This PDF file contains the front matter associated with SPIE Proceedings Volume 8389, including the Title Page, Copyright information, Table of Contents, Authors, Introduction (if any), and Conference Committee listing.

In future optical networks, versatile functionalities will be required for the optical network subsystems to fully utilize the spectral resources with low energy consumption. The key technologies are the spectral efficient MUX/DEMUX technique and flexible control of optical channels with high frequency granularity. An orthogonal frequency division multiplexing (OFDM) and Nyquist wavelength division multiplexing (N-WDM) are the most promising candidates of spectral efficient multiplexing techniques, and all-optical (AO) processing is expected to reduce the energy consumption. In an AO-OFDM systems, discrete Fourier transform (DFT) and inverse DFT (IDFT) are performed in optical domain by specially designed arrayed waveguide gratings (AWGs). In our experiment, 12.5 GHz spaced AO-OFDM system has been successfully demonstrated with no guard interval. In N-WDM systems, the Nyquist signal is generated by using carrier-suppressed return-to-zero (CS-RZ) signal and optical Nyquist filtering, which is achieved with two flat-top AWGs and optical interleaver, and the 25 Gbaud signals are successfully multiplexed in the experiment. Although both AO-OFDM and N-WDM can achieve the highest spectral efficiency, N-WDM is more suitable for flexible optical networks. This is because the N-WDM channels have less spectral overlap with the other channels than AO-OFDM, owing to its rectangular shaped compact spectrum. Therefore, N-WDM channel can be easily multiplexed and demultiplexed by optical filters. At an optical network node, channel defragmentation is indispensable technology to flexibly control the optical channels. We have experimentally demonstrated a format independent optical channel defragmentation with N-WDM signal. We believe these technologies are promising for future flexible optical networks.

A multicore fiber (MCF)-based mode multiplexer/demultiplexer (MUX/DEMUX) that can overcome the alignment issue of the fiber-based mode MUX/DEMUX is proposed. Design concept and fabrication results of the MCF-based mode MUX/DEMUX for two-spatial-mode operation (LP₀₁ and LP₁₁) (2M-MUX/DEMUX) and for three-spatial-mode operation (LP₀₁, LP_11a, and LP_11b) (3M-MUX/DEMUX) are presented. The fabricated 2M-MUX/DEMUXes for C-band or L-band, using the same MCF with different elongation ratios demonstrate a coupling efficiency of greater than 90% over each band. Finally, a 3M-MUX/DEMUX with a fan-in/fan-out device is presented. The selective excitation of LP₀₁, LP_11a, and LP_11b modes depending on input ports is experimentally demonstrated.

Recently, few-mode fiber (FMF) based mode division multiplexing (MDM) transmission together with multi-input multi-output (MIMO) signal processing technique is ideal candidate to solve future single mode fiber (SMF) capacity crunch. Most existing mode division multiplexers/demultiplexers (MMUX/DEMMUX) have a specific mode orientation for high-order non-circular symmetric mode. Taking the phase plate based DEMMUX as example and converting LP₁₁ mode to fundamental LP₀₁ mode, we need optimize input mode orientation the same as the phase pattern of phase plate. In this submission, we propose and experimentally demonstrate a spatial mode rotator based on mechanically induced twisting and bending in a step-index FMF. We theoretically find that the mode coupling strength between vector modes with similar propagation constants is determined by the FMF bending and twisting. When the input LP₁₁ mode cluster including TE₀₁, HE2_1a, HE_21b, and TM₀₁ mode are properly perturbed, the output optical field is superposed as LP₁₁ mode with a rotation. Therefore, the proposed spatial mode rotator is composed of three FMF coils with a radius of 16 mm, while the number of each coil is 2, 1, and 2, respectively. Consequently, we are able to rotate the LP₁₁ mode with arbitrary angle within 360° range using the same conventional configuration of polarization controller (PC). The insertion loss of proposed spatial mode rotator is less than 0.82 dB, when the operation wavelength varies from 1540 nm to 1560nm. In particular, from the measured mode profile, there exists little crosstalk between LP₀₁ mode and LP₁₁ mode during mode rotation operation.

We discuss a parallel-configuration-free architecture for a photonic ADC from the view point of power consumption and briefly review and introduce our proposed approach as a typical example and current state-of-the-art experimental results.

We report a six mode spatial multiplexer with high efficiency and high mode selectivity, based on the technique of Multi-Plane Light Conversion (MPLC). Using this mode selective multiplexer, we demonstrate a total insertion loss in a six-mode fiber below 5 dB and a mode-to-mode selectivity greater than 20 dB over a broad wavelength range from 1530 to 1565 nm. Furthermore, this device can address any spatial mode profile of any few-mode fiber with high fidelity. This mode-multiplexer proves to be fully compatible with a wavelength- and space-division multiplexed optical transmission line.

As the bit rates of routed data streams exceed the throughput of single wavelength-division multiplexing channels, spectral and spatial traffic aggregation become essential for optical network scaling. These aggregation techniques reduce network routing complexity by increasing spectral efficiency to decrease the number of fibers, and by increasing switching granularity to decrease the number of switching components. Spectral aggregation yields a modest decrease in the number of fibers but a substantial decrease in the number of switching components. Spatial aggregation yields a substantial decrease in both the number of fibers and the number of switching components. To quantify routing complexity reduction, we analyze the number of multi-cast and wavelength-selective switches required in a colorless, directionless and contentionless reconfigurable optical add-drop multiplexer architecture. Traffic aggregation has two potential drawbacks: reduced routing power and increased switching component size.

A wavelength cross-connect switch (WXC) is proposed and demonstrated. The cross-connect optics have orthogonal imaging systems that operate differently in the switching and spectral planes. The switching plane has 2f Fourier optics with a Rayleigh length. On the other hand, the spectral plane has 4f imaging optics. Two types of switching engines, microelectromechanical system (MEMS) mirrors and liquid crystal on silicon (LCOS), are applied for the same cross-connect optics. The 5×5 WXC with MEMS mirrors has a 100 GHz channel spacing, which is compatible with the International Telecommunication Union (ITU) grid. On the other hand, the WXC with LCOS has a variable channel spacing. The characteristics of two types of WXC are compared. In addition, the port count, which is one of the important parameters, is discussed.

High-capacity fiber-optic communications are promising technologies to satisfy people’s continuously growing demands for bandwidth hungry data services. Multi-wavelength optical circuit switching (OCS) technology is already widely deployed, however, with the limited number of transceivers equipped at each optical node and other constraints, the number of lightpaths which can be established and employed simultaneously in an optical network is restricted. This reduces the utilization efficiency of wavelength resources. Comparing to OCS, dynamic optical switching systems such as optical packet switching (OPS) offer higher efficiency in terms of wavelength resource utilization and have the potential to share more of the wavelength resources on fiber-links between larger numbers of users simultaneously. In such networks, bursty input signals or changes in traffic density may cause optical power surges that can damage optical components or impose gain transients on the signals that impair signal quality. A common approach for reducing gain transients is to employ electrical automatic gain control (AGC) or optical gain-clamping by optical feedback (OFB). AGC may be limited by the speed of the feedback circuit and result in additional transients. Meanwhile OFB can clamp the gain of power varying optical signals without transient but can introduce amplitude fluctuations caused by relaxation oscillations in the lasing cavity for large input power fluctuations. We propose and demonstrate a novel scheme for suppressing the power transients and the relaxation oscillations. This scheme can be utilized in optical amplifiers even if the optical feedback is employed.

In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using Wavelength Division Multiplexing-Nyquist (WDM-Nyquist) and Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) approaches with 12.5 GHz channel spacing. We evaluate through simulation the performance of the two techniques for generating Dual Polarization Quadrature-Amplitude Modulation based on 16 (DP-16QAM). We first study the robustness of CO-OFDM system to the receiver constraints such as Analog-to-Digital Converters (ADCs) speed and the receiver bandwidth in Back-to-Back link (Optical Signal-to- Noise Ratio (OSNR)) and over longhaul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that CO-OFDM requires 6 Samples per Symbol (SpS) with a large receiver bandwidth (2.25× Baud rate) to achieve the same performance of WDM-Nyquist system in terms of SNR. However, the CO-OFDM system needs more than 6 SpS to achieve the same distances as WDM-Nyquist. We also study the impact of the input power level in terms of OSNR for CO-OFDM and WDM-Nyquist systems in order to evaluate the robustness of both systems to the nonlinear effects.

Unrepeatered transmission systems provide a cost-effective solution to transmit high capacity channels in submarine networks to communicate between coastal population centers or in terrestrial networks to connect remote areas where service access is difficult. The main goal of unrepeatered systems has traditionally been to achieve the longest reach, however, increasing traffic demands now require unrepeatered systems to support both longer reach and higher transport capacity. As a result, transmission rate of unrepeatered systems has quickly moved from 10 Gb/s to 40 Gb/s or 100 Gb/s. This paper reviews the key basic technologies, with a specific focus on Raman amplification, required for long-reach, high-capacity unrepeatered optical transmission systems. We will discuss novel Raman amplification schemes, enhanced remote optically pumped amplifiers (ROPA), ultra-low loss / large effective area fibers, and coherent transmission with advanced modulation format and high FEC coding gain. We will also report recent experimental demonstrations that show how these technologies have been combined to achieve industry’s leading capacity and reach transmission.

In this paper, we present a novel technology for photonic cross-connect (PXC) in spatial mode domain for the realization of advanced and flexible optical transmission of spatial modes. The PXC is a kind of all -optical devices to switch highspeed optical signals for mode-division multiplexing (MDM) network and it is able to perform signal labeling in the spatial mode domain similar to current photonic switching in the wavelength domain. In addition, parallel and simultaneous mode conversion can be realized using multiplex holograms in a photorefractive crystal (PRC). In our experiment, during the recording process, a rewritable hologram is recorded in the PRC (LiNbO₃) through the interference between the signal beam with certain input mode and the reference beam with the phase distribution of the desired output mode. Signal beams are generated by computer generated hologram (CGH) using a spatial light modulator (SLM) instead of an optical fiber emergent beam, and reference beams are generated by phase only modulation using another SLM. Subsequently, during the converting process, the input signal beam is converted into the desired output mode through the holographic diffract ion in the crystal and free-space propagation by an optical lens. By using phase code multiplexing method, parallel mode conversions can be realized. We performed an experiment on parallel mode conversions of several different conversion pairs. Signal beams and reference beams intersected in the PRC with an angle of 18.43 degree. The intensity distributions of converted modes were observed by CCD camera set on the Fourier plane. We confirmed that the two modes inter-conversion of LP11 with LP21 was successfully implemented.

Digital nonlinear compensation techniques have been thought to be keys to realize further spectrally efficient optical fiber communication systems. The most critical issue of the digital nonlinear compensation algorithms has been their computational complexity, or gate count of digital signal processing circuit. Among several approaches, digital nonlinear compensation algorithms based on perturbation analysis are attractive in terms of the hardware efficiency because the algorithms can compensate the accumulated nonlinear noise over all transmission spans with only one stage. In this paper, we discuss three approaches to sophisticate the perturbation nonlinear compensation. First, we illustrate a perturbation-based post-equalization method to improve the robustness to transceiver device imperfections. We next propose and numerically evaluate a symbol degeneration method to extend the perturbation nonlinear compensation methods to higher-order QAM without increasing the computational complexity. Finally, we discuss a sub-band processing of perturbation nonlinear compensation for further computational complexity reduction. By combining the perturbation method with Nyquist frequency division multiplexing, the computational complexity of perturbation calculation is reduced by a factor of more than 10 for 3000-km single-channel transmission of 128 Gbit/s dualpolarization QPSK with only 0.1 dB performance degradation.

We demonstrate an integrated-optic device for multiplexing an OFDM signal based on optical IFFT. The silica waveguide-based multiplexer is composed of four inputs followed by mutually connected directional couplers, an array of delay lines, and a combiner. Four signals modulated with different sequences of data are fed into the multiplexer, and an optical OFDM signal is generated through the IFFT process directly in the optical domain. We report the configuration, operating principle, and experimental results to indicate that the multiplexer operates properly. We successfully generated 40 and 80 Gbit/s OFDM signals with the multiplexer.

Fiber nonlinearity and equalization-enhanced phase noise (EEPN) generate rapid perturbations and critically limit the system capacity and range of long-haul optical transmission. It is possible to cancel the rapid perturbations by introducing a particular correlation between multiple signals at the transmitter and analyzing the received signals using digital signal processing. In this paper, we review our proposed techniques to cancel rapid perturbations of polarization multiplexed signals due to fiber nonlinearity and EEPN. Numerical simulation of quaternary phase-shift keying based signals shows 1.2 dB and 0.5 dB improvement respectively from the proposed cancellation techniques for fiber nonlinearity and EEPN.

Recently, offset-QAM based coherent WDM (CoWDM) has been proposed to build up spectrally-efficient multi-carrier superchannels. Compared with Nyquist wavelength division multiplexing (N-WDM) and orthogonal frequency division multiplexing (OFDM), offset-QAM based CoWDM can relax the stringent transmitter-side requirements for spectrum shaping and achieve significant transmission performance improvement. In order to efficiently utilize the sampling rate of commercially available analog-to-digital converter (ADC) and decrease the receiver-side implementation complexity, multi-carrier group detection scheme is investigated in offset-QAM based CoWDM where multiple carriers are simultaneously detected within single coherent receiver, followed by carrier separation in the digital domain through the 4-point discrete Fourier transform (DFT) method at the baseband. Here, we demonstrate a transmission of five-carrier 100 Gb/s polarization-multiplexed offset-16QAM signal with 12.5 GHz channel spacing. Through 3-carrier group detection, the sampling rate per-carrier is reduced to 1.33 times symbol rate in terms of 50 GS/s ADC and there is only 0.35 dB required OSNR penalty at BER=10^-3 compared with conventional single channel coherent detection. Meanwhile, good tolerance of coherent receiver analog bandwidth is secured and receiver bandwidth is reduced to 8 GHz. Moreover, 0.5 dB required OSNR penalty at BER=10^-3 is obtained given 18 GHz ADC bandwidth. Besides, we find that side carriers suffer from severer performance degradation than the central carrier with limited ADC resolution and only 0.08 dB and 0.2 dB required OSNR penalty at BER=10^-3 are secured with 6 bits ADC resolution for central carrier and side carriers, respectively.

A novel fiber characterization technique is introduced that combines two holographic procedures for selective fiber-mode excitation and complete fiber-mode analysis. The fiber’s transmission matrix is constructed by directly measuring the response of the excited modes in terms of the entire guided mode spectrum. By applying a spatial multiplexing scheme for the modal decomposition, the transmission matrix is rapidly determinable, whereas the amount of needed measurements is proportional to the number of guided modes. Our technique characterizes the impact of the fiber on the mode signals and enables the investigation of underlying physical effects as well as signal correction schemes.

In multi mode optical fibers degenerated modes occur, which cannot be discriminated by their propagation properties. Hence, in principle any arbitrary superposition of these degenerated modes can be used to build an equivalent set of modes. In a perturbed system this degeneracy can be broken, and as a consequence -not every superposition represents real modes of the fiber. In mode division multiplexing system this leads to high inter-modal crosstalk, if unsuitable (initially degenerated) modes are chosen. Based on the analysis of the fiber’s transmission matrix, we present a measurement scheme to prove degeneracy breaking and to identify physical non-degenerated modes.

This work reviews the latest advancements in coherent self-homodyne detection (SHD) using signals with polarizationor space-multiplexed pilot tones (PTs) originating from the same light source, towards the implementation of low-cost coherent receivers. The coherency between signals and PTs drastically reduces laser linewidth requirements, enabling the use of high-order modulation formats with low-cost DFB lasers. In this work, we revise the application of SHD in high-capacity space-division multiplexed links using multi-core fibers, outlining optical signal-to-noise ratio, skew and phase noise requirements of such systems. Furthermore, we evaluate the application of SHD for the implementation of laser-less optical network units in passive optical networks, as well as recent developments in digital SHD techniques.

Exponentially expanding various applications in company with proliferation of mobile devices make mobile traffic exploded annually. For future access network, bandwidth efficient and asynchronous signals converged transmission technique is required in optical network to meet a huge bandwidth demand, while integrating various services and satisfying multiple access in perceived network resource. Orthogonal frequency division multiplexing (OFDM) is highly bandwidth efficient parallel transmission technique based on orthogonal subcarriers. OFDM has been widely studied in wired-/wireless communication and became a Long term evolution (LTE) standard. Consequently, OFDM also has been actively researched in optical network. However, OFDM is vulnerable frequency and phase offset essentially because of its sinc-shaped side lobes, therefore tight synchronism is necessary to maintain orthogonality. Moreover, redundant cyclic prefix (CP) is required in dispersive channel. Additionally, side lobes act as interference among users in multiple access. Thus, it practically hinders from supporting integration of various services and multiple access based on OFDM optical transmission In this paper, adaptively modulated optical filter bank multicarrier system with offset QAM (AMO-FBMC-OQAM) is introduced and experimentally investigated in uplink optical transmission to relax multiple access interference (MAI), while improving bandwidth efficiency. Side lobes are effectively suppressed by using FBMC, therefore the system becomes robust to path difference and imbalance among optical network units (ONUs), which increase bandwidth efficiency by reducing redundancy. In comparison with OFDM, a signal performance and an efficiency of frequency utilization are improved in the same experimental condition. It enables optical network to effectively support heterogeneous services and multiple access.

In this works, we have demonstrated a VOA integrated with mPDs, based on silica-on-silicon PLC and flip-chip bonding technologies. The suspended ridge structure was applied to reduce the power consumption. It achieves the attenuation of 30dB in open loop operation with the power consumption of below 30W. We have applied two-step flipchip bonding method using passive alignment to perform high density multi-chip integration on a VOA with eutectic AuSn solder bumps. The average bonding strength of the two-step flip-chip bonding method was about 90gf.

Knowledge of fiber devices ageing is one of necessary conditions for successful applications of fiber communication systems into hard environmental surrounding and for application of fiber sensors. This paper deals with finding of typical ageing markers during the process of accelerated ageing.