Polarization-filtering and polarization-maintaining low-loss negative curvature fibers

The Development and Progression of Micro-Nano Optics

Micro-Nano optics is one of the most active frontiers in the current development of optics. It combines the cutting-edge achievements of photonics and nanotechnology, which can realize many brand-new functions on the basis of local electromagnetic interactions and become an indispensable key science and technology of the 21st century. Micro-Nano optics is also an important development direction of the new optoelectronics industry at present. It plays an irreplaceable role in optical communication, optical interconnection, optical storage, sensing imaging, sensing measurement, display, solid-state lighting, biomedicine, security, green energy, and other fields. In this paper, we will summarize the research status of micro-nano optics, and analyze it from four aspects: micro-nano luminescent materials and devices, micro-nano optical waveguide materials and devices, micro-nano photoelectric detection materials and devices, and micro-nano optical structures and devices. Finally, the future development of micro-nano optics will be prospected.

Spectral dependence of principal axes in anti-resonant hollow-core fibers with different numbers of capillaries

We report on measurements highlighting the spectral dependence of the principal axes' angular orientation that is present within three hollow-core fibers samples of various geometries. Hollow-core anti-resonant fibers (ARFs) with six, five, and four capillaries are investigated in several transmission windows. It is shown that the six-capillary fiber structure demonstrates a much smaller shift in the principal axes' orientation, in comparison with five- and four-capillary structures. The four-capillary structure has a 90° shift of its principal axes' orientation inside even- and odd-numbered transmission windows. These results corroborate the suggestion that the six-capillary ARF structure is a great candidate for polarization-maintaining operation over a wide spectral bandwidth.

High birefringence, single-polarization, low loss hollow-core anti-resonant fibers

We present a novel hollow-core anti-resonant fiber (HC-ARF) with a cladding ring, two nested resonant tubes and two nested silicon tubes. The cladding ring in the fiber contributes to decrease the fundamental mode (FM) loss of x-polarization and enlarge the polarization-extinction ratio (PER). In addition, the nested silicon tubes can improve birefringence greatly. The combination of cladding ring, nested resonant tubes and nested silicon tubes can make the fiber obtain low FM loss, single-polarization, and high birefringence. Specifically, the proposed HC-ARF exhibits total FM loss of x-polarization, PER, and birefringence of 0.89 dB/km, 4432, 3.07×10^-4, respectively, at 1.55 µm. Moreover, the y-bend direction has a great influence on the propagation properties of the fiber. The fiber in the x-bend direction has low total bend-loss of 0.004 dB/m for a small bend radius of 5.8 cm.

Discovering extremely low confinement-loss anti-resonant fibers via swarm intelligence

In this work, we obtain extremely low confinement-loss (CL) anti-resonant fibers (ARFs) via swarm intelligence, specifically the particle swarm optimization (PSO) algorithm. We construct a complex search space of ARFs with two layers of cladding and nested tubes. There are three and four structures of cladding tubes in the first and second layer, respectively. The ARFs are optimized by using the PSO algorithm in terms of both the structures and the parameters. The optimal structure is obtained from a total of 415900 ARFs structures, with the lowest CL being 2.839×10^-7 dB/m at a wavelength of 1.55 µm. We observe that the number of ARF structures with CL less than 1×10^-6 dB/m in our search space is 370. These structures mainly comprise four designs of ARFs. The results show that the optimal ARF structures realized by the PSO algorithm are different from the ARFs reported in the previous literature. This means that the swarm intelligence accelerates the design and invention of ARFs and also provides new insights regarding the ARF structures. This work provides a fast and effective approach to design ARFs with special requirements. In addition to providing high-performance ARF structures, this work transforms the ARF designs from experience-driven to data-driven.

Hollow-core mode propagation in an isomeric nested anti-resonant fiber

We present a modified fiber model based on the nested hollow core anti-resonant fiber that enables the stable transmission of the orbital-angular-momentum mode HE₂₁. By replacing a pair of nested anti-resonant tubes in the horizontal axis with resonant tubes, the coupling between core mode and cladding mode has been increased. Therefore, the relative strength of fundamental mode HE₁₁ and the first higher mode HE₂₁ has been modified. The numerical simulation results indicate that the loss ratio of the lowest loss HE₁₁ to HE₂₁ can be optimized to more than 187, while the HE₂₁ still maintains a low confinement loss as 0.0027 dB/m. Our research has brought about a solution of low loss hollow core mode propagation in optical fiber. Those properties will make this fiber an ideal medium for blue-detuned atomic guidance.

Epsilon negative-based, broadband single-polarization single-mode hollow core anti-resonant photonic crystal fiber

A broadband single-polarization single-mode (SPSM) hollow core anti-resonant photonic crystal fiber (HC-ARPCF) is proposed and analyzed by the finite element method in this paper. The HC-ARPCF design consisted of outer semicircular cladding tubes and inner circular cladding tubes. The SPSM behavior is achieved through controlling the effective material absorption loss (EML) by loading epsilon negative (ENG) material in the selected semicircular cladding tubes. Optimization of the configuration parameters is conducted to yield a large loss difference (LD) between one of the two orthogonally polarized fundamental modes and all the other unwanted modes. Therefore, only one desired mode will exist after a proper propagation distance, i.e., SPSM guidance. Specially, the optimal design provides a 288 nm (from 1408 nm to 1676 nm and from 1680 nm to 1700 nm) bandwidth in terms of 40 dB/m minimum LD (MLD) and 168 nm (from 1452 nm to 1620 nm) bandwidth in terms of 100 dB/m MLD. Furthermore, this fiber also exhibits a large effective mode area and near-zero dispersion properties over the entire operation bandwidth. The proposed HC-ARPCF may find its applications in polarization maintaining and high-power laser systems.

Enhanced birefringence in conventional and hybrid anti-resonant hollow-core fibers

A hollow-core anti-resonant fiber (HC-ARF) design based on hybrid silica/silicon cladding is proposed for single-polarization, single-mode and high birefringence. We show that by adding silicon layers in a semi-nested HC-ARF, one of the polarization states can be strongly suppressed while simultaneously maintaining low propagation loss for other polarization states, single-mode and high birefiringence. The optimized HC-ARF design exhibits propagation loss, high birefringence, and polarization-extinction ratio of 0.05 dB/m, 0.5 × 10^-4, >300 respectively for y-polarization while the loss of x-polarization is >5 dB/m at 1064 nm. The fiber also has low bend-loss and thus can be coiled to a small bend radii of 5 cm having ≈0.06 dB/m bend loss.

Birefringent large-mode-area anti-resonant hollow core fiber in the 1.9 µm wavelength window

We report on the development and characterization of a birefringent large-mode-area anti-resonant silica fiber. The fiber structure is composed of six non-touching capillaries. The birefringence results from the breaking of the circular symmetry of an air core with increasing of the diameters of two capillaries located across the fiber diameter. We depart from earlier designs of polarizing hollow core fibers, in which coupling of the guided modes was intentionally facilitated with the cladding layout. Instead, with the help of numerical simulations, we enhance birefringence in our design by varying the capillary wall thickness between the larger- and smaller-diameter capillary sections of the cladding. The fiber has a large, elliptical core with semi-axes of ∼55 and 41 µm in diameter, an effective area of the fundamental mode of 1200µm², and a total outer diameter of 127 µm. The cladding is composed of two pairs of smaller capillaries, which are 18 µm in diameter with 1.66 µm thick walls, and two larger capillaries with a 24 µm diameter and 1.14 µm thick walls, located across the diagonal of the fiber. Measured group birefringence over 1820-1920 nm wavelengths is monotonically increasing from 0.4×10^-4 to 2.0×10^-4, while its phase birefringence is from 5×10^-6 to 1.1×10^-5. Despite this, the fiber holds polarization with a 12 dB polarization extinction ratio at 1900 nm over a 1.5 m long sample.

Birefringence properties of anti-resonant octagonal-core and nodeless hollow-core fibers

We present experimental results of birefringence property measurements for two types of negative curvature anti-resonant hollow-core fibers (AR-HCFs). Both AR-HCFs have a core of 50 µm in diameter, providing an effective area of the fundamental guided mode larger than 1000µm². Measurements were carried out at wavelengths of 2.25, 2.35, and 2.45 µm. The obtained results demonstrate that both fiber types have birefringence axes that do not correspond to core symmetry axes. The proposed technique for the birefringence axes orientation measurement could be applied to other kinds of HCFs at various wavelengths.

Single-polarization single-mode double-ring hollow-core anti-resonant fiber

A novel single-polarization single-mode double-ring hollow-core anti-resonant fiber with two single-polarization regions (1545-1553 nm and 1591-1596 nm) is proposed. Single-polarization guidance is achieved by coupling a polarized fundamental mode and silica mode by using different tube thicknesses. Specifically, when the wavelength is 1550 nm, only a single x-polarized fundamental mode with a low loss of 0.04 dB/m is propagated by a polarization extinction ratio of 17662 and minimum higher-order mode extinction ratio of 393 by optimizing the structural parameters. Furthermore, this fiber also exhibits high-performance bend resistance. The x-polarized FM loss is as low as 0.11 dB/m with single-polarization single-mode guidance when the proposed fiber was bent at a bend radius of 8 cm toward the x-direction.

Geometry of Chalcogenide Negative Curvature Fibers for CO2 Laser Transmission

We study the impact of geometry on leakage loss in negative curvature fibers made with As 2 Se 3 chalcogenide and As 2 S 3 chalcogenide glasses for carbon dioxide (CO 2 ) laser transmission. The minimum leakage loss decreases when the core diameter increases both for fibers with six and for fibers with eight cladding tubes. The optimum gap corresponding to the minimum loss increases when the core diameter increases for negative curvature fibers with six cladding tubes. For negative curvature fibers with eight cladding tubes, the optimum gap is always less than 20 μ m when the core diameter ranges from 300 μ m to 500 μ m. The influence of material loss on fiber loss is also studied. When material loss exceeds 10 2 dB/m, it dominates the fiber leakage loss for negative curvature fiber at a wavelength of 10.6 μ m.