Solid-core Photonic Crystal Fiber Research Articles

Sub-100-fs 187 GHz mode-locked fiber laser using stretched-soliton effects

Current pulsed fiber lasers that are capable of delivering stable sub-100-fs pulses at megahertz repetition rates require intracavity pulse energies in the nanojoule range. Scaling these lasers to gigahertz repetition rates necessitates, therefore, very high average power levels and complex cladding-pumped configurations. Here we report a type of stretched-soliton all-fiber laser that generates broadband, soliton-like pulses at 1.55 μm with intracavity pulse energies of only tens of picojoules. In the laser cavity, strong dispersion management leads to a temporal breathing ratio of ∼70, while the weak residual anomalous dispersion is perfectly balanced by the low Kerr nonlinearity, resulting in the formation of temporally stretched, hyperbolic-secant pulses. A lumped wavelength-dependent attenuator compensates for the effects of the gain filtering on the pulse spectrum, ensuring intracavity pulse self-consistency. This unique stretched-soliton mechanism, combined with a harmonic mode-locking technique based on intense optoacoustic interactions in solid-core photonic crystal fiber, yields for the first time stable gigahertz-rate, sub-100-fs, dispersive-wave-free pulse trains at moderate pump powers.

Numerical analysis of photonic crystal fiber based hemoglobin sensor

Optical fiber sensor for measuring hemoglobin (Hb) concentrations of human peripheral blood based on photonic crystal fiber (PCF) is numerically proposed in this work. It presents a simple and accurate method to measure Hb concentration. In this paper, we have numerically analyzed a solid-core PCF being infiltrated with Hb by using full vectorial finite element method (FEM) based solver. From the imaginary part of the fundamental mode effective index we obtain the confinement loss of the fiber for different Hb concentrations. As Hb concentration increases, confinement loss increases indicating the amount of Hb present. By tailoring the pitch constant and diameter of the holes, we have also deduced the dependence of sensor performance on these parameters.

Gigahertz-repetition-rate Tm-doped fiber laser passively mode-locked by optoacoustic effects in nanobore photonic crystal fiber

We report a Tm-doped soliton fiber laser passively mode-locked by intense optoacoustic interactions in a short length of solid-core silica photonic crystal fiber (PCF) with a nanobore in core-center. A repetition rate of 1.446GHz pulse is achieved, corresponding to the 52nd harmonic of the 27.8MHz cavity round-trip frequency. Strong optoacoustic interactions in this PCF-based, Tm-doped fiber laser ensure stable and repeatable gigahertz-rate pulse train generation at 1.85μm wavelength, with a high supermode noise suppression ratio and low pulse timing jitter.

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In this paper, solid-core Photonic Crystal Fiber (PCF) type Endless Single Mode (ESM) has been modeled f by using Finite Element Method (FEM). The calculation of effective index of the fundamental mode of PCF have been investigated to study the modal properties. Results for effective index, effective area , nonlinear coefficient and the dispersion are presented. COMSOL Multiphysics software (4.4) has been used to calculate the effective index of the supported mode of the fiber, Hexagonal geometry with sex ring structure is used to model the fiber; however, the model can also be applied to any kind of PCF geometry.

Photonic crystal fiber based optical studies of oil deterioration by near field imaging

Mode pattern changes of LMA-20 solid core photonic crystal fiber, caused by change in refractive index of fluid infiltrated into its micro structured cladding has been theoretically modeled and experimentally verified through simple low cost near field CCD imaging of distal tip of infiltrated samples. This technique tracks degradation induced fractional changes in the oil index, over a large range from +30% to ⿿30% through the mode pattern changes associated with shifts from index guidance to multi-waveguide and band gap guidance. Simple estimation of fluid index by visual tracking of transmission band edges and quantification within transmission region through MFD changes extracted from recorded mode patterns are reported.

Numerical analysis of supercontinuum generation in photonic-crystal fibers with zero dispersion wavelengths in telecommunication windows

We used a Fourth-Order Runge-Kutta in the Interaction Picture Method for simulating supercontinuum generation (SCG) in a designed solid-core photonic crystal fiber (PCF) with zero dispersion wavelength (ZDW) at 800nm and other solid-core PCF with ultra-flattened dispersion in the range of 1300nm to 1550nm obtaining a SCG with a bandwidth of 850, 1200, and 2300nm using a femtosecond laser in the three communication windows. Here we achieved ZDW close to the first, second and third communication windows which gives us the possibility to obtain a wide spectrum at these points with good quality in the 40-dB bandwidth for SCG with flat spectrum. The design of the two PCFs proposed here is analyzed numerically using finite element method (FEM) and we showed the results when we used a pump wavelength in normal and anomalous dispersion regimes close to ZDW points of these two PCFs for SCG.

Reducing losses in solid-core photonic crystal fibers using chlorine dehydration

The fabrication of photonic crystal fibers (PCFs) involves the stacking of multiple preform elements, providing many opportunities for contamination by water vapor or dust particles and causing increased fiber loss. Even after manufacture, diffusion of water vapor into the hollow channels is known to cause a slow increase in loss if the fibers are stored in a humid environment. In this paper we report a systematic study of three methods to reduce OH-related loss in solid-core PCFs: (1) treating the stack (primary preform) with chlorine or oxygen; (2) treating the cane (intermediate preform) with chlorine or oxygen; and (3) using a dry gas for pressurization of the hollow channels during the final step of fiber drawing. Each treatment is independently found effective in reducing OH-related loss, although stack treatment alone is not sufficient if the canes are subsequently stored for a longer time. On the other hand, chlorine-treatment of the canes and/or using a suitably dry gas using fiber drawing significantly lowers the loss even when the canes have been stored for more than two years in a closed tube at room temperature and at relative humidities in the range ~20% to ~50%.

Modal Excitations in Fully and Partially Ethanol-Filled Photonic Bandgap Fibers and Their Applications as Fiber Sensors

The light guidance characteristics of the fully and partially ethanol-filled photonic bandgap fibers (PBFs) are investigated and their applications as modal interferometers (MIs) for temperature sensing are demonstrated. Different from the ethanol-filled solid core photonic crystal fibers (PCFs), the ethanol-filled PBFs are much easier to excite more high order cladding modes, and the effective refractive index difference between the interference modes can reach 26.6 times bigger than that of the ethanol-filled solid core PCF. Without using special splicing techniques, just splicing a short section of the fully or partially ethanol-filled PBF between the single mode fibers, a PBG-based MI can be constructed with a high thermal sensitivity. Moreover, the thermal sensitivity can be adjusted within a large range by selectively filling the air core and/or air claddings of the PBF with ethanol. Experimental results show that the fully ethanol-filled PBF-based MI has the thermal sensitivity up to -292 pm/°C while that of the partially ethanol-filled PBF-based MI is changed to -120 pm/°C. They are 43.8 and 18 times bigger than that of the unfilled PBF-based MI.

Wideband tuning of four-wave mixing in solid-core liquid-filled photonic crystal fibers.

We present an experimental study of parametric four-wave mixing generation in photonic crystal fibers that have been infiltrated with ethanol. A silica photonic crystal fiber was designed to have the proper dispersion properties after ethanol infiltration for the generation of widely spaced four-wave mixing (FWM) bands under 1064nm pumping. We demonstrate that the FWM bands can be tuned in a wide wavelength range through the thermo-optic effect. Band shifts of 175 and over 500nm for the signal and idler bands, respectively, are reported. The reported results can be of interest in many applications, such as CARS microscopy.

Current sensing using circularly birefringent twisted solid-core photonic crystal fiber.

Continuously twisted solid-core photonic crystal fiber (PCF) exhibits pure circular birefringence (optical activity), making it ideal for current sensors based on the Faraday effect. By numerical analysis, we identify the PCF geometry for which the circular birefringence (which scales linearly with twist rate) is a maximum. For silica-air PCF, this occurs at a shape parameter (diameter-to-spacing ratio of the hollow channels) of 0.37 and a scale parameter (spacing-to-wavelength) of 1.51. This result is confirmed experimentally by testing a range of different structures. To demonstrate the effectiveness of twisted PCF as a current sensor, a length of fiber is placed on the axis of a 7.6 cm long solenoid, and the Faraday rotation is measured at different values of dc current. The system is then used to chart the wavelength dependence of the Verdet constant.

Human Immunoglobulin Class G (IgG)) Antibody Detection With Photonic Crystal Fiber

Dye-free antibodies were identified in a less than 5-nL volume with a solid-core photonic crystal fiber (SC-PCF). The all-silica fiber contained micrometer-sized features with a 3- ${\mathbf {\mu }}$ m diameter core supported by a steering wheel-shaped lattice. These structures can be employed to monitor the presence of immunobased assays and susceptible secondary antigens specific to the detection application. A 0.8-m section of SC-PCF was filled with a 4.47-nL antibody sample and a LED light source in the 1300 $\text{-}$ 1700 nm range was employed. Although similar sensing configurations exist, the novelty of this investigation is the detection of this particular antibody. This experiment uniquely investigates the spectral characteristics of purified human immunoglobulin class G (IgG) (format-UNLB) in aqueous media. The absorption spectra for the monoclonal antibodies were collected with a conventional optical spectrum analyzer. The antibody solution exhibited two distinct absorption peaks, a water-linked absorption peak between 1400 and 1470 nm, with a maximum absorption power of 1.65 nW, and an antibody-linked absorption peak between 1485 and 1590 nm, with a maximum absorption power of 3.2 nW.

Temperature insensitive PCF interferometer coated with graphene oxide tip sensor

We report a simple, compact, and robust photonic crystal fiber (PCF)-based Mach–Zehnder modal interferometer coated with graphene oxide (GO) for monitoring refractive index (RI) of analyte (sucrose). GO is prepared by Hummers method, and the fabrication of sensing probe is achieved by splicing single-mode fiber with solid core PCF followed by collapsing of air holes at the end face of PCF. The PCF along with the collapsed region is functionalized and then coated with GO. The proposed tip sensor in reflection mode can be used for the detection of RI of a small quantity of sucrose in either intensity or/and wavelength interrogation. Our experimental results show that the sensor has wavelength sensitivity as high as 230-nm/RIU along with very high intensity sensitivity of 130 dB/RIU with negligible shift in interference pattern with rise temperature.

Fiber in-line Fabry–Pérot interferometer for simultaneous measurement of reflective index and temperature

A fiber in-line Fabry–Perot interferometer is presented. The sensing head consists of a micro ellipsoidal air cavity and a small section of solid-core photonic crystal fiber. The reflective index (RI) and temperature can be interrogated simultaneously through a fast Fourier transform and by tracing the dip wavelength shift of the reflective spectrum. Experimental results show that the RI amplitude and wavelength sensitivities are 5.30/RIU and 8.46×10−1 nm/RIU in the range from 1.34 to 1.43, and the temperature amplitude and wavelength sensitivities are 6.8×10−4/°C and 2.48×10−3 nm/°C in the range from 15°C to 75°C, respectively. Easy fabrication, a simple system, and simultaneous measurement make it appropriate for dual-parameter sensing application.

Fabry-Perot based strain insensitive photonic crystal fiber modal interferometer for inline sensing of refractive index and temperature.

We report a highly stable, compact, strain insensitive inline microcavity-based solid-core photonic crystal fiber (SCPCF) modal interferometer for the determination of the refractive index (RI) of an analyte and its temperature. The interferometer is fabricated by splicing one end of SCPCF with single-mode fiber (SMF) and the other end with hollow-core PCF. This is followed by cleaving the part of the solid glass portion possibly present after the microcavity. The formation of the cavities at the end faces of the SCPCF results in reduction of the period of the interference pattern that helps in achieving distinctiveness in the measurement. Three sensor heads have been fabricated, and each has a different length of the collapsed region formed by splicing SMF with SCPCF. The response of the sensors is found to be sensitive to the length of this collapsed region between SMF and SCPCF with a sensitivity of 53 nm/RI unit (RIU) and resolution of 1.8×10(-4) RIU. The temperature response of the sensor is found to be linear, having a temperature sensitivity of 12 pm/°C. In addition to these findings, the effect of strain on the proposed structure is analyzed in both wavelength and intensity interrogation.

Soliton and Four-Wave Mixing Effects Induced by the Third-Order Dispersion in a Photonic Crystal Fiber With Femtosecond Pulses Pumping at Normal-Dispersion Regime

With the homemade solid-core silica-based photonic crystal fiber (PCF), we observe the generation of soliton and four-wave mixing (FWM) when the femtosecond pulse is pumped at 0.822 $\mu\hbox{m} $ , belonging to the normal-dispersion regime. It is generally acknowledged that FWM is unrelated to third-order dispersion, whereas we use the fourth-order Runge–Kutta method to simulate the PCF properties by taking into account the third-order dispersion or not; the result we got is different from the conventional one. The numerical simulations are greatly consistent with the experiment results, and the FWM is dominated by negative fourth-order and negative sixth-order dispersion in the experiment. The main dynamic process is explained as the soliton, and the FWM generation can be induced by third-order dispersion. We indicate that low Raman threshold has played a very active role in this process, and we propose a conception of stimulated FWM effect in this paper.

Multimode Brillouin spectrum in a long tapered birefringent photonic crystal fiber.

We investigate the stimulated Brillouin scattering (SBS) in a long tapered birefringent solid-core photonic crystal fiber (PCF) and compare our results with a similar but untapered PCF. It is shown that the taper generates a broadband and multipeaked Brillouin spectrum, while significantly increasing the threshold power. Furthermore, we observe that the strong fiber birefringence gives rise to a frequency shift of the Brillouin spectrum which increases along the fiber. Numerical simulations are also presented to account for the taper effect and the birefringence. Our findings open a new means to control or inhibit the SBS by tapering photonic crystal fibers.

Numerical analysis of supercontinuum generation in high birefringent solid core photonic crystal fiber

A solid core high birefringent photonic crystal fiber (PCF) is designed for supercontinuum (SC) generation. The effective refractive index, effective area, nonlinear coefficient, birefringence and dispersion characteristics of the PCF are investigated using the finite element method. The birefringence value of this PCF reaches the magnitude of 10−3 which is required for high precision applications in optical systems. In order to study SC generation higher order dispersion terms and nonlinear coefficient of the birefringent PCF are calculated separately for both the orthogonally polarized modes. Numerical simulation of SC generation in the proposed PCF is analyzed using the coupled nonlinear Schrodinger equation and split step Fourier transform method. The results show that the SC generation in PCF is strongly affected by the input polarization angle, pulse duration, peak power and initial frequency chirp.

Investigation of high birefringence and chromatic dispersion management in photonic crystal fibre with square air holes

In this article, a solid core photonic crystal fibre (PCF) with square air holes is proposed and numerically analysed. The confinement loss, the chromatic dispersion and the birefringence are calculated for both triangular and square lattices by using a full vector finite difference time domain (FV-FDTD) method and the perfectly matched layers (PML) boundary conditions. Two main applications are then investigated: high birefringence and chromatic dispersion management. For the first one, simulation results indicate that high birefringence of 2.5×10−3 is achieved at the wavelength 1.55μm with a very low bending loss of 1.8×10−3 dB/km for bent radius of 2mm. In the second application, ultra-flattened chromatic dispersion over a wide band of wavelengths from 1μm to 1.8μm can be obtained with both positive and negative regimes.

Phase Sensitivity to Acoustic Pressure of Microstrustured Optical Fibers: A Comparison Study

Recently, photonic crystal fibers (PCFs) have attracted many researchers because of their unique properties, and design flexibility that can’t be realized by conventional fibers. One of the fruitful areas of research is the optical fiber hydrophone. In this paper, the finite element solver (FES), COMSOL multiphysics, is used to study and compare the response to acoustic pressure of a hollow-core photonic band gap fiber (HC-PBF), a solid-core photonic crystal fiber (SC-PCF), and a conventional single-mode fiber (SMF) for different acoustic pressures in the frequency range from 10 kHz to 50 kHz. The key structural factors affect the sensitivity to acoustic pressure (S) of the microstructured fibers are studied and a mathematical formula describes the relation of S and the dominant structural factor is proposed. Simulation results of the investigated optical fibers show that the normalized responsivity (NR) of the HC-1550, LMA-5, and SMF are -344 dB, -367.5 dB, and -366 dB, respectively. The proposed simulation results are in good agreement with published theoretical and experimentally measured results. The proposed results indicate the significance of the HC-PBFs in the future hydrophone systems and are useful for the design of microstrustured optical fibers for sensing applications.

Deep-ultraviolet to mid-infrared supercontinuum generated in solid-core ZBLAN photonic crystal fibre

Silica-based photonic crystal fibre has proven highly successful for supercontinuum generation, with smooth and flat spectral power densities. However, fused silica glass suffers from strong material absorption in the mid-infrared (>2,500 nm), as well as ultraviolet-related optical damage (solarization), which limits performance and lifetime in the ultraviolet (<380 nm). Supercontinuum generation in silica photonic crystal fibre is therefore only possible between these limits. A number of alternative glasses have been used to extend the mid-infrared performance, including chalcogenides, fluorides and heavy-metal oxides, but none has extended the ultraviolet performance. Here, we describe the successful fabrication (using the stack-and-draw technique) of a ZBLAN photonic crystal fibre with a high air-filling fraction, a small solid core, nanoscale features and near-perfect structure. We also report its use in the generation of ultrabroadband, long-term stable, supercontinua spanning more than three octaves in the spectral range 200–2,500 nm. A low-loss ZBLAN micro-structured fibre is used to generate a supercontinuum spanning from the UV to the mid-IR (200 nm–2,500 nm). The material has high resistance even after extended operation and can withstand large spectral power densities.