Hollow-core Photonic Bandgap Fiber Research Articles

Realization of low confinement loss acetylene gas sensor by using hollow-core photonic bandgap fiber

Realization of low confinement loss acetylene gas sensor by using hollow-core photonic bandgap fiber

Guiding Pure Vector Mode in Hollow Core Fiber Based on a Momentum Selection Theory

The attraction of hollow core fibers (HCF) lies in the long-distance mode retention ability and the transmission speed close to physical limit. Long-term efforts have been made to get a balance between large core and pure mode. However, the unique light guide mechanism of HCFs makes it a difficult question to decrease the number of the allowed modes. New theory of mode control in such fibers is desired. In this paper, we propose a new space for observing optical states based on the principle of representation transformation, so-called the wave vector space (k-space). The mode observation in the k-space provides a different perspective where the mechanical properties of the light are more obvious. We observe typical fiber modes in the k-space and clarify differences of their momentum characteristics, based on which a mode selection principle is proposed. As a theoretical proof of the principle, a novel 19-cell hollow-core photonic bandgap fiber (HC-PBGF) structure that only supports single pure vector mode is exhibited. The designed optical fiber supports only TE01 mode over a bandwidth of 80 nm with the lowest loss of 0.8 dB/km. This example proves the practicality of the proposed momentum selection theory and will inspire breakthroughs in other optical studies.

Crossings in photonic crystal fiber with hybrid core and design of broadband dispersion compensating photonic crystal fiber

A photonic crystal fiber (PCF) with sub-wavelength air inner core and Ge-doped concentric ring outer core is proposed. The full vector finite element method with perfectly matched layer is used for simulation. Mode crossing phenomenon which can be controlled through the hollow core diameter is investigated. A PCF with an effective compensated dispersion range of ±1.38 ps/nm/km from 1460 nm to 1637 nm wavelength is designed. The dispersion compensating PCF (DCPCF) can compensate for the dispersion and dispersion slope of a standard single mode fiber (SMF) at the same time. The kappa value matches very well with that of the commercial single mode fiber. Moreover, the figure of merits inside air core region of the proposed DCPCF is improved by 21.3 dB at 1550 nm wavelength compared to a hollow core photonic bandgap (PBG) fiber. This field enhancement can effectively reduce the material loss and the nonlinear accumulation in dispersion compensation fibers.

Backscattering in antiresonant hollow-core fibers: over 40 dB lower than in standard optical fibers

The elastic backscattering of light in optical fiber is a fundamental phenomenon that sets the ultimate performance of several fiber systems such as gyroscopes and bidirectional transfer links. Until now, efforts to reduce the backscattering coefficient have yielded limited results, with the lowest value sitting at around − 76 d B / m in Ge-free silica-core fiber at 1.55 µm. Here, we present what we believe to be the first measurement of backscattering from a low-loss antiresonant hollow-core fiber and show that it is more than 40 dB below reported values in silica-core fiber and hollow-core photonic bandgap fiber. The record-low level of − 118 d B / m measured with our custom-built optical frequency-domain reflectometer is in good agreement with simulations in which we assume the scattering to originate from the intrinsic surface roughness. Our demonstration also shows that a tailored instrument can localize and quantify weak faults within a hollow-core fiber, enabling its detailed characterization.

Surface-Mode Resonance Coupling Effect and High-Temperature Sensing Characteristics in Hollow-Core Photonic Bandgap Fibers

Surface-Mode Resonance Coupling Effect and High-Temperature Sensing Characteristics in Hollow-Core Photonic Bandgap Fibers

Polarization Effects on Thermally Stable Latency in Hollow-Core Photonic Bandgap Fibers

Conveyance of light in air endows hollow-core optical fibers with remarkably low sensitivity of the propagation delay to temperature changes. This sensitivity was demonstrated to be further reduced and even made negative (crossing zero) in photonic bandgap type of hollow core fibers. When operating long lengths of this fiber close to the zero sensitivity wavelength, it was observed experimentally that there is a small residual variation in propagation delay which had no apparent correlation to imposed temperature changes. In this article, we analyze the polarization effects that give rise to this variation, showing that the highest level of practically achievable thermal stability of the latency is limited by polarization mode dispersion. We show measurements of differential group delay between polarization modes in long lengths of photonic bandgap fiber at various temperatures and focus on spectral regions where thermally stable latency is predicted and measured. Our experimental observations, corroborated by numerical simulations, indicate the presence of strong polarization mode coupling in the fibers in addition to birefringence. The detailed understanding gained through this study allows us to propose practically achievable (i.e., manufacturable) fiber designs with up to three orders of magnitude lower polarization mode dispersion at wavelengths where the latency is insensitive to thermal fluctuations. This paves the way to fibers with polarization independent and thermally stable latency to serve a multitude of applications.

In-line polarization controller for hollow core photonic bandgap fiber

We demonstrate an in-line polarization controller for hollow core photonic bandgap fiber made by inserting a length of the fiber into a standard, off-the-shelf, 3-paddle controller as widely used for polarization control using standard single mode fibers. Although the operational principle of this 3-paddle controller is very different when using hollow core photonic bandgap fiber rather than SMF effective polarization control is readily achieved.

Multispecies Continuous Gas Detection With Supercontinuum Laser at Telecommunication Wavelength

Supercontinuum (SC) lasers provide an excellent opportunity for absorption spectroscopy by virtue of their high brightness and large bandwidth. Here we present the detection of multiple industrial toxic gasses from 1480 nm to 1700 nm, with a simple custom SC laser source. Using readily available optical components, we demonstrate an all-fiber system for the detection of ammonia (NH3) and methane (CH4) in a 2.4 m long hollow-core photonic bandgap fiber with 20- $\mu \text{m}$ core diameter. The responsivity, selectivity, and performance of the system for continuous detection are demonstrated.

1 × N (N = 2, 8) Silicon Selector Switch for Prospective Technologies at the 2 μm Waveband

The 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> waveband, specifically near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9~\mu \text{m}$ </tex-math></inline-formula> , is an imperative resource that could possibly be exploited in future communications systems. This is due to the promising infrastructural developments at the wavelength region (hollow-core photonic bandgap fiber, thulium-doped fiber amplifier) near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9~\mu \text{m}$ </tex-math></inline-formula> . In this work, we report the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times N$ </tex-math></inline-formula> selector switch based on Mach-Zehnder interferometers operating near the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9~\mu \text{m}$ </tex-math></inline-formula> wavelength region. As an elementary cell ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N $ </tex-math></inline-formula> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</i> ), an insertion loss as low as 1.1 dB, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{P}_{\pi }$ </tex-math></inline-formula> of 23 mW, 10-90% switching time of lower than 38 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> and a crosstalk of lower than −25 dB from 1880 to 1955 nm has been determined. In order to prove scalability, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</i> switch <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(N $ </tex-math></inline-formula> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8)</i> is demonstrated, indicating crosstalk as low as −21 dB, considering all possible switching configurations across the abovementioned wavelength region. Insertion loss levels are examined.

Improving the sensitivity of the HC-PBF based gas sensor by optimization of core size and mode interference suppression

A hollow-core photonic bandgap fiber for gas sensing with high sensitivity was designed. Some undesirable parameters like mode interference and propagation losses can deteriorate the performance of PBF. By selecting an accurate and reasonable size of the fiber core, consequently modification the shape and size of the first row of holes surrounding the hollow-core, we could improve light intensity profile in the fiber core. According to the simulation results, at a reasonable core radius the relative sensitivity of gas sensor was improved to 96.57%. In addition, by mode interference suppression, we could minimize the effect of mode mismatch. Furthermore, by optimization of fiber structural parameters like lattice constant and air holes diameter, the PBF was single-mode. Considering the operation wavelength λ = 1.55 µm which is approximately equal to the acetylene gas absorption line, this fiber is suitable to be a high sensitivity gas sensor to detect absorbing gases.

Simulating gravity-assisted loading of laser-cooled atoms into a hollow-core photonic-bandgap fiber

We numerically simulate gravity-assisted loading of laser-cooled atoms into a hollow-core fiber. For this, we compute the trajectories of falling atoms and test the success or failure of loading with a range of atoms’ initial positions and velocities. By overlapping these results with the position and velocity distribution of the trapped atomic cloud, the number of loaded atoms is estimated without a random sampling process. We present our predictions for the atomic cloud’s loading efficiency into a photonic-bandgap fiber with a 7.5 μm-diameter hollow core for various experimental conditions, such as the initial temperature, the cloud position and size, and the dipole trap power, and compare the predictions to experimental data. Our approach reduces the computational resources and time compared to the Monte-Carlo approach used in previously reported works.

Single-photon-level narrowband memory in a hollow-core photonic bandgap fiber

An experimental platform operating at the level of individual quanta and providing strong light-matter coupling is a key requirement for quantum information processing. In our work, we show that hollow-core photonic bandgap fibers filled with laser-cooled atoms might serve as such a platform, despite their typical complicated birefringence properties. To this end, we present a detailed theoretical and experimental study to identify a fiber with suitable properties to achieve operation at the single-photon level. In the fiber, we demonstrate the storage and on-demand retrieval as well as the creation of stationary light pulses, based on electromagnetically induced transparency, for weak coherent light pulses down to the single-photon level with an unconditional noise floor of 0.017(4) photons per pulse. These results clearly demonstrate the prospects of such a fiber-based platform for applications in quantum information networks.

Compact silicon photonic hybrid ring external cavity (SHREC)/InGaSb-AlGaAsSb wavelength-tunable laser diode operating from 1881-1947 nm.

In recent years, the 2 µm waveband has been gaining significant attention due to its potential in the realization of several key technologies, specifically, future long-haul optical communications near the 1.9 µm wavelength region. In this work, we present a hybrid silicon photonic wavelength-tunable diode laser with an operating range of 1881-1947 nm (66 nm) for the first time, providing good compatibility with the hollow-core photonic bandgap fiber and thulium-doped fiber amplifier. Room-temperature continuous-wave operation was achieved with a favorable on-chip output power of 28 mW. Stable single-mode lasing was observed with side-mode suppression ratio up to 35 dB. Besides the abovementioned potential applications, the demonstrated wavelength region will find critical purpose in H2O spectroscopic sensing, optical logic, signal processing as well as enabling the strong optical Kerr effect on Si.

Low-Loss Low-Back-Reflection Coupling of Hollow-Core Photonic Bandgap Fiber With Integrated-Optic Circuit in Fiber Optic Gyroscope

Photonic bandgap fiber-optic gyroscope has excellent environment adaptability and shows great prospect. The coupling between hollow-core photonic bandgap fiber coil and integrated-optic circuit is a crucial technology in photonic bandgap fiber-optic gyroscope. A low-loss low-back-reflection method for the coupling between a hollow-core photonic bandgap fiber and integrated-optic circuit is proposed. The end-face of the hollow-core photonic bandgap fiber only needs to be flat-cleaved with a general fiber cleaver. The optimal coupling angle is determined and experimentally verified to overcome the effect caused by the air gap between angle-cleaved integrated-optic circuit and flat-cleaved hollow-core photonic bandgap fiber end-face. Experimental results reveal that the coupling loss and back-reflection of the hollow-core photonic bandgap fiber with the integrated-optic circuit are better than ~ 3.2 dB and ~ -43 dB, respectively. Compared with conventional butt coupling and fusion splicing, the coupling performance of the proposed method is significantly improved, which can achieve low-loss, low-back-reflection, and high reliability. The method provides a foundation for the coupling between hollow-core photonic bandgap fiber coil and integrated-optic circuit in fiber optic gyroscope.

Temperature-Independent Gas Pressure Sensor with High Birefringence Photonic Crystal Fiber-Based Reflective Lyot Filter.

A novel temperature-independent gas pressure sensor based on a reflective fiber Lyot filter is presented in this paper. The reflective fiber Lyot filter is simply consist of a fiber polarizer and a segment of hollow-core photonic bandgap fiber (HB-PCF). The HB-PCF plays the role of birefringent cavity in the reflective fiber Lyot filter and works as the sensor head in the gas pressure sensor. Experiment results show that the responses of the sensor to gas pressure and temperature are 3.94 nm/MPa and −0.009 nm/°C, indicating that the proposed gas pressure is sensitive to gas pressure rather than temperature. Coupled with the advantages of simple structure, easy manufacture, high sensitivity and temperature independent, the proposed reflective fiber Lyot filter-based gas pressure sensor holds great potential application in the field of gas pressure monitoring.

SiN-SOI Multilayer Platform for Prospective Applications at 2 μm

Silicon photonics at the 2 μm waveband, specifically the 1.9 μm wavelength region is strategically imperative. This is due to its infrastructural compatibility (i.e., thulium-doped fiber amplifier, hollow-core photonic bandgap fiber) in enabling communications, as well as its potential to enable a wide range of applications. While the conventional Silicon-on-Insulator platform permits passive/active functionalities, it requires stringent processing due to high-index contrast. On the other hand, SiN can serve to reduce waveguiding losses via its moderate-index contrast. In this work, by demonstrating SiN passives and Si-SiN interlayer coupler with favorable performance, we extend the Si-SiN platform to the 1.9 μm wavelength region. We report waveguide propagation loss of 2.32 dB/cm. Following, trends in radiation loss with regards to bending radius is analyzed. A high performance 3-dB power splitter with insertion loss and bandwidth of 0.05 dB and 55 nm (1935--1990 nm) respectively is introduced. Lastly, Si-SiN transition loss as low as 0.04 dB is demonstrated.

High-efficiency Raman conversion in SF6- and CF4-filled hollow-core photonic bandgap fibers.

We present a comparative experimental investigation of vibrational stimulated Raman scattering in hollow-core photonic bandgap fibers pressurized with sulfur hexafluoride (${{\rm SF}_6}$SF6) and tetrafluoromethane (${{\rm CF}_4}$CF4) gases. Nanosecond-duration pulses at a wavelength of 1030 nm are coupled into the gas-filled fiber, and the first and second Stokes orders are measured at the fiber output. We characterize the conversion process as a function of gas, fiber length, and input power. With a 15 m fiber filled with ${{\rm SF}_6}$SF6, we obtain conversion efficiency to the first Stokes of 55.7% at an input peak power of 0.63 kW. In comparison, with ${{\rm CF}_4}$CF4, we obtained a higher conversion threshold and maximum conversion efficiency of 45.4%. To the best of our knowledge, this is the first reported conversion experiment with hollow-core fibers filled with ${{\rm SF}_6}$SF6 gas.

Highly sensitive gas refractive index sensor based on hollow-core photonic bandgap fiber.

A highly sensitive gas refractive index (RI) sensor based on hollow-core photonic bandgap fiber (HC-PBF) and Fourier transform white-light interferometry was experimentally demonstrated. HC-PBFs with lower loss than hollow silica tubes render a longer air cavity for the Fabry-Perot interferometers (FPIs) without a great deal of compromise to the fringe visibility of interference. Fourier transform phase demodulation method was employed in the experiment and a directly proportional relationship between the phase sensitivity and cavity length was demonstrated. For a cavity length of ∼24.9 mm, the sensor's gas RI sensitivity reaches up to 50775.54 µm/RIU in an air RI range from 1.000 to 1.030. Considering the cavity length demodulation resolution of 0.06 µm achieved by this method, the sensor can detect gas RI change with a resolution of 10-6 RIU, which can meet the sensing demand for almost all the gases. Moreover, the gas RI sensitivity and measurement range can be improved further by lengthening the HC-PBF. The high sensitivity, large dynamic range and good linearity of the proposed sensor make it a good candidate for biosensing, monitoring of modern chemical industry or gas laser systems.

High-speed uni-traveling carrier photodiode for 2 μm wavelength application

Current optical communication systems operating at the 1.55 μm wavelength band may not be able to continually satisfy the growing demand on data capacity within the next few years. Opening a new spectral window around the 2 μm wavelength with recently developed hollow-core photonic bandgap fiber and a thulium-doped fiber amplifier is a promising solution to increase transmission capacity due to the low-loss and wide-bandwidth properties of these components at this wavelength band. However, as a key component, the performance of current high-speed photodetectors at the 2 μm wavelength is still not comparable with those at the 1.55 μm wavelength band, which chokes the feasibility of the new spectral window. In this work, we demonstrate, for the first time to our knowledge, a high-speed uni-traveling carrier photodiode for 2 μm applications with InGaAs/GaAsSb type-II multiple quantum wells as the absorption region, which is lattice-matched to InP. The devices have the responsivity of 0.07 A/W at 2 μm wavelength, and the device with a 10 μm diameter shows a 3 dB bandwidth of 25 GHz at −3 V bias voltage. To the best of our knowledge, this device is the fastest photodiode among all group III-V and group IV photodetectors working in the 2 μm wavelength range.

Design of a dispersion-engineered broadband Ge11.5As24Se64.5-Si3N4 strip–slot hybrid waveguide with giant and flat dispersion over 350 nm for on-chip photonic networks

We propose a new strip–slot hybrid waveguide with extreme large and flat dispersion over broad wavelength range. The strong resonance coupling between the strip and slot modes has been employed to obtain a high dispersion at desired wavelength. The properties of dispersion are analyzed using the finite-difference time-domain method. All numerical simulation results reveal that for the optimized waveguide structure, a maximum dispersion of −1.54×106 ps nm−1 km−1 and dispersion full width at half-maximum of 2.5 nm at 1.55μm are obtained. By cascading the strip–slot hybrid waveguides with varied width and height, a large and flattened dispersion of −9.8×105 ps nm−1 km−1 covering 350 nm is achieved. Moreover, dispersion compensation of 100 Gbit/s return-to-zero on-off-keying optical-time-division-multiplexing signals after 50-km single mode fiber transmission, and after 7-km hollow-core photonic band-gap fiber transmission are demonstrated, separately. Such a waveguide will find widespread applications in on-chip all-optical signal processing.