Stacked optical modules and ordinary optical modules

Stacked (parallel) optical modules use multiple fiber cores simultaneously for high-speed transmission, while ordinary optical modules use standard duplex connections with fewer fibers, impacting cost, fiber usage, and network scalability.Overview of Optical ModulesOptical modules are essential components in fiber optic communication systems, converting electrical signals into optical signals and vice versa. They typically include a Transmitter Optical Sub-Assembly (TOSA) with a laser, a Receiver Optical Sub-Assembly (ROSA) with a photodetector, functional circuits, a control board (PCBA), housing, and optical interfaces . These modules operate at the physical layer of the OSI model and are classified by speed, wavelength, fiber type, and connector type.Ordinary Optical ModulesOrdinary optical modules, often used in duplex configurations, transmit data over two fibers—one for sending and one for receiving. For example, in a 40GbE network using duplex multimode modules (like Juniper JNP-QSFP-40G-LX4), two modules are required per link, along with MTP-LC fiber distribution boxes and 24-core backbone cables . The advantages of ordinary modules include:Compatibility with existing 10GbE infrastructure, reusing LC multimode patch cords.Lower fiber cost since fewer fibers are needed.Simpler deployment in networks with limited fiber availability.Stacked (Parallel) Optical ModulesStacked or parallel optical modules, such as 40GBASE-SR4 QSFP+, use multiple fiber cores simultaneously (typically 8 out of 12 cores in an MTP fiber) to achieve higher data rates. Deployment requires:MTP patch cords and backbone cables.MTP-MTP bundled fan-out trunk cables to connect multiple links.Each link uses multiple fibers, increasing fiber consumption . Advantages of parallel modules include:Higher link density and support for high-speed transmission (40GbE and above).Scalability for future upgrades to 100GbE or 400GbE networks.Efficient use of high-speed transceivers in data centers. However, parallel modules generally increase fiber cost due to the additional fibers required and more complex cabling.Key DifferencesFeatureOrdinary Optical ModulesStacked (Parallel) Optical ModulesFiber usage2 fibers per link8 or more fibers per linkDeployment costLowerHigher due to extra fiber and fan-out cablesCompatibilityCan reuse existing 10GbE LC infrastructureRequires MTP cabling and parallel-ready transceiversScalabilityLimited for high-speed upgradesHigh, suitable for 40GbE, 100GbE, and beyondNetwork densityModerateHigh, supports multiple high-speed linksChoosing Between the TwoThe choice depends on network requirements:Cost-sensitive or legacy networks: Ordinary duplex modules are preferred for reusing existing fiber and minimizing expenses.High-speed, high-density data centers: Parallel optical modules are ideal for maximizing throughput and future-proofing the network. In summary, stacked optical modules provide higher speed and scalability at the expense of increased fiber and cabling costs, while ordinary optical modules offer cost efficiency and compatibility with existing infrastructure .