Using PEEK Coating for Fiber Optics

Download the PEEK Coated Fiber Evaluation

What are the benefits of PEEK?

The main benefits of PEEK include its bio-compatibility, excellent purity and resistance to EtO, Gamma and autoclave sterilization. PEEK’s ability to handle repeat flexing and wear makes it an interesting choice for surgical robots. When looking at PEEK as a coating for optical fiber we find the material can reduce redeployments and extend life while still allowing strain, vibration, pressure and other factors from the environment being sensed to transfer.

What are some of the challenges of using PEEK as a coating for Optical Fiber? How did Zeus overcome them?

PEEK exhibits compressive strength and instability during temperature fluctuations which can induce attenuation. Challenges can occur when dealing with optical fiber containing gratings. We found in fiber Bragg ratings that compression could cause deformed peaks.

Our goal at Zeus was to offer a PEEK coated optical fiber that is stable during extreme temperature fluctuations, allowing the optical fiber to retain the benefits of PEEK coating during temperature fluctuations, and allowing the optical fiber to be protected without attenuation inducing compression.

Tell us a bit about Luna’s OBR 4600 that was used alongside PEEK coating. What are its advantages?

Luna’s OBR 4600 is the industry’s first zero dead zone ultra-high resolution reflectometer with Rayleigh backscatter level sensitivity for interrogating fiber optic components or systems. The OBR uses swept wavelength coherent interferometry to measure minute reflections in an optical system as a function of its length. The technique measures the full scale response of a device, including both the phase and amplitude. That is then presented graphically providing the user with an unprecedented inspection and diagnostic capability for their component or network.

One of the advantages to using the OBR is the ability to measure the evolution of the polarization states along the fiber providing an indication of distributed birefringence. In this case we measured the polarization state of the PEEK coated optical fiber and also the reference optical fiber and compared them. The evolution of the OBR receiver polarization states as a function of the optical fiber length appeared to be what we’d expect from a coiled section of optical fiber where the S and P states from the fringes with a period on the order of a few meters is consistent with the birefringence beat length induced by coiling the optical fiber. There did not appear to be any inconsistencies in viewing the differences between the reference or the PEEK suggesting that minimal if any residual strain had been induced by the coating process that would affect the optical properties.

What was the average variation of the PEEK coated optical fibers’ attenuation during temperature cycling?

The average variation of PEEK coated optical fibers’ attenuation during temperature cycling is within a 0.02 decibels (dB) of the control fiber. This variation shows that the stability of PEEK is not significantly affected by the temperature cycling or thermal shock. It was also observed that the PEEK coated fiber showed significantly less loss at the tightest bend radius over the control fiber.

What is required of the optical fiber to put PEEK on it?

The primary coating of the optical fiber must be able to withstand our proprietary process. We can largely determine feasibility by reviewing the optical fiber data sheet and confirm process ability with a short validation run. This can also be influenced by the required properties of the final product.

How long of a continuous length can you produce?

We have run links well over one kilometer.  However, the quality of the optical fiber, the specification of the final product, as well as many other attributes can go in to determining the continuous length we can actually achieve. This will be something that again we would have to determine on a case by case basis

Can you hand strip the PEEK for splicing?

PEEK cannot be easily stripped by hand. It can be thermally or chemically stripped effectively. There are some commercial strippers capable of stripping PEEK, but you should consult the manufacturer on how this affects the number of uses between cleaning and other parameters involved in the use.  PEEK can be stripped chemically using a similar method common to polyimide.

Does the thickness of the coating affect the performance of the optical fiber?

In our experience we have not seen a correlation between the thickness and the performance of the actual optical fiber itself.

Why doesn't the OBR have a dead zone?

Optical Time Domain Reflectometers get reflection distance information by sending out a short optical pulse and recording the time at which the reflected light returns.  A particularly bright reflection will blind the receiver for a short time, preventing observation of a second reflection peak in the “dead zone” behind the first.

The OBR is based on Optical Frequency Domain Reflectometry. It sweeps a tunable laser over a wide optical frequency range, interferes a local copy of the laser beam with one returning from the test device, records the resulting interference fringes, and computes the distance to a particular reflection event from the interference fringe frequency.  This process efficiently separates light reflected from nearby points along the fiber without the “dead zone” problem.

How is the OFDR system so accurate?

The distance accuracy is tied with the fidelity of the tunable laser that we use to sweep the wavelengths making our measurements. The laser is calibrated on every sweep to a NIST certified internal gas absorption cell for wavelength alignment. Precise knowledge of the optical frequency range that the laser scans over leads to precise knowledge of the distance scaling. This is what allows the OBR to provide the highest spatial resolution and accuracy of a commercially available reflectometer on the market today.

Where can our readers go to find out more?

Visit zeusinc.com to learn more about Thermally Stable PEEK coated optical fiber including a test study and technical information or contact Jason Fant, Global Market Manager – Fiber Optics at  [email protected]

Visit Lunainc.com to learn more about fiber optic testing equipment or contact Matthew Davis, Lead Research Engineer [email protected].

About Jason Fant and Matthew Davis

Jason Fant is Global Market Manager at Zeus Industrial Products.

He is responsible for market and business development in the fiber optics industry.A Six Sigma Green Belt, Fant is IAPD certified and is a SPIE member.

Matthew Davis is a lead research engineer at Luna Innovations.

A specialist at integrating fiber optic sensing technology into harsh environments such as turbine engines, wind tunnels, and nuclear reactors.

Davis holds a BS in Mechanical Engineering from Virginia Tech.