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Coreless Termination Fiber
Ø125 µm Glass Rod
Shown is a comparison between a standard fiber with a core (left) and our coreless termination fiber (right).
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Adding a coreless fiber as an end cap to terminate a fiber reduces the power density, which protects the fiber.
Thorlabs' Coreless Termination Fiber consists of a pure silica glass rod and an acrylate coating. Where a standard optical fiber would have an inner core, our coreless termination fiber simply has a glass rod without a distinct core or cladding (as seen in the figure above). The absence of a waveguide makes this termination fiber useful for reducing back reflections or to prevent damage to the fiber end face in high-power applications. Coreless fiber can be attached to the end of an optical fiber using a fusion splicer.
Prevent Laser-Induced Fiber Damage
A coreless fiber end cap can have a short length of approximately a millimeter, though the appropriate length will vary based on the wavelength and power of the source and the standard fiber that is being capped. Ideally, the end cap should have an end face cleaved at about 8° on the non-spliced side to reduce back reflections. Additionally, the coating of the termination fiber should be stripped to minimize light leakage. Similar to the return loss application described above, the fiber end cap should not be connectorized. Please note that end caps are not necessary if the fiber laser source is spliced directly to the standard fiber, as no air-to-glass interface would be present.
This end-cap method is also useful for sealing off the air holes in photonic crystal fiber to prevent water from entering.
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Light is coupled from free space into a standard optical fiber with coreless end caps spliced to either side. On the right, back reflections are prevented from re-entering the core of the standard optical fiber.
Reduce Back Reflections
Since the coating on the coreless fiber has a higher index of refraction than the glass rod, much of the loss occurs where the coating is left intact, as shown by the image below. Thus, for minimizing back reflections, as much of the coating as possible should be retained during splicing. Please note that the end of the termination fiber should be scissor cut for best results and that the termination fiber is not intended to be connectorized. With this application, our splice protector sleeves or fiber recoaters are useful for protecting the fiber joint.
Intact Coating Reduces Back Reflections