Length Of Photonic Crystal Fiber Research Articles

High-Sensitivity Refractive Index Sensing Based on an SNPNS Composite Structure

In this paper, we design and demonstrate an all-fiber-sensitive refractive index (RI) sensor based on the Mach–Zehnder interferometer (MZI). It is constructed by splicing two no-core fibers (NCFs) and a photonic crystal fiber (PCF) between two single-mode fibers (SMFs) to obtain an SMF–NCF–PCF–NCF–SMF composite structure (SNPNS). A study of the effect of varying PCF lengths on the RI reveals that the shorter the length, the higher the sensitivity. The maximum RI sensitivity of 176.9 nm/RIU is attained within the RI range of 1.3365–1.3767 when the PCF length in the SNPNS structure is 3 cm. Meanwhile, the sensor exhibits a high stability in water, with an RSD of only 0.0019% for the interference trough over a duration of two hours. This proposed sensing structure offers the advantages of a large extinction ratio, small size, low temperature sensitivity, and simple fabrication, exhibiting a great potential in RI measurements.

Numerical investigation of a wideband supercontinuum source based on a large-mode-area photonic crystal fiber pumped at 1.3 μm

A numerical investigation was conducted to obtain a supercontinuum spanning about two octaves using a large mode area photonic crystal fiber (PCF) pumped at 1.3 μm. In our study, a 1.3 μm femtosecond laser and a silica-based large mode area PCF were selected as the pump source and nonlinear medium, respectively. The nonlinear Schrodinger equation was solved with split-step Fourier method to simulate the evolution of pulse and the broadening of spectrum. The effect of several parameters including the length of PCF, the pulse width, and the average pump power on characteristics of the output spectrum was studied. The simulation results revealed that the supercontinuum extended from near 600 nm to over 2450 nm at 20 dB with length of 30 cm, pulse width of 100 fs and average power of 12 W, respectively. This work proved this large mode area PCF a potentially excellent medium for supercontinuum source and provided some theoretical guidance for future experiments.

An Intensity-Demodulated Fiber-Optic Magnetometer Based on Nanostructured Magnetic Fluid-Filled Fluidic Photonic Crystal Fibers.

An intensity-demodulated fiber-optic magnetometer is proposed and experimentally investigated, which is fabricated via fusion splicing a segment of photonic crystal fiber (PCF) between single-mode fibers (SMFs), with the cladding air holes of PCF filled with magnetic fluid. Using the magneto-optical properties of the magnetic fluid, the transmission spectrum is changed with an external magnetic field. Based on the intensity variations in the transmission spectrum, the magnetic field is detected, and a sensitivity of 0.238 dB/mT is obtained at 1550.03 nm with the length of PCF 5.5 cm. By converting light signals into electrical signals, a sensitivity of 0.003 V/mT is achieved. The fiber-optic magnetometer possesses the advantages of simple fabrication, compact/robust structure, and low cost.

Study on preparation and curvature sensing performance of dual-core photonic crystal fibers

A method of fabricating dual-core photonic crystal fiber(PCF) using secondary drawing technique is presented. The diameter of fiber core can be reduced to 4μm by placing the thin preform into glass sleeve for secondary drawing. Dual-core PCF, partial dual-core PCF and non-centrosymmetric dual-core PCF are successfully prepared by secondary drawing technology combined with air pressure regulation. A curvature sensing system is built. When the length of partial dual-core PCF is 105 mm, the measured curvature sensitivity is −3.79944 nm/m−1. Through the water bath temperature experiment, the measured temperature sensitivity is 21 pm/∘C, and the cross interference caused by temperature value on curvature value is very small. When the length of non-centrosymmetric dual-core PCF is 207 mm, the curvature sensitivity measured by forward bending and negative bending is 4.68429 nm/m−1 and −4.68808 nm/m−1, respectively. The measured temperature sensitivity is −13 pm/∘C, and the cross interference of temperature on curvature can be ignored.

Structural Analysis of Nano Core PCF With Fused Cladding for Supercontinuum Generation in 6G Networks

AbstractThe Sixth Generation (6G) networks have identified the use of frequency range between 95 GHz and 3 THz with a targeted data rate of 1 Terabytes/second at the access network for holographic video applications. As is demands broadening of spectrum at the core network, this paper proposes a Supercontinuum Generation (SCG) through photonic crystal fiber (PCF) as it provides excellent broadening of the optical spectrum. Discussed in the paper is supercontinuum generation at high pumping power as per the standards specified by the International Telecommunications Union. The proposed PCF is designed with silicon nanocrystal core and the cladding microstructures is arranged in a fusion approach to effectively optimize the optical parameters such as dispersion, nonlinearity, birefringence, group‐velocity dispersion, and confinement loss. The fused cladding comprises of a flower‐cladding assembly in which air‐holes arrangement is inspired from petals in a pleated structure. Such arrangement is shown here to provide high nonlinearity and negative dispersion for high power supercontinuum generation. The novel nanocore assembly with improved structural constraints delivers a non‐linearity of 6.37 × 106 W−1 km−1 and a negative dispersion of −142.1 (ps/nm‐km) at 1,550 nm. Moreover, a supercontinuum spectrum is generated using different pulse widths ranging from 350 to 650 ps with 25 kW pump power for PCF lengths of 10 and 15 mm.

Temperature-Insensitive Gas Pressure Sensor Based on Photonic Crystal Fiber Interferometer

A temperature-insensitive gas pressure sensor was proposed and experimentally investigated. This sensor was based on a photonic crystal fiber sandwiched between two single-mode fibers, where the impact of length on the performance of the sensor has been studied. Air holes of photonic crystal fiber were employed as gas or liquid inlet and outlet channel which provide the medium for direct interaction between the light transmitted in the fiber and the target gases. The experimental results show that the length of photonic crystal fiber has little effect on the sensitivity to gas pressure. The photonic crystal fiber interferometer has a high gas pressure sensitivity of 2.39 nm/MPa when gas pressure increases from 100 KPa to 900 KPa. The demonstrated gas pressure sensor has excellent stability and reversibility with negligible temperature cross-sensitivity. The proposed photonic crystal fiber interferometer can also be used for liquid sample detection with high refractive index (RI) sensitivity of 3026 nm/RIU when the length of photonic crystal fiber is 1 cm at a RI range of 1.334-1.34. Therefore, the proposed photonic crystal fiber interferometer holds a great potential in applications for chemical gas leakage detection and biochemical sensing.

A Method for Suppressing Error of Fiber Optic Current Transformer Caused by Temperature Based on λ/4 Wave Plate Fabricated With Polarization-Maintaining Photonic Crystal Fiber

The beat length of λ/4 wave plate of fiber optic current transformer (FOCT) will change with the temperature fluctuation of environment, which will result in additional phase error, reducing the accuracy of current measurement. In the paper, we presented a FOCT based on λ/4 wave plate fabricated with polarization maintaining photonic crystal fiber (PCF). Combined with error model caused by λ/4 wave plate in FOCT, we analyzed the specific mechanism of temperature influence on λ/4 wave plate. Aiming at the problem of fusing PCF to panda polarization maintaining fiber, we optimized the related parameters of fiber fusion splicer to reduce the fusion loss of the fiber. It was experimentally verified that the beat length of PCF is less sensitive to temperature than that to elliptical core polarization maintaining fiber. Finally, we measured current of FOCT utilizing two kinds of λ/4 wave plates in full temperature range from -40 °C to 70 °C. It was verified that it is insensitive to temperature for FOCT when utilizing PCF λ/4 wave plate, with the corresponding system current measurement accuracy 0.5S level.

Optical fiber temperature sensor with Vernier effect formed by Mach–Zehnder interferometer cascaded Sagnac interferometer based on Hollow-core photonic crystal fiber

This research proposes a Mach–Zehnder interferometer (MZI) based on hollow-core photonic crystal fiber (PCF) and a Sagnac interferometer (SI) based on polarization maintaining fiber (PMF). A stable reference interferometer is formed by using PCF which is insensitivity to temperature and the temperature monitoring is realized by using PMF which is sensitivity to temperature. The two interferometers are cascaded through a 3 dB optical fiber coupler to generate the Vernier effect by controlling the lengths of the two fibers, thereby improving the temperature sensitivity of the sensing structure. The length of PCF is 1.22 mm and PMF is 1.65 m, the experimental results show that the highest temperature sensitivity of 12.02 nm/°C is obtained. The proposed sensor not only has ultra-high temperature sensitivity, but also has scarcely response to physical quantities, such as refractive index, strain and so on. This sensor has reduced the generation of cross-talk in the measurement process, and has great application prospects in several fields.

Analysis of filtering and refractive index sensing characteristics based on gold-coated photonic crystal fiber

A gold-coated photonic crystal fiber (PCF) with dual functions of filtering and refractive index sensing is proposed. The gold layer is deposited in two open grooves, which make it easy to manufacture. For the filtering characteristics, it can achieve high loss at the wavelength of 1550 nm. The results show that the confinement losses of the x - and y -polarized modes are 0.012 dB/cm and 445.10 dB/cm, respectively. When the crosstalk is greater than 20 dB, it shows high bandwidth of 910 nm for the PCF length of 3 mm. For the sensing characteristics, it shows a maximum sensitivity of 4000 nm/RIU for an analyte range of 1.39–1.40. It also has a high figure of merit with a maximum value of 45.45 R I U − 1 and a low detection limit (56.13 nm). Owing to the excellent performance of the gold-coated PCF in filtering and sensing, it will become a suitable candidate for optical communication and sensing systems.

Ultra-Compact 50 W Flat Supercontinuum Generation in Single-Stage Self-Q-Switched Fiber Laser With Photonic Crystal Fiber

An all-fiber supercontinuum (SC) laser source with 50.7 W average output power and spectrum ranging from 500 nm to 2400 nm is demonstrated. With the generation of high peak power nanosecond pulses and photonic crystal fiber (PCF) in the self-Q-switched fiber laser, the output SC shows good spectral width and flatness which has a 20 dB bandwidth of 1900 nm except the 1064 nm peak. The effect of the PCF length on the spectral characteristics and output power of SC were carefully studied. To the best of our knowledge, this is the highest power of SC generated in a single-stage fiber laser with such a broadband spectrum. This ultra-compact SC generation method has the merits of simple structure, low cost and good robustness, which provide an easily available SC generation method for various practical applications.

Pulse Shape Estimation in a DSR Fiber Laser Using the Genetic Algorithm

Exploiting the computing power of the genetic algorithm, a numerical study of dissipative soliton resonance (DSR) in a ring laser mode-locked by a real saturable absorber (SA) is conducted. A section of photonic crystal fiber (PCF) is inserted into the laser cavity design to facilitate accurate control of both dispersion and nonlinearity. The influence of the cavity parameters on the evolution of the DSR pulses is systematically analyzed. The genetic algorithm demonstrates that the generation of DSR square pulses depends directly on the PCF dispersion, the PCF nonlinearity, the PCF length, and the modulation depth of the SA. Finally, the sensitivity of the DSR pulse width, peak power and energy to perturbations in a few key design parameters are highlighted.

Octave-spanning supercontinuum generation in infrared by MoS2-filled hollow core fiber

We report the generation of an infrared (IR) supercontinuum spanning over an octave using a centimeter (6 cm) length of photonic crystal fiber (PCF) filled with MoS2, which has a considerably large nonlinear refractive index. The fiber is pumped with a femto-second laser pulse with an infrared wavelength of 2080 nm, pumping intensity of 336.76 GW/cm2, peak power of 0.75 GW, and pulse width of 150 fs. With the assistance of highly nonlinear MoS2, a supercontinuum bandwidth that remarkably extends from 1400 to 2700 nm below 20 dB is achieved. This supercontinuum bandwidth significantly exceeds the previously reported spectra for other nonlinear glass-based optical fibers, even with a fairly short fiber length. Furthermore, this short fiber length allows PCF to be more efficiently utilized, and is expected to be suitable for various applications, such as broadband light source through liquid-based fibers and waveguide-based optical communications, especially in the IR region.

Cancer cell detection by a heart-shaped dual-core photonic crystal fiber sensor

This paper contributes a novel design of sensor with a heart-shaped dual-core photonic crystal fiber (PCF) to detect cancerous cells in human cervical, blood, adrenal glands, and breast. Cancer-infected cells and their normal cells are considered in liquid form having their own refractive indices. In the designed PCF, the two heart-shaped cores separated by a large circular air hole serve as two independent waveguides. The large circular air hole is infiltrated by sample cells from different body parts. Detection of cancer-contaminated cells by the proposed PCF is based on the mode-coupling theory. According to the mode-coupling theory, the guided optical light transmits periodically from one core to another, throughout the PCF length. During this transmission, the optical light interacts with the cancerous cell, which is filled in the center air hole of the PCF. Due to this interaction, the dip wavelength of the transmission spectrum is sensitive to the corresponding cancerous cell filled in the center air hole of the PCF. The variation in the PCF transmission spectrum for cancerous cells and their normal cells is observed by using the finite element method. The dip wavelength shift of the cancer cell in reference to its normal cell has been measured from the transmission spectrum to determine the sensing performance of the proposed sensor. The sensitivity achieved of the proposed sensor for cervical cancer cell, blood cancer cell, adrenal gland cancer cell, and breast cancer cells are 7916.67 nm/RIU, 8571.43 nm/RIU, 9285.71 nm/RIU, and 10,000 nm/RIU, respectively, with a maximum detection limit of 0.024. Therefore, the proposed PCF sensor suggests high sensitivity with a rapid cancer detection mechanism.

All Polarization-maintaining Passively Mode-locked Ytterbium-doped Fiber Lasers, Behavior under Two Different Cavity Configurations

ABSTRACT In this work, we review our recent investigations on the behavior of a polarization-maintaining passively mode-locked ytterbium-doped laser in two different cavity configurations, namely: fiber-ring (FR) and Fabry-Perot (FP). Opposed to standard configurations that rely on the use of strong filtering within the cavity by including an ad hoc component with this purpose, here the filtering action is solely performed by the spectral overlapping of the different components within the fiber lasers. We found that the lack of a specific filter within the cavity does not deteriorate the performance as compared with previous works. We also report the changes in the output light pulses when the net dispersion of the cavity was varied. Additionally, different lengths of an ad hoc anomalous polarization-maintaining (PM) photonic crystal fiber (PCF) were used as intracavity dispersion compensator, to shift the operation of the laser from net-normal to the net-anomalous regime. The shortest output light pulses [6 ps (FR) and 8 ps (FP)] were obtained when the net-cavity dispersion approached zero. Since the obtained light pulses were far to be transform-limited, we also discuss the possibility of out-of-cavity recompression by using the same PM-PCF mentioned above. After recompression, pulse widths of 3 ps were obtained, limited by the available length of PM PCF.

Sensing characteristics of photonic crystal fiber Sagnac interferometer based on novel birefringence and Vernier effect

In this paper, the sensing characteristics of a photonic crystal fiber (PCF) Sagnac interferometer based on flat-phase birefringence, zero-group birefringence and the Vernier effect have been studied. The temperature-sensitive liquid is filled into the air holes of the PCF. We realize flat-phase birefringence, by which the sensitivity can reach 4.9 nm/°C and 3.5 nm/°C. We find a new phenomenon in that there are more interference fringes appearing near the zero-group-birefringence wavelength with the environment changing. Highly sensitive sensors with −19.9 nm/°C and 28.6 nm/°C are obtained. We also demonstrate that two cascaded Sagnac interferometers based on PCF can realize the Vernier effect. The sensitivities are 1 nm/°C (single Sagnac interferometer) and 10.4 nm/°C (cascaded Sagnac interferometers), and the sensitivity is improved by more than 10 times. The sensitivity is inversely proportional to the difference between free spectral range (FSR)1 and FSR2, and the highest sensitivity reaches 23.2 nm/°C (−58 500 nm/RIU, resolution: 3.419× 10−7 RIU) by optimizing the PCF length in Sagnac interferometer 2. The average sensitivity based on two cascaded PCF Sagnac interferometers is up to −309 957 nm/RIU and the resolution is 6.453× 10−8 RIU as the refractive index of the analyte varies from 1.33 to 1.331, which is very competitive in the field of chemical sensing.

A Vectorial Analysis of the Curvature Sensor Based on a Dual-Core Photonic Crystal Fiber

A novel curvature sensor was proposed based on a dual-core photonic crystal fiber (PCF) that was spliced between two single-mode fibers (SMFs). The sensor sensitivity was investigated both analytically and experimentally, and the influence of the PCF length and temperature on the sensor performance was also analyzed. The results showed the sensor had different sensitivity with different bending direction and its highest sensitivity can reach 10.14 nm/m−1. It also showed great insensitivity to temperature interference. Being of simple structure and good mechanical strength, this curvature sensor has great application potential in various fields, such as architecture, machinery, robot, wearable sensor, and so on.

Photonic crystal fiber based wide-range of refractive index sensor with phase matching between core mode and metal defect mode

A high sensitivity wide range surface plasmon resonance (SPR) refractive index sensor based on photonic crystal fiber (PCF) has been proposed in this paper. The finite element method (FEM) is used to calculate and analyte the structure of PCF. The optical properties of the PCF are investigated by adjusting the refractive index of liquid analyte. By optimization, the fiber sensor achieves a high linearity refractive index sensitivity of 0.9979 and 1931.03 nm / RIU over a refractive index range from 1.350 to 1.460 and achieves a short PCF length of 1 mm. It is allowed the sensor to be small enough to be integrated into inspection equipment,and expected to gain important applications in the fields of biological monitoring, environmental monitoring, and chemical production.

Photonic crystal all-fiber Mach-Zehnder Interferometer sensor based on phase demodulation

Abstract In this paper, a phase demodulation of photonic crystal fiber Mach-Zehnder Interferometer (MZI) sensor based on fiber ball symmetrical structure was proposed and experimentally demonstrated in this paper. The MZI was realized by spliced a certain length of photonic crystal fiber between two single-mode fiber ball. The measurement of temperature was realized by analyzing the phase variation of the selected dominant mode, which showed more robust and accurate compared with the conventional peak wavelength tracking technique. The spectral characteristics at different photonic crystal fiber (PCF) lengths were analyzed. The proposed sensor has the advantages of compact structure, simple manufacturing process, and high reliability.

Elliptical-hole PCF structure with selective Y-axis gold coating for tunable single-polarization band-stop filtering

An elliptical-hole photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed, which can work as a tunable single-polarization band-stop filter (BSF). Theoretical results show that the proposed structure is very sensitive to the polarization of the guided modes, due to its high birefringence coefficient and strong SPR effect. It can achieve single-polarization single-mode (SPSM) filtering without liquid filled in the gold coated air holes. At resonant wavelength, the loss of the y polarization fundamental mode reaches 792.16 dB cm−1, but the loss of the x polarization fundamental mode is only 0.52 dB cm−1, causing that the extinction ratio is as high as 688 dB and the bandwidth is larger than 520 nm with the PCF length of 1 mm. When liquids with the refractive index (RI) ranging from 1.44 to 1.48 are filled in the gold coated air holes, the PCF could be used as a BSF to filter the x polarization fundamental mode selectively on the premise of SPSM filtering. And the center wavelength of the BSF is extremely sensitive to the liquid RI with a high sensitivity of 16 820 nm/RIU, which indicates a potential application in RI sensing. The proposed PCF realizing the integration of SPSM filter and BSF is available for compact optical communication systems.

Highly sensitive strain sensor based on a novel Mach–Zehnder mode interferometer with TCF-PCF-TCF structure

We have demonstrated a high-sensitivity strain sensor based on a novel photonic crystal fiber (PCF) interferometer by means of splicing two sections of thin core fibers (TCF) with a piece of PCF between two single mode fibers (SMFs). The proposed MZI has exhibited an excellent fringe visibility as high as 21 dB in air. Particularly, the measurement range was up to 4 mε and a strain sensitivity of −1.89 pm/µε was achieved. It was found that the strain sensitivity of the MZI was weekly dependent on the PCF length. The measured sensitivities of the MZI with 25 mm, 30 mm and 35 mm PCF at ∼1590 nm were −1.83 pm/µε, −1.85 pm/µε and −1.77 pm/µε, respectively. Moreover, the temperature characteristics of the sensor were also investigated. Additionally, the sensor has advantages of simplicity of fabrication, low cost, compact size as well as large strain measurement range.