Simultaneous transmit receive optical module

Simultaneous transmit/receive optical modules enable bidirectional communication over a single fiber using wavelength separation or integrated optical assemblies.

BiDi (Bidirectional) Optical Modules

BiDi SFP modules are optical transceivers that allow data to be transmitted and received simultaneously over a single strand of single-mode fiber, instead of the traditional two-fiber setup . They achieve this by using two different wavelengths: one for transmission (TX) and one for reception (RX). Each end of the link uses complementary wavelength pairs, so BiDi modules must be deployed in matched pairs to function correctly . Common types include 155M, 1G, and 10G BiDi SFPs, supporting legacy networks and high-bandwidth Ethernet applications . Inside a BiDi module, the transmitter optical subassembly (TOSA) and receiver optical subassembly (ROSA) are integrated into a single connector, often called a BOSA, with an optical filter separating the wavelengths . This design reduces fiber usage, lowers infrastructure costs, and simplifies network deployment, especially in fiber-constrained environments .

Transmit-Receive Optical Subassemblies (TROSA)

A TROSA is a highly integrated optical front-end used in coherent transceivers, combining electrical-to-optical and optical-to-electrical conversions in a single assembly . It integrates RF circuits, drivers, transimpedance amplifiers, and photonic integrated circuits (PICs) to enable high-speed bidirectional communication. TROSA modules are used in metro, regional, and long-haul networks, supporting very high data rates (up to 1.2 Tb/s) and advanced coherent DSPs . Unlike BiDi SFPs, TROSA modules are designed for coherent optical systems, providing high performance, low noise, and tunable wavelength operation. They are suitable for dense, high-capacity networks where integration and signal quality are critical .

How Simultaneous Transmission Works

Simultaneous transmit/receive over a single fiber relies on wavelength division multiplexing (WDM) or integrated optical assemblies:

• WDM-based BiDi modules: Use different wavelengths for TX and RX, separated by optical filters to prevent interference .
• Power coupler method: Combines signals of the same wavelength in both directions, ensuring back-reflected light remains below the noise floor .
• TROSA modules: Convert electrical signals to modulated light and vice versa, integrating multiple optical and electronic functions in a single package for coherent transmission .

Advantages

• Fiber efficiency: Reduces the number of fibers required by half in BiDi systems .
• Cost savings: Lower cabling, installation, and maintenance costs .
• High-speed capability: Supports modern Ethernet and coherent optical networks .
• Compact integration: TROSA modules combine multiple functions in a single assembly, reducing footprint and power consumption .

Applications

• Data centers: High-density, fiber-constrained environments.
• Metro and enterprise networks: Upgrading legacy fiber infrastructure without laying additional fiber.
• Long-haul coherent networks: TROSA modules for high-capacity, low-noise transmission.
• Industrial and telecom environments: Where fiber availability is limited or costly. In summary, simultaneous transmit/receive optical modules, whether BiDi SFPs or TROSA-based coherent transceivers, enable efficient bidirectional communication over a single fiber, leveraging wavelength separation or integrated optical assemblies to optimize fiber usage, reduce costs, and support high-speed network applications .