Architectural Survey Evaluates Scalable Optical Interconnect Port Limits in Data Centers

In a comprehensive review of data center network architectures published in Discover Networks, researcher Mohsin Fayyaz evaluates design constraints governing optical switch scalability and introduces a novel Enhanced Port Count interconnect architecture designed to overcome electronic switching bottlenecks. Modern web-based cloud computing applications, including high-performance computing, content delivery, video streaming, enterprise systems, artificial intelligence, and machine learning, require immense computing power and memory resources provisioned through data center networks. Because modern internet traffic predominantly originates or terminates inside these facilities, network operators face pressure to replace complex electronic switching fabrics with high-capacity optical alternatives. Within optical interconnects, port count and blocking probability serve as critical parameters directly influencing overall network latency, routing complexity, and power consumption. When interconnect port counts remain low, the network requires a higher hop count, forcing packets through successive store-and-forward mechanisms that introduce latency, inflate routing overhead, and escalate energy consumption across interconnected high-performance servers.

Driven by traffic demands from sixth-generation cellular networks, the Internet of Things, and compute-heavy platforms like social networks, search engines, and vast email repositories, data centers increasingly process machine-to-machine traffic that requires fast optical switches with low end-to-end latency. Silicon photonics has emerged as a promising high-speed interconnect technology because it offers reduced energy consumption per gigabit per second while detecting, guiding, and modulating optical signals using standard complementary metal-oxide-semiconductor fabrication, unlocking cost and performance scaling advantages over traditional optical interconnects. Furthermore, optical interconnects can dynamically reconfigure network topology at runtime via software-controlled optical circuit switching using software-defined networking, though this approach remains constrained by reconfiguration latency. Because optical switches operate without internal data buffering and exhibit non-zero reconfiguration delays, deploying all-optical networks requires sophisticated scheduling policies and queue-length adaptations, effectively modeling zero in-network buffering fabrics as centralized crossbar switches connecting distributed end hosts.

Expanding optical port counts requires strategic implementation of multiplexing schemes, including time, space, and wavelength multiplexing or their cascaded combinations across successive routing stages. In optical time division multiple access, network nodes share a transmission medium across assigned time slots to prevent collisions, achieving peak performance under full traffic loads while wasting bandwidth when lower traffic leaves slots underutilized. Because optical fibers support ultra-short pulses generated by mode-locked lasers in the one to ten picosecond range, this approach demands rigorous clock synchronization and calibrated fiber delay lines to align data into exact time frames. Conversely, optical space division multiplexing scales port counts across multiple spatial channels, such as few-mode or multi-core fibers, using optical splitters based on broadcast principles. However, optical splitting reduces signal amplitude and degrades the optical signal-to-noise ratio, risking bit errors, packet retransmissions, increased latency, and wasted bandwidth unless signal quality stays above an acceptable threshold.

Optical wavelength division multiplexing contributes substantial transmission capacity, channel reconfigurability, and cost reduction by routing multiple wavelengths across shared physical pathways, yet its operational scale is bounded by inter-channel crosstalk, light source spectral widths, photodetector sensitivity, and non-linear phenomena like Raman scattering and stimulated Raman scattering. To direct wavelengths between sources and destinations, optical interconnects use either broadcast-and-select structures based on splitters or wavelength-routing mechanisms that steer signals by tuning optical source wavelengths or performing intermediate wavelength conversions. At the component level, physical port limits depend directly on the structural characteristics of specialized optical hardware. Arrayed waveguide gratings achieve higher port counts by scaling interference orders or waveguide channels, while micro-electro-mechanical systems switches steer optical beams using electrostatically tilted micro-mirrors along dual axes, where stringent micron-scale actuator precision, manufacturing imperfections, and susceptibility to external mechanical vibrations or physical shocks restrict mirror tilt angles and ultimate scalability.

The survey systematically examines the port count formulations and hardware constraints of established reconfigurable architectures documented in optical networking literature, beginning with the Proteus and DOS frameworks. The Proteus architecture incorporates electronic top-of-rack switches linked to optical multiplexers, wavelength selective switches, and micro-electro-mechanical systems optical switches, reusing optical wavelengths across separate server racks to maximize scalability. In Proteus, total supported port count is mathematically defined by multiplying the rack count, which equals the number of micro-electro-mechanical systems switch ports, by the port count of each rack, corresponding to the multiplexer port capacity. In contrast, the DOS reconfigurable architecture integrates a centralized loop-back buffer, tunable wavelength converters, and arrayed waveguide gratings to execute dynamic wavelength-based packet routing under centralized control. When target output ports experience contention or temporary unavailability, optical signals in the DOS architecture are routed to electrical loop-back buffers, with aggregate port scaling determined directly by the physical port capacity of the underlying arrayed waveguide grating.

Continuing the structural analysis of prior designs, the review details the Petabit and Energy Efficient interconnect architectures, each employing distinct physical routing principles. The Petabit architecture relies on optical wavelength division multiplexing across a cascaded three-stage topology comprising input modules, center modules, and output modules fabricated from arrayed waveguide gratings, alongside tunable wavelength converters that dynamically shift carrier wavelengths to facilitate extensive wavelength reuse. Because the light path is strictly wavelength-engineered through internal phase shifts across multiple stages, the total port capacity of the Petabit architecture scales quadratically as the square of individual arrayed waveguide grating port counts. Meanwhile, the Energy Efficient architecture partitions network servers across clustered circuit boards that separate communication into optical inter-board channels and electrical intra-board links. Utilizing vertical-cavity surface-emitting lasers as direct optical transmitters, this architecture eliminates external modulators to conserve operating power proportional to the number of active lasers, with total network port count scaling as the product of board counts and per-board transmitter channels established by optical coupler ports.

The author further evaluates the port limitations of distributed-control, frequency-division, multiplane, and ring-based optical interconnect models. The Distributed Control architecture deploys multiple queued buffers alongside autonomous space switches and contention-resolution blocks equipped with wavelength converters, scaling total port count as the product of available buffers and per-buffer wavelength channels constrained by switch and multiplexer limits. The optical orthogonal frequency division multiplexing architecture modulates electrically generated signals onto optical carriers routed through cyclic arrayed waveguide gratings, establishing multiple-input multiple-output communication where total ports equal cyclic grating ports multiplied by supported sub-carriers per rack. In the Multiplane architecture, network cards house fixed-wavelength lasers routed through space switches and optical couplers governed by inter-card schedulers, capping scalability at the minimum interface limits between space switches and couplers. Finally, the Microsecond architecture adopts a unidirectional optical ring topology where nodes add or drop distinct optical wavelengths using wavelength selective switches and add-drop multiplexers, yielding total port capacity restricted to the minimum port boundary of those selective elements.

To surpass the port scaling boundaries identified across these eight historical designs, the author introduces the Enhanced Port Count architecture, a multistage optical network that cascades distinct multiplexing technologies and optical routing components to achieve unprecedented port density. On the transmitter side of the architecture, optical data undergoes three sequential processing stages, beginning with a wavelength multiplexing stage where identical wavelengths are organized into thirty-two distinct groups, with each group containing five hundred and twelve optical wavelengths. In the subsequent optical code division multiple access stage, each wavelength group is assigned a unique optical code, allowing the combination of wavelength and code to uniquely designate an individual server node within a rack. These optical code division multiple access encoders are constructed using parallel configurations of fiber delay lines, where input pulse widths correspond to channel bandwidth and multiple pulse copies are selectively transmitted or suppressed based on the assigned code pattern. In the third transmitter stage, optical space division multiplexing isolates individual racks through large-scale one-hundred-and-twenty-eight by one-hundred-and-twenty-eight optical switches.

The receiving subsystem of the Enhanced Port Count architecture mirrors the transmitter pipeline, accepting incoming transmissions from all sender racks and routing them through three consecutive decoding stages. Received optical signals first pass through wavelength demultiplexing, followed by optical code division multiple access demultiplexers that evaluate the thirty-two operational codes per rack using fiber delay lines arranged in reverse structural order, before final space-division routing. Based on physical device benchmarks documented across literature—including five-hundred-and-twelve by five-hundred-and-twelve micro-electro-mechanical switches, one-by-thirty-two wavelength selective switches, five-hundred-and-twelve-channel arrayed waveguide gratings, thirty-two-by-one couplers, five-hundred-and-twelve-port multiplexers, and one-by-one-hundred-and-twenty-eight space switches—the Enhanced Port Count architecture achieves superior port density. By integrating five-hundred-and-twelve multiplexer ports with thirty-two coupler ports, each rack accommodates sixteen thousand three hundred and eighty-four operational nodes, while one-hundred-and-twenty-eight power splitter ports allow network operators to establish one hundred and twenty-eight distinct racks, enabling the proposed design to demonstrate the largest aggregate port count among all evaluated optical interconnect architectures.

Computer simulations of the proposed Enhanced Port Count architecture conducted in the OptiSystem simulation platform confirm operational viability while uncovering key physical layer design trade-offs. Bit error rate evaluations and eye diagram analyses demonstrated that signal transmission fidelity improves markedly at higher received optical power levels, indicating that the optical transmit power of modulating lasers must be elevated to maintain required data integrity. This power requirement stems directly from the fiber delay lines utilized inside the optical code division multiple access encoders and decoders, as sequential optical propagation through multiple delay lines introduces noticeable signal attenuation. In summarizing the survey’s conclusions, the research highlights that optical port scalability in modern data centers remains fundamentally constrained by synchronization precision and acceptable latency in time-multiplexed systems, optical signal-to-noise ratios in space-multiplexed networks, and physical channel crosstalk alongside available spectral bandwidth in wavelength-multiplexed fabrics. Consequently, future research efforts must focus on evaluating novel modulation formats capable of mitigating signal degradation, lowering bit error rates, and further expanding interconnect port counts across high-capacity data center environments.

Subject of Research: Optical interconnect port count scaling in data center networks

Article Title: A survey on pushing the port count limits for optical interconnects in data center networks

Article References: Fayyaz, M. (2026). A survey on pushing the port count limits for optical interconnects in data center networks. Discover Networks, 2(1), Article 22. https://doi.org/10.1007/s44354-026-00036-z

Image Credits: AI Generated

DOI: 10.1007/s44354-026-00036-z

Keywords: optical interconnects, data center networks, port count scalability, optical switching, wavelength division multiplexing, space division multiplexing, optical CDMA, network architecture, survey, pushing, port, count