Optical Fiber Coupler Research Articles

Anticrossing and Mode Coupling in Bent All-Glass Leakage Channel Microstructured Optical Fibers with Large Mode Area

This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped silica glass elements with reduced refractive index, different diameters, and different distances between them. We determined the spatial distributions of the electric field components of different modes in addition to the usual parameters such as effective refractive indices, bending losses, and spatial intensity distributions. A detailed analysis showed that three modes for each polarization have to be considered to correctly calculate the bending losses. Two pairs of these three modes couple in two distinct bending radius ranges, specifically near 3.68 cm and near 5.95 cm, and the mode coupling in these pairs is resonant. The resulting bending losses of the LC MOF for two polarizations are very close to each other and have two maxima at bending radii of 3.68 cm and 5.95 cm. However, the nature of these maxima is not resonant; they are caused by the combined influence of all three modes, each of which has specific dependencies of losses and other parameters on the bending radius that exhibit quasi-resonant behavior near the corresponding bending radii.

Displaced thinned single-mode fiber Mach-Zehnder interferometer tested for temperature and curvature applications

This article explains the features and qualities of employing a thinned manufacturing fiber to assemble a Mach-Zehnder interferometer (MZI) for detecting two physical variables: temperature and curvature. The MZI comprises a filter by splicing core-offset sections of a thinned fiber (TF) cladding diameter of 80 μm in an SMF-TF-SMF configuration. The TF splices act as the arms of the MZI, while the mismatch diameter sections serve as optical fiber couplers. The optical spectrum analyzer (OSA) detects the transmitted light and analyzes its optical transmission characteristics, showing 11 peaks of modal interferences into the longitude region. As a result of the experimental arrangement, the curvature and temperature sensitivities are 0.49 nm/m−1, 0.01 nm/°C, and 0.09 nm/°C for temperatures of 0–60 °C and 70–130 °C, respectively. The proposed sensor has potential advantages for measuring refractive index, pH, torsion, curvature, and temperature.

High efficiency deep ultraviolet micro-LED and optical fiber coupling for low power charge management applications

During space gravitational wave detection missions, it is necessary to manage the charge accumulated on the surface of the test mass. A common method involves using optical fibers to transmit ultraviolet (UV) light, leveraging the photoelectric effect for charge management. An important issue in this process is achieving efficient coupling between the UV light source and the optical fiber. In this paper, for the first time we proposed to use DUV micro-LEDs as light sources for charge management systems, which will have lower power consumption. We conducted simulations to investigate the effect of the size ratio between deep ultraviolet (DUV) micro-LEDs and optical fibers on the coupling efficiency. We further employed a direct coupling method to conduct coupling experiments of DUV micro-LEDs and optical fibers with varying wavelengths and sizes. The simulation and experiment results both indicate that, under the influence of both size and divergence angle, there exists an optimal DUV micro-LED size responsible for maximum coupling efficiency between DUV micro-LEDs and optical fibers which is 80 μm when the optical fiber size is 1000 μm. Applying the 80 μm DUV micro-LED in charge management experiments demonstrated the feasibility of using DUV micro-LEDs as light sources for low power charge management systems, achieving rapid charge–discharge rates and high photoelectric current at lower driving electrical power.

Modeling of Fiber Optic Acoustic Coupler for Ultrasonic Sensing

Abstract Fiber Bragg grating (FBG) sensors have been applied in the remote bonding configuration for structural health monitoring, in which ultrasonic modes are propagated along the optical fiber to the sensor. Recently coupling of the ultrasonic mode from optical fiber to optical fiber through an adhesive coupler has also been demonstrated. This paper develops a finite element (FE) model to describe the coupler behavior as a function of the fiber and coupler properties, for future optimization of couplers. The FE model is validated with previous experimental data. We also compare the FE model to three theoretical models (spring and damper frictional contact models and coupled mode theory). The results show that the FE model and spring well replicate the experimental results. Future work will use the resulting FE and spring models to derive solutions for the coupling coefficient as a function of the geometrical and material parameters of the coupler.

Discovering novel optical solitons of two CNLSEs with coherent and incoherent nonlinear coupling in birefringent optical fibers

Discovering novel optical solitons of two CNLSEs with coherent and incoherent nonlinear coupling in birefringent optical fibers

Loss analysis of a grating coupler for single-mode fiber coupling into an SOI waveguide

Silicon-on-insulator (SOI) technology is widely used in silicon photonic integrated circuits. How to improve the coupling efficiency of the light coupling in free space and optical fibers into waveguides on SOI must be discussed. Grating coupling is a commonly used and highly efficient coupling method. This article discusses the causes of loss in grating couplers from three aspects: transmission, reflection, and mode mismatch, and proposes corresponding loss reduction solutions. The coupling efficiency of Si and SiN grating couplers optimized according to the loss reduction scheme has been improved by 25% and 45%, respectively.

Single-to-four core optical fiber coupling using a two-photon polymerization produced waveguide

Optical coupling between single core to multi-core optical fibers usually takes place by means of optical fiber fan-ins / fan-outs, delicate free space optics, or laser inscribed freeform waveguides. In the present work, the two-photon polymerization technique is used for the first time to create a waveguide manifold on top of a four-core optical fiber tip as a means to couple light into and from a single core optical fiber, in a fast and low-cost fashion. It is demonstrated that the performance is influenced by the numerical aperture mismatch between the fabricated and the coupled waveguides. Insertion losses below 5 dB are observed when the numerical aperture mismatch is minimized, with further reduction potential, making this approach applicable to sensing or tweezer applications.

Monolithically integrated multimode interference coupler-based master oscillator power amplifier with dual-wavelength emission around 830 nm

A monolithically integrated dual-wavelength multimode interference coupler-based master oscillator power amplifier is presented. It consists of two shallowly etched, laterally separated ridge waveguide laser cavities as master oscillators with individual distributed Bragg reflector gratings as cavity mirrors. A deeply etched coupling section containing S-bend shaped waveguides and a multimode interference coupler is used to couple the laser emission of the master oscillators into a shallowly etched single waveguide serving as power amplifier. Changing the etch depth for the coupling section enables a compact device layout. In addition, increased radiation angles of modes not coupled into the power amplifier help to suppress beam steering, otherwise indicated by laterally separated far-field intensity distributions. The device provides 0.5 W of dual-wavelength emission around 830 nm in individual and common operation. As designed, both emission wavelengths are separated by 0.5 nm with spectral widths below 20 pm, limited by the spectral resolution of the spectrometer. Both peak wavelengths remain within spectral windows of 50 pm within the available power range. This enables full flexibility selecting operating points for applications such as shifted excitation Raman difference spectroscopy and the generation of THz emission by photomixing. The emission wavelengths can additionally be non-continuously tuned by applying a heater current to resistors implemented next to the distributed Bragg reflector gratings. As an example, selected spectral distances of 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated. Near field widths of 5 μm and far field angles of 17° result in beam propagation ratios of 1.4 (1/e2) in all operation modes and enable easy beam shaping or optical single-mode fiber coupling.

Low-Loss Fluoride Optical Fiber Coupler for Mid-Infrared Applications

Low-Loss Fluoride Optical Fiber Coupler for Mid-Infrared Applications

A multi-core fiber coupler without a central core

An efficient method for fabricating multi-core fiber couplers based on the thermal diffusion technique is proposed to realize the connection of single-mode fibers to multi-core fibers without a central core. The fabrication efficiency of the multi-core fiber coupler is improved by fiber-loaded hydrogen. The simulation results show that the single-mode fiber and the multi-core fiber can be coupled stably and efficiently by using the designed double-clad fiber to connect the single-mode fiber and the multi-core fiber. Double-clad fiber and multi-core fiber were loaded with hydrogen to enhance the dopant diffusion rate. Three-dimensional refractive index measurements of the multi-core fiber coupler show that the dopant diffusion rate and the diffusion zone length of the hydrogen-loaded fiber are significantly increased compared to the original fiber. These enhancements contributed to the shorter fabrication time of multi-core fiber couplers. The multi-core fiber couplers fabricated by thermal diffusion technology have the advantages of high coupling efficiency, high integration, simple manufacture, and high mechanical strength. Enhancing the diffusion rate of optical fibers by using the hydrogen loading method will increase the application potential of multi-core optical fiber couplers prepared by thermal diffusion technology, and accelerate the translation of multi-core fibers toward optical communication and optical fiber sensing.

Combined enhancement of fiber-optic laser-induced breakdown spectroscopy coupling spatial confinement and double-pulse irradiation

The mechanism of double-pulse laser irradiation under spatial confinement remains unclear due to complex plasma plume dynamics and multiple shock waves interactions. In this study, coupling of spatial confinement and...

Measurement of Cutting Temperature in Interrupted Machining Using Optical Spectrometry.

This research presents an experimental study focused on measuring temperature at the tool flank during the up-milling process at high cutting speed. The proposed system deals with emissivity compensation through a two-photodetector system and during calibration. A ratio pyrometer composed of two photodetectors and a multimode fiber-optic coupler is employed to capture the radiation emitted by the cutting insert. The pyrometer is calibrated using an innovative calibration system that addresses theoretical discrepancies arising from various factors affecting the measurement of cutting temperature. This calibration system replicates the milling process to generate a calibration curve. Experimentally, AISI 4140 steel is machined with coated tungsten carbide inserts, using cutting speeds of 300 and 400 m/min, and feed rates of 0.08 and 0.16 mm/tooth. The results reveal a maximum recorded cutting temperature of 518 °C and a minimum of 304 °C. The cutting temperature tends to increase with higher cutting speeds and feed rates, with cutting speed being the more influential factor in this increase. Both the pyrometer calibration and experimental outcomes yield satisfactory results. Finally, the results showed that the process and the device prove to be a convenient, effective, and precise method of measuring cutting temperature in machine processes.

Fabrication and characterization of indium fluoride multimode fused fiber couplers for the mid-infrared.

Results of the fabrication and characterization of optical fiber couplers made of multimode step-index fluoroindate (InF3) fibers are presented. The fabrication setup was customized for this type of glass with a constant source of controlled nitrogen flow heated to a target temperature with an accuracy ±1°C. Combined with a novel fast fusion approach and with excellent control of the viscosity throughout the process, the clean gas flow and well-controlled temperature enable the fabrication of fused fiber couplers absent of any noticeable crystallization. A coupling ratio of 45/55 was achieved, with an excess loss of 0.35 dB, at 1.7 µm. To the best of our knowledge, this represents the first low excess loss (<1 dB), multimode, InF3 fiber couplers.

Multimode optical fiber interrogator-based LiDAR for intravenous drip monitoring

A novel intravenous dripping monitoring system is proposed and demonstrated. The system employs a multimode optical fiber-based and low-cost LiDAR. By using an ESP32 microchip, a TF-mini-s LiDAR module is controlled. Both devices are embedded in a 3D-printed casing, and by using a multimode optical fiber coupler, the system interacts with a typical intravenous system. This interrogator configuration has a high-resolution time of 20 ms, a good signal-to-noise ratio (<13 dB), low power consumption, and maximal flow rate monitoring of 93 drops per minute. The proposed system is a novel-intensity LiDAR application that can be applied in micro-fluidics, agriculture, and drug delivery monitoring.

Silicon-Cantilever-Enhanced Single-Fiber Photoacoustic Acetylene Gas Sensor.

A single-fiber photoacoustic (PA) sensor with a silicon cantilever beam for trace acetylene (C2H2) gas analysis was proposed. The miniature gas sensor mainly consisted of a microcantilever and a non-resonant PA cell for the real-time detection of acetylene gas. The gas diffused into the photoacoustic cell through the silicon cantilever beam gap. The volume of the PA cell in the sensor was about 14 μL. By using a 1 × 2 fiber optical coupler, a 1532.8 nm distributed feedback (DFB) laser and a white light interference demodulation module were connected to the single-fiber photoacoustic sensor. A silicon cantilever was utilized to improve the performance when detecting the PA signal. To eliminate the interference of the laser-reflected light, a part of the Fabry-Perot (F-P) interference spectrum was used for phase demodulation to achieve the highly sensitive detection of acetylene gas. The minimum detection limit (MDL) achieved was 0.2 ppm with 100 s averaging time. In addition, the calculated normalized noise equivalent absorption (NNEA) coefficient was 4.4 × 10-9 W·cm-1·Hz-1/2. The single-fiber photoacoustic sensor designed has great application prospects in the early warning of transformer faults.

Design and Experimental Analysis of an Optical Fiber Coupling System for a Ground-based Telescope with Adaptive Optics

Astronomy photonics has opened up a new era for the application of astronomical optical instruments. The fiber coupling system serves as the crucial link between the telescope and photonic devices. This paper explores a beam shaping method that utilizes a coupled lens to enhance the efficiency of coupling light into an optical single mode fiber. Compared to directly coupling the telescope beam into the fiber, this approach offers improved coupling efficiency and greater adjustment tolerance. The laboratory-based optical fiber coupling system described in this study comprises an imaging component with an F/50 ratio and a fiber coupling component. Theoretical analysis indicates that optimal coupling efficiency is achieved when the diameter of the focusing spot, limited by diffraction, matches the fiber core size. Any axial error, position error, or tip-tilt error between the lens and the fiber will reduce the coupling efficiency. Experimental results confirm that the coupling system achieves an efficiency of approximately 70%, which is close to the theoretical limit of 78%. These findings underscore the effectiveness of the fiber coupling method.

Asymmetric Curvature Side-Polished Optical Fiber Coupler

Asymmetric Curvature Side-Polished Optical Fiber Coupler

Single-mode optical fiber couplers made of fluoride glass.

We demonstrate the first single-mode optical fiber couplers made with ZBLAN optical fiber. Couplers are fabricated using a controlled tapering procedure enabling high reproducibility while limiting glass crystallization. A coupling ratio of up to 41%/59% in cross/through ports with an excess loss of 2.5 dB is obtained at a wavelength of 2.73 μm. In addition, the stability of a coupler with traces of surface crystallization is tested at ambient atmosphere over a period of more than 90 days.

Design and Simulation Analysis of Piezoelectric Ceramic Tube-Based Fiber Optic Nutator Applied to an Intersatellite Laser Communication System

The signal-receiving end of acquisition, pointing, and tracking (APT) systems applied to intersatellite laser communication terminals usually uses a fast-steering mirror (FSM) to control the fiber-coupling process, has a complex structural design, and induces large errors in the nonideal coaxial optical path. Herein, we propose a fiber-optic nutator using a piezoelectric ceramic tube (PCT) as the driving unit that allows scanning in the focal plane of the light signal to achieve active fiber coupling in the APT system. Specifically, this article describes the structural design principle of a PCT-based fiber optic nutator, establishes a simulation model of the mechanism, and proves the correctness of the simulation model by measuring the deflection angle of a PCT based on a parallel light collimator. The minimum accuracy of the designed nutator was 0.145 μm, the maximum nutation radius R was 20.09 μm, and the maximum nutation bandwidth was 20 kHz, as determined through simulation. Finally, the design parameters of the nutator were evaluated. The PCT-based fiber optic nutator, which met the design parameters, structurally replaced the fiber optic coupling component FSM and fine tracking camera in conventional APT systems successfully. Therefore, the PCT-based fiber optic nutator allows the active coupling control of signal light to a single-mode fiber (SMF) based on energy feedback on a theoretical basis and promotes the lightweight design of relay optical paths in APT systems. In addition, with future work in optimization of the nutation control algorithm, the scanning range and accuracy of the nutator can be improved.

Investigation of mode coupling in strained and unstrained multimode step-index POFs using the Langevin equation

The Langevin equation (LE) is used to evaluate mode coupling in multimode step-index polymer optical fiber (SI POF) that is both unstrained and strained. The numerical solution of the LE matches the numerical solution of the power flow equation (PFE). Strain-induced mode coupling is noticeably stronger in strained fiber than in unstrained fiber of the same types. Therefore, compared to similar lengths for unstrained fibers, the coupling length of the equilibrium mode distribution (EMD) is attained and the length of fiber required to produce a steady-state distribution (SSD) are both much shorter for strained fibers. We have demonstrated that the mode coupling in strained and unstrained multimode SI POFs that comes from the random perturbations (RPs) of the fiber can be successfully treated by the LE. The study's findings can be used to improve communication and sensory systems that use multimode SI POFs under different bending circumstances. Additionally, it is crucial to be able to compute the modal distribution of the SI POFs used in the optical fiber sensory system at a specific length and under various bending scenarios.