Transparent Optical Paths Research Articles

Large-scale silicon photonics switch based on 45-nm CMOS technology

In optical networks for telecom and datacom, an unprecedented energy efficient system is demanded since the amount of data traffic is rapidly increasing while a significant improvement of the energy efficiency in electronics devices such as switch ASICs is no longer expected. To overcome the energy constraints, introduction of energy-efficient optical circuit switching (OCS) to the conventional electrical packet switching network is considered. The energy consumption of the OCS is almost independent of the bandwidth because the transparent optical path with no optical-to-electrical/electrical-to-optical signal conversion supports an ultrawide bandwidth of highly multiplexed optical signals. In the OCS, high-speed and large-port-count optical switches are essential. We have been working on optical switches based on CMOS-compatible silicon photonics that offer fast switching, compactness, low power consumption, and low cost. By using our 45-nm CMOS process, we have recently demonstrated a low loss 32 × 32 silicon photonics switch and its performance improvements of wide operation bandwidth, polarization-independent operation, and so forth. In this paper, we review the recent progress of our silicon photonics switches. We discuss the importance of the silicon photonics switches for a sustainable optical network with a comparison of other switching technologies and explain comprehensively how our numerous achievements are advanced and related to each other.

Provisioning of dynamic traffic in mixed-line-rate optical networks with launch power determination

In mixed-line-rate (MLR) networks, different line rates on different wavelengths can coexist on the same fiber. MLR architectures can be built over transparent optical networks, where the transmitted signals remain in the optical domain along the entire path. Along the transparent optical path, a signal experiences various physical layer impairments (PLIs), and its quality degrades as it travels through each optical component. One of the major factors that affect the transmission quality is the launch power of the optical signal. The power must be large enough to ensure noise resiliency at the receiver, but it must be below the limit where fiber nonlinearities distort the signal. Moreover, high launch power is disruptive not only for the actual lightpath itself but also for neighboring lightpaths, and this effect is particularly critical in MLR networks since advanced modulation techniques used for high line rates are highly susceptible to PLIs. In this study, we investigate the problem of determining the appropriate launch power for provisioning of dynamic connection requests in MLR networks. By setting the appropriate launch power for each connection, we aim to maximize the number of established connections. We propose two different heuristics to determine the appropriate launch power of a lightpath. Worst-case best-case average (WBA) is based on optical reach of signal in a transparent optical network. In impairment-aware launch power determination (I-ALPD), current state of the network and impairments are evaluated to determine the launch power. The proposed approaches are practical and can adapt to the needs of network operators. Simulation results show that the performances of the proposed approaches show better results than the existing schemes in terms of blocking probability and bandwidth blocking ratio.

Free space adaptive optical interconnect at 1.25 Gb/s, with beam steering using a ferroelectric liquid-crystal SLM

A free space adaptive optical interconnect is reported, in which an optically modulated channel from a vertical-cavity surface-emitting laser at 1.25 Gb/s is steered using reconfigurable binary phase gratings displayed on a ferroelectric liquid crystal on silicon (LCOS) spatial light modulator (SLM), to correct for misalignment. The optical system, and addressing scheme to maintain a transparent optical path, is described. The measured optical losses total 13.6 dB, sufficient to give a bit error rate (BER) of 10/sup -12/ with current optical transmitter and receiver technology. This is, to our knowledge, the first demonstration of a high-speed data transmission through an adaptive optical interconnect using an off-the-shelf commercial ferroelectric display panel.

PDL-induced channel power divergence in a metro WDM network

In this letter, we report on the effect of polarization-dependent loss (PDL) on the performance of a metro wavelength-division-multiplexing transparent optical network. We show that dynamic channel-by-channel power equalizers are needed in such networks for compensating the significant amount of PDL-induced channel power divergence that accumulates in transparent optical paths.

Transparent optical path and crosstalk monitoring scheme for arrayed waveguide grating-based optical cross connect

We propose and demonstrate a transparent optical path monitoring scheme for optical cross connects (OXCs) where arrayed waveguide gratings (AWGs) are used as multiplexer/demultiplexer with periodicity and routing properties. Crosstalk induced by partial failure of optical switches can also be detected at certain level by using a real-time FFT to process the data.

The Modular WDM-Gridconnect as a Passive Routing Structure with Distributed Interfacing Capabilities

For communication services over transparent optical paths, specified in terms of bit rate and bit error probability, the maximum length is determined by detrimental physical effects like dispersion, crosstalk, noise or nonlinearities. Therefore, fiber-optic wide area networks employing wavelength division multiplexing (WDM) and optical bypassing have to be divided into several small transparent partitions. In this paper a scheme accounting for sufficiently short optical paths is introduced which is called Modular WDM-Gridconnect. In this approach the burden of interconnecting different network partitions (i.e., by using an overlay transport system as an interface) is spread over almost all nodes of the network. This property is referred to as distributed interfacing. The network can be extended step-by-step in a modular fashion adding no more than two nodes to the coverage area at a time. The advantageous properties of such an arrangement as compared to a straightforward partitioning are characterized by the cumulative transit traffic and the path lengths in a Modular WDM-Gridconnect cluster.