OSFP vs QSFP丨C-LIGHT

Since 2024, data center networks have been undergoing a generational leap from 400G to 800G, and 1.6T is poised for large-scale deployment in AI computing clusters. As the physical carrier of this transition, the form factor of optical transceivers has become a critical decision point affecting network architecture, supply chain strategy, and long-term TCO. The two major camps—QSFP-DD and OSFP—are engaged in fierce competition, each grounded in distinct technical philosophies and industry alliances, shaping the infrastructure landscape of the 800G era.

Packaging Evolution: The Technical Lineage from QSFP to 800G

Form Factor Divergence in the 400G Era

In the 100G era, QSFP28 became the absolute mainstream due to its mature ecosystem and broad compatibility. However, the bandwidth density requirements of 400G led to a divergence in packaging technologies: the traditional QSFP electrical interface supported only 4 lanes, meaning that achieving 400G required 100G PAM4 modulation per lane, placing extremely high demands on signal integrity; alternatively, an 8-lane 50G NRZ approach could be used, but this necessitated an increase in physical size.

This technical divergence gave rise to two evolutionary paths: the conservative evolution camp extended the QSFP foundation while maintaining backward compatibility, ultimately resulting in QSFP-DD; the radical reconstruction camp pursued a complete redesign optimized for thermal management and scalability, resulting in OSFP.

QSFP-DD: Incremental Innovation with Compatibility at Its Core

QSFP-DD (Quad Small Form-factor Pluggable Double Density) is defined by the QSFP-DD MSA (Multi-Source Agreement), with backward compatibility as its core philosophy. The "Double Density" nomenclature reflects its design characteristic—integrating eight electrical lanes into a compact form factor, doubling the density of QSFP28 while preserving mechanical compatibility.

Core Technical Specifications:

Physical Dimensions: 78.5mm (L) × 18.35mm (W) × 8.75mm (H)
Electrical Interface: 8 lanes, each supporting 50G PAM4 (for 400G) or 100G PAM4 (for 800G), backward compatible with 4-lane QSFP28
Thermal Design Power (TDP): Standard up to 12W, extended version up to 15W
Thermal Capability: The 8.75mm height restricts heatsink size; modules in the 15-20W range for 800G face thermal challenges

The greatest advantage of QSFP-DD lies in backward compatibility—QSFP-DD ports can accept QSFP+/QSFP28 modules, negotiating down to 4-lane operation, enabling phased upgrades without wholesale equipment replacement. In terms of ecosystem, QSFP-DD has garnered widespread adoption from Cisco, Juniper Networks, Arista, Dell, and the majority of traditional data center switch vendors.

OSFP: Performance-Oriented Redesign

OSFP (Octal Small Form-factor Pluggable) is defined by the OSFP MSA, developed by a consortium including Google and Arista, prioritizing thermal headroom and forward-looking electrical signal transmission. Its core design philosophy is optimized for 800G and higher bandwidths.

Core Technical Specifications:

Physical Dimensions: 100.4mm (L) × 22.5mm (W) × 13.0mm (H)
Electrical Interface: 8 electrical lanes, natively designed for 800G (8×100G PAM4), with reserved expansion capability for 1.6T
Thermal Design Power (TDP): Supports up to 20-25W, providing margin for higher-power 800G and beyond modules
Thermal Capability: Larger volume accommodates larger heatsinks, supporting higher-power silicon photonics and DSP chips; some variants feature an integrated heatsink mounted directly on the module, delivering superior thermal performance

OSFP's core strengths include robust thermal management, native 800G design, a clear evolutionary path to 1.6T, and additional pins supporting advanced CMIS 5.0 management features (real-time monitoring of temperature, voltage, and optical power). Its primary limitation is the lack of backward compatibility—an OSFP port cannot accept QSFP series modules, requiring a wholly new infrastructure. OSFP has garnered strong support primarily from hyperscale operators, and vendors like Arista, Cisco, and several white-box switch manufacturers now offer native OSFP platforms.

Core Differences Between QSFP-DD and OSFP

In practice, neither form factor holds absolute dominance. Each has its valid application scenarios, and the optimal choice depends on specific infrastructure requirements rather than market trends. QSFP-DD is generally favored in cloud services, telecom, and enterprise data centers where power efficiency, compact size, and infrastructure compatibility are paramount; OSFP excels in high-density GPU clusters and HPC environments while providing a clear path to 1.6T and beyond.

C-LIGHT OSFP and QSFP Product Portfolio

As a manufacturer established in 2011 with 15 years of deep professional experience in optical transceivers, C-LIGHT's product portfolio encompasses a comprehensive range of high-speed optical modules including 800G, 2×400G, 400G, 200G, and 100G, as well as interconnect products such as AOCs, ACCs, and DACs. These are widely deployed in AI computing clusters, data center networks, telecom carrier networks, and enterprise applications.

800G Series Products

C-LIGHT's 800G series optical modules are available in both OSFP and QSFP-DD mainstream form factors, fully compliant with IEEE 802.3 series communication protocols, CMIS Rev5.0 interface protocols, and corresponding MSA packaging standards.

OSFP Form Factor: Features an 8-lane electrical interface, achieving 800 Gbps aggregate bandwidth through PAM4 modulation technology, specifically engineered for the stringent demands of ultra-high bandwidth and low latency in AI cluster and hyperscale data center internal and external interconnects. Products cover multiple reach options: VR8 (50m), SR8 (100m), DR8 (500m), 2xFR4 (2km), and 2xLR4 (10km). Among these, the 800G OSFP ZR+ supports metro/long-haul transmission up to 450km using DCO coherent technology.

QSFP-DD Form Factor: Adds a second row of electrical contacts to the standard QSFP design, expanding the high-speed lanes from 4 to 8 to achieve 800 Gbps aggregate bandwidth. This form factor is physically backward compatible with previous-generation QSFP modules, facilitating seamless upgrades within data centers.

400G Series Products

C-LIGHT's 400G series optical modules are offered in both QSFP-DD and OSFP form factors, supporting a full spectrum of applications from short-reach multimode to ultra-long-haul coherent transmission, with reaches extending from 100 meters to over 500 kilometers.

QSFP-DD Form Factor: Adopts a "double density" design, achieving 400 Gbps transmission bandwidth via 8 electrical lanes, each utilizing 50G PAM4 modulation. Key specifications include SR8 (100m/MMF), DR4/DR4+ (500m/SMF), and FR4 (2km/SMF/CWDM). Additionally, C-LIGHT's 400G QSFP-DD FR4 optical module is a hot-pluggable coherent module designed for 400GbE applications, enabling 2km transmission over single-mode fiber.

OSFP Form Factor: Provides greater thermal headroom and higher power capacity, suitable for high-power 400G optical module application scenarios.

1.6T OSFP-RHS Series

Targeting next-generation AI data centers, C-LIGHT has introduced the 1.6T OSFP-RHS optical module. This product employs the OSFP form factor, delivering 1.6Tbps transmission capacity. The RHS (Reduced HeatSink) design features a thinner heatsink profile compared to standard OSFP modules, optimized for integration with cold-plate or liquid cooling systems while maintaining compatibility with QSFP-DD interfaces. The module utilizes 8×200G PAM4 modulation, integrates a DSP and Forward Error Correction (FEC) to ensure signal integrity, and its low-power architecture and hot-plug capability make it an ideal choice for high-density, low-latency optical interconnects. Currently available in 2x800G DR8 (500m/MPO-12) and 2x800G FR4 (2km/Dual LC/APC) configurations.

Broader QSFP Product Portfolio

In addition to 400G/800G high-speed products, C-LIGHT possesses a comprehensive product accumulation across the QSFP series:

100G QSFP28 Series: Includes ER4 (40km long-reach), CWDM, and other specifications. The 100G QSFP28 ER4 optical module utilizes 1310nm wavelength laser technology, achieving 40km long-distance transmission over single-mode fiber via LAN-WDM technology.

128G QSFP+ Series: Features a four-lane parallel design, with each lane supporting 32Gbps transmission for an aggregate bandwidth of 128Gbps, meeting the demands of high-performance storage networks and HPC scenarios.

40G/100G Multi-Rate QSFP: Covers transmission distances from 100m to 40km, compliant with the SFF-8472 interface protocol and QSFP MSA packaging protocol.

Market Trends and Selection Guidance

Market Outlook

Driven by AI computing clusters and large-scale data center construction, optical modules are undergoing rapid iteration from 400G to 800G and 1.6T. According to industry forecasts, global demand for 800G optical modules will reach approximately 40 million units in 2026, while 1.6T demand, fueled by AI computing power, will surge to 15-20 million units. The global market for 400G/800G optical components was valued at approximately USD 9.4 billion in 2025 and is projected to reach USD 35.2 billion by 2035, with a CAGR of approximately 14.1% from 2026 to 2035.

In terms of market acceptance, QSFP-DD dominates traditional data center and cloud service scenarios due to its broad equipment compatibility and mature supply chain ecosystem; OSFP, leveraging its superior thermal capability and clear evolutionary path to 1.6T, is capturing an increasing share in AI/ML clusters and hyperscale data centers.

Selection Guidance

Scenarios for Choosing QSFP-DD:

Existing infrastructure predominantly QSFP28-based, with a desire for phased, smooth upgrades
Traditional enterprise data centers or cloud service scenarios where power efficiency and space compactness are priorities
Need for compatibility with mainstream vendor equipment such as Cisco, Juniper, and Dell

Scenarios for Choosing OSFP:

Greenfield AI training/inference cluster deployments with explicit requirements for thermal capability and higher power budgets
Hyperscale data centers with future upgrade plans to 1.6T
Use of Arista switches or white-box switches with native OSFP support
Pursuit of advanced features such as signal integrity and integrated management functions

It is worth noting that interoperability solutions exist between the two form factors. Beyond direct 400G-to-400G connections, 800G ports can interconnect between the two port types via breakout configurations—for example, an 800G OSFP module with heatsink top can fan out to 2×400G QSFP-DD ports, enabling flexible network architectures.

For network planners and procurement professionals, the choice between QSFP-DD and OSFP hinges on a thorough assessment of existing infrastructure status, business growth expectations, and long-term evolution planning. With its comprehensive portfolio spanning both QSFP-DD and OSFP form factors across 400G, 800G, and 1.6T data rates, C-LIGHT provides flexible, reliable, one-stop high-speed optical interconnect solutions tailored to diverse network architectures.