Wavelength Division Multiplexing Optical Interconnects Research Articles

Athermal and widely tunable VCSEL with bimorph micromachined mirror.

We demonstrate an athermal and electrostatically-tunable 850 nm-band MEMS VCSEL for the first time. The thermal wavelength drift is compensated by the thermal actuation of a cantilever-suspended mirror with a bimorph effect. At the same time, the resonant wavelength can be continuously tuned by electro-static force as a voltage is applied in the cantilever structure. A continuous wavelength tuning of 10 nm is obtained with a low thermal wavelength drift, which is 10 times smaller than that of conventional VCSELs. Our athermal and tunable VCSELs enable us to reduce the channel spacing in course wavelength division multiplexing optical interconnects even under uncooled operations.

Gigabits-per-Second Signal Transmission from Single-Mode Vertical-Cavity Surface-Emitting Laser via Thin-Film Waveguide for Wavelength-Division-Multiplexing Optical Interconnect Board

A wavelength-division-multiplexing (WDM) optical interconnect board providing broad-band transmission from a two-dimensional (2D) array of vertical-cavity surface-emitting lasers (VCSELs) to a 2D array of photodetectors is one of the attractive candidates for constructing future ultrahigh performance signal processing systems. Focusing grating couplers and distributed Bragg reflectors were integrated into a thin-film glass waveguide to form free-space-wave optical add/drop multi/demultiplexers required for the WDM optical interconnect board. A single-mode VCSEL was placed at the focal point of a focusing grating coupler, and a diverging wave from VCSEL was coupled and collimated into the waveguide. After 15 mm propagation, the guided wave was dropped by an optical drop demultiplexer to a focusing wave in free space. VCSEL was driven directly by a pulse pattern generator and the transmitted signal was detected. An open eye diagram of a 1 Gbps pseudo-random-binary-sequence non-return-to-zero signal was confirmed.

WDM Optical Interconnects: A Balanced Design Approach

In this paper, we develop a new design approach to wavelength division multiplexing (WDM) optical interconnects with the objective of designing cost-effective and scalable interconnects. Our design philosophy strikes a balance between switching and conversion costs, and requires wavelength conversion only between two fixed and predefined wavelengths. The proposed design approach exploits the potential of the wavelength exchange optical crossbar (WOC) - a device that can switch signals simultaneously and seamlessly both in space and wavelength domains. We propose a novel crossbar switch that minimizes hardware and control complexity and use it as a building block for developing a new class of three-stage Clos-like WDM optical interconnects. The design space of the proposed interconnect is characterized and its hardware complexity is analyzed. We also show that the proposed crossbar switch and the new class of WDM interconnects admit most existing routing algorithms with simple modifications. In addition, we show that our design approach can be generalized to develop a class of k-stage interconnects, 3 < k les 2 log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> N-1.

WDM optical interconnects with recirculating buffering and limited range wavelength conversion

All-optical communication, in particular, wavelength-division-multiplexing (WDM) technique, has been proposed as a promising candidate to meet the ever-increasing demands on bandwidth from emerging bandwidth-intensive computing/networking applications. However, with current technology, the cost of optical communication, especially the cost of optical buffering and wavelength conversion, remains a major concern for such applications. In this paper, we study WDM optical interconnects that utilize low cost recirculating buffering and limited range wavelength conversion. We first consider the packet scheduling problem in this type of interconnect, and formalize the problem of maximizing throughput and minimizing packet delay as a matching problem in a bipartite graph. We give an optimal parallel algorithm for this problem that runs in O(Bk/sup 2/) time, compared to O((N+B)/sup 3/k/sup 3/) time if directly applied to existing matching algorithms for general bipartite graphs, where N is the number of input/output fibers of the interconnect, B is the number of fiber delay lines, and k is the number of wavelengths. We also consider efficient switching fabric designs for this type of interconnect. We distinguish between the switching fabric connecting the input fibers to the output fibers and the switching fabric connecting the input fibers to the delay lines and show that by adopting the idea of concentration, the cost of the latter can be reduced significantly in terms of the number of crosspoints.

Cost-effective designs of WDM optical interconnects

Optical communication, in particular, wavelength-division-multiplexing (WDM) technique, has become a promising networking choice to meet ever-increasing demands on bandwidth from emerging bandwidth-intensive computing/communication applications, such as data browsing in the World Wide Web, multimedia conferencing, e-commerce, and video-on-demand services. As optics becomes a major networking media in all communications needs, optical interconnects will inevitably play an important role in interconnecting processors in parallel and distributed computing systems. We consider a cost-effective design of WDM optical interconnects for current and future generation parallel and distributed computing and communication systems. We first categorize WDM optical interconnects into two different connection models based on their target applications: the wavelength-based model and the fiber-link-based model. Most of existing WDM optical interconnects belong to the first category. We then present a minimum cost design for WDM optical interconnects under wavelength-based model by using sparse crossbar switches instead of full crossbar switches in combination with wavelength converters. For applications that use the fiber-link-based model, we show that network cost can be significantly reduced, and present such a minimum cost design for WDM optical interconnects under this model. Finally, we generalize the idea used in the design for the fiber-link-based model to WDM optical interconnects under the wavelength-based model, and obtain another new design that can trade off switch cost with wavelength converter cost in this type of WDM optical interconnect. The results in this paper are applicable to any emerging optical switching technologies, such as SOA-based and MEMS-based technologies.

Designing WDM optical interconnects with full connectivity by using limited wavelength conversion

Optical communication, in particular, wavelength-division-multiplexing (WDM) technique, has become a promising networking choice to meet ever-increasing demands on bandwidth from emerging bandwidth-intensive computing/networking applications. A major challenge in designing WDM optical interconnects is how to provide maximum connectivity while keeping minimum hardware cost. The overall hardware cost of a WDM optical interconnect includes not only the cost of switching elements, but also the cost of wavelength conversion. Previous work mainly focused on minimizing hardware cost without taking into consideration the type of wavelength converters used. In this paper, we design WDM optical interconnects with full connectivity by using the low cost limited wavelength converters. We present optimal WDM optical interconnects for both permutation and multicast in single stage and multistage implementations. We also discuss the impact of the relationship between the number of fibers and the number of wavelengths per fiber on the optimal design. As can be seen, the newly designed WDM optical interconnects have minimum hardware cost in terms of the number of crosspoints and wavelength conversion cost.

Optimal scheduling algorithms in WDM optical interconnects with limited range wavelength conversion capability

Optical communication is a promising candidate for many emerging networking and parallel/distributed computing applications because of its huge bandwidth. Wavelength division multiplexing (WDM) is a technique that can better utilize the optical bandwidth by dividing the bandwidth of a fiber into multiple wavelength channels. In this paper, we study optimal scheduling algorithms to resolve output contentions in bufferless time slotted WDM optical interconnects with wavelength conversion ability. We consider the general case of limited range wavelength conversion with arbitrary conversion capability, as limited range wavelength conversion is easier to implement and more cost effective than full range wavelength conversion, and it also includes full range wavelength conversion as a special case. We first consider the conversion scheme in which each wavelength can be converted to multiple wavelengths in an interval of wavelengths and the intervals for different wavelengths are ordered. We show that the problem of maximizing network throughput can be formalized as finding a maximum matching in a bipartite graph. We then give an optimal scheduling algorithm called the first available algorithm that runs in O(k) time, where k is the number of wavelengths per fiber. We also study the case where the connection requests have different priorities. We formalize the problem as finding an optimal matching in a weighted bipartite graph and give a scheduling algorithm called the downwards expanding algorithm that runs in O(kD + Nklog(Nk)) time where N is the number of input fibers of the interconnect and D is the conversion degree. Finally, we consider the circular symmetrical wavelength conversion scheme and give optimal scheduling algorithms for nonprioritized scheduling in O(Dk) time and prioritized scheduling in O(k/sup 2/+Nklog(Nk)) time.