Large Core Diameter Research Articles

Structure modeling and manufacturing PCFs for the range of 2–25 μm

Photostable and flexible materials transparent at the wide spectral range are necessary for the development of optical fiber units. Solid solutions of silver and monadic thallium halides are the most suitable crystal media for this purpose. The goal of our research was the search of optimum structure for the fibers with a single mode operation and a rather large core diameter. We modelled fiber structures (solid-core, hollow-core, active-core PCF) with various ratio of inserts diameters and increments between the inserts, basing on two crystal systems: AgCl-AgBr and AgBr-TlI. Then we chose the single mode fiber structure and manufactured it by means of extrusion.

Towards the use of bioresorbable fibers in time-domain diffuse optics.

In the last years bioresorbable materials are gaining increasing interest for building implantable optical components for medical devices. In this work we show the fabrication of bioresorbable optical fibers designed for diffuse optics applications, featuring large core diameter (up to 200 μm) and numerical aperture (0.17) to maximize the collection efficiency of diffused light. We demonstrate the suitability of bioresorbable fibers for time-domain diffuse optical spectroscopy firstly checking the intrinsic performances of the setup by acquiring the instrument response function. We then validate on phantoms the use of bioresorbable fibers by applying the MEDPHOT protocol to assess the performance of the system in measuring optical properties (namely, absorption and scattering coefficients) of homogeneous media. Further, we show an ex-vivo validation on a chicken breast by measuring the absorption and scattering spectra in the 500-1100 nm range using interstitially inserted bioresorbable fibers. This work represents a step toward a new way to look inside the body using optical fibers that can be implanted in patients. These fibers could be useful either for diagnostic (e. g. for monitoring the evolution after surgical interventions) or treatment (e. g. photodynamic therapy) purposes. Picture: Microscopy image of the 100 μm core bioresorbable fiber.

플라스틱 광섬유를 사용한 통신망에서 OCDMA의 성능 분석

본 논문은 플라스틱 광섬유(POF)를 연결한 네트워크에서 광 부호분할다중접근(OCDMA)기술의 성능을 분석한다. 최근에 POF는 무게가 가볍고, 중심선의 직경이 크며, 유연하고, 쉽게 설치할 수 있는 특성이 있기 때문에 POF를 이용한 광전송은 커다란 주목을 받고 있다. 특히 POF의 광대역(broad band) 특성은 OCDMA기술에 기초한 네트워크 연결 전송매체로서 각광을 받고 있다. 일반적인 OCDMA 시스템은 전송로의 수량이 BER특성에 의해서 단지 제한된 단위만을 동시에 연결하고 전송할 수 있다. 이러한 문제를 해결하기 위하여 본 논문에서는 새로운 다우선 예약프로토콜을 제안하였다. 이 프로토콜과 분산 조정 알고리듬을 이용하여, 통신로 내부와 목표지로 가는 정보의 충돌을 피할 수 있다. 이 프로토콜은 시간지연이 서로 다른 다매체정보의 전송을 효과적으로 지원할 수 있다. 데이터 분석과 모의실험을 실행하여, 여러 시스템 매개변수에 의존하는 네트워크 출력과 평균지연을 조사했다. 그 결과, OCDMA기술에 근거한 POF를 네트워크를 사용하는 다우선 예약 프로토콜이 효율적이라는 것을 확인할 수 있었다. In this paper, the performance of the optical code-division multiple access (OCDMA) technology on a plastic optical fiber (POF) access network, which had received much attention due to its low weight, large core diameter, flexibility, easy installation, and especially its high bandwidth, is analyzed. Recently, POF was a very attractive candidate for transmission media in an access network based on OCDMA technology. But the conventional OCDMA system only allows finite units to transmit and access simultaneously according to the number of channels which are restricted by BER, and so, in this paper, to resolve this problem a novel multi-priority reservation protocol is also proposed. By using this reservation scheme and a distributed arbitration algorithm, channel collision and destination conflict could be avoided. And this protocol can efficiently support the transmission of multimedia messages that require the different time-delay. The network throughput and average delay using various system parameters have been investigated by numerical analysis and simulation experiments. These results shows that the multi-priority reservation protocol in this POF access network based on OCDMA technology is valid and efficient.

Multi-watt mid-infrared supercontinuum generated from a dehydrated large-core tellurite glass fiber

We report for the first time multi-watt mid-infrared supercontinuum (SC) output from a dehydrated tellurite step-index fiber. The tellurite glass preform is melted in a dry-atmosphere filled glovebox and the water impurity in the glass has been reduced to 1ppm level. The fiber has a large core diameter of 12 µm and a numerical aperture (NA) of 0.21. Using the amplified Raman-shifted soliton pulses from a 1.55 µm erbium-doped fiber laser as the pump, a broadband 2-3 µm supercontinuum with a 3dB bandwidth of 985 nm has been generated from an 80cm-long dehydrated tellurite glass fiber. The power spectral density of the SC is above 3.5 dBm/nm in the whole range of 2-3 µm. The net output power of the supercontinuum from the tellurite fiber is measured to be 2.1 W. To the best of our knowledge, this is the highest average power of mid-IR SC generated from a tellurite fiber. The spectral density of above 3 dBm/nm is also one of the highest spectral densities of a SC achieved in 2.5-3 μm range from an oxide glass fiber.

Design and analysis of a modified segmented cladding fiber with large mode area

This paper proposes a novel segmented cladding fiber structure for large mode area properties. In this structure a thin ring is placed between the high index core and nonuniform cladding. It is called Single-Ring Segmented-Cladding Fiber (SR-SCF). The novel fiber offers the possibility of single-mode(SM) operation from 1µm to 1.7µm with a large core diameter. With illustrations, the fiber has a better SM operation than segmented-cladding fiber (SCF) is demonstrated. A large effective area of 1000µm2 is achieved. The SM operation with very high suppression of the higher order modes can arise by 76%. Moreover, mode spacing between the adjacent modes (LP01 and LP11) is also improved significantly. Besides, the bending property is analyzed. It is found that the fiber is insensitive to bending angle ranging from −180° to 180° at bending radius of 30cm. The proposed fiber will play an important role in developing high power fiber laser, fiber amplifier and high power delivery application.

Analytic model for the complex effective index dispersion of metamaterial-cladding large-area hollow core fibers.

We present a mathematical model that allows interpreting the dispersion and attenuation of modes in hollow-core fibers (HCFs) on the basis of single interface reflection, giving rise to analytic and semi-analytic expressions for the complex effective indices in the case where the core diameter is large and the guiding is based on the reflection by a thin layer. Our model includes two core-size independent reflection parameters and shows the universal inverse-cubed core diameter dependence of the modal attenuation of HCFs. It substantially reduces simulation complexity and enables large scale parameter sweeps, which we demonstrate on the example of a HCF with a highly anisotropic metallic nanowire cladding, resembling an indefinite metamaterial at high metal filling fractions. We reveal design rules that allow engineering modal discrimination and show that metamaterial HCFs can principally have low losses at mid-IR wavelengths (< 1 dB/m at 10.6 µm). Our model can be applied to a great variety of HCFs with large core diameters and can be used for advanced HCF design and performance optimization, in particular with regard to dispersion engineering and modal discrimination.

An analysis of W-shaped plastic optical fibers by WKB approximation

The graded-index plastic optical fiber, because of its relatively large bandwidth and core diameter, is the type of fiber that is used in a majority of the fiber optic systems in existence today. Especially the type of optical fiber known as the W-fiber has some desirable properties and unique characteristics not found in matched-cladding fibers. In this work, by Wentzel–Kramers–Brillouin (WKB) method, the total number of modes of the graded-index W-shaped plastic optical fiber is theoretically reviewed. The obtained formula for the total number of modes of W-shaped optical fibers arises from an approximation of the WKB integral, which preserves the general validity requirements of the method. Also, by assumption that all modes were excited uniformly, the computational analyses investigating near- and far-field power distribution in W-shaped plastic optical fibers was carried out.

110 W all-fiber picosecond master oscillator power amplifier based on large-core-diameter ytterbium-doped fiber.

We demonstrate an all-fiber picosecond fiber laser in a master oscillator power amplifier configuration. The seed source is a soliton-type passively mode-locked Yb-doped fiber laser by a semiconductor saturable absorber mirror and chirped fiber Bragg grating. The pulse width of the seed laser is 4.5 ps with a repetition rate of 15 MHz. A highly doped active fiber with a large core diameter (50 μm) is employed to boost the average power of the seed pulses to 117 W with 11 ps pulse width and 709 kW peak power. The corresponding output beam quality factor at maximum output power is 3.7. The all-fiber construction of the whole laser system enables compact size and robust operation.

Large-mode-area fibers operating near single-mode regime.

Lower NA in large-mode-area fibers enables better single-mode operation and larger core diameters. Fiber NA has traditionally been limited to 0.06, mostly due to the control tolerance in the fabrication process. It has been recognized recently that transverse mode instability is a major limit to average power scaling in fiber lasers. One effective method to mitigate this limit is to operate nearer to the single-mode regime. Lower fiber NA is critical in this since it allows relatively larger core diameters which is the key to mitigate the limits imposed by nonlinear effects. We have developed a fabrication process of ytterbium-doped silica glass which is capable of highly accurate refractive index control and sufficient uniformity for LMA fibers. This process is also capable of large-volume production. It is based on a significant amount of post-processing once the fiber preforms are made. We have demonstrated 30/400 and 40/400 LMA fibers with a NA of ~0.028 operating very close to the single-mode regime. The second-order mode cuts off at ~1.2μm and ~1.55µm respectively. We have also studied issues related to bend losses due to the low NA and further optimization of LMA fibers.

A new method to gently place biopsy needles or treatment electrodes into tissues with high target precision

We present a new core needle biopsy and treatment electrode precision placement technique which, regardless of needle size, target lesion hardness and elasticity, makes it possible to precisely place an image guided device inside the abnormal tissue. Once inside the abnormal lesion, multiple tissue samples can be collected using a dedicated trocar and collecting system. Our unique “Fourier” driver substitutes the commonly used spring-loaded device or complements the jerky insertion technique used by experienced interventional physicians. It enables the physician to precisely and with extreme tactility maneuver even large diameter core needles or treatment-electrodes into the lesion using only a diminutive external force. This is achieved by applying supporting servo-controlled mechanical high-acceleration micro-pulses, proportional to the average vector directed by the physician. The Fourier-needle or Fourier-electrode stands completely non-moving when the system automatically goes into full idling. This means that the angle of attack successively and arbitrary can be aligned to hit the target, becoming successively symmetrically inserted into even small tumors to be treated as well as exactly hit any point outlined by real time ultrasound guiding. This kind of biopsy needle or treatment electrode placement results in a uniquely accurate and less traumatic procedure. Due to the risk of disseminating viable tumor cells the precision placement device can be combined with a computer controlled anti-seeding system, denaturizing tumor cells detached during penetration of the biopsy needle or treatment electrode.

Vapor phase doping process for fabrication of rare earth doped optical fibers: Current status and future opportunities

Emerging application of rare‐earth (RE) doped optical fibers in high power lasers requires preforms with stringent geometrical and optical properties. This in turn demands more versatile and reliable process technology which brought Vapor Phase Doping (VPD) into prominence. This technology has immense potential to overcome fiber fabrication related challenges viz, dopant‐rich phase separation, RE uniformity in radial as well as longitudinal direction, “star‐like” defect elimination from core‐clad boundary and refractive index (RI) adjustment which results in improved beam quality and power stability of fiber laser. Further, high power lasers demand LMA active fibers with large core diameter and low numerical aperture (NA) which is easily producible by VPD method as it permits deposition of multiple RE doped core layers in a reproducible “in situ” manner. So, the prime focus is to optimize process technology to produce low RI, large core fibers. This article gives an overview of the comprehensive effort made by the global researchers to overcome challenges of VPD method and to demonstrate a standardized process technology for RE doping in silica glass preform.

Investigation on Yb3+-doped silica glass using sol-gel method and laser melting technology

Rare earth doped silica glass can be used as the central material of optical fiber, which can be applied to the fiber laser. It becomes a focus in the field of laser materials. Compared with different kinds of rare earth elements, ytterbium is regarded as a promising laser nuclear fusion material due to its simple level structure, strong energy conversion efficiency, long fluorescent lifetime, etc. Nowadays, the usual fabrication method of optical fiber preform is the chemical vapor deposition (CVD). However, the preform made by CVD has low doping concentration, few kinds of doping elements, low homogeneity and hard-to-make into optical fiber of large core diameter. To solve these problems, a noble method, which is called non-chemical vapor deposition (Non-CVD), is developed. Sol-Gel method is a kind of Non-CVD, which can perfectly solve the inhomogeneity in material. The glass has harmonious component since the whole process is at a liquid level.Sol-Gel method is a liquid phase synthesis method. The raw materials, including TEOS, absolute ethyl alcohol, ammonium hydroxide and deionized water, are uniformly mixed and become gel from sol through the hydrolysis and condensation. AlCl3 and YbCl36H2O are also added as the dopants. After that, heat the gel and let the hydroxyl and organic release, then we will be able to obtain the SiO2-doped powder. Combining with the laser melting technology, the ytterbium doped silica glass is made. It is known from the DSC-TG curve of xerogel that during the heating process, water and organic are expelled from the system. It needs a holding period at 500 ℃ to ensure that the water and organic are expelled adequately. Moreover, the FTIR spectrum shows that after high temperature treatment the OH- concentration in the xerogel decreases dramatically. The physical and spectrum properties of ytterbium doped silica glass are also tested. The Yb-doped silica glass which shows the amorphous state has good optical properties. The absorption spectrum and fluorescence spectrum demonstrate the typical absorption peak and emission peak of Yb3+, respectively. The density and refractive index of the glass are 2.409 g/cm3 and 1.462, respectively. The fluorescence lifetime () of the silica glass is 0.88 ms, the corresponding emission cross-section (emi) is 0.54 pm2, and the gain coefficient (emi) is 0.48 pm2m. In conclusion, the Yb-doped silica glass is successfully prepared by the Sol-Gel method combined with laser melting technology, which possesses good physical and optical properties. This work is meaningful for preparing high-performance Yb-doped fiber, and even for developing the high power laser.

Core diameter of bone marrow aspiration devices influences cell density of bone marrow aspirate in patients with severe peripheral artery disease

Background aimsBone marrow (BM) transplantations are an accepted therapeutic strategy for hematologic conditions. In the past decades, interest for BM-derived cell therapy has extended toward the field of regenerative medicine. Irrespective of the treatment strategy, its success depends on the amount of cells available for transplantation. Both patient and procedural factors have been shown to influence the cell density of the BM aspirate. In the present study, the influence of core diameter of the BM aspiration device on cell density of the BM aspirate is studied. MethodsBM harvesting procedures performed in a clinical trial investigating the effect of BM cell therapy in patients with severe peripheral artery disease were retrospectively studied (clinicaltrials.govNCT00371371). Patients underwent BM harvesting through the use of either a 15-gauge (n = 85) or an 8-gauge (n = 75) needle. The numbers of harvested white blood cells (WBC) and CD34+ hematopoietic cells (HPC) were quantified. ResultsThe amount of WBC per milliliter of BM aspirate was significantly higher when the 8-gauge needle (27.8 × 106 WBC/mL [95%CI 25.4–30.5 × 106]) was used compared with the smaller 15-gauge core needle (20.1 × 106 WBC/mL [95% confidence interval (CI), 18.7–21.7 × 106], P < 0.001). For the amount of CD34+ HPC, a similar pattern was observed (185 × 103 HPC/mL [95% CI, 161–213 × 103]; 114 × 103 HPC/mL [95% CI, 96–134 × 103]; P < 0.001). ConclusionsThe application of a BM aspiration device with a larger core diameter is associated with an increased cell density of the BM aspiration product in patients with severe peripheral artery disease.

Manipulation of Random Lasing Action From Dye-Doped Liquid Crystals Infilling Two-Dimensional Confinement Single Core Capillary

The experimental detail of a random lasing action from dye-doped nematic liquid crystals (LCs) inside single-core capillaries with a core diameter below 50 μm was investigated. The resonant characteristics, including the number of emission spikes, the full width at half maximum (FWHM), and the estimated Q-factor, were shown to depend on the core diameter of a capillary. In contrast with a capillary with a larger core diameter and having various emission spikes, only three emission spikes were excited from a capillary with a 10-μm core diameter, owing to the smaller effective area of the pump beam. However, the decrease in the amplitude of emission spikes and the broadening of the linewidth accompanying the higher lasing threshold from a capillary with a 50-μm core diameter are attributed to the decrease in the pump fluence and the increase in the scattering loss, respectively. In this paper, a random laser (RL) with the shortest FWHM emission peak of about 0.47 nm and the highest Q-factor of about 1268 was generated from the capillary with a 20-μm core diameter. By means of temperature adjustment, the emission spectra of the RL that is related to the birefringence and alignment ordering of the LC molecules inside a capillary with a 20-μm core diameter can be effectively altered. Our experiments show that the RL, revealing adjustable output emission spectra, can be a promising device in using remote sensing applications.

Effect of spatial coherence on damage occurrence in multimode optical fibers.

We investigate the influence of spatial coherence on damage occurrence in highly multimode optical fibers using ultraviolet (UV) nanosecond pulses, with the aim of delivering high fluence in the UV. In some cases, the optical damage is initiated below the fiber facet damage threshold and takes place along the propagation path; such damage is believed to be caused by local constructive interference, creating "hot spots." In order to reduce the degree of spatial coherence, we used a large-diameter core (1.5mm) fiber as a mode scrambler. Different lengths of this large core fiber were used to deliver energy to a fiber core with a smaller diameter (0.6mm), in which the damage occurrence was observed. The experimental results indicate that there is a correlation between the degree of spatial coherence and the occurrence of optical damages, typically observed a few millimeters from the fiber facet. Numerical simulations, based on the beam-propagation method, support the degradation of spatial coherence, due to the excitation of high-order modes. Finally, by degrading the spatial coherence of the beam, we establish a new record by delivering more than 100mJ via a 1.5mm core diameter fiber in the UV, corresponding to ∼26 times the critical power for self-focusing. Our work sheds light on the ability to deliver high energies of nanosecond-pulsed UV laser radiation through multimode optical fibers.

Impact of Mode Filtering on the Performance of Femtosecond Pulse Amplification in a Large Mode Area Fiber

We experimentally investigated the impact of the mode filtering technique on the performances of pulse amplification in a fiber with a large core diameter. The technique was applied to a femtosecond pulse amplifier, and was based on a large area double-clad Yb-doped fiber. The mode filtering enabled selective excitation of the lowest transverse mode with minimal contamination of higher order modes. The output pulses with 110 fs duration, > 30 nJ pulse energy (> 3 W average power), and clean spatial/temporal profiles were successfully generated. Benefits of this technique are also discussed.

石英光子晶体光纤中高功率中红外超连续谱的产生

Non-silica fibers have the intrinsic limitations in high power supercontinuum generation.High power mid-infrared supercontinuum generation in silica photonic crystal fiber is firstly investigated in our studies. The dispersion of fiber is designed to be beneficial to supercontinuum broadening to mid-infrared region. Meanwhile,to withstand high pumping power,a relatively large core diameter is essential. On the premise of supercontinuum broadening to 3. 4 μm,fiber length is optimized to reduce the loss of the optical fibers. The results show that it is feasible to generate supercontinuum spectrum with 20 d B-bandwidth covering from 1 550 nm to 3 420 nm by injecting 1. 95 μm picosecond pulse into silica photonic crystal fiber with appropriate dispersion. The average power of the supercontinuum spectrum can reach 56. 6 W.

High Power Spark Delivery System Using Hollow Core Kagome Lattice Fibers.

This study examines the use of the recently developed hollow core kagome lattice fibers for delivery of high power laser pulses. Compared to other photonic crystal fibers (PCFs), the hollow core kagome fibers have larger core diameter (~50 µm), which allows for higher energy coupling in the fiber while also maintaining high beam quality at the output (M2 = 1.25). We have conducted a study of the maximum deliverable energy versus laser pulse duration using a Nd:YAG laser at 1064 nm. Pulse energies as high as 30 mJ were transmitted for 30 ns pulse durations. This represents, to our knowledge; the highest laser pulse energy delivered using PCFs. Two fiber damage mechanisms were identified as damage at the fiber input and damage within the bulk of the fiber. Finally, we have demonstrated fiber delivered laser ignition on a single-cylinder gasoline direct injection engine.

A Study on Cutting Glass Fibers by CO&lt;sub&gt;2&lt;/sub&gt; Laser

This The multi-mode fiber has been widely used in high data traffic applications since the transmitting rate of interface between data storages was larger than the capacity of fiber-optic communication with single mode fiber. The quality of end surface of fiber dominates the data transmitting efficiency. A good cutting end surface of single mode fiber can obtain by the traditional mechanical fiber cleaving methods. But, the multi-mode fiber has much larger core diameter than single mode fiber’s and the quality of cutting end surfaces which cut by the traditional mechanical fiber cleaving methods was not good enough. In the recent year, the pulse CO2 laser processing methods were introduced to cleave the fibers. In this research, a glass fiber laser cutting system was developed. The shapes of laser focusing spot and the concepts of laser cutting optical design were discussed in this paper. The experimental results show that the fiber cutting end surfaces with great quality, which were inspection by interferometer, can be obtained by the developed laser cutting system.

Fiber-optic evanescent wave sensor with a segmented structure.

A segmented structure optic fiber sensor is proposed and demonstrated; it is based on evanescent wave absorption theory. The waveguide modes of the segmented structure are simulated and analyzed by using the beam propagation method, which shows the high-order modes are excited repeatedly at the first transition of each segmented region. The effect of the number of segments and the core diameters on the sensitivity of the sensors is investigated experimentally. The sensitivity of the sensors is tested by using different concentrations of methylene blue solution. The experimental results show that our sensor's sensitivity is ∼0.0476 L/g, which is two times higher than that of the conventional single straight sensor, with the same core diameters and length of the sensing region, and the absorbance is linearly proportional to the number of segments, while being inversely proportional to the residue core diameter of the etched segments within the concentration range from 2 to 14 g/L. These results are consistent with theoretical models and simulation analysis. The proposed sensor not only has high sensitivity, but it is also robust due to the large core diameter of the segmented region, which is suitable for materials spectrum measurements.