Fiber Directional Coupler Research Articles

Direct laser-written optomechanical membranes in fiber Fabry-Perot cavities

Integrated micro- and nanophotonic optomechanical experiments enable the manipulation of mechanical resonators on the single phonon level. Interfacing these structures requires elaborate techniques limited in tunability, flexibility, and scaling towards multi-mode systems. Here, we demonstrate a cavity optomechanical experiment using 3D-laser-written polymer membranes inside fiber Fabry-Perot cavities. Vacuum coupling rates of g0/2π ≈ 30 kHz to the fundamental megahertz mechanical mode are reached. We observe optomechanical spring tuning of the mechanical resonator frequency by tens of kilohertz exceeding its linewidth at cryogenic temperatures. The direct fiber coupling, its scaling capabilities to coupled resonator systems, and the potential implementation of dissipation dilution structures and integration of electrodes make it a promising platform for fiber-tip integrated accelerometers, optomechanically tunable multi-mode mechanical systems, and directly fiber-coupled systems for microwave to optics conversion.

High-performance designs for fiber-pigtailed quantum-light sources based on quantum dots in electrically-controlled circular Bragg gratings.

We present a numerical investigation of directly fiber-coupled hybrid circular Bragg gratings (CBGs) featuring electrical control for operation in the application relevant wavelength regimes around 930 nm as well as the telecom O- and C-band. We use a surrogate model combined with a Bayesian optimization approach to perform numerical optimization of the device performance which takes into account robustness with respect to fabrication tolerances. The proposed high-performance designs combine hybrid CBGs with a dielectric planarization and a transparent contact material, enabling > 86% direct fiber coupling efficiency (> 93% efficiency into NA 0.8) while exhibiting Purcell factors > 20. Especially the proposed designs for the telecom range prove robust and can sustain expected fiber efficiencies of more than (82.2±4.1)-5.5+2.2% and expected average Purcell factors of up to (23.2±2.3)-3.0+3.2 assuming conservative fabrication accuracies. The wavelength of maximum Purcell enhancement proves to be the most affected performance parameter by the deviations. Finally, we show that electrical field strengths suitable for Stark-tuning of an embedded quantum dot can be reached in the identified designs. Our work provides blueprints for high-performance quantum light sources based on fiber-pigtailed and electrically-controlled quantum dot CBG devices for quantum information applications.

High-sensitivity vector bend sensor based on a fiber directional coupler inscribed by a femtosecond laser.

In this Letter, we demonstrate a high-sensitivity vector bend sensor based on a fiber directional coupler. The fiber directional coupler is composed of two parallel waveguides inscribed within a no-core fiber (NCF) by a femtosecond laser. Since the two written waveguides have closely matched refractive indices and geometries, the transmission spectrum of the fiber directional coupler possesses periodic resonant dips. Such a fiber directional coupler exhibits a good bending-dependent spectral shift response due to its asymmetric structure. Experimental results show that bending sensitivities of -97.11 nm/m-1 and 58.22 nm/m-1 are achieved for the 0° and 180° orientations in the curvature range of 0-0.62 m-1, respectively. In addition, the proposed fiber directional coupler is shown to be insensitive to external humidity changes, thus improving its suitability in high-accuracy bending measurements.

Characteristic analysis of core radius, core refractive index, mismatched phase constant and coupling efficiency about 2 × 2 fiber directional coupler based on MATLAB

When two parallel waveguides are close to each other, the power of the two adjacent waveguides will be periodically converted to form a directional coupled waveguide system (). The transverse coupling between two parallel waveguides can be described by mode coupling theory. However, in practical application, due to the limitation of equipment or manual computing capacity, it is impossible to quickly calculate the coupling efficiency of two optical fibers through the current specific formula. Through the form of MATLAB programming, it can determine whether the fiber is a single-mode fiber, solve the characteristic equation to obtain the propagation constant, integrate the coupling coefficients K12 and K21, solve the coupling efficiency in the fiber, and finally output in the form of graphics. The results show that for the directional coupler composed of two fibers, if the core radius and core refractive index change, the mismatching phase constant and coupling efficiency will change correspondingly, and the calculated results are in good agreement with the predicted results. On this background, this paper proposes the form of MATLAB programming to calculate coupling efficiency. The coupling efficiency of fiber directional couplers is analyzed. The theory gives accurate results within the actual parameters.

Design study for an efficient semiconductor quantum light source operating in the telecom C-band based on an electrically-driven circular Bragg grating.

The development of efficient sources of single photons and entangled photon pairs emitting in the low-loss wavelength region around 1550 nm is crucial for long-distance quantum communication. Moreover, direct fiber coupling and electrical carrier injection are highly desirable for deployment in compact and user-friendly systems integrated with the existing fiber infrastructure. Here we present a detailed design study of circular Bragg gratings fabricated in InP slabs and operating in the telecom C-band. These devices enable the simultaneous enhancement of the X and XX spectral lines, with collection efficiency in numerical aperture 0.65 close to 90% for the wavelength range 1520 - 1580 nm and Purcell factor up to 15. We also investigate the coupling into a single mode fiber, which exceeds 70% in UHNA4. Finally, we propose a modified device design directly compatible with electrical carrier injection, reporting Purcell factors up to 20 and collection efficiency in numerical aperture 0.65 close to 70% for the whole telecom C-band.

Characteristic Analysis of Core Radius, Core Refractive Index, Mismatched Phase Constant and Coupling Efficiency About 2×2 Fiber Directional Coupler Based on Matlab

Characteristic Analysis of Core Radius, Core Refractive Index, Mismatched Phase Constant and Coupling Efficiency About 2×2 Fiber Directional Coupler Based on Matlab

Characteristic Analysis of Core Radius, Core Refractive Index, Mismatched Phase Constant and Coupling Efficiency About 2×2 Fiber Directional Coupler Based on Matlab

Characteristic Analysis of Core Radius, Core Refractive Index, Mismatched Phase Constant and Coupling Efficiency About 2×2 Fiber Directional Coupler Based on Matlab

Analysis of Kerr type nonlinear single-mode triangular index fiber directional coupler by a simple method

We present the coupling characteristics of directional coupler comprising two identical single-mode triangular index fibers both in the presence and the absence of Kerr nonlinearity. Triangular index fibers of some typical V numbers are chosen for our investigation. Our analysis is based on the simple series expression for the fundamental modal field for triangular index fiber developed by Chebyshev technique. Analytical expression of the coupling length in the absence as well as in the presence of Kerr nonlinearity is prescribed. Using the said expression of coupling length, we apply a method of iteration to evaluate the said coupling parameter in the presence of Kerr nonlinearity. We also show that our results match excellently with the exact results obtainable by rigorous finite-element technique. The execution of our formalism requires little computation. Thus our simple but accurate formalism to study the triangular index directional coupler will prove a suitable alternative to the existing rigorous methods in the field of nonlinear optics. This user-friendly method will prove beneficial to the scientists and technologists working in the field of nonlinear optics.

Optical waves/modes in a multicomponent inhomogeneous optical fiber via a three-coupled variable-coefficient nonlinear Schrödinger system

Recent progress in optical fibers is impressive, while nonlinear Schrödinger-type models are seen in fiber optics and other fields (such as ferromagnetism, plasma physics, Bose–Einstein condensation and oceanography). Hereby, our symbolic computation on a three-coupled variable-coefficient nonlinear Schrödinger system is performed, for the picosecond-pulse attenuation/amplification in a multicomponent inhomogeneous optical fiber with diverse polarizations/frequencies. For the slowly-varying envelopes of optical modes, we obtain a similarity reduction, an auto-Bäcklund transformation and some analytic solutions, which rely on the optical-fiber variable coefficients, i.e., the fiber loss/gain, nonlinearity and group velocity dispersion. Relevant variable-coefficient constraints are presented. Our results might be of some use in the construction of logic gates, optical computing, soliton switching, design of fiber directional couplers, quantum information processing, soliton amplification in the wavelength division multiplexing systems, solitonic studies in the all-optical devices and birefringence fiber systems.

Monitoring of Various Stages of Malaria Using Miniature Fibre Coupler Sensor Device

A micrometer size, simple, and low-cost sensor for continuous monitoring of human blood during malarial infection at its various stages is proposed in this work. The sensor comprises a light source, silica fiber directional coupler, and an optoelectronic photodetector. The sensor is simulated for fiber diameters from 1–1.8 #x03BC;m and optimization is done. The sensor produces a photocurrent of a few mA, which gives the level of infection. It can detect a change in refractive index, of the order of 10−5, and needs a small sensing length of a few μm. It can be potentially built as an integrated embedded device.

Integrated optical multi-ion quantum logic.

Practical and useful quantum information processing requires substantial improvements with respect to current systems, both in theerror rates of basic operations and in scale. The fundamental qualities of individual trapped-ion1 qubits are promising for long-term systems2, but the optics involved in their precise control are a barrier to scaling3. Planar-fabricated optics integrated within ion-trap devices can make such systems simultaneously more robust and parallelizable, as suggested by previous work with single ions4. Here we use scalable optics co-fabricated with a surface-electrode ion trap to achieve high-fidelity multi-ion quantum logic gates, which are often the limiting elements in building up the precise, large-scale entanglement that isessential to quantum computation. Light is efficiently delivered to a trap chip in a cryogenic environment via direct fibre coupling on multiple channels, eliminating the need for beam alignment into vacuum systems and cryostats and lending robustness to vibrations and beam-pointing drifts. This allows us to perform ground-state laser cooling of ion motion and to implement gates generating two-ion entangled states with fidelities greater than 99.3(2) per cent. This work demonstrates hardware that reduces noise and drifts in sensitive quantum logic, and simultaneously offers a route to practical parallelization for high-fidelity quantum processors5. Similar devices may also find applications in atom- and ion-based quantum sensing and timekeeping6.

Low loss and polarization-insensitive coupling length for a terahertz fiber directional coupler with symmetric dual-suspended core structure

In this work, a terahertz (THz) fiber directional coupler with a symmetric dual-suspended core structure has been proposed for realizing low loss and polarization-insensitive coupling length in the THz frequency region. The fiber core of the directional coupler consists of two round solid dielectric rods supported by two intersecting thin dielectric layers. Numerical simulations performed using the full-vector finite element method show that a short polarization-independent coupling length can be obtained by adjusting the geometric parameters of the fiber. Moreover, a low-loss THz fiber directional coupling performance can also be achieved at a central frequency of 1.00-THz and approximately 0.16 THz of bandwidth. For example, a coupler with a length of 0.421 cm has a transmission loss of 0.30 dB and 0.26 dB for the x- and y-polarization modes, respectively.

Indoor HDTV Broadcasting through Line-of-Sight Optical Wireless Link with Direct Fiber Coupling Transmitter

Indoor HDTV Broadcasting through Line-of-Sight Optical Wireless Link with Direct Fiber Coupling Transmitter

A simple but accurate formalism for study of single-mode graded index fiber directional coupler in presence of Kerr nonlinearity

This paper presents performance of directional coupler consisting of two identical single-mode graded index fibers in presence as well as in absence of Kerr type nonlinearity. In this context, parabolic and step index fibers of some typical V numbers are used. Here, we employ a simple series expression for fundamental modal field for such fibers prescribed by Chebyshev formalism. Analytical expression of the coupling length of the directional coupler is formulated. Here, we apply method of iteration in order to take care of nonlinearity. The concerned evaluation involves little computation. Thus, the formalism developed for study of nonlinear directional coupler can be treated as an accurate but simple alternative to the existing complicated methods available in literature. This user friendly method will prove beneficial to the scientists and technologists working in the field of nonlinear optics.

Method for direct coupling of a semiconductor quantum dot to an optical fiber for single-photon source applications.

We present an effective method for direct fiber coupling of a quantum dot (QD) that is deterministically incorporated into a cylindrical mesa. For precise positioning of the fiber with respect to the QD-mesa, we use a scanning procedure relying on interference of light reflected back from the fiber end-face and the top surface of the mesa, applicable for both single-mode and multi-mode fibers. The central part of the fiber end-face is etched to control the required distance between the top surface of the mesa and the fiber core. Emission around 1260 nm from a fiber-coupled InGaAs/GaAs QD is demonstrated and its stability is proven over multiple cooling cycles. Moreover, a single photon character of emission from such system for a line emitting above 1200 nm is proven experimentally by photon autocorrelation measurements with an obtained value of the second order correlation function at zero time-delay well below 0.5.

Mesoporous Silica Coated Silica Fiber Directional Coupler for Ammonia Gas Sensing for Medical and Industrial Applications

Mesoporous Silica Coated Silica Fiber Directional Coupler for Ammonia Gas Sensing for Medical and Industrial Applications

The effect of relative phase on the stability of temporal dark soliton in $${{\mathcal {PT}}}$$ PT -symmetric nonlinear directional fiber coupler

In this paper, we numerically investigate the effect of relative phase on the stability of dark solitons in $${\mathcal {PT}}$$ -Symmetric nonlinear directional coupler (NLDC), by considering gain in the bar and loss in the cross in the range of $$\theta =0^\circ$$ to $$180^\circ$$ . The $${\mathcal {PT}}$$ -Symmetric perturbed eigenfunctions are used to study the soliton stability. The results of simulations are shown that in the first half region of the relative phase the soliton is unstable while in the second one, is stable. In the stable region gain and loss cancel each other and also the perturbed eigenfunctions have no effect on solitons while in the unstable region solitons are amplified in the bar and attenuated in the cross except for some small intervals which the roles are changed. The behavior of such perturbation can be interpreted as self all-optical phase soliton switching and optical logic gates.

A novel and accurate method for analysis of single-mode dispersion-shifted and dispersion-flattened fiber directional coupler

Employing the simple series expression for fundamental mode based on Chebyshev technique, we present a simple but accurate analysis of coupling characteristics of identical single-mode dispersion-shifted trapezoidal and dispersion-flattened graded W and step W fibers directional couplers. Analytical expressions of the relevant parameters are formulated and the concerned calculations require simple and little computations. We show that our formulations on coupling characteristics of such type of fibers directional couplers provide excellent results.

Design of A Microchip Optical Switching Driven by Low Direct-current Voltage

A microchip optical switching based on a directional fiber coupler has been successfully fabricated by using silicon-on-insulator with two steps of photolithography and dry etching methods. Each waveguide has 1.75 μm width, 2 μm high and the distance between the waveguides at the coupling region was 2 μm. Metal aluminum layer with 4 μm width was attached at the coupling region due to switch the optical signal from a waveguide to another. The coupled mode theory was determined to model the coupling power at the coupling region. Experimental results have shown a good agreement of switching power at the coupling as function of increment of direct current voltage. It has been obtained that to switch the signal described by the switching region that occurs for the applied DC voltage in range of 18 volt to 32 volt. Certainly, an adjustable optical switching driven by low direct current voltage promises wide range of its application in optical network and sensor application.

General N-dark vector soliton solution for multi-component defocusing Hirota system in optical fiber media

In the normal dispersion regime of optical fibers with third-order dispersion and self-steepening higher-order effects, the propagation of ultrashort pulses is govern by the multi-component defocusing Hirota system. The general N-dark vector soliton solution is firstly constructed by the binary Darboux transformation. From obtained multi-dark soliton solutions, it is found that the collisions between or among vector dark solitons in this multi-component system are elastic, and vector dark solitons retain their shape and intensity only with a slight change in their phase. The results might be useful for applications about vector dark soliton in fiber directional couplers, optical switching and quantum information processors.