Transmitting high power laser light through fiber optic cables has been used in industrial environments for years. Designing fiber optic cables for industrial environments requires robust solutions able to handle high power losses without compromise either to process quality or to safety. Internal water cooling, where the optical fiber is in direct contact with water, in combination with an efficient cladding mode-stripper the optical fiber cable has superior advantages handling high power losses. In this paper we will present recent power-handling data for the new series of the well-known standards QBH and QD (LLK-D) fiber optic cables launched by Optoskand. The new series are designed with a combination of materials and internal water cooling.
Constant advancement in laser sources leads to commercial and industrial lasers with ever higher output powers and brilliance. The increasing capabilities of diode laser sources in particular produces extreme challenges for fibre launching. The difficulties arise due to the nature of the diode lasers, which are often designed with a numerical aperture (NA) exceeding the optical fibre’s NA and a spot size overfilling the fibre core so as to maintain the best possible brilliance. In addition to these properties, the spot imaged onto the fibre facet is typically rectangular. The combination of these properties result in an imperfect launch efficiency, forcing the connector built around the optical-fibre to cope with the radiation which is “lost” from the core of the fibre. Improvements in the Optoskand SMAQ connector are discussed, along with the presentation of results showing the increased power- and loss- handling capabilities when used with a variety of diode laser sources at 976nm. The sources used in the tests are optimised for an optical-fibre of core diameter (Ø) 200μm and NA of 0.22. The sources range in maximum power from 150W to 1000W with a coupling efficiency of between 80 and 90%. Additional complimentary results are shown for a Ø=400μm fibre guiding light of NA=0.12 where launch efficiency is 90 to 95%.
In industrial applications using high-brilliance lasers at power levels up to and exceeding 20 kW and similarly direct
diode lasers of 10 kW, there is an increasing demand to continuously monitor component status even in passive
components such as fiber-optic cables. With fiber-optic cables designed according to the European Automotive Industry
fiber standard interface there is room for integrating active sensors inside the connectors. In this paper we present the
integrated active sensors in the new Optoskand QD fiber-optic cable designed to handle extreme levels of power losses,
and how these sensors can be employed in industrial manufacturing. The sensors include photo diodes for detection of
scattered light inside the fiber connector, absolute temperature of the fiber connector, difference in temperature of
incoming and outgoing cooling water, and humidity measurement inside the fiber connector. All these sensors are
connected to the fiber interlock system, where interlock break enable functions can be activated when measured signals
are higher than threshold levels. It is a very fast interlock break system as the control of the signals is integrated in the
electronics inside the fiber connector. Also, since all signals can be logged it is possible to evaluate what happened inside
the connector before the interlock break instance. The communication to the fiber-optic connectors is via a CAN
interface. Thus it is straightforward to develop the existing laser host control to also control the CAN-messages from the
High laser power levels in combination with increasing beam quality bring optics performance into focus, particularly
with regard to systems with low focal shifts along the optical axis. In industrial applications, this often influences the
overall performance of the process, especially if the focal shift is comparable to or in excess of the Rayleigh length. It is
commonly accepted that the focal shifts are of thermal nature where lens material, lens coating, geometry and surface
contamination all contribute to the direction and extent of the focal shifts. In this paper we will present a novel design of
lens packages where a patented all-in-quartz concept is explored. By mounting quartz lenses in hermetically sealed
quartz tubes and applying water cooling on the perimeter of the quartz tubes we will reduce or eliminate a number of
contributing factors to focal shift problems. The hermetic sealing, carried out in a clean-room environment, will
minimize lens surface contamination. Differences in thermal expansion between lens and housing are eliminated as the
lens and housing will be of the same material. Absorption of scattered laser light will be efficient as the energy is
removed quickly by cooling water and not absorbed by fixed surroundings. Finally, indirect heating from the housing
transmitted by radiation and convection to the lenses is avoided. Values of the normalized System Focal Shift Factors
(SFSF) for the all-in-quartz optics will be compared to standard lens assemblies at multi-kW laser power levels.
Small fibre connectors capable of handling medium powered lasers are available on the market from multiple suppliers.
Typical connector types are the SMA905 and LD80. The capability to handle power losses, for example radiation falling
outside the fibre core is, due to the small size and restrictive design, limited. A new type of SMA fibre connector,
designed for high-power loss capability will be presented. The basic principle is to strip off the losses in terms of
radiation rather than being absorbed in the fibre connector. The radiation is instead absorbed in the female connector
housing or within the laser housing, where it can easily be cooled away. In this paper both the principles and
measurement of power capability are presented. Furthermore, in order to give a perspective of the available high-power
SMA fibre connectors on the market today, a comparison between the best competitive products is presented.
Fiber-to-fiber coupling between two different fibers is a state of the art technology. Products are available on the market
where multimode fibers can be coupled with very low power loss, at very high powers (multi-kilowatt). We have,
however, always been forced to accept a certain loss in beam quality, manifesting as an increase in the Beam Parameter
Product (BPP). In fundamental-mode fiber-to-fiber coupling no beam quality is lost. We instead expect to have a certain
power loss in the coupling.
This paper addresses the problems in free-space fundamental-mode fiber-to-fiber coupling, including theoretical
estimations of expected power loss, estimated demands on the stability of the optics as well as measured values on a
fundamental mode fiber-to-fiber coupler.
The theoretical calculations of the sensitivity of the coupling efficiency due to radial misalignment and defocus
(longitudinal displacement) have been confirmed experimentally. Experimental results at 100 W laser power include
88% coupling efficiency using a large mode area fiber with mode-field diameter (MFD) of 18 μm and 75 % coupling
efficiency using a single-mode fiber with MFD of 6.4 μm.
High laser power levels combined with increasing beam quality bring optics performance into focus. The subject of
optics performance is a hot topic, but lack of a common nomenclature, as well as of proper measurements, makes the
situation confusing. This paper will introduce a nomenclature for comparing the performance of different types of optics.
Further, the paper will present a test setup for characterizing optics, along with test results for different optics materials
and designs. The main influence of high power levels on optics is a focal shift along the optical axis. In industrial
applications, this might influence the performance of the process, especially if the focal shift is in the range of the
Rayleigh length. In the test setup that is to be presented, the optics are exposed to a high power beam, and a pilot beam is
used for measuring the change in focal position. For a proper description of optics performance, the laser beam
parameters should not influence the measured results. In the nomenclature that will be presented, the performance is
related to the Rayleigh length for a fundamental mode beam. The performance of optics when used with multimode
beams will be presented.
For high power laser applications where optical fibers are used the main problem is to keep the power losses as small as possible. To fullfill this demand it is important to utilize the power from the laser efficently and avoid damages on the fiber due to high temperature caused by radition outside the fiber core.
Thererfor the design has to be made in a robust way that protect the fiber from damages caused by the high power.
Depending on the beam quality from the laser two different kind of fibers have to be used, a fiber with polymer cladding for high NA and silica cladded fibers for lower NA. In both cases the core is made of fused silica. Since there is always some radiation not keept within the fibre core the cooling is of great importance. The radiation can be caused by scattering light from the beam itself or from back reflection in the application.
Different kind of design used to keep the power losses as small as possible as well as design of efficient cooling systems will be discussed in this paper. Experimental results from our development of optical fibers will be present.