Hollow fibers with a silver reflective coating enable convenient delivery of high energy pulsed lasers. Coupling efficiency can be near 100% and pulse dispersion is negligible. Such fibers have been used in CARS experiments, delivering 50 mJ / 5 ns pulse laser beams with wavelengths at 532 nm and 607 nm over a 5 m length.
Fiber Internal Diameter (ID)
Overall transmission in hollow fibers depends strongly on the fiber internal diameter (ID). We offer four different standard ID size options ranging from ID = 500 µm to 1500 µm, and all of these fibers are multimode. Bending of the fiber will affect the beam quality and lead to higher loss. For best results, an input beam should be focused straight into the hollow fiber with a relatively long focal length optic such that the focused spot size is about ½ the fiber ID.
Silver Reflective Layer
For the visible to NIR wavelength range (λ = 400 – 1600 nm), a bare silver layer is deposited on the inside of glass capillary tubing. The surface quality of the silver layer is vitally important, and Guiding has developed coating techniques to minimize surface roughness enabling relatively high transmission.
NIR Coating
For applications above 1000 nm (λ = 1000 – 5000 nm) we offer an optimized NIR coating. This silver coated hollow fiber has a customized dielectric layer for the ideal NIR transmission
Coupling
Coupling into silver-only hollow fibers is similar to coupling into our Mid-IR fibers, see here for more details. In general, a relatively long focal length lens should be used with the beam focused straight into the fiber.
Effective N.A.
The output divergence angle listed in the table above can be thought of as the effective numerical aperture (NA) of the fiber. The term “effective” NA is used since this is not equivalent to the NA for a solid core fiber. A solid core fiber works on the principle of total internal reflection, and for such fibers the NA is a strict cut-off in terms of acceptance angle. In contrast, our hollow core fibers are essentially a reflective light pipe (i.e., waveguide), and here the term, effective NA, can be thought of as an optimal coupling angle, but is not a strict cut-off. The hollow fibers will guide light at a higher NA; however, the further one gets from optimal coupling, the lower the transmission and the further from single-mode performance. More information on coupling can be found here.
Related Publication:
A. Alexander, P. Hsu, J. A. Wehrmeyer, S. Roy, J. R. Gord, and J. M. Kriesel ” Gas-Phase Temperature Measurements at the Exhaust of a J85 Engine using Coherent Anti-Stokes Raman Scattering “, 53rd AIAA Aerospace Sciences Meeting. January 2015
Kriesel, Jason M., Gat, Nahum, and Plemmons, David, “Fiber Optics for Remote Delivery of High Power Pulsed Laser Beams,” Proceedings of the 48th AIAA Aerospace Sciences Meeting, Orlando, FL, January 2010.
Aluminum hollow core fibers
Hollow glass waveguides coated with a reflective aluminum layer provide an excellent fiber optic delivery solution for ultra-violet (UV) lasers spanning the wavelength range from 100 – 400 nm. For vacuum UV wavelengths the fibers can be purged with an inert gas.
Coupling
Coupling into aluminum coated hollow fibers is similar to coupling into our Mid-IR fibers, see here for more details. In general, a relatively long focal length lens should be used with the beam focused straight into the fiber.
Additional Information
Additional information on aluminum coated hollow fibers can be found in the following article:
Yuji Matsuura and Mitsunobu Miyagi, “Hollow Optical Fibers for Ultraviolet and Vacuum Ultraviolet Light”, IEEE J. Selected Topics in Quantum Electronics, VOL. 10, NO. 6, (2004).
Connector Options
Fibers can be packaged with standard SMA 905, FC/PC type connectors, or left bare. The FC connectors have a 2 mm key. With the “bare” fiber option, there is no connector on the end of the fiber.
Jacket Options
Fibers can be packaged with or without a protective jacket. We use standard furcation tubing, the fiber sits in an inner tube, surrounded by aramid fibers, with a PVC jacket on the outside. The jacket comes in a choice of different colors. For fibers with an ID < 750 µm, the jacket diameter is 3.0 mm, and for fibers with ID ≥ 750 µm, the jacket diameter is 3.8 mm.
Custom Bundles
Guiding Photonics assembles custom bundles that enable delivery of multiple laser sources in a single connector. Note: the fibers are side-by-side rather than fused. In addition to hollow fibers for the Mid-IR, we can also include standard solid core fibers for visible, NIR, and SWIR wavelengths.
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