Birefringent Photonic Crystal Fiber Research Articles

Numerical Analysis of Large Negative Dispersion and highly Birefringent Photonic Crystal Fiber

This article deals with a study of proposed PCF in which a fiber core is surrounded by square shaped air holes arranged in circular rings in the cladding region. Parametric variation of proposed fiber is measured by varying the square air hole number in the core region, length of square air hole and also for hole packing density ratio (HPD) variation from visible to near-infrared (NIR) wavelength range. The parametric analysis shows that zero dispersion wavelength (ZDW) varies for all possible parametric variations mentioned above. The maximum negative dispersion value of −810 ps/nm/Km is obtained at 1.55 μm for 3 square air holes in fiber core while minimum confinement loss value is 1.23 × 10-5dB/m at the same wavelength. Besides this, the birefringence and nonlinear coefficient values were also found high as 3.6 × 10-3 and 75 W-1 km-1, respectively at 1.55 μm. Hence, the proposed PCF can be better used in four wave mixing, solitons generation, polarization maintaining fiber and optical sensor applications.

고복굴절 광자결정 광섬유 기반 직렬형 광섬유 투과형 격자를 이용한 스트레인 및 온도의 분리 측정에 관한 연구

고복굴절 광자결정 광섬유 기반 직렬형 광섬유 투과형 격자를 이용한 스트레인 및 온도의 분리 측정에 관한 연구

A comparative study of birefringence in photonic crystal fiber employing various lattice geometries with all-circular air holes

This article presents a detail theoretical investigation on birefringence characteristics for various highly birefringent photonic crystal fiber designs based on triangular, square, and circular-lattice geometry. In order to compare the results, a systematic comparative study is then performed. It is shown that the birefringence of any particular lattice geometry can be modulated by modifying the structural anisotropy (asymmetry) of that geometry. The variations of birefringence with normalized wavelength have been evaluated for various asymmetric designs of a lattice geometry and variation for other lattice geometries have thereby been determined and compared. These photonic crystal fibers are composed of a solid silica core surrounded by cladding of circular air-holes. The birefringence is due to large axial anisotropy introduced into the fiber by a prefer arrangement of air-holes in the fiber cladding. A finite difference mode-convergence analysis is implemented to determine the required modal indices of the photonic crystal fiber, which is then used to calculate the birefringence of the fiber. Based on the results, the birefringence is found to be largely dependent on the lattice geometry associated as well as the degree of asymmetry. Numerical results show that for a particular type of asymmetric design triangular-lattice geometry is the best choice in terms of high birefringence. One of the considered designs based on triangular-lattice geometry, formed by omitting three adjacent air-holes at the centre, can considerably enhance the birefringence as high as 12.6×10−3 at normalized frequency 0.48.

Endlessly single-mode photonic crystal fiber with high birefringence for sensing applications

A novel type of highly birefringent photonic crystal fiber is designed, which yields to promise a very large birefringence [Formula: see text] with flat dispersion at the operating wavelength 1550 nm. By employing the FDTD method, other properties, such as dispersion, walk-off effect and [Formula: see text]-parameters, are highly optimized using lattice period of air holes.

Low loss and highly birefringent photonic crystal fibre for terahertz applications

A highly birefringent photonic crystal fibre, with horizontal arrangement of three elliptical air holes in the core and hexagonal arrangement of circular air holes in the cladding, has been proposed for transmission of terahertz waves. Guiding properties of the fibre have been rigorously investigated using finite element method with perfectly matched layer boundary conditions. It has been demonstrated that high birefringence of 0.08 can be achieved with low effective material loss of 0.03 cm−1 at 1.3 THz. Moreover, it has been shown that about 42 % of useful power flows through the elliptical core air holes. Near-zero flattened dispersion of 1.18 ± 0.01 ps/THz/cm is obtained for the x-polarisation mode of the fibre. Other important optical properties such as confinement, bending and total losses have also been investigated; further strengthening potential applicability of the proposed fibre for next-generation terahertz research.

Surface plasmon induced broadband single-polarization filter based on high birefringence photonic crystal fiber

A broadband and single-polarization filter based on high birefringence photonic crystal fiber (HB-PCF) with selectively infiltrated gold wires and liquid crystal is proposed, and its filtering characteristics are studied by the full-vector finite element method (FV-FEM). Two gold wires are selectively filled on both sides of the liquid crystal core to act as two defect cores. The results show that the confinement loss of x-polarized core mode is much larger than that of y-polarized core mode in the wavelength range of 0.85–1.75 μm. The confinement losses of x- and y-polarized core modes are 99.87 dB/cm and 0.001 dB/cm at 0.88 um, 726.50 dB/cm and 0.004 dB/cm at 1.02 um, and 474.60 dB/cm and 0.046 dB/cm at 1.30 um, respectively. The bandwidth with extinction ratio less than 20 dB is 900 nm. Moreover, compared with the traditional structures, we find that our structure has higher birefringence. High birefringence helps to separate the resonant wavelengths of x- and y-polarized core modes. Therefore, the excellent properties of the proposed filter can make it widely used in sensing systems and broadband optical communication systems.

Simultaneous measurement of strain and temperature based on a long-period fiber grating written on high birefringence photonic crystal fiber concatenated with a Faraday rotator mirror

Here we report simultaneous measurement of strain and temperature, carried out by incorporating a long-period fiber grating (LPFG) written on high birefringence photonic crystal fiber (HBPCF), referred to as an HBPC-LPFG, and a Faraday rotator mirror (FRM) concatenated in series with the LPFG. The HBPC-LPFG used as a sensor head was fabricated by irradiating CO2 laser pulses to unjacketed HBPCF with line-by-line technique. The HBPC-LPFG connected in series with the FRM exhibits a polarization-independent wavelength-dependent loss spectrum in its reflection spectrum, which has two resonance dips (RDs) with different cladding-mode orders, designated as RDs 1 and 2. As the two RDs in the fabricated HBPC-LPFG ended with the FRM have dissimilar cladding-mode orders, their strain sensitivities and their temperature sensitivities are different from each other. For the two RDs with resonance wavelengths of λ1 = ∼1470.5 nm and λ2 = ∼1495.1 nm, strain and temperature responses were investigated in an applied strain range from 0 to 1790 μe (step: 179 μe) and an ambient temperature range from 30°C to 95°C (step: 5°C), respectively. The strain sensitivities of the RDs 1 and 2 were measured to be approximately −0.77 and −1.07 pm / μe at room temperature, and the temperature sensitivities of the RDs 1 and 2 were measured as ∼10.44 and ∼8.56 pm / ° C without applied strain, respectively. Owing to their linear and independent responses to strain and temperature, strain and temperature changes applied to the HBPC-LPFG can be simultaneously estimated from the measured wavelength shifts of the RDs 1 and 2 using their predetermined strain and temperature sensitivities.

Ultra-high birefringence and nonlinearity photonic crystal fiber with a nanoscale core shaped by an air slot and silicon strips

A novel polarization-maintaining photonic crystal fiber (PCF) with high birefringence and nonlinearity was designed and numerically optimized. By embedding high-index silicon strips and a low-index nanoscale air slot at the core region, X- polarization mode could be well confined in the low-index slot region due to the discontinuity of its electric displacement field vector at the silicon-air interface, whereas Y-polarization mode was dominated by total internal reflection (TIR) induced by elliptical air holes of the inner cladding, which resulted in a birefringence up to 10−1 order. Moreover, according to the antiresonant reflecting guidance mechanism, when the width of silicon strips was adjusted to 0.12 μm, an ultrahigh birefringence of ~0.94 at 1.55 μm could be obtained. In addition, benefiting from the tight field confinement and highly nonlinear silicon, an ultrahigh nonlinear coefficient of up to 2.4 × 106 W−1 km−1 can be achieved at the wavelength of 1.55 μm. Furthermore, the low confinement loss can also be yielded in our proposed PCF. With these advantages, the proposed PCF will offer important potential applications in optical communications, supercontinuum generation and other fields.

Design of highly-sensitive fiber thermal anemometer based on reflective photonic crystal fiber loop mirror

• A reflective fiber loop mirror is firstly used in flow rate sensing. • The proposed sensor exists an infinite temperature-sensitivity point, which can be adjusted. • The fiber thermal anemometer has high sensitivity and long-distance sensing capability. A highly-sensitive fiber thermal anemometer was proposed and numerically designed based on reflective fiber loop mirror (RFLM). One ethanol-infiltrated birefringent photonic crystal fiber (BPCF) was imbedded in the RFLM as the sensing head, whose output interference spectrum was sensitive to surrounding temperature. Laser was used to heat the BPCF to a fixed temperature, but the temperature changed with the variation of surrounding flow rate. Therefore, the flow rate could be measured by monitoring the wavelength shift of the output spectrum. Through numerical analyses on the characteristics of the RFLM, the relationship between the flow rate and the temperature of the BPCF was numerical studied and then the structure parameters of the BPCF were optimized. Finally, numerical results showed that the maximum detectable flow rate could be enlarged to 20.8 m/s with the detection limit of 0.3 m/s, when the laser power was 100 mW. In addition, the defined quality parameter Q demonstrated that the sensitivity was improved to about 20 times.

Design of an elliptical air-hole dual-core photonic crystal fiber for over two octaves spanning supercontinuum generation

A highly birefringent polarization-maintaining dual-core photonic crystal fiber (DC-PCF) structure with elliptical air holes around the cores has been designed for possible supercontinuum generation over two octaves spanning a spectral bandwidth in the 400- to 1800-nm wavelength range. The supercontinuum (SC) spectrum covers the near-UV, visual, and near-infrared regions of electromagnetic spectra when a hyperbolic secant pulse of 50 fs duration, 322 mW average power, and 80 MHz repetition rate corresponding to 4.03 nJ energy is launched into the DC-PCF around a 1060-nm pumping wavelength. The generated SC spectrum satisfies the necessary requirements for applications in biophotonics, telecommunications, and frequency metrology.

A simple design of highly birefringent and nonlinear photonic crystal fiber with ultra-flattened dispersion

We present a compressed hexagonal photonic crystal fiber (CH-PCF) based on a simple structure with ultra-flattened dispersion, high birefringence and nonlinearity. The propagation characteristics are studied accurately by utilizing full vector finite-element method (FEM). Numerical results indicate that the birefringence of 1.59 × 10−2 was obtained with high nonlinear coefficient of 42.58 W−1 km−1(X) and 52.80 W−1 km−1(Y) at an effective wavelength of 1.55 μm. Furthermore, CH-PCF presents an ultra-flattened dispersion with variation of ± 3.4 ps/nm/km(X) and ± 1.6 ps/nm/km(Y) over 1.3 μm to 1.8 μm (0.5 μm bandwidth), respectively. In addition, this circular-hole structure can be fabricated conveniently at most easy compared with complex designs, which is an advantage for practical applications such as dispersion compensation and nonlinear optics application.

Surface Plasmon Resonance Induced High Sensitivity Temperature and Refractive Index Sensor Based on Evanescent Field Enhanced Photonic Crystal Fiber

An ultra high-sensitivity temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR) effect in D-shape high birefringence photonic crystal fiber (PCF) is presented and discussed by the finite element method (FEM). The designed PCF is polished to enhance the interaction of the evanescent field with the external medium, ultimately improving the sensing performance. The influence of three different plasma materials, gold, silver and aluminum, on the sensing performance was investigated. Finally, the chemically stable plasma material gold is selected to coat on flat surface of D-shape PCF for SPR sensing, realizing the sensitive real-time monitoring of RI and temperature. The sensing performance was greatly improved, with a wide RI (1.43 to 1.50) and temperature (36 $^{\circ }$ C to 86 $^{\circ }$ C) detection range, and the corresponding maximum sensitivity was 44850 nm/RIU and −16.875 nm/ $^{\circ }$ C, respectively. Furthermore, the sensitivity is not particularly sensitive to the sizes of the designed air holes, which leads to a sensor with high structure tolerance. Numerical results show that the coating thickness not only affects the sensitivity but also the detection range of the sensor, so we can tune the RI and temperature detection range by adjusting the gold film thickness to meet specific detection requirements. The sensor with enhanced sensitivity, tunable detection range, and high fabrication tolerance has a wide application prospect in the field of life science research, chemical production, and environmental monitoring.

고복굴절 광자결정 광섬유 기반 광섬유 투과형 격자를 이용한 스트레인 및 온도 분리 측정 광섬유 센서에 관한 연구

In this paper, we propose an optical fiber sensor capable of separately measuring strain and temperature by incorporating a fiber transmission grating (FTG) based on high birefringence photonic crystal fiber (HBPCF). Since the FTG written on HBPCF (referred to as the HBPC-FTG) has different effective refractive indices according to the principle axis of HBPCF, its resonance wavelength also depends on input polarization. When orthogonally polarized light passes through the HBPC-FTG used as a sensor head, therefore, its transmission spectrum has two clearly different resonance dips (referred to as Dips 1 and 2). They are obtained at one and the other of two orthogonal input polarization. The measured strain sensitivities of these dips are -0.83pm/με for Dip 1 and -1.43pm/με for Dip 2 in applied strain range from 0 to 1960με, and the temperature sensitivities are measured as 8.0pm/℃ at Dip 1 and 4.8pm/℃ at Dip 2 in applied temperature range from 30 to 80℃. Since the strain and temperature responses of the two dips of the HBPC-FTG are highly linear and uncorrelated, the proposed sensor can discriminate strain and temperature changes simultaneously applied to the sensor head by using a simple sensitivity coefficient matrix.

Refractive index sensor based on selectively liquid infiltrated birefringent photonic crystal fiber

We propose a highly sensitive micro-fluidic refractive index (RI) sensor based on birefringent photonic crystal fiber (B-PCF) in this article. A single microchannel is infiltrated with liquid analyte, situated next to the core to attract mode field with analyte. The proposed sensor structure works on total internal reflection (TIR) mechanism. It is optimized and its sensitivity is numerically analyzed in detail using Finite Element Method (FEM). All the simulation results apprise that the structural parameter variation influences a little on the sensitivity of the refractive index sensor which suppress the necessity of the precise processing. A high sensitivity of 15428.50nm/RIU is achieved by this sensor with birefringence ∼ 10-4 in the RI range from 1.36 to 1.41 with a resolution of 5×10-6 RIU. The proposed highly sensitive RI sensor may be a potential candidate for chemical and industrial sensing applications.

Chalcogenide-glass polarization-maintaining photonic crystal fiber for mid-infrared supercontinuum generation

In this paper, we report the design and fabrication of a highly birefringent polarization-maintaining photonic crystal fiber made from chalcogenide glass, and its application to linearly-polarized supercontinuum generation in the mid-infrared region. The fiber was drawn using the casting method from As38Se62 glass which features a transmission window from 2 to 10 μm and a high nonlinear index of 1.13 × 10–17 m2 W−1. It has a zero-dispersion wavelength (ZDW) at 4.56 μm for the fast axis and 4.68 μm for the slow axis and, at average ZDW, a large birefringence of 6.5 × 10–4 and consequently strong polarization maintaining properties are expected. Using this fiber, we experimentally demonstrate supercontinuum generation spanning from 3.1 to 6.02 μm and 3.33–5.78 μm using femtosecond pumping at 4 μm and 4.53 μm, respectively. We further investigate the supercontinuum bandwidth versus the input pump polarization angle and we show very good agreement with numerical simulations of the two-polarization model based on two coupled generalized nonlinear Schrödinger equations.

Dual-cladding high birefringence photonic crystal fiber with elliptical-core

A novel elliptical core photonic crystal fiber (EC-PCF) is proposed with a trapezoidal outer cladding and three different inner claddings in this paper. The material of proposed fiber is a combination of the background material of silica and core material of As2S3. Using the finite element method (FEM) with the boundary condition of the circular perfectly matched layer (C-PML), the effect of different inner cladding structures (ellipse plus circles, strip circles, and hexagonal circles) on birefringence and nonlinear coefficients is analyzed. Simulation results show that the inner cladding has revealed a high birefringence in the order of 3.3136 × 10-1 with strip circles, while the nonlinear coefficients for x- and y-polarization is 2.81 × 104 w−1/km and 2.09 × 104 w−1/km at an operation wavelength of 1.55 μm, respectively. The demonstration of our proposed fiber can supply a feasible method for optical communication and supercontinuum generation.

Analysis of a Magnetic Field Sensor Based on a Sagnac Interferometer Using a Magnetic Fluid-Filled Birefringent Photonic Crystal Fiber

A magnetic field sensor based on a Sagnac interferometer using a magnetic fluid-filled birefringent photonic crystal fiber (MF-BPCF) was proposed and studied by finite element method. Two large air holes in the birefringent photonic crystal fiber were designed to fill with magnetic fluid. The MF-BPCF in the proposed Sagnac interferometer acted as the sensing head. As magnetic field perpendicular to the MF-BPCF, magnetic fluid was anisotropic. The characteristics of the output spectrum of the Sagnac interferometer was simulated. The results showed that when the phase difference $\phi$ satisfied integer multiples of $2\pi$ , several dip wavelengths appeared. Not only the intensity but also the direction of the magnetic field was measured. The measuring sensitivity could be further promoted by making the dip wavelength approach $\lambda _{B_g=0}$ .

Asymmetrical photonic crystal fiber based on the surface plasmon resonance sensor and analysis by the lower-birefringence peak method

A lower-birefringence peak method is used to investigate a new birefringence photonic crystal fiber (PCF) based on the surface plasmon resonance (SPR) sensor with an asymmetrical configuration. The novel method can determine the resonance wavelength and resonance intensity by the appearance of the lower peak and overcome deficiencies of the reported zero-birefringence point method. Upper and lower gaps are designed in the air holes to enhance the birefringence of the sensor as well as coupling efficiency between the plasmonic mode and core-guided mode. The dependence of the sensing performance on the structure parameters is discussed considering the depth of penetration of the evanescent wave and location of light confinement analysis. A maximum spectral sensitivity of 16,700 nm/RIU can be obtained in a broad refractive index (RI) detection range from 1.33 to 1.42 and the corresponding RI resolution is 5.99×10−6RIU.

Relative dispersion slope matched highly birefringent and highly nonlinear dispersion compensating hybrid photonic crystal fiber

In this study, we developed the optimum design for a highly birefringent hybrid photonic crystal fiber (Hy-PCF) based on an adapted structure for broadband compensation covering the S, C, and L communication bands, i.e., wavelengths from 1400 nm to 1625 nm. The simulation results showed that high birefringence of 3.039 × 10−2 was obtained with a high nonlinear coefficient of 33.76 W−1 km−1 at an effective wavelength of 1550 nm. The fiber also exhibited dispersion compensation properties over a broad range of wavelengths covering the S to L communication bands. The proposed design achieved a negative dispersion coefficient of −378.6 ps/(nm-km) at an effective wavelength of 1550 nm. This fiber also had a relative dispersion slope of 0.003623 nm−1 at an operating wavelength of 1550 nm, which is very close to that of a single mode fiber. This Hy-PCF is suitable for high bit rate communication systems because it allows single mode operation, as well as for optical sensing applications due its high birefringent property.

Distributed Hydrostatic Pressure Measurement Using Phase-OTDR in a Highly Birefringent Photonic Crystal Fiber

Although distributed fiber-optic sensing of axial strain and temperature is a well-established technique, there are almost no demonstrations of distributed hydrostatic pressure sensing. The main obstacle for such measurements is the low sensitivity to pressure of standard optical fibers. Structured fibers, such as photonic crystal fibers, can be made pressure sensitive by means of an optimized arrangement of their internal microstructure. In this paper, we demonstrate - for the first time to our knowledge -distributed birefringence and hydrostatic pressure measurements based on phase-sensitive optical time-domain reflectometry (OTDR) in highly birefringent photonic crystal fibers. We study the response to hydrostatic pressure of two dedicated pressure-sensitive photonic crystal fibers in the range from ~0.8 to ~67 bar with a 5-cm spatial resolution using a phase-OTDR approach. We find differential pressure sensitivities between the slow and fast polarization axes of the studied fibers of -219 MHz/bar and 95.4 MHz/bar. These values are ~3.8 to ~8.8 times larger than those demonstrated previously in distributed pressure measurements with other photonic crystal fibers.