Optical Waveguide Theory

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

/pdf/instabilities-breathers-and-rogue-waves-in-optics-252ilwzt4i.pdf

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

A novel linear cavity erbium-doped fiber (EDF) laser based on a structured chirped fiber Bragg grating (CFBG) filter is proposed for stable single-polarization (SP) single-longitudinal-mode (SLM) operation. For the first time, to the best of our knowledge, a structured CFBG filter with an ultranarrow transmission band which is generated by tapering directly on CFBG is used to select the laser longitudinal mode. The SLM operation is obtained by using the structured CFBG together with an unpumped EDF acting as a saturable absorber. The fluctuations of the laser peak power and center wavelength are less than 0.07 dB and 1 pm in 1 h, respectively. The stable SP operation is achieved by using the inline broadband polarizer. The measured 20 dB laser linewidth is about 27.7 kHz, which indicates the laser linewidth is approximately 1.39 kHz FWHM.

Stable single-polarization single-longitudinal-mode linear cavity erbium-doped fiber laser based on structured chirped fiber Bragg grating.

Core-cladding mode coupling of tilted long period fiber gratings in dual-mode fibers

A novel four-air-hole multicore dual-mode large-mode-area fiber: Proposal and design

In this paper we propose a magnetically tunable plasmons resonator based on a graphene-coated nanowire. Due to the magneto-optical effect under an external magnetic field, the circumferential propagation of graphene plasmons on a magneto-optical nanowire becomes non-reciprocal with the modal indices depend on plasmons traveling directions (clockwise or anti-clockwise). When coupled with a graphene sheet waveguide, the two components form a graphene plasmons filter for which the shift direction of transmittance spectrum is determined by the direction of input plasmons. The resonant wavelengths of resonator are obtained through resonant cavity theory and verified by numerical solutions. Furthermore, the non-reciprocal transmittance enables such structures to achieve the function of a plasmons isolator where the isolation could be tuned by the amplitude of an external magnetic field and the enabled plasmons propagation direction could be switched by reversing the direction of external magnetic field. Under proper structural parameters and magnetic field, an isolation ratio over 25 dB is obtained. The proposed magnetically tunable plasmons resonator may provide new inspiration to graphene plasmonics devices.

Magnetically tunable non-reciprocal plasmons resonator based on graphene-coated nanowire

We propose and investigate a modified multitrench fiber (MTF) design with two gaps numerically through the scalar FD-BPM algorithm. Excellent potential in mode area scaling, suppression of high-order modes (HOMs), and resistance to bending is demonstrated. Loss ratio between HOMs and the fundamental mode is more than 50 possibly over a wide range of high-index-ring thickness, gap width, bending radius, and bending orientation. Therefore, the required fabrication accuracy decreases. At 1050-nm wavelength and 20-cm bend radius, large effective mode area (920 μm2 ) is achievable with high loss ratio (>100). The fabricating technologies, carving grooves in the ordinary MTF and inserting rods in these grooves, can be possibly used to fabricate our modified two-gap-MTF.

Shuisheng Jian

Papers

Stable single-polarization single-longitudinal-mode linear cavity erbium-doped fiber laser based on structured chirped fiber Bragg grating.

Core-cladding mode coupling of tilted long period fiber gratings in dual-mode fibers

A novel four-air-hole multicore dual-mode large-mode-area fiber: Proposal and design

Magnetically tunable non-reciprocal plasmons resonator based on graphene-coated nanowire

A Modified Bend-Resistant Multitrench Fiber With Two Gaps