Hollow-core Photonic Bandgap Fiber Research Articles

Monitoring Raman emission through state population in cold atoms confined inside a hollow-core fiber.

We study the spontaneous Raman emission in an ensemble of laser-cooled three-level Λ-type atoms confined inside a hollow-core photonic-bandgap fiber using a novel approach to observe the process. Instead of detecting the emitted light, we measure the number of atoms in the ground state as a function of Raman pump time, which eliminates the need to suppress the pump photons with a high-resolution filter. We describe how this measurement can be used to detect superradiant emission from the atomic ensembles and estimate the number of atoms required to observe Raman superradiance in atomic clouds inside a hollow-core fiber.

Low-Loss and Low-Back-Reflection Hollow-Core to Standard Fiber Interconnection

We present a new approach to permanently inter-connect hollow-core fiber (HCF) to solid-core fiber, which does not involve fusion splicing. Our approach is based on a modification of the glue-based fiber-array technology routinely used for fiber pigtailing of planar lightwave circuits. The resulting interconnection provides for a low insertion loss due to the fact that the HCF microstructure is not deformed during the gluing (low temperature) process that is almost impossible to achieve with the standard (high temperature) fusion splicing method. Furthermore, this low-temperature technique enables the deposition and preservation of thin films deposited at the solid-to-hollow core fiber interface, allowing for additional functionality without the introduction of extra losses or any increase in complexity. To demonstrate this, we have applied an anti-reflection (AR) coating. A further feature of our approach is the ability to control very precisely the length of the graded-index (GRIN) fiber mode field (MF) adapter inserted in between the standard single-mode fiber (SMF-28) and the HCF. We show experimentally how the length of the GRIN fiber MF adapter influences the coupling between the SMF-28 and the fundamental as well as the higher-order modes of the HCF. We coupled between SMF-28 [10 $\mu \text{m}$ mode field diameter (MFD)] and the fundamental mode of a 19-cell hollow-core photonic bandgap fiber (HC-PBGF, 21.1 $\mu \text{m}$ MFD) with the lowest-ever reported insertion loss of 0.30dB per interface.

7-cell hollow-core photonic bandgap fiber with broad spectral bandwidth and low loss.

The limited spectral bandwidth achieved in state-of-the-art hollow-core photonic bandgap fibers (HC-PBGF) has hindered its implementation in a wide range of applications. Here we demonstrate that broad spectral bandwidth and low loss can be simultaneously achieved in 7-cell HC-PBGF. Several 7-cell HC-PBGFs operating at 1550 nm telecom band and 1 μm laser band are present. One of the fibers exhibits a minimum loss of 6.5 dB/km at 1633 nm and a 3 dB bandwidth of 458 nm, approaching a bandwidth to central wavelength ratio of 26%. This is to our knowledge the broadest bandwidth achieved in triangular lattice HC-PBGF and the lowest transmission loss in 7-cell HC-PBGF.

Optimization of silica glass capillary and rods drawing process.

Diameter fluctuations of silica glass rods and capillaries, during drawing process have been studied. We investigated an influence of drawing conditions on the quality of capillaries and rods. We fabricated two preforms made from different quality material. Fabricated preforms were used to draw microstructured fibers. Full Text: PDF ReferencesS. Habib et al., "Broadband dispersion compensation of conventional single mode fibers using microstructure optical fibers", Int. J. Lig. Opt. 124, 3851-3855 (2013) CrossRef A. Ziolowicz et al. "Overcoming the capacity crunch: ITU-T G.657.B3 compatible 7-core and 19-core hole-assisted fibers", Proc SPIE 10130, 101300C (2017) CrossRef T.M. Monro et al. "Sensing with microstructured optical fibres", Meas. Sci. Technol. 12, 854-858 (2001) CrossRef G. Statkiewicz-Barabach et al.,"Hydrostatic Pressure and Temperature Measurements Using an In-Line Mach-Zehnder Interferometer Based on a Two-Mode Highly Birefringent Microstructured Fiber", Sensors 2017, 17, 1648 (2017) CrossRef T. Yoon, M. Bajcsy, "Laser-cooled cesium atoms confined with a magic-wavelength dipole trap inside a hollow-core photonic-bandgap fiber", Phys. Rev. A 99, 023415 (2019) CrossRef A.N. Ghosh et al., "Supercontinuum generation in heavy-metal oxide glass based suspended-core photonic crystal fibers", J. Opt. Soc. Am. B 35, 2311-2316 (2018) CrossRef G. Wójcik et al. "Microbending losses in optical fibers with different cross-sections", Proc. SPIE 10830, 108300H (2018) CrossRef F. Xu, Selected topics on optical fiber technology and applications (IntechOpen 2018) CrossRef

Low-loss hollow-core photonic bandgap fiber with isolated anti-resonance layer

In this study, a low-loss hollow-core photonic bandgap fiber (HC-PBF) with an isolated anti-resonance layer is proposed. The fiber cladding structure is the same as that of conventional HC-PBF, while the fiber core is surrounded and formed by an isolated anti-resonance layer which separates the core from the cladding. Simulation results show that the overlap between the fundamental mode and silica-air interfaces is dramatically reduced owing to introduction of the isolated anti-resonance layer, and the fiber loss lower than 3.5 dB/km can be achieved with only ∼13-μm core diameter and ∼8-μm mode field diameter at 1550 nm

Molecular dispersion spectroscopy in a CO2-filled all-fiber gas cells based on a hollow-core photonic crystal fiber

CO2 sensing using self-fabricated all-fiber gas cells based on a hollow-core photonic crystal fiber and chirped laser dispersion spectroscopy (CLaDS) is presented. I show that CLaDS enables significant reduction of optical fringes arising from the mutlimode nature of the air-core photonic bandgap (PBG) fiber, hence improving the gas sensing system’s stability and performance. By carefully selecting modulation frequency, it is possible to match the period of interference signal (resulting from coupling between fiber’s guided modes) and, therefore, suppress its contribution to the retrieved signal. CLaDS enables successful use of hollow-core PBG fibers in gas sensing applications.

Laser-cooled cesium atoms confined with a magic-wavelength dipole trap inside a hollow-core photonic-bandgap fiber

We report loading of laser-cooled caesium atoms into a hollow-core photonic-bandgap fiber and confining the atoms in the fiber's 7 $\mu m$ diameter core with a magic-wavelength dipole trap at $\sim$935 nm. The use of the magic wavelength removes the AC-Stark shift of the 852nm optical transition in caesium caused by the dipole trap in the fiber core and suppresses the inhomogeneous broadening of the atomic ensemble that arises from the radial distribution of the atoms. This opens the possibility to continuously probe the atoms over time scales of a millisecond -- approximately 1000 times longer than what was reported in previous works, as dipole trap does not have to be modulated. We describe our atom loading setup and its unique features and present spectroscopy measurements of the caesium's D$_{2}$ line in the continuous wave dipole trap with up to $1.7 \times 10^{4}$ loaded inside the hollow-core fiber.

Femtosecond fiber laser at 780 nm for two-photon autofluorescence imaging

We present an Er-doped fiber (Er:fiber)-based femtosecond laser at 780 nm with 256 MHz repetition rate, 191 fs pulse duration, and over 1 W average power. Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193 fs pulse duration and 2.43 W average power. Over 40% frequency doubling efficiency is obtained by a periodically poled lithium niobate crystal. Delivering through a hollow-core photonic bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.

All-fiber Yb:fiber frequency comb

We demonstrate an all-fiber Yb:fiber frequency comb with a nonlinear-amplifying-loop-mirror-based Yb:fiber laser oscillator. The fiber-spliced hollow-core photonic bandgap fiber was used as dispersion compensator, which was also directly spliced to a piece of tapered photonic crystal fiber for an octave-spanning spectrum. The spectrum of the compressed 107 fs laser pulses was broadened, covering 600 nm to 1300 nm in a high-nonlinearity tapered fiber for f to 2f beating. The signal-to-noise ratio of offset frequency was measured to be 22 dB.

A hollow-core photonic band-gap fiber based methane sensor system capable of reduced mode interference noise

The performances of infrared absorption spectroscopic gas sensors using a hollow-core photonic band-gap fiber (HC-PBF) as an absorption cell are usually limited by mode interference of the multimode HC-PBF. To minimize the effect of mode interference, a free space coupling structure was proposed for mode transfer from a single mode fiber (SMF) to a HC-PBF and also from the HC-PBF to a photo-detector. The parameters of the free space coupling structure were optimized based on a detailed theoretical analysis and numerical simulation, and the mode inference reduction was experimentally verified. Wavelength modulation spectroscopy (WMS) combined with the second harmonic (2f) detection was utilized in methane (CH4) measurements by targeting an absorption line at 1653 nm. Using a ∼2 mW laser and a 0.45 m-long HC-PBF for CH4 detection at atmospheric pressure, the optimized sensor demonstrated a 1σ detection limit of ∼4.35 parts per million in volume (ppmv) with a 0.5 s averaging time and a minimum detection limit of ∼360 parts per billion in volume (ppbv) with an averaging time of 75 s. The proposed structure can also be used in a HC-PBF-cell based infrared absorption gas sensor system for the detection of any gas species for suppression of mode interference.

Measurement of high pressure and high temperature using a dual-cavity Fabry-Perot interferometer created in cascade hollow-core fibers.

A compact dual-cavity Fabry-Perot interferometer (DC-FPI) sensor is proposed and demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) spliced with a hollow-core fiber (HCF). The HC-PBF, which has low transmission loss, was used as the first FPI cavity and also acted as a bridge between the lead-in single-mode fiber and the HCF. The HCF was used as the second FPI cavity and also acted as a micro gas inlet into the first FPI cavity. A DC-FPI sensor with different cavity lengths of 226 and 634μm in the first FPI and the second FPI was created. Both gas pressures ranging from 0-10MPa and temperatures ranging from 100-800°C were measured using the DC-FPI sensors together with a fast Fourier transform and phase-demodulation algorithm. Experimental results showed that the first FPI cavity was gas pressure sensitive but temperature insensitive, while the second FPI cavity was temperature sensitive but gas pressure insensitive. A high gas pressure sensitivity of 1.336μm/MPa and a temperature sensitivity of 17nm/°C were achieved in the DC-FPI sensor. Moreover, the cross sensitivity between the gas pressure and temperature was calculated to be ∼-15 Pa/°C and ∼0.3°C/MPa. The proposed DC-FPI sensors provide a promising candidate for the simultaneous measurement of high pressures and high temperatures at some precise locations.

High-sensitivity gas pressure sensor based on hollow-core photonic bandgap fiber Mach-Zehnder interferometer.

We propose and experimentally demonstrate a highly sensitive gas pressure sensor based on a near-balanced Mach-Zehnder interferometer (MZI) and constructed by hollow-core photonic bandgap fiber (HC-PBF) in this paper. The MZI is simply constructed by fusion splicing two HC-PBFs, which are of slightly different lengths, between two 3-dB couplers. The two output ends of each coupler are approximately equal in length, to ensure that the optical path variations of the MZI only result from the differences in the lengths between the two HC-PBFs. To apply the MZI for gas pressure sensing, a femtosecond laser is employed to drill a micro-channel in one of the two HC-PBF arms. The experiment result shows that the proposed MZI based gas pressure sensor achieves an ultrahigh sensitivity, up to 2.39 nm/kPa, which is two orders of magnitude higher than that of the previously reported MZI-based gas pressure sensors. Additionally, the effects resulting from the absolute length and relative length of the two HC-PBFs on gas pressure sensing performance are also investigated experimentally and theoretically, respectively. The ultra-high sensitivity and ease of fabrication make this device suitable for gas pressure sensing in the field of industrial and environmental safety monitoring.

Properties of a novel hybrid hollow core photonic crystal fiber

Abstract We present a novel hybrid hollow-core photonic crystal fiber, which can confine and guide light in subwavelength-diameter air holes of core. The propagation mechanism of low-refractive-index hole is studied by evanescent field coupling and electromagnetic theory of optical waveguide transmission. The unique transmission characteristics in the novel fiber with new propagation mechanism are shown. The evanescent-field power fraction in the core holes can be changed flexibly between 10% and 50%. The confinement loss is very low in the broadband wavelength range 1–1.8 μm, which is not limited by surface modes and photonic bandgap effect appearing in hollow-core photonic bandgap fibers. The excellent characteristics of matching mode area, high birefringence, single polarization and single mode in hollow-core fiber are obtained. The two-zero dispersion, broadband flattened dispersion and dispersion compensation properties of hollow-core fiber are also presented. The novel hybrid photonic crystal fiber has the characteristics of solid core fibers and is suitable for the application as hollow core fibers.

Combining Hollow Core Photonic Crystal Fibers with Multimode, Solid Core Fiber Couplers through Arc Fusion Splicing for the Miniaturization of Nonlinear Spectroscopy Sensing Devices

The presence of fiber optic devices, such as couplers or wavelength division multiplexers, based on hollow-core fibers (HCFs) is still rather uncommon, while such devices can be imagined to greatly increase the potential of HCFs for different applications, such as sensing, nonlinear optics, etc. In this paper, we present a combination of a standard, multimode fiber (MMF) optic coupler with a hollow core photonic bandgap fiber through arc fusion splicing and its application for the purpose of multiphoton spectroscopy. The presented splicing method is of high affordability due to the low cost of arc fusion splicers, and the measured splicing loss (SL) of the HCF-MMF splice is as low as (0.32 ± 0.1) dB, while the splice itself is durable enough to withstand a bending radius (rbend) of 1.8 cm. This resulted in a hybrid between the hollow core photonic bandgap fiber (HCPBF) and MMF coupler, delivering 20 mW of average power and 250-fs short laser pulses to the sample, which was good enough to test the proposed sensor setup in a simple, proof-of-concept multiphoton fluorescence excitation-detection experiment, allowing the successful measurement of the fluorescence emission spectrum of 10−5 M fluorescein solution. In our opinion, the presented results indicate the possibility of creating multi-purpose HCF setups, which would excel in various types of sensing applications.

Experimental Study on the Concept of Hollow-Core Photonic Bandgap Fiber Stethoscope

An experiment is proposed to show the feasibility of using hollow-core photonic bandgap fibers (HC-PBF) in the fiber-optic interferometric stethoscopes to generally improve the sensitivity and overcome the problems associated with the electronic stethoscopes. In the experiment, the HC-1550 is used as a measuring arm of an unbalanced Mach-Zehnder interferometer (MZI) and the conventional single-mode optical fiber (SMF) is used as an isolated reference arm. Detection and demodulation of the relative phase shift is performed passively using phase-generated carrier homodyne technique (PGC). The proposed results indicate the significance of using HC-PBFs in the future stethoscopes.

Investigation of transmission loss dependence on core surround parameters in 7-cell hollow-core photonic-bandgap fibers

In designing photonic-bandgap fibers, the most effective and well-known approach utilized to suppress surface modes is the T ∼ S / 2 rule, which translates to using a core surround with only half the thickness of the average cladding strut. We investigate transmission loss in a commercial 7-cell hollow-core photonic-bandgap fiber. To reduce transmission loss at 1550 nm, we apply the T ∼ S / 2 rule to suppress the surface modes. While the strut surface modes are suppressed, the rod surface modes (RSMs) are blueshifted to wavelengths near 1550 nm because the round-core diameters of the cladding-layer corners resting against the fiber core are quite small, which leads to the coupling between the fundamental mode and the RSMs. This induces attenuation at 1550 nm, which indicates that the T ∼ S / 2 rule is applicable only within certain limits. By optimizing the round-core diameters of the corners resting against the fiber core, we obtain a structure that is free of surface modes, with the subsequent transmission loss at 1550 nm being ∼10 dB / km lower than that of the original fiber. Moreover, we propose a simple method to modify the round-core diameters to aid in surface-mode suppression.

Opto-Electron Eng, 2018, 45(9)] Hollow-core photonic bandgap fibers: properties and sensing technology

In this paper, the unique properties of the hollow-core photonic bandgap fiber (HC-PBF) are reviewed, and a variety of sensing and device applications of this type of fiber in recent years are introduced. Low-loss light transmission in air core is an important characteristic of the HC-PBF, which provides light-matter interaction channel with high energy density and long interaction distance. In addition, the air-propagation of the light in fiber also reduces the impacts of fiber material properties (such as infrared absorption, thermos-optical effect) on propagating light, hence offers an efficient platform for the sensing applications such as trace gas / liquid detection, optical fiber gyro sensing. The fine micro-structure in HC-PBF exhibits novel mechanical and thermal properties, which would be beneficial to the sensing applications such as sound wave and vibration detection. The HC-PBF’s porous structure can also be locally modified by using various post-processing techniques, such as local heat treatment, micromachining and selective filling, which would enable further function extension or performance enhancement. The flexibility of the fiber has been used to develop new optical fiber devices, such as grating, polarizer and polarization interferometer. At present, the development of HC-PBF sensing technology has greatly expanded the sensing ability and application range of optical fiber. It is an important direction for the development of all-optical devices and optical integration technology.

Experimental study on an interferometric strain sensor based on hollow-core photonic bandgap fiber for intrusion detection

In this paper, the design and preliminary performance results of a Mach–Zehnder interferometric (MZI) strain sensor based on hollow-core photonic bandgap fiber (HC-PBG) for intrusion detection are proposed. An experiment is conducted to test the system before deployment in the field. Firstly, to judge the necessity of using the HC-PBG, an experiment is performed to compare the normalized strain responsivity (NR) of the HC-1550 and the conventional SMF-28. By interchanging the investigated optical fibers as a sensing arm of the MZI, it is possible to compare the obtained results with a conventional standard silica fiber and the HC-PBG. The experimental results show that the NR of the HC-PBG is about 3.6 – 5.3 dB better than that of the SMF depending on the frequency in the frequency range 500 Hz to 2 kHz. Secondly, we concentrate our study and measurements on the HC-1550. A simulation of intrusion detection is introduced by using the proposed interferometric fiber-optic strain sensor to detect the dynamic strain induced phase shift as a result of varying the amplitude and frequency of the input signals to a PZT tube. The investigated input signal frequencies are from 500 Hz to 2 kHz. An experiment is performed to measure the induced strain from the PZT for different input voltages and frequencies, and using the phase generated carrier (PGC) demodulation technique for extracting the measured signal information. This technique is an effective way to test the performance and the functionality of the system in lab before the field trials. Experimental results show the importance of using HC-PBG for sensing applications and the ability of the system to effectively be used for borders monitoring and securing important facilities.

Investigation of A Slow-Light Enhanced Near-Infrared Absorption Spectroscopic Gas Sensor, Based on Hollow-Core Photonic Band-Gap Fiber.

Generic modeling and analysis of a slow-light enhanced absorption spectroscopic gas sensor was proposed, using a mode-tuned, hollow-core, photonic band-gap fiber (HC-PBF) as an absorption gas cell. Mode characteristics of the un-infiltrated and infiltrated HC-PBF and gas absorption enhancement of the infiltrated HC-PBF were analyzed. A general rule of microfluidic parameters for targeting different gas species in the near-infrared was obtained. Ammonia (NH3) was used as an example to explore the effects of slow light on gas detection. The second harmonic (2f) signal and Allan deviation were theoretically investigated based on the derived formulations.

Nondestructive determination of the core size of a hollow-core photonic bandgap fiber using Fabry-Perot interference.

In this Letter, we propose a simple and nondestructive method for the determination of the core size of a hollow-core photonic bandgap fiber (HC-PBF) and its axial uniformity based on a Fabry-Perot cavity induced by a pair of opposite silica-air interfaces within the hollow core. The experimental results indicate that the core size test of the HC-PBF has a nanometer-level precision, and its axial uniformity test has an ultimate spatial resolution of tens of microns. The method provides an effective and precise tool for the investigation of the hollow-core size and its longitudinal evolution.