XPO structural optical modules integrate eight OSFP/QDD units into a single module, which can be regarded as an eight-in-one combined version of standard OSFP/QDD modules. Visually, it simply stacks eight OSFP modules into two layers, leading many people to wonder why it is defined as an ultra-high-density pluggable solution. Here we elaborate on how XPO boosts integration density effectively.

Superficially, the layout of XPO modules seems to leave little room for package size reduction, yet the actual volume gap is striking. The total volume of eight side-by-side OSFP modules (excluding heat sink fins) reaches 2.35x105 mm3, while that of an XPO module is only 1.428x105 mm3 , achieving a notable size reduction.

From the switch perspective, taking a 204.8T switch as an example, deploying 16 pieces of 12.8T XPO modules takes up around 70% less overall space compared with traditional OSFP switches equipped with 256 pieces of 1.6T OSFP optical modules. This huge advantage mainly benefits from the built-in liquid cooling structure inside XPO modules. It eliminates the need for bulky dedicated heat sinks matched with optical modules, greatly cutting down the overall height of single-layer switches.
Now let’s look into the core reasons why XPO features smaller dimension and higher packaging density than eight separate OSFP modules, taking the 12.8T XPO module as an example:

PCBA Layout
It adopts two reversely installed 6.4T PCBA boards, with each board corresponding to four OSFP channels. The integrated board design optimizes layout space for optoelectronic components, breaking the layout limitations caused by fixed width of traditional OSFP circuit boards.
Heat Dissipation Structure
A built-in thin liquid cooling plate is configured inside. All heat-generating components on the two reversed PCBA boards dissipate heat through liquid cooling fins. This cooling structure is thinner than the combined heat fin structure of two stacked OSFP modules, efficiently compressing the overall module height.

Structural Components
One complete XPO module only uses one set of structural adhesive. Compared with eight separate OSFP modules, it saves extra shell wall thickness space and reserves more room for optoelectronic component arrangement.
Electrical Interface
RF signal interfaces and power interfaces are arranged separately, with power ports placed between liquid cooling pipeline inlets and outlets. This design simplifies RF pin routing and effectively suppresses signal crosstalk.

Optical Interface
It still adopts 8×8-channel MPO ports without changing fiber connection modes, maintaining full compatibility with existing standard pluggable OSFP modules.
To sum up, XPO realizes smaller size mainly for two reasons: built-in liquid cooling structure replaces bulky external heat fins to reduce module thickness; integrated eight-unit design cuts redundant structural space and further optimizes overall dimensions.

Competitive Relationship Between CPO and XPO
CPO is widely recognized as the mainstream future trend of optical modules, while XPO has also drawn wide attention at this year’s OFC exhibition.
In terms of packaging density, CPO outperforms XPO by a large margin, so downstream chip manufacturers and ASIC developers prefer to adopt CPO packaging solutions. Nevertheless, CPO involves highly sophisticated manufacturing processes and keeps high production costs. Its mass application heavily relies on high-level integration of upstream semiconductor components, and currently faces prominent challenges in product yield and operational reliability.
Optical module manufacturers are more proficient in mature pluggable OSFP production processes and lack sufficient motivation to promote CPO. Under CPO architecture, optical module makers have fewer business links, while semiconductor manufacturers occupy longer industrial value chains. Hence module suppliers tend to continue developing pluggable optical module solutions.
In general, XPO serves as a transitional product that extends the development cycle of pluggable optical modules. In the long run, the boundaries between equipment users and component suppliers are gradually blurring.
Whether it is CPO that integrates optical devices into switches, or XPO that embeds switch-related designs into optical modules, both approaches aim to elevate packaging density essentially. The future development trend depends on which side achieves faster technological breakthroughs in integration level and operational reliability: client-side ASIC chips or lane-side PIC/EIC chips.