400G DR4 vs FR4 vs LR4: Which Optical Standard Do You Need?

400G DR4, FR4 and LR4 all deliver 400GbE over single-mode fibre, but they target different link architectures and distances. DR4 uses parallel single-mode optics and four 100G optical lanes. It is commonly associated with short data-centre links and can support 4 x 100G breakout architectures when the exact module, cabling, far-end optics and host platform support that design. FR4 uses wavelength-multiplexed single-mode optics over a duplex fibre pair. It is commonly selected where a duplex-fibre 400G link is required and the link distance is beyond typical DR4 reach. LR4 also uses wavelength-multiplexed single-mode optics over a duplex fibre pair and is intended for longer 400G single-mode links than FR4. HOW TO CHOOSE Start with the physical link: required reach, installed fibre, connector and whether breakout is required. Then confirm the form factor, coding and host-platform support. FORM FACTOR STILL MATTERS The optical standard does not define the host module shell. Photon Optics lists 400G products across QSFP-DD, QSFP112 and OSFP. Check the exact host port before selecting an optic. COMPATIBILITY Do not select an optic from speed and reach alone. Host platform, port type, coding and firmware requirements can matter. Photon Optics only publishes compatibility where approved evidence is available. Photon Optics products are manufactured to order. Typical manufacturing and delivery lead time is 2-3 weeks.