Dispersion-flattened Photonic Crystal Fiber Research Articles

Design of dispersion-flattened photonic crystal fiber with 800 nm wide low-dispersion band

We propose a new design for a dispersion-flattened photonic crystal fiber with 800 nm wide low-dispersion band by employing the imaginary-distance beam propagation method and the transparent boundary condition using BeamPROP simulation software. The chromatic dispersion of the fiber is −1.4 to 4.8 ps/nm·km in an 800 nm wavelength range of 1.1–1.9 μm. The effective mode area at a wavelength of 1.55 μm is 12.2 μm2 and the fiber can be easily joined to conventional nonlinear optical fiber with a small core. The calculated effective index is extremely linear via the wavelength, and the decision coefficient with an approximately straight function is 0.999996, this means the waveguide dispersion of the proposed PCF completely compensates for the material dispersion curves.

Designing Dispersion Flattened Photonic Crystal Fiber For Wideband Applications

In this paper, we proposed a dispersion flattened photonic crystal fiber (PCF) for having very low dispersion for wide bandwidth as well as low confinement loss. The proposed fiber has been numerically analyzed for Silica core as well as Borosilicate crown glass core with square lattice air holes. In the proposed design we have used elliptical air holes in the inner ring whereas outer rings are circular. Finite Element Method based software tool is used to analyze the proposed design. This comparison of core materials deduces that Borosilicate crown glass PCF produces negative dispersion, making it a good candidate to be used as Dispersion Compensating Fiber (DCF), whereas Silica PCF provides nearly zero dispersion at wavelength range 1.35 µm to 1.70 µm.

Design and Characterization of an Ultra Low Loss, Dispersion-Flattened Slotted Photonic Crystal Fiber for Terahertz Application

Abstract A novel photonic crystal fiber (PCF) based on TOPAS, consisting only rectangular slots is presented and analyzed in this paper. The PCF promises not only an extremely low effective material loss (EML) but also a flattened dispersion over a broad frequency range. The modal characteristics of the proposed fiber have been thoroughly investigated using finite element method. The fiber confirms a low EML of 0.009 to 0.01 cm−1 in the frequency range of 0.77–1.05 THz and a flattened dispersion of 0.22±0.01 ps/THz/cm. Besides, some other significant characteristics like birefringence, single mode operation and confinement loss have also been inspected. The simplicity of the fiber makes it easily realizable using the existing fabrication technologies. Thus it is anticipated that the new fiber has the potential to ensure polarization preserving transmission of terahertz signals and to serve as an efficient medium in the terahertz frequency range.

Highly birefringent large negative dispersion-flattened photonic crystal fibre for broadband residual dispersion compensation

A triangular lattice photonic crystal fibre is presented in this paper for residual dispersion compensation. The fibre exhibits a flattened negative dispersion of −992.01 ± 6.93 ps/(nm-km) over S+C+L wavelength bands and −995.83 ± 0.42 ps/(nm-km) over C-band. The birefringence is about 4.4 × 10−2 at the excitation wavelength of 1550 nm which is also very high. Full vector finite element method (FEM) with a perfectly matched absorbing layer (PML) boundary condition is applied to numerically investigate the guiding properties of this PCF. The fibre operates at fundamental mode only. All these properties endorse this fibre as a suitable candidate for compensating residual dispersion and polarization maintaining applications.

Design and characterization of a low-loss, dispersion-flattened photonic crystal fiber for terahertz wave propagation

A porous core photonic crystal fiber, based on Topas, with ultra-low effective material loss and near zero flattened dispersion properties is proposed for efficient polarization preserving transmission of terahertz waves. The Finite Element Method (FEM) with a Perfectly Matched Layer (PML) boundary condition is used to compute the modal characteristics of the fiber that confirms a lower Effective Material Loss (EML) of 0.034cm−1, lower confinement loss of the order of 10−3.7cm−1, higher effective mode area of 0.6×106μm2 and a flattened dispersion variation of 0.09ps/THz/cm. In addition, some other characteristics including birefringence, single mode operation, core power fraction and Figure of Merit (FOM) of the proposed fiber are also discussed. To simplify the fabrication process, only circular shaped air holes with a conventional hexagonal structure in the cladding is deployed. It is anticipated that, this newly proposed waveguide will open a new window for further terahertz research and broadband transmission of terahertz radiation.

Investigation on chalcogenide and silica based photonic crystal fibers with circular and octagonal core

In this paper, a novel chalcogenide and silica photonic crystal fiber (PCF) structure is designed with circular air-holes located in the cladding and the various optical properties, namely, dispersion, nonlinearity and group velocity dispersion parameters are compared for two different core structures, namely, circular and octagonal. The objective is to obtain high nonlinearity with dispersion flattened PCF. The prime focus is to obtain high non-linear effects as it plays great role in speed and capacity of optical communications. The proposed chalcogenide octagonal and circular PCF exhibits a dispersion of +77.55ps/(nmkm) and +77.34ps/(nmkm), respectively, whereas, the nonlinearity is in the order of 4506W−1km−1 and 4498W−1km−1, respectively. Also, the silica octagonal and circular PCF exhibits a dispersion of +19.03ps/(nmkm) and +0.97ps/(nmkm) respectively, whereas the nonlinearity is in the order of 169.41W−1km−1 and 182.41W−1km−1 respectively.

Characteristics of Highly Birefringent Photonic Crystal Fiber with Defected Core and Equilateral Pentagon Architecture

A novel high birefringence and nearly zero dispersion-flattened photonic crystal fiber (PCF) with elliptical defected core (E-DC) and equilateral pentagonal architecture is designed. By applying the full-vector finite element method (FEM), the characteristics of electric field distribution, birefringence, and chromatic dispersion of the proposed E-DC PCF are numerically investigated in detail. The simulation results reveal that the proposed PCF can realize high birefringence, ranging from 10-3 to 10-2 orders of magnitude, owing to the embedded elliptical air hole in the core center. However, the existence of the elliptical air hole gives rise to an extraordinary electric field distribution, where a V-shaped notch appears and the size of the V-shaped notch varies at different operating wavelengths. Also, the mode field diameter is estimated to be about 2 μm, which implies the small effective mode area and highly nonlinear coefficient. Furthermore, the investigation of the chromatic dispersion characteristic shows that the introduction of the elliptical air hole is helpful to control the chromatic dispersion to be negative or nearly zero flattened over a wide wavelength bandwidth.

Tailoring of nearly zero flattened dispersion photonic crystal fibers

This work theoretically tailored the dispersion in a photonic crystal fiber (PCF), and then designed two types of nearly zero dispersion flattened PCFs (DFPCFs) by rod-doping or liquid-filling some of the cladding holes. The numeric results show that the DFPCF type 1, rod-doped with arbitrary indices, achieves the dispersion values between 0±1ps/nmkm over a bandwidth range of 460nm. The DFPCF type 2, filled with the available liquids, performs the dispersion values between 0±1.5ps/nmkm over a bandwidth range of 520nm. Finally, the confinement losses of the two types of DFPCFs are estimated. The numeric results show that the confinement losses of the two types of the proposed DFPCFs are extremely low, in the order of 10−5 or 10−6dB/km, which even can be disregarded.

基于光子晶体光纤中简并四波混频效应的高效可调谐偏振不敏感波长变换器

A high-efficiency tunable polarization-insensitive all-optical wavelength convertor for 10 Gb/s return-to-zero on-off keying (RZ-OOK) signals using degenerate four-wave mixing (FWM) in a highly nonlinear photonic crystal fiber (PCF) is demonstrated. The residual birefringence in the 50 m dispersion-flattened PCF with 11 W-1mkm-1 nonlinear coefficient guarantees the FWM-based wavelength conversion to be polarization-insensitive when the pump polarization is exactly at 45d to the birefringent axes of the PCF. Experimental results show that with 45d pump launch, the polarization dependence of FWM in the PCF can be decreased to less than 0.6 dB over the entire 25 nm conversion bandwidth. The optical signal-to-noise ratios (OSNR) of the converted signals are better than 40 dB and the conversion efficiencies are better than -15 dB over the conversion range with 10 Gb/s signal polarization-scrambled.

Ultra-flattened chromatic dispersion and highly nonlinear photonic crystal fibers with ultralow confinement loss employing hybrid cladding

In this paper, two new types of dispersion-flattened photonic crystal fibers (DF-PCFs) with highly nonlinear and ultralow confinement loss are proposed. These new PCF structures adopt hybrid cladding with different air-holes diameters, pitches and air-holes arranged fashions. In order to analyze the proposed PCFs, the full-vector finite element method with anisotropic perfectly matched layers has been used. Results show that the ultra-flattened dispersion of 0.931ps/(nmkm) (DF-PCF1) and 1.533ps/(nmkm) (DF-PCF2) can be achieved in the wavelength range from 1.3 to 1.6μm with confinement losses lower than 0.001dB/km in the same wavelength range. Meanwhile, the nonlinear coefficients of our proposed PCFs are greater than 23.83W−1km−1 (DF-PCF1) and 29.65W−1km−1 (DF-PCF2) at the wavelength of 1.55μm, and two near-zero dispersion values of 0.328ps/(nmkm) (DF-PCF1) and −0.015ps/(nmkm) (DF-PCF2) can also be obtained at the same wavelength. Furthermore, the influence of manufacturing imperfections of parameters on dispersion and nonlinearity is discussed to verify the robustness of our design.

Nearly zero dispersion-flattened photonic crystal fiber with fluorine-doped three-fold symmetry core

A novel design of a photonic crystal fiber is presented. A nearly zero dispersion regime of operation has been achieved by using a three-fold symmetry core, which is improved by the avoidance of high-index doping in a central region. The core consists of pure silica surrounded by three fluorine-doped regions and three airholes. It can be confirmed by the numerical simulations using the finite difference frequency domain method that flattened dispersion characteristics upon wavelength over the range of 1250 to 1700 nm can be achieved in an optical fiber. Further, the potential fiber geometry imperfections caused some concern. Finally, the presented fiber design is compared to selected fiber designs with a dispersion close to zero.

Highly Nonlinear Dispersion-Flattened Photonic Crystal Fiber with High Birefringence

Highly Nonlinear Dispersion-Flattened Photonic Crystal Fiber with High Birefringence

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.

Improved flatness and tunable bandwidth of the supercontinuum generation in all-normal dispersion-flattened PCF using Littman–Metcalf optical bandpass filter

We have proved that in an all-normal dispersion-flattened photonic crystal fiber (PCF), the four-wave mixing (FWM) process dominantly affects the flatness of the generated supercontinuum (SC). The numerical results show that pulses with steepened edges can enhance the FWM conversion efficiency during the SC’s generation and the minima of the spectral oscillatory structure will be smoothed. A double-pass Littman–Metcalf optical bandpass filter is used to make the 1.60ps hyperbolic-Secant shaped pulses obtain steepened edges. The experimental results show that the flatness of the SC generated from the 4nm filtered pulses is improved by 0.21dB. The SC with 10–65nm tunable bandwidths is obtained by adjusting the filter bandwidth from 1nm to 7nm. Further numerical results show that the filter induced SC’s flatness improvement is more effective for pulses with 2.0–4.0ps FWHM. The improved SC can be used for applications which require stable modulation carriers and flexible bandwidth.

Flatly broadened supercontinuum generation in dispersion-flattened photonic crystal fibre using compressed picosecond pulses

We experimentally demonstrated the use of a standard single mode fibre as a picosecond pulse compressor before a 80 m long dispersion-flattened photonic crystal fibre for broadening the supercontinuum. The effects of compressor length and fibre input power on the supercontinuum bandwidth and flatness are investigated experimentally and numerically. An analytical expression of the optimal input power for a fixed length compressor to generate the broadest supercontinuum is obtained and verified. Compared with only using photonic crystal fibre, the generated supercontinuum’s − 20 dB bandwidth is broadened from 74.1 to 264.2 nm covering the S + C + L + U bands by using a 20 m long standard single mode fibre with an optimal peak input power of 114.27 W.

Enhanced Efficiency of Multiple Four-Wave Mixing Induced by Modulation Instability in Low-Birefringence Fibers

Modulation instability (MI) induced by two strong beams and a weak beam via cross phase modulation is investigated. Multiple four-wave-mixing (FWM) processes associated with the MI in low-birefringence fibers are studied both theoretically and experimentally. The coupled-mode equations describing the MI-induced FWM nonlinear interactions between pump waves and sideband waves are derived. Theoretical and experimental results show that, on the assistance of MI, new optical frequencies can be generated quite efficiently from multiple FWM processes. More than eleven sidebands are experimentally achieved by the MI-driven multiple FWM processes. The transfer of energy from pumps to sidebands can be dramatically enhanced by the MI-induced parametric process. The experimental observations by using a piece of highly nonlinear dispersion-flattened photonic-crystal fiber confirm our theoretical predictions.

Scalar generalized nonlinear Schrödinger equation-quantified continuum generation in an all-normal dispersion photonic crystal fiber for broadband coherent optical sources

We quantitatively predict the observed continuum-like spectral broadening in a 90-mm weakly birefringent all-normal dispersion-flattened photonic crystal fiber pumped by 1041-nm 229-fs 76-MHz pulses from a solid-state Yb:KYW laser. The well-characterized continuum pulses span a bandwidth of up to 300 nm around the laser wavelength, allowing high spectral power density pulse shaping useful for various coherent control applications. We also identify the nonlinear polarization effect that limits the bandwidth of these continuum pulses, and therefore report the path toward a series of attractive alternative broadband coherent optical sources.

Design of fiber parametric wavelength converters based on photonic crystal fibers with two zero-dispersion wavelengths

We propose the design method of fiber parametric wavelength converters based on dispersion-flattened photonic crystal fibers (PCFs) with two zero-dispersion wavelengths (ZDWs). Analytical expressions of the optimum signal frequency and maximal pump tuning range are deduced. By our method, the tuning ranges can be considerably broadened with a relatively low pump power and short fiber. This is because the fourth-order dispersion coefficient of two ZDW PCFs can be 1-2 orders of magnitude larger than those of one ZDW fiber and are effectively utilized to compensate the linear phase mismatch due to the second-order dispersion, resulting in a low phase mismatch for a widely tunable pump. To exemplify the effectiveness of our method, a PCF based on lead-silicate glasses with two ZDWs spaced 127-nm apart is presented. Numerical simulations show that based on this PCF a transparent wavelength conversion with a 117-nm pump tuning range can be achieved with only a 3.7-m-long fiber and 0.532 W pump power.

Design of double cladding dispersion flattened photonic crystal fiber with deformation insensitive outer cladding air-holes

A design of double cladding dispersion flattened photonic crystal fiber (DF-PCF) is proposed. To employ traditional stack and draw technology, the cladding of the DF-PCF is consisted of triangular periodic air-holes with the same hole to hole pitch. Simulation results show that the small air-holes in the inner cladding are mainly for dispersion management. The large air-holes in the outer cladding are mainly used for light confinement and have little impact on the dispersion tailoring. Thus, the dispersion profile of the double cladding DF-PCFs is insensitive to the deformation of air-holes in the outer cladding. Considering that the larger air-holes are apt to deform in the drawing procedure, the characteristics mentioned above make the realization of DF-PCFs relative easy by employing conventional stack and draw technology and modest air-hole rings (less than 10 rings) in the cladding.

Design of Nearly Zero Dispersion Flattened Photonic Crystal Fiber with Double Cladding

A novel design of nearly zero dispersion Battened photonic crystal fiber (PCF) with double cladding is proposed. To employ traditional stack and draw technology, the cladding is composed of a traditional triangular lattice of air-holes and silica. The dispersion of the fiber is mainly engineered by the small air holes in the inner cladding, which are easily preserved in the fiber drawing procedure. The large air-holes in the outer cladding are mainly for light confinement. Thus, the dispersion property of the PCF is insensitive to the deformation of the air holes in the outer cladding. Using 8 layers of air-hole ring, the loss of the fundamental mode for the PCF is as low as 0.13 dB/km at 1.55 μm. The dispersion of the PCF fluctuates from −0.023 to 0.021 ps·km−1 nm−1 in the range 1.45–1.625 μm.