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

By using thin membrane plating technology in collimating lens, we successfully manufacture a 16×10Gbit/s multiplexer
basing on the combination of fiber and space structure method. The multiplexer is flexible according to your practical
need that can output 20, 40, 80, or 160Gbit/s signal. For 20, 40, 80 or 160Gbit/s multiplexer, insertion loss is 3.5dB, 7dB,
10.5dB and 14dB respectively. The low insertion loss provides maximum transmission power. It also has such features:
high time-delay accuracy, polarization insensitivity, broadband, very short coherence length, high time-delay accuracy,
and excellent temperature stability. It differs from the structure of general Mach-Zehnder interferometer. It has the
structure of Michelson interferometer.

Study on the time delay error for 160Gbit/s multiplexer

Signal processing is studied for Sagnac fiber distributed sensors. Wavelet denoising and wavelet decomposition are comparatively used to analyze signals in frequency domain to give smoothed frequency spectra, based on which null frequencies of the spectra are found more accurately. The analysis is helpful to more accurately locate the disturbance.

Signal processing of Sagnac fiber interferometer used as distributed sensor with wavelets

In this presentation, the universal structure of one-dimensional photonic crystal (1-D PC) is constructed, and its optical transmission properties are analyzed by transfer matrix method (TMM). A case that there are two kinds of medium as a period is studied in detail. It is concluded that the reflectivity in photonic band-gap (PBG) increases with the increasing of periodical number, and the bandwidth of PBG has direct relation with the difference between two kinds of dielectric constant, three methods for extending PBG are discussed. When defect layer is inserted, a defect mode appears in the PBG. The concept of optimal periodical number is presented, and it is found that this optimal periodical number is only relative to the ratio of dielectric constant (K). Using multi-objective optimization method, we educe the curve and equation relation between optimal periodical number and K for the first time. In addition, the change in the number of defect mode with the variation of the defect layer's thickness is analyzed, and it is explained by the theory of F-P cavity.

Analysis and simulation on transmission properties of one-dimensional photonic crystal

The analysis of the group delay ripple (GDR) generated by chirped fiber gratings is developed based on the Fabry-Perot (F-P) resonator. It shows clearly how the GDR is generated and why the periods of GDR varies along the chirped fiber gratings. It could also explain why apodization could suppress the GDR and how apodization affects the chirp of the grating. The theory could be used to devise the apodization of fiber gratings.

The generation of group delay ripple of chirped fiber gratings

Demultiplexing for OTDM networks utilizing a pair of concatenated electroabsorption modulators (EAMs) is presented and demonstrated experimentally. 80Gbit/s OTDM signal is demultiplexed to base rates of 20 and 10Gbit/s with the two EAMs, respectively. The two EAMs combined with a 10GHz clock recovery module based on phase-locked loop is introduced to extract the frame clock from 80Gbit/s OTDM signal. Keywords-optical time division multiplexing (OTDM); demultiplexing;clock recovery (CR), electrical absorption modulator(EAM).

Shuisheng Jian

Papers

Study on the time delay error for 160Gbit/s multiplexer

Signal processing of Sagnac fiber interferometer used as distributed sensor with wavelets

Analysis and simulation on transmission properties of one-dimensional photonic crystal

The generation of group delay ripple of chirped fiber gratings

Clock Recovery and Demultiplexing for 80Gbit/S OTDM System