Photonic Crystal Fiber: Theory and Fabrication

Design and fabrication of bismith-silicate photonic crystal fiber

Researchers at the University of Adelaide, Australia, and the Islamic University of Technology, Bangladesh, report the optimum design for a porous photonic crystal fibre capable of terahertz frequency transmission. Photonic crystal fibres (PCFs), also known as micro-structured optical fibres (MOFs), are a new class of optical fibre. The significance of PCFs is their remarkable optical properties, such as providing single mode operation, high birefringence, and controllable chromatic dispersion characteristics, which are not obtainable using conventional optical fibres. As a result, PCFs are used extensively in different medical imaging applications, for example, in Optical Coherence Tomography (OCT). OCT is an imaging technology that allows non-invasive cross-sectional imaging of biological tissue. Bringing such techniques into the terahertz domain will be assisted by the development of PCFs that operate in the terahertz regime. There are different types of PCFs, including solid core PCF, hollow core PCF and porous core PCF. A solid core PCF experiences large material loss, which is a property that makes these PCFs unsuitable for terahertz signal transmission. In a hollow core PCF, the loss is greatly reduced, but such fibres operate over a narrow frequency range. To overcome the described disadvantages of solid core and hollow core fibres, porous core fibres were introduced. A porous core fibre contains a number of micro-structured air holes in the core. The advantage of the porous structure is that the fibre global parameters, including air hole size, pitch distance (centre-to-centre distance between air holes), core diameter and shape of air holes can be tuned as required for different applications. Thus, for porous fibre PCFs, the effective material loss, birefringence, dispersion, confinement loss, numerical aperture and other modal properties can be obtained by design. Nowadays, PCFs are used in the field of sensing, biomedical imaging, time domain spectroscopy, security, detecting DNA hybridisation and bio-sensing, skin cancer and breast cancer detection, and in communication applications. However, there are no previously reported articles on terahertz PCFs with sufficient numerical aperture (NA) to be used for OCT applications. In this issue of Electronics Letters, Saiful Islam and colleagues propose a terahertz PCF with high birefringence, high NA, and near zero dispersion variation. The measured high birefringence is reported to be due to the elliptical-shaped asymmetrical structure of the air holes inside the core. The asymmetrical structure of air holes created a refractive index difference between the polarisation modes, thus generating birefringence. The observation of high NA is reported to be due to the high birefringence and high modal effective area. Moreover, flattened dispersion is reported due to the waveguide structure and chosen materials that the waveguide was formed of. The kagome-based PCF has the advantage that it has a significantly lower confinement loss than other PCF structures. Terahertz time-domain spectroscopy set-up in the National T-Ray lab at the University of Adelaide. Saiful Islam at the University of Adelaide. The reported simulations in this Letter have allowed for rapid design optimisation that can now be experimentally tested. The major challenge of a PCF design is to anticipate difficulties in fabrication. Thus, the fabrication possibilities of a PCF must be addressed. For accuracy, obtaining correct parameters to describe the structural and optical properties of the fibre, such as refractive index, material absorption loss, relative permittivity and relative permeability, is of great importance. S. Islam states that ‘‘Our PCF design was produced with ease of fabrication in mind, allowing future realisation. Thus, applications in THz-OCT, chemical sensing, and multichannel communications are envisaged.’’ S. Islam and colleagues are currently using photonic crystal fibres to design chemical sensors for skin cancer detection. Non-invasive breast cancer detection is possible via detecting the presence of certain protein markers in human saliva. The authors are also designing sensors to detect hazardous chemicals for security applications. ‘‘We are planning to extend our PCF designs with the use of graphene or gold coasting to exploit surface plasmons for enhanced sensing’’, explains S. Islam. In practice, PCFs are limited to reasonably simple geometries due to difficulties in fabrication. However, emerging techniques exploiting developments in 3D printing are promising methods to overcome current limitations. S. Islam predicts that ‘‘It is possible that in the next decade will we begin to see more sophisticated PCFs with remarkable properties that are not deemed practical in today's technology.’’

Since the first experimental demonstration of a photonic crystal fiber (PCF) in 1996 by Knight et al. the optical properties and the fabrication of such fibers have attracted significant attention. The fiber structure with a lattice of air holes running along the length of the fiber provides a large variety of novel optical properties and improvements compared to standard optical fibers. The stack-and-pull procedure used to manufacture PCFs is a highly flexible method offering a large degree of freedom in the fabrication of PCFs with specific characteristics. A few of the remarkable optical properties of silica based PCFs are described and their applications within sensors are summarized.

We present experimental analysis of supercontinuum generation obtained for highly birefringent and highly nonlinear dual-mode fiber. A specific difference between the zero dispersion wavelength of fundamental mode and higher order mode in such fiber gives possibility of a normal and an anomalous dispersion regime pumping, depending on the mode, which is excited. The nonlinear effects responsible for the generation of broadband spectrum of the light are analyzed when the fiber is pumped by the pulse pump source operating at the wavelength of 1064nm. Full Text: PDF References J. M. Dudley, G. Goëry, and C. Stéphane, "Supercontinuum generation in photonic crystal fiber", Reviews of modern physics 78(4), 1135 (2006). CrossRef J. C. Knight, and D. V. Skryabin, "Nonlinear waveguide optics and photonic crystal fibers", Opt. Express, 15(23), 15365-15376 (2007). CrossRef Z. Holdynski et al., "Experimental study of dispersion characteristics for a series of microstructured fibers for customized supercontinuum generation", Opt. Express 21(6), 7107-7117 (2013). CrossRef M. Napierala et al., "Influence of photonic crystal fiber manufacturing inaccuracies on supercontinuum generation", SPIE Photonics Europe, International Society for Optics and Photonics, p. 91361M-91361M-6 (2014). CrossRef J. M. Dudley, and J. R. Taylor: Supercontinuum generation in optical fibers (Cambridge University Press, 2010). CrossRef P. Falk, M. H. Frosz, and O. Bang, "Supercontinuum generation in a photonic crystal fiber with two zero-dispersion wavelengths tapered to normal dispersion at all wavelengths", Opt. Express 13(19), 7535?7540 (2005). CrossRef A. Hartung, A. M. Heidt, and H. Bartelt, "Design of all-normal dispersion microstructured optical fibers for pulse-preserving supercontinuum generation", Opt. Express, 19, 7742-7749 (2011). CrossRef B. Jinendra, K. Ranka, R. S. Windeler, and A. J. Stentz, "Optical properties of high-delta air?silica microstructure optical fibers", Opt. Lett., 25, 796-798 (2000). CrossRef J. C. Knight et al., "Anomalous dispersion in photonic crystal fiber", IEEE Photon. Technol. Lett. 12(7), 807?809 (2000). CrossRef T. Tenderenda et al., "Fibre Bragg Gratings written in highly birefringent microstructured fiber as very sensitive strain sensors", SPIE Photonics Europe, International Society for Optics and Photonics, p. 84260D-84260D-8 (2012). CrossRef T. Tenderenda et al., "Highly birefringent dual-mode microstructured fiber with enhanced polarimetric strain sensitivity of the second order mode", Opt. Express, 20, 26996-27002 (2012). CrossRef K. Stepien et al., "Fiber Bragg gratings in hole-assisted multicore fiber for space division multiplexing", Opt. Lett., 39, 3571-3574 (2014). CrossRef http://www.lumerical.com/tcad-products/mode/. DirectLink

In this study, the design and characterization of a photonic crystal fiber (PCF) as a light source for a mid-infrared supercontinuum generation (SCG) is presented. This PCF is based on a highly nonlinear chalcogenide $${\text{As}}_{40}{\text{Se}}_{60}$$ As 40 Se 60 background material with a hexagonal structure arrangement of air-holes rings. The PCF parameters such as the chromatic dispersion (D), the effective refractive index ( $${n}_{eff}$$ n eff ) and the nonlinear coefficient (γ) have been investigated. We study the stimulated SCG in two types of dispersion regimes: anomalous and all-normal dispersion (ANDi). We initiate the study by sending a 28.4 fs wide optical pulse with a peak power of 10 kW and a central wavelength of 2.8 µm through a 2 cm long PCF. In the anomalous dispersion, we demonstrate the generation of coherent and broadband SCG spectrum spanning the wavelength region from 1.6 to 7.8 µm. While, in the ANDi regime we demonstrate the generation of a broad, ultra-flat-top and highly coherent SCG spectrum extending from 2 to 4 µm at 6 dB spectral flatness. Thus, we achieve ultra-flat SCG spectrum source with a bandwidth as wide as 2400 nm within only 2 cm propagation length of the proposed PCF. This spectrum range is very suitable for variety of applications in mid-infrared region such as optical metrology, frequency comb generation, and optical coherence tomography (OCT). Results further demonstrate that with an applied pump power of 15 kW through the ANDi regime, a flat spectral bandwidth of 380 nm (wavelengths ranging from 1260 to 1640 nm) at just 3 dB spectral flatness is achieved. This band covers the five-telecommunication optical bands O-, E-, S-, C- and L-bands that comply with ITU-T-compliant wavelengths for wavelength division multiplexing (WDM) applications like coarse WDM (CWDM) and dense WDM (DWDM).

In this work, we review recent progress on the realization of chalcogenides Photonic Crystal Fibers (PCFs). We present the fabrication of chalcogenide PCFs with a solid core for three different glass compositions containing a variety of chalcogens. We show that the Stack and Draw technique currently used for silica PCFs can be problematic in the case of chalcogenides glasses. We present correct PCF design enables a significant improvement of final fiber losses. We obtained a lowest attenuation of 3 dB/m at 1.55 μm, of 4.5 dB/m at 3.39 μm and 6 dB/m at 9.3 μm. We also present experimental demonstration of self phase modulation spectral broadening around 1,55 μm. Moreover, we investigate the Brillouin and Raman scattering properties of a GeSbS PCF.

Highly sensitive photonic crystal fiber liquid sensor in terahertz frequency range

Recently developed optical fibers rely on an array of air holes in the cladding to confine light to the fiber core as opposed to conventional telecommunications fibers that require a refractive index difference produced by different composition glasses in the core and cladding regions. Holey fibers have been fabricated by drawing an array of tubes stacked around a solid central core. In this paper, we describe a new technique to produce the holes (or pores) in the cladding region. These new fibers have been made by drawing a preform, consisting of a porous outer cladding region surrounding a solid central core region, into a fiber. During the fiber drawing process, the pores initially present in the preform cladding region are drawn into small, long, thin tubular pores. Controlling the dimensions and distribution of the pores in the preform can control the physical dimensions and distribution of the pores in the fiber. In some of the preforms, the porous cladding region in the preform was prepared by sol gel techniques. The preform fabrication process and fiber drawing process used to produce these new holey fibers as well as the results of the morphological study elucidating the size, shape and distribution of the porous phase are presented.

The increasing demand for novel fiber design has brought major challenges with the current fabrication methods. Additive manufacturing is an innovative fabrication process that has been attracting attention to the optical fiber community. 3D printed porous bodies from commercial silica powder were produced based on selective laser sintering (SLS). Complex structures such as antiresonant fiber (ARF), photonic crystal fiber (PCF) and multicore fiber (MCF) preforms were produced by this method. Additionally, a multi-material fiber with a silica cladding and a GeO2-SiO2 core was fabricated from a 3D printed preform. The optical and physical properties of the fabricated 3D printed structures were reported. This Dataset support paper delivered at the International Society for optics and Photonics.SPIE Photonic West 1-6 Feb. 2020. San Francisco.

Simulations of selectively filled photonic crystal fibers using finite elements method were performed. Different patterns of filling were modeled and compared to an empty and fully filled fiber. Dependence of effective refractive indices of guided modes, phase birefringence and confinement losses on guided wavelength was investigated. A comparison of width of photonic bandgaps in different structures was made. Full Text: PDF ReferencesPh. St. J. Russell, "Photonic-Crystal Fibers", J. Lightwave Technol. 24, 4729 (2006) CrossRef Y. Han, S. Tan, M. K. K. Oo, D. Pristinski, S. Sukhishvili, and H. Du, "Towards Full-Length Accumulative Surface-Enhanced Raman Scattering-Active Photonic Crystal Fibers", Adv. Mat. 22, 2647 (2010) CrossRef S. Ertman, A. H. Rodríguez, M. M. Tefelska, M. S. Chychłowski, D. Pysz, R. Buczyński, E. Nowinowski-Kruszelnicki, R. Dąbrowski, and T. R. Woliński, "Index Guiding Photonic Liquid Crystal Fibers for Practical Applications", J. Lightwave Technol. 30, 1208 (2012) CrossRef K. Mileńko, S. Ertman, T. R. Woliński, "Numerical Analysis of the Phase Birefringence of the Photonic Crystal Fibers Selectively Filled with Liquid Crystal", Mol. Cryst. Liq. Cryst. 596, 4 (2014) CrossRef Y. Wang, C. Liao, X. Zhong, Z. Li, Y. Liu, J. Zhou, and K. Yang, "Selective-fluid-filled photonic crystal fibers and applications", Proc. SPIE 8914, 89140J-1 (2013) CrossRef F. Wang, W. Yuan, O. Hansen, and O. Bang, "Selective filling of photonic crystal fibers using focused ion beam milled microchannels", Opt. Express 19, 17585 (2011) CrossRef T. Martynkien, G. Statkiewicz-Barabach, J. Olszewski et al., "Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure", Opt. Express 18, 15113 (2010) CrossRef B. T. Kuhlmey, R.C. McPhedran, C. M. de Sterke, "Modal cutoff in microstructured optical fibers", Opt. Lett. 27, 1684 (2002) CrossRef

Typical optical sensors based on D-shape fibers use standard step-index single-mode fibers (SMF) with a circular core. Multi-mode fibers, fibers with elliptical or rectangular cores, and photonic crystal fibers (PCF) are also used to achieve the best possible sensor performance. However, since the presented sensors differ not only in geometry but, most importantly, in the materials and core sizes, it is difficult to compare their properties directly. In this paper, we numerically analyzed the influence of the shape and size of the core on the sensing performance, with all other relevant parameters being equal. Full Text: PDF References D. Jauregui-Vazquez, J. P. Korterik, C. E. Osornio-Martinez, J. M. Estudillo-Ayala, H. L. Offerhaus, J. A. Alvarez-Chavez, "A strain reflection-based fiber optic sensor using thin core and standard single-mode fibers", Opt. Comm. 522, 128659 (2022). CrossRef H. H. Liu, D. J. Hu, Q. Z. Sun, L. Wei, K. W. Li, C. Liao, B. Li, C. Zhao, X. Dong, Y. Tang, Y. Xiao, G. Keiser, P. Shum, "Specialty optical fibers for advanced sensing applications", Opto-Electron Sci. 2(2), 220025 (2023). CrossRef K. Gasior, T. Martynkien, P. Mergo, W. Urbanczyk, "Fiber-optic surface plasmon resonance sensor based on spectral phase shift interferometric measurements", Sensors and Actuators B: Chemical 257, 602 (2018). CrossRef Y. Ying, G. Si, F. Luan, K. Xu, Y. Qi, H. Li, "Recent research progress of optical fiber sensors based on D-shaped structure", Opt. & Laser Techn. 90, 149 (2017). CrossRef J. Homola, Surface Plasmon Resonance Based Sensors (Berlin, Springer 2006). CrossRef K. Gasior, T. Martynkien., M. Napiorkowski, K. Zolnacz, P. Mergo, W. Urbanczyk, "A surface plasmon resonance sensor based on a single mode D-shape polymer optical fiber", J. Opt. 19, 025001 (2017). CrossRef Q. Wang, W. M. Zhao, "A comprehensive review of lossy mode resonance-based fiber optic sensors", Opt. Lasers in Engineering 100, 47 (2018). CrossRef K. Gasior, T. Martynkien, G. Wojcik, P. Mergo, W. Urbanczyk, "D-shape polymer optical fibres for surface plasmon resonance sensing", Opto-Electron. Rev. 24(4), 209 (2016). CrossRef G. Stepniewski, A. Filipkowski, D. Pysz, J. Warszewski, R. Buczynski, M. Smietana, R. Kasztelanic, "From D-shaped to D-shape optical fiber – A universal solution for sensing and biosensing applications: Drawn D-shape fiber and its sensing applications", Measurement 222, 113642 (2023). CrossRef R. Kasztelanic, H. T. Nguyen, D. Pysz, H. Thienpont, T. Omatsu, R. Buczynski, "Free-Form Optical Fiber with a Square Mode and Top-HatIntensity Distribution", Adv. Science 11, 2402886 (2024). CrossRef J.W. Fleming, "Dispersion in GeO2-SiO2 glasses", Appl. Opt. 23, 4486-4493 (1984). CrossRef T.A. König, P.A. Ledin, J. Kerszulis, M.A. Mahmoud, M.A. El-Sayed, J.R. Reynolds, V.V. Tsukruk., "Electrically Tunable Plasmonic Behavior of Nanocube–Polymer Nanomaterials Induced by a Redox-Active Electrochromic Polymer", ACS Nano 8, 6182-6192 (2014). CrossRef I.Z. Kozma, P. Krok, E. Riedle, "Direct measurement of the group-velocity mismatch and derivation of the refractive-index dispersion for a variety of solvents in the ultraviolet", J. Opt. Soc. Am. B 22, 1479-1485 (2005). CrossRef

This study presents the development and modeling of a photonic crystal fiber (PCF) sensor designed for detecting harmful chemicals in polycarbonate plastics. The sensor features a wheel-shaped PCF structure with a floral pattern in the initial cladding layer. The focus is on two significant chemical compounds commonly found in plastics, bisphenol A (BPA) and bisphenol S (BPS). The individual sensitivities of the sensor to these compounds are measured, achieving relative sensitivities of 90.716% for BPS and 84.688% for BPA. The effective refractive indices for BPS and BPA are found to be 1.499 and 1.550, respectively. Additionally, the study analyzes confinement loss and nonlinearity of the proposed structure when exposed to these compounds, demonstrating low confinement loss and high nonlinearity, which are desirable attributes for sensing applications. The octagonal floral structure of the PCF sensor shows potential for a variety of applications, including chemical and biochemical sensing and nonlinear optics. The propagation characteristics and performance of the wheel-shaped hollow-core PCF have been thoroughly analyzed within the wavelength range of 1.5 μm to 2.5 μm. The sensor, utilizing silica as the background material, exhibits high sensitivity and low confinement loss. The analysis indicates that increasing the number of air holes in the cladding and enlarging the core size, where electromagnetic waves interact with the analyte, can further enhance sensitivity and detection accuracy with minimal losses. The PCF sensor offers real-time, label-free detection of chemical compounds with a high birefringence of -9.594×10-5, a highest refractive index (RI) of 1.550, and an effective area of 4.373×10-12 m2 for BPS at 1.2 μm. The proposed method yields negligible confinement loss, making it suitable for applications in optical fiber sensing, optical waveguides, and various photonic devices.

Fiber Bragg gratings have been essential elements in fiber optical communication for more than two decades. Although writing gratings using different inscription methods in step-index fibers has become a standard procedure, femtosecond laser based fabrication of such gratings in specialty fibers such as photonic crystal fibers (PCFs) has proven not to be straightforward. This is due to the presence of air holes in the cladding region, which impede sufficient amounts of optical energy to reach the core region. An important consequence of the presence of air holes in the cladding, which is sometimes disregarded, is the non-uniform distribution of the laser intensity in the core region, which results in an equally non-uniform refractive index change in the PCF core cross-section. To study this issue we have built a dedicated model based on coupled mode theory that allows estimating the reflectivity of the grating by modeling the intensity distribution in the PCF core region and the resulting non-linear refractive index change using empirical data. We clearly see that the limited overlap of the fiber mode with the index change reduces the reflectivity of the grating, and that the extent of this effect depends on the angular orientation of the PCF with respect to the direction of the inscription beam and on the laser beam focusing optics.

Refractive index sensor based on evanescent field effects in hollow core PCF for detection of analytes over extended E+S+C+L+U communication bands

Effect of photonic crystal fiber background materials in sensing and communication applications