QSFP / QSFP-DD Immersion Extender: Moving Optical Transceivers Outside the Cooling Liquid

Immersion cooling is becoming increasingly important in AI, HPC, cloud, and high-density data centers as server and switch power density continues to rise.

However, deploying high-speed networking equipment inside dielectric cooling liquid creates an important challenge:

Does every optical transceiver also need to operate directly inside the immersion fluid?

Not necessarily.

Instead of immersing the optical transceiver itself, another practical architecture is to use a QSFP / QSFP-DD Immersion Extender.

The extender plugs into the high-speed switch or network interface located inside the immersion tank and extends the electrical interface to a position outside the liquid. The actual optical transceiver can then be installed externally in a dry and accessible environment.

For Taiwan manufacturer Optech, this provides an alternative approach to immersion networking:

Keep the switch port inside the liquid, but move the real optical transceiver outside the immersion environment.

Optech can provide and customize:

• QSFP28 Immersion Extender
• QSFP56 Immersion Extender
• QSFP-DD Immersion Extender
• Custom cable lengths
• Custom mechanical structures
• Application-specific connector arrangements
• Project-specific high-speed electrical designs
• Customized labels and serial numbers
• Taiwan manufacturing
• TAA options for eligible projects

This architecture can help customers simplify immersion system design while continuing to use conventional optical transceivers outside the cooling liquid.

What Is a QSFP / QSFP-DD Immersion Extender?

A QSFP Immersion Extender is a high-speed extension assembly designed to relocate the pluggable optical transceiver away from the submerged networking equipment.

In a conventional network:

Switch Port → Optical Transceiver → Fiber

In an immersion architecture using an extender:

Immersed Switch Port → Immersion Extender → External Optical Transceiver → Fiber

The switch remains inside the dielectric cooling liquid, while the optical module is physically moved outside the tank.

This approach creates an important separation between:

Immersion-side electrical connectivity

and

Dry-side optical connectivity

For some liquid-cooled data center architectures, this can significantly simplify optical deployment.

Why Move the Optical Transceiver Outside the Immersion Liquid?

Optical transceivers contain a combination of:

• optical engines
• lasers
• photodiodes
• DSPs
• PCBs
• adhesives
• labels
• plastics
• metal housings
• optical connectors
• thermal materials

A standard optical module is normally designed for air-cooled operation.

If the entire transceiver is immersed, engineers must consider whether every material and component is suitable for continuous exposure to the specific cooling fluid.

An extender architecture can reduce this challenge by keeping the optical module outside the liquid.

Key Benefits of the Immersion Extender Architecture

1. Keep Standard Optical Transceivers Outside the Liquid

This is the most important advantage.

Instead of requiring every optical transceiver to be specially designed for immersion, the extender moves the optical module to a dry external environment.

This can reduce concerns related to:

• cooling-fluid compatibility
• label degradation
• optical connector contamination
• adhesive compatibility
• plastic swelling
• long-term material exposure
• optical interface maintenance

The optical module can operate in a more conventional environment while the switch remains immersion-cooled.

2. Easier Optical Transceiver Replacement

Optical transceivers are field-replaceable components.

If a module is submerged inside an immersion tank, replacing it may require additional operating procedures.

With an Immersion Extender, the optical transceiver can be positioned outside the tank, where technicians can access it more easily.

This can simplify:

• module replacement
• troubleshooting
• upgrades
• compatibility changes
• spare management
• routine maintenance

3. Reduce Direct Fluid Exposure for Expensive Optical Modules

As network speeds increase from 100G to 200G, 400G, 800G, and beyond, optical transceivers become more sophisticated and valuable.

Moving these modules outside the cooling fluid can help isolate them from direct chemical exposure.

This is especially attractive for high-speed optics containing advanced DSPs, optical engines, and complex packaging.

4. Continue Using Conventional Optical Modules

One potential advantage of the extender concept is the ability to continue using familiar pluggable optics outside the tank.

Depending on the host interface and validated configuration, customers may be able to use their preferred:

• SR optics
• DR optics
• FR optics
• LR optics
• CWDM optics
• single-mode optics
• multimode optics

without redesigning the optical transceiver itself specifically for immersion.

Final compatibility should always be validated against the actual host, extender length, signal integrity requirements, and transceiver configuration.

5. Simplify Optical Connector Maintenance

Fiber connector cleanliness is critical to optical performance.

Dust, contamination, residue, and improper connector mating can cause:

• increased insertion loss
• reduced receive power
• link instability
• BER degradation

Keeping the optical transceiver and fiber connector outside the immersion liquid can make connector inspection and cleaning much easier.

6. Separate Cooling Design from Optical Design

An Immersion Extender allows engineers to treat the system as two functional zones:

Inside the tank:
High-density liquid-cooled switches and electronics.

Outside the tank:
Optical transceivers, fiber connections, and serviceable network interfaces.

This separation can simplify system architecture and maintenance planning.

Optech QSFP28 Immersion Extender

The QSFP28 Immersion Extender is intended for systems using QSFP28-class interfaces.

QSFP28 is widely associated with high-speed network applications such as 100G connectivity and related breakout architectures.

An Optech QSFP28 Immersion Extender can be evaluated for applications such as:

• immersion-cooled switches
• 100G server connectivity
• AI infrastructure
• storage networks
• HPC systems
• cloud data centers

Instead of positioning the QSFP28 optical transceiver directly inside the cooling liquid, the extender relocates the module to an external dry-side location.

This can help customers retain standard QSFP28 optical modules while integrating immersion cooling into the network.

Optech QSFP56 Immersion Extender

For higher-speed architectures, Optech can also support QSFP56 Immersion Extender solutions.

QSFP56 interfaces are commonly associated with higher-lane-rate network applications, including 200G-class connectivity depending on platform configuration.

The extender concept provides the same basic benefit:

Immersed network equipment → electrical extension → external QSFP56 optical transceiver

Potential applications include:

• AI computing clusters
• high-speed server networks
• storage fabrics
• HPC infrastructure
• liquid-cooled switches
• high-density data center racks

Because higher electrical lane rates place greater demands on signal integrity, cable length, PCB design, connector characteristics, and host configuration become increasingly important.

Optech can therefore work with customers on project-specific validation.

Optech QSFP-DD Immersion Extender

For modern 400G and higher-speed data center networks, QSFP-DD has become an important pluggable form factor.

Optech's QSFP-DD Immersion Extender is intended to help customers relocate a QSFP-DD optical module from the immersion environment to an external serviceable location.

This architecture can be relevant for:

• 400G AI networks
• cloud data centers
• high-density switch fabrics
• storage networks
• GPU clusters
• HPC environments
• immersion-cooled Ethernet switches

Instead of exposing an expensive QSFP-DD optical module directly to dielectric fluid, the optical transceiver can remain outside the tank.

This can be particularly useful when customers want to use different optical reaches from the same immersed switch platform.

For example, the external module could potentially be selected according to the required link:

Short reach → SR / DR-class optics

Medium reach → FR-class optics

Longer reach → LR-class optics

subject to host and extender validation.

One Immersed Switch, Multiple Optical Options

A major architectural advantage of the extender concept is flexibility.

The immersed switch itself does not necessarily need to be physically redesigned every time the optical requirement changes.

The customer may be able to change the dry-side optical module according to:

• fiber type
• transmission distance
• remote equipment
• wavelength
• network topology
• customer platform
• upgrade requirements

This can potentially provide more deployment flexibility than permanently integrating the optical engine inside the immersion environment.

Ideal Application Scenario 1: Immersion-Cooled AI Switches

Modern AI switches can consume substantial power, particularly as port speeds increase.

Immersion cooling can help remove heat from the switch electronics efficiently.

An Immersion Extender can then relocate the optical modules outside the cooling tank.

The architecture becomes:

Liquid-Cooled AI Switch → Optech Immersion Extender → External Optical Transceiver → Fiber Network

This configuration can combine:

• high-density switch cooling
• external optical serviceability
• flexible reach selection
• simpler optical maintenance

Ideal Application Scenario 2: GPU and AI Training Clusters

Large AI training clusters can contain hundreds or thousands of network links.

At this scale, maintenance efficiency becomes extremely important.

If every optical transceiver is submerged, routine replacement can become more complicated.

By moving the transceivers outside the immersion tanks, technicians can potentially perform:

• module replacement
• fiber inspection
• compatibility changes
• optical power troubleshooting
• spare replacement

without accessing the optical module deep inside the immersion environment.

Ideal Application Scenario 3: HPC and Supercomputing

HPC systems increasingly combine high power density with demanding network bandwidth.

Immersion cooling can support the computing hardware while extender-based optical connectivity provides a separation between:

liquid-cooled electronics and serviceable optical infrastructure.

This can be useful in research laboratories, universities, supercomputing centers, and advanced computing facilities.

Ideal Application Scenario 4: High-Density Cloud Data Centers

Cloud operators often require flexibility because network topology and optical reach can change over time.

Keeping the optical module outside the cooling liquid makes it easier to change the transceiver type when upgrading or reconfiguring the network.

For example, a customer may change from one optical reach to another without redesigning the entire immersed switch interface.

Ideal Application Scenario 5: Liquid-Cooled Network Test Systems

Immersion Extenders can also be valuable during engineering validation.

A customer developing a liquid-cooled switch or server platform may want easier access to different optical modules during testing.

An external transceiver location allows engineers to test multiple:

• module vendors
• reach types
• firmware versions
• compatibility codes
• fiber configurations

without repeatedly working inside the liquid tank.

Why Signal Integrity Matters

An Immersion Extender is not simply a mechanical extension cable.

It must carry very high-speed electrical signals between the immersed host port and the external optical module.

As data rates increase, several factors become important:

• insertion loss
• return loss
• impedance control
• crosstalk
• connector performance
• PCB design
• cable construction
• cable length
• host SerDes performance
• module electrical characteristics
• FEC margin

Therefore, the maximum practical extender length cannot be determined only by mechanical requirements.

It must also be validated against the actual electrical interface and target network speed.

This is an important area where Optech's project-specific customization capability can provide value.

Optech Customization Capability

Immersion systems vary significantly between customers.

The distance between the switch and tank wall may differ. The optical transceiver may need to be mounted above, beside, or behind the tank. Different projects may also require different cable routing, mounting brackets, or labeling.

Optech can work with customers to customize the Immersion Extender according to the actual system.

Possible customization areas include:

Cable Length

The extender length can be designed around the physical dimensions of the customer's immersion tank and network layout, subject to high-speed signal integrity validation.

Mechanical Design

Customers may require different:

• connector housings
• brackets
• retention mechanisms
• cable exit directions
• mounting positions
• pull tabs
• strain relief designs

Optech can evaluate project-specific mechanical requirements.

Cable and Material Selection

Materials located inside or near the cooling fluid can be evaluated according to the coolant used by the customer.

Customers should provide the exact cooling-fluid manufacturer and model whenever possible.

Connector Configuration

Optech can evaluate different host and external-side configurations according to:

• QSFP28
• QSFP56
• QSFP-DD
• platform layout
• space limitations
• cable routing

Signal Integrity Optimization

High-speed extension requires careful electrical design.

Depending on the project, Optech can work with the customer around:

• cable construction
• trace requirements
• connector design
• electrical loss budget
• target speed
• SerDes environment

Mechanical Mounting Outside the Tank

The external optical module needs a secure and serviceable mounting location.

Optech can work with customers on application-specific structures or external cages according to project requirements.

Labels and Serial Numbers

Customers can request customized:

• Optech P/N
• customer P/N
• serial numbers
• QR codes
• barcodes
• logos
• country-of-origin labels

Why the Immersion Extender Approach Can Reduce Project Complexity

There are two basic approaches to optical connectivity in immersion cooling:

Approach A: Put the optical transceiver directly inside the liquid

or

Approach B: Keep the optical transceiver outside the liquid using an extender

Both can be valid depending on the system.

However, the extender architecture can offer specific benefits when customers want to reduce changes to their existing optical module ecosystem.

Instead of qualifying every optical transceiver against the coolant, the customer can focus immersion compatibility primarily on the components that actually enter the liquid.

This can potentially reduce the qualification scope for optical modules.

Immersion Optical Transceiver vs Immersion Extender

The correct architecture depends on the customer's cooling system, required speed, equipment design, maintenance strategy, and network topology.

QSFP28 vs QSFP56 vs QSFP-DD Immersion Extenders

Optech's extender portfolio can address different generations of network interfaces.

The exact supported speed, cable length, host equipment, and module configuration should be confirmed for each project.

A Practical Immersion Network Architecture

A typical deployment could look like this:

AI / HPC Switch Inside Immersion Tank
↓
Optech QSFP / QSFP-DD Immersion Extender
↓
External Dry-Side Optical Transceiver
↓
LC or MPO/MTP Fiber
↓
Remote Switch / Server / NIC / Data Center Network

This architecture allows the optical portion of the link to remain serviceable outside the tank while the high-power networking equipment receives the thermal benefits of immersion cooling.

What Information Should Customers Provide to Optech?

To evaluate a QSFP / QSFP-DD Immersion Extender project efficiently, customers should provide as much of the following information as possible:

• Extender type: QSFP28 / QSFP56 / QSFP-DD
• Target data rate
• Switch manufacturer and model
• Port configuration
• Ethernet or InfiniBand
• Target optical transceiver
• Required extender length
• Tank dimensions
• Switch position inside the tank
• External optical module location
• Cable exit direction
• Cooling-fluid manufacturer
• Cooling-fluid model
• Single-phase or two-phase immersion
• Operating temperature
• Sample quantity
• Estimated annual quantity
• TAA requirement
• Customized label or serial-number requirement

Even if the complete specification is not available, Optech can work with customers during the early design stage.

From Engineering Sample to Volume Production

Because a high-speed Immersion Extender must satisfy both mechanical and signal-integrity requirements, Optech recommends a qualification-based project approach.

A typical process can include:

Requirement Review → Mechanical Design → High-Speed Electrical Design → Material Selection → Sample Production → Signal Integrity Testing → Host & Transceiver Compatibility Testing → Immersion Evaluation → Customer Qualification → Volume Production

This helps customers validate the complete link before moving into large-scale AI or HPC deployment.

Taiwan Manufacturing and TAA Options

Supply-chain origin is increasingly important for government, public-sector, research, education, and regulated infrastructure projects.

Optech is a Taiwan-based optical networking and high-speed interconnect manufacturer.

For eligible product configurations, Optech can support Taiwan-origin and TAA-oriented Immersion Extender solutions.

Depending on the project, Optech can also support documentation such as:

• Country of Origin
• manufacturing information
• product serial-number records
• customer-specific labels
• product traceability
• project compliance documentation

Final TAA status should be confirmed according to the exact manufacturing configuration and applicable procurement requirements.

Why Choose Optech for QSFP / QSFP-DD Immersion Extenders?

An Immersion Extender sits between two very different engineering environments:

high-speed electrical networking and immersion liquid cooling.

That means customers need more than a standard extension cable.

Optech can work with customers on:

• QSFP28 Immersion Extender
• QSFP56 Immersion Extender
• QSFP-DD Immersion Extender
• high-speed electrical extension design
• custom cable lengths
• custom mechanical structures
• cooling-fluid material considerations
• external transceiver mounting
• switch compatibility
• optical module compatibility
• customized labels
• serial-number management
• OEM / ODM requirements
• engineering samples
• qualification testing
• Taiwan manufacturing
• TAA options
• volume production

This enables Optech to participate from the first system concept through final production deployment.

Ready for Your Immersion Cooling Project?

As AI and HPC systems move toward greater power density, immersion cooling is becoming an important part of next-generation data center design.

But immersion cooling does not necessarily mean that every optical transceiver must also be submerged.

With Optech QSFP / QSFP-DD Immersion Extenders, customers can move the actual optical transceiver outside the cooling liquid while keeping high-power networking equipment inside the immersion environment.

This approach can provide:

• easier optical maintenance
• reduced direct fluid exposure
• greater optical module flexibility
• simpler fiber connector management
• easier module replacement
• customized tank-to-dry-side connectivity
• support for existing optical transceiver ecosystems

Optech welcomes QSFP28, QSFP56, and QSFP-DD Immersion Extender inquiries, engineering samples, customization projects, TAA requirements, and volume orders.

Contact Optech for custom design, samples, project evaluation, pricing, and mass-production support.

 

FAQ

1. What is a QSFP / QSFP-DD Immersion Extender?

A QSFP / QSFP-DD Immersion Extender is a high-speed extension assembly used to move the pluggable optical transceiver away from networking equipment submerged in immersion cooling liquid.

The switch-side interface remains inside the immersion environment, while the actual optical transceiver is positioned outside the liquid.

2. Why move the optical transceiver outside the immersion tank?

Keeping the optical transceiver outside the tank can reduce direct cooling-fluid exposure and simplify module replacement, fiber cleaning, compatibility changes, troubleshooting, and maintenance.

3. Does Optech offer QSFP28 Immersion Extenders?

Yes. Optech can support QSFP28 Immersion Extender projects and customize the design based on the target host, cable length, mechanical layout, and cooling environment.

4. Does Optech offer QSFP56 Immersion Extenders?

Yes. Optech can evaluate QSFP56 Immersion Extender requirements for higher-speed AI, HPC, storage, and data center networks.

5. Does Optech offer QSFP-DD Immersion Extenders?

Yes. QSFP-DD Immersion Extender solutions can be developed for high-density networking applications such as 400G-class AI and cloud data center environments, subject to host and signal-integrity validation.

6. Can I use a normal optical transceiver outside the immersion tank?

That is one of the main objectives of the architecture. The external transceiver can potentially be selected from conventional compatible optics, provided the complete host-extender-module link is electrically and functionally validated.

7. Can the external transceiver be changed from DR to FR or LR?

Potentially yes, provided the host interface and extender support the selected module. Keeping the optical transceiver outside the tank can make it easier to change optical reach or fiber type without modifying the immersion-side hardware.

8. Does extender cable length affect performance?

Yes. High-speed electrical interfaces are sensitive to insertion loss, return loss, crosstalk, impedance, and other signal-integrity parameters. Longer cable lengths can reduce electrical margin, so the required length must be evaluated for the actual data rate and platform.

9. Can Optech customize the extender length?

Yes. Optech can develop project-specific lengths according to the immersion tank layout, subject to electrical signal-integrity validation.

10. Can Optech customize the mechanical structure?

Yes. Optech can evaluate custom mounting structures, cable exit directions, connector housings, strain relief, external cages, labels, and other mechanical requirements.

11. Does the extender itself need to be immersion compatible?

The portion of the extender exposed to cooling fluid must be evaluated for the customer's specific immersion environment, including materials, cable construction, and mechanical components.

12. What cooling-fluid information should the customer provide?

Customers should preferably provide the coolant manufacturer, exact fluid model, immersion type, operating temperature, and expected exposure conditions.

13. Is this solution suitable for AI data centers?

Yes. The architecture can be particularly useful in high-density AI and HPC environments where switches benefit from immersion cooling but operators prefer to keep serviceable optical modules outside the liquid.

14. Can it be used in Ethernet and InfiniBand networks?

Potentially yes, depending on the host platform, data rate, electrical interface, FEC, and module requirements. The specific application should be validated before production.

15. Does Optech provide TAA options?

Optech can support Taiwan-origin and TAA-oriented options for eligible product configurations. Final TAA status should be confirmed based on the specific manufacturing process and procurement requirements.

16. Can customers order engineering samples?

Yes. Optech welcomes engineering sample and joint qualification projects before volume production.

Conclusion

The QSFP / QSFP-DD Immersion Extender introduces a different way to design optical connectivity for immersion-cooled data centers.

Rather than requiring the optical transceiver itself to remain submerged, the extender allows customers to:

keep the high-power switch inside the liquid while moving the actual optical transceiver outside the tank.

For many AI, HPC, cloud, and high-density networking projects, this can make maintenance easier, reduce optical-module fluid exposure, simplify connector management, and preserve greater flexibility in transceiver selection.

With QSFP28, QSFP56, and QSFP-DD Immersion Extender products, along with custom cable lengths, mechanical design, project engineering, Taiwan manufacturing, OEM/ODM support, and TAA options, Optech can work with customers from prototype development through volume deployment.

Optech welcomes customization projects, engineering samples, qualification requests, and volume orders for QSFP / QSFP-DD Immersion Extenders.