This PDF file contains the front matter associated with SPIE Proceedings Volume 11435, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

With the rapid growth of some novel services (e.g. video services), the demand for network bandwidth increases dramatically, which induces an intensive desire in allocating network bandwidth with high flexibility and efficiency. However, the traditional wavelength-division-multiplexing (WDM) optical networks lack mechanism to realize dynamic and efficiency resource allocation. Therefore, elastic optical networks (EONs) have been proposed to accommodate diverse services with heterogeneous network bandwidth and many techniques have been introduced into EONs. Among them, advanced reservation (AR) technique, which has obvious advantage in improving networking performance, has attracted growing interest. Thus, some algorithms employing AR technique have been proposed for EONs. In the traditional slack-based AR algorithm, the starting-time of arriving services can be postponed to release any possible conflicts between the AR services and other existing services, so as to increase the success probability of accommodating the arriving services. However, the traditional algorithm neglected spectrum fragments remained in the network. In this paper, we proposed an Invalid Spectrum Rate (ISR) based scheduling with advance reservation algorithm to optimize the starting-time of arriving services with a comprehensive consideration of both the allocated spectrum and the fragmented spectrum in monitoring the usage of the spectrum before services arrive. In addition, a network load threshold is set on the basis of ISR to trigger the postponement of an arriving request, which help reduce the service blocking probability. The performance of the ISR based scheduling algorithm with different thresholds and different delay times are evaluated by comprehensive simulations and implementations. Experimental results verify that a lower network load and service blocking probability can be achieved by the proposed algorithm compared with the traditional AR algorithm.

With the increased quantity of Internet traffic, improving spectrum utilization has become a hot topic in the field of optical communication. However, the traditional wavelength-division-multiplexing (WDM) optical networks assign a constant spectral bandwidth (e.g. 50-GHz) to heterogeneous services and thus have limited flexibility and efficiency in spectrum utilization during service accommodation. In order to improve the efficiency in accommodating diverse services with heterogeneous bandwidth requirements, elastic optical networks (EONs) have been proposed. In these networks, spectrum resources can be allocated to different services flexibly according to their respective bandwidth requirements, so that the flexibility and efficiency of spectrum utilization can be remarkably improved. But the spectrum continuity and contiguity constraints in spectrum allocation may induce some isolated, non-aligned and small-sized spectrum segments, which are known as spectrum fragments. With the accumulation of spectrum fragments, the available spectral resources can be exhausted and the networking performance can be affected. Thus, spectrum fragmentation has become an important issue in EONs, and many algorithms have been proposed to reduce the number of spectrum fragments. Among these proposed algorithms, most of them were focus on the defragmentation along normal working paths for services, which might induce traffic disruption for existing service connections and had limited survivability for transmission failure. In order to alleviate the traffic interruption in spectrum defragmentation and improve the survivability for any link failure in transmission, we propose a spectrum defragmentation algorithm based on path-switching mechanism for 1+1 protection in EONs in this paper. Different from previous protection-path-based defragmentation algorithms, the proposed algorithm employs path-switching mechanism to realize active switching between the working path and the protection path according to the usage of the spectrum in the network, so that the two paths can be regarded as their mutual backup paths in the spectrum defragmentation along each of them. In this way, the protection path cannot only provide the survivability for the working path, but also alleviate the traffic disruption during the defragmentation along the working path, while the working path can alleviate the traffic disruption during the defragmentation along the protection path. Simulation results show that the proposed algorithm can realize low blocking probability with reduced traffic disruption for 1+1 protection in EONs.

Nowadays, with the increasing complexity of network structure and the application of diverse kinds of services, some problems, such as multicast-enabled routing, spectrum allocation and traffic protection, have become complicated in elastic optical networks (EONs). Since the transmission failure in EONs may lead to traffic interruption and thus causes serious economic loss, their ability to provide different modes of transmission, including unicast and multicast transmissions, with survivability is highly desirable. In this paper, aiming at improving the service blocking performance in realizing efficient protection for multicast services in EONs, we propose a leaf-looping based multicast protection algorithm, namely Multicast Protection with Leaf Loops (MPLL), which divides the destination nodes of multicast services into several groups according to their distance and constructs one loop for each group to provide protection for each destination node in the group. In constructing each destination loop, the shortest path algorithm is employed to minimize the cost of each generated loop. Besides, distance-adaptive spectrum allocation strategy is adopted for resource assignment to reduce the spectrum consumption in the proposed algorithm. In the research of protection technology, traditional P-cycle technology is an efficient optical network protection strategy, which has the characteristics of fast loop recovery speed and effective network recovery capacity. However, the P-cycle protection technology is pre-computed, which cannot meet the requirements of dynamic recovery. The leaf loops proposed in this paper are generated dynamically according to the destination nodes generated by each service, and can meet the dynamic business requirements. In addition, under the same blocking conditions, MPLL saves more path resources than P-cycle based algorithms in the protection path. Simulation results show that the proposed MPLL algorithm can realize multicast protection for EONs with low service blocking probability and high flexibility.

Flexible grid optical networks (FGONs), a.k.a. elastic optical networks, have attracted intensive research interest due to its advantage over the traditional wavelength division multiplexing optical networks in accommodating diverse services with high spectral flexibility and utilization efficiency. Sophisticated routing and spectrum assignment (RSA) algorithms are the key enabling technologies to realize the flexibility and the efficiency in FGONs, but most of these RSA algorithms neglected some small-sized, isolated spectral bands generated in the spectrum allocation procedures. These spectral bands, known as spectrum fragments, are caused by the continuity and the contiguity constraints in spectrum allocation and can hardly be utilized by the successive service requests. With the accumulation of spectrum fragments, the available resources of FGONs can be exhausted and their networking performance will be greatly affected. Therefore, spectrum fragmentation has become an important issue in FGONs, and many defragmentation algorithms, including both the preventive and the reactive spectrum defragmentation algorithms, have been proposed to reduce spectrum fragments. In this paper, we will review the current defragmentation algorithms for FGONs and analyze the characteristics of these algorithms first. Given the fact that most of the current defragmentation algorithms were designed for the point-to-point services in FGONs, we will then address the issue of designing the defragmentation algorithms for other kinds of services (e.g. multicast services) in FGONs. After that, we will demonstrate a spectrum defragmentation algorithm for multicast services in FGONs together with its simulation results.

Electro-optic (EO) modulators based on ultrathin silicon were studied by using the finite element method (FEM), the thickness and the width of the thin silicon waveguide core are 60 nm and 1 μm. The impacts of the parameters of the electrode on the electro-optic overlap integral factor was analyzed. The electrode for the TE mode operation were optimized. Results show that gold electrode putting on the oxide buffer at the position of 1.4 μm, and the width of the gold electrode is 10.8 μm can produce a good overlap integral factor as high as 0.6 and the impedance is about 50 Ω.

In this paper, an algorithm based on homomorphic deconvolution is proposed to give an accurate estimation of nonlinear phase in the beat signal in optical frequency domain reflectometry (OFDR). Nonlinearities in the beat signal are obtained by using an auxiliary interferometer. After converting to cepstrum domain and filtering, the nonlinearity can be separated from the beat signal. Then, the deskew filter is used to eliminate the nonlinearity. In the proposed algorithm, no approximations are used, so the estimation is theoretically unbiased. Certain simulations are performed to verify the versatility and effectiveness of the proposed algorithm. The nonlinearities are accurately estimated and eliminated by the method, which improves the spatial resolution of the OFDR system.

In this paper, we proposed a promising nonlinearity (NL) estimation technique based on error vector correlation (EVC) function, which is robust against ASE noise. The method is demonstrated to estimate NL power accurately in 112 Gb/s polarization-multiplexed quadrature phase-shift keying (PM-QPSK) simulation system, 224 Gb/s PM-16-quadrature amplitude modulation (PM-16-QAM) system and 672 Gb/s wavelength division multiplexed (WDM) PM-16-QAM system. For all of these three systems, the maximum estimation error of NL power is lower than 1 dB for 2400 km transmission link with launch power varying from 0 to 8 dBm per channel when the OSNR range used in simulation of QPSK and 16-QAM system are 12 ~ 30 dB and 18 ~ 36 dB respectively.

This study evaluates the polarization state persistence of differently polarized light as they propagate through wet haze (PM2.5), in forward transmission. The investigated wavelength range extends from ultraviolet (UV) to short-wave infrared (SWIR) light. Using a polarization tracking Monte Carlo simulation for a range of particle sizes, wavelengths, relative refractive indices, and propagation distances, we find that both vertically-linearly- and right-handed-circularly-polarized light show superior polarization state persistence at a wavelength of 2.4μm. While the persistence increases gradually for increasing wavelengths, the study also reveals an anomaly, a persistence peak for wet haze with 2μm particles and 0.36μm wavelength. We further compare the polarization state persistence characteristics of vertically linearly and right circularly polarized light. Circular polarization persists better than linear for wet haze in wavelengths of 0.36, 0.543, and 1μm. While with the increase of wavelength and the decrease of particle size, linear polarization gradually persisted better than circular polarization.

We designed an annular blazed grating to achieve maximum optical power in the +1st transmitted order at a fixed diffraction angle. We performed theoretical analysis and simulations on the designed grating, where the incident beam (wavelength: 1550 nm) was perpendicular to the grating surface. The diffraction efficiency in the +1st transmitted order was dependent on the blaze angle (or modulation depth) and period for a refractive index of 1.49. The diffraction efficiency in the +1st transmitted order was maximum (85.94%) at a modulation depth and period of 2.18 μm and 3.96 μm, respectively, and the corresponding diffraction angle was 45.3°.

We present a method for complex spectrum analysis of periodic optical signal with multi-level modulation format. The information of the complex spectrum can be extracted with ultra-low sampling rate in the proposed method, and the temporal information reconstructed by inverse Fourier transform can be used to monitor the performance of the optical signal. Besides, the proposed method is transparent to symbol rate and modulation format. The spectral amplitudes and phases are measured accurately in the simulation based on the proposed method for a 28 GBaud Quadrature-Phase-ShiftKeying (QPSK) signal with a 400-bit pattern and a 28 GBaud 16-Quadrature-Amplitude-Modulation(16QAM) signal with a 560-bit pattern. Moreover, we analyze the performance of the reconstructed signal under different linewidth and optical signal-to-noise ratio (OSNR) by simulation. The Q-factor of the reconstructed 28-GBaud QPSK signal reduces when the linewidth of laser increases and the OSNR of signal decreases.

A broadband THz metamaterial absorber was designed based on the transmission line theory, and the inductive mesh structure was selected as the meta-surface. The absorber samples were fabricated by electrohydrodynamics(EHD)-based printing technology, which is a cost-effective and high-precision technology for flexible electronic device fabrication. The absorption in (98-353) GHz exceeded 90%, and the experimental data matched well with the theoretical and simulation results. It was also proven that the absorption spectra were insensitive to the linewidth and surface resistance of the inductive mesh structure, so that the design has high tolerance to possible fabrication error.

Traditional Visible Light Communication (VLC) based indoor positioning algorithm needs long time for positioning processing. An improved k-means method is presents in this paper which allows the positioning terminal to receive the signal strength information generated by different LEDs, and the improved k-means method is implemented to establish the fingerprint database. The triangle positioning method will be firstly used to roughly determine the position, and then adopt the fingerprint matching method for accurate locating. Simulation results show that compared with the traditional fingerprint-based method, the improved k-means method has improved the computing efficiency of positioning process.

This paper proposes an innovative approach to improve the adjustable bandwidth of the LED, a pre-equalization circuit is used at the end of the transmitting system in the traditional visible light communication system. However, the preequalization circuit causes a large amount of energy loss while increasing the adjustable bandwidth of the LED. To save energy on the pre-equalization circuit, we adopt an advance approach known as, non-orthogonal multiple access (NOMA) [1] in our visible light communication system (VLC). By adopting this method, different signals can be provided by different variation of power with the help of transmitter, without increasing the adjustable bandwidth of the LED. These signals are superimpose in the power domain and after this process signals are transmitted through LED. In the receiver module, serial interference cancellation (SIC) technology is adopted to demodulate these singles. Simulation results will show that our proposed system can save a large amount of energy on the pre-equalization circuit.

This paper presents our recent studies on photonic devices based on antisymmetric Bragg gratings (ASBGs). ASBGs can realize backward mode conversion between the fundamental and first order transverse electric mode, i.e., TE₀ and TE₁. If a π phase shift is inserted in the middle of ASBG, light resonance along with mode conversion can be set up. We call this new resonance as the “Hybrid mode resonance”. Based on this structure, several photonic devices are realized. For example, we experimentally demonstrated an on-chip light filter with dropped reflected light. It can be equivalent to the light circulator in some cases and benefits the application to photonic integrated systems. Besides, other photonic devices such as single wavelength resonator and narrow band reflector are also realized. We think the proposed grating structure may give a new way to design high-performance photonic devices.

A photonics-based inverse synthetic aperture radar (ISAR) for near-field RCS calculation is proposed. The proposed radar implements the function of radar range profile target recognition, 2D ISAR image and near-field RCS calculation. Firstly, a photonics-based ISAR is proposed with a frequency-quadrupled linear frequency-modulated continuous wave (LFMCW) signal covers 18-26 GHz. A 2D ISAR image with 2 cm*2 cm resolution is obtained. Secondly, a method of calculating the RCS from the ISAR image is also proposed. According to the Parseval theorem, by summing the pixel values of target area 2D ISAR image and multiplying by the scaling factor, the mean RCS value of target in the radar working band can be obtained. In the experimental demonstration, the standard metal spheres with diameters of 10 cm, 15 cm and 20 cm are tested 1.2 m away from the radar. The testing results show that the difference between the RCS test value and the theoretical value is less than 1.31 dB.

The sixth generation of mobile communication (6G) represents the future of wireless communication development, which will introduce many new services and applications. Next generation optical network will introduce Artificial Intelligence (AI) based technology including traffic classification, prediction, virtual topology design, path calculation, etc. It is possible to introduce a new joint space-time-spectrum software definition network (STS-SDN) and multi-dimensional space cloud architecture for 6G oriented next generation optical networks. It will realize coordinated resource optimization in multiple dimensions such as space, time, frequency, and polarization domain under the support of multi-core, less-mode, polarization multiplexing and spectrum slicing in the physical layer.

A combined routing and core-spectrum assignment (RCSA) scheme is proposed for spatial division multiplexing elastic optical networks (SDM-EONs). The improved algorithm will evaluate resource availability based on existing link status and select suitable core combination for transmission. The service requirements will be reasonably allocated spectrum resource depending on the assessment of the crosstalk effects between different cores and frequency spectrum availability. Simulation results show that the proposed algorithm can improve both the resource utilization and blocking probability compared with traditional algorithms.

Network function virtualization (NFV) is a promising technology that has attracted much attention in both academia and industry. With IT resource virtualization, NFV paradigm could decouple network functions (NFs) from special-purpose hardware equipment, providing more flexibility to network service providers and facilitating a better sharing of physical infrastructure when implementing NFs. Meanwhile, with the introduction of flexible-grid elastic optical networks (EONs) and virtualized transponders (vTPs), a new concept of resource virtualized elastic optical networks (RvEON) is emerged in this context, which has not only realized link-tier spectrum virtualization in each fiber link, but also realized node-tier TP virtualization within each substrate node. In this paper, we for the first time study how to implement efficient virtual network function service chaining (VNF-SC) in inter-DC RvEONs, taking into account subcarrier and modulation resources of the vTPs equipped in network nodes, in addition to fiber-link spectrum and IT resources. First, an integer linear programming (ILP) model for the VNF-SC deployment problem is formulated for jointly allocating these multi-dimensional resources. Then, for scalability, we also propose a heuristic based on Maximum Reuse with Decentralization Principle (MR-DP). The main idea behind the heuristic is that deploying the VNFs in a much more load-balanced manner can facilitate to maximize reuse the most existing VNFs to save the IT resources. The simulation results indicate that the proposed MR-DP heuristic can allow the minimum number of the deployed VNFs, while consuming the similar amount of other resources, compared with other two benchmark schemes.

NIM has built three cesium fountain clocks in Beijing area. NIM5 fountain clock has been reported to BIPM since 2014. The microwave synthesizer and computer control system of NIM5 had been modified recently. The type-B uncertainty is 9×10⁻¹⁶, limited by the interferometric switch in the microwave chain. NIM5-M has been sent to 32 km away from NIM and compared with NIM5 via fiber link. The new NIM6 fountain clock has been built and evaluated, the results are presented in the paper. The direct comparison of NIM5 and NIM6 has also been done, a relative frequency difference of 4.4×10⁻¹⁶ was obtained for 20 days averaging time, consistent with the total uncertainty of the two clocks.

According to TWSTFT, two way optical fiber time and frequency transfer(TWOTFT) was designed.TWOTFT in real time based on the instant exchange of time transfer data via optical fiber was implemented. One kind of time and frequency standard disciplined by UTC(NIM) (National Metrology Primary Standard of China), called NIMDO, was constructed using TWOTFT for accurate and precise time synchronization, whose time difference from UTC(NIM) could be less than 1 ns, which is much better than NIMDO via GNSS (Global Navigation Satellite System) time transfer method (based on GPS (Global Positioning System) time transfer).