As the traffic demands of data centers and metropolitan networks grow exponentially, the performance requirements for optical transmission systems have evolved from "good enough" to "precise matching." In the realm of 100G optical modules, the integration of single-fiber bidirectional (BIDI) technology with long-distance transmission capabilities is rewriting the traditional rules of optical communication engineering.
The most significant difference between the 100G BIDI module in QSFP28 packaging and traditional modules lies in the innovation of its duplex mode. Conventional 100G optical modules use a four-lane design, with each 25G channel corresponding to a separate fiber pair, much like a four-lane highway running in parallel. In contrast, the BIDI module employs wavelength division multiplexing (WDM) technology to integrate the transmitter and receiver into a single fiber. Its internal grating filter can precisely separate the 1310nm and 1550nm wavelength bands, akin to installing an intelligent traffic light system on a single-lane road to achieve collision-free bidirectional traffic. This design directly doubles the utilization rate of fiber resources, which is revolutionary for the existing fiber conduit resources of operators.
Achieving 80-kilometer transmission is not simply a matter of increasing signal power; it is the symphony of multi-layer error correction techniques. The module's built-in avalanche photodiode (APD) has a sensitivity of -24dBm, equivalent to capturing the faint glow of a firefly in the deep sea at a depth of a thousand meters. The forward error correction (FEC) algorithm uses third-generation Reed-Solomon encoding, with an error correction capability reaching an error rate of 1E-5. This is like accurately identifying and correcting three spectators who shouted the wrong slogan in a stadium of a million people. More crucially, the dynamic power control algorithm can adjust the transmit power in real-time according to link loss, much like an autonomous vehicle adjusting its throttle based on road conditions. This keeps the optical power fluctuation within ±0.5dB, avoiding the accumulation of nonlinear effects during long-distance transmission.
The engineering design of the module strictly adheres to the dual constraints of the IEEE 802.3bm and QSFP28 MSA multi-source agreements. In terms of the transmitter eye mask metric, the rise/fall time of the optical signal is compressed to within 12ps, equivalent to requiring a sprinter's reaction error at the start to be less than one hundred billionth of a second. The dispersion tolerance metric reaches 8000ps/nm, meaning that after traveling through 80 kilometers of fiber, the "step misalignment" of different wavelength components of the optical signal must be controlled within a precision of one ten-thousandth of the diameter of a human hair. Behind these stringent standards is the requirement to ensure interoperability between devices from different manufacturers with a reliability rate of 99.999%.
In actual deployment, a provincial operator has transformed its metropolitan core ring network, which originally required 16 fiber pairs, into an 8-fiber full-duplex architecture by deploying this module. The saved fiber resources can support the 5G backhaul needs for the next five years. More notably, the module's operating temperature range of -40℃ to 85℃ has been demonstrated in a data center application in a desert region. The module maintained zero errors after a 72-hour high-temperature stress test at 65℃. Its heat dissipation structure, which combines aluminum nitride ceramic substrates with microchannels, has a thermal conductivity efficiency more than three times higher than that of traditional materials.
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