Coherent Lite: Technology, Applications and Forecast – 2Q26

Coherent Lite is a lower cost, lower power version of the coherent optics that power long haul and metro networks. Designed to work at shorter distances (<20km), Coherent Lite uses cheaper and less complex DSPs and optics to bring the benefits of coherent optics to campus and intra-datacenter interconnect. Several customers have expressed interest in Coherent Lite at 800G and 1.6T, but none have placed volume orders to date. The next apparent market opportunity for Coherent Lite is now a custom Google project at 2.4T and potential future broad-based business at 3.2T.

This Cignal AI report continues our coverage of Coherent Lite with the latest status, including an estimate of the potential size of the 2.4T market and suggestions about the opportunities for a 3.2T solution to be used inside the datacenter.

Table of Contents

Definition and History

Standards-based Coherent Lite is defined by the OIF, which originally specified an 800G version based on 400ZR called 800LR. With the move to 1.6T, the designation officially changed to 1600 Coherent Lite.

Google first presented the concept in 2021 (see the IEEE presentation). Google’s presentation reviews the convergence of specifications of direct-detect PAM4 and coherent DSPs, particularly as PAM4 speed reached 200G/lane. There was concern among some at Google that PAM4 could not deliver adequate reach at 200G/lane for datacenter applications, and these concerns were voiced at OFC 2022 (see OFC 2022 Show Report). This led to the first proposals of Coherent Lite at the OIF.

When originally proposed by Google, Coherent Lite at 800Gbps was deemed necessary because the performance of 200G/lane PAM4 was uncertain, especially beyond a few kilometers. 800LR, as it was called, was defined for 10km reach and C-band operation. Eventually, PAM4 performance at 200G/lane was shown to work at up to 10km, which met the requirements for datacenter deployment and eliminated any need for a Coherent Lite solution at 800G. A few 800G coherent DSPs were built, but no volume was deployed. However, even with a vanishingly small potential market, component vendors viewed their experience with 800LR as an important proof point for Coherent Lite at higher speeds.

At 1.6T, the OIF project got a new name, Coherent Lite, and an expanded application space. The primary applications were 2km (competing with FR optics) and 10km (campus interconnect), but the application space was expected to expand as individual operators and vendors came up with new ways to deploy the technology. As with 800LR, the driver behind 1.6T was the concern that PAM4 at 200G/lane would not meet span budgets, requiring Coherent Lite for interconnections beyond 10km or with high span losses (e.g. OCS). Originally, Amazon pushed 1.6T Coherent Lite as a campus interconnect solution, but eventually it moved on to other options. No large operators are currently purchasing 1.6T Coherent Lite. However, component vendors plan to leverage 1.6T Coherent Lite development into a 3.2T option, where PAM4 is almost certainly out of gas at 2km.

In Cignal AI’s OFC 2026 Show Report, we detailed Google’s efforts to bring a 2.4T Coherent Lite to the market. Google sees 2.4T Coherent Lite as a way to increase the traffic density on its optical circuit switch (OCS) ports.