非空气-石英结构PCF的带隙特性分析

光子晶体光纤是近十来年兴起的一个新兴的研究领域,是现今纤维光学的研究重点,光子带隙特性是光子晶体光纤区别传统光纤的主要特征。本文利用全矢量平面波展开法对非空气-石英结构PCF的带隙特性进行分析,并且重点讨论空气孔内填充介电材料对光子带隙存在的影响。     

Mid-infrared gas sensing using a photonic bandgap fiber

We demonstrate methane sensing based on Fourier transform infrared spectroscopy using a hollow-core photonic bandgap fiber guiding in the mid-infrared and idler pulses from a femtosecond optical parametric oscillator. Transmission measurements are presented for several fibers, and sensing is demonstrated using a fiber whose bandgap overlaps the methane fundamental absorption lines. The gas filling process of the air core is described, and qualitative methane concentrations measurements to 1000 ppm (parts in 10(6)) are reported. Operation down to 50 ppm based on our current experiment is predicted.     

空芯光子晶体带隙光纤用于甲烷检测的研究

基于甲烷的光谱吸收理论,设计了一套利用空芯光子晶体带隙光纤(HC-PBGF)做传感气室的全光纤甲烷检测系统。根据HITRAN2012数据库和HAWKS软件确定甲烷的检测波长;利用气泵在HC-PBGF两端形成压力差来加快甲烷气体的扩散,利用反射镜延长光程至2倍;通过实验得到190s后气体扩散完成,0.5h内系统示值波动为0.012%,平均重复率为99.63%。最后配制0~2.5%浓度的甲烷气体进行浓度检测,得出甲烷浓度与相对吸收强度呈线性关系,线性度为99.92%。该系统成功实现了将HC-PBGF的空芯结构用于甲烷的吸收检测,加快了系统的响应速度,实现了仪器的小型化,使在线检测更加方便。     

Hollow-core photonic bandgap fibre: new light guidance for new science and technology

We review the progress made on the fabrication and applications of hollow-core photonic crystal fibres (HC-PCFs). The mechanism of the light guidance in these fibres is described along with their dispersion properties. We review the HC-PCF fabrication, the different results achieved in the fields of laser-induced particle guidance, low-threshold stimulated Raman scattering in hydrogen (vibrational and rotational), laser frequency metrology and quantum optics. Finally, we show the different new prospects opened up by these fibres.     

Highly birefringent photonic crystal fibers with near-zero dispersion at 1550 nm wavelength

This paper presents highly birefringent photonic crystal fibers with simultaneously near-zero dispersion and low confinement losses. The finite difference time domain method with anisotropic perfectly matched layer boundaries is used as the simulation software. According to simulation, it is shown that photonic crystal fibers with hybrid cladding and artificial defects along one of the orthogonal axes sufficiently results in a very high birefringence of the order 10^?2 which is two orders of magnitude higher than that of the conventional polarization maintaining fibers. Such a fiber also assumes both near-zero dispersion and low confinement losses at the 1550 nm wavelength. Optical fibers with novel properties such as high birefringence, near-zero dispersion, and low confinement losses may have applications in optical sensing applications.     

Analysis of strictly bound modes in photonic crystal fibers by use of a source-model technique

We describe a source-model technique for the analysis of the strictly bound modes propagating in photonic crystal fibers that have a finite photonic bandgap crystal cladding and are surrounded by an air jacket. In this model the field is simulated by a superposition of fields of fictitious electric and magnetic current filaments, suitably placed near the media interfaces of the fiber. A simple point-matching procedure is subsequently used to enforce the continuity conditions across the interfaces, leading to a homogeneous matrix equation. Nontrivial solutions to this equation yield the mode field patterns and propagation constants. As an example, we analyze a hollow-core photonic crystal fiber. Symmetry characteristics of the modes are discussed and exploited to reduce the computational burden.     

基于1550nm的全固态PBG—PCF的设计

设计了一种三角晶格结构的全内反射型光子晶体光纤,并在其包层孔内分别填充折射率为n=1．55～3．35（△n=0．3）的介电材料,使其等效为全固态光子带隙型光子晶体光纤,利用全矢量平面波展开法对其带隙特性进行分析,发现随着折射率的增加,光子带隙的位置逐渐向长波方向移动,导模也越来越少。设计一种工作波长为1550nm的全固态光子带隙型光子晶体光纤,计算得到其对应的归一化传播常数β=8．2时,导模的宽度大约为100nm。该光纤在光电转换或者电光转换等方面具有潜在的应用价值。     

Dispersion analysis of hollow-core modes in ultralarge-bandwidth all-silica Bragg fibers with nanosupports

Dispersion of the fundamental confined modes in hollow-core all-silica Bragg fibers with nanosupports is analyzed. The transfer-matrix formalism is applied. Anomalies in the group-velocity dispersion are evidenced at long wavelengths, toward the upper limit of the bandgap. The results confirm that, as in microstructured photonic crystal fibers, this anomalous dispersion is due to prevention of the confined hollow-core modes from crossing the surface modes, the avoided crossings are more apparent in the variation of group velocity with wavelength. The dependence of these avoided crossings on the hollow-core radius and the layer thicknesses is briefly analyzed.     

光子晶体纤维的制备及应用

光子晶体纤维是一种具有结构色的纤维,其无需染色就具有颜色亮丽、永不褪色、色彩饱和度高等特点,符合当前绿色、环保的要求,拥有广阔的发展前景。概述了光子晶体的原理、制备方法及应用,重点探讨了光子晶体纤维的制备方法,介绍了目前研究报道的多层膜干涉、自组装、电泳沉积、静电纺丝和热压印等方法,并讨论了这些方法的优缺点。     

Improved hollow-core photonic crystal fiber design for delivery of nanosecond pulses in laser micromachining applications

We report the delivery of high-energy nanosecond pulses (approximately 65 ns pulse width) from a high-repetition-rate (up to 100 kHz) Q-switched Nd:YAG laser through the fundamental mode of a hollow-core photonic crystal fiber (HC-PCF) at 1064 nm. The guided mode in the HC-PCF has a low overlap with the glass, allowing delivery of pulses with energies above those attainable with other fibers. Energies greater than 0.5 mJ were delivered in a single spatial mode through the hollow-core fiber, providing the pulse energy and high beam quality required for micromachining of metals. Practical micromachining of a metal sheet by fiber delivery has been demonstrated.     

Reconstruction of polarization-shaped laser pulses after a hollow-core fiber using backreflection

We present a method to reconstruct the pulse shape of polarization-shaped femtosecond laser pulses after a hollow-core photonic crystal fiber by reflecting the pulses back through the fiber. First, a procedure is introduced to receive the optical fiber properties and generate parametrically shaped pulses after propagation through the fiber. Changes of the fiber's birefringence by mechanical stress are examined to investigate the correlation between the pulse shapes after one and two passes through the fiber. Finally, we demonstrate the characterization of the pulse after one pass through the fiber by calculating the pulse shape from the measured pulse after two passes.     

Writing and probing light-induced waveguides thanks to an endlessly single-mode photonic crystal fiber

We demonstrate writing and probing of light-induced waveguides in photorefractive bulk LiNbO3 crystal using an endlessly single-mode photonic crystal fiber. The optical waveguides are written at visible wavelengths by slightly raising the ferroelectric crystal temperature to benefit from the pyroelectric-driven photorefractive effect and the guiding properties are investigated at telecom wavelengths using the same photonic crystal fiber. End butt coupling with this photonic crystal fiber enables writing and probing of optical waveguides due to the self-alignment properties of spatial solitons.     

Design of high-bandwidth one- and two-dimensional photonic bandgap dielectric structures at grazing incidence of light

We propose one-dimensional photonic bandgap (PB) dielectric structures to be used at grazing incidence in order to obtain an extended bandgap exhibiting considerably reduced reflection loss and dispersion compared to similar structures used at a normal incidence of light. The well-known quarter-wave condition is applied for the design in this specific case, resulting in resonance-free reflection bands without drops in reflection versus wavelength function and a monotonous variation of the group delay dispersion versus wavelength function, which are important issues in femtosecond pulse laser applications. Based on these results we extend our studies to two-dimensional PB structures and provide guidelines to the design of leaking mode-free hollow-core Bragg PB fibers providing anomalous dispersion over most of the bandgap.     

Coherent control of excited atomic states inside a three-dimensional photonic bandgap

We demonstrate the coherent control of the excited state of an atom embedded in three-dimensional photonic bandgap (3D PBG) structures. The coherent control allows us to obtain a long-lifetime Rabi oscillation or several types of steady-state inversion, depending on the laser phase, in which the relaxation of an excited atom is strongly suppressed. Such a coherent control suggests the possibility of extending the atomic system to a low loss quantum logic gate for optical quantum computation.     

光子晶体传感器的研究进展

光子晶体是一类具有光子能带和带隙的新型光学材料,近年来已成为传感器技术领域的研究热点。光子晶体微腔、光子晶体波导、光子晶体光纤在传感器领域得到了广泛应用,而凝胶光子晶体、反蛋白石光子晶体、分子印迹光子晶体则实现了化学生物传感器的"裸眼检测技术"。重点分类介绍了一维、二维、三维光子晶体的制备及其在传感器领域的应用进展。     

Generation of a train of ultrashort pulses using periodic waves in tapered photonic crystal fibres

We consider a light wave propagation in tapered photonic crystal fibres (PCFs) wherein the wave propagation is described by the variable coefficient nonlinear Schrödinger equation. We solve it directly by means of the theta function identities and Hirota bilinear method in order to obtain the exact periodic waves of sn, cn and dn types. These chirped period waves demand exponential variations in both dispersion and nonlinearity. Besides, we analytically demonstrate the generation of a train of ultrashort pulses using the periodic waves by exploiting the exponentially varying optical properties of the tapered PCFs. As a special case, we discuss the chirped solitary pulses under long wave limit of these periodic waves. In addition, we derive these types of periodic waves using the self-similar analysis and compare the results.     

Modeling of dispersion and nonlinear characteristics of tapered photonic crystal fibers for applications in nonlinear optics

In this article, we investigate for the first time the dispersion and the nonlinear characteristics of the tapered photonic crystal fibers (PCFs) as a function of length z, via solving the eigenvalue equation of the guided mode using the finite-difference frequency-domain method. Since the structural parameters such as the air-hole diameter and the pitch of the microstructured cladding change along the tapered PCFs, dispersion and nonlinear properties change with the length as well. Therefore, it is important to know the exact behavior of such fiber parameters along z which is necessary for nonlinear optics applications. We simulate the z dependency of the zero-dispersion wavelength, dispersion slope, effective mode area, nonlinear parameter, and the confinement loss along the tapered PCFs and propose useful relations for describing dispersion and nonlinear parameters. The results of this article, which are in a very good agreement with the available experimental data, are important for simulating pulse propagation as well as investigating nonlinear effects such as supercontinuum generation and parametric amplification in tapered PCFs.     

Investigation of structural dependence of host erbium-doped triangular-lattice PCF on lasing properties and design of high performance laser

A detailed study is presented on the lasing properties of an erbium-doped photonic crystal fiber (PCF) laser. The effects of the host PCF’s structure and laser parameters on continuous-wave laser emission are analyzed by considering the confinement and overlap of pump and signal fields in the gain medium for varying values of pitch, hole diameter, and doping radius. For analysis, we used a finite-difference mode-calculation algorithm devised with standard population and propagation rate-equation solver. Our analysis, applied to an experimentally realized PCF laser, reproduces the observed/reported data, thereby showing the efficacy of our analysis. Finally, a fiber geometry to realize a laser with threshold as low as 6?mW using a short fiber length of 0.52?m is prescribed. The aim of the design is to greatly reduce splice loss with standard single-mode SM28/G.652 fiber while maintaining the optimum performance. These results are new in PCF laser research and should be useful in realizing high performance PCF-based laser devices.     

Recent Progress in Nanolaser Technology

Nanolasers are key elements in the implementation of optical integrated circuits owing to their low lasing thresholds, high energy efficiencies, and high modulation speeds. With the development of semiconductor wafer growth and nanofabrication techniques, various types of wavelength-scale and subwavelength-scale nanolasers have been proposed. For example, photonic crystal lasers and plasmonic lasers based on the feedback mechanisms of the photonic bandgap and surface plasmon polaritons, respectively, have been successfully demonstrated. More recently, nanolasers employing new mechanisms of light confinement, including parity–time symmetry lasers, photonic topological insulator lasers, and bound states in the continuum lasers, have been developed. Here, the operational mechanisms, optical characterizations, and practical applications of these nanolasers based on recent research results are outlined. Their scientific and engineering challenges are also discussed.     

Hierarchical nanoparticle bragg mirrors: tandem and gradient architectures

To manipulate electrons in semiconductor electronic and optical devices, the usual approach is through materials composition, electronic bandgap, doping, and interface engineering. More advanced strategies for handling electrons in semiconductor devices include composition-controlled heterostructures and gradient structures. By analogy to the manipulation of electrons in semiconductor crystals by electronic bandgaps, photons in photonic crystals can be managed using photonic bandgaps. In this context, the simplest photonic crystal is the Bragg mirror, a periodic dielectric construct whose photonic bandgap is engineered through variations of the optical thickness of its constituent layers. Traditionally the materials comprising these periodic dielectric layers are nonporous, and they have mainly been used in the field of optical and photonic devices. More recently these Bragg mirrors have been made porous by building the layers from nanoparticles with functionality and utility that exploit their internal voids. These structures are emerging in the area of photonic color-coded chemical sensing and controlled chemical release. Herein, a strategy for enhancing the functionality and potential utility of nanoparticle Bragg mirrors by making the constituent dielectric layers aperiodic and porous is described. It is exemplified by prototypical tandem and gradient structures that are fully characterized with regards to their structure, porosity, and optical and photonic properties.