Bridging a 30km span on a single fiber strand pushes the physical limits of standard QSFP28 thermal and optical envelopes. While the 100G BIDI QSFP28 30km (often classified as 100G-ER1-BX) offers an elegant solution for regional aggregation, its deployment demands a rigorous understanding of APD (Avalanche Photodiode) mechanics and chromatic dispersion. At this distance, the link is no longer "plug-and-play"; it is a precision-engineered optical path.
To achieve a 30km reach without mid-span amplification, the 100G BIDI 30km module employs an APD receiver instead of the standard PIN photodiode used in 10km variants. The APD provides the necessary gain to detect weakened PAM4 signals after they have undergone ~15-18dB of attenuation across the fiber span and multiple patch transitions.
Because of the extreme sensitivity of the APD, testing this module with a short patch cable without at least 10dB of fixed attenuation will likely cause permanent damage to the receiver. Always verify link loss before final insertion.
At 30km, chromatic dispersion (CD) begins to manifest as a significant penalty on 100G PAM4 signals. Univiso's ER1-BX modules utilize advanced DSP (Digital Signal Processing) to compensate for this pulse spreading, but the engineering margin remains tight.
| Parameter | 100G BIDI 30km Spec (BX30) | Required Operational Margin |
|---|---|---|
| Optical Budget | 18.0 dB (min) | Maintain 3.0 dB for aging |
| TX Wavelength Pair | 1271nm / 1331nm | Verify U/D pairing at ODF |
| Receiver Sensitivity | -19.0 dBm (APD) | Avoid power > -7.0 dBm |
| Modulation | 100G PAM4 | Requires Host KP4 FEC |
Before commissioning a 30km BIDI link for high-capacity IP backhaul, NOC teams should execute the following protocol:
OTDR Span Audit: Verify the fiber run does not exceed 16dB total loss, including splices at the 1331nm window.
Reflectance Check: Ensure all LC/UPC or LC/APC connectors have a return loss of >35dB to prevent multi-path interference (MPI) which degrades PAM4 eye diagrams.
Host FEC Synchronization: Manually set the switch port to use IEEE 802.3bj/bm KP4 FEC. Standard 100G BIDI 30km links will not stabilize without active error correction.
Thermal Clearance: Ensure the 100G-BX30 is placed in a high-airflow slot, as the APD and internal laser coolers typically draw 4.0W to 4.5W.
The QSFP28 100G BIDI 30km is a powerful tool for service providers looking to double their capacity over long-haul municipal fiber. By strictly adhering to APD protection protocols and ensuring clean fiber paths, Univiso clients can achieve carrier-grade 99.999% uptime on links that were previously thought to require expensive dual-fiber ER4 optics.
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