Ion-Doped Photonic Crystal Fiber Lasers

Compared with conventional solid-state lasers, fiber lasers have the advantages of small size, simple cooling system, and good output beam quality, enabling them an extended service lifetime in industrialized environments. Periodically arranged photonic crystals have been the most important gain medium for high-power laser applications, which overcame the problems in fiber lasers such as small mode field, low degree of nonlinearity, and non-adjustable dispersion. In this mini-review, we summarize the recent advances of typical ion-doped photonic crystal fiber lasers doped, discuss the challenges, and provide an outlook on the future developments in ion-doped photonic crystal fiber lasers.

FIELD DESORPTION MICROSCOPY OF CARBON-COATED FIELD ELECTRON EMITTERS

Полевые электронные эмиттеры в форме металлического острия с пленкой углерода на поверхности обладают рядом перспективных эксплуатационных свойств. Характеристики эмиттера зависят от фазового состава, толщины и однородности пленки. Определение параметров пленок толщиной в один или несколько моноатомных слоев представляет определённые трудности. В данной работе образование и характеристики углеродных наноструктур на поверхности полевых эмиттеров из иридия и рения исследуются с помощью полевой десорбционной микроскопии непрерывного режима. На полевых десорбционных изображениях области углеродных наноструктур проявляются в виде локальных вспышек (лавинообразная десорбция). При покадровом анализе видеозаписей вспышек обнаружено несколько стадий формирования вспышек и выявлены различия в протекании десорбции с углеродных наноструктур на иридии и на рении. Обнаруженные различия объясняются образованием на иридии однослойного, а на рении многослойного графена. Десорбционные изображения выявляют неоднородности и локальные различия толщины пленки. Показано, что полевая десорбционная микроскопия непрерывного режима позволяет определять закономерности формирования полевых десорбционных изображений различных углеродных наноструктур, в частности, однослойного и многослойного графена на поверхности полевого эмиттера, и проводить диагностику поверхности после науглероживания и контролировать однородность получаемого покрытия. Получаемые данные полезны для разработки технологии эффективных полевых электронных эмиттеров. Field electron emitters in the form of a metal tip with a carbon film on the surface have a number of promising operational properties. The characteristics of the emitter depend on the phase composition, thickness and uniformity of the film. Determining the parameters of films with a thickness of one or more monoatomic layers presents certain difficulties. In this paper, the formation and characteristics of carbon nanostructures on the surface of field emitters made of iridium and rhenium are studied using continuous-mode field desorption microscopy. In the field desorption images, the regions of carbon nanostructures appear as local flashes (avalanche-like desorption). Frame-by-frame analysis of flash video recordings revealed several stages of the flash formation and revealed differences in the desorption from carbon nanostructures on iridium and rhenium. The found differences are explained by formation of the single-layer graphene on iridium and a multilayer graphene on rhenium. Desorption images reveal inhomogeneities and local differences in the film thickness. It is shown that continuous-mode field desorption microscopy makes it possible to determine the regularities of formation of the field desorption images of various carbon nanostructures, in particular, the single-layer and multilayer graphene on the surface of the field emitter, and to diagnose the surface after carburization. Besides, control the uniformity of the resulting coating is possible. The obtained data are useful for developing technology of the effective field electronic emitters.

Study on the high birefringence and low confinement loss terahertz fiber based on the combination of double negative curvature and nested claddings

A novel double negative curvature nested fiber structure is designed by adding extra circular cladding tubes to enhance the birefringence and reduce the confinement loss. The fiber structure is composed of eight circular cladding tubes and two semi-elliptical nested tubes. The transmission performances of terahertz fiber, including birefringence, confinement loss, dispersion and effective mode field area, are studied by changing the parameters of cladding tubes. In the frequency range of 1.75 - 2.6 THz, the broad bandwidth of 850 GHz with high birefringence (above 10-4) can be achieved. The confinement loss of y-polarization mode with the frequency of 2.575 THz can be as low as 0.00231 dB/cm. The waveguide dispersion coefficient is between ±0.188 ps/(THz•cm) in the frequency range of 2.0 - 2.475 THz. The maximum effective mode field area of x- polarization mode is 2.618×10-6 m2 at 2.6 THz.

Characteristics of Collimators Based on the Large-Mode-Area CMCF for Coupling Laser Beam

A new collimator based on a homemade concentric multilayer-core fiber (CMCF) is proposed and experimentally demonstrated. This collimator was fabricated using a tail fiber with large mode area and single-mode operation. By exploiting the optical transmission matrix, the propagation characteristic and coupling mechanism of this CMCF-based collimator was introduced meticulously. The coupling losses of the laser beam using this collimator in the off-axis, angular, and axial deviations were analyzed separately. In order to determine the relationship between the geometric redundancy of this collimator and the effective mode field area of the tail fiber, the corresponding mathematical model was established. Through model calculation and experiment measurement, the coupling properties of the collimator were improved effectively. Compared with the common SMF-based collimator, the declination redundancy of the CMCF-based one improved by 20%, which could make the coupling of the optical fiber collimator easier. Therefore, this collimator has potential application value in the laser diode coupling unit and high-speed optical communication system.

Er-Doped Tapered Fiber Amplifier for High Peak Power Sub-ns Pulse Amplification

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.

Hemi-Ellipsoidal microlensed fiber based on polishing and polymer technology

This paper represents a development of a new advanced technology to fabricate and characterize micro-collimators with hemi-ellipsoidal microlenses at single-mode fibers outputs. The proposed method utilizes the controlled mechanical micromachining technique based on the variation of the speed of the fiber around its axis in both X and Y directions followed by the injection of a quantity of polydimethylsiloxane (PDMS) to form the hemi-ellipsoidal microlenses. The experimental results show that this technique allows to obtain a wide variety of ellipticity diameters ratios from 0.68 to 0.84. An elliptical ratio of radii of curvature Ry/Rx in a range of 0.51 at 0.86 is also obtained. In this investigation a mode field diameters MFD in an interval between 3.26 µm and 9.93 µm have been realized. The measurement results demonstrate that the proposed technology allows to fabricate hemi-ellipsoidal microlenses having an MFD ellipticity ratios of about 0.60 to 0.97 in near field promising for micro-collimator suitable to match an elliptical laser beam to the circular one of a fiber.

Study of a sub-wavelength scale plasmonic traveling wave amplifier with electrically pumped multiple quantum wells

We propose a hybrid gap plasmonic traveling wave amplifier (TWA) with electrically pumped multiple quantum wells (MQW). This TWA has deep sub-wavelength mode field scale and works at 1310nm window. For the polarization-independent amplification we design the InGaAlAs tensile-strain MQW. And we analyze this plasmonic TWA’s optical, electrical and thermal characteristics by finite element method. First we get the suitable trade-off point between the affordable mode propagation loss and moderate mode field size by adjusting the gap width and height. Second we find that the narrower the MQW, the higher the MQW local gain. Third, our device has good thermal performance as the plasmonic wave power is less than 5μw. Simulation results suggest that the independent polarization gain appears at 1317nm wavelength. And at this wavelength 3.60/cm mode gain and 161nm mode width are obtained as the 9.39kA/cm^2injection current and 10nm×240nm gap size.