Type Of Photonic Crystal Fiber Research Articles

Fiber guiding at the Dirac frequency beyond photonic bandgaps

AbstractLight trapping within waveguides is a key practice of modern optics, both scientifically and technologically. Photonic crystal fibers traditionally rely on total internal reflection (index-guiding fibers) or a photonic bandgap (photonic-bandgap fibers) to achieve field confinement. Here, we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures. Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers. What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation. We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps. This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps, thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding. The result presented here demonstrates the discovery of a new type of photonic crystal fibers, with unique characteristics that could lead to new applications in fiber sensors and lasers. The Dirac equation is a special symbol of relativistic quantum mechanics. Because of the similarity between band structures of a solid and a photonic crystal, the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons, phonons, and electrons.

Design of highly nonlinear photonic crystal fibers with flattened chromatic dispersion.

A novel (to our knowledge) type of photonic crystal fiber (PCF) with high nonlinearity and flattened dispersion is proposed. The propagation characteristics of chromatic dispersion, effective area, and nonlinearity are studied numerically by using the full-vector finite element method. Several PCF designs with high nonlinearity and nearly zero flattened dispersion or broadband flattened, and even ultraflattened, dispersion over different wavelength bands are obtained by optimizing the structural parameters. One optimized PCF has a nearly zero ultraflattened dispersion of 2.3 ps/(nm·km) with a dispersion variation of 0.2 ps/(nm·km) over the C+L+U wavelength bands. In addition, the dispersion slope and nonlinear coefficient at 1.55 μm can be up to 2.2×10(-3) ps/nm(2)·km and 33.2 W(-1)·km(-1), respectively. The designs proposed in this paper have bright prospects for applications in all-optical format conversion, supercontinuum generation, optical wavelength conversion, and many other fields.

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.

Circular Photonic Crystal Fibers: Numerical Analysis of Chromatic Dispersion and Losses

Detailed numerical analysis for dispersion properties and losses has been carried out for a new type of Photonic crystal fiber where the air-holes are arranged in a circular pattern with a silica matrix called as Circular Photonic Crystal Fiber (C-PCF). The dependence of different PCF geometrical parameters namely different circular spacings, air-hole diameter and numbers of air-hole rings are carried out in detail towards practical applications. Our numerical analysis establishes that total dispersion is strongly affected by the interplay between material dispersion and waveguide dispersion. For smaller air-filing fraction, adding extra air-hole rings does not change dispersion much whereas for higher air-filling fraction, the dispersion nature changes significantly. With proper adjustment of the parameters ultra-flattened dispersion could be achieved; though the application can be limited by higher losses. However, the ultra-flat dispersion fibers can be used for practical high power applications like supercontinuum generation (SCG) by reducing the loss at the pumping wavelength by increasing the no of air-hole rings. Broadband smooth SCG can also be achieved with low loss oscillating near-zero dispersion fiber with higher no of air-hole rings. The detail study shows that for realistic dispersion engineering we need to be careful for both loss and dispersion.

Long period fiber gratings written in photonic crystal fibers by use of CO2 laser

Photonic crystal fibers are usually divided into two different types of fibers: solid-core photonic crystal fibers (PCFs) and air-core photonic bandgaps fibers (PBFs). We presented the fabrication methods and applications of long period fiber gratings (LPFGs) written in these two types of photonic crystal fibers by use of a CO2 laser. A stain sensor with a high sensitivity was demonstrated by use of an LPFG written in solid-core PCFs. An in-fiber polarizer based on an LPFG was fabricated by use of a focused CO2 laser beam to notch periodically on a PCF. A novel LPFG was written in an air-core PBF by use of a CO2 laser to collapse periodically air holes in the fiber cladding.

Experimental demonstration of a high-sensitivity humidity sensor based on an Agarose-coated transmission-type photonic crystal fiber interferometer

We present a detailed study of a high-sensitivity relative humidity (RH) sensor based on Agarose-coated transmission type photonic crystal fiber interferometer for what is the first time to our knowledge. The sensor shows a wavelength shift of approximately 56 nm for a humidity change of 58% RH. The repeatability of the coating layer formation and the evolution of the coating layers on passing the device though Agarose solution multiple times are studied in detail by observing the spectral shift resulting from the effect on the effective index of the cladding mode. Also, a detailed study is reported of the sensor performance in terms of its sensitivity, repeatability, and long-term stability. The sensor shows a linear response for an RH change in the range of 40%-80% RH with a humidity resolution of 0.017% RH and a higher humidity resolution of 0.007% RH in the range 80%-95% RH. The measurement accuracy of the sensor in the RH range 40%-80% is ±2% RH, and in the range 80%-95%, the accuracy is about ±1% RH. The response time of the sensor is 86 ms, when RH jumps from 50% to 90%. The temperature dependence of the sensor is found to be ~0.27 nm/°C, which is quite small compared to the RH sensitivity of the sensor.

Fiber Optic Hybrid Device for Simultaneous Measurement of Humidity and Temperature

A novel fiber optic hybrid device for simultaneously measuring temperature and relative humidity (RH) is proposed and demonstrated in this paper. The device is composed of a fiber Bragg grating (FBG) and a reflection type photonic crystal fiber interferometer (PCFI) infiltrated with humidity sensitive material Agarose. The Agarose infiltrated PCFI is used to monitor the RH and an in-line FBG is used to monitor the temperature. The temperature is measured by detecting the shift in the Bragg wavelength and the humidity is measured by monitoring the change in the optical power of the reflected spectrum. The sensor shows a temperature sensitivity of 9.8 pm/°C and an optical power variation of >7 dB for an RH change of 75%, with less cross sensitivity.

Optimization of highly nonlinear dispersion-flattened photonic crystal fiber for supercontinuum generation

A simple type of photonic crystal fiber (PCF) for supercontinuum generation is proposed for the first time. The proposed PCF is composed of a solid silica core and a cladding with square lattice uniform elliptical air holes, which offers not only a large nonlinear coefficient but also a high birefringence and low leakage losses. The PCF with nonlinear coefficient as large as 46 W−1 · km−1 at the wavelength of 1.55 μm and a total dispersion as low as ±2.5 ps · nm−1 · km−1 over an ultra-broad waveband range of the S—C—L band (wavelength from 1.46 μm to 1.625 μm) is optimized by adjusting its structure parameter, such as the lattice constant Λ, the air-filling fraction f, and the air-hole ellipticity η. The novel PCF with ultra-flattened dispersion, highly nonlinear coefficient, and nearly zero negative dispersion slope will offer a possibility of efficient super-continuum generation in telecommunication windows using a few ps pulses.

Polarization Properties of Polymer Photonic Crystal Fiber with Square-Lattice Elliptical Air-Hole

A novel type of photonic crystal fiber for high birefringence and zero-walkoff is proposed based on polymer, the fiber is composed of a solid polymer core and a cladding with square lattice elliptical air-holes along the fiber length. The optical birefringence and polarization-dependent leakage loss are studied numerically based on the full-vector finite element method(FEM). Numerical results show that the proposed fiber has heightened modal birefringence of the order of 10-2; and the leakage loss is reduced to 0.08dB/m at wavelength of 0.65μm when it has 10 rings of elliptical air-holes. So the proposed PCFs may be useful in the field of high birefringence polarization-maintaining optical communication.

Investigation of high birefringence and negative dispersion photonic crystal fiber with hybrid crystal lattice

Aiming at the requirements of high birefringence and negative dispersion in fiber-optic communication and sensing systems, a novel type of photonic crystal fiber (PCF) is proposed. In this structure, rectangular holes are arranged as hybrid lattice in the core and two bigger air holes symmetrical in the first cladding layer are added to gain high birefringence. Simulation results show that this kind of PCF exhibits high birefringence with a level of 10−2, which will obtain better polarization. The negative dispersion is obtained over a wide wavelength range simultaneously, which has important applications in designing of dispersion compensation fibers.

Propagation Properties and Stress Sensitivity of S-PCF, H-PCF and O-PCF

Propagation properties of square, hexagonal and octagonal lattice photonic crystal fibers (PCFs) have been analyzed here for both stressed and unstressed conditions. The analysis has been carried out using finite element method. All types of PCFs are investigated here by varying number of air hole rings with same design and operating parameters. The results show that external stress causes PCFs deformation as well as change of propagation properties and this effect is not same for different types of PCFs. We have found that hexagonal PCFs are comparatively more sensitive than square and octagonal for birefringence properties. Furthermore propagation properties of octagonal PCFs remain almost unchanged with the increase of external stress. It is also found that PCFs with lower number of number of air hole rings is comparatively highly sensitive than higher number of air hole rings.

Design of Photonic Crystal Fibers Based Polarization Splitter with Hollow Ring Defects

A novel photonic crystal fibers (PCFs) based polarization splitter is proposed in this paper. It is designed by highly birefringent dual-core PCFs which hollow ring defects are used in its one direction to break the structural symmetry. Compared to the previous methods achieving high birefringence, this new type of PCFs can partly overcome the design and fabrication limitations for the PCF-based polarization splitter. Its transmission properties, coupling lengths for the two orthogonal polarizations and the performance of the proposed polarization splitter are investigated respectively. The results show that a 0.676-mm-long polarization splitter can be obtained. When the splitting ratio is better than -15dB, its bandwidth is about 45.8nm.

Analysis of Fresnel Loss at Splice Joint Between Single-Mode Fiber and Photonic Crystal Fiber

An analysis of Fresnel loss at splice joint of single-mode fiber (SMF) and two types of photonic crystal fibers (PCFs) using improved full-vectorial effective index methods is presented. The effects of air-hole size () d , air-hole spacing () Λ , longitudinal misalignment between spliced SMFs and PCFs on the Fresnel loss is analyzed and is shown that when Λ and the dopant concentration in the core of PCFs increases or the ratio / d Λ decreases, the Fresnel loss will decrease. The results of the analysis may be used by network designers to predict over all loss when employing PCF-based devices in optical fiber networks.

Guided-wave-coupled nitrogen vacancies in nanodiamond-doped photonic-crystal fibers

Zero-phonon-line (ZPL) emission of nitrogen vacancies (NVs) is coupled to the guided modes of solid- and hollow-core nanodiamond-doped photonic-crystal fibers (PCFs). Both types of PCFs are tailored toward enhancing ZPL emission coupling to the fiber modes. In solid-core PCFs, this involves enhancing the evanescent field of the waveguide modes supported by an ultrasmall fiber core. In hollow-core PCFs, the NV emission spectrum is matched with the transmission band of the fiber, controlled by the photonic bands of the fiber cladding.

Numerical analysis of a novel high birefringence photonic crystal fiber

In order to confine mode field energy effectively and obtain high birefringence, a new type of photonic crystal fiber (PCF) is proposed, which consists of air cores arrayed with pentagonal core and hexagonal cladding. Investigations show that high birefringence can be obtained by changing the aperture of the two symmetry holes outside the core. Simulation results show that the birefringence of this PCF reaches the magnitude of 10−3 which fulfills the requirements of high precision applications in optical systems. In addition, nonlinear coefficient reaches the magnitude of 103km−1w−1 after optimization, which will find application in nonlinear optics.

A New Design of Photonic Crystal Fiber with Fattened Dispersion and Low Effective Mode Area

We propose a novel type of photonic crystal fiber with low fattened dispersion and high nonlinearity for four wave mixing. The dispersion and nonlinearity coefficient are investigated simultaneously by using the full vectorial finite element method with anisotropic perfectly matched layers. The optimized result has been obtained by adjusting the design parameter of the proposed fiber, which has dispersion is -1.53 ps•nm−1 km−1 at wavelength of 1.55μm, and in addition the relatively small effective mode area of 2.23μm2 is obtained at the same wavelength, which will induce higher nonlinearity coefficient is close 54.8 W-1• km-1 at the wavelength of 1.55μm. The proposed PCF is suitable for applications as a chromatic dispersion controller, dispersion compensator, or as candidate for the nonlinear optical systems because of its small effective mode area.

Extremely large birefringence and shifting of zero dispersion wavelength of photonic crystal fibers

Three different types of photonic crystal fibers have been investigated which promise very large birefringence. The first type fiber is band gap guiding, the second index guiding, while the third type is index guiding with high refractive index circular and elliptical regions in the innermost ring. The birefringence, group velocity dispersion, modal effective index and mode field area of these fibers have been numerically estimated by employing finite difference time domain method. When elliptical regions are introduced in the first and second rings with the combination of small circular regions, each of these proposed fibers exhibits large birefringence with shifted zero dispersion point. Among these three different types of fibers, the band gap guiding photonic crystal fiber promises the largest birefringence (∼5.45×10−2) reported so far. The value of the birefringence and group velocity dispersion of these fibers can be controlled by controlling the hole pitch. Largest birefringence is achieved with a specific value of hole pitch.

Characteristics Analysis of High Birefringence Photonic Crystal Fiber with Pentagonal Air-Core

A new type of photonic crystal fiber (PCF) with pentagonal air-core is proposed, which consists of octagonal air holes in the cladding. In addition, five elliptical air holes are embedded in the inner layer to enhance the birefringence characteristic. Characteristics of this PCF are analyzed by using of Finite Element Method (FEM). Numerical results show that this kind of PCF exhibits high birefringence with the level of 0.001 after optimization, which will find application in optical sensing systems.

Characteristics Analysis of High Birefringence Photonic Crystal Fiber with Pentagonal Air-Core

A new type of photonic crystal fiber (PCF) with pentagonal air-core is proposed, which consists of octagonal air holes in the cladding. In addition, five elliptical air holes are embedded in the inner layer to enhance the birefringence characteristic. Characteristics of this PCF are analyzed by using of Finite Element Method (FEM). Numerical results show that this kind of PCF exhibits high birefringence with the level of 0.001 after optimization, which will find application in optical sensing systems.

Characteristic analyses of high birefringence and two zero dispersion points photonic crystal fiber with octagonal lattices

Aiming to the requirements of high birefringence and multiple zero dispersion points of optic-fiber sensing and communication systems, a new type of photonic crystal fiber (PCF) is proposed. The cladding is arrayed by octagonal air holes, and two big elliptical air holes are added in inner cladding to increase the birefringence. Numeral results show that this type of PCF exhibits high birefringence with a level of 10-3 when wavelength ranges from 0.8-2 m, which fulfils the requirement of high birefringence, and two zero dispersion points are obtained after optimization. In addition, high nonlinear coefficient with a level of 10-2 m-1W-1 is obtained, which could be used in the case where the nonlinearity is highly required.