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High-Power, End-Capped Single Mode Fiber Optic Patch Cables
AR-Coated, End-Capped FC/PC Connector to Scissor-Cut End
FC/PC-Terminated End has AR Coating and Coreless End Cap
Coreless End Cap
Standard Optical Fiber
Operation NotesThe AR-coated, FC/PC connector is meant for free-space applications only and will be damaged if it comes into contact with another connector tip.
The FC/APC connector
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Coupling Light into Standard Fiber vs.
Thorlabs offers patch cables with a coreless end cap and an antireflection-coated FC/PC connector on one end. The AR coating provides <0.25% reflectance in the 1030 - 1120 nm range and minimizes reflections when launching out of the fiber into free space. The end cap reduces the power density to a level below the damage threshold, making the FC/PC connectors on these patch cables capable of handling CW powers of up to 15 W.
Item # P5-1064HE-2 has one FC/PC connector with an end cap and an AR coating, and one uncoated FC/APC connector.
When coupling or collimating light with these patch cables, we advise starting with the beam at very low power. After ensuring the beam is properly aligned and the coupling efficiency is optimal, slowly increase the power to the desired level. Please see the Handling tab and the Damage Threshold tab for other special guidelines for handling high-power fiber optic cables.
Fiber-to-Free Space Coupling
Note: The AR-coated end is meant for free-space applications (e.g., collimation) and will be damaged if it comes into contact with another connector tip.
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Cross Section of Standard Fiber vs. Coreless Fiber
Prevent Laser-Induced Damage
Custom end-capped patch cables are also available; contact Tech Support for details. Thorlabs can also manufacture these cables in custom lengths and with certain custom fibers. Please contact your local Tech Support office for assistance in ordering these items.
IMPORTANT NOTE: Before using these fibers with your equipment, make sure that you are familiar with all operating and safety instructions provided with your light source. Carefully read the below information; proper operation and handling of these devices is imperative to prevent damage to fiber and related equipment.
1. Before attaching the provided fibers to your system, inspect both the input and output connector ends. The end faces should be clean and as free from contamination as possible. If not, clean the ends as outlined in the cleaning section below. Check the fiber ends both before connecting the fiber and also after disconnecting the fiber. It is very easy for contaminants to be transferred from one connector to another if proper care is not taken.
2. To avoid damage to the fibers being used, turn the source off, or reduce the power level to less than 50 mW before attaching the fiber. If any optics have to be aligned, then perform the initial alignment at low power (<50 mW). Only after the optics are fully aligned and locked should the laser power be increased.
3. It is recommended that the laser power be increased by only 250 mW every few minutes, and that the output power from the fiber should be monitored, to ensure that the coupling efficiency is not changing with power.
4. The beam must be free from hot spots (localized energy spikes). If hot spots are present in the beam then the energy density must be calculated for that localized area to ensure it doesn't exceed the damage threshold of the fiber.
5. The energy must be well within the MFD of the fiber. For example, if the MFD is 6.0 ± 0.5 µm, then the input beam should be ≤5.1 µm (i.e. 10% below the minimum possible MFD).
6. Do not use any index matching gel, thread locking fluid, or any lubricants with the connector. Do not use in the presence of chemical fumes or oils.
7. Products must be used in a clean environment in order to ensure spotless end faces. Any speck of dust adhering to the end face can easily lead to the degradation or destruction of the fiber.
The AR-coated, FC/PC connectors are not designed to be mated with other patch cables and should not be used in mating sleeves or fixed attenuators. The coating will be damaged if it comes into contact with another connector tip. The uncoated, FC/APC connector on the P5-1064HE-2 can be mated to another FC/APC connector with a mating sleeve.
Use filtered compressed air to blow any dust or dirt off the ferrule when finished. Do not use any type of cleaning solution such as isopropyl alcohol to clean fiber end face. Carefully inspect the tip of the fiber with fiber scope. The tip should be free of all contaminants. Continually clean the caps and the fiber tip before and after each use to help prevent contamination. See our fiber optic cleaning products for cleaning supplies.
When not in use, the ends of the fiber and the connector receptacles should be covered with the supplied caps. This will help protect the connectors from dirt and contamination. It is only recommended to use the dust caps supplied with the cables. Only the Thorlabs caps supplied with the cable are approved for use in sterilization procedures. Any other caps often are contaminated with mold release agents, which can get onto the fiber ends. This contamination is extremely difficult to see, and resists cleaning.
Laser-Induced Damage in Silica Optical Fibers
The following tutorial details damage mechanisms relevant to unterminated (bare) fiber, terminated optical fiber, and other fiber components from laser light sources. These mechanisms include damage that occurs at the air / glass interface (when free-space coupling or when using connectors) and in the optical fiber itself. A fiber component, such as a bare fiber, patch cable, or fused coupler, may have multiple potential avenues for damage (e.g., connectors, fiber end faces, and the device itself). The maximum power that a fiber can handle will always be limited by the lowest limit of any of these damage mechanisms.
While the damage threshold can be estimated using scaling relations and general rules, absolute damage thresholds in optical fibers are very application dependent and user specific. Users can use this guide to estimate a safe power level that minimizes the risk of damage. Following all appropriate preparation and handling guidelines, users should be able to operate a fiber component up to the specified maximum power level; if no maximum is specified for a component, users should abide by the "practical safe level" described below for safe operation of the component. Factors that can reduce power handling and cause damage to a fiber component include, but are not limited to, misalignment during fiber coupling, contamination of the fiber end face, or imperfections in the fiber itself. For further discussion about an optical fiber’s power handling abilities for a specific application, please contact Thorlabs’ Tech Support.
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Undamaged Fiber End
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Damaged Fiber End
There are several potential damage mechanisms that can occur at the air / glass interface. Light is incident on this interface when free-space coupling or when two fibers are mated using optical connectors. High-intensity light can damage the end face leading to reduced power handling and permanent damage to the fiber. For fibers terminated with optical connectors where the connectors are fixed to the fiber ends using epoxy, the heat generated by high-intensity light can burn the epoxy and leave residues on the fiber facet directly in the beam path.
Damage Mechanisms on the Bare Fiber End Face
Damage mechanisms on a fiber end face can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber. However, unlike bulk optics, the relevant surface areas and beam diameters involved at the air / glass interface of an optical fiber are very small, particularly for coupling into single mode (SM) fiber. therefore, for a given power density, the power incident on the fiber needs to be lower for a smaller beam diameter.
The table to the right lists two thresholds for optical power densities: a theoretical damage threshold and a "practical safe level". In general, the theoretical damage threshold represents the estimated maximum power density that can be incident on the fiber end face without risking damage with very good fiber end face and coupling conditions. The "practical safe level" power density represents minimal risk of fiber damage. Operating a fiber or component beyond the practical safe level is possible, but users must follow the appropriate handling instructions and verify performance at low powers prior to use.
Calculating the Effective Area for Single Mode and Multimode Fibers
As an example, SM400 single mode fiber has a mode field diameter (MFD) of ~Ø3 µm operating at 400 nm, while the MFD for SMF-28 Ultra single mode fiber operating at 1550 nm is Ø10.5 µm. The effective area for these fibers can be calculated as follows:
SM400 Fiber: Area = Pi x (MFD/2)2 = Pi x (1.5 µm)2 = 7.07 µm2 = 7.07 x 10-8 cm2
To estimate the power level that a fiber facet can handle, the power density is multiplied by the effective area. Please note that this calculation assumes a uniform intensity profile, but most laser beams exhibit a Gaussian-like shape within single mode fiber, resulting in a higher power density at the center of the beam compared to the edges. Therefore, these calculations will slightly overestimate the power corresponding to the damage threshold or the practical safe level. Using the estimated power densities assuming a CW light source, we can determine the corresponding power levels as:
SM400 Fiber: 7.07 x 10-8 cm2 x 1 MW/cm2 = 7.1 x 10-8 MW = 71 mW (Theoretical Damage Threshold)
SMF-28 Ultra Fiber: 8.66 x 10-7 cm2 x 1 MW/cm2 = 8.7 x 10-7 MW = 870 mW (Theoretical Damage Threshold)
The effective area of a multimode (MM) fiber is defined by the core diameter, which is typically far larger than the MFD of an SM fiber. For optimal coupling, Thorlabs recommends focusing a beam to a spot roughly 70 - 80% of the core diameter. The larger effective area of MM fibers lowers the power density on the fiber end face, allowing higher optical powers (typically on the order of kilowatts) to be coupled into multimode fiber without damage.
Damage Mechanisms Related to Ferrule / Connector Termination
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Plot showing approximate input power that can be incident on a single mode silica optical fiber with a termination. Each line shows the estimated power level due to a specific damage mechanism. The maximum power handling is limited by the lowest power level from all relevant damage mechanisms (indicated by a solid line).
Fibers terminated with optical connectors have additional power handling considerations. Fiber is typically terminated using epoxy to bond the fiber to a ceramic or steel ferrule. When light is coupled into the fiber through a connector, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, into the ferrule, and the epoxy used to hold the fiber in the ferrule. If the light is intense enough, it can burn the epoxy, causing it to vaporize and deposit a residue on the face of the connector. This results in localized absorption sites on the fiber end face that reduce coupling efficiency and increase scattering, causing further damage.
For several reasons, epoxy-related damage is dependent on the wavelength. In general, light scatters more strongly at short wavelengths than at longer wavelengths. Misalignment when coupling is also more likely due to the small MFD of short-wavelength SM fiber that also produces more scattered light.
To minimize the risk of burning the epoxy, fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. Our high-power multimode fiber patch cables use connectors with this design feature.
Determining Power Handling with Multiple Damage Mechanisms
When fiber cables or components have multiple avenues for damage (e.g., fiber patch cables), the maximum power handling is always limited by the lowest damage threshold that is relevant to the fiber component. In general, this represents the highest input power that can be incident on the patch cable end face and not the coupled output power.
As an illustrative example, the graph to the right shows an estimate of the power handling limitations of a single mode fiber patch cable due to damage to the fiber end face and damage via an optical connector. The total input power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at any given wavelength (indicated by the solid lines). A single mode fiber operating at around 488 nm is primarily limited by damage to the fiber end face (blue solid line), but fibers operating at 1550 nm are limited by damage to the optical connector (red solid line).
In the case of a multimode fiber, the effective mode area is defined by the core diameter, which is larger than the effective mode area for SM fiber. This results in a lower power density on the fiber end face and allows higher optical powers (on the order of kilowatts) to be coupled into the fiber without damage (not shown in graph). However, the damage limit of the ferrule / connector termination remains unchanged and as a result, the maximum power handling for a multimode fiber is limited by the ferrule and connector termination.
Please note that these are rough estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, these applications typically require expert users and testing at lower powers first to minimize risk of damage. Even still, optical fiber components should be considered a consumable lab supply if used at high power levels.
In addition to damage mechanisms at the air / glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. These limitations will affect all fiber components as they are intrinsic to the fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.
A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing the risk of damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.
Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV or short-wavelength light, and thus, fibers used at these wavelengths should be considered consumables.
General Cleaning and Operation Guidelines
Tips for Using Fiber at Higher Optical Power