied for low concentration in-situ deafness gene DNA detection. The simulation results show that the phase sensitivity of the high-order interference mode (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21a</sub> ) is about 6 times higher than that of the low-order (LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11b</sub> ), which is different from the traditional wavelength coded demodulation method. Hybridization experiments of complementary and non-complementary deafness gene DNA fragments were carried out, and the sensing system was obtained to screen for complementary gene fragments. DNA complementary fragments with concentrations as low as 1 nM can be detected with a corresponding phase variation of 7.32 °. The limit of detection is as low as 0.089 nM. The experiment and theoretical analysis prove that this fiber optic biosensor can obtain high sensitivity and signal-to-noise ratio with phase-demodulation high-order intermodal interference scheme, which provides an alternative for the subsequent studies of high sensitivity and high precision sensors.

High temperature and strain dual-parameters fiber sensing based on intermodal interference and femtosecond laser fabricated fiber Bragg grating

In this paper, the sensor was proposed by combination of grapefruit photonic crystal fiber (GPCF) and femtosecond laser fabricated fiber Bragg grating (FBG) based on Sagnac interferometer. The GPCF was sandwiched between two single-mode fibers (SMFS) to form a SMF-GPCF-SMF structure, which was based on intermodal interference. The FBG with a central wavelength of 1535.32 nm was inscribed through polyimide coating and cladding by the femtosecond laser point-by-point inscribing method. The spectrum drift data of sensing structure were collected and the dual-parameters matrix of temperature-strain was constructed to realize the simultaneous measurement of temperature and strain. The experimental results showed that the linear range of the strain measurement was from 0 με to 2,000 με at different temperature, the wavelength of FBG and GPCF was red drift and blue drift, respectively, the average strain sensitivity at different temperature was 1.25 pm/με and −2.05 pm/με, all the linearity R2 are higher than 0.999, and has the high repeatability. The linear range of temperature measurement was from 20 °C to 450 °C, the wavelength of FBG and GPCF was red drift and blue drift, respectively, the temperature sensitivity of FBG and GPCF was 15.17 pm °C−1 and −8.87 pm °C−1, the linearity was 0.99983 and 0.99989, respectively.

Infrared and visible image fusion based on infrared background suppression

Because infrared images emphasize thermal targets while visible images provide a wealth of textural information, fusing the two modal images improves the human perception of the scene. When it comes to image fusion, it is essential to investigate the informative regions of both modal images and to leverage this prior knowledge during the fusion phase, in case of image degradation due to intermodal image interference. To this purpose, we present a fusion model in which the fusion process is guided by a thermal target mask, therefore alleviating cross-modal interference. This mask is created by suppressing the background of the infrared image, allowing thermal objects to be highlighted significantly, enabling for exploration of the associated regions. In addition, a two-channel multi-scale feature extraction network is designed to retain the semantic information from the two source images. We verify the presented model’s effectiveness using the public datasets, and the fused image of our method completely maintain the infrared image’s thermal targets and the visible image’s background texture information. Extensive experiments on publicly available datasets demonstrate that our model outperforms other state-of-the-art models in terms of both visual assessment and objective assessment.

Spatiotemporal mode-locked fiber laser based on dual-resonance coupling long-period fiber grating.

Spatiotemporal mode-locked (STML) fiber lasers have become an excellent platform in nonlinear optics research due to the rich nonlinear evolution process. In order to overcome modal walk-off and realize phase locking of different transverse modes, it is usually crucial to reduce the modal group delay difference in the cavity. In this paper, we use long-period fiber grating (LPFG) to compensate the large modal dispersion and differential modal gain in the cavity, realizing the spatiotemporal mode-locking in step-index fibers cavity. The LPFG inscribed in few-mode fiber could induce strong mode coupling, which has wide operation bandwidth based on dual-resonance coupling mechanism. By using dispersive Fourier transform involved intermodal interference, we show that there is a stable phase difference between the transverse modes constituting the spatiotemporal soliton. These results would be beneficial for the study of spatiotemporal mode-locked fiber lasers.

Recursive ESPRIT Algorithm for Multi-User OAM Low-Overhead AoA Estimation

Multi-user orbital angular momentum (MU-OAM) wireless backhaul systems require precise alignment of transmitted and received OAM beams in line-of-sight (LoS) scenarios. Therefore, a crucial feature for a macro base station (MBS) is to accurately obtain the angle of arrival (AoA) of OAM beams from the small base stations (SBSs) in the system. Considering the limitations of existing OAM-based AoA estimations, we propose a novel super-resolution AoA estimation method, denoted as the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">recursive estimation of signal parameters via rotational invariance techniques (ESPRIT)</i> method. The proposed technique is fundamentally different from traditional ESPRIT algorithm: It is not based on the displacement-invariant array structure, but on the recursive characteristic of Bessel functions in OAM signals. With this method, the inter-mode interference of the LoS MU-OAM system can be significantly suppressed by less training overhead, and the performance is close to that of the ideal system.