Search

In this paper, a germanium doped silica-based single-mode fiber for high speed optical communication link has been proposed. It is found that the proposed fiber is suitable for three transmission widows an excellent result at the third transmission window. Here, attenuation loss, dispersion, mode field diameter, bending loss, and material loss of the proposed fiber has been analyzed. It is found that dispersion such as material dispersion and waveguide dispersion is very low at the third transmission window (1550 nm), which is used for high speed optical fiber communication link. In addition to this, at the third transmission window, micro bending loss is almost disappeared and macro bending loss is also very low (0.00101 dB/km). All these analysis has been done using FDTD technique.

We present a new concept of 3D polymer-based 1 × 4 beam splitter for wavelength splitting around 1550 nm. The beam splitter consists of IP-Dip polymer as a core and polydimethylsiloxane (PDMS) Sylgard 184 as a cladding. The splitter was designed and simulated with two different photonics tools and the results show high splitting ratio for single-mode and multi-mode operation with low losses. Based on the simulations, a 3D beam splitter was designed and realized using direct laser writing (DLW) process with adaptation to coupling to standard single-mode fiber. With respect to the technological limits, the multi-mode splitter having core of (4 × 4) μm2 was designed and fabricated together with supporting stable mechanical construction. Splitting properties were investigated by intensity monitoring of splitter outputs using optical microscopy and near-field scanning optical microscopy. In the development phase, the optical performance of fabricated beam splitter was examined by splitting of short visible wavelengths using red light emitting diode. Finally, the splitting of 1550 nm laser light was studied in detail by near-field measurements and compared with the simulated results. The nearly single-mode operation was observed and the shape of propagating mode and mode field diameter was well recognized.

Fiber-chip edge couplers are extensively used in integrated silicon photonic for the coupling of light between optical fibers and planar silicon waveguide circuits. Here, we experimentally demonstrate three kinds of edge couplers with eased fabrication process, two fork shape, and one dual-trident SWG shape, based on Silicon-on-Insulator platform. A commercial lensed fiber with mode field diameter of 6 μm is used. The coupling performance and fabrication tolerance are theoretically analyzed and verified by 3D-FDTD simulation. The experimental results show that these edge couplers pose low coupling losses and large bandwidths simultaneously. At the wavelength of 1.55 μm, the coupling losses are 1.25 dB/facet, 1.49 dB/facet, 1.82 dB/facet for fork1, fork2, and dual-trident SWG couplers, respectively. The measured wavelength bandwidths in which the loss below 2 dB are 114 nm, 102 nm, 92 nm, respectively.

A depressed cladding waveguide composed of 36 parallel tracks is inscribed in high purity 70TeO2-22WO3-8Bi2O3 glass by femtosecond laser operating at 1030 nm. The Sellmeier formula for the refractive index of the investigated glass is obtained for the range of 1170–2350 nm. The module of the negative refractive index change in a track is found to increase with increasing wavelength in the range of 640–2000 nm. The waveguide shows single mode behavior in the wavelength range of 1700–2100 nm with mode field diameter (MFD) of 20 μm. The propagation loss is predominantly due to scattering in the waveguide. Spectrum broadening as large as 503 nm was demonstrated in a 14 mm long waveguide pumped by femtosecond pulses at 1950 nm. In the low input pulse energy region, the spectrum broadening is well described by generalized nonlinear Shrodinger equation (GNLSE) taking into account Kerr and the Raman nonlinearities under the assumption of constant MFD along the waveguide. Under higher energy pumping, an extra broadening was observed that is attributed to the focusing effect of Kerr lens in the waveguide mode.

In this paper, the modal characteristics of ring core fibers (RCFs) have been studied and a comprehensive review of recent work of ring core fibers is presented. Next, we investigate the ring core fiber parameters and their effects on the design performance in terms of effective mode index, mode group delay, mode field diameter, and differential group delay. Finally, A RCF design considerations for achieving high mode channel count and low crosstalk performances in weakly coupled MIMO transmission have been examined.

We developed a Ti/Au bilayer optical superconducting transition edge sensor (TES) laying on an optical fiber self-aligned structure. The bilayer approach enables us to control the superconducting transition temperature T C , which results in 8-μm-square-sized TES with T C as high as 314.0 mK. Moreover, the TES device is micro-machined so that it can be easily assembled with an optical fiber via a self-aligned method. Our TES device achieved a system photon detection efficiency (PDE) of 83.6% at 940 nm with an energy resolution of 0.21 eV. Electrical and effective time constants (rise time and decay time) were as short as 74 and 75 ns, respectively. We also theoretically analyzed the imperfect system PDE. According to this analysis, the imperfection originated mainly from misalignment between the TES and the optical fiber, and the system PDE will be increased up to >95% by use of an optical fiber with a smaller mode field diameter.

The evolution of microstructured optical fibers with hexagonal array (H-MOFs) of air-holes rooted in the background of undoped silica has led to the realization of an ideal host for encouraging and technologically entitled optical properties. We focus to explore the divergence of radiation into free space from the end-facet of solid-core H-MOFs by using the improved theoretical model. Also, we investigated the wavelength dependence of beam divergence angle for principal core mode of H-MOFs under step-index fiber approximation (SIFA). Experimental results have been included for comparison.

Reducing the mode size mismatch between high-index-contrast silicon waveguide and single-mode fiber takes an important role in photonic integration. A low-loss and broadband silicon-nitride-assisted edge coupler for the coupling of light between silicon wire waveguides and high numerical aperture fiber is proposed and optimized for TE polarization. The mode size converter is composed of silicon inverse taper waveguides in the core and two silicon nitride interlayers spaced by silica in cladding layers. The edge coupler is characterized by cleaved high numerical aperture fiber (mode field diameter is about $6.5~\mu \text{m}$ ). With the help of refractive index matching oil ( $n =1.46$ ), the coupling loss for TE polarized light input is 0.35 dB at 1570 nm. The 1-dB bandwidth is 95 nm. The 1-dB alignment tolerances are higher than ± 2.5 and $\pm ~1~\mu \text{m}$ in the horizontal and vertical directions, respectively, and higher than $25~\mu \text{m}$ in the axial direction.

We design a panda type four-core fiber with a comparable optical property of the polarization maintenance single mode fiber (PM-SMF) and can support 8 non-polarization-degenerate eigenmodes with a birefringence of approximate 3.24 × 10-4 over the wavelength range from 1288 to 1630 nm. In particular, only four stress rods are efficiently used to achieve the PM characteristics for each core, in comparison with traditional design of panda type PM-SMF. Meanwhile, we identify that the optimal configuration of stress rods can not only enhance the birefringence, but also further suppress the crosstalk (XT) between two primary eigenstate of polarization (ESOP) arising in adjacent cores, although the corresponding XT at secondary ESOP remains unchanged. Moreover, our numerical results show that both chromatic dispersion (CD) together with mode field diameter (MFD) and the bending sensitivity are consistent among four cores. We believe that such specialty multi-core fiber is ideal for compact and cost-effective fiber-optic gyroscope (FOG) application, besides the potential in the MIMO-free spatial division multiplexing (SDM) interconnection.

Traditional fusion splicing technologies are not usable for the high-index core triangular lattice microstructured optical fibres (MOFs), as the characteristic air-holes pattern often collapse during splicing, significantly increasing splice losses due to distortion of the waveguiding structure. The low-loss splicing of MOF and the traditional single-mode fibre (SMF) can be achieved by enlarging the mode-field diameter (MFD) of MOF, facilitating to an optimum mode-field match at the splicing interface. Using our recently developed improved field model Sharma and Sharma (2016), we aim to investigate the modal characteristics of high-index core MOF as a mode-field expander, and low-loss splicing between an MOF and the standard step-index single-mode fiber by using controlled all air-hole collapse method. For comparison, experimental and the numerical simulation results have been included, as available in the literature. Relative errors are also given.

The all-fiber platform of laser system attracts increasing attention due to possibility to achieve outstanding characteristics simultaneously combined with usage convenience. However, the latter is minimized without providing flexible laser radiation delivery by using optical fibers. Passive large mode area (LMA) fibers should deliver a high-power beam without significant quality deterioration and maintain stable performance caused by environmental vibrations, which accompanies routine operations. The proposed approaches for the LMA fibers are chirally coupled core fibers, multicore fibers, low NA all-silica fibers, photonic crystal fibers and hollow core fibers. Most outstanding results shows that hollow core fiber structure allows to achieve core diameter about 60 µm with effectively single mode (ESM) operation at 1 µm, mode field diameter (MFD) about 40 µm [1] and fundamental mode attenuation about 0.017 dB/m. However, demanding manufacturing process together with necessity to seal input and output makes industrial application of hollow core fibers less attractive comparatively to the all-silica fibers. Typical core diameter for conventional all-silica low-NA LMA fibers, does not exceed 30 µm with MFD less than 20 µm. At the same time increase of the core diameter significantly increase the bending losses.

Chirped Pulse Amplification (CPA) is nowadays a widely used method in laser industry to achieve highly energetic ultra-short pulses. To make it as robust and compact as possible, a fibered approach is highly desirable when possible. Nevertheless, the high power density into the core of a fiber may induce detrimental nonlinear effects leading to spectral and temporal quality degradation of the optical pulses. To mitigate this, large Mode Field Diameter (MFD) fibers have been largely studied [1] – [2] . Despite their efficiency, such fibers often lead to spatial beam degradation and non-monolithic set-ups. Fibers with a longitudinally increasing MFD called taper fiber have emerged since 2008 [3] . This geometry results in an all-fiber setup combined with a good beam quality thanks to adiabatic transition of the fundamental mode [3] – [4] and a efficient pump absorption due to non-reciprocal light propagation along the fiber [3] – [4] . We investigate here the ability of this type of fiber to amplify ultra-short pulses beyond 100 µJ in a CPA architecture while keeping pulse compressibility below few picoseconds.

A kind of bending-insensitive multicore fiber (MCF) is proposed. The core adopts a low-mode gradient index structure to form a seven-core few-mode fiber. The finite element method is used to simulate and analyze the bending loss of the central core and the outer core, the crosstalk between the core modes, and the influence of core parameters on the crosstalk performance. Data simulation results show that even for a small bending radius of 5 mm, the bending loss of this MCF is much lower than the attenuation loss of the fiber, and the crosstalk between the adjacent cores is less than −20 dB. Therefore, independent information transmission between cores can still be realized under a small bending radius.

Infrared photonic-crystal fibers (IR PCF) based on AgClxBr l-x and AgBrxIl-x crystals have been developed for operation at a CO 2 laser wavelength (10.6 µm). The prospects of using fiber optics, including those with a photonic structure, in medical technologies as a conductor of laser radiation are considered. The advantages and disadvantages of unjacket and two-layer fibers, as well as the versatility and uniqueness of photonic crystal fibers are shown. The process of designing optical fibers with a photonic structure is presented, from the stages of mathematical and computer modeling to seven-stage extrusion and properties study. In computer simulations, plane wave and finite element methods were used to analyze the band structure and mode analysis, respectively. In the properties' study, a CO 2 laser and a Spiricon Pyrocam III camera were used. The model was verified with a real fiber by measuring the radiation distribution in the far zone. High convergence of simulation results with the fabricated fiber is obtained. Thus, infrared fibers with an increased mode field diameter were obtained, which are flexible, easy to sterilize and safe for humans for medical applications.

Fiber-to-chip optical interconnects is a big challenge in silicon photonics application scenarios such as data centers and optical transmission systems. An edge coupler, compared to optical grating, is appealing to in the application of silicon photonics due to the high coupling efficiency between standard optical fibers (SMF-28) and the sub-micron silicon wire waveguides. In this work, we proposed a novel fiber–chip edge coupler approach with a large mode size for silicon photonic wire waveguides. The edge coupler consists of a multiple structure which was fulfilled by multiple silicon nitride layers embedded in SiO2 upper cladding, curved waveguides and two adiabatic spot size converter (SSC) sections. The multiple structure can allow light directly coupling from large mode size fiber-to-chip coupler, and then the curved waveguides and SSCs transmit the evanescent field to a 220 nm-thick silicon wire waveguide based on the silicon-on-insulator (SOI) platform. The edge coupler, designed for a standard SMF-28 fiber with 8.2 μm mode field diameter (MFD) at a wavelength of 1550 nm, exhibits a mode overlap efficiency exceeding 95% at the chip facet and the overall coupling exceeding 90%. The proposed edge coupler is fully compatible with standard microfabrication processes.

Trace detection and identification of hazardous volatile explosives has been a key challenge to the scientific community past many decades. Commercially available various analytical and spectroscopic techniques suffer from low sensitivity, swabbing of surfaces and low detection limit. Triacetone Triperoxide (TATP), used in improvised explosive devices IEDs vaporizes readily at room temperature and has a vapour signature. However, explosive trace detectors (ETDs) are incompetent to detect TATP due to absence of chromophoric groups. We have investigated the novel hollow core photonic crystal fibres (HC-PCFs) based Raman sensor for real time monitoring of such volatile explosives in airport security. Raman scattering, a powerful, non-destructive tool provides molecular fingerprinting and is a potential candidate for detection of trace explosives but suffer from weak signal strength. Simultaneous confinement of pumped light and gas in HCFs allows greater light gas interaction providing an excellent optical sensing platform. These sensors can be easily incorporated at the security terminals or baggage counters with the existing metal detection systems. This paper reports investigations carried out on the HC-PCF designed using COMSOL Multiphysics software. The Raman signal being dependent on its intensity and mode area, simulations were conducted to analyse PCF parameters like confinement losses and mode field diameter/ effective mode area and its associated wavelength dependency. Theoretical study carried out on the HC-PCF also revealed that mode field confinements within the hollow core can be modified to suit specific laser wavelengths and confinement losses can be reduced to achieve Raman signal enhancement by optimizing their geometrical parameters like air-hole size and pitch/ hole-to-hole distance.

The need for the enhancement of channel capacity of optical fiber, space division multiplexing (SDM) transmission fibers- such as the multicore fiber, the multimode fiber and the few-mode multicore fiber, etc., - have been researched for long-distance communication system. In this paper, a special type of homogeneous multicore fiber structure is introduced and the array of holes is placed between each core. The normalized propagation constant, mode field diameter (MFD) of LP 01 mode of this structure are studied here. The empirical relation between normalized propagation constant and V number of LP 01 mode of a single core single-mode fiber is compared with simulation results of LP 01 mode of a multicore fiber. The mode field diameter of MCF is derived by noting the beam radius where the intensity drops to 1/e2 of the intensity on the beam axis. The theoretical prediction match well with COMSOL results. These results are useful for the investigation of the detailed characteristics of different types of MCF.

In this paper, we have developed Yb-doped fiber suitable for creation of all-fiber seed laser schemes operating near 977 nm. The fiber was based on a ring-doping design (cladding was partially doped with Yb-ions), which allowed us to fabricate a relatively small core and provide mode field diameter (MFD) of the active fiber comparable with standard fibers (to achieve small splicing losses with commercially available optical fibers) and, simultaneously, increase absorption from the cladding to keep a reasonably high lasing efficiency. So MFDx of the fiber was 12 μm, MFDy was 14 μm. Outer silica cladding of the active fiber was decreased to diameter of 80 μm and a special pump and signal combiner was used to inject pump and signal into the active fiber. Based on the developed Yb-doped fiber an all-fiber polarization maintaining mode-locked laser with central wavelength around 977 nm was demonstrated for the first time. SESAM was used as a saturable absorber. The laser was self-starting for pump powers above 4.6 W, with the output power of 3 mW. The autocorrelation was the best fitted with sech2 profile and pulse duration was estimated to be as long as 9.5 ps. The fundamental cavity frequency corresponded to the pulse repetition rate of 33.532 MHz. Signal-to-noise ratio measured in the radio frequency range was more than 50 dB, the line width was below 1 kHz, which indicate ultimate stability of the fabricated mode-lock laser. acceptedVersion

Optical interconnects in data centers have traditionally used 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) in combination with multimode fiber, having a reach up to 100 m in length. Longer links typically use standard single-mode fiber in conjunction with either InP-based edge-emitting lasers or silicon photonic transmitters operating in the 1310 nm or 1550 nm window. Single-mode GaAs-based VCSELs operating at 1064 nm offer another path for achieving longer system reach. Potential advantages of these VCSELs include better power efficiency, modulation speeds reaching 50 Gbps and large-scale fabrication volumes. The longer wavelength is also beneficial due to the lower attenuation and chromatic dispersion of optical fibers at that wavelength. However, one practical issue for single-mode transmission is that the G.657 standard for single-mode fiber requires that the 22-meter cable cutoff wavelength be less than 1260 nm, and these fibers are typically few-moded at 1064 nm. The large differences between the group velocities of the LP01 and LP11 modes can lead to degradation of the system performance due to multi-path interference if the higher order modes are present. To resolve this quandary, we have designed and validated the performance of a new optical fiber which is single-moded at wavelengths less than 1064 nm, but also has G.657- compliant mode field diameter and dispersion characteristics that enable it to be used in the 1310 nm window.

We propose to use high numerical aperture single mode optical fibers like photonic crystal fiber for lensless in-line holographic microscopy. Highly divergent beam helps to overcome the spatial sampling limitation of the image sensor. In this paper, a submicron lateral resolution has been demonstrated, with an imaging sensor of pixel pitch 1.12 μm and a photonic crystal fiber of mode field diameter 1.8 μm. In earlier methods of single-shot lensless imaging, submicron resolution has been obtained at very small working distance and field of view. The proposed method improves the resolution without compromising the working distance. A working distance (but not limited to) ~ 1.7 mm with a field of view ~ 1.4 mm has been demonstrated.

We developed a highly efficient double-clad Yb-doped polarization-maintaining fiber to be implemented for small-signal amplification near 0.976 μm. The fiber was designed to have a relatively small mode field diameter compatible with standard step-index single-mode optical fibers. Another feature of the fiber was a small threshold for 0.976 μm signal amplification, which was achieved by a creation of a thin inner cladding (80 μm diameter). The unique design of the fiber allowed us to construct successfully an all-fiber picoseconds mode-locked laser at 0.98 μm for the first time to the best of our knowledge.

We demonstrated the generation of narrow spectral bandwidth, high energy picosecond pulses from a low repetition rate SESAM mode-locked laser seeded Yb-doped fiber MOPA system. A short large mode field diameter gain fiber (DCF-30/250) was adopted to efficiently reduce the influence of nonlinear effects. The maximum pulse energy of 12.36 μJ, ∼60 ps pulses with a narrow bandwidth was obtained at a repetition rate of 5 MHz, corresponding to the peak power of 0.2 MW and average output power of 64 W. The optical-to-optical conversion efficiency was ∼64% in such a low repetition rate all-fiber laser design. The output pulse spectra and temporal trace of the MOPA system for different output powers was investigated by simulation. The simulation results were in agreement with experiment but further showed that the spectral splitting would occur as output power increased.

As the size of research objects reaches the nanometer level, there is an increasing desire to trap and detect nanoparticles. However, the means to trap and study individual nanoparticles is not mature. Here, we propose and demonstrate a method for trapping a single nanoparticle stably and moving it in a three-dimensional space using a single-mode optical fiber probe based on a strong convergent LP 11 mode beam. The small mode field diameter of the LP 11 beam and the particular probe structure are combined to obtain a nanoscale convergence area to trap a 100 nm nanoparticle stably. The proposed optical fiber tweezers have the advantages of high spatial resolution, simple structure, and easy operation. They are expected to be developed to control organelles in single cells, screen particles of different sizes, and extract virus cells.

The diffraction beam characteristics of tapered-platform fiber are demonstrated by theoretical analysis and experimental measurement. The tapered-platform fiber is designed and fabricated. Based on light ray theory, the Gauss beam lens conversion model is established and the outgoing beam of the tapered-platform fiber end-face is analyzes. The transmission characteristics at the near field and far field spatial distribution of the tapered-platform fiber are measured with visible light, which are showing the evolution of tapered-platform fiber in optical transmission and mode spot. A CCD based video zoom microscope system is built to record cone optical fiber diffraction, and the diffraction pattern of tapered-platform fiber diffraction field in different locations is tested. The results show the diffraction field of tapered-platform fiber is Gauss beam, this research will provide important reference to the application of tapered-platform fiber.

Potential niches for a power-over-fiber (PoF) technique can be found in hazardous areas that require controlling unauthorized access to risk areas and integration of multiple sensors, in scenarios avoiding electromagnetic interference, and the presence of ignition factors. This paper develops a PoF system that provides galvanic isolation between two ends of a fiber for remotely powering a proximity sensor as a proof of concept of the proposed technology. We analyze scalability issues for remotely powering multiple sensors in a specific application for the hazardous environment. The maximum number of remote sensors that can be optically powered and the limiting factors are also studied; considering different types of multimode optical fibers, span lengths, and wavelengths. We finally address the fiber mode field diameter effect as a factor that limits the maximum power to be injected into the fiber. This analysis shows the advantages of using step-index versus graded-index fibers. This work was supported in part by the Spanish Ministerio de Economía, Industria y Competitividad, Comunidad de Madrid and H2020 European Union Programme under Grants TEC2015-63826-C3-2-R and S2013/MIT-2790, in part by FSE, and in part by 5G PPP BlueSpace Project under Grant 762055. Publicado

Remotely directional transmission of terahertz (THz) wave in free space is essential in fields of astronomy, space and ground based communications, as well as sensing for atmospheric pollutants, etc. In previous studies, large-aperture halfway mirrors were employed in order to fully collect and then focus the heavily naturally diffracted beam of THz wave to the final target. In this case, however, the broad THz beam not only made a large-size transmission system, but also led to a heavy energy loss due to water vapor absorption within the beam cross-section. Here, we theoretically proposed two index-guiding-based THz waveguide structures composed of plasma filament arrays in air, i.e., hollow cylindrical plasma (HCP) waveguide and free-space photonic crystal (FPC) waveguide (triangular lattice point matrix with a central point defect). Both structures have been demonstrated to well support THz propagation modes, which were confined inside the tiny central air core of the waveguide for an attenuation length up to hundreds of meters. Compared with each other, the FPC waveguide exhibited better performances, including smaller mode field diameter, longer attenuation length and better single-mode property for a broad THz band, making this scheme a promising candidate for long-distance guidance of THz waves in the atmosphere.

This paper presents the results of a study of the refractive-index dispersion for the AgBr–TlI, AgBr–TiBr0.46I0.54, and AgCl–AgBr crystal systems in the spectral range from 0.4 to 56 µm, along with the results of the development and fabrication of single-mode microstructured IR fibers by extrusion from solid solutions of metal halides. The fibers had a central insert 16 µm in diameter of composition 2.6 mol% TlI in AgBr, located in a matrix of composition 2.3 mol% TlI in AgBr with external diameter 525 µm. Inserts with diameter 16 µm of composition 2.0 mol% TlI in AgB were placed in the matrix in hexagonal order. The distribution of the radiation emitted from the fibers in the far field at wavelength 10.6 µm was studied, along with the influence of local heating of a section of the fiber on the transport of the IR radiation. The mode-field diameter was experimentally estimated as 120±30µm. The fibers were suitable for transporting both laser and thermal radiation from heated objects to a thermal viewer.

An approach to obtain single-mode operation on a semirectangular large core area Flat Fiber (FF) slab waveguide is proposed. A new design of FF with two defect eye holes is presented, and its single-mode guiding is analyzed by simulation. To validate the simulation results, a proof of concept FF with a core area $ > 1200{\rm{\ \mu }}{{\rm{m}}^2}$ was fabricated, and its modal behavior was examined. It was found that higher order propagation modes could be discriminated from the large core area by introducing a high-refractive index region in the FF eye holes. Experimental results confirmed a single Gaussian mode profile (mode field diameter of $ \approx745{\rm{\ \mu m}})$ output of this large core FF, thus validating the simulation results.

A fiber optic accelerometer–magnetometer (FOAM), which can measure acceleration and magnetic field simultaneously, based on fiber laser sensing is proposed. The principle of the FOAM and the theory of the mixed signal of acceleration and magnetic field are presented. To verify the theory, an FOAM was fabricated and tested. The measured acceleration sensitivity and the sensitivity of magnetic flux intensity were 9.75 pm/g (19.78 dB, re: 0 dB = 1 pm/g) within 100–250 Hz, and 0.955 pm/T/mA@725 Hz, respectively, which were close to the theoretical values. A test of simultaneously measuring acceleration and magnetic field was performed. The results show that the responding mixed signal achieves a good SNR. It proves that the function of the sensor has been realized and the theory of mixed signal is reliable.

In this paper, the strain insensitive single mode optical fiber with low nonlinear effects and ultra low bending loss (BL), appropriate for small curvature radius installation, is presented. The suggested design method is based on the reverse engineering which evaluates the refractive index profile considering proper mode field diameter (MFD) value. Then, so as to attain the desired bending loss and strain response for the optical fiber, the optimization tool of the evolutionary genetic algorithm (GA) is employed to determine the optical and geometrical parameters of the structure. In the first designed fiber, the calculations for BL, MFD, effective area (Aeff), and effective refractive index (neff) sensitivity to strain in the well-known wavelength of 1.55 µm are 0.0018 dB per each turn of 5 mm curvature radius, 8.53 µm, 58 µm2, and 4.5 × 10-8 µɛ-1, respectively. Furthermore, the effect of placing raised outer cladding in the fiber structure is investigated which exhibits the MFD of 8.63 µm, 0.0093 dB BL for single turn of 5 mm radius, and 87 µm2 Aeff at 1.55 µm. In this case the strain sensitivity of 6.7 × 10-8 µɛ-1 is calculated for the neff. The mentioned effective area is magnificently large in the domain of bend insensitive fibers. In the meantime, the designed structures are insensitive to strain which is a crucial feature in applications with small curvature radius.

The work is devoted to the problem of the integration of the photonic integrated circuit with optical fiber. In the standard single mode fibers mode field diameter is greater than the mode field diameter in the waveguide in 3–10 times, so coupling of light has high losses. It was considered lateral coupling between lensed tapered fiber and a small diameter waveguide. It was performed an analytical calculation with the gaussian approximation and modelling of fiber tapered lens for input radiation into the waveguide using the method of propagating beam. As a result, the analytical calculation and simulation derived an optimum radius of curvature of the tapered lens for an effective input of optical radiation in an arbitrary waveguide with a diameter of 3 microns. Lensed tapered fibers were made up by chemical etching followed by arc melting technology and it was received a set of samples with a radius of curvature from 6 to 16 microns. Mode field diameter of samples was measured by the transverse offset technique in the near field, and the focal length was measured by the method of the Fabry-Perot interferometer. The error of measured parameters is no more than 30%, and results are confirmed with analytical calculation and modeling.Received 07.03.2017; accepted 11.05.2017

Efficient edge coupling into a silicon waveguide is demonstrated using an optical fiber axicon lens operating at 1550 nm. The axicon was fabricated on the cleaved endfacet of an SMF-28e optical fiber using a focused ion beam milling process. The lens converts the guided mode of the optical fiber (mode field diameter of 10.4 $\mu$ m) into a Bessel-type beam with an extended depth of focus, which was verified both experimentally and by three-dimensional finite-difference time-domain simulations. Axicon lenses with a diameter of 15 $\mu$ m and heights of 3.5 and 5.0 $\mu$ m were fabricated, and their focusing effect optically characterized through high-resolution confocal imaging, showing a focal spot size of 3.57 and 2.34 $\mu$ m, respectively. The coupling efficiency from the axicon into a silicon-on-insulator photonic integrated circuit is comparable to that of a commercial tapered lensed fiber, and in some cases slightly higher. Due to the extended depth of focus, the axicon lens also offers a larger alignment tolerance in the longitudinal direction.

This work presents fast and simple method for design and computing parameters of precision spatial positioning scheme for mode division multiplexing (MDM) system channels placement over optical fiber core end. Proposed solution is based on combination of well known mode field overlap integral method and earlier on developed modified Gaussian approximation. Computation results showed that fitting of MDM channel mode field radius and its corresponding offset launching position in relation to optical fiber core center provides transmission of the almost total channel injected mode power to only one particular excited fiber mode with the same azimuthal order. This work presents results of proposed method approbation for computation of spatial positioning scheme for modes of 5-channel MDM system placement over few-mode optical fiber 42/125 core end.

In view of mode field matching problem between the polarization-maintaining photonic crystal fiber and the conventional optical fibers, the polarization and mode field distribution characteristics of photonic crystal fiber were analyzed and investigated by using a finite element method. The loss mainly comes from the mismatch of two kinds of optical fiber mode field diameter (MFD). The collapse of air hole in photonic crystal fiber can be accurately controlled by heating photonic crystal fiber with fusion splicer, and MFD of photonic crystal fiber can be increased. We presented changing the fusion parameters of fusion splicer to reduce the fusion splicing loss and improve the splicing quality between PCFs and PMF with arc discharge of fusion splicer. Finally, we get a loss of 0.8dB for the later from PCF to PMF, and 0.5dB from PMF to PCF. At the same time, tensile strength is better than 100kpsi.

For getting a faithful performance in optical fiber communication, the biggest parameter which dwindles the response of communication is a loss factor. Under this, various kinds of losses can be considered. So as to reduce the effect of same, the kinds of losses should be measured accurately or precisely and then should try to reduce the same also. Accordingly, here few techniques of measurement of losses towards degree of closeness which in turn beneficial to compare and enhance the performance by taking proper action against is focused or reviewed, such as-optical fiber (Single Mode Step Index) cable is twisted then checked the performance with respect to macro bend loss and wrapping turn loss. Mode Field Diameter (MFD) and Spectral Attenuation measurement technique reviewed here. Also, quantification of macro bend loss by two-point bend method and prediction of worst-case macro bending loss in Bend Insensitive Fiber (BIF) using a geometrical parameter. This entire is reviewed in this paper and compared.

The photonic nanojet (PNJ) generated by a shaped optical fiber tip is an attractive technology for laser micro-machining. The working distance has the same order of size as the fiber core diameter; therefore, multimode (MM) fibers are generally preferred. However, the PNJ is due to the fundamental mode and, therefore, the energy coupled on the high-order modes does not contribute to the process. We demonstrate the benefit of a large-mode-area (LMA) optical fiber in the generation of the PNJ. A homemade 40 μm mode field diameter LMA fiber is compared with a 100/140 MM-shaped fiber tip. Similar micro-peaks are obtained, and an energy gain is demonstrated. The coupled energy required was eight times less intense with the LMA fiber, which may open new possibilities for laser micro- and nano-processing.

In this paper, an optical strain sensor with automatic temperature compensation is presented. The strain sensitivity is 198.547 pm/μe, which is nearly 2.8 times that of the latest generation multilayer optical fiber strain sensor based on mode field diameter (70.77 pm/μe). This increase in sensitivity is due to the particular structure within which the optical fiber sensor is installed. This structure amplifies the applied strain and transfers it to the optical fiber. In order to compensate for the temperature effects, employing a negative temperature expansion (NTE) element is essential. In addition, applying an initial strain is required to adjust the system performance. As a result, the entire sensor system is automatically compensated for the temperature with less than 1 percent error.

Bone strain measurement is a case of interest and demanding task for osteogenic adaption responses. In this paper, a novel biocompatible optical sensor for the bone axial strain measurement was proposed. In case modern multilayer single mode WII type optical fibers are well designed, they exhibit superior characteristics compared to conventional metal strain gauges (SGs). Furthermore, they could be strong competitors for SGs based on fiber Bragg grating (FBG) devices. In this study, mode field diameter (MFD) was selected as the indirect parameter for sensing task, which was totally a new approach. The strain sensitivity of 70.7733 pm/μe was obtained. Moreover, temperature sensitivity was–3.0031 × 10–6 pm/°C, which was negligible and removed the temperature compensation complexity for the sensor structure presented. The satisfactory property achieved for the designed sensor is as a result of multilayer fiber’s complicated structure as well as the design procedure based on evolutionary genetic algorithm (GA). In addition, the sensor demonstrated a reliable performance as its sensitivity was independent of the magnitude of the applied load.

Gain enhancement of single-mode Cr-doped crystalline core fiber (SMCDCCF) with longer fiber length fabricated by online laser-heated pedestal growth (LHPG) technique is demonstrated. In comparison with the SMCDCCF fabricated without online growth, the online technique enables real-time monitoring and controlling small molten zone in the LHPG to achieve longer length with better uniformity and smaller core diameter of the SMCDCCFs. The SMCDCCF exhibits a length of 10.6 cm, a core diameter of 25 mu m, and a V-value of 2.40, which confirms the LP01 single-mode operation by the far-field pattern measurement. A 3.9-dB gross gain and a 1.9-dB net gain of the SMCDCCF at the wavelength of 1400 nm were obtained. The gross and net gains are the highest yet reported of the SMCDCCFs. Further development on higher gain of the SMCDCCF may be functioned the SMCDCCF as a broadband fiber amplifier for use in the next-generation fiber transmission systems.

In this article, the strain behaviour of the depressed inner core triple clad single mode optical fiber is investigated. Both tensile and compressive types of axial strain are considered in simulations. The modal analysis of the fiber structure is based on linear polarization (LP) approximation method. Mode field diameter (MFD) of the fiber is selected as the indirect parameter for strain sensing task and investigating the MFD behaviour of the fiber, the strain sensitivity is augmented through independent adjustment of the structural parameters. Subsequently, a design procedure based on evolutionary genetic algorithm (GA) is introduced for consideration of simultaneous effect of all hyper-parameters of the fiber which yields the strain sensitivity of 15.96 pmμe−1. The substantial sensitivity attained is as the inherence of complicated configuration in multilayer fiber as well as the GA based method. Furthermore, negligible temperature sensitivity of −6.97 × 10−7 pmC−1 removes the temperature compensation technique which is inevitable stage of fiber optic measurement systems. Additionally, the simulation results admit the stable strain response of the proposed structure.

Optical fibres having a radially nonuniform acoustically antiguiding structure produced by codoping their core with alumina and germania have been fabricated and investigated. The influence of the shape of the antiguiding acoustic refractive index profile and fibre core diameter on the stimulated Brillouin scattering (SBS) threshold and spectrum in the fibres has been assessed. An increase in SBS threshold by 4.4 dB with respect to a germanosilicate fibre having the same mode field diameter has been demonstrated.

This paper reports proof-of-principle of an optical fiber Bragg grating (FBG) operating as an electric field sensor. The system is based on a semiconductor diode laser, emitting around 1577.5 nm that interrogates the fiber sensor around its maximum reflectivity point. The application of a strong electric field causes a small variation of the optical path length of the waveguide due to electrostriction and thus perturbs the grating peak reflectivity wavelength. Calibration and dynamic range tests are performed using a parallel-plate capacitor to create a variable electric field (1-100 kV/cm). A great potential is pointed out in view of possible field applications for voltage graduation in power generators.

A Single-mode flat fiber investigated by mode matching filtering technique is presented. This class of rectangular optical fiber employed a mode filtering technique to filter high order modes. Fresnel leakage loss induced the propagation modal loss favors fundamental mode, whereas significantly filtered higher-order mode due to modal loss. This resulting mode operation can be expanded via high-aspect-ratio. We numerically analyze the via full-vectorical numerical analysis. We also cover the dispersion analysis to be estimated around wavelength of 1268 nm.

A relative humidity sensor based on a graphene oxide-coated few-mode fiber Mach-Zehnder interferometer (MZI) is proposed in this paper. The MZI was made by splicing a segment of the few-mode fiber (FMF) between two segments of a no-core fiber (NCF) and two segments of a single mode fiber (SMF) located outside the two NCFs. The core and cladding of the FMF acted as interferometric arms, while the NCFs acted as couplers for splitting and recombining light due to mismatch of mode field diameter. The cladding of the FMF was corroded with hydrofluoric acid, and a layer of graphene oxide (GO) film was coated on the corroded cladding of FMF via the natural deposition method. The refractive index of GO varied upon absorption the water molecules. As a result, the phase difference of the MZI varied and the wavelength of the resonant dip shifted with a change in the ambient relative humidity (RH). High humidity sensitivity of 0.191 and 0.061 nm/%RH in the RH range of 30-55% and 55-95%, respectively, were achieved experimentally. The high sensitivity, compact size, and simple manufacturing of the proposed sensor could offer attractive applications in fields of chemical sensors and biochemical detection.

We propose a fiber-chip edge coupler based on a subwavelength grating in silicon-on-insulator (SOI) platform for coupling to cleaved and high numerical aperture (HNA) optical fibers (mode field diameter of 6.3 μm). Its robustness to fabrication errors and high tolerance to fiber misalignment (±1.5 μm for a 1 dB of excess loss) make it suitable for high-volume production, being a potential candidate for data center applications. Simulation results show a 1 dB bandwidth higher than 200 nm, a polarization dependent loss lower than 0.5 dB, and minimum coupling losses of 1.47 and 1.39 dB for TE and TM modes, respectively, considering a 204 μm-long mode converter.

The simultaneous measurement of the numerical aperture (NA) and mode field diameter (MFD) of single-mode fibers was performed on several commercial fibers by means of digital image processing of the output light projected into a screen. In addition, the changes induced by core diffusion in an ultra-high (UH) NA fiber at several heat depositions from a CO2 laser source were measured. The measurement method was demonstrated to be useful to monitor the adiabaticity of this process, by taking the product of the NA and MFD to verify if it remains constant. The method provides a cheap alternative to measure these optical fiber parameters by using simple optomechanical elements and a readily available smartphone camera, and it can be easily implemented in the laboratory.

In silicon photonics, optical coupling between optical fibers and silicon photonics chips still remains a big issue to be improved. Recently we have developed a new surface coupler consisting of a vertically-bent silicon waveguide using ion implantation as a bending method. This bending method enabled bending of silicon waveguide terminals to the vertical surface direction with curvature radii as small as several μm and bending of propagation direction of light to the surface direction with broadband wavelength property. In our initial studies, to couple the propagated light with optical fibers efficiently, we taper-narrowed the tips of the waveguide terminals from 440 nm to ~200 nm to expand the mode field and obtained a coupling loss of ~2 dB in TE-polarization mode for a lensed fiber with a beam diameter of 2 μm. We are now developing couplers with high coupling efficiencies for 5 μm mode field diameter fibers. Such mode field diameters are available by HNA fibers and position alignment accuracy can be mitigated to a micron level. In addition, HNA fibers can be fusion-spliced to standard single mode fibers. Using 3D-FDTD simulation we have demonstrated that 2 dome. In practice, such a structure could be fabricated successfully and 5 dB coupling with a 5 μm mode field diameter lensed fiber has been demonstrated in our initial experiment

We designed and fabricated a graded-index (GI) multicore fiber (MCF) compatible with both standard multimode and single-mode fiber for high density optical interconnect application in large-scale data centers. The proposed fiber supports long-distance multimode transmission at 850 nm as well as quasi-single mode transmission at 1310 nm and 1550 nm. The parameters of the GI-MCF have been optimized to obtain both a small differential mode delay at 850 nm and a small mode field diameter mismatch of less than 0.5 μm with single-mode fiber at 1310 nm and 1550 nm with a negligible inter-core crosstalk. In experiment, we successfully realized the multimode operation over 1 km-long GI-MCF at 850 nm and the quasi-single mode operation over 12.4 km-long GI-MCF at 1310 nm and 1550 nm at a data rate of 7×10-Gb/s. The multi-wavelengths multicore transmission was demonstrated for the first time. The experiment results imply that the proposed GI-MCF satisfies various requirements in such as operating wavelength, accessible distance and interconnect density of large-scale data center, and can effectively reduce the fiber numbers and system complexity.

We have designed, fabricated and tested edge couplers for silicon photonics with etched lenses targeting industry-standard SMF-28 fibers as well as future alignment and dust-tolerant expanded-beam connectors. These edge couplers are based on a Si inverse taper combined with a SiON ridge waveguide and etched lens fabricated on a silicon-on-insulator (SOI) platform. The lens structures were designed for coupling to SMF-28 fibers with a 1/e mode field diameter (MFD) of 10.4 micrometers in the telecommunications C-band. Alternate lens designs targeted expanded beams with 30 micrometer horizontal MFD. The measured SMF-28 lensed couplers exhibited a 1 dB bandwidth exceeding 150 nanometers, polarization dependent loss (PDL) of less than 1 dB and coupling efficiency better than -4.8 dB across the S-, C- and L-bands with only horizontal beam expansion.

We propose and design a fiber with logarithmic-index profile for orbital angular momentum (OAM)transmission. The designed fiber shows favorable performance of low mode crosstalk and tensile invariance property of mode field diameter (MFD).