Optical Waveguide Theory

Curious wave phenomena that occur in optical fibres due to the interplay of instability and nonlinear effects are reviewed.

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Instabilities, breathers and rogue waves in optics

Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.

Space-division multiplexing: the next frontier in optical communication

Optical fiber gratings have developed into a mature technology with a wide range of applications in various areas, including physical sensing for temperature, strain, acoustic waves and pressure. All of these applications rely on the perturbation of the period or refractive index of a grating inscribed in the fiber core as a transducing mechanism between a quantity to be measured and the optical spectral response of the fiber grating. This paper presents a relatively recent variant of the fiber grating concept, whereby a small tilt of the grating fringes causes coupling of the optical power from the core mode into a multitude of cladding modes, each with its own wavevector and mode field shape. The main consequence of doing so is that the differential response of the modes can then be used to multiply the sensing modalities available for a single fiber grating and also to increase the sensor resolution by taking advantage of the large amount of data available. In particular, the temperature cross-sensitivity and power source fluctuation noise inherent in all fiber grating designs can be completely eliminated by referencing all the spectral measurements to the wavelength and power level of the core mode back-reflection. The mode resonances have a quality factor of 105, and they can be observed in reflection or transmission. A thorough review of experimental and theoretical results will show that tilted fiber Bragg gratings can be used for high resolution refractometry, surface plasmon resonance applications, and multiparameter physical sensing (strain, vibration, curvature, and temperature).

Tilted fiber Bragg grating sensors

An ultralow bending-loss trench-assisted single-mode optical fiber is designed and fabricated in this letter. The experimental results show that the fiber can support an ultralow bending loss of 0.05 dB/turn at a sharp bend radius of 5 mm at 1550 nm. This letter is considered to be of significance for the design and fabrication of bend insensitive fibers (BIFs), specifically for verifying the value of trench-assisted BIF designs. Furthermore, the fast growth of fiber-to-the-home applications will benefit from this letter.

Ultralow Bending-Loss Trench-Assisted Single-Mode Optical Fibers

The invention discloses a large-mode-area multimode fiber laser in single-mode operation, and relates to a fiber laser. The fiber laser solves the problems of higher mechanical strength and high-precision control of production process required for a doped multimode fiber. One end of a microstructure fiber (5) of the laser is aligned and connected with the doped multimode fiber (4), and the other end of the microstructure fiber (5) is clung to a high-reflection end dichroic mirror (6) or connected with a fiber grating (8); and the other end of the doped multimode fiber (4) is aligned with an output end dichroic mirror (7) tilting 45 degrees. Pumping light is coupled from the two ends of the laser into the laser. The microstructure fiber (5) has the function of filtering higher-order modes apart from the fundamental mode in the multimode fiber, and an all-fiber integrated fiber laser can be designed, which greatly improves the operation stability of the laser to cause the fiber laser to have the output beam quality close to a diffraction limit. The large-mode-area multimode fiber laser is widely applied to industrial processing, medical treatment, high-precision measurement, precision welding and the like.

Single-mode operated large mold field area multi-mode optical fiber laser

Three-layered single mode fibers with a GeO2 and F co-doped inner core are proposed. Stimulated Brillouin scattering properties in the fibers are investigated for the discriminative sensing of strain and temperature. The optical properties of the proposed fibers are designed to be well compatible with those of the widely used standard single mode fibers. The acoustic properties, including effective acoustic velocity, Brillouin frequency shifts, and peak Brillouin gain efficiencies of the first three acoustic modes, are numerically calculated and elaborately analyzed under different structural and doping parameters. The co-doped fibers with three different structural and doping parameters are chosen for simultaneous sensing of temperature and strain because of their capability of supporting two comparable peaks, which can be easily identified and distinguished in the Brillouin gain spectrum. The sensing properties of the fibers are estimated and discussed. The temperature and strain sensitivities as well as the temperature and strain errors are calculated to be comparable to those of the few mode fibers and multimode fibers.

SMFs With a Ge/F Co-Doped Inner Core for SBS-Based Discriminative Sensing of Temperature and Strain

A novel tunable all-fiber birefringent filter based on elliptical-core spun fiber (ECSF) is presented. It is the first time to build a discrete model of spun fiber by using Jones matrix analysis. The transmission characteristics of proposed filter are studied and discussed in detail, while a generalized formulation to express the transmissivity of the birefringent filter is derived. On this basis, the effect factors of filter characteristic are deeply analyzed and simulated. Compared with the conventional fiber-optic Solc filter, the proposal is easy fabricated and implemented with low loss. By utilizing appropriate length and parameters of the ECSF, a narrowband and high-extinction ratio periodic optical filter is realized. The proposed filter also can be finely tuned covering one free spectral range, which has potential applications for fiber sensing and flexible multi-wavelength fiber laser.

Solc-Like Tunable Birefringent Fiber Filter Based on Elliptical-Core Spun Fiber

An optimal refractive index profile of pure silica core optical fiber (PSCF) was designed, in combination with the characters of the modified chemical vapor deposition (MCVD) process. Techniques of preform fabrication by a new furnace round heating MCVD process and fiber drawing process were reviewed. Difficulties in doping fluorine in silica, widening the depressed-index cladding and maintaining the index of fiber core were discussed. Methods used to overcome these difficulties were given at the same time. Additionally, the optimal refractive index profiles of PSCF were presented.

Shuisheng Jian

Papers

Ultralow Bending-Loss Trench-Assisted Single-Mode Optical Fibers

Single-mode operated large mold field area multi-mode optical fiber laser

SMFs With a Ge/F Co-Doped Inner Core for SBS-Based Discriminative Sensing of Temperature and Strain

Solc-Like Tunable Birefringent Fiber Filter Based on Elliptical-Core Spun Fiber

Study on pure silica core optical fibers