When an Off-the-Shelf Cable Isn’t the Right Answer

Sometimes choosing a cable is straightforward. The operating conditions are known, the dimensions are generous and a standard product does everything the system requires.

Other projects are very different.

The cable may need to fit through an unusually small opening. It might have to support a significant mechanical load while remaining light enough for a moving platform. It could spend its working life underwater, repeatedly travel on and off a reel, carry optical data and electrical power together, or operate in conditions where an ordinary commercial cable simply wasn’t designed to survive.

These are the situations where a purpose-built cable starts to make sense.

Linden Photonics designs and manufactures cables around real application requirements. Our work includes custom fiber optic cables, hybrid constructions, specialty copper cables and tether solutions for demanding environments.

Rather than starting with the question, “Which standard cable is closest?”, we can start with a more useful one:

What does the cable actually have to do?

That difference often leads to a much better solution.

 

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What Is a Purpose-Built Cable?

A purpose-built cable is designed or adapted for a particular piece of equipment, operating environment or technical requirement.

It isn’t simply a standard cable with a different jacket color.

The design can involve the fibers or conductors inside the cable, but it also considers the physical characteristics that determine how the cable behaves once it is installed or deployed.

That could include:

• Outside diameter
• Overall cable weight
• Tensile strength
• Flexibility
• Bend performance
• Fiber count and fiber type
• Electrical conductors
• Shielded or twisted pairs
• Buoyancy
• Jacket construction
• Temperature requirements
• Water exposure
• Repeated deployment and retrieval
• Abrasion and mechanical handling
• Connector requirements
• Packaging or spooling requirements

A cable can look suitable on paper and still be wrong for the application if these factors aren’t considered together.

For engineers working on a particularly demanding project, our guide on how to specify a custom fiber optic cable for harsh environments explains many of the questions worth answering at the beginning of the design process.

Purpose-Built Fiber Optic Cables

Fiber optic cable is widely selected where bandwidth, transmission distance, low weight or resistance to electromagnetic interference is important.

In specialist systems, however, choosing the optical fiber is only part of the job.

The cable surrounding that fiber still has to survive whatever happens to it in the real world.

A cable running inside protected equipment has very different mechanical requirements from one being lowered into the ocean, routed through moving machinery or repeatedly deployed from a spool.

Linden Photonics develops rugged and custom fiber optic cable constructions for applications where standard commercial products may not provide the right combination of size, strength, flexibility and environmental protection.

Depending on the project, a purpose-built fiber optic cable can be developed around factors such as:

• Singlemode or multimode fiber
• Fiber count
• Compact diameter
• Higher tensile requirements
• Controlled flexibility
• Underwater use
• Buoyancy
• Rugged handling
• Temperature exposure
• Radiation exposure
• Connectorization
• Deployment method

What matters most is not creating the cable with the longest specification sheet. It is identifying the characteristics that matter to the actual application.

Hybrid Cables: When One Cable Has Several Jobs

Some systems need more than optical communication.

They may require power for a vehicle or instrument, electrical signals for control and fiber for high-speed data. Running separate cables for each function is possible, but it can increase weight, routing complexity and the number of connections required.

A purpose-built hybrid cable can bring several of those functions into one construction.

A hybrid design may combine:

• Optical fibers
• Power conductors
• Copper signal conductors
• Twisted pairs
• Shielded pairs
• Application-specific components

Linden Photonics already manufactures hybrid designs, including fiber-and-power cable configurations for demanding applications.

The real advantage isn’t simply having fewer individual cables. In compact equipment, tethered systems or moving platforms, combining functions can make the whole system easier to package and deploy.

It also creates an engineering challenge.

Optical fibers and electrical conductors do not necessarily have the same physical behavior. Strength members, insulation, jacket materials and the arrangement of the internal components therefore need to work as a complete cable rather than as a collection of unrelated parts.

That is exactly the kind of problem a purpose-built approach is intended to solve.

Specialty Copper Cables

Not every difficult application needs fiber.

There are still many situations where copper is the right choice for power, control, sensing or data, but a conventional commercial wire or cable doesn’t provide the required combination of dimensions and mechanical performance.

Linden Photonics applies experience gained from miniature, high-strength fiber and hybrid designs to specialty copper cable construction as well.

Depending on the requirement, purpose-built copper cables can incorporate features such as twisted pairs, shielded twisted pairs, high-voltage conductors, different insulation systems and specialized jacket constructions.

The goal remains the same: build the cable around its job.

Small, Light and Strong: The Trade-Off Is the Design

Many custom cable enquiries begin with requirements that appear to conflict.

“Can we make it smaller but still increase the working load?”

“Can we keep the cable flexible without sacrificing strength?”

“Can we add power conductors but avoid making the tether too heavy?”

“Can we make it buoyant while keeping the diameter under control?”

These aren’t unusual questions.

They are often the heart of the design.

Adding material can make a cable stronger, but it can also increase diameter, weight and stiffness. Reducing diameter may solve a packaging problem while creating a new challenge elsewhere. A material that works well mechanically may not be appropriate for the operating temperature or environment.

Purpose-built cable engineering is therefore about balancing requirements rather than maximizing one number at the expense of everything else.

For many projects, smaller, lighter and stronger isn’t a marketing phrase. It is the engineering problem that has to be solved.

Purpose-Built Cables for Underwater Systems

Marine applications make cable design particularly interesting because the cable becomes part of the mechanical system.

It may be dragged through water, repeatedly bent, wound onto drums, exposed to abrasion or required to behave in a very particular way relative to the vehicle or instrument connected to it.

A normal cable that simply happens to tolerate water is not necessarily an effective subsea cable.

Linden Photonics manufactures underwater and subsea fiber optic cables for demanding marine applications where factors such as tensile strength, bend performance, abrasion, handling and buoyancy have to be considered along with optical performance.

Typical applications can include:

• Underwater instrumentation
• Marine sensing
• Subsea communication
• Remotely operated vehicles
• Research equipment
• Temporary subsea links
• Defense-related marine systems
• Tethered underwater platforms

Projects involving subsea systems can also explore Linden’s broader Marine and Subsea capabilities.

Buoyancy Changes the Way a Cable Behaves

An underwater cable doesn’t necessarily need to sink.

In fact, depending on the system, a heavily sinking cable can create unwanted drag, interfere with vehicle movement or increase the risk of contact with underwater surfaces.

Positive, neutral and negative buoyancy can each be useful in the right situation.

The best option depends on how the cable is deployed and what is connected to it.

This is particularly important in remotely operated systems where the tether can have a direct effect on the movement and efficiency of the vehicle.

Linden’s experience includes buoyancy-controlled fiber optic and hybrid constructions developed specifically for these kinds of demanding marine applications.

Purpose-Built ROV Tethers

An ROV tether is a particularly good example of a cable that cannot be selected on electrical or optical specifications alone.

The tether is the vehicle’s physical connection to the surface.

It may carry data. It may also carry power. At the same time, it has to handle movement, bending, pulling and the hydrodynamic effects of being dragged through water.

Weight matters.

Diameter matters.

Strength matters.

Flexibility matters.

And the correct buoyancy can matter just as much.

Linden Photonics manufactures ROV cables and tethers ranging from fiber-only designs to hybrid configurations incorporating power conductors.

Purpose-built construction allows tether diameter, strength and buoyancy to be considered around the vehicle and mission instead of forcing the ROV design to accommodate an unsuitable standard cable.

Robotics and Moving Systems

Cables behave differently when they move.

A cable permanently secured inside a machine may experience relatively predictable loads. A cable connected to robotics, moving equipment or a tethered platform may bend thousands of times, twist, pull against guides or pass repeatedly over drums and mechanisms.

That changes the design priorities.

Linden’s work with robotics applications reflects the need for lightweight, compact and mechanically capable cables where movement forms part of normal operation.

When discussing a purpose-built cable for a moving system, it is useful to know not only the maximum load but also how the cable will move during everyday use.

That information can be more useful than a single tensile-strength number.

Aerospace Applications

Aircraft and spacecraft leave very little room for unnecessary weight.

Cable designs may also have to cope with demanding temperature, vibration, mechanical and packaging requirements.

For this reason, an aerospace cable may need to achieve a combination that would be unnecessary in a conventional installation: small diameter, low mass, dependable optical performance and high mechanical reliability.

Linden Photonics develops cable technologies for aerospace applications where compact size and performance in demanding environments are important.

Defense Applications

Defense platforms present another broad range of operating conditions.

Some systems require compact internal cabling. Others involve rugged field deployment, underwater equipment, tethered vehicles, sensing or specialized communication links.

There isn’t one cable construction that is right for all of those applications.

Purpose-built engineering allows cable size, strength, fibers, conductors and environmental performance to be matched more closely to the equipment and mission.

You can learn more about Linden’s experience with defense cable applications.

Purpose-Built Doesn’t Always Mean Starting From Scratch

A custom requirement doesn’t automatically mean designing an entirely new cable from the first layer outward.

That would often be unnecessary.

Linden Photonics has developed numerous fiber optic, hybrid, underwater, tether and specialty cable constructions over many years.

An existing design may already provide most of what a project needs.

For example, an established cable construction might only need a different fiber count, conductor arrangement, tensile requirement, diameter, jacket or buoyancy target.

Starting with proven cable technology and adapting it where appropriate can be a practical route to a purpose-built solution.

The important point is that the final configuration suits the application rather than being chosen simply because it happened to exist in a catalog.

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What Information Helps When Designing a Purpose-Built Cable?

You do not have to arrive with a finished cable drawing.

In fact, discussing the application first can sometimes reveal requirements that would otherwise be missed.

Useful information includes:

What needs to travel through the cable?

This might be singlemode fiber, multimode fiber, power, control signals, copper data conductors or some combination of them.

What is the available space?

If the cable has to pass through a gland, housing, tube or other restricted opening, maximum outside diameter may be one of the most important parameters.

What load will it experience?

Working load, maximum tensile load and the way the cable is supported can all influence the construction.

Will the cable move?

If it will be reeled, deployed, retrieved, bent, dragged or attached to moving equipment, explain the expected movement.

Where will it operate?

Underwater use, temperature extremes, radiation exposure, industrial environments and other conditions may influence fiber, jacket and material choices.

Is weight important?

For aerial systems, robotics, subsea vehicles and compact equipment, cable weight can affect far more than installation convenience.

What buoyancy is required?

For underwater applications, identify whether positive, neutral or negative behavior is preferred.

How long is the cable?

Length can affect electrical requirements, attenuation considerations, mechanical handling and packaging.

How will it terminate?

Connector requirements and termination methods should be considered early rather than added after the cable construction has already been finalized.

Providing this information gives the engineering team a much clearer picture of the real problem.

When Should You Consider a Purpose-Built Cable?

A custom cable is worth discussing when:

• Available cables are too large.
• Standard products are unnecessarily heavy.
• More tensile strength is required.
• The cable must operate underwater.
• Buoyancy needs to be controlled.
• Optical fiber and electrical power need to be combined.
• An unusual conductor arrangement is needed.
• Temperature or radiation is a concern.
• The cable will undergo repeated deployment.
• Tight equipment packaging restricts available diameter.
• Existing cables have experienced premature failure.
• The cable forms part of a robotic or tethered system.
• Several separate cables could potentially be combined.
• The equipment is being designed around a particular cable envelope.

There is another less technical warning sign.

If an engineering team is spending significant time redesigning equipment simply to accommodate the closest available commercial cable, it may be worth asking whether the cable should instead be designed around the equipment.

Why Linden Photonics?

Linden Photonics has been developing specialty cable technology since 2002, with particular experience in compact, high-strength optical fiber, hybrid and specialty cable designs for demanding applications.

Our capabilities extend across:

• Custom fiber optic cable
• Hybrid fiber and power cable
• Specialty copper cable
• ROV tether cable
• Underwater and subsea cable
• Buoyancy-controlled cable
• Compact cable designs
• High-strength constructions
• Aerospace applications
• Defense systems
• Robotics
• Marine research
• Harsh-environment applications

For customers, however, the most useful capability may simply be the opportunity to discuss the problem before deciding what the cable should look like.

Have a Cable Requirement That Doesn’t Fit the Catalog?

You don’t need to know the final part number before contacting us.

Tell us what the cable needs to carry, where it will operate, how it will be handled and which dimensions or performance requirements cannot change.

From there, Linden Photonics can determine whether an existing cable construction is suitable, whether it can be adapted, or whether a new purpose-built design makes more sense.

Helpful information includes:

• Fiber type and count
• Electrical conductor requirements
• Cable length
• Maximum outside diameter
• Working and maximum tensile loads
• Operating temperature
• Buoyancy requirements
• Flexibility requirements
• Deployment method
• Connector requirements
• Drawings or existing specifications
• Prototype quantity
• Expected production volume

Have an unusual cable requirement? Request a quote from Linden Photonics and tell us what your application needs the cable to do.

Purpose-Built Cable FAQs

What is a purpose-built cable?

A purpose-built cable is designed or adapted around a particular application rather than being selected solely from a standard product range. Fiber type, electrical conductors, size, weight, strength, flexibility, buoyancy and operating environment can all influence the final construction.

Does Linden Photonics manufacture custom cables?

Yes. Linden Photonics develops custom and application-specific fiber optic, hybrid and specialty cable solutions for demanding applications.

Can optical fiber and electrical power be combined in one cable?

Yes. Hybrid cable constructions can incorporate optical fibers and electrical conductors within the same cable. The appropriate arrangement depends on power requirements, fiber count, mechanical loads, diameter and the intended application.

Can a purpose-built cable be made smaller than a standard cable?

Potentially. Cable diameter depends on the fibers, conductors, strength requirements, insulation, jacket and other mechanical requirements. Compact construction is one of the areas that can be considered during custom cable development.

Can Linden develop purpose-built underwater cables?

Yes. Linden manufactures specialized underwater and subsea cable constructions for applications including ROV systems, marine sensing, research equipment and other underwater platforms.

Can cable buoyancy be customized?

Buoyancy can be an important design consideration for underwater applications. The preferred behavior depends on the vehicle, deployment method, water environment and other mechanical requirements.

Does a custom cable have to be designed completely from scratch?

Not necessarily. An existing Linden Photonics construction may provide a suitable starting point and can potentially be modified around the application’s fiber, conductor, dimensional, mechanical or environmental requirements.

What should I provide when requesting a custom cable quote?

Start with the application. Include the required fibers or electrical conductors, approximate length, diameter restrictions, tensile loads, operating environment, temperature, buoyancy requirements, movement or deployment conditions, connectors and anticipated quantity. A finished cable drawing is not necessarily required to begin the discussion.