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We experimentally demonstrate a novel ultrabroadband and wide-angle unidirectional coupling scheme by combining the coupling effect of single nanoslit and chirped grating effect. The operation principle is numerically and experimentally clarified through analysis and compare. Numerical analysis shows that the fabricated chirped-nanoslits grating could unidirectionally couple surface plasmon polaritons from free-space light over an ultrabroadband (1.3 $\mu$ m) and wide-angle ( ${\text{30}}^{\circ }$ ) ranges. Excellent unidirectional coupling performance with extinction ratio ER $>10$ dB (a peak value ER = 22 dB) over an ultrabroad operating bandwidth of 300 nm and wide angular range of ${\text{26}}^{\circ }$ is experimentally demonstrated.

An efficient and unidirectional optical coupling scheme for metal-dielectric-metal (MDM) waveguides with wide-angle and ultra-broadband efficiency is proposed and demonstrated. Based on joint effects of the plasmonic critical angle phenomenon (PCA), the zero-order grating resonance, and the first-order Fabry–Perot (FP) resonance of the MDM waveguide, the illuminated light could be efficiently coupled into MDM plasmonic waveguide with angular-full-width-half-maximum (AFWHM) widen to 50° over a broad wavelength range 750–1000 nm. The operation principle and performance of the structure are clarified and theoretically illustrated.

A new coupling scheme for unidirectional coupling of surface plasmons from free-space light over a broad-angle range is proposed and theoretically investigated. Firstly, the property of strong asymmetric excitation is found in the single wide defect, especially the single dielectric ridge, which is due to the excitation of asymmetric mode in the wide defect under oblique incidence. Then we show that the strong asymmetric excitation by single ridge still exists in the periodic dielectric ridge grating. By cascading the asymmetric mode excitation peak and the grating resonance angle peak, the angular-full-width-half-maximum (AFWHM) is broadened to $39^\circ$ . Finally, the AFWHM is further broadened to $52^\circ$ by utilizing the chirped ridge grating and a remarkable property of wide flat-top angular response is achieved.

An efficient plasmonic dichroic splitter based on periodic metallic nanoslits milled in the metal–dielectric–Si hybrid plasmonic waveguide is proposed and investigated. The backside incident photons illuminated on the dichroic splitting structure are coupled and launched into the hybrid plasmonic modes propagating to the left- or right-side depending on the wavelength. Proof-of-principle demonstrations show that the good coupling and splitting performances with coupling efficiency 0.5 and high splitting ratios 26.4 dB at wavelength 1310 nm (right:left power contrast), and 0.46 and 21.7 dB at wavelength 1550 nm (left:right power contrast) are achieved, respectively. The operation principle is clarified and the performance is discussed.

A compact unidirectional plasmonic coupler based on asymmetric cascaded nanoslits is proposed and theoretically analyzed. The incident photons illuminated on the structure are unidirectionally coupled into the metal–insulator–metal waveguide. The operation principle is clarified and a universal theoretical model based on coupled-mode equations is developed to facilitate structure design. Proof-of-principle demonstrations show that an ultrahigh extinction ratio ER $= 43.8$ dB at a specific wavelength and broadband of 160 nm covering a wide angular range from −20° to 15° with ER ≥ 10 dB are achieved.

A compact ultrabroadband coupling and binary encoding structure based on an array of aperiodic nanoslits cascaded by two different pairs of grooves in a metallic-dielectric-air waveguide is proposed and theoretically analyzed. The nanoslits array function as a broadband antenna to couple the incident lights into surface plasmon polaritons (SPPs) over an ultrawide wavelength range (spectral full-width-half-maximum >430 nm). The two ports composed of different grooves exhibit different transmission for the coupled multiwavelength SPPs. After traveling through different ports, the incident lights dropping in different wavelength ranges are differentiated and endowed with different logic state encodings. The operation principle is clarified and a coupled-mode model is developed for facilitating design.

A new scheme for unidirectional coupling of surface plasmon polaritons (SPPs) from freely propagating light into a metal-insulator-metal waveguide is proposed, which is composed of an asymmetric double-slit of different widths sandwiched by symmetric grooves. A theoretical model based on coupled-mode equations is developed to facilitate structure design and elucidate the underlying physical mechanism. With the model, the asymmetric double-slit with different widths is designed for unidirectional launching of SPPs with an ultrahigh extinction ratio of 44.8 dB at the wavelength 800 nm. A method of stepwise design is proposed for simplicity of design and convenience of analysis. Proof-of-principle demonstrations show that an ultrahigh extinction ratio of 37.1 dB and significant field enhancement for the proposed whole structure are obtained. In addition, an ultracompact plasmonic dichroic splitter based on the asymmetric double-slit with high extinction ratios of 24.2 and $-$ 21.8 dB at splitting wavelengths of 800 and 900 nm is achieved, and the lateral dimension of the plasmonic dichroic splitter is only 760 nm.

Although the surface Plasmon resonance (SPR) sensor is a mature technology, currently, the sample temperature needs to be carefully considered and controlled because SPR signals vary with temperature. This poses a large challenge in the applications where the sample temperature changes during measurement or an SPR sensor operates in different environmental temperatures. This paper proposes and experimentally demonstrates, for the first time to our knowledge, a solution to simultaneously measuring refractive index and temperature based on conventional SPR sensors, thus, not only requiring no temperature control/calibration during the measurement but also enabling SPR sensors for in-situ operations.

We propose and numerically investigate a plasmonic triple-wavelength demultiplexing structure based on metal-insulator-metal waveguides with side-coupled nanodisk cavities. The structure consists of three output channels, each of which is sandwiched by two nanodisk cavities and functions as a dual stop-band filter. The operation principle and transmission characteristics are analyzed by using the temporal coupled-mode theory and the finite-difference time-domain method. Simulation results show that the demultiplexed wavelength of each channel can be effectively tuned by adjusting the geometrical parameters of the structure. The proposed structure will find potential applications in photonic-integrated circuits and ultracompact optical communication systems.

A new bidirectional polarization splitting coupler based on a metal thin film perforated with periodic slits and coated with dielectric is proposed and theoretically investigated. The back-side incident light coupled to the metal-dielectric-air waveguide is split and launched into TM plasmonic and TE photonic modes simultaneously. The operation principle is clarified and theoretically illustrated using the fully vectorial aperiodic Fourier modal method. Polarization extinction ratios better than 15 dB and crosstalk less than 15 dB are achieved for both polarizations over C-band ranging from 1530 to 1570 nm.

A compact plasmonic wavelength demultiplexing structure based on arrayed metal–insulator–metal (MIM) plasmonic nano-disk cavities is proposed and numerically investigated by utilizing finite-difference time-domain (FDTD) method. The structure consists of a bus waveguide perpendicularly coupled with a series of nano-disk cavities through slit-waveguides. A model based on resonator theory is used to design the operating wavelength of the structure. Simulation results show that compared with the directly side-coupled nano-disk structure, the narrower transmission linewidth of each channel could be obtained through the coupling between fore-end slit-waveguide and nano-disk cavity. The transmission wavelength and bandwidth of the structure can be tuned by adjusting the geometrical parameters and the refractive index of cavities. The proposed structure will be useful in ultra-compact optical devices for optical communications and computing.

We theoretically investigate a widely-used plasmonic structure composed of a nano-slit aperture surrounded by surface corrugations. A systematical semi-analytical theory in form of two nested coupled-mode models is developed to provide intuitive physical pictures. Based on the theory, figures of merit (FoMs) of the structures designed for normal and for oblique incidence/beaming are defined for the first time to incorporate the interlinks among key structural parameters, making global optimization simple and efficient. Both the theory and the FoMs are quantitatively validated with exhaustive calculations and shown to be highly accurate on performance prediction and structural optimization. With the theory and the FoMs, an efficient, effective and standard recipe is introduced for optimal structure design. We believe this work will help to understand the mechanisms of and to facilitate the design of such a structure in various configurations used in various applications.

In wavelength division multiplexed optical networks each connection is assigned a light-path. Given a set of connection requests, how to set up a light-path for each of them is called the static routing and wavelength assignment (RWA) problem. The physical networks impose significant effects on the number of wavelengths required to accommodate all the connections as light-paths are directly set up on it. Wavelength requirements in the small-world and scale-free networks are investigated in this paper for the first time to the best of our knowledge. The two important characteristics of networks are considered: average shortest path length and 1-shell structure. Wavelength requirements in the case of network evolution are investigated, too. Mean light-path length is proved to be directly proportional to the average shortest path length of networks. Simulation results have shown that fewer wavelengths are required in networks with smaller average shortest path lengths, and the rate of increase of the number of wavelengths required is smaller too while traffic load and network size increasing. The emergence of 1-shell structure may result in the increase of the number of wavelengths required due to lack of flexibility in 1-shell structure. The larger the cardinality of 1-shell is, the more wavelengths the network requires.

We propose a hybrid C-band erbium-doped fiber amplifier (EDFA) and L-band Raman fiber amplifier (RFA) using a single pump laser diode. The optimum pump sharing ratio to EDFA/RFA is 1/10 with a total pump power of 660 mW. Using multiple fiber Bragg gratings (FBGs) with various reflectivities at different positions along the dispersion compensation fiber, the optimum dispersion compensation and power equalization for C + L-band channels are simultaneously realized. With an input power of −20 dBm/ch, the signal power variation among the channels is reduced from 9.8 dB to less than ±0.5 dB. Two pump reflectors are introduced to increase the pumping efficiency.

The wide field-of-view (FOV) optical receiver has many advantages in optical wireless communication, sensing and detection. However, the FOV is limited by some tradeoffs of the receiver’s components employing conventional optical devices. Furthermore, present mechanisms to extend the FOV are not effective. To realize the wide FOV receiver effectively, we propose surface plasmon polaritons (SPPs) as the potential candidate. Two examples are presented to lively illustrate SPPs’ striking power to offer unexpected solutions to conventional problems. It is shown that unusual conditions should be explored to make use of SPPs under some circumstances. Excitations of localized SPPs, which are independent of the incidence angle, are suggested as the mechanism for the wide FOV receiver. Some progress in the optimization of SPPs’ excitation at oblique incidence is also reported.

In future high-capacity wavelength division multiplexed (WDM) optical networks, the failure of a network component such as a fiber link can lead to severe disruption in the networks’ traffic. Hence, it is imperatively important to provide fast and full protection in WDM optical networks. In this paper, we propose a new approach, called shared preconfigured protection cycles (shared-p-cycles), for the design of survivable WDM networks. We develop an integer linear program (ILP) formulation to solve the problem of shared-p-cycles design for WDM networks with and without wavelength conversion. Numerical results show that the shared-p-cycles design is more efficient in the use of spare capacity and requires much less spare capacity than the conventional p-cycles design.

A novel nonlinear electrical equalizer (NLEE) based on Volterra theory is proposed for mitigating intra-channel nonlinearities in pseudo-linear coherent optical communication systems. According to the temporal matching condition of intra-channel nonlinear pulse interactions, we just select specific nonlinear terms and reduce the computation complexity considerably. Numerical simulations of 10GBaud coherent quadrature phase-shift keying (QPSK) transmission show that the simplified NLEE can efficiently mitigate intra-channel nonlinearities.

Electrical post-compensation of intrachannel nonlinearities in 10GBaud coherent QPSK transmission systems is proposed. The channel inversion method is implemented with a coarse split-step Fourier algorithm through digital signal processing at the receiver side. Simulation results show that simultaneous compensation of intrachannel nonlinearities and chromatic dispersion can be achieved with much simplified signal processing structure. The required optical signal-to-noise ratio at certain bit error ratio is remarkably reduced when the intrachannel nonlinearities induced impairments are dominant.

In transport control protocol (TCP) over optical burst switching (OBS) networks, TCP window size and OBS parameters, including assembly period and burst dropping probability, will impact the network performance. In this paper, a parameter window data dropping probability(WDDP), is defined to analyze the impact of the assembly and the burst loss on the network performance in terms of the round trip time and the throughput. To reduce the WDDP without introducing the extra assembly delay penalty, we propose a novel TCP window based flow-oriented assembly algorithm dynamic assembly period (DAP). In the traditional OBS assembly algorithms, the packets with the same destination and class of service (CoS) are assembled into the same burst, i.e., the packets from different sources will be assembled into one burst. In that case, one burst loss will influence multiple TCP sources. In DAP, the packets from one TCP connection are assembled into bursts, which can avoid the above situation. Through comparing the two consecutive burst lengths, DAP can track the variation of TCP window dynamically and update the assembly period for the next assembly. In addition, the ingress node architecture for the flow-oriented assembly is designed. The performance of DAP is evaluated and compared with that of fixed assembly period (FAP) over a single TCP connection and multiple TCP connections. The results show that DAP performs better than FAP at almost the whole range of burst dropping probability.

We propose an all-optical modulation formats combination scheme that merges an amplitude-shift keying (ASK) signal and a differential phase-shift keying (DPSK) signal into a single differential phase amplitude-shift keying (DPASK) signal based on parametric amplification in a highly nonlinear fiber. By optimizing the power of the ASK channel, formats combination of ASK and DPSK to DPASK signal is successfully demonstrated by computational simulation. The demodulation process of the generated DPASK pulses is investigated and the relationship between optical signal-to-noise ratio (OSNR) penalty and the input ASK power is presented. The proposed scheme may be used for increasing spectral efficiency and all-optical logic device.

We present the principle of cascade arrangement of irregular optical phased arrays. The optical phased-array beam deflector comprises arrayed optical waveguides that are spaced irregularly and arranged in a two-stage cascade. Relations between optical path differences and corresponding center-to-center spacings among elements in each stage are found, and phase matches between the two stages are achieved. Simulation shows a wide scanning angle with dramatically suppressed sidelobes.

We propose a simple and stable structure to realize a tunable negative coefficients microwave photonic notch filter. A 3 × 3 coupler based Sagnac loop interferometer with an asymmetrically placed phase modulator is used to acquire the notches. Our system is simply implemented and with good stability. Theoretical analysis and experimental results are presented and show a good agreement. The structure is proved to be a robust filter with more than 35 dB rejection deep notches.