100GBASE-LR1: Why the SFP-DD Module Has Only One TX and RX Port
The 100GBASE-LR1 SFP-DD datasheet lists a dual-lane host interface next to a single wavelength optical specification, and the module has exactly one TX port and one RX port. Customers who read both lines together often ask whether the module uses polarization multiplexing to carry two lanes on one fiber.
It does not. The dual-lane reference describes two electrical host lanes running between the host ASIC and the module, not two optical signals. A gearbox function inside the module combines those two electrical lanes into one 106.25 Gbps PAM4 optical signal on a single wavelength near 1311nm before the transmitter. Polarization multiplexing plays no part in the 100GBASE-LR1 PHY.
What the Dual-Lane Host Interface Actually Describes
The dual-lane spec on the datasheet refers to 100GAUI-2, the electrical interface between the host ASIC and the module, defined in IEEE 802.3cd Annex 135F/G. 100GAUI-2 runs two electrical lanes, each at 26.5625 GBd PAM4 for 53.125 Gbps per lane, encoded with RS-FEC(544,514). It describes the host side of the module only, not how many wavelengths leave on the fiber side. Juniper's 100G transceiver reference lists 100GAUI-2 as the two-lane electrical interface used by SFP-DD and SFP56-DD optics, while listing the optical interface for those same parts as a single wavelength. The SFP-DD MSA hardware specification defines this same two-lane PAM4 electrical host side for SFP-DD modules generally.
How the Module Converts Two Electrical Lanes Into One Optical Lane
Inside the module, a gearbox function takes the two 53.125 Gbps PAM4 electrical lanes from the host and combines them into a single 106.25 Gbps PAM4 optical lane before the signal reaches the laser. This lane-rate conversion is a known design pattern in SFP and QSFP form factors. A general note on module gearboxes states that converting between electrical lane counts and optical lane counts, once considered too power hungry for pluggable modules, is now not uncommon. Juniper's transceiver documentation shows the same split for LR1-class SFP-DD optics: 100GAUI-2 on the host side, one optical wavelength on the line side.
Why There Is Exactly One TX Port and One RX Port
100GBASE-LR1, defined in IEEE 802.3cu-2021 Clause 140, is a genuinely single-wavelength PHY, nominal 1311nm, reaching 10km over single-mode fiber through a duplex LC connector. The optical signal is one PAM4 lane at 53.125 GBd, 2 bits per symbol, for a 106.25 Gbps line rate, carried by one EML laser and received by one PIN photodiode. EDGE's 100G-SFP-DD-10 documents a TX and RX operating band of 1304 to 1317nm around that same nominal wavelength, confirming a single optical lane, one transmitter and one receiver. The term single lambda, as used here, means this fixed single wavelength. That is a different mechanism from the CWDM-grid single-lambda approach used on some other 100G modules, which selects one of several channels, 1271, 1291, 1311 or 1331nm, from four electrical host lanes. 100GBASE-LR1 has no channel selection.
Why This Is Not Polarization Multiplexing
100GBASE-LR1 encodes its single optical lane with PAM4, an amplitude modulation scheme, at 53.125 Gbaud. Polarization-division multiplexing is a different coding family. In the Ethernet standards it appears only on the coherent 100GBASE-ZR PHY, IEEE 802.3ct, which uses DP-DQPSK and has no relationship to 100GBASE-LR1's direct-detect PAM4 design. LR1 and ZR are separate PHYs built for different reach and detection requirements, and neither uses the other's coding scheme.
100GBASE-LR1 Compared With 100GBASE-LR4
100GBASE-LR4, defined in IEEE 802.3ba Clause 88, reaches the same 10km distance using four separate WDM wavelengths at 25.78 Gbps NRZ each, an older and different mechanism than LR1's single PAM4 wavelength. The 100GBASE LR vs LR4 comparison covers the full spec breakdown between the two PHYs.
EDGE's 100G-SFP-DD-10 SFP-DD transceiver implements the single-wavelength 100GBASE-LR1 PHY described above. For volume pricing or help matching host port electrical interfaces on a mixed-vendor deployment, contact our sales team.
Frequently Asked Questions
Can 100GBASE-LR1 and 100GBASE-LR4 optics be mixed on the same link?
100GBASE-LR1 (IEEE 802.3cu) and 100GBASE-LR4 (IEEE 802.3ba) are different PHYs with different optics. LR1 uses one PAM4 wavelength near 1311nm; LR4 uses four WDM wavelengths at 25.78 Gbps NRZ each. EDGE does not run per-chassis interop testing across PHY types, so confirm both ends of the link use the same 100GBASE PHY type before ordering.
What is the difference between 100GAUI-2 and 100GAUI-4?
Both are electrical host interfaces for the 100GBASE-LR1 optical PHY, not different optical specs. 100GAUI-2, defined in IEEE 802.3cd Annex 135F/G, is a 2-lane PAM4 host interface used by SFP-DD and SFP56-DD LR1 modules. 100GAUI-4, defined in IEEE 802.3cd Annex 135D/E, is a 4-lane NRZ host interface used by QSFP28 LR1 modules. Both feed the same single-wavelength LR1 optical PHY; the host electrical lane count depends on module form factor.