Making Path Selection Bright: A Routing Algorithm for On-Chip Benes Networks

Vertical stacking is a novel technique for creating nonblocking (crosstalk-free) optical multistage interconnection networks (MINs). In this paper, we propose a new class of optical MINs, the vertically stacked Benes (VSB) networks, for crosstalk-free realization of permutations in a single pass. An N x N VSB network requires at most O(N log N) switching elements, which is the same as the Benes network, and much lower overall hardware cost than that of the existing optical MINs built on the combination of horizontal expansion and vertical stacking of banyan networks, to provide the same crosstalk-free permutation capability. Furthermore, the structure of VSB networks provides a more flexible way for constructing optical MINs because they give more choices in terms of the number of stages used in an optical MIN. We also present efficient algorithms to realize crosstalk-free permutations in an N x N VSB network in time O(N log N), which matches the same bound as required by the reported schemes.

Scalability analysis methodology for passive optical interconnects in data center networks using PAM

A new parallel algorithm for route assignment in Benes-Clos network is studied. In packet switching systems, switch fabrics must be able to provide internally conflict-free paths simultaneously and to accommodate packets requesting for connections in real-time as they arrive at the inputs. Most known sequential route assignment algorithms, such as the looping algorithm for Benes (1962) networks or Clos (1953) networks, are designed for circuit switching systems where the switching configuration can be rearranged at a relatively low speed. Most existing parallel routing algorithms are not practical for packet switching because they either assume the set of connection requests is a full permutation or fail to deal with output contentions among the set of input packets. We develop a parallel routing algorithm by solving a set of Boolean equations which are derived from the connection requests and the symmetric structure of the Benes network. Our approach can handle both the partial permutations and the output contention problem easily. The time complexity of our algorithm is O(log/sup 2/N), where N is the network size. Furthermore, we extend the algorithm and show that it can be applied to the Clos network if the number of central modules is a power of two.

Here a 1×5 microfluidic optical switch using double drives is proposed. It has a simple structure and ignorable polarization dependent loss. First, the switch with the straight waveguide structure is discussed. Then, various optimization schemes are used, where the oblique waveguide structure and the method of constant refractive index ratio of interface significantly reduce the insertion loss. The final optimization results show that the 1×5 optical switch has smaller insertion loss and crosstalk than general optical switches. For 1550 nm wavelength, the insertion losses of five exit ports are 0.27 dB ∼ 0.47 dB, and the crosstalks are −24.8 dB ∼ −66.5 dB. For 1310 nm wavelength, the insertion losses are 0.13 dB ∼ 0.23 dB, and the crosstalks are −25.6 dB ∼ −70.8 dB. Our work can promote the application of microfluidics in the optical communication and provide a reference for finding waveguide optical switches with low insertion loss.

The fast development of translucent Optical Burst Switching (OBS) technology, which employs multiple wavelengths per fiber, increases the size (i.e., the number of ports) as well as the cost and power consumption of Optic Cross-Connects (OXCs). This paper studies the impact of OBS network parameter settings, where switching is performed at the Waveband Switching (WS) granularity using an end-to-end grouping method to reduce the number of lightpaths and switch ports. The simulation results illustrate that using OBS networks with WS by the suitable parameter settings, namely the Burstification Time (BT) and waveband granularity, offers considerable energy savings in the core network compared to using an OBS network without WS, where overall power consumption is decreased by maximizing BT values and waveband granularity.

Large-scale optical switching matrix is the core technology of automatically switched optical network. With the significant increase of the matrix size, the study showed that the nonlinear factors, such as the correlation of the wavelength, phase and polarization between the optical switches have major impacts for the system performance. Because the full-size optical simulation is not available now, the research will be a great significance that we establish an overall model with not only considering the performance of optical switch unit, but also reflecting the structural characteristics of the network.In this paper, we calculated the transmission field of 2×2 Mach –Zehnder(MZI) silica on silicon thermo optic(TO) switch with different structure by using the finite difference beam propagation method(BPM). On the basis of optimization design, we constructed and simulated the large-scale 16×16 MZI silicon-based SiO2 Silica on silicon thermo switching matrix. The results are: In TE Mode, for Crossbar and banyan structures, insertion losses are 13.35 dB and 4.3638 dB; crosstalk losses are 27.125~29.0173 dB and 42.2318-43.7159 dB; extinction ratios are 29.57 dB and 26.79 dB respectively.

Optical circuit switching may be instrumental in meeting the cost, energy, and aggregate bandwidth requirements of future data center networks. However, conventional MEMS beam-steering cross-connects cannot provide submillisecond switching with the port count necessary for data centers. Here, we investigate a novel noncrossbar selector switch architecture and pupil-division switching layout to improve optical switching performance by relaxing the requirement of arbitrary switch configurability. This architecture and switch design enable MEMS beam-steering micromirrors to scale to microsecond response speeds while supporting high port count and low loss switching, and can realize a number of useful interconnection topologies. We present the design, fabrication, and experimental characterization of a proof-of-principle prototype using a single comb-driven MEMS mirror to achieve 150 μs switching of 61 ports between four preprogrammed interconnection mappings. We demonstrate the scalability of this switch architecture with a detailed optical design of a 2048-port selector switch with 20 μs switching time.

Microring-based optical switches are promising for wavelength-selective switching with the merits of compact size and low power consumption. However, the large insertion loss, the high fabrication, and the temperature sensitivity hinder the scalability of silicon microring optical switch fabrics. In this paper, we utilize a three-dimensional (3D) microring-based optical switch element (SE) on a multi-layer Si3N4-on-SOI platform to realize high-performance large-scale optical switch fabrics. The 3D microring-based SE consists of a Si/Si3N4 waveguide overpass crossing in the bottom and the top layers, and Si3N4 dual-coupled microring resonators (MRRs) in the middle layer. The switch is calibration-free and has low insertion loss. With the 3D microring-based SEs, we implement an 8×8 crossbar optical switch fabric. As the resonance wavelengths of all SEs are well aligned, only one SE needs to be turned on in each routing path, which greatly reduces the complexity of the switch control. The optical transmission spectra show a box-like shape, with a passband width of ∼69 GHz and an average on-state loss of ∼0.37 dB. The chip has a record-low on-chip insertion loss of 0.52–2.66 dB. We also implement a non-duplicate polarization-diversity optical switch by using the bidirectional transmission characteristics of the crossbar architecture, which is highly favorable for practical applications. 100 Gb/s dual-polarization quadrature-phase-shift-keying (DP-QPSK) signal is transmitted through the switch without significant degradation. To the best of our knowledge, this is the first time that 3D MRRs have been used to build highly scalable polarization-diversity optical switch fabrics.

In the past research, optical interconnection has successfully developed into an emerging technology due to its compatibility with CMOS, where an efficient and reconfigurable optical switch operating at ultra-low programming energy is a key element to realize optical signal routing and switching. Here we numerically demonstrate an optical switch operating in the telecommunications band, which shows a 20 dB switch ratio and insertion loss of 0.8 dB. The device is implemented in waveguide-coupled micro-ring resonator (MRR) using the phase materials Sb2Se3, which exhibits high contrast in its optical properties upon transitions between its crystalline and amorphous structural phases.

To achieve complex functionality with small size, weight and power, photonic integrated circuits (PIC) are expanded from two-dimensional (2D) to three-dimensional (3D). In this paper, a new design for a scalable 3D silicon optical switch is proposed. Key elements, including silicon electro-optic switches, crossings, and interlayer transitions are used to define and optimize the 3D optical switching network. The architecture is based on CLOS architecture, which can be extended to multiple layers. Silicon-based two- and three-layer switches are carefully designed and analyzed as an example based on the transfer matrix technique (TMT). In a 4×4 two-layer optical switch, the average insertion loss at 1550 nm wavelength is ∼4.16 dB, and ∼3.69 dB for the “all-cross” and “all-bar” states, respectively. In a 4×4 three-layer optical switch, the average insertion loss at 1550 nm wavelength is ∼5.96 dB, and ∼5.41 dB for the “all-cross” and “all-bar” states, respectively. The architecture also shows the scalability of both the port number and the layer number. The scalable 3D architecture proposed could improve the interconnect density twice and thrice in a single-layer design.

Based on optofluidics and the principle of total internal reflection, a 1×2 few-mode waveguide optical switch is proposed. The proposed few-mode optical switch has small volume, low insertion loss and simple structure. It can be directly connected with a few-mode fiber to reduce the coupling loss. The mode field distribution and transmission characteristics of the two-mode switch (LP01 and LP11) are discussed. After the optical switch structure parameters are optimized, the minimum insertion losses are respectively 0.54 dB and 0.42 dB at two output ports, and the crosstalks are respectively -20.4 dB and -48.0 dB. The transmission characteristics of the four-mode switch (LP01, LP11, LP02 and LP21) are also analyzed. The insertion losses of four-mode optical switch are less than 0.34 dB, and the crosstalks are less than -23.19 dB. Our work provides a new method for seeking high-performance, miniaturized and integrated fewmode optical switches.

We investigate the improvement of an insertion loss in silicon arrayed waveguide grating (AWG), by analyzing the multimode generation due to the field-mismatching effect. 8 channel silicon AWGs on a 6” SOI wafer are fabricated with an ultra-shallow etching structure and various aperture size of arrayed WGs. Our experimental results demonstrate the improved insertion loss and crosstalk characteristics. The fabricated AWG shows an insertion loss less than 1 dB with a crosstalk of -23.2 ~ -25.6 dB, exhibiting ~2.5 dB improvement of insertion loss and ~5 dB improvement of crosstalk, compared to our reported result.

The optical network-on-chip (ONoC) has the advantages of high bandwidth, low latency and high performance, so it has gradually become a research hotspot of on-chip communication systems. The in-depth research on wavelength division multiplexing (WDM) technology has further improved the bandwidth of on-chip communication. What follows is the influence of the crosstalk noise which is inevitable because of the structure and material of the optical device itself. Crosstalk noise has become an important factor restricting the on-chip technology of the optical interconnect. A five-port WDM-based optical router named Nerx with high optical signal-to-noise ratio (OSNR) is proposed in this paper for reducing the insertion loss and crosstalk noise. Nerx uses fewer optical switch elements and guarantees the connectivity between any two ports. Compared with Crux and Crossbar optical routers, experiments show that Nerx can achieve 20 optical channels and has a 5.6 dB improvement in average OSNR.

Data rates are continuing to increase for box-to-box, rack-to-rack, board-to-board, and chip-to-chip interconnects for terabit switches and routers, multiprocessor computers and high-end servers. The increase in individual line rates and bandwidth drives the need to replace copper interconnects with optical interconnects. Fiber optics are advantageous for these applications because they allow for longer link lengths, increased bandwidth, smaller cables and connectors, less susceptibility to electromagnetic interference, and potentially lower power dissipation, depending on the data rate and link length. Towards this direction, this thesis aims to design and demonstrate low-cost, low-latency, high throughput, rack-to-rack optical interconnect architectures for exascale (i.e., performing 10^18 floating point operations per second) high-performance computing (HPC) systems and data centers. In particular, a novel, cost-effective, optical interconnect architecture for ultrafast optical switching, based on semiconductor optical amplifiers (SOAs), is studied. The proposed design of a fast N×N all-optical, wavelength-space crossbar switch for optical interconnects uses a minimum number of ON/OFF gates. This thesis compares and proves the superiority of the proposed architecture with respect to its originally-proposed counterpart, both theoretically and experimentally. Additionally, in order to increase the capacity and to minimize the impact of transmission effects (especially self-gain modulation (SGM), cross-gain modulation (XGM), self-phase modulation (SPM), cross-phase modulation (XPM), and polarization dependent gain (PDG)), we investigate the performance of conventional binary intensity modulation (IM), in conjunction with direct detection, as well as of advanced, more resilient, spectrally-efficient modulation formats (e.g., Differential Phase Shift Keying (DPSK), Orthogonal Frequency Division Multiplexing (OFDM), Polarization Division Multiplexed Quadrature Phase Shift Keying (PDM-QPSK), Single (SP)- and PDM- 16-ary Quadrature Amplitude Modulation (16QAM) in conjunction with coherent detection). Finally, as a seperate research activity, we study the performance of point-to-point links based on vertical-cavity surface-emitting lasers (VCSELs) and single- or multi- mode fibers, in conjuction with IM/DD, four-level Pulse Amplitude Modulation (4-PAM), and OFDM, to enable state-of-the-art, high-capacity, low-cost optical interconnects.

Current electronic broadband switch matrices employ discrete semiconductor devices or VLSI chips. Isolation between ON- and OFF-states degrades and crosstalk between input and output lines of these electronic switch matrices increases at high operation frequencies. These will limit electronic switch matrices to low-frequency or low-bit-rate operations. In addition, optical-to-electrical (electrical-to-optical) conversions at the input (output) ends are required for these switch matrices to be used in a fiber environment. One way to achieve broadband, low-crosstalk, and high-isolation switching and to eliminate E/O and O/E conversions is to use optical switches. This paper describes an optical broadband switching architecture using optical/optoelectronic logic gates. Input and output signals are optical. No E/O or O/E conversions are needed for this architecture. The optical/optoelectronic logic gates that can be employed in this architecture are reviewed. Performance of this architecture is evaluated by calculating the crosstalk, isolation, insertion loss, switch matrix size, drive power, and switching speed. Technologies needed for hybrid and monolithic implementations of this architecture are also identified.