Multi-core Photonic Crystal Fiber Research Articles

Research on the preparation of multi-core photonic crystal fiber and the curvature sensing performance of three-core photonic crystal fiber

Two- and three-core photonic crystal fibers are prepared by using the same photonic crystal fiber preform structure. Not only the fiber diameter is reduced to standard size of 125μm, but also the core diameter is reduced to below 4μm. A curvature and temperature sensing system is built, and the curvature and temperature sensing performance of the three-core optical fiber is tested. When the length of three-core optical fiber is 150 mm, the measured curvature sensitivity is −7.27069 nm/m−1 in the range of 0 to 0.990 m−1, and the temperature sensitivity is −34 pm/°C during the temperature reduction from 75 to 45 °C. When the length of three-core photonic crystal fiber is 68 mm, the curvature sensitivity and temperature sensitivity are 2.42419 nm/m−1 and −7 pm/°C, respectively. In a small range of temperature, the sensor is insensitive to temperature, and the cross interference of temperature to curvature is very small.

Design of a multi-core photonic crystal fiber supporting 518 OAM modes

A multi-ring core photonic crystal fiber (PCF) with seven high-index ring regions is designed for the transmission of multiple orbital angular momentum (OAM) modes. The new structure which has an optimized air hole arrangement shows improved transmission quantity and number of OAM modes. Numerical analysis reveals that the PCF can transmit 518 OAM modes in the range of 1.4–1.75 µm stably while avoiding cross talk from the adjacent ring core resulting in a low cross talk of merely −208.5dB, confinement loss less than 10−9dB/m, as well as mode quality greater than 0.925. The results disclose a new method to increase the communication capacity and suggest that the PCF has great application potential.

Design of a Novel 1x4 Two-Dimensional Demultiplexer Based on Multicore Photonic Crystal Fiber

Design of a Novel 1x4 Two-Dimensional Demultiplexer Based on Multicore Photonic Crystal Fiber

Numerical analysis of strongly coupled multicore photonic crystal fibres for multiplexer and de-multiplexer applications

In this study, the coupling properties of multicore photonic crystal fibers (MCPCFs) are analyzed numerically using COMSOL Multiphysics 5.5, based on the finite element method. The dependence of the coupling properties on the structure of the MCPCFs and the wavelength are investigated to realize applications such as multiplexers-demultiplexers for wavelength division multiplexing. The effective mode indexes and transverse electric field distributions of multiple cores are evaluated for different spatial configurations of identical and non-identical cores. A slight change in the central core diameter relative to adjacent cores leads to non-identical cores that lead to wavelength-dependent coupling properties, such as the coupling lengths and strength of the coefficients. The results show that the coupling lengths become longer and the strength coefficients become smaller as the wavelength decreases for non-identical cores than the identical cores. The introduction of anisotropy to all core diameters shows that the coupling lengths become longer and the strength of the coefficients become smaller as the wavelength decreases as well, and both values become lower than the ones for non-identical cores. These results prove that coupling lengths of MCPCF couplers are significantly shorter in μm compared to conventional multicore optical fiber couplers.

Design and analysis of surface plasmon resonance sensor based on multi-core photonic crystal fiber

A three-core photonic crystal fiber refractive index sensor based on the surface plasmon resonance effect is proposed. The three cores of this sensor are symmetrical about the center. The gold film deposited outside the fiber structure makes this sensor contact with the analyte directly, which not only reduces the complexity of the fabrication but also makes the limiting loss very low. The sensing performance of the proposed sensor is investigated by using the finite element method. Numerical results show that the loss spectra of the x-polarized core mode are consistent with the y-polarized core mode. The sensor realizes the sensing detection of the analyte refractive index ranging from 1.37 to 1.42. When the analyte’s refractive index is 1.42, the maximum wavelength sensitivity of 2427 nm/RIU for x and y polarization, the corresponding maximum resolution can reach 4.12 × 10−5 RIU.

Design and Optimization of a Single-Mode Multi-Core Photonic Crystal Fiber With the Nanorod Assisted Structure to Suppress the Crosstalk

We propose and design a novel homogeneous nanorod-assisted multi-core photonic crystal fiber (NA-PCF), and it utilizes the flexibility of photonic crystal fiber (PCF) for air-hole design, NA-PCF applied to multi-core fiber (MCF) communication system. High refractive index nanorods are introduced in the center of the seven cores which are further surrounded by a periodical arrangement of air-holes. The air-holes and the nanorods work together to greatly suppress the crosstalk (XT) between the cores. By comprehensively balancing the influence of various parameters on XT, single-mode cutoff wavelength (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cc</sub> ) and the effective mode field area (A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ), simulation results show that the NA-PCF has a A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> of about 70.26 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , XT of about -50.58 dB/km, relative core multiplicity factor (RCMF) of 4.7 and λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cc</sub> of 1530 nm. This designed structure targets applications in large-capacity long-distance MCF communication.

Multi-Core Surface Plasmon Resonance Refractive Index Sensor on Photonic Crystal Fiber

In this research work, low refractive index (RI) detection done on multi-core photonic crystal fiber (PCF) based highly sensitive surface plasmon resonance (SPR) sensor is propounded. Sensing the changes in neighboring medium’s refractive index is done by placing the plasmonic material i.e. Silver (Ag) over the crystal structure of fiber. On top of the Silver, a threadlike film of titanium dioxide (TiO2) is deposited to prevent oxidation of plasmonic material silver. Peak wavelength sensitivity thus achieved by this sensor is 127,600 nm/RIU and similarly, peak amplitude sensitivity achieved is 2561 RIU-1, respectively. Subsequently making this sensor suitable candidate for various applications such as biosensing, sensing organic compounds and chemicals, inspecting pharmaceuticals and other detections.

Phase-locked and mode-locked multicore photonic crystal fiber laser with a saturable absorber.

Multicore photonic crystal fiber (MC-PCF) can scale the output power with the number of cores by spatial beam combining if the in-phase mode is selected. We demonstrated simultaneous realization of phase-locked and mode-locked laser using Yb-doped 7-core MC-PCF by a semiconductor saturable absorber placed in the near-field inside a resonator. High energy 333 nJ pulses were obtained directly from a mode-locked fiber laser oscillator at a 42.4 MHz repetition rate with an average power of 14.1 W at 24 W excitation. We observed the direct output pulse width of 52 ps assuming a sech2 profile. However, it might be noise-like pulses because of no variation when we performed pulse compression. Single-pulse operation was achieved by increasing the bandwidth of the intracavity filter. In this case, 137 nJ, 42.4 MHz pulses were generated with a 5.8 W average power and the compressed output pulse width was 8.6 ps.

低串扰高密度复合型多芯光子晶体的光纤理论研究

低串扰高密度复合型多芯光子晶体的光纤理论研究

Analysis of Light Propagation in Identical and Non-Identical Multicore Photonic Crystal Fibers

Multicore photonic crystal fibers (MPCF) with identical and non-identical cores are analyzed numerically using Comsol Multiphysics software. Investing coupling between cores limiting by parameters, such as the slight change in central core diameter; the separation distance between cores and the wavelength were investigated. Controlling these parameters allows predicting the mode propagation. Moreover, anisotropy in all cores diameters of multicores photonic crystal fibers, as a result, the change of all core diameters simultaneously lead to different of coupling behavior, suppresses the coupling between the core modes by inducing a small mismatch between the modes such that the core modes to be uncoupled through this change. Then this leads to the light mode propagate independently of their neighbors and gives rise to the mode to primarily remain in a certain region of the MPCF array. These properties suggest that multicore PCFs could be a novel candidate for both multiplex or de-multiplex.

True-Time Delay Line Based on Dispersion-Flattened 19-Core Photonic Crystal Fiber

A novel design of a tunable True-Time delay line (TTDL) based on a multicore photonic crystal fiber (PCF) is proposed. It enables simultaneous transport and processing of microwave photonic signals over a broad radiofrequency processing range. Independent group delay behavior in 19 different cores characterized by a constant differential group delay between cores provides TTDL operation on 19 signal samples. The 19-core PCF structure allows tailoring the chromatic dispersion range between 1.5 and 31.2 ps/nm·km, which translates into a very broad microwave signal processing range from a few up to tens of GHz. A near-zero dispersion slope reduces the time delay errors in the TTDL's operation to less than 5% in a 40-nm optical wavelength range, thus ensuring its satisfactory performance. Its performance as a TTDL is evaluated in terms of higher-order dispersion as well as other degradation effects such as crosstalk and nonlinear fiber response. A high index contrast between core and cladding, between 0.3 to 1.5%, enables low intercore crosstalk and confinement losses as well as greater robustness against fiber bends and twists. Fabrication of this type of MCF might be possible although it will prove challenging. This work advances the state-of-the-art of a TTDL based on SDM technology by increasing the number of samples and microwave processing range.

Multi-direction bending sensor based on supermodes of multicore PCF laser.

A multi-direction bending sensor based on the 18-core photonic crystal fiber (PCF) is demonstrated in this paper. The design of the sensor is discussed theoretically and experimentally. The PCF serves as the laser gain medium and the sensing medium simultaneously in the fiber laser sensor. The operating wavelength of the proposed PCF laser sensor is about 1032.32 nm. A CMOS image capture system is used to acquire the distribution of supermodes in the PCF laser. Based on the normalized intensity distribution of supermodes, six directions can be measured. The sensor also shows the ability to measure bending radius within 0.11 m. Then, the thermal effects of the bending sensor have been analyzed and the sensing system shows a low temperature crosstalk.

A visible light RGB wavelength demultiplexer based on silicon-nitride multicore PCF

One of the main obstacles that limited the performances in visible light networking system is the ability to transmit high data communication rate. In order to overcome this obstacle, we propose a novel design for an RGB demultiplexer based on silicon-nitride (Si3N4) multicore photonic crystal fiber (PCF) structure. The new design is based on replacing several air-holes zones with Si3N4 rods along the fiber length that enable the controlling of the coupling length size between neighboring cores. The locations of the Si3N4 rods and the geometrical parameters of the PCF were analyzed and simulated utilizing the beam propagation method (BPM) combined with Matlab codes. Results show that RGB operated wavelengths can be demultiplexed after light propagation of 5.5 mm with an excellent crosstalk of −20.766 to −23.95 dB and a large bandwidth of 5.9–16.3 nm.

An Eight-Channel C-Band Demux Based on Multicore Photonic Crystal Fiber.

A novel eight-channel demux device based on multicore photonic crystal fiber (PCF) structures that operate in the C-band range (1530–1565 nm) has been demonstrated. The PCF demux design is based on replacing some air-hole areas with lithium niobate and silicon nitride materials over the PCF axis alongside with the appropriate optimizations of the PCF structure. The beam propagation method (BPM) combined with Matlab codes was used to model the demux device and optimize the geometrical parameters of the PCF structure. The simulation results showed that the eight-channel demux can be demultiplexing after light propagation of 5 cm with a large bandwidth (4.03–4.69 nm) and cross-talk (−16.88 to −15.93 dB). Thus, the proposed device has great potential to be integrated into dense wavelength division multiplexing (DWDM) technology for increasing performances in networking systems.

Fiber Bragg grating inscription in multi-core photonic crystal fiber by femtosecond laser

The inscription of fiber Bragg grating (FBG) in a pure-silica multi-core photonic crystal fiber (PCF) using femtosecond laser and phase mask is reported. Three resonant dips are observed in the transmission spectrum due to the multiple supermodes transmitted in the PCF. The induced refractive index modulation of 2.2 × 10−4 is achieved for a peak power density of 4.8 × 1013 W/cm2 without any fiber sensitization. The experimental results show that type II grating is inscribed and it has high thermal stability. The temperature corresponding to 50% decrease in transmission loss of the FBG is about 970 °C. The central wavelengths of the three dips linearly shift with pressure sensitivity of −4.8 pm/MPa and strain sensitivity of 1.2 pm/με. This FBG will find applications in optical fiber sensing under high temperature.

High-power visible-enhanced all-fiber supercontinuum generation in a seven-core photonic crystal fiber pumped at 1016 nm.

An 80W 350-2400nm monolithic supercontinuum (SC) source is reported. The high-power SC is generated in a uniform multi-core photonic crystal fiber (PCF) pumped by a 1016nm pulsed fiber laser. The specially designed PCF has seven 4.5μm diameter cores, a 0.85 air-filling fraction, and a zero dispersion wavelength (ZDW) of 991nm. The 1016nm pulsed laser delivers up to 114W average power, which is believed to be the highest currently reported for picosecond fiber lasers working below 1020nm. In order to ensure a robust and compact all-fiber structure, the pump laser is fusion spliced to the PCF using a selective air-hole collapse technique, achieving an ultra-low splicing loss of 0.2dB despite the severe mode field mismatch. The proximity of the pump wavelength to the ZDW of PCF leads to enhanced visible generation. The output SC has a high spectral density of up to 108mW/nm (at 580nm) and over 50mW/nm across the entire visible waveband. The achieved short-wavelength edge and high-spectral-power density in the visible region, to the best of our knowledge, are the best results reported for high-power visible SC sources.

Ultraviolet-extended flat supercontinuum generation in seven-core photonic crystal fiber

We report the experimental results of ultraviolet-extended broadband supercontinuum (SC) generation in a carefully designed uniform seven-core photonic crystal fiber (PCF) pumped by Ti:sapphire femtosecond laser at 800 nm. Three different PCFs of various core diameters are fabricated to achieve group-velocity matching for ultraviolet components. A wide optical spectrum spanning down to 350 nm is obtained, which is the shortest wavelength SC generation in multicore PCF to date. High spectral flatness (10 dB) has been achieved in the entire visible window.

Design of 4 × 1 Power Beam Combiner Based on MultiCore Photonic Crystal Fiber

A novel concept of 4 × 1 power beam combiner based on multicore photonic crystal fiber is described. The light coupling obtained by integrating small air-holes in the multicore photonic crystal fiber (PCF) structure allows light coupling between coherent laser sources to the central core. The beam propagation method (BPM) and coupled mode theory were used for analyzing the proposed device. Simulation results show that four coherent fiber laser sources of 1 µm in a multicore PCF structure can be combined into one source after 2.6 mm light propagation, with a power efficiency of 99.6% and bandwidth of 220 nm. In addition, a higher 8 × 1 ratio combiner was demonstrated, based on the proposed device. Thus, the device can be very useful to combine beams.

Study on coherent coupling of multi-core PCFs

In this work, we used R-Soft software to simulate the coupling between multi-core photonic crystal fibers (PCFs) with different core diameters and distances. The simulation results show that the core distance within two wavelengths, different core diameters between the mode fields can be effectively coupled. The results are consistent with the evanescent wave propagation length of calculation. According to the designed structure based on the high temperature melting method, the multi-core PCF can be obtained by using two times technique of the optical fiber drawing tower. The core production of (2-, 7-, 19-core PCF) of coherent synthesis experiment, observed apparent interference fringes in the experiment, which shows that the mode fields of the multiple cores meet the coherent conditions. This article provides a theoretical basis and guidance to effectively achieve a coherent coupling for the further design and preparation of multi-core fibers (more than 19 cores).

Power splitting of 1 × 16 in multicore photonic crystal fibers

A novel concept of 1×16 power splitter based on a variable multicore photonic crystal fiber (PCF) structure is described.Numerical simulations showed how the optical signal can be split in a PCF structure having dimensions of 60μm×60μm×3.582mm.The coupled mode analysis and beam propagation method (BPM) was used for analyzing the multicore PCF based 1×16 splitter.The input optical signal at a wavelength of 1.55μm inserted into the central core was divided into sixteen output cores, each with a 6.25% of the total power. The full width half maximum (FWHM) bandwidth found for each core was 100nm.