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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.

A tapered Er-doped fiber amplifier for high peak power pulses amplification has been developed and tested. The core diameter changed from 15.8 µm (mode field diameter (MFD) 14.5 µm) to 93 µm (MFD 40 µm) along 3.7 m maintaining single-mode performance at 1555 nm (according to the S2-method, the part of the power of high-order modes does not exceed 1.5%). The amplification of 0.9 ns pulses with spectral width below 0.04 nm up to a peak power above 200 kW (limited by self-phase modulation) with a slope pump-to-signal conversion efficiency of 15.6% was demonstrated.

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.

The spot size at which the electric field distribution for higher-order modes in few-mode fibers (FMFs) is approximated by a higher-order Gaussian profile is a promising parameter for estimating various transmission characteristics. To establish a technique for measuring the mode field diameter (MFD) corresponding to higher-order Gaussian spot size for any-order mode in FMFs, we investigate the relation between the higher-order Gaussian spot size and the values yielded by conventional MFD definitions. We then present formulas that output the MFD values corresponding to higher-order Gaussian spot size. Some examples of the MFD values for typical few-mode fibers determined experimentally and numerically are also shown.

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.

Up to now, there have been no complete theoretical researches and field experiment reports on the fiber fusion loss at high altitude. Therefore, we have conducted an exploratory study on the fiber splicing loss at high altitude, and firstly analyze the influence of mode field diameter mismatch, axial offset, angle tilt or end face gap affected by high altitude on splice loss, and then discuss the influence of fusion-splicing parameters on splice loss. Besides, a mathematical model for reducing the splicing loss of single-mode fiber at high altitude is established by combining the effects of temperature, humidity, oxygen content, atmospheric pressure, gale and gravity. We have conducted repeated field fusion experiments in different altitude areas (53, 2980, 4000, 4200, 4300, 5020, and 5200 m) more than once, hence obtaining a large number of field experimental data, making a deep comparison between typical “plain” area and typical “high altitude” area. The splice loss of most fusion points achieved successfully has been reduced by at least 0.07 dB. The simulation results are basically consistent with the theoretical analysis. Ultimately, the method proposed has been directly applied to on-site splicing engineering in high altitude environment and achieves good results.

We demonstrate a Yb-doped hybrid fiber with anomalous dispersion in the 1 μm spectral range, where asymptotically single-mode behavior is achieved with a differential mode amplification technique. The fiber has a dispersion of 70-100 ps/(nm·km) in the spectral range from 1.020 μm to 1.055 μm and a sharp dispersion peak (approximately 400 ps/(nm·km) near 1.064 μm) caused by the modes anti-crossing. The relatively large hybrid mode field diameter (8 μm) allows us to demonstrate high-peak-power femtosecond pulse generation via nonlinear chirped pulse compression in both dispersion regimes. Operation near 1.064 μm allows us to compress narrowband (3 dB spectral width of 2 nm) 6 ps pulses down to a duration of 250 fs with a peak power of 3.3 kW. Operation in the spectral region with a nearly constant anomalous dispersion is found to be optimal for the compression of wideband pulses. In particular, 1 ps pulses centered at 1.03 μm with a spectral width of approximately 11 nm are compressed down to 90 fs with a peak power of approximately 10 kW, which to the best of our knowledge is the best result for all-fiber (i.e., without external bulk compressors) systems operating near 1 μm.

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.

This Letter reports on a large mode area pixelated Bragg fiber in which some high refractive index rods were replaced by boron-doped rods that allows polarization maintaining behavior while keeping single-mode behavior. The realized all-solid fiber has a core diameter of 35 µm. The fundamental mode is circular with a 25 µm mode field diameter around 1 µm wavelength, and the polarization extinction ratio reaches 30 dB. Finally, this fiber is single-mode and bendable up to a 20 cm radius with fundamental mode losses lower than 0.3 dB/m.

A novel design of solid core photonic crystal fiber (PCF) has been proposed with seven rings rhombus inside eight rings hexagonal structure. Waveguide properties have been numerically investigated by utilizing the full vectorial finite element method (FEM). Here the paper elaborates PCF characteristic like confinement loss, dispersion properties, normalize frequency, mode field diameter, effective area, and nonlinear coefficient with asymmetric cladding designed and investigated. Silica is used as background material. The calculated value shows the ultra-low confinement loss in 1.1 µm to 1.7 µm, low negative dispersion -400ps/km-nm achieved in solid core. The high nonlinear coefficient 3.1661762 W-1km-1 and 3.141089 W-1km-1 at 1.55 µm in xpolarization and y-polarization mode respectively achieved. PCF achieved low confinement loss and better mode field diameter for remote sensing application.

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.

Universal fiber is a multimode fiber that has an LP01 mode field diameter approximately matched to that of standard single-mode fiber. It can transmit both multimode and single-mode signals using transceivers designed for either multimode fiber or single-mode fiber. By using universal fibers, one can bridge the needs for both single-mode and multimode transmission through a uniform and simplified cable infrastructure to accommodate the full distance range needed, while having upgradability from 10G to 40G to 100G and to even higher data rates. We build on our previous work that analyzed the dependence of LP01 mode-field diameter on fiber parameters, and the coupling loss for both single-mode and multi-mode transmission, with a further study of mode coupling and multiple path interference associated with single-mode operation. We demonstrate system performance in both single-mode and VCSEL-based multimode transmissions for a number of 100G transceiver types using a QSFP form factor − the preferred choice in data centers.